Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
http://personal.inet.fi/koti/tom.eklund/aurora.html
Very High EnergyAstronomy
brief summary of lecture available at:http://ihp-lx2.ethz.ch/AstroTeilchen/
Dr. Adrian Biland / [email protected]
HPK E24, 044 633 2020
15.May.2009 A.Biland: Very High Energy Astronomy 2
Cosmic RayOrigins
15.May.2009 A.Biland: Very High Energy Astronomy 3
pppp
Charged Particles deflected by omnipresent magnetic fields …
!!
Need Photons (or Neutrinos) to be able to identify sources
15.May.2009 A.Biland: Very High Energy Astronomy 4
Location of Sourcespropagation of highest energetic protonsin galactic B-field (galactic plane):
If protons > 1020eV exist, they can beused to do ‘CR-Astronomy’ ....
Latest results from AUGER indicate that at least perpendicular to the galactic
plane, the effect of galactic magnetic field is much smaller
==> CR-Astronomy already possible at ~1019 eV ???
(But: if particles are Fe (as indicated by AUGER measurements), AUGER
result would ask for extremely low intergalactic B-field
Maybe reason for AUGER anisotropy is just based on the structure of the B-
field of our Galaxy: low field perpendicular to the plane ==> less shielding
power than for extragalactic particles coming along the galactic plane)
15.May.2009 A.Biland: Very High Energy Astronomy 5
AUGER (south)
black circles: all events >1018eV seen by AUGER (3o error)red stars: position of nearby AGNs (<200Mpc)==> seem correlated ==> nearby AGNs could be sources of >1018eV particles ==> no problem with GZK
Science,9.11.07
This is no proof that nearby AGNs (Active Galactic Nuclei: galaxies with huge
central black holes ‘swallowing’ large amount of material) are the real sources.
High density of AGNs probably indicates regions with high mass-density and
high dark-matter content
==> result indicates that highest energy particles come from nearby
(extragalactic!) regions with high mass density
Any possible type of cosmic accelerator could be the source
Ruled out:
-galactic origin (would expect to concentrate in galactic plane)
-isotropic distribution
15.May.2009 A.Biland: Very High Energy Astronomy 6
Key Questions
Distribution of sources: - few bright point-like sources ? - many faint sources/ diffuse ?Type of sources: - astrophysical (“stars”,fields) ? - new physics (decay of heavy part.)?
Location of sources:nearby (solar system) ?galactic? extragalactic? universal?
15.May.2009 A.Biland: Very High Energy Astronomy 7
Location of SourcesFrom p+X --> "0+Y , "0 --> ! ! Search for ! with characteristic spectra(mainly at rather low energies...)
==>1) ~same CR everywhere in our Galaxy ==> (probably) not local/solar origin 2) far less CR in Large Magellanic Cloud ==> not extragalactic/universal origin
15.May.2009 A.Biland: Very High Energy Astronomy 8
Location of SourcesFrom magnetic field strengths:
==> [for GeV … TeV energies]
1) CR can enter/escape solar system ==> (probably) not solar origin
2) CR confined/shielded by galactic field ==> not extragalactic origin
15.May.2009 A.Biland: Very High Energy Astronomy 9
Location of Sources
Most probably, main componentof CR has galactic origin
(arguments not valid for highest energies: - low contribution to "0 production - can escape/enter galactic field ==> highest energy CR probably extragal.)
15.May.2009 A.Biland: Very High Energy Astronomy 10
Acceleration Mechanism?
CR acceleration process(es) must explain:
-how to reach huge particle-energies-how to reach high fluxes-power-law in spectra E-2.7 up to knee, but because of easier ‘leakage’ at high energies, assumed initial spectrum ~E-2.1
15.May.2009 A.Biland: Very High Energy Astronomy 11
Collisionless Acceleration(first proposed by Fermi 1949):
Assume a particle with velocity v scattersat (magnetic) cloud moving with velocity uwith |v| >> |u|
Not collision with a single molecule, butelastic(!) scattering with whole cloud (m~!)
What’s the particle energy after scatter ?15.May.2009 A.Biland: Very High Energy Astronomy 12
Collisionless AccelerationMust average over all scattering angles …
Rough estimate:take average of extreme cases, classical
Case 1:#E1=0.5m(v+2u)2-0.5mv2
=0.5m(4uv+4u2) > 0Case 2:#E2=0.5m(v-2u)2-0.5mv2
=0.5m(-4uv+4u2) < 0Average:#E =0.5(#E1+#E2)= 4mu2
in average: pos. energy gain
magnetic
magnetic
15.May.2009 A.Biland: Very High Energy Astronomy 13
‘2nd Fermi’Rough estimate: #E ~ 4u2
relativistic treatment, averaging over all
angles ==> #E ~ 8/3u2
(for particles having v >> u ==> need rather high energy seed particles ?!! )
2nd order process (u2) ==>
called ‘2nd order Fermi acceleration’
or short ‘2nd Fermi’
Why so interesting ?
15.May.2009 A.Biland: Very High Energy Astronomy 14
‘2nd Fermi’
Assume many scatterings e.g. on many magnetic bubbles[looks like multiple scattering in normal matter]
after n scatterings: total gain =n#E==> can reach any Energy
(if initial seed particles exist ....)
15.May.2009 A.Biland: Very High Energy Astronomy 15
‘2nd Fermi’Assume, particles have probability P toescape the acceleration region after eachscattering (= acceleration step)
==> after step k:
Ek = E0 + k#E Nk = PNk-1 = PkN0
==> power law spectrum !!!
15.May.2009 A.Biland: Very High Energy Astronomy 16
‘2nd Fermi’- can reach high energies- automatically produces power law- can produce large flux (high energydensity in astrophysical B-fields)
but:very slow: - (#E/E ~ (u/v)2, u << v ) ==> gain very little energy per scatter
15.May.2009 A.Biland: Very High Energy Astronomy 17
‘1st Fermi’Look for 1st order (linear) process: #E ~ u
static
B-field
e.g.: reflection on shock front (can have strong B-fields)and back-reflection from static B-field(magnetic cloud)
#E = E2-E1 = 0.5m(v+2u)2-0.5mv2
= 2m(uv + u2) ~ uv v>>u
#E/E ~ uv/v2
~ u/v
But: need very extended,strong B-field to deflect very high energies ???
15.May.2009 A.Biland: Very High Energy Astronomy 18
Cosmic AcceleratorsMaximum energy that can be reached byFermi acceleration is defined by the sizeand strength of a B-field region(if curvature radius > size ==> all particles escape, no further acceleration possible)
Estimates claim that galactic sources cannot accelerate to >1015eV,hypothetical extragal. sources not >1018eV
But recent results indicate that <B> wasunderestimated ==> higher acceler.possible?
15.May.2009 A.Biland: Very High Energy Astronomy 19
'Hillas' Plot:
Magn. field vs.size of mostenergeticastrophys.object classes
100 EeV= 1020eV 1ZeV= 1021eV
?
?
x LHC
15.May.2009 A.Biland: Very High Energy Astronomy 20
MeasuringVery High Energy
Photons
15.May.2009 A.Biland: Very High Energy Astronomy 21
Cosmic microwave background, ~3 mm
satellites
rockets
ra
dio
tele
scopes
" - rays
Earth surface
optical
Telescopes Cherenkov telescopes
particle detectors
fluorescence detectors
ballo
ons
The windowsof Astronomy 50% of incident
radiation absorbed
3 1026 Hz
"-rays
"-rays
For which wavelengths is it possible to measure photons from ground ?
15.May.2009 A.Biland: Very High Energy Astronomy 22
X-ray and !-ray Astronomy
!
e+e–
Focusing instruments Coded masks, collimators(i.e. INTEGRAL)
Compton telescopes
COMPTEL
Pair conversion telescopes
(until ~300 GeV)
keV MeV GeV
XMM
Newton
Energies above few 100eV, no materials known that could work as lenses etc.
==> need other techniques to identify the direction of flight of a photon to be able
to identify (point like) sources of radiation
One could use long narrow tubes/collimator systems, but this would limit the FoV
as well as resolution to opening angle of the device
X-rays can be reflected on very small angles ==> possible to focus if using huge
instruments
few MeV: use complicated system of transparent and blocking regions (‘coded
masks’) ==> pattern of passing photons tells position of source
>10MeV: use Compton effect: MeV photon induces emission of lower energy e-
in upper detector (--> 1.Position). In lower detector, absorb the MeV photon (-->
Energy, 2.Position --> Direction). Spatial resolution limited by scattering angle of
photon (can be estimated by knowing energy of e- in upper detector)
15.May.2009 A.Biland: Very High Energy Astronomy 23
Pair Conversion Principle (Satellite)
ca
lori
me
ter
tr
acke
r
A
C s
hie
ld
!
e+e–
EGRET
Three main parts:
An “active shield”against chargedcosmic rays (particledetector set in anti-coincidence)
A tracker todetermine thetrajectory of the e±
A calorimeter formeasuring theenergy.
EGRET (on board of COMPTON GammaRay Observatory-Satellite 1991-2000)
Pair conversion: GeV photon produces e+e- pair; these can be measured with
standard particle physics detectors and therefore the initial direction and energy
of the photon be reconstructed (within resolution of the detector)
==> each individual photon can be measured ==> 3 detected photons from same
point in the sky can be sufficient to identify a source (for low diffuse background
flux)
15.May.2009 A.Biland: Very High Energy Astronomy 24
R. Dubois, SLAC
GLAST/FERMI MissionGLAST measures the direction,energy and arrival time ofcelestial gamma rays
LAT measures gamma-rays in theenergy range ~20 MeV - 300 GeV(There is no experiment now covering this range)
GBM provides correlative observations oftransient events in the energy range~20 keV – 20 MeV
Orbit: 550 km,
28.5o inclination
Lifetime: 5 years
(minimum)
Launch: June 2008
significant improvements compared to EGRET
LAT: Large Area Telescope [main instrument]
GBM: GLAST Burst Monitor
15.May.2009 A.Biland: Very High Energy Astronomy 25
GLAST LAT, Sketch of a Tower
12 layers Si +
3% X0 of Pb
4 layers Si +
18% X0 of Pb
2 layers Si (no Pb)
0
17
0
7
8 layers CsI
Each TKR layer consists of2 Si layers rotated by 90°(X,Y) and Pb plates
Thin Pb
Thick Pb
Blank (no Pb)
Each CAL layer consists of12 crystals and each layeris rotated with respect withthe next so that it canprovide X and Ymeasurements! Detector
silicon microstrip detectors allow very precise measurements of particle
trajectories
Energy measured in calorimeter (very heavy ==> rather small total area ....)
15.May.2009 A.Biland: Very High Energy Astronomy 26
DAQElectronics
Grid
Tracker
Calorimeter
ACD ThermalBlanket
•Array of 16 identical“Tower” Modules,each with a tracker(Si strips) and acalorimeter (CsI withPIN diode readout)and DAQ module.
•Surrounded by finelysegmented ACD (Anti-Coincidence Detector)(plastic scintillatorwith PMT readout).
GLAST LAT instrument
R. Dubois, SLAC
15.May.2009 A.Biland: Very High Energy Astronomy 27
GLAST design goals
-Low profile for wide field of view-Segmented anti-coincidence shield (ACD) to minimize self-veto at high E.-Fine-segmented calorimeter:enhanced background rejection and shower leakage correction.-High-efficiency, precise track detectors located close to the conversions foils to minimize multiple-scattering errors.-Modular, redundant design.-No consumables.-Low power consumption (580 W)
15.May.2009 A.Biland: Very High Energy Astronomy 28
Old vs. New Space Detectors
B. D
egra
nge
Caution about usually quoted high-energy limit of the energy ranges:
GLAST will be able to measure a 300GeV photon if it hits the detector. But even
for the brightest known sources, GLAST will only catch very few photons
>100GeV during 10 years of operation because of intrinsically limited size of such
satellites...
15.May.2009 A.Biland: Very High Energy Astronomy 29
Old vs. New Space Detectors
15.May.2009 A.Biland: Very High Energy Astronomy 30
FERMI (formerly known as GLAST)
4 daysskymap!!!
