The future of ground-based The future of ground-based gamma ray astronomygamma ray astronomy

Where do we go?Where do we go?

OutlineOutline

…… …… ……

Panic !Panic !

Where do we stand ?Where do we stand ?And how did we get here?And how did we get here?

WhippleWhipple19681968

H.E.S.S.H.E.S.S.20032003

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Horan & Weeks 2003

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Experimentalsensitivity in Crab Units

late 1980’s

late 1990’s

mid-2000’s

Theoryprediction (SN 1006)“Heinz Völk Units”

Inefficientinjection

High B, low density

1000000

100000000

Radio

Optical

UV

X-Ray

Gamma

IR

1

100

10000

101210610010-6Energy [eV]

Peak detected flux /Detection threshold

Neutrinos (?)

Flux sensitivityFlux sensitivity

Is there a future of ground-based Is there a future of ground-based gamma ray astronomy ?gamma ray astronomy ? Physics issuesPhysics issues Instruments to address these issuesInstruments to address these issues

Wish listWish list

Improved sensitivity

Improvedangular

resolution

Wider energy coverage

Large solid angle coverage

Larger effectivearea

Sensitivity ~ E-0.8 Aeff1/2 bg

-1/2 -1

Horan & Weeks 2003

Sensitivity:Sensitivity:a no-brainera no-brainer

Angular resolution:Angular resolution:

Crab viewedwith EGRET

Crab viewedwith HEGRA-CT

Angular resolution:Angular resolution:Source structureSource structure

ChandraSN 1006

Typical TeVbeam sizeJ. Hiraga ASCA/Chandra

Wide energy coverage:Wide energy coverage:Acceleration mechanismAcceleration mechanism

Interactionwith extragalacticbackground light(EBL)

Cosmologyand structureof space-time

AGNs

Wide energy coverage:Wide energy coverage:Gamma ray horizon, IR & cosmologyGamma ray horizon, IR & cosmology

Blanch & Martinez 2004

Simulatedmeasurements

Different EBL models

Large solid angle coverageLarge solid angle coverage

Surveys: New sources Surveys: New sources not visible in other not visible in other wavelengthswavelengths

Monitoring of bursts Monitoring of bursts and transients (AGN, and transients (AGN, GRB, GRB, Quasars,…)Quasars,…)

HEGRA unidentifiedCygnus source

Large effective area / rate:Large effective area / rate:MWL correlation of flux and index in AGNsMWL correlation of flux and index in AGNs

Whipple Mkn 421

Need a smart new idea!Need a smart new idea!

If I had one, I wouldn’t tell you …from now on: brute force approach …

will concentrate on future beyond will concentrate on future beyond current generationcurrent generation

A biased view!

Sensitivity, angular resolution:Sensitivity, angular resolution:seems hard to beat Cherenkov telescopesseems hard to beat Cherenkov telescopes

I believe that Cherenkov telescopes are good for I believe that Cherenkov telescopes are good for at another Generation beyond CANGAROO / at another Generation beyond CANGAROO / H.E.S.S. / MAGIC / VERITASH.E.S.S. / MAGIC / VERITAS

Should know: where are the fundamental limits of Should know: where are the fundamental limits of the technique?the technique?

Ultimate limit: use all photonsUltimate limit: use all photons

Fit to distribution(x,y,x,y,t)

here: using cruderepresentation ofdistr. function,can probably dobetter

Shower fluctuations:Shower fluctuations:angular resolution: fit to angular resolution: fit to allall photons photons

0.008O/√ETeV

with geomag. fieldin bending plane

How many photons are needed?How many photons are needed?

relativeto PMTquantumefficiency

1 TeV

100 GeV

10 GeV

1 GeV

shower fluctuations

photonstatistics

Shower fluctuations:Shower fluctuations:background rejectionbackground rejection

1 TeV

2 TeV p

x [m]

y

[m]

Rejection: few 10-4

y

[m]x [m]

y

[m]

100 GeV

200 GeV p

Rejection: ~ 10-2

Conclude:Conclude:

With enough light (few 10 p.e./GeV), should be With enough light (few 10 p.e./GeV), should be able to gain factor ~3 from angular resolutionable to gain factor ~3 from angular resolution

Similar factor from background rejection (p)Similar factor from background rejection (p)

Larger telescopesLarger telescopes (Dense) telescope arrays for low energies(Dense) telescope arrays for low energies Small pixels Small pixels advanced photon detectors advanced photon detectors High altitudeHigh altitude

Bonus at low energy: geomagnetic cutoffBonus at low energy: geomagnetic cutoff

Optimum telescope sizeOptimum telescope size

10 m 20 m 30 m

Cost per area

Fixed costs dominate(Control, camera)

Dish cost dominates

Dish size > shower size, depth of field problem ?

