grad student talk 1-Feb-06 1

Studying Astrophysics and Studying Astrophysics and Particle Physics with Gamma Particle Physics with Gamma

Rays: Rays: what we may learn with the what we may learn with the upcoming GLAST missionupcoming GLAST mission

-and--and-The UW Contributions to GLASTThe UW Contributions to GLAST

Toby BurnettUniversity of Washington

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Context: the photon spectrumContext: the photon spectrum

GAP!

GLAST

(Mike Turner 1989)

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““Seeing” the Universe with gamma Seeing” the Universe with gamma raysrays

the plot and the charactersthe plot and the charactersSource

propagation

“Telescope”

• Massive black holes (AGN, blazars)

• GRB (stellar collapse, magnetars)

• Pulsars (neutron stars)

• CR interactions

• WIMP annihilation?

• Primordial black holes?

• absorption by IR

• Dispersion?

• EGRET / BATSE

• GLAST: LAT/GBM

• MILAGRO (EAS)

• Whipple

• HEGRA

• HESS

• VERITAS

Satellite

Cherenkov

Observer

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Objective: detect gamma rays from Objective: detect gamma rays from astronomical sources with astronomical sources with

Largest possible energy range

High acceptance, A A: effective area, including photon cross section

: field of view

: instrumental efficiency, including dead time

Good energy resolution for spectral measurements

Good angular resolution (buzz-word from telescopes: “point spread function”, or PSF)

Good signal/noise

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ConstraintsConstraints

Good acceptance, PSF: must use pair conversion process

Compton: lose direction information, not high energy

Lower limit: ~20 MeV

Site:Earth surface: use atmosphere as a target

Minimum energy ~100 GeV

Small , but large A

Low Earth orbitMinimum energy 20 MeV

Large , but A limited by launch vehicle

ee*

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Pair conversion detector design & Pair conversion detector design & requirementsrequirements

Anticoincidence shield:required by very high flux of cosmic rays relative to gammas (~104)

Must be very efficient

Segmented to reduce self-veto

Conversion foil (W):High Z

thick for large A

thin for good PSF

Tracking (Si strips)Good efficiency, coverage

Small pitch

CalorimeterThick to contain shower

Thin to reduce mass for launch

Segmented for shower pattern recognition

e+ e– calorimeter (energy measurement)

particle tracking detectors

conversion foil

anticoincidenceshield

Pair-Conversion Telescope

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1970’s technology: CGRO and EGRET/BATSE1970’s technology: CGRO and EGRET/BATSE

Launched on shuttle Atlantis 1991, deorbited 2001

Instruments:•Burst And Transient Source Experiment (BATSE) (30 - 500 keV)•Compton imaging Telescope (1 - 30 MeV)•Oriented Scintillator Spectrometer Experiment (50 keV - 10 MeV)•Energetic Gamma-Ray Telescope (EGRET) (30 MeV - 30 GeV)

Active 1991-1996

Tracking technology: 81 cm square wire spark chambers, 1 mm spacing

Calorimetry: NaI crystals

Triggering: Anticoincidence dome, TOF100 ms deadtime

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DeploymentDeployment

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EGRET’s view of the universeEGRET’s view of the universe

Galactic center

3C279 (blazar)

Vela ( radio pulsar)

Crab (radio pulsar)

Geminga (radio-quiet pulsar)

PKS 0202-512 (blazar)

Isolated neutron star?

SN remnant?

Point things: near and far

Diffuse things: CR interactions in matter

Orion Cloud

LMC

EGRET all-sky survey (E>100 MeV)

Extragalactic diffuse

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Introducing GLAST Introducing GLAST

LAT: 20 MeV – >300 GeV

GBM: 10 keV – 25 MeV

Large Area Telescope (LAT)

GLAST Burst Monitor (GBM)

An International Science Mission

Large Area Telescope (LAT)

GLAST Burst Monitor (GBM)

Spacecraft (Spectrum Astro)

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The CollaborationThe Collaboration

US: Stanford, SLAC, GSFC, NRL, Ohio State, UCSC, Sonoma State, UW

Japan: Tokyo, Hiroshima

Italy: Bari, Padova, Perugia, Pisa, Rome, Trieste, Udine

France: Saclay, Ecole Polytechnique (Paris), Bordeau, Montpellier

Sweden: Stokholm

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OurOur launch vehicle: Boeing Delta IIH launch vehicle: Boeing Delta IIH

Launch: from Cape Canaveral - September 2007

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Calorimeter

e+ e–

ACD

Tracker

Overview of the LATOverview of the LATPrecision Si-strip Tracker 18 XY tracking planes. Single-sided silicon strip detectors (228 m pitch) Measure the photon direction; gamma ID.