3 month skymap: already better than EGRET 10y sensitivity (just published, >200 pointlike sources…)
The FERMI 'bright source list' is not yet an official catalogue
Since spectral and temporal informationl missing, difficult to compare with
EGRET catalogues (FERMI will publish first catalogue in Sept. 2009)
For sure, FERMI will deliver very interesting results ….
(and from Sept. 2009 on, all data will become public !!!)
15.May.2009 A.Biland: Very High Energy Astronomy 31
FERMI: Pulsars
FERMI already discover new class of pulsars ….
15.May.2009 A.Biland: Very High Energy Astronomy 32
FERMI: Pulsars
Must be somewherea calibrationproblem inEGRET and/orFERMI …
Vela-Pulsar
FERMI already discover new class of pulsars ….
15.May.2009 A.Biland: Very High Energy Astronomy 33
FERMI: GRBsGRB080916C, z~4.2first clear indication forGRB emission >1GeV …
New hope for GRB detections with ground based VHE telescopes …
15.May.2009 A.Biland: Very High Energy Astronomy 34
Limitations of Space-bound !-rayTelescopes in the VHE Range
-Small effective areas result in extremelylow detection rates at E >30 GeV, evenfor strongest sources :
$Crab,E>30GeV ~ 0.2 photons/cm2/year
-Calorimeter depth !10 radiation lengths,corresponding to ~ 1 ton per m2
(which is already very expensive to put into orbit …)
==> showers leak out of the calorimeter ==> limited Energy-resolution
15.May.2009 A.Biland: Very High Energy Astronomy 35
Advantages of Space-bound !-rayTelescopes in the VHE Range
• No background (CR vetoed)
• Large field of view (FOV)
• Full sky coverage
• 100% duty cycle
• Rather good angular resolution• Rather good energy resolution
Cover detector with e.g. scintillators
==> if (charged) CR particle crosses detector, it leaves signal in scintillator
==> veto ==> background-free
Problem: shower-particles can escape calorimeter and hit veto-counter
15.May.2009 A.Biland: Very High Energy Astronomy 36
Alternatives to Space-bound!-ray Telescopes in VHE Range ?
!-rays produce air-showers like charged CR==> is it possible to use air-shower detectors to measure !-rays ???
Main Problem:Charged CR much more abundant (~105)than !-ray ==> how to distinguish ???
Ground based instruments are orders of magnitude less expensive, but can they
do the job ???
15.May.2009 A.Biland: Very High Energy Astronomy 37
Extensive Air Showers (EAS)
Electromagnetic Hadronic
Electromagnetic showers are more regular and better confined
Electromagnetic showers do not contain muons
15.May.2009 A.Biland: Very High Energy Astronomy 38
Shower front evolutionShower particles form roughly a disk-shaped front (or very flat cone) of few ns thickness, traveling at speed"c towards the ground
Sketch of shower development
Use arrival time distribution to estimate direction of incident particle
Use intensity of signal to estimate energy of incident particle
15.May.2009 A.Biland: Very High Energy Astronomy 39
Tibet Air Shower Array
To improve gamma-identification sensitivity of EAS detectors: increase size of
total detector as well as reduce distance between individual detector stations.
Additionally go to higher altitudes to be closer to the shower maximum ==>
catch more particles
15.May.2009 A.Biland: Very High Energy Astronomy 40
Tibet Air Shower ArrayFurther improvement:
use better coverage of detector area==> ARGO-YBJ 75x78 m2 RPCs (under construction)
RPC: Resistor Plate Chamber
Allows to cover rather large area without major gaps for reasonable price
15.May.2009 A.Biland: Very High Energy Astronomy 41
Water Cherenkov Detectors
MILAGRO: -full detection coverage -some CR rejection (µ-detection)
idea: second layer of PMTs only sensitive to muons (did not really work out; later
abandoned)
15.May.2009 A.Biland: Very High Energy Astronomy 42
MILAGRO
upgrade: using ‘outriggers’ (cherenkov water tanks)
Using simple water tanks with one PMT significantly enhances area (~20000 m2)
==> higher sensitivity
15.May.2009 A.Biland: Very High Energy Astronomy 43
MILAGRO
northern sky (MILAGRO), status 2007
2007
2003
15.May.2009 A.Biland: Very High Energy Astronomy 44
MILAGROextendedregions ofbright TeV! emissionfrom the‘Cygnus’region(crosses: unident. EGRET contours: expected "0 from CR+ ISM)
15.May.2009 A.Biland: Very High Energy Astronomy 45
Near(?) FutureProposed ‘MILAGRO upgrade’:
High Altitude Water Cherenkov (HAWC):
- higher altitude (4000m a.s.l. ?) ==> lower E-threshold ( 700 GeV ?)
- larger area ==> higher sensitivity (factor 10 ?)
a.s.l. : ‘above sea level’
15.May.2009 A.Biland: Very High Energy Astronomy 46
Status of VHE-! Air Shower Detectors
Advantages:- high duty cycle- large field of view/full sky coverage- possibility to see extended sources- high energy- large active area
Disadvantages:- limited CR rejection ==> low sensitivity- high energy threshold (TeV)
15.May.2009 A.Biland: Very High Energy Astronomy 47
Measurement of Gamma Rays
Air-shower detectors have too low sensitivity andtoo high energy threshold(but are interesting because of ‘full’ sky coverage)
How to improve ???
Needed:
- lower energy threshold (i.e. see showers not reaching ground ?!?!?!)
- better gamma/hadron separation
==> how to reach ???
Main problems are:
- gamma-hadron separation, since there are far more hadronic than photonic
showers
- angular resolution ( O(degree) ) ==> difficult to identify sources
Main advantage:
- ‘full’ sky coverage (at least northern or southern hemisphere); not possible with
other ground-based detection techniques
15.May.2009 A.Biland: Very High Energy Astronomy 48
Cherenkov Effect
First seen by Marie Curie:all radioactive sourcesshowed similar blue gloomin water … ???
Explained by P.Cherenkovin his PhD Thesis (1934):
15.May.2009 A.Biland: Very High Energy Astronomy 49
Cherenkov EffectMedium, refractive index n
Charged particle with v < c/ntraverses medium==> local, shorttime polarization of medium
Reorientation of electricdipoles results in (very faint)isotropic radiation
15.May.2009 A.Biland: Very High Energy Astronomy 50
Cherenkov Effect
v > c/n==> radiation from different points along the trajectory arrive in phase within narrow light-cone at the observer ==> bright light
Similar to sonic boom if v > cacoustic
cos # = 1/$n
15.May.2009 A.Biland: Very High Energy Astronomy 51
Cherenkov Effect1948: P.M.S. Blackett suggests:
shower particles are highly relativistic;refractive index of air > 1
==> must radiate Cherenkov light
huge CR-flux==> CR-induced Cherenkov light contributes O(10-4) of total night sky light (during new-moon)
[ duration of flash of individual shower O(3 ns) ]
15.May.2009 A.Biland: Very High Energy Astronomy 52
Cherenkov Radiation of Shower
( %&1 for 21 MeV e- )
(simplified)
v>c/n; $ = v/c > 1/n; $min=1/n
(for $ ~ 1)
E=" mec2
in water:
E ~0.775MeV
Detailed explanation of Cherenkov radiation can be found in many textbooks (e.g.
Jackson: “Classical Electrodynamics”
For modern experiments, treatment of atmosphere much more complicated
(taking into account temperature, humidity, ....)
15.May.2009 A.Biland: Very High Energy Astronomy 53
Cherenkov Radiation of ShowerAt higher altitudes: lower air-density==> refractive index closer to 1==> smaller Cherenkov-angle==> rather flat distribution of !cherenkov on ground
15.May.2009 A.Biland: Very High Energy Astronomy 54
Cherenkov Radiation of Shower
Hump-structureindependentof initialenergy,as long asshower diesout beforereachingobserver(not true if E >> 1TeV)
15.May.2009 A.Biland: Very High Energy Astronomy 55
Cherenkov Radiation of Shower
for each e- inthe shower !!!
energy loss by Cherenkov radiation ~ 5000 times less than by ionization
(fluorescence light), but because of beamed direction easier to distinguish from
night-sky background
15.May.2009 A.Biland: Very High Energy Astronomy 56
Cherenkov Radiation of ShowerNot all !cherenkov reach observer:1) Rayleigh scattering (by air molecules)
15.May.2009 A.Biland: Very High Energy Astronomy 57
Cherenkov Radiation of ShowerNot all !cherenkov reach observer:2) Mie scattering (by dust particles)
15.May.2009 A.Biland: Very High Energy Astronomy 58
Cherenkov Radiation of ShowerNot all !cherenkov reach observer:3) Absorption (by Ozone, H2O, … )
15.May.2009 A.Biland: Very High Energy Astronomy 59
Cherenkov Radiation of ShowerNot all !cherenkov reach observer:==> have to measure 300…700 nm
15.May.2009 A.Biland: Very High Energy Astronomy 60
Cherenkov Radiation of Shower
primary particle enters atmosphere
produces air-shower
shower-particles emit !cherenkov ==> light pool
detector anywhere in light pool sees shower
problem: background light...
And biggest problem: how to distinguish hadronic and photonic showers
15.May.2009 A.Biland: Very High Energy Astronomy 61
Sampling Cherenkov Telescopese.g.: operational(2007): STACEE, CACTUS (USA), ... decommissioned: GRAAL (Spain), CELESTE (France), …
15.May.2009 A.Biland: Very High Energy Astronomy 62
Sampling Cherenkov TelescopesSecondary optics concentrates !cherenkovfrom each heliostat into a dedicated PMT ==> measure !chr distribution on ground
15.May.2009 A.Biland: Very High Energy Astronomy 63
Sampling Cherenkov Telescopes
STACEE
15.May.2009 A.Biland: Very High Energy Astronomy 64
Sampling Cherenkov Telescopes
15.May.2009 A.Biland: Very High Energy Astronomy 65
Sampling Cherenkov Telescopes
Advantages: - huge mirror area ==> low energy threshold, good energy resol. - excellent pointing - inexpensive (daytime: powerplant; night: telescope)Disadvantages: - tiny FoV (difficult for searches) - limited directional choice - limited gamma/hadron separation ==> large BG - short duty cycle (need dark nights, good weather)
==> no new VHE source found with this technique(but spectra of few known sources extended to lower energies)
15.May.2009 A.Biland: Very High Energy Astronomy 66
Sampling Cherenkov Telescopes
How to improve ?
- need dedicated telescopes for free pointing- need larger FoV (at least few degrees)- need better gamma/hadron separation [how to get more information about the shower parameters than just distribution of Cherenkov-light on ground ???]
