GLAST Large Area Telescope:

Transcription

1 Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Project Overview Robert P. Johnson Santa Cruz Institute for Particle Physics Physics Department University of California at Santa Cruz LAT Tracker Subsystem Manager Representing the LAT Collaboration Robert P. Johnson SpacePart

2 Gamma-ray Large Area Space Telescope GLAST Mission High-energy gamma-ray observatory; 2 instruments: - Large Area Telescope (LAT) - Gamma-ray Burst Monitor (GBM) Launch (2006): Delta 2 class Orbit: 550 km, 28.5 o inclination Mission operations Science - LAT Collaboration - GBM Collaboration - Guest Observers Lifetime: 5 years (minimum) Alerts Large loads TOO commands Spacecraft, GBM data Burst and transient Alerts Routine Data Mission Ops Center Observatory safety Spacecraft health Commanding Mission scheduling Level 0 processing GBM data handling GRB Coordinates Network LAT Data Schedules Spacecraft data for archiving Status Command Loads GLAST Observatory: Spacecraft LAT ~20 MeV and up GBM 20 kev to 20 MeV Status Command Loads GBM Data LAT Inst. Ops. Center LAT data handling Instrument performance Level 1 data processing; selected higher level processing Support LAT Collaboration Science Investigation Science Support Center Science scheduling Archiving Guest Observer Support Standard product processing GBM Inst. Ops. Center Instrument performance Standard product processing Robert P. Johnson SpacePart

3 GLAST Science Opportunities Active Galactic Nuclei Isotropic Diffuse Background Radiation Endpoints of Stellar Evolution Neutron Stars/Pulsars Black Holes Cosmic Ray Production: Identify sites and mechanisms Unidentified Gamma-ray Sources Gamma-Ray Bursts Dark Matter Solar Physics DISCOVERY! 40 increase in sensitivity over EGRET Robert P. Johnson SpacePart

4 Scientific Heritage: CGRO-EGRET EGRET All-Sky Map (E> 100MeV) Cygnus Region 3C279 Vela Geminga Crab PKS Cosmic Ray Interactions With ISM PSR B PKS LMC Robert P. Johnson SpacePart

5 LAT Performance Predictions Plots from our original proposal to NASA Robert P. Johnson SpacePart

6 271 sources 172 sources are unidentified 3 rd EGRET Source Catalog Robert P. Johnson SpacePart

7 LAT Source Catalogs 5σ sources from a simulated 1-year all-sky survey. M31 > 1 GeV LAT Catalog: ~10,000 sources GRB, AGN, 3EG + Gal. plane & halo sources Robert P. Johnson SpacePart

8 Science capabilities transient sensitivity 100 sec 1 orbit* The LAT wide field-of-view provides excellent sensitivity to transients. EGRET Fluxes - GRB (100sec) - PKS flare - 3C279 flare - Vela Pulsar - Crab Pulsar - 3EG (SNR g Cygni?) 1 day^ - 3EG C279 lowest 5s detection - 3EG (AGN) - Mrk Weakest 5s EGRET source All 3EG sources + 80 new in 2 days ~200 g bursts per year AGN flares > few min *zenith-pointed, ^ rocking all-sky scan Robert P. Johnson SpacePart

9 Tracker-Detected Photons > 100 MeV GLAST Gamma-Ray Bursts The LAT should detect 200 GRB per year with E>100 MeV, with a third of them localized to better than 10, in real time. Excellent wide field monitor for GRB. Rapid GRB alert: ~12 s to the ground. With a 10µs dead time, GLAST will see nearly all of the high-e photons. The GBM will provide a hard x-ray trigger for GRB, allowing measurements with as few as 1 high-e photon. Sizes of GLAST GRB Error Regions Simulated one-year GLAST scan, assuming a spectral index of % Containment Radius (arc minutes) Robert P. Johnson SpacePart σ localization accuracy (arc min.)

10 LAT Science Capabilities - Resolution Unidentified EGRET Sources Greatly improved source localization, continuous monitoring of transient behavior, and rapid GRB notification will aid the search for counterparts and the identification of sources and bursts. Source localization (68% radius): g bursts Unidentified EGRET sources 0.3 to 1 1 to tens of arcmin > 1 GeV M31 > 1 GeV Cygnus region (15 0 x 15 0 ), Eγ > 1 GeV Robert P. Johnson SpacePart

11 GLAST Working Together with ACTs For a typical source, the LAT sensitivity is GLAST capabilities nicely complement a good match to those of the coming generation of ground-based atmospheric and cherenkov HESS. telescopes. MAGIC, VERITAS, Predicted GLAST measurements of Crab unpulsed flux in the overlap region with ground-based atmospheric cherenkov telescopes. Robert P. Johnson SpacePart