Hodoscopic CsI Calorimeter Array of 1536 CsI(Tl) crystals in 8 layers. (8 X0) Measure the photon energy; image the shower.

Segmented Anticoincidence Detector (ACD) 89 plastic scintillator tiles. Reject background of charged cosmic rays; segmentation removes self-veto effects at high energy.

Electronics System Includes flexible, robust hardware trigger and software filters.

1.7 m

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Performance: 1970’s vs 1990’s technologyPerformance: 1970’s vs 1990’s technology

EGRET LAT

Energy Range 30 MeV to 30 GeV 20 MeV to 300 GeV

Effective Area 1500 cm2 10000 cm2

Field of View 0.5 sr 2 sr

Acceptance 0.07 m2 sr 2 m2 sr

Angular Resolution 60 @100 MeV0.50 @ 10 GeV

30 @100 MeV0.10 @ 10 GeV

Deadtime 100 ms 25 s

Sensitivity (> 100 MeV) 10-7 cm-2 s-1 4x10-9 cm-2 s-1

Consumables Spark chamber gas None

Lifetime <5 yrs 10 yrs?

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Data handling and analysisData handling and analysis

Not an imaging device – no pixels as suchDoes that make it not a “telescope”? Webster says: Telescope \Tel"e*scope\, n. [Gr. ? viewing afar, farseeing; ? far, far off + ? a watcher, akin to ? to view: cf. F. t['e]lescope. See Telegraph, and -scope.] An optical instrument used in viewing distant objects, as the heavenly bodies.

Instead of collecting photons with ccd pixels, we record “events”, caused by single incoming photons

trigger logic, including possibility of veto of background (EGRET had both “A-dome” and TOF requirement to keep rate well below 10 Hz.)Many channels to calibratePattern recognition Event reconstructionDiscrimination against backgroundCalibration of response to photons

grad student talk 1-Feb-06 16

Software, software!Software, software!

Vital part of processing.

Onboard filter to handle high trigger ratepart of extensive onboard software to control instrument, acquire data, send to “SSR”.

All in straight C, written under strict NASA rules for flight software

Ground software Packages managed by CMT, with visual interface MRvcmt

Runtime framework: Gaudi

All code in OO C++.gcc / emacs on linux; Visual Studio on Windows

I/O data uses ROOT

Analysis plots generated by ROOT.

grad student talk 1-Feb-06 17

GLAST and the UW groupGLAST and the UW group

We joined in the formulation phase, in 1994

Now it is an international $500M DOE/NASA mission

Local people who have made contributionsSawyer Gillespie, undergraduate, staff for 2 years

Sean Robinson, PhD 2004 on wavelet analysis

Theodore Hierath, REU, current graduate student

Jon Chandra, graduate student

Marshall Roth, undergraduate

Scott Haynes, undergraduate

Bruce Blesnick, masters student

Todd Olson, staff, computer support

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Essential tools: Monte Carlo and Event Essential tools: Monte Carlo and Event visualizationvisualization

Monte Carlogeometry

XML description

managed by “visitors” (gang of 4 Visitor pattern)

particle sourcesalso XML

object factories

composite sources (Composite pattern)

physics of particles in matter: Geant4 (replacing THB’s Gismo)

<box name="CsISeg" sensitive="intHit" detectorTypeREF="eDTypeCALXtal" XREF="CsISegLength" YREF="CsIWidth" ZREF="CsIHeight" materialREF="crystalMat" > </box>

<stackX name="CsIDetector" > <axisMPos volume="CsISeg" ncopyREF="nCsISeg" > <idField name="fCALSeg" value="0" step="1" /> </axisMPos> </stackX>