- need money ....... (and brilliant ideas)
15.May.2009 A.Biland: Very High Energy Astronomy 67
Imaging Cherenkov Telescopes
1st generation (since ~1950)
directional light-collector + fast camera + trigger+ DAQ ==> …
Crimea
Harwell
light collector: increase number of collected cherenkov photons
fast, high sensitivity camera: able to measure very shorttime light-flashes
Trigger: electronics to identify fast flashes in real-time
Data AcQuisition (DAQ): write triggered signal to storage medium for detailed
offline analysis
15.May.2009 A.Biland: Very High Energy Astronomy 68
Imaging Cherenkov Telescopes
2nd generation:
a) WHIPPLE-telescope (Arizona, USA):
10m tesselated main reflector (Cotton-Davies = spherical)
Pixelized PMT-camera
Operational 1968 - …
(several upgrades (mainly camera improvements); 2nd telescope added, but too low quality => never used)
Usually diameter is given as size of reflector ( ==>taking into account gaps,
WHIPPLE ~70m2 collecting area)
15.May.2009 A.Biland: Very High Energy Astronomy 69
Imaging Cherenkov Telescopes
WHIPPLE:1989: breakthrough (after 21 years of operation) first VHE source found (Crab) (ApJ, 342:379-395, 1989)key ingredients:use ‘high resolution’ PMT camera (39 PMTs)use precise Monte Carlo simulations==> detailed image analysis to reject CR
15.May.2009 A.Biland: Very High Energy Astronomy 70
Imaging Cherenkov TelescopesAt higher altitudes: lower air-density ==> refractive index closer to 1 ==> smaller Cherenkov-angle(==> rather flat distribution of !chr on ground)
==> direction of !chr correlated with height of emission
15.May.2009 A.Biland: Very High Energy Astronomy 71
Imaging Cherenkov TelescopesCherenkov-Telescopesdo not measure!chr-distributionon ground, butmeasure (fractionof) total showerdevelopment==>can be used toidentify/rejecthadronic showers
15.May.2009 A.Biland: Very High Energy Astronomy 72
Hillas - ParametersAdditional parameters:
SIZE = Integral (~energy)
CONCentration
= % of signal within
highest N pixels
ASYMmetry
= signal(<dist) /
signal(>dist) (head / tail)
LEAKage
= % of signal in
outermost pixels (edge of camera)
Definitions:
15.May.2009 A.Biland: Very High Energy Astronomy 73
Hillas - Parameters
Definitions: ‘alpha’ correlatedto shower direction(parallel to telesc.- axis: alpha = 0)
Hadron-showers showflat alpha-distribution
Assume VHE gammas coming from source pointed at with the telescope ==>
have alpha ~0
Hadronic showers come from all directions ==> have flat alpha distribution
==> looking at potential source for extended time, expect a peak at 0 in alpha
distribution
Problem: much more hadronic events ==> takes (too) long time to get (tiny)
signal out of statistical fluctuations
==> use other Hillas parameters to reduce number of hadronic showers in the
sample
15.May.2009 A.Biland: Very High Energy Astronomy 74
Hillas - Parameters
!,e: single electromagnetic shower
p: collection of many electromagnetic sub-showers (plus hadronic core plus muons) [ p+X "0 + "-"+ ... !! µ e
==> p-shower images are typically wider and less smooth than !-shower images
==> statistically, expect different images
15.May.2009 A.Biland: Very High Energy Astronomy 75
Hillas - Parameters(for single telescope)
Very High Energy( > 100 GeV):
!- and hadron-showers showrather differentdistributions forHillas parameters ==>good hadronrejection
Caution: exist far more hadron showers !!!15.May.2009 A.Biland: Very High Energy Astronomy 76
Hillas - Parameters(for single telescope)
Below ~100 GeV:
!- and hadron-showers showrather similarHillas-parameters(hadron-showers consistof fewer subshowers;more statist.fluctuations)
==>hadron rejectionfar more difficult
Caution: exist far more hadron showers !!!
MAGIC (and soon MAGIC-II and HESS-II; later CTA) try to reduce energy
threshold far below 100 GeV
Much more difficult than expected few years ago ....
15.May.2009 A.Biland: Very High Energy Astronomy 77(W.Hofmann, HESS)
1/10000 s (100 µs)
1/100000 s ( 10 µs)
1/1000000 s ( 1 µs)
1/10000000 s
(100 ns)
1/100000000 s
( 10 ns)
Fast Camera is important !
Night Sky
Background ~ 100 Million
photons (in same
wavelenght-band
as cherenkovlight)
hit each PMT
per second
(new-moon night;
much more with
partial moonlight)
Cherenkovflash(for low energy)
~100 photons
distributed over
~4 PMTs
15.May.2009 A.Biland: Very High Energy Astronomy 78(W.Hofmann, HESS)
1/10000 s (100 µs)
1/100000 s ( 10 µs)
1/1000000 s ( 1 µs)
1/10000000 s
(100 ns)
1/100000000 s
( 10 ns)
Fast Camera is important !
15.May.2009 A.Biland: Very High Energy Astronomy 79(W.Hofmann, HESS)
1/10000 s (100 µs)
1/100000 s ( 10 µs)
1/1000000 s ( 1 µs)
1/10000000 s
(100 ns)
1/100000000 s
( 10 ns)
Fast Camera is important !
15.May.2009 A.Biland: Very High Energy Astronomy 80(W.Hofmann, HESS)
1/10000 s (100 µs)
1/100000 s ( 10 µs)
1/1000000 s ( 1 µs)
1/10000000 s
(100 ns)
1/100000000 s
( 10 ns)
Fast Camera is important !
15.May.2009 A.Biland: Very High Energy Astronomy 81(W.Hofmann, HESS)
1/10000 s (100 µs)
1/100000 s ( 10 µs)
1/1000000 s ( 1 µs)
1/10000000 s
(100 ns)
1/100000000 s
( 10 ns)
Fast Camera is important !
15.May.2009 A.Biland: Very High Energy Astronomy 82
Fast Camera is important !
Use (expensive) readout electronics (FADCs):
VERITAS: 2ns (2006) MAGIC: 3ns (2003) --> 0.5ns (2007)
==> camera time-resolution shorter than duration of cherenkov-flash ==> additional information to distinguish between hadron and gamma showers (MAGIC: improve sensitivity ~50% )
[‘DOMINO’ chip developed at PSI will significantly lower the cost]
15.May.2009 A.Biland: Very High Energy Astronomy 83
Air Shower Pictures
Statistically,different showertypes producedifferent showerimages ==>try to get rid ofnon-gammashowers
(WHIPPLE)15.May.2009 A.Biland: Very High Energy Astronomy 84
Imaging Cherenkov Telescopes
WHIPPLE: Crab (1989):
Rather difficult to convince people(after many false-detections by other experiments…)
On: point telescope to potential VHE source
Off: point telescope to region in sky from where no VHE expected
15.May.2009 A.Biland: Very High Energy Astronomy 85
Imaging Cherenkov Telescopes
WHIPPLE: Mkn421: Nature, 358,477-478,1992
2nd source found: Extragalactic (AGN)
improved analysisand more data ==> also muchmore convincingsignal from Crab
Active Galactic Nucleus:
Galaxy with huge central Black Hole (109 solar masses), large accretion disk and
huge jets perpendicular to the disk (see later)
15.May.2009 A.Biland: Very High Energy Astronomy 86
Imaging Cherenkov TelescopesCAT (France):1996-2000
pioneering fine-pixelPMT-camera: only 5m reflector, but 546 PMT-camera
==> better imageparameter reconstruction
(==> WHIPPLE upgraded accordingly)
15.May.2009 A.Biland: Very High Energy Astronomy 87
Imaging Cherenkov Telescopes‘HEGRA System’La Palma, 1996-2000
5 telescopes,each 3.5m reflector,271 PMT pixel camera
pioneering ‘stereo approach’
15.May.2009 A.Biland: Very High Energy Astronomy 88
Imaging Cherenkov Telescopes
Stereo Approach:Several telescopes (separated 80...150m)measure the identical shower(all telescopes ‘sitting’ in same light pool)
==> possible to reconstruct 3dimensional image of the shower
==> better hadron rejection better angular resolution better energy reconstruction
(but: more telescopes = higher cost ...)
4 telescopes observing individual showers: improve statistics by factor 4
==> gain in sensitivity =sqrt(4) = 2
4 telescopes observing identical showers stereo: statistics not improved
(even lowered), but better hadron rejection
==> gain in sensitivity >3
15.May.2009 A.Biland: Very High Energy Astronomy 89
Imaging Cherenkov Telescopes2000: ~10 sources foundmost by Imaging Air Cherenkov Telescopes (IACT)
Next step (3rd generation telescopes): start data-taking WHIPPLE VERITAS (4x12m) 2007 CAT HESS (4x12m) 2004 HEGRA MAGIC (1x17m) 2004 CANGAROO CANGAROO-III 4x10m 2002(first experiment in southern hemisphere)
Upgrades going on: MAGIC: 1x17m ---> 2x17m stereo (2009) HESS: 4x12m ---> 4x12m + 1x28m (2010 ?) CTA?: ~100 telescopes 24m, 12m, 6m south+northern site
15.May.2009 A.Biland: Very High Energy Astronomy 90
VHE Detectors 2007:
15.May.2009 A.Biland: Very High Energy Astronomy 91
Imaging Cherenkov TelescopesAdvantages: - ‘good’ !/hadron separation - good pointing capability - high sensitivity (huge active area) - rather low energy threshold
Disadvantages: - small FoV (cannot do full-sky) - short duty cycle (dark, clear nights) - more expensive than sampling telescop. (but much cheaper than satellites)
15.May.2009 A.Biland: Very High Energy Astronomy 92
H.E.S.S. “High Energy Stereoscopic System”
http://www.mpi-hd.mpg.de/hfm/HESS/ (main contributors: Germany, France )
Khomas Highlands, Namibia, 1800m asl
15.May.2009 A.Biland: Very High Energy Astronomy 93
H.E.S.S.Southern site optimal for observation ofgalactic sources ( SNR, PWN, surprises...)(especially around galactic center)
Phase I:-4 x 12m telescopes, 120m separation; square-aluminized glass mirrors; round; 60cm-spherical dish; f/d = 1.2-high-resolution PMT-camera, 5o FoV
(original plan Phase-II --> 16x12m replaced by construction of 1x28m )
15.May.2009 A.Biland: Very High Energy Astronomy 94
H.E.S.S.
HEGRA
HESSHESS basicallyblown-up copy ofHEGRA telescopeswith CAT-cameras
known technology==> can immediat.start datataking
15.May.2009 A.Biland: Very High Energy Astronomy 95
H.E.S.S.Many important new discoveries within first few years of operation:
-scan of inner part of our galaxy
-first millisecond-pulsar in VHE (no pulsation)-dark accelerators-high-redshift AGNs
15.May.2009 A.Biland: Very High Energy Astronomy 96
VERITAS“Very Energetic Radiation Imaging Telescope Array System”
http://veritas.sao.arizona.edu (main contributors: USA, UK, ...) located at Mt.Hopkins parking lot; Northern site
artist view
15.May.2009 A.Biland: Very High Energy Astronomy 97
VERITASFirst 3rd generation proposal
Phase I:- 4 x 12m telescopes;- spherical; round glass mirrors- high resolution PMT-camera; 3.5o FoV- blown-up carbon copies of WHIPPLE- 500MHz FADCs
Original plan for Phase-II: 7x12mabandoned ....
15.May.2009 A.Biland: Very High Energy Astronomy 98
VERITAS-known hardware (1st telescope ready since 2003)-very experienced physicists (WHIPPLE)-terrible problems with: - founding (many $$$ into GLAST) - location(s): already 2nd location had to be abandoned because of legal problems with native americans; operate from parking lot...
==> limited physics outcome yet (but catching up fast; today, most sensitive array)
15.May.2009 A.Biland: Very High Energy Astronomy 99
CANGAROO-III“Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback” (3rd upgrade)
http://icrhp9.icrr.u-tokyo.ac.jp/ Whomera, Australia (170m asl !!!)
15.May.2009 A.Biland: Very High Energy Astronomy 100
CANGAROO-III
1x 3.8m ---> 1x 10m ---> 4x 10m
- First telescope in southern hemisphere- First 3rd generation telescope starting datataking (2002)
Big problems with: - telescope hardware (e.g. mirror ageing, lightning destroyed electronics, ...)
- analysis reliability (many ‘discoveries’ disagree with HESS; several cross-checks with MAGIC confirm HESS)
===> unknown status & future ...
Let’s hope they will recover soon !!!
Don’t forget: at first, HUBBLE was a complete failure ....
15.May.2009 A.Biland: Very High Energy Astronomy 101
MAGIC“Major Atmospheric Gamma-ray ImagingCherenkov” Telescope
http://wwwmagic.mppmu.mpg.de/Main contributors: Germany,Spain,Italy,Switzerland, ...location: Roque de los Muchachos, Canary Islands, 2200m asl
Switzerland (ETH) joined October 2003 (at inauguration), i.e. no influence on
design and construction ....
