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GLAST Large Area Telescope: Launched and Being Commissioned

The GLAST Large Area Telescope (LAT) has been launched and is currently being commissioned. It is a joint effort between NASA and the DOE, with contributions from international partners. The LAT is a significant improvement over its predecessor, EGRET, with increased sensitivity, localization, and observing efficiency. It will help answer important questions about supermassive black holes, gamma-ray bursts, cosmic rays, solar flares, and more.

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GLAST Large Area Telescope: Launched and Being Commissioned

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  1. GLAST Large Area Telescope: Launched and Being Commissioned Richard Dubois Stanford Linear Accelerator Center richard@slac.stanford.edu for the LAT Collaboration

  2. 25.6 Degree Orbit SAA http://observatory.tamu.edu:8080/Trakker/ Circular orbit, 565 km altitude (96 min period), 25.6 deg inclination

  3. GLAST LAT Collaboration United States • California State University at Sonoma • University of California at Santa Cruz - Santa Cruz Institute of Particle Physics • Goddard Space Flight Center – Laboratory for High Energy Astrophysics • Naval Research Laboratory • Ohio State University • Stanford University (SLAC and HEPL/Physics) • University of Washington • Washington University, St. Louis France • IN2P3, CEA/Saclay Italy • INFN, ASI Japanese GLAST Collaboration • Hiroshima University • ISAS, RIKEN • Tokyo Inst of Technology Swedish GLAST Collaboration • Royal Institute of Technology (KTH) • Stockholm University PI: Peter Michelson(Stanford & SLAC) ~270 Members (including ~90 Affiliated Scientists, plus 37 Postdocs, and 48 Graduate Students) Cooperation between NASA and DOE, with key international contributions from France, Italy, Japan and Sweden. Managed at Stanford Linear Accelerator Center (SLAC).

  4. GLAST Key Features • Compared to EGRET: • > 100 MeV, 1 yr • sensitivity x25 • localization x102 • field of view x5 • observing efficiency x2 • deadtime x10-3 • Two GLAST instruments: • LAT: • high energy (20 MeV – >300 GeV) • GBM: • low energy (8 keV – 30 MeV) • Huge field of view • LAT: 20% of the sky at any instant; in sky survey mode, expose all parts of sky for ~30 minutes every 3 hours. GBM: whole unocculted sky at any time. • Huge energy range, including largely unexplored band 10 GeV - 100 GeV • Large leap in all key capabilities, transforming our knowledge of the gamma-ray universe. Great discovery potential. Large Area Telescope (LAT) Spacecraft Partner: General Dynamics GLAST Burst Monitor (GBM)

  5. Some Questions GLAST Will Address • How do super massive black holes in Active Galactic Nuclei create powerful jets of material moving at nearly light speed? What are the jets made of? • What are the mechanisms that produce Gamma-Ray Burst (GRB) explosions? What is the energy budget? • What is the origin of the cosmic rays that pervade the galaxy? • How does the Sun generate high-energy gamma-rays in flares? • How has the amount of starlight in the Universe changed over cosmic time? • What are the unidentified gamma-ray sources found by EGRET? • What is dark matter? 9 yrs EGRET 1 yr (sim) GLAST

  6. Pair-Conversion Telescope anticoincidence shield conversion foil particle tracking detectors e– • calorimeter • (energy measurement) e+ Experimental Technique • Instrument must measure the direction, energy and arrival time of gamma rays over a large energy range (~20 MeV to > 300 GeV) • Technique: Pair Conversion Telescope • Concept: • Photon interactions in GLAST energy range dominated by pair conversion • Determine the photon direction • Clear signature for background rejection • Basic requirements • Must detect gamma-rays with high efficiency • Must be able to reject much larger flux (104:1) of cosmic ray backgrounds • Must have a large acceptance (Field Of View) • Must have good energy resolution over wide range of incident photon energies • Some Definitions: • Effective Area (Aeff): • (Total Geometric Acceptance) • (conversion probability) • (all detector and reconstruction efficiencies). • Real rate of detecting gamma rays is (flux) • Aeff • Point Spread Function (PSF): • Angular resolution of instrument, after all detector and reconstruction algorithm effects. The 2-dimensional 68% containment is the equivalent of ~1.5 (1-dimensional error) if purely Gaussian response. The non-Gaussian tail is characterized by the 95% containment, which would be 1.6 times the 68% containment for a perfect Gaussian response.

  7. The GLAST Observatory LAT GBM Sodium Iodide Detector GBM Bismuth Germanate Detector

  8. e– e+ Overview of LAT • Precision Si-strip Tracker (TKR) 18 XY tracking planes. Single-sided silicon strip detectors (228 mm pitch) Measure the photon direction; gamma ID. • Hodoscopic CsI Calorimeter(CAL) Array of 1536 CsI(Tl) crystals in 8 layers. 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. Tracker ACD [surrounds 4x4 array of TKR towers] Calorimeter Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV - >300 GeV.