<source name="all_gamma" flux="1.0"> <spectrum escale="GeV"> <particle name="gamma"> <power_law emin="0.01778" emax="17.78“ gamma="1"/> </particle> <solid_angle mincos="0" maxcos="1.0"/> </spectrum> </source>

grad student talk 1-Feb-06 19

The Framework: combine simulation, The Framework: combine simulation, reconstruction, event display and some reconstruction, event display and some

analysisanalysis

grad student talk 1-Feb-06 20

The GLAST Data Challenge 2The GLAST Data Challenge 2

We are in the midst of preparing a major end-to-end simulation:

Orbit: start 1-1-08 for 56.3 days (a precession period)Best estimates of particle backgroundsUse scanning/rocking mode (most likely for first year, perhaps entire mission)Now running special Monte Carlo runs to characterize instrument

Background: ~ 1 day (all we can do!)Photons: 10 M at all angles and energiesUse the above to define responses

Defining model of gamma ray sky, including all the known sources, some speculation.

Test with special parametric Monte Carlo based on previous analysis.

The “real” run, for later this year, will use full Monte Carlo with gamma sources, with sampling from the 1-day background

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The orbitThe orbit

Trigger rate (~8 kHz) is dominated by charged particles! Only 1-2 Hz are actual gammas from space.

Orbit and pointing mode: create 56.3 days with rocking, sun-avoidance

ra

dec

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Particle fluxes: dramatic fluctuations!Particle fluxes: dramatic fluctuations!

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Our current modelOur current model

log10(E/1 MeV)

E*f

lux,

(m

-2 s

-1)

galactic protons

He, CNO

Galactic electrons

Albedo gammasecondary protons

secondary e±

grad student talk 1-Feb-06 24

Background SimulationBackground Simulation

Select an orbit time, and a 1-second duration.

Generate the ~50 K incoming particles, with random directions, energies, and spread out over a sphere with cross sectional area 6 m2

Send each into the detector: Discard if no trigger (missed or hits did not satisfy a trigger condition) ~8 kHz remain (20% deadtime)

Apply the onboard filter code that checks for obvious charged, non-interacting particles: ~700 Hz remain

Fully analyze these, corresponding to the downlink rate

Run 8640 such jobs, starting every 10 sec, for 10% of a full day. (using the UW physics condor system for up to 64 jobs)

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What is Condor?What is Condor?

Invented, maintained at UW-Madison.

Basis for managing jobs in much of the “grid”, now called Open Science Grid

Now installed on all physics dept lab and undergraduate machines: ~60 machines, ~25 Gflops of Windows cycles available (except when the machines are used!).

[Note, the UW astronomers are ‘way ahead of us in sharing desktops]

All are welcome: see http://glast-ts.phys.washington.edu/condor/for instructions on how to participate

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The rates, from 864 jobs run at UWThe rates, from 864 jobs run at UW

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Also generate signal eventsAlso generate signal events

All-gamma sample: uniform in log(E) from 16 MeV to 160 GeV, and in the upper hemisphere

Rather different from actual source, but easy to characterize response for given incoming gammas.

Try to estimate reliability of energy and direction measurement

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Background rejection – very difficultBackground rejection – very difficult

Create many variables to measure gamma-like, or charged particle-like quantities

extra hits around a found track

correlation of track direction with hit ACD tile (if any)

correlation of track direction with direction of CAL shower

etc.

Feed them to a set of classification tree trainers (code written for D0 single top analysis)

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A preliminary bottom lineA preliminary bottom line

grad student talk 1-Feb-06 30

Pixels or photons?Pixels or photons?

Astronomers prefer pixels, but physicists like photons!Focusing devices (mirrors, lenses) convert direction to position, CCD’s collect photons, define the pixels

From SDSS web site:

“On a clear, dark night, light that has traveled through space for a billion years touches a mountaintop in southern New Mexico and enters the sophisticated instrumentation of the SDSS's 2.5-meter telescope. The light ceases to exist as photons, but the data within it lives on as digital images recorded on magnetic tape. Each image is composed of myriad pixels (or picture elements); each pixel captures the brightness from each tiny point in the sky.”