15.May.2009 A.Biland: Very High Energy Astronomy 102
MAGICNorthern site optimal for extragalacticsources: AGN, galaxy-clusters, GRBs
Phase-I:1x 17m dish; parabolic; f/d=1quadratic mirrors: aluminum on honeycombhigh-resolution PMT-camera, 3.5o FoV ( 1.8oTrigger )
300MHz FADCs ( ---> 2GHz )a lot of new technology ==> needed more time to understand the system
(today, lowest energy threshold of all CherernkovTelescopes)
Problem: need long time to understand the hardware and systematic effects ==>
less efficient than H.E.S.S. (also less than 50% of money available)
Side remark:
in past, very heated discussion between H.E.S.S. and MAGIC design:
HESS: many medium-sized telescope (initial design: 16x12m) for stereo
MAGIC: few large telescopes (17m, abandoned plan for a 30m)
Today: HESS going for a single(!) 28m telescope
15.May.2009 A.Biland: Very High Energy Astronomy 103
MAGIC Support StructureKeep total
weight as low
as possible to
allow for fast
repositioning
!
use carbon-fibrecell-structure :
strong, but not
very rigid
!Mirror segments
will defocus
when moved
! need AMC
15.May.2009 A.Biland: Very High Energy Astronomy 104
Future PlansCurrent 3rd generation telescopes proofVHE sky much richer than expected fewyears ago
Need:- higher sensitivity (more sources)
- lower energy threshold (distant sources)- higher max. energy (highest energy/source)- better energy- and angular- resolution
(correlation with other wavelengths, morphology of sources, ...)
15.May.2009 A.Biland: Very High Energy Astronomy 105
Very Near Future
MAGIC: 2nd telescope incommisioning-phase==> soon stereo
2010(?): upgrade MAGIC-I camera with higher sensitivity photo-sensors
MAGICMAGIC
MAGIC-IIMAGIC-II
Picture taken June 2006Picture taken June 2006
15.May.2009 A.Biland: Very High Energy Astronomy 106
Very Near FutureH.E.S.S.: build 28m telescope by 2010 (but rather low sensitivity photo-sensors)
12m 28m 12m
option to include a AMC still under discussion…
15.May.2009 A.Biland: Very High Energy Astronomy 107
Near(?) Future‘Cherenkov Telescope Array CTA’: (pan-european project)goal: - improve sensitivity by factor >10 - increase energy coverage by factor >10
==> need ~100 telescopes
==> must reduce cost per telescope15.May.2009 A.Biland: Very High Energy Astronomy 108
Mid FutureOther plans: use much higher sensitivity photo- sensors
e.g. APDs as used in CMS
relative
sen
sitivity
G-APD
PMTs andimprovements
Recent measurements done by our group show that the values from
HAMAMATSU (used for the plot) are too optimistic [by ~20%]
Also new PMT develompments under way
But: one of the two PMT producers worldwide just went out of business (Feb.
2009)
15.May.2009 A.Biland: Very High Energy Astronomy 109
Mid FutureETH [our institute] +PSI have lot ofexperience in using APD (140’000 in CMS)
==> very ambituos goal: build a firstG-APD camera by 2010together with PSI, Uni Wurzburg, Uni Dormund;mount camera in refurbished 3m HEGRA telescope to gainexperience; use this telescope for dedicated observations
Tests with prototype of first camera-module just started …
If successful: important for CTA upgrades
For next few years, PMT are much cheaper per cm2 than G-APDs
But G-APD prices could drop significantly when produced in large amount (since
they will probably be used in medical equipment, huge demand possible)
15.May.2009 A.Biland: Very High Energy Astronomy 110
Near Future
==> DWARF
15.May.2009 A.Biland: Very High Energy Astronomy 111
Detector Sensitivities
CTA (?)
HESS,MAGIC
15.May.2009 A.Biland: Very High Energy Astronomy 112
"-Origins
15.May.2009 A.Biland: Very High Energy Astronomy 113
Top-Down Scenario
HE and VHE gamma could originate from:
- decay of very heavy particles;
(topological defects)
==> would contribute to diffuse radiation; do not expect point sources
[New Physics...]
(soon a AUGER publication ruling out Top-Down also forhighest energy charged CR)
Several HE and VHE sources identified, but we cannot (yet) measure how much
they contribute to the flux of charged Cosmic Ray (CR) particles.
15.May.2009 A.Biland: Very High Energy Astronomy 114
Bottom-Up ScenarioVHE gamma get energy from interactionof VHE/UHE charged particles:
e-, p, (ions) + - Matter - Radiation (low energy !) - B-fields (see Pulsars)
"-
"0
"+
!! (TeV)
p+ (>>TeV)
matter Inverse Compton
! (TeV)
e- (TeV) Synchrotron! (eV-keV)
! (eV)
B
15.May.2009 A.Biland: Very High Energy Astronomy 115
e- Interaction with B-Field
combined effects:‘Synchrotron-Self-Compton effect’ (SSC)
e- beam in B-field produces !synchrotron that get additional energy by IC with e- from same beam (not necessarily identical e-)
==> synchrotron radiation (~keV) and IC radiation (VHE) are coupled ==> |B|
15.May.2009 A.Biland: Very High Energy Astronomy 116
Exist Point Sources ?
What about VHE ?
We know from EGRET there exists many point-like sources (galactic and
extragalactic) of HE gamma-rays.
Are there also sources of VHE gamma-rays ???
If yes: are they correlated ???
15.May.2009 A.Biland: Very High Energy Astronomy 117
EGRET <--> VHE ?
Trevor Weekes (2002): (Spokesman WHIPPLE)
“If you concentrate too much on the EGRET, you might miss a crucial part of the full picture”
15.May.2009 A.Biland: Very High Energy Astronomy 118
EGRET <--> VHE ?“You can find many pictures of egrets, many pictures of elephants, but only few pictures of egrets and elephants”T.Weekes
Only few EGRET sources are also strong at VHE
Many VHE sources have not been seen by EGRET
EGRET: <10GeV (old)IACTs: >300GeV
==> important to close the gap:
GLAST/FERMI; MAGIC,HESS,VERITAS,(CTA)
15.May.2009 A.Biland: Very High Energy Astronomy 119
! from PeV 'Accelerator'
EGRET/ IACTFERMI
similar 2-bump structure for electrons (SSC)
15.May.2009 A.Biland: Very High Energy Astronomy 120
GalacticVHE " Sources
15.May.2009 A.Biland: Very High Energy Astronomy 121
Where to Look ?Search for (rather) unknown sources of CR
At the moment, full-sky monitoring devicesnot sensitive enough. (FERMI >10GeV ?)
Observe only some selected candidates ?==> very biased results
Best compromise:scan a rather small region of the sky,but also look at selected interesting objects
see http://www.mpi-hd.mpg.de/hfm/HESS/ (H.E.S.S.) and http://wwwmagic.mppmu.mpg.de/ (MAGIC)
15.May.2009 A.Biland: Very High Energy Astronomy 122
Where to Look ?Scan will still be biased- is selected region characteristic- difficult to see weak sources- difficult to see very extended sources- difficult to distinguish sources along sameline of sight
- ...
btw: background limited observation ==> sensitivity ~ sqrt(observ.time) !!!
15.May.2009 A.Biland: Very High Energy Astronomy 123
Where to Look ?Central part of our Galaxy has highestdensity of possible source candidates
Equatorial plane tilted vs. milky-way ==> central region best observable from southern hemisphere ==> H.E.S.S. (scan +/- 30o)
btw: latest observations indicate our galaxy is not a pure spiral like Andromeda,
but has a central bar ...
15.May.2009 A.Biland: Very High Energy Astronomy 124
Galactic Sources2003: only 3 galactic VHE sources known2004: scan of the galactic center region with the H.E.S.S. telescope:
Exposure Time:
ApJ 636 (2006) 777-797
Two special regions have much longer exposure time, because extended
observation of specially interesting objects done.
15.May.2009 A.Biland: Very High Energy Astronomy 125
Probably, there are far more weaker sources. But would need more observation
time ....
(There are many other interesting objects in the sky)
15.May.2009 A.Biland: Very High Energy Astronomy 126
CR Power Requirements
Power needed to maintain (galactic) CR:
CR Energy-density: ~1eV / cm3
CR density: ~stable >108 years CR age (@few GeV): ~107 years(~lifetime)
L = (Volume)*(E-density)/(lifetime) ~ "(15kpc)2(200pc) * 1eVcm-3 / 107y ~ 5 1040 erg/s = 5 1033 J/s
If a body is directly exposed to CR, the chemical composition at it’s surface
gets modified by spallation processes.
Comparing chemical composition at surface and inside of e.g. moon-stones
(concentrating on abundances of long-living radioactive isotopes and their
decay products), one can conclude that CR intensity has not drastically
changed over long time
15.May.2009 A.Biland: Very High Energy Astronomy 127
1) Supernova (SN)Already 1911 (before Hess showed extraterrestrial origin !)
Zwicky postulated SN as sources for CR !
Kinetic Energy emitted by typ-II SN:
Typically, ~10Mo ejected, v~5 108 cm/sOn average: 1 SN / 30 years in our Galaxy
==> LSN ~ 3 1042 erg/s = 3 1035 J/s
==> have to convert few% of kinetic SN Energy into CR-Energy (reasonable ?)
==> SN are candidates for CR sources ?(more than 99% of total SN Energy emitted in form of neutrinos ==> ' Astronomy?!)
15.May.2009 A.Biland: Very High Energy Astronomy 128
Supernova Remnant (SNR)Models show that (type-II) Supernovae usually produce two shock waves; v1 < v2 (shell-type SNR)
Energy loss at outer shock:#E1 = 2m(-v1v)
Energy gain at inner shock:#E2 = 2m(v2v) , v>>v2>v1
#E=#E1+#E2=2mv(v2-v1)#E/E = 4(v2-v1)/v
15.May.2009 A.Biland: Very High Energy Astronomy 129
Supernova RemnantShock waves from SN have typicallifetime ( ~ 1000y , v1,2 ~ 106m/s
Energy gain per cycle: En+1=En(1+))Escape Probab. per cycle: P
===> spectral index ! ~ P/) ...===> Supernova Remnants (SNR) seemexcellent accelerators up to ~100 TeV(B-field ~0.1G ==> larmor radius too large...)
VHE photons must be emitted by higher energetic charged particles
==> detection of VHE photons assumed to be proof for particle acceleration
But looking into details, many open questions …. (see next week)
15.May.2009 A.Biland: Very High Energy Astronomy 130
Identified SNRImportant question:e- or p assource particle?
e.g. RXJ 1713Contours: X-ray (ASCA)
Colour: VHE (H.E.S.S.)
[Nature 432(2005)]
excellent spacialagreement ofemission morphology==>indication for e- (?)
For SSC model (e-), expect highly correlated X-ray (synchrotron) and VHE
(inv.Compton) radiation
15.May.2009 A.Biland: Very High Energy Astronomy 131
Identified SNR
but X-ray and VHE spectra do not really agree for simple SSC models (neither in shape nor in intensity)
VHE spectrum good fit with"0 prediction ==> p beam dump(?)[no correlation with X-ray needed]
RXJ 1713
15.May.2009 A.Biland: Very High Energy Astronomy 132
Identified SNR
Contours: VHE emission (HESS)
Color code: mass distribution(?) ( CO-emission )
==> disfavors proton model ... ?!?!?!?!==> need more sources to understand ....
RXJ 1713
For beam-dump, expect highest VHE radiation from regions with highest mass
density
Spacial origin of VHE radiation: agrees with e-, disagrees with p
Spectrum of radiation: disagrees with e-, agrees with p
My personal view: all acceleration models discussed in the literature are
oversimplified ==> must be wrong (or at least: incomplete)
Acceleration probably includes turbulent magneto-plasma-hydrodynamics that is
far from understood even in the laboratory
15.May.2009 A.Biland: Very High Energy Astronomy 133
2) Neutron Star (NS)Shrinking core of progenitor starAngular momentum conserved ==> *NS ~ 2"/30ms (rNS ~ 20km)
Special case: ‘Pulsar’ Strong, short radio and X-ray pulses with extremely precise timing
Slow deceleration: #T/T ~ 10-14
15.May.2009 A.Biland: Very High Energy Astronomy 134
Neutron StarRotational Energy: Erot ~ 1043 J
Energy loss (deceleration): #E~ -0.3 1028J/s
Lifetime: ( ~ 108 y
#NS in Galaxy: n ~ 106
==> total Energy emitted: n#E ~ 1034J/s compare #ECR ~ 5 1033J/s==> NS could maintain CR (if acceleration!)