Triggering on low-energyshowers becomes very complex

Focus & depth of fieldFocus & depth of field

Example:Cherenkovimages in a20 m telescope

Focus at infinity Focus on shower head

Optimum focus Focus on shower tail

Practical limitaround 30 mdiameter ?Telescope size =shower width

Practical thresholdsPractical thresholds

A. Plyasheshnikov

30 m telescope

@ 1.8 km

@ 5 km

Effect of geomagnetic cutoff

A. Plyasheshnikov

Large TelescopesLarge TelescopesTechnical designcomplete

Super CANGAROO(M. Mori)

see also:ECO 1000

Improved photon detectorsImproved photon detectors

PMT

GaAs NIM A518, 615

Thinned CCD

PMT GaAs CCDSignal: 1 : 2.2 : 4.5S/√B: 1 : 1.1 : 1.4

Self-quenchingGeiger-modeavalanche cells

Russian groups,MPI Munich/Semicond. Lab

ALMA site ?ALMA site ?10 GeV Gamma

5 km

2 km

A. Konopelko

Courtesy NRAO/AUI and ESO

VHE physicists dream ?VHE physicists dream ?

High-resolution modeHigh-resolution mode Survey / monitoring modeSurvey / monitoring mode Large-area modeLarge-area mode Halo of nano-telescopes for 10+ TeVHalo of nano-telescopes for 10+ TeV

Survey instrumentsSurvey instruments

Cherenkov telescopes with Cherenkov telescopes with large cameras and Gascoigne large cameras and Gascoigne aspheric corrector plate … aspheric corrector plate … could imagine 10could imagine 10oo to 15 to 15oo diameterdiameter

Fresnel lens wide-angle Fresnel lens wide-angle instrumentsinstruments

• nontrivial Fresnel lensnontrivial Fresnel lens

• huge focal plane (10huge focal plane (1055+ channels)+ channels)

• would probably want several would probably want several (stereo) instruments of 10 m class(stereo) instruments of 10 m class

HAWC: A Next HAWC: A Next Generation All-Sky VHE Generation All-Sky VHE Gamma-Ray TelescopeGamma-Ray Telescope

from G. Sinnis

Median Energy 180 GeV

(Milagro ~3 TeV)

Angular resolution ~1Angular resolution ~1oo

Sensitivity 50 mCrab / y for steady sources,Sensitivity 50 mCrab / y for steady sources,

~ 10 h for 1-Crab flare ~ 10 h for 1-Crab flare (H.E.S.S.: 30 sec)(H.E.S.S.: 30 sec)

ConclusionsConclusions

Try to get (at least) one Cherenkov telescope Try to get (at least) one Cherenkov telescope system with sub-mCrab sensitivity @ 100 GeV to system with sub-mCrab sensitivity @ 100 GeV to TeV energies, O(10 GeV) thresholdTeV energies, O(10 GeV) threshold

and and

one wide-angle 100 GeV survey instrumentone wide-angle 100 GeV survey instrument

Unite communityUnite community

Develop low-cost, no-frills production techniquesDevelop low-cost, no-frills production techniques

• Honeycomb foil mirrors a la Durham ?Honeycomb foil mirrors a la Durham ?

• ASIC for signal storage, trigger, digitisationASIC for signal storage, trigger, digitisation

• ……

no magnetic field (< few 10 nT)atmospheric depth adjustable from 2 r.l. upcombine perfect angular resolution (no low-energy stragglers) with large detection area

Gamma-ray

~ 10 kmParticleshower

~ 1o

Che

renk

ov li

ght

~ 120 m

Veto (Drift chamber)

replaces geostationarycommunicationsatellites

SummarySummary

I’m afraid I have nothing really I’m afraid I have nothing really substantial to say …substantial to say …

but nevertheless it is hard to fit within but nevertheless it is hard to fit within

less than ½ hour !less than ½ hour !