For astronomers, pixels are the data

grad student talk 1-Feb-06 31

Our data comes as individual photonsOur data comes as individual photons

Two image processing approachesIndividual photons

Advantage: keep all the information

Disadvantage: processing time: scales with exposure

Fill pixelsAdvantage: all astronomical tools work, easy to deal with:Almost all EGRET analysis was with 0.5 deg pixels

Disadvantage: loose resolution for high-energy photons

grad student talk 1-Feb-06 32

Problems with binning: IProblems with binning: I

Angular resolution varies dramatically with energy:

expect 1/E from multiple scattering

measure E-0.8

Images don’t show localization without removing low energies, increasing resolution

Full information not used in point source searches

Gamma energy (MeV)

Res

olut

ion

scal

e fa

ctor

(

deg)

WMultiple scatter

conversion

Note: 68% containment is ~3

4 decades of energy: 3 decades in resolution!

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Problems with binning: IIProblems with binning: II

Need a spherical projection to 2-d that defines pixels with:

Equal area

No discontinuities (like poles, wrap-around)

Pixels ~uniform in shape (square, triangular)

Simple mapping to/from actual coordinates

Neighbors easy to find

Cartography defines ~150 including equal-area Hammer-Aitoff.

None are appropriate, really want a tesselization based on a regular polygon

The Hammer-Aitoff: popular in astronomy

WMAP microware

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Solution from WMAP: HEALPixSolution from WMAP: HEALPix

Hierarchical Equal Area isoLatitude Pixelization

WMAP and COBE data binned this way

Adopted by Planck

Original code in f90, we now “wrap” C++ subset

Level 3: 768 pixels

Level 9: 3,145,728 pixelsLevel 10: 12,582,912 pixels

Note: Npix = 12*4level

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12 to 48 pixels (level 0 to 1)12 to 48 pixels (level 0 to 1)(with “nested” indexing)(with “nested” indexing)

0 1 2 3

4 5 6 7

8 9 10 11

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Application to GLASTApplication to GLAST

Take advantage of Hierarchical property, easy to correlate index for contained pixels.

Create pixels in sparse structure according to 8 bins in photon energy, sorted according to position.

Make selecting subset according to outer pixel level easy for projection integrals

Numerous low energy photons are effectively binned

Rare high energy photons occupy own pixels

Can solve database indexing

Gamma energy (MeV)

Res

olut

ion

scal

e fa

ctor

(

deg)

6

78

9

10111213

level

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Apply it to the 56-day simulated data Apply it to the 56-day simulated data setset

Low levels: saturated, many photons/pixel.

High levels: single photons (diffuse); multiple photons (point sources)

1.7M photons w/ E>100 MeV

300 K pixels.

grad student talk 1-Feb-06 38

Count Map Images: 0.1 deg pixelsCount Map Images: 0.1 deg pixels

E>100 MeV

E>1 GeV

~4 M pixels for full sky, > photons, not adequate for 100 GeV.

Intensity is the number of photons in the pixel

grad student talk 1-Feb-06 39

Healpix Healpix densitydensity image imageConstruct 0.1 deg image with density at center of display pixel: sum of counts/solid angle for all contained Healpix pixels in that direction.High energy photons count according to resolution

grad student talk 1-Feb-06 40

Image generation: define a Image generation: define a densitydensity function function

High energy photons are more localized: we express this by defining photons/area

Easily determined from the data base and the Healpix code.

3C273: density vs. all photons above 100 Mev

grad student talk 1-Feb-06 41

Point Source Detection: work in Point Source Detection: work in progressprogress

Motivation was to create a manageable data set for study of point sources, allowing quick projection integrals for candidates

This is actually a “Hough transform”, allowing easy detection of point sources. Comparison with other fixed-scale binning methods is in progress.

Applying wavelet technology developed by Sean Robinson

Allows quick measurement of intensity, position, significance.

Precision expected to be close, within 20% of formal maximum likelihood analysis

grad student talk 1-Feb-06 42

Science GroupsScience Groups

CatalogsDiffuse (Galactic & Extragalactic) and Molecular CloudsBlazars and Other AGNsPulsars, SNRs, and PlerionsUnidentified Sources, Population Studies, and Other Galaxies

Dark Matter and New PhysicsGamma-Ray BurstsSources in the Solar SystemCalibration and Analysis MethodsMultiwavelength Coordinating Group