( but Pulsars also expected to emit comparable energy by gravity waves ? )
15.May.2009 A.Biland: Very High Energy Astronomy 135
Neutron StarFast rotation, huge B-field (>>1012G)
If B tilted relative to * ==> spinning B-field --> strong E-field
max. value: E ~ 1015V/mi.e. charged particle can gain 1000TeV/m !
NS can transform Erot into EkinCR…But: can CR escape NS region ???
15.May.2009 A.Biland: Very High Energy Astronomy 136
Neutron StarProblem: huge B-field ==> Gyro-radius (Larmor-radius) r[km] = E[MeV] / 30*B[G]
i.e. E = 100 TeV = 100 106 MeV B = 1012G r = 3 10-5km = 3mm !!!
==> particles can not escape ! (?)
15.May.2009 A.Biland: Very High Energy Astronomy 137
Neutron StarElectrons immediately lose energy by Synchrotron-radiation (far less efficient for Protons)
Also VHE photons can not escape becauseof Magneto-pair production: !VHE + B --> e+ e-
!VHE + B --> !+ !
15.May.2009 A.Biland: Very High Energy Astronomy 138
Neutron Star
Photons can onlyescape close tomagnetic polesof Neutron Star
==> pulsation
Exist two models for the escape of high-energy particles from Pulsars:Outer gap ; Polar cap/Slot gap(regions where conditions of B and E field could allow escape of particles and/or VHE photons)
15.May.2009 A.Biland: Very High Energy Astronomy 139
Red:Polar Cap
Blue:Outer Gap
Full:Young Pulsar
Hashed:Old Pulsar
15.May.2009 A.Biland: Very High Energy Astronomy 140
Crab PulsarDepending on model, pulsed emission shouldhave cutoff at few 10 GeV; finally seen byMAGIC in 2008!
Polar cap completelyruled out; but alsoouter gap model hasdifficulties to explainmeasurement
pulsed emission
Pulsed emission seen by EGRET for several Pulsars up to ~10GeV
Different Pulsar models predict different cutoff energies for same object.
VHE measurement of one single pulsar gives more information about pulsar
models than >1000 pulsars meaured with extreme precision with radio
telescopes…
15.May.2009 A.Biland: Very High Energy Astronomy 141
Pulsar-Wind-Nebula Plerion / Pulsar Wind Nebula (PWN): SuperNova remnant or nearby high density cloud disturbed by huge energy outflow from Pulsar
Crab (SN1054)
Charged particles accelerated in huge (rotating) B-field of Neutron star
Probably, the beamed, relativistic mass outflow from neutron star induces shock-
wave in SNR and disturbs spherical symmetry
PWN shock-wave accelerates CR particles to extremely high energies via Fermi
acceleration
==> p and/or e- emit VHE photons
Also possible that a relativistic particle beam travels much farther and is dumpedinto a rather far away gas cloud (producing beamed "0), or inducing shock-waves
and acceleration-processes there. Even a photon-beam might be able to induce
shock-waves in distant gas-clouds.
15.May.2009 A.Biland: Very High Energy Astronomy 142
Identified PWN Crab well known in all wavelengths,also by EGRET very close (~2kpc) ==> very bright
found by WHIPPLE, seen by ‘all’ experiments
no other known candidate on line of sight =>no doubt
Crab is used as ‘standard’ candle in VHE observations
Measured fluxes and experimental sensitivities often given relative to Crab-flux
(advantage: the large, unknown systematic uncertainties cancel)
Crab is a northern source, badly visible for southern experiments like HESS
15.May.2009 A.Biland: Very High Energy Astronomy 143
Possible PWNSeveral sources from the HESS scan haveknown pulsars ~nearby, but no proof theseare the accelerators that light up theVHE emission; some sources are extended.
( Beamed relativistic emission from strong pulsars could travel rather long distance until VHE gamma emission is initiated:
- high matter density: shock waves - high B-field: SSC mechanism from e-
15.May.2009 A.Biland: Very High Energy Astronomy 144
Possible PWNTwo sources on nearly same line of sight(but could have large separation in distance)
color: H.E.S.S. ; triangles: positions of known pulsars
telescoperesolution(PSF) ==>extendedsources
Point Spread Function (PSF)
15.May.2009 A.Biland: Very High Energy Astronomy 145
Possible PWNTriangles: known PulsarsWhite circles: known SNR
White dotted: unid EGRET
point-likesource foldedwith experimentresolution
==> extended15.May.2009 A.Biland: Very High Energy Astronomy 146
Possible PWN
HESS J1834:(cross-checked MAGIC)
some agreement withhigh mass density regions(contours) could beindication for abeam-dump ....[higher resolution VHE images would be helpful, but intrinsic limit of IACT technique]
Imaging Air-shower Cherenkov Telescope (IACT)
15.May.2009 A.Biland: Very High Energy Astronomy 147
3) Binary SystemsBinary systemof a largestar and acompact,heavy object(Neutron star or Black Hole)
Mass transferfrom largestar tosmall object
15.May.2009 A.Biland: Very High Energy Astronomy 148
Binary Neutron StarConstant matter flux from star speeds upthe rotation of Pulsar ->‘millisecond Pulsar’
Known to emit ~1031 J/s (per system) in X-ray
If similar amount of Energy emitted in CR==> few 100 Binaries could make major contribution to total CR Energy
15.May.2009 A.Biland: Very High Energy Astronomy 149
Binary Neutron StarEnergy gain in Binary system:Gravitational acceleration of proton:
#E=-!G mpMNS/r2dr=G mpMNS/RNS~ 70MeV
But mass flow >>1030 protons / second ==> huge total energy to be emitted
Same processes like on Neutron Stars,plus additional acceleration processespossible in accretion disk (e.g.shock waves)
Physics in accretion disk highly controversial
RNS
Inf.
15.May.2009 A.Biland: Very High Energy Astronomy 150
micro-QuasarBlack hole instead of Neutron star==> even more gravitational Energy pumpedinto accretion disk
relativistic jets perpendicular to accr.disk(similar as in real Quasars, but factor 106 smaller dimensions …)==> can be used as laboratory-model ofQusars ?!!!
15.May.2009 A.Biland: Very High Energy Astronomy 151
X-ray BinariesTwo possibilities for VHE production:micro-Quasar: Pulsar Wind Nebula:form. of accretion disk emission from pulsar interactsand relativistic jets with the ‘atmosphere’ of the(like in real Quasars) heavy star (mass flow and light)
VHE emission from Quasars: see next week
15.May.2009 A.Biland: Very High Energy Astronomy 152
X-ray BinariesX-ray Binaries
variablevariable flux: flux: [orbital phase][orbital phase]
--marginal detection [0.2-0.4] marginal detection [0.2-0.4] (X-ray?)(X-ray?)
--maximum flux atmaximum flux at [0.5-0.7] [0.5-0.7] (Radio?)(Radio?)
(~16% (~16% of Crab flux)of Crab flux)--orbital modulationsorbital modulations (==>emission is produced in the(==>emission is produced in the interplay of interplay of both objects ?)both objects ?)--low emission at low emission at periastron periastron [0.2][0.2]-hints for periodicity-hints for periodicity ??????
(no measurements [0.8-1.0] and [0.0-0.1] (no measurements [0.8-1.0] and [0.0-0.1] because because of coincidence with full moon )of coincidence with full moon )
Science 312, 1771 (2006)Science 312, 1771 (2006)LS I +61 303 (MAGIC detection)
Can only observe 1-2 hours per night for few months per year ...
Seems better correlation with Radio emission than with X-ray (but not enough
VHE and X-ray data yet to take a conclusion)
15.May.2009 A.Biland: Very High Energy Astronomy 153
X-ray BinariesX-ray Binariescompanion: B0 companion: B0 Ve Ve star with star with circumstellar circumstellar disc, 10.7mag; disc, 10.7mag; distancedistance 2kpc2kpchighly eccentric orbit(0.7); highly eccentric orbit(0.7); period=26.5dperiod=26.5d (from X-ray and radio modulation)(from X-ray and radio modulation)compact jets (100AU) resolved in radio;compact jets (100AU) resolved in radio; marginally assoc.marginally assoc. EGRET source EGRET source Radio-bursts at phase [0.5-0.8], X-ray burst around [0.3]Radio-bursts at phase [0.5-0.8], X-ray burst around [0.3]
(assuming(assuming periodicity...) periodicity...)
Green contours: positional uncertainty of unidentified EGRET sources
15.May.2009 A.Biland: Very High Energy Astronomy 154
X-ray BinariesLS 5039: ( science 309, 746 (2005)
similar object(?), detected by HESS
3.9 days orbit;excellent agreement withX-ray periodicity
discussions going on if these objects shall be renamed !-ray binaries
(probably more energy emitted by !-rays than by X-rays)
15.May.2009 A.Biland: Very High Energy Astronomy 155
X-ray Binaries
not only flux, but also spectrum depends on orbital phase;ev. interaction of VHE and optical photons ?
LS 5039
15.May.2009 A.Biland: Very High Energy Astronomy 156
4) Galactic CenterGalactic black hole (~106 Msun):shock-waves and strong B-fields==> accelerator ????
but also many other objectsin very crowded area couldbe accelerators ....
15.May.2009 A.Biland: Very High Energy Astronomy 157
Galactic CenterVHE emission claimed byWHIPPLE, CANGAROO, HESSbut completely incompatiblespectra ==> who is correct ?
==> measured byMAGIC (only possibleunder very large zenithangle ==> Ethreshold~1TeV)
==> excellent agreement with HESS,CANGAROO ruled out
Spectral shape and no indication for cutoff up to >10TeV excludes (most) Dark
Matter models as dominant source for the radiation
(see later)
15.May.2009 A.Biland: Very High Energy Astronomy 158
Galactic Center
not possibleto decide (yet)
about originof VHEradiation
MAGIC and HESS: no indication for variability on month/years-scale (else could rule out SNR)
SNR (and PWN) are expected to show constant emission
Black hole induced emissions can show dramatic variability (see next week), but
also have steady emission for long time
15.May.2009 A.Biland: Very High Energy Astronomy 159
Galactic Center RegionAdditionally fromextended HESSmeasurements:
after removing signal from point-sources, clear indication for~diffuse radiationfrom the vicinityof the galacticcenter;good agreement withmass distribution==> CR beam dump ?
J1747: PWN
J1745: GC(?)
15.May.2009 A.Biland: Very High Energy Astronomy 160
Galactic Center Region
Taking into account thesteepening of spectrumbecause high energyprotons can leave thegalactic mag.Field,VHE spectrum still indisagreement withmeasured CR-spectrum
==>indication for recent/ongoing CR production ?!
If diffuse emission would be induced from beam-dump of galactic CR, the
observed spectrum should agree with predictions from the ‘Diffuse model’.
The observed deviation can indicate the emission is not induced by CR, or the
CR spectrum close to the galactic center is different than in our neighborhood
(e.g. close to a very strong CR source, the average CR age is much lower and
therefore the spectrum harder [highest energy particles had not yet enough time
to escape])
15.May.2009 A.Biland: Very High Energy Astronomy 161
5) 'Dark Accelerators'Some VHE sources foundhave now known astro-physical counterpart !!!(but has nothing to do with Dark Matter or Dark Energy)
White circle and triangle:nearby SNR; can not bethe accelerator
But: could exist nearbypulsar (not visible if weare not in emission direction)
15.May.2009 A.Biland: Very High Energy Astronomy 162
Galactic VHE sources 2007
galactic VHE sky is far richer than expected .....
