1. grad student talk 1-Feb-061 Studying Astrophysics and Particle Physics with Gamma Rays: what we may learn with the upcoming GLAST mission -and- The UW Contributions to GLAST Toby Burnett University of Washington

2. grad student talk 1-Feb-062 Context: the photon spectrum GAP! GLAST (Mike Turner 1989)

3. grad student talk 1-Feb-063 “Seeing” the Universe with gamma rays the plot and the characters Source 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 Observ er

4. grad student talk 1-Feb-064 Objective: detect gamma rays from 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

5. grad student talk 1-Feb-065 Constraints 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 orbit Minimum energy 20 MeV Large , but A limited by launch vehicle

6. grad student talk 1-Feb-066 Pair conversion detector design & requirements Anticoincidence shield: required by very high flux of cosmic rays relative to gammas (~10 4 ) 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 Calorimeter Thick to contain shower Thin to reduce mass for launch Segmented for shower pattern recognition  e+e+ e–e– calorimeter (energy measurement) particle tracking detectors conversion foil anticoincidence shield Pair-Conversion Telescope

7. grad student talk 1-Feb-067 1970’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, TOF 100 ms deadtime

8. grad student talk 1-Feb-068 Deployment

9. 9 EGRET’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

10. grad student talk 1-Feb-0610 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)

11. grad student talk 1-Feb-0611 The 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

12. grad student talk 1-Feb-0612 Our launch vehicle: Boeing Delta IIH Launch: from Cape Canaveral - September 2007

13. grad student talk 1-Feb-0613 Calorimeter e+e+ e–e–  ACD Tracker Overview of the LAT Precision 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 X 0 ) 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

14. grad student talk 1-Feb-0614 Performance: 1970’s vs 1990’s technology EGRETLAT Energy Range30 MeV to 30 GeV20 MeV to 300 GeV Effective Area1500 cm 2 10000 cm 2 Field of View0.5 sr2 sr Acceptance0.07 m 2 sr2 m 2 sr Angular Resolution6 0 @100 MeV 0.5 0 @ 10 GeV 3 0 @100 MeV 0.1 0 @ 10 GeV Deadtime100 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?

15. grad student talk 1-Feb-0615 Data handling and analysis Not an imaging device – no pixels as such Does 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.Telegraph- scope 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 calibrate Pattern recognition Event reconstruction Discrimination against background Calibration of response to photons

16. grad student talk 1-Feb-0616 Software, software! Vital part of processing. Onboard filter to handle high trigger rate part 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.

17. grad student talk 1-Feb-0617 GLAST 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 contributions Sawyer 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

18. grad student talk 1-Feb-0618 Essential tools: Monte Carlo and Event visualization Monte Carlo geometry XML description managed by “visitors” (gang of 4 Visitor pattern) particle sources also 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" >

19. grad student talk 1-Feb-0619 The Framework: combine simulation, reconstruction, event display and some analysis

20. grad student talk 1-Feb-0620 The 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 backgrounds Use 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 energies Use 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

21. grad student talk 1-Feb-0621 The 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

22. grad student talk 1-Feb-0622 Particle fluxes: dramatic fluctuations!

23. grad student talk 1-Feb-0623 Our current model log 10 (E/1 MeV) E*flux, (m -2 s -1 ) galactic protons He, CNO Galactic electrons Albedo gamma secondary protons secondary e ±

24. grad student talk 1-Feb-0624 Background 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 m 2 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)

25. grad student talk 1-Feb-0625 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

26. grad student talk 1-Feb-0626 The rates, from 864 jobs run at UW

27. grad student talk 1-Feb-0627 Also 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

28. grad student talk 1-Feb-0628 Background 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)

29. grad student talk 1-Feb-0629 A preliminary bottom line

30. grad student talk 1-Feb-0630 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

31. grad student talk 1-Feb-0631 Our data comes as individual photons Two image processing approaches Individual photons Advantage: keep all the information Disadvantage: processing time: scales with exposure Fill pixels Advantage: 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

32. grad student talk 1-Feb-0632 Problems 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) Resolution scale factor  (deg)  W Multiple scatter conversion Note: 68% containment is ~3  4 decades of energy: 3 decades in resolution!

33. grad student talk 1-Feb-0633 Problems 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

34. grad student talk 1-Feb-0634 Solution 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 pixels Level 10: 12,582,912 pixels Note: N pix = 12*4 level

35. grad student talk 1-Feb-0635 12 to 48 pixels (level 0 to 1) (with “nested” indexing) 0 1 2 3 4 567 8 9 10 11

36. grad student talk 1-Feb-0636 Application 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) Resolution scale factor  (deg) 6 7 8 9 10 11 12 13 level

37. grad student talk 1-Feb-0637 Apply it to the 56-day simulated data set 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.

38. grad student talk 1-Feb-0638 Count 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

39. grad student talk 1-Feb-0639 Healpix density image Construct 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

40. grad student talk 1-Feb-0640 Image generation: define a density 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

41. grad student talk 1-Feb-0641 Point Source Detection: work in progress 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

42. grad student talk 1-Feb-0642 Science Groups Catalogs Diffuse (Galactic & Extragalactic) and Molecular Clouds Blazars and Other AGNs Pulsars, SNRs, and Plerions Unidentified Sources, Population Studies, and Other Galaxies Dark Matter and New Physics Gamma-Ray Bursts Sources in the Solar System Calibration and Analysis Methods Multiwavelength Coordinating GroupCatalogs Diffuse (Galactic & Extragalactic) and Molecular Clouds Blazars and Other AGNs Pulsars, SNRs, and Plerions Unidentified Sources, Population Studies, and Other Galaxies Dark Matter and New Physics Gamma-Ray Bursts Sources in the Solar System Calibration and Analysis Methods Multiwavelength Coordinating Group