  9. LAT Construction: An International Effort Integration & Data System: US ACD: US Calorimeter: US, France, Sweden Tracker: US, Italy, Japan

  10. GLAST MISSION ELEMENTS Large Area Telescope & GBM m • sec GPS • - • Telemetry 1 kbps GLAST Spacecraft • TDRSS SN S & Ku DELTA 7920H • • S - - • GN • LAT Instrument Science Operations Center (SLAC) White Sands Schedules Mission Operations Center (MOC) GLAST Science Support Center HEASARC Schedules GRB Coordinates Network GBM Instrument Operations Center Alerts Data, Command Loads

  11. Operating modes LAT sensitivity on 4 different timescales: 100 s, 1 orbit (96 mins), 1 day and 1 year • In survey mode, the LAT observes the entire sky every two orbits (~3 hours), each point on the sky receives ~30 mins exposure during this time. • GBM sees entire unocculted sky. • Multiwavelength campaigns with the LAT will be limited only by the ability to coordinate to other observations in other wavebands. • Can also perform pointed observations of particularly interesting regions of the sky.

  12. In Orbit: Single Events in the LAT The green crosses show the detected positions of the charged particles, the blue lines show the reconstructed track trajectories, and the yellow line shows the candidate gamma-ray estimated direction.  The red crosses show the detected energy depositions in the calorimeter.  

  13. Calorimeter Calibration with Ions Proton MIP Ion peaks are used for calibrations • Heavy ions probe the higher energy ranges • Peak positions stable to < 1% over days elapsed Non-Interacting Heavy Ion C N O Carbon peak vs time Fe

  14. Vela – early returns Soup to nuts: everything works! timing background rejection alignment EGRET on-pulse off-pulse • precise ephemerides of many pulsars provided by Parkes, Jodrell Bank, Green bank, Nançay, Arecibo, Hartbeesthoek, Urumqi, RXTE, XMM... • good timing of the EGRET pulsars • selecting on-pulse shows point source • evaluate PSF • alignment of LAT to sky (fit to several point sources)

  15. Rates & Deadtime ~2 kHz trigger rate ~500 Hz downlink rate ~1 Hz source photon rate 26 ms deadtime: for GRBs! Software filter on board reduces downlink rate to ~500 Hz 100:1 background rej done on ground Oscillations due to geomagnetic latitude variations and orbital effects

  16. GLAST/LAT performance Energy Resolution: ~10% (~5% off-axis) PSF (68%) at 100 MeV ~ 3.5o (thin section) PSF (68%) at 10 GeV ~ 0.1o Field Of View: 2.4 sr Point Source sens. (>100 MeV): 3x10-9 cm-2 s-1

  17. Year 1 Science Operations Timeline Overview Start Year 1 Science Ops Start Year 2 Science Ops “first light” whole sky LAT, GBM turn-on check out Observatory renaming spacecraft turn-on checkout sky survey + ~weekly GRB repoints + extraordinary TOOs pointed + sky survey tuning week week week week month 12 m o n t h s LAUNCH L+60 days 2nd GLAST Symposium initial tuning/calibrations in-depth instrument studies Release Flaring and Monitored Source Info GBM and LAT GRB Alerts continuous release of new photon data GI Cycle 1 Funds Release GI Cycle 2 Proposals Fellows Year 1 Start LAT Year 1 photon data release PLUS LAT Year 1 Catalog and Diffuse Model LAT 6-month high-confidence source release, GSSC science tools advance release

  18. Data Release plan and operations • First Year observations - Sky Survey • After initial on-orbit checkout (60 days), the first year of observations will be a sky survey. • Repoints for bright bursts and burst alerts will be enabled • Extraordinary ToOs will be supported. • First year data will be used for detailed instrument characterization and key projects (catalog, background models etc). • First Year Data release • All GBM data • Information on all LAT detected GRB (flux, spectra, location) • High level LAT data (time resolved flux/spectra) on ~20 selected sources and on all sources which flare above 2x10-6, continued until the source flux drops below 2x10-7 (rate ~ 1-4 such objects per month). • The LAT team will produce a preliminary source list after ~6 months on a best effort basis • Subsequent years: Observing plan driven by guest observer proposal selections by peer review. Default is sky survey mode. • All data publicly released within 72 hours through the Science Support Center (GSSC). • See http://glast.gsfc.nasa.gov/ssc/data/policy/ for more details

  19. LAT First Year Source Monitoring List • provided for daily and weekly integrations for all sources. • a “quicklook” analysis, priority is to get the results out as quickly as possible. Tables will be updated as analysis and calibrations improve.

  20. The LAT’s First Public Volley: 3C454.3 ATel

  21. Outlook • LAT Launch and Turn On have been huge successes!! • Commissioning nearly complete: no real surprises yet. LAT is stable! • Initial post-launch calibrations complete • Enter survey mode after L+60 • Will already have surpassed the EGRET dataset • First year data will be used for detailed instrument characterization and key projects (catalog, background models etc). • First Year Data release • Start releasing GRBs & selected light curves in mid August • preliminary source catalog after ~6 months on a best effort basis • GLAST to be renamed in “First Light” ceremony on Aug 5 • Lots of excitement to come!

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