Source Type Discovery reference
Crab Nebula PWN Weekes et al., ApJ 342 (1989) 379
PSR 1706-44 PWN Kifune et al., ApJL 438 (1995) L91
Vela X PWN Yoshikoshi et al.,ApJL 487 (1997) L65
RX J1713.7-3946 SNR Muraishi et al., A&A 354 (2000) L57
Cassiopeia A SNR Aharonian et al., A&A 370 (2001) 112
TeV 2032+4130 ? Aharonian et al., A&A 393 (2002) L37
RCW 86 SNR Watanabe et al.,28th ICRC (2003) 2397
Sgr A* ??? Tsuchiya et al., ApJL606 (2004) L115
G0.9+0.1 PWN Aharonian et al., A&A 432 (2005) L25
MSH 15-52 PWN Aharonian et al., A&A 435 (2005) L17
RX J0852.0-4622 SNR Katagiri et al., ApJ 619 (2005) L163
HESS J1303-631 PWN Aharonian et al., A&A 439 (2005) 1013
PSR 1259-63 Bin Aharonian et al., A&A 442 (2005) 1
HESS J1614-518 ? Aharonian et al.,Science 307(2005) 1938
HESS J1616-508 ? Aharonian et al.,Science 307(2005) 1938
HESS J1640-465 SNR? Aharonian et al.,Science 307(2005) 1938
HESS J1804-216 ? Aharonian et al.,Science 307(2005) 1938
HESS J1813-187 SNR Aharonian et al.,Science 307(2005) 1938
HESS J1825-137 PWN Aharonian et al.,Science 307(2005) 1938
HESS J1834-087 ? Aharonian et al.,Science 307(2005) 1938
HESS J1837-069 ? Aharonian et al.,Science 307(2005) 1938
LS 5039 Bin Aharonian et al.,Science 309(2005) 746
LSI 61+303 Bin Albert et al., Science 312 (2006) 1771
HESS J1632-478 ? Aharonian et al., ApJ 636 (2006) 777
HESS J1634-472 ? Aharonian et al., ApJ 636 (2006) 777
HESS J1702-420 ? Aharonian et al., ApJ 636 (2006) 777
HESS J1708-410 ? Aharonian et al., ApJ 636 (2006) 777
HESS J1713-381 SNR Aharonian et al., ApJ 636 (2006) 777
HESS J1745-303 ? Aharonian et al., ApJ 636 (2006) 777
HESS J1418-609 PWN Aharonian et al., A&A 456 (2006) 245
HESS J1420-607 PWN Aharonian et al., A&A 456 (2006) 245
Source Type Discovery reference
HESS J1718-385 PWN Aharonian et al., A&A 472 (2007) 489
HESS J1809-193 PWN Aharonian et al., A&A 472 (2007) 489
Westerlund 2 OC Aharonian et al., A&A 467 (2007) 1075
HESS J0832+058 ? Aharonian et al., A&A subm.
MGRO J1908+06 ? Abdo et al., ApJ 664 (2007) L91
MGRO J2019+41 ? Abdo et al., ApJ 664 (2007) L91
MGRO J2031+37 ? Abdo et al., ApJ 664 (2007) L91
MAGIC J0616+025 ? Albert et al., ApJL accepted
W28 SNR Aharonian et al., in prep.
HESS J1912+101 PWN Aharonian et al., in prep.
Cygnus X-1 Bin Albert et al., ApJL 665 (2007) L51
HESS J1427-608 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1626-490 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1702-420 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1708-418 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1731-347 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1841-055 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1857+026 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1858+020 ? Kosack et al., 30th ICRC, Merida, 2007
HESS J1908+063 ? Djannati et al. 30th ICRC, Merida, 2007
Kes 75 PWN Djannati et al. 30th ICRC, Merida, 2007
G21.5-0.9 PWN Djannati et al. 30th ICRC, Merida, 2007
HESS J1357-645 PWN Lemiere et al., 30th ICRC, Merida, 2007
HESS J1809-193 PWN Lemiere et al., 30th ICRC, Merida, 2007
Type Candidates:
SNR (shell-type) Supernova Remnant
PWN Pulsar Wind Nebula / Plerion
Bin Gamma-ray Binary / Microquasar
OC Open Cluster
? Unidentified, incl. ‘Dark Accelerators’
also: diffuse emission from Galactic Center Region
few new sources found in 2008; expect ~20 new ones from HESS later this year
(improved analysis of the galactic-scan data)
15.May.2009 A.Biland: Very High Energy Astronomy 163
Stellar Wind ???HESS:‘Westerlund 2’ is a young stellar cluster containing manyheavy stars (==>strong stellar winds?).Possible explanations for VHE source could be collidingstellar winds forming shock-waves ....
extended
If this is correct, it would be the first galactic VHE object having ‘normal’ stars as
initiator of the acceleration.
All other identified galactic sources have SNR or PWN as origin (i.e. remainders
of a SuperNova explosion)
Starburst regions believed to be interesting, because they are expected to host
quite many SuperNovae ==> many SNR and PWN as accelerators. But it
seems, that already before the Supernova explosion, VHE acceleration is
possible
15.May.2009 A.Biland: Very High Energy Astronomy 164
Extra-GalacticVHE " Sources
15.May.2009 A.Biland: Very High Energy Astronomy 165
Where to Look ?Search for (rather) unknown sources of CR
At the moment, full-sky monitoring devicesnot sensitive enough at VHE
Observe only some selected candidates ?==> very biased results
But only possibility ...
15.May.2009 A.Biland: Very High Energy Astronomy 166
Galaxy Classification
Active
Galactic
Nucleus
LBL HBL
Milkyway,
Andromeda,
...
Exist other (incompatible)classification schemes …
HBL are a tiny fraction of all galaxies, but assumed best candidates to look for
VHE emission
15.May.2009 A.Biland: Very High Energy Astronomy 167
Active Galactic Nuclei (AGN)Huge (108-1010Mo)Black Hole withhigh mass inflow
==>
Accretion-disk,two relativisticjets
Variable inflow==>variable emissionsin what energy regime?
15.May.2009 A.Biland: Very High Energy Astronomy 168
AGN ClassificationMost probably,the differentAGN-classes justindicate underwhat angle welook at theobject ...
BL-Lacs:look directlyinto one of the relativistic jets==> expecthigher energiesfrom Lorentz boost
15.May.2009 A.Biland: Very High Energy Astronomy 169
Spectral Energy Density (SED)dependencies between different wavelengthscan help to understand basic mechanisms
radio optical Xray EGRET IACT FERMI
Coloured and black data from different observation periods ==> significant
varibility in VHE, X-ray, optical
Is there a correlation ???
15.May.2009 A.Biland: Very High Energy Astronomy 170
AGN Morphology
Probably several shock waves in jet ==> several VHE sources ?!
radio
IACTs (and GLAST) have by far not good enough angular resolution to be able to
distinguish between possible emission from the core and the different ‘knots’ ...
15.May.2009 A.Biland: Very High Energy Astronomy 171
AGN MorphologyAt least in radio(highest resolution),the emission cancome from several‘blobs’ that cantravel with differentvelocities along thejet axis
IACTs (and FERMI)have not good enoughangular resolution tosee such details==> see only average
Because of viewing angle, the different blobs seem to have velocities higher than
speed of light
(‘superluminal motion’)
15.May.2009 A.Biland: Very High Energy Astronomy 172
AGN Variability
Four 3-years 'light-curves' (flux vs. time)of radio measurements with same telescope
Is there anything common ?
15.May.2009 A.Biland: Very High Energy Astronomy 173
AGN VariabilityIt is the same source …
Longest measurement of an AGN with identical(!) telescope
15.May.2009 A.Biland: Very High Energy Astronomy 174
AGN Variability
At least at lowenergies (optical,radio), AGNs show variabilityat any timescale(years<->minutes)
15.May.2009 A.Biland: Very High Energy Astronomy 175
AGNs @ VHE ?Major questions:- which AGNs emit also at VHE ?- how do AGNs accelerate particles (thatemit VHE photons) ?
- how do AGNs look at VHE (spectra,variability, ...) ?
- correlations between VHE and otherenergies ?
- ...- but also: use VHE photons as tools toinvestigate fundamental physics questions(extreme energies@extreme distances; see next week)
15.May.2009 A.Biland: Very High Energy Astronomy 176
AGNs @ VHEStatus 2003:~4 VHE emitters known (all HBL-type)
VHE flux highlyvariable:-intensity can change factor >>10: ‘flares’-variations seen on timescales ~ 1day
good agreement between experiments==> confidence in IACT method
existed also several dubious claims of other VHE AGNs, but most not confirmed
(and/or ruled out by new observations)
15.May.2009 A.Biland: Very High Energy Astronomy 177
sometimes the spectral index changes with flux
AGNs @ VHE
15.May.2009 A.Biland: Very High Energy Astronomy 178
often exists goodcorrelation betweenVHE and X-ray flux
but indication of ‘orphan flares’ (VHE without corresponding X-ray)
AGNs @ VHE
15.May.2009 A.Biland: Very High Energy Astronomy 179
AGNs @ VHE
huge variabilities …=> need luck to catch a AGN in flaring state(most known sources invisible in 'low state')
15.May.2009 A.Biland: Very High Energy Astronomy 180
AGNs @ VHE
15.May.2009 A.Biland: Very High Energy Astronomy 181
AGNs @ VHEbiased because of ‘hunt for flares’}
exists a ‘quiet state’VHE emission, oronly during flaringactivity ??????
The old Whipple telescope is mainly used to monitor 'known sources' to get an
unbiased selection;
MAGIC is regularily monitoring few 'known sources' for same reason
ETH + Uni Wuerzburg + Uni Dortmund are refurbishing an old HEGRA telescope
for constant monitoring of the brightest VHE-AGNs in the northern sky….
15.May.2009 A.Biland: Very High Energy Astronomy 182
AGN VHE ‘Dogmas’until ~2004, many people believed to‘know’ about VHE emissions from AGNs:
- only HBLs are potential VHE emitters ( ‘Blazar Sequence’ )- minimal timescale for variability ~ radius of central Black Hole ( ~1hour )- potential origin of VHE radiation must berather close to the central Black Hole
15.May.2009 A.Biland: Very High Energy Astronomy 183
Only HBLs ???if you only look at HBLs, you will only see HBLs...
already HEGRA found hint for VHE emission fromthe giant radio-galaxy M87 (confirmed by HESS,MAGIC,VERITAS)
‘very nearby; mis-aligned Blazar ==> no real problem’
2006: MAGIC sees VHE emission from the LBL ‘BL Lacertea’2006: MAGIC sees VHE emission from the FSRQ ‘3C279’2008: VERITAS sees VHE emission from LBL/IBL ‘W Comae’===> ‘Blazar Sequence’ is dead !!!!
2009: HESS sees VHE emission from Cen-A (similar to M87 or first VHE-detection of a Seyfert ?)
HBL: high frequency peaked Bl-Lac object
LBL: low frequency peaked Bl-Lac object
IBL: intermediate frequency peaked Bl-Lac object
FSRQ: flat spectrum radio quasar
15.May.2009 A.Biland: Very High Energy Astronomy 184
Only HBLs ???
Active
Galactic
Nucleus
LBL HBL
Milkyway,
Andromeda,
...
M87HEGRA, ... 3C279
MAGIC
BL LacMAGIC
.... more to come ....
In the case of Blazars, the relativistic jet is directly pointing towards the observer
==> if emission is coming from the jet, expect higher energies because of
Lorentz-boost
15.May.2009 A.Biland: Very High Energy Astronomy 185
1h Shortest Variability ???From the two best (longest) investigatedVHE HBLs (until 2005):
- Mkn 501 exhibits strong flux variabilityon the month-year scale, but not shorter
- Mkn 421 exhibits stron flux variabilitydown to the minimal ~1h timescale
?? both objects should be rather similar ??
15.May.2009 A.Biland: Very High Energy Astronomy 186
MAGICMAGIC
X-rayX-ray
OpticalOptical
full-moonfull-moonCrabCrab
Markarian Markarian 501501
Mkn501: nearby AGN, z = 0.034Mkn501: nearby AGN, z = 0.034- well known VHE source - well known VHE source (detected by WHIPPLE 1995)(detected by WHIPPLE 1995)-- has large flux variations has large flux variations ( O(20) on years scale)( O(20) on years scale)
MAGIC observationMAGIC observation scheduled to measurescheduled to measure ‘‘low-statelow-state’’ spectra in spectra in June/July 05June/July 05
but:but: strong VHE flares seenstrong VHE flares seen (X-ray counterpart ?)(X-ray counterpart ?)
15.May.2009 A.Biland: Very High Energy Astronomy 187
Markarian Markarian 501501
AGN jets have sizes >105 LyBH has radius ~ 1 Light-hour
observer
2min bins
Mrk501
~similar
But variability within minutes==> small emission region or extreme boost factors
MAGIC
2min binwidth
Many people did not trust us ...
15.May.2009 A.Biland: Very High Energy Astronomy 188
1h Shortest Variability ???
Later, H.E.S.S. alsofound short variabilityfrom PKS-2155==> no doubt possible(pure serendipity detections)
Shortest observed variabilities probably just limited by sensitivity of observatory
Observed very fast VHE variabilities are shorter(!) than what has ever been seen
in optical/radio/X-ray/... !!!
(because of huge active area of Cherenkov Telescopes, we can measure shorter
variations)
15.May.2009 A.Biland: Very High Energy Astronomy 189
Spectral ShapeNot only flux canchange drasticallywith time, alsothe shape of thespectrum can varysignificantly==>every flare looksdifferent ???
try to find ‘quiet’ state ...
Mkn 421
15.May.2009 A.Biland: Very High Energy Astronomy 190
Origin of VHE ???‘Misaligned Blazar’ M87: very close, not looking into jet ==> possibility to see the origin??
IACTs (and GLAST) have not good enough angular resolution
but doing Multi-Wavelength might help ???
15.May.2009 A.Biland: Very High Energy Astronomy 191
Origin of VHE ???
M87: VHE vs. Xraycorrelation better ifassuming emissionfrom Core than fromblob HST-1 ?!!!
triggered by MAGIC
15.May.2009 A.Biland: Very High Energy Astronomy 192
VHE @ AGN StatusMany excitingAGN resultsfrom the past4 years
analysis andobservations andtelescope improvgoing on ...
?
15.May.2009 A.Biland: Very High Energy Astronomy 193
VHE @ AGN Status“There is something wrong with ...
... common assumptions about the gamma-ray generation mechanism
... common assumptions about the basic physical parameters of blazars
... common assumptions about the nature of TeV sources “
Esko Valtaoja, ‘Workshop on AGN and relatedFundamental Physics in VHE Astronomy’
Jerisjaervi, Finland, April 2008
Every theoretician has a different model that can ‘easily’ explain all observations
But all models get into trouble if trying to combine with results from radio and X-
ray
Need much more data; long-time and full multi-wavelength coverage
(still difficult to convince other astronomers: bright VHE sources usually ‘boring’
for radio, X-ray, ... )
15.May.2009 A.Biland: Very High Energy Astronomy 194
Physics usingVHE "-rays
15.May.2009 A.Biland: Very High Energy Astronomy 195
VHE as ToolEven if the sources and mechanisms ofVHE are not understood, one can tryto use them as tools to do physics inregions not accessible in laboratories.
Use- highest energy photons- longest distancesto investigate questions from cosmologyand fundamental physics ....
15.May.2009 A.Biland: Very High Energy Astronomy 196
e.g. extreme B-fieldsIn the extreme B-fields close to e.g. thesurface of Pulsars expect Quantum-effects
- quantum-synchrotron radiation==> 'curvature radiation'
- magneto-pair production ( !+B --> e+e- )- etc.
Recent detection of the high-energy end of(V)HE emission from Crab-Pulsar by MAGICallows to test such predictions
15.May.2009 A.Biland: Very High Energy Astronomy 197
e.g. Extragal. Background Light (EBL)
Universe is not transparent for VHE photons !!!
Usually people use the term ‘Extragalactic Background Light’ (EBL)
but correct term would be ‘Metagalactic Radiation Field’ (MRF)
15.May.2009 A.Biland: Very High Energy Astronomy 198
EBL
Intrinsic spectrum + EBL density+ Distance = Measured spectrum
Intrinsic spectrum + EBL density+ Measured spectrum = Distance...
(but what is intrinsic spectrum ???)
==> IF(!) intrinsic spectrum is know [e.g. typical AGN spectrum], could serve as
independent method to measure huge distances with different systematics than
SN1a method ==> independent cross checks possible (Dark Energy !!!)
15.May.2009 A.Biland: Very High Energy Astronomy 199
EBLDensity of CMB canbe measured [andcalculated] with veryhigh precision (WMAP)
Density of EBL cannot be measureddirectly: too highforeground contrib.from galactic objectsplus IR emission fromdetector
Redshifted Redshifted Redshifted
star light dust emission Big Bang
IR
Redshifted star-lightcontains info about all stargenerations since BigBang
15.May.2009 A.Biland: Very High Energy Astronomy 200
EBL
Upper limit fromdirect measurem
Lower limit from‘galaxy count’:sum of all infowe have aboutknown astronom.objects
15.May.2009 A.Biland: Very High Energy Astronomy 201
EBLKnown:-measured spectrum-distance (ident. AGNs)
Assumed (models):intrinsic spectrum can’tbe harder than 1.5 (?)
==> unfold measuredspectrum with differentEBL possibilities andcheck if intrinsic ok measured unfolded
Higher redshift AGNs show more absorption ==> better suited
Learned that current AGN models are too simplistic, so the assumption about the
intrinsic spectrum might be wrong
==> important to also measure (unabsorbed) nearby AGNs !!!
15.May.2009 A.Biland: Very High Energy Astronomy 202
EBL
If assumptionabout intrinsicspectrum iscorrect, VHEmeasurementsalready excludehigh EBL density
15.May.2009 A.Biland: Very High Energy Astronomy 203
EBL
VHE measurements start to touch lower limits ???
15.May.2009 A.Biland: Very High Energy Astronomy 204
EBL
Because of 'extreme' redshift z>0.5, thespectrum of 3c279 contains most information (but unfortunately rather low statistics)
3C279
Unfortunately, 3C279 (like all AGNs) shows chaotic flaring behaviour
==> don’t know when one should observe
==> don’t know how long it takes to get higher quality data
==> Need higher sensitivity observatories !!!
3c279 is another AGN-type (FSRQ) than the usual HBLs
==> we know even less about the intrinsic spectrum …
15.May.2009 A.Biland: Very High Energy Astronomy 205
EBL
When/if MAGIC gets more signal from3C279, expect much better constraints ...
3C279
But the detection of 3c279 already clearly proves the universe to be rather
transparent at VHE
==> huge potential for MAGIC-II, HESS-II, CTA, …
15.May.2009 A.Biland: Very High Energy Astronomy 206
EBL StatusOpen question in cosmology: what was first ?- first star generations (from small star-size gas clumps) combine later to form a galaxy [these stars contribute to EBL; difficult to include in galaxy count]
- first galaxy-size gas clumps are separated into star-size clumps and then form first stars [i.e. already very first stars included in galaxy count EBL limit]
VHE observations indicate that lower limits fromgalaxy counts represent (almost) full EBL density(?)==> galaxies formed first ???
Are first stars created independently or as a complete galaxy ???
15.May.2009 A.Biland: Very High Energy Astronomy 207
EBL StatusVery recent star-formation modelsshow that very first stars might havebeen fueled by DarkMatter annihilationinstead of H->He fusion
==> might have had different emission than normal stars==> would contribute to EBL different than assumed in predictions
high precision EBL results from Cherenkov telescopes could be theonly possibility to find evidence for ‘DarkMatter Stars’ ??
If Dark Matter is 'neutralino-type', such DarkMatter stars would have
masses >>100M_sun,
Radii >>1 Atronomical unit (150 Mio km) I.e. really huge, but low density
surface temp ~5000K (like sun), I.e. very cold for such heavy objects
lifetime ~ few Mio years; unclear what happens when all DM fuel consumed
(my personal opinion: collapse continues ==> 'standard' first stars)
15.May.2009 A.Biland: Very High Energy Astronomy 208
Quantum Gravity ?
Sloth Sloth (few large steps)(few large steps) and Ant and Ant (many small steps)(many small steps) have same velocity have same velocity on flat surfaceon flat surface
On uneven ground,On uneven ground,Ant seems to beAnt seems to beslowerslower (follow structures) (follow structures)
QG couldQG could makemakespace foam-like;space foam-like;long wavelengthlong wavelengthless affectedless affected==>==>Low energy Low energy ""seem fasterseem faster
violate violate Lorentz Lorentz Invariance !Invariance !
Big Problem in Fundamental Physics:
Standard Model Particle Physics and General Relativity can not (yet) be
combined into one uniform theory
But in most extreme conditions, SM and GR predictions are inconsistent
Quantum Gravity is one group of Meta-theories that might solve the problem, but
so far no QG predictions within experimental reach ...
15.May.2009 A.Biland: Very High Energy Astronomy 209
Quantum Gravity ?These classes of QG-theory describe justa Taylor-expansion
#c/c = +(an#E/MQG)n
==> effect can be both possibilities(lower energy photons faster or slower than higher energy ones)
[ 'mountain with tunnel': ant can go through tunnel, while sloth must climb over the mountain ==> seems slower ]
15.May.2009 A.Biland: Very High Energy Astronomy 210
MAGIC:Mkn501 flare June 2005:
Energy dependentarrival time ???
Full unbinned analysis:-max likelihood-‘energy cost function’==> delay ~30sec/TeV
Possible reasons for delay:-acceleration at source-emission from source-transport between source and
observer(all three types would contain interesting physics)
But: why no dispersion ??????
0.25- 0.6 0.25- 0.6 TeVTeV
0.6 - 1.2 0.6 - 1.2 TeVTeV
1.2 - 10 1.2 - 10 TeVTeV
Quantum Gravity ?
15.May.2009 A.Biland: Very High Energy Astronomy 211
Assuming energy-independent emission time,dispersion because of Quantum-Gravity effects #c/c = -#E/MQG1 or #c/c = -(#E/MQG2)2
MQG1 = (0.47+0.31-0.13) 1018 GeV ?? MQG2 = (0.61+0.49-0.14) 1011 GeV ?? [ but be careful with statistics of ‘1’ ] or 95% lower limits: MQG1 > 0.21 1018 GeV ; MQG2 > 0.27 1011 GeV much better than any other measurement [at that time] (the main constraint is not coming from the maximum time delay, but from the duration of the flare <==> limit on maximum dispersion)
Quantum Gravity ?
15.May.2009 A.Biland: Very High Energy Astronomy 212
unexpected detection of very short AGN flaresallow to investigate unexplored physics rangebut:
Need many short flares at varying z !!!! (to distinguish source-intrinsic vs. transport effects; HESS PKS-2155 flare shows no clear time-delay)
Is analysis sensitive to short flares ????? A short flare might go undetected if source is in quiet state, because 10min flare smeared out over 2h observation .....
Apply different rules than for source detection ???
Optimal procedure to find short flares ?!
Quantum Gravity ?
15.May.2009 A.Biland: Very High Energy Astronomy 213
Quantum Gravity ?Want to measure #t = #c * dist ~ #E * dist
Possibilities: Pulsars: #t very precise, #E rather small, dist very small
GRBs: #t rather precise, #E small, dist huge
AGNs: #t rather precise, #E large, dist large
Current results (linear term): Crab Pulsar EGRET: MQG1 > 0.2 1016GeV MAGIC: > 0.8 [2009] GRBs SWIFT: > 0.9 FERMI: >130. [2009] AGN MAGIC: > 21. (*) H.E.S.S: > 70.
(*) MAGIC Mkn501 flare by far best limit for MQG2 and higher order15.May.2009 A.Biland: Very High Energy Astronomy 214
Current StatusMany new VHE sources found,but very difficult to understand physicsprocesses....
Need extended multi-wavelength campaigns: radio + optical + X-ray + GeV + TeV ...
Extremely difficult to organize for variable objectsNot even known if variability is to be expectedsimultaneous and on same time-scale in differentE-bands/wavelenghts
Theory (model building) suffers from ‘GiGo’ effect(Garbage in ==> Garbage out)
Soon GLAST/FERMI will do full-time coverage in GeV range, but we lose most
important X-ray satellite (running out of consumables)
Other difficulty: objects interesting (=bright) in TeV usually very faint
(=uninteresting) for e.g. radio community
==> have to convince many different communities to spend large amount of
scarce observation time on (for them) uninteresting sources without any
guarantee for success !!! (many people more interested in finding 'new source'
than in 'understanding physics')
[plus: campaign must be organized well in advance, but e.g. the few IACTs might
finally be hindered by bad weather during the observation...]
15.May.2009 A.Biland: Very High Energy Astronomy 215
Cosmic AcceleratorsDifferent classes of accelerators actingon completely different time scales:
Typical values: GRB: ~10-7 y AGN (flares): ~10-3 y SNR: ~103 y Neutron Stars: ~107 y (AGN (steady): >108 y?
(remind: CR flux ~stable since 108 y)
(probably also different energy scales ....)15.May.2009 A.Biland: Very High Energy Astronomy 216
Cosmic Accelerators
Problem:-plethora of known classes of astrophys. objects can contribute to CR
-most classes confirmed as accelerators by Cherenkov telescopes (see next week)
-different accelerators should be efficient in different energy ranges or result in different spectral indices
=> why so little structure in CR spectrum ?
15.May.2009 A.Biland: Very High Energy Astronomy 217
Cosmic AcceleratorsProblem:What is accelerating?
But also: Why so little structure in CR spectrum ???
15.May.2009 A.Biland: Very High Energy Astronomy 218
Dark Matter
15.May.2009 A.Biland: Very High Energy Astronomy 219
76th Anniversary:
Fritz Zwicky, 1933: Velocity dispersion ofComa cluster indicates Dark Matter (DM) , , - 1000 km/s . M/L - 50”If this overdensity is confirmed we would arriveat the astonishing conclusion that dark matter ispresent [in Coma] with a much greater densitythan luminous matter.”
==> Evidence for DM (1) 15.May.2009 A.Biland: Very High Energy Astronomy 220
Evidence for DM (2)Measurements of rotational speedof stars in galaxies:
must exist ‘non-visible’, gravitational halo
KEPLER:Gravity / Centripetal Acceleration
!
GM
r2
=v
2
r
Data: ! ~ "onstan#
==> Evidence for DM (2)
15.May.2009 A.Biland: Very High Energy Astronomy 221
Evidence for DM (3)Colliding galaxies (e.g. ‘bullet cluster’):- collisions of stars very unlikely- galaxies consists mainly from gas and dust==> gas heated up by friction => visible
can also measuregravitational massdistribution by weaklensing of backgroundgalaxies==>matter==mass (frictionless !!!)
==> Evidence for DM (3)
majority of gravitational mass was not affected by galaxy collision ==> has no
friction, i.e. no interaction
15.May.2009 A.Biland: Very High Energy Astronomy 222
Evidence for DM (4)
==> Evidence for DM (4)
00121121= 1.02±0.02= 1.02±0.02 0033= 0.73±0.04= 0.73±0.04 00MM=0.27±0.04=0.27±0.04
( (00DMDM=0.23±0.04, =0.23±0.04, 00bb=0.044±0.004)=0.044±0.004)
Hubble constant h= HHubble constant h= H00/100km/100km-1-1ss-1-1MpcMpc-1-1 = 0.71 = 0.71+ 0.04– 0.03
! Cosmological Scales:Cosmological Scales: Cosmic Microwave Background (CMB), recent WMAP data:
CMB anisotropies " stringent constraints on cosmological parameters CMB ## large scale structure data (2dFGRS) ## Lyman 4 ## BB BB NucleosynthesisNucleosynthesis
! Galactic scale Galactic scale ## scale of galactic clusters scale of galactic clusters (rotational curves):
" Evidence is compelling, however, does not allow to determine total amount of DM in Universe
Non-baryonic DM needed for structure formationNon-baryonic DM needed for structure formation
15.May.2009 A.Biland: Very High Energy Astronomy 223
DM information from Astro
Have no ideaabout DE;
What is DMmade of ???==>particle physics
bullet cluster
It is very simple:
the dark area between
the stars
this is the dark matter
Composition of the universe: 4% ‘barionic matter’ (SM); only small fraction luminous 23% ‘dark matter’ (DM): normal gravitation, but not SM 73% ‘dark energy’ (DE): negativ gravitation, ???
15.May.2009 A.Biland: Very High Energy Astronomy 224
SupersymmetrySUSY: extension of 'Standard Model' (SM),invented to overcome some intrinsic problemsof the SM
In many incarnations, it predicts theexistence of a massive, stable particlehaving only weak interaction with normalmatter (plus gravity) => LSP
This particle could naturally explain DM
Lightest supersymmetric Particle (LSP)
15.May.2009 A.Biland: Very High Energy Astronomy 225
GUTELW RGE
Supersymmetry SUSYMSUGRA Assumptions:
" Unify Higgs and scalar sector at the GUT scale" Unify all trilinear couplings at the GUT scale" Break radiatively the electroweak symmetry
Only FIVE parameters leftmo m1/2 Ao tan% sign(µ)
!
(˜ s , ˜ c )L
!
( ˜ u , ˜ d )L
!
˜ " o
!
˜ " ±1
2
34
1
2
Mass
!
˜ g
!
( ˜ u , ˜ d )R
!
(˜ s , ˜ c )R
!
h
!
H,A,H±
!
˜ t 1
!
˜ b 1
!
( ˜ b , ˜ t )2
!
˜ e R
!
˜ µ R
!
( ˜ " , ˜ e )L
!
( ˜ " , ˜ µ )L
!
( ˜ " ,#2)
L
!
˜ " 1
Schematic Particle Spectrum
LEP limits: Mass of sparticles > Ebeam tan% > 2.5
mh > 114.4 GeV m5± > 103.5 GeV m56 > 58.6 GeV
15.May.2009 A.Biland: Very High Energy Astronomy 226
Search for SUSYa) creation at colliders: (simulation)
n leptons + n jets + missing ET
Mass reach for gluino and squark
~ 2-3 TeV
Typical event signature in CMS Detector at LHC:
15.May.2009 A.Biland: Very High Energy Astronomy 227
Search for SUSYb) direct search: when LSP interacts with nucleus, the nucleus recoils,
hits surrounding atoms and releases energy in the
form of heat or light ( LSP = lightest SUSY particle) Interaction of LSP with ordinary matter: few events/kg/year
Main problem: background events fromdetector impurities (radioactivity) and CR~106 times higher than expect. SUSY rate
Ni = detector mass / atomic mass of nuclei species in% = % energy density / % mass (local % density)
<&i%> = scattering &, averaged over the relative % velocity w.r.t. detector
!
R " Ni
i
# n$ <%i$ >
scattering cross sections depends on SUSY parameters (several orders of
magnitude ...)
15.May.2009 A.Biland: Very High Energy Astronomy 228
Search for SUSYmany detectors worldwidetwo main detector techniques:- Heating due to recoiling nucleus giving up its kin. energy: need cryogenic detectors (T ~ mK)
- Scintillation: excited ions produced via recoiling nucleus,e.g.
Liquid Argon Liquid Xenon
NaI
in preparation: ArDMA.Rubbia (ETH) et al. [ Lilian Kaufmann ]
15.May.2009 A.Biland: Very High Energy Astronomy 229
Direct Searches
R. Mahapatra,Talk at DarkMatter 2008,UCLA, Feb. 2008
New CDMSresult
Xenon 10
15.May.2009 A.Biland: Very High Energy Astronomy 230
Direct SearchesOther idea: earth moving relative to DM
==> look for yearly modulation in the signal(background and other systematics cancel?)
DAMA experiment sees strong yearly modulation
Overall motionOverall motionof solar system:of solar system:
220 220 km/skm/sEarth orbits sun
at 30km/sat 30km/s
NorthernNorthernsummersummer
NorthernNorthernwinterwinter
Net velocity: 235 Net velocity: 235 km/skm/s
Net velocity: 205 km/sNet velocity: 205 km/s
If our solar system moves If our solar system moves through a high density of through a high density of LSP gasLSP gas$$ one expects periodic one expects periodic seasonal variations seasonal variations (few %) of the signal (few %) of the signal
15.May.2009 A.Biland: Very High Energy Astronomy 231
Direct Searches
DAMA result disagreeswith other experiments
Generally assumed thatDAMA oscillation is realNot induced by DM butby unknown yearlysystematic effect(temp., pressure, ????)
New CDMSresult
Xenon 10
DAMAdetection
???
DAMA first published in 2005
significantly improved measurement since then, effect still exists (and many
possible detector systematics (claimed to be) excluded
15.May.2009 A.Biland: Very High Energy Astronomy 232
Search for SUSYc) indirect searches:LSP is stable ==> can not decaybut LSP is ‘Majoranaparticle’ ==> 2 LSPscan annihilate intoSM particles
15.May.2009 A.Biland: Very High Energy Astronomy 233
Indirect Search! most interesting, because can be traced to source; but:
! only produced in higher order or secondary processes
==> rare or rather low (for IACTs) energy ?!!! production would be perfect signal (E! = LSP mass !), but extremely rare
15.May.2009 A.Biland: Very High Energy Astronomy 234
Indirect SearchExpected flux depends on SUSY parametersand on DM-mass distribution:
Flux calculationFlux calculation:
!
" =N(#$)
4% m&2'
1
()d) *2++ ds
Particle physics CDM density distribution
look for regions with high 72
==> high gravity (low luminosity)
-Galactic Center: nearby ==> possible to measure 7(r) ?-Dwarf Galaxies: rather near, very low luminosity-Galaxy-clusters: extremely high gravity
-center of sun, center of earth: very nearby, but low gravity
CDM density distribution not well known ==> uncertainty in flux prediction by
several orders of magnitude
15.May.2009 A.Biland: Very High Energy Astronomy 235
Indirect SearchProblems:-Galactic center: HESS/MAGIC=>other bright VHE source-Dwarf Galaxies: expected to be dim (MAGIC obs. Draco)-Galaxy clusters: too extended; other VHE sources-center sun|earth: not observable
Other possible sources:-’minihalos’: N-body simulations predict much more DM clumps than known Dwarf galaxies-Intermediate Mass Black Holes: ~104 Mo could have accreted huge amount of DM since big bang ==> extremely bright
Problem minihalos, IMBH: nothing but DM annihilation==> invisible for astro ==> don’t know where to look
15.May.2009 A.Biland: Very High Energy Astronomy 236
15.May.2009 A.Biland: Very High Energy Astronomy 237
Search StrategySatellites (GLAST,AGILE) discovercandidates(Unid. with veryhard spectra),
IACTs (MAGIC,HESS,VERITAS,CTA) find cutoffas smoking gun
AGILE,
GLASTMAGIC,
HESS,
VERITAS
old plot; more striking including intermed. Bremsstr.15.May.2009 A.Biland: Very High Energy Astronomy 238
Complementarity between direct detection andindirect detection through gamma-rays: Scan ofWMAP-compatible MSSM models
Present approximate limitfrom direct searches(Xenon10 and CDMSexperiments)
Approximate reach ofGLAST and IACTs (?)
15.May.2009 A.Biland: Very High Energy Astronomy 239
Dark Matterexist many more models:
0
-10
-20
-30
log (,
int /
1pb)
-10-15 0-5 5 10 15
log (m / 1GeV)
-40 keV GeV MGUT
Schematic representation of some DM Candidates
Roszkowski, hep-ph/0404052 v1
'
Axion
Gravitino
WIM
Pzi
llas
5KK
WIMPs
WIMP = Weakly Interacting Massive Particle
!! (Standard Model) Neutrinos (Standard Model) Neutrinos
!! Sterile Neutrinos Sterile Neutrinos
!! AxionsAxions
!! Supersymmetric Supersymmetric candidates:candidates:%% NeutralionsNeutralions
%% Sneutrinos Sneutrinos
%% Gravitinos Gravitinos
%% Axinos Axinos
!! DM from Little Higgs ModelsDM from Little Higgs Models
!! Kaluza-Klein Kaluza-Klein States (ED)States (ED)
!! Superheavy Superheavy DM: DM: WIMPzillasWIMPzillas
!! •• •• •• ••
standard model neutrino as main component of DM ruled out by experiments
15.May.2009 A.Biland: Very High Energy Astronomy 240
As in every problem in Astro-Particle Physics, we might notyet have asked to correct question; but maybe very close...