12 Probing the Optical-UV EBL GLAST will contribute statistical power: 1) Detect thousands of blazars; measure spectra of several hundred above 10 GeV: instead of peculiarities of individual sources, look for systematic effects vs. redshift. 2) GLAST energy range is key for cosmological distances: (TeV-IR is more local, due to opacity). Effect is dependent on model details: Work together with ground-based observatories TeV g s sensitive to IR GeV g s sensitive to UV Robert P. Johnson SpacePart

13 GLAST LAT Overview: Design Si Tracker pitch = 228 µm channels 185 Watts Self triggering 12 layers 2.8% X layers 18% X layers CsI Calorimeter Hodoscopic array 8.4 X bars cm cosmic-ray rejection shower leakage correction g e + e Data acquisition 3000 kg, 650 W (allocation) 1.8 m 1.8 m 1.0 m 20 MeV 300 GeV ACD Segmented scintillator tiles efficiency Minimal self veto Grid (& Thermal Radiators) Flight Hardware & Spares 16 Tracker Flight Modules + 2 spares 16 Calorimeter Modules + 2 spares 1 Flight Anticoincidence Detector Data Acquisition Electronics + Flight Software Robert P. Johnson SpacePart

14 GLAST LAT Overview: Performance Single Photon Angular Resolution: MeV GeV Point Source Sensitivity: < 6 x 10-9 ph cm -2 s -1 (est. performance: < 3 x 10-9 ph cm -2 s -1 ) 40 times EGRET s sensitivity Wide Energy Range: 20 MeV - >300 GeV g Wide Field of View (> 2 sr) Low dead time: < 100 ms/event Large Effective Area (A eff ) peak > 8,000 cm 2 e + e Good Energy Resolution DE/E ~ 10%; 100 MeV 10 GeV ~ < 20%; 10 GeV 300 GeV Robert P. Johnson SpacePart

15 1997 Beam Test Verify Simulations Model Small-aperture first prototype Tagged g beam at SLAC X Projected Angle 3-cm spacing, 4% foils, MeV Data Monte Carlo Containment Space Angle (deg) 10 1 Monte Carlo GLAST Data 68% Containment 95% Containment (errors are 2σ) Energy (MeV) Published in NIM A446(2000), 444. Robert P. Johnson SpacePart

16 Beam Test Engineering Model (Dec 1999) Beam Test in SLAC s Endstation A CsI Calorimeter Full-scale LAT module Test Fabrication Methods Verify Performance Resolution & Efficiency Trigger Simulation Silicon Tracker ACD Robert P. Johnson SpacePart

17 Occupancy GLAST Beam-Test Tracker Performance The Tracker must operate 885,000 channels on a power budget of less than 200 Watts and achieve low noise for triggering. The requirements were met: 99% efficiency with <10 4 noise occupancy. This was accomplished with only 200 µw of power per channel. Efficiency Hit efficiency versus threshold for 5 GeV positrons. Layer 10 x Layer 10 y 10-5 Layer 6x 100,000 triggers Strip Number Noise occupancy and hit efficiency for one layer, using in both cases the same 170 mv threshold. No channels were masked Threshold (mv) Detector Ladder Robert P. Johnson SpacePart Hit Efficiency Cosmic Rays Electron Beam Layer 6x

18 Balloon Flight (Summer 2001) The beam-test module (Tracker, Calorimeter, ACD) was also flown on a balloon to an altitude of 38 km. The instrument performed well throughout the flight and was not damaged by the shock of the parachute and the hard landing (up to 50 g). Robert P. Johnson SpacePart

19 Some Balloon Flight Data Trigger rate vs atmospheric depth Single photon conversion Time A C D ACD and Calorimeter pulse-height distributions for single charged particles. alpha CAL ACD MIP efficiency >99.95% proton Robert P. Johnson SpacePart

20 LAT Status and Schedule January 2002: NASA PDR & DOE Baseline Review in January A few subsystems were not baselined for various reasons. April 2002: SLAC internal review recommends 6 month schedule increase: Solve budget profile problems. Get spacecraft design going to allow LAT interface design to mature. ASIC development delays in detector subsystems. July/August 2002: complete PDR and Baseline Review Winter 2003: Critical Design Review Subsystems are starting fabrication of Engineering Models (flight design): Complete calorimeter module Complete Tracker mechanical/thermal module (no functional detectors) Several functional Tracker trays. ACD components (not full system) DAQ electronics modules Some early procurements in progress: >2000 SSD delivered by HPK SSD ladder assembly soon Tracker closeout carbon-carbon Calorimeter crystals & PIN diodes Engineering still in progress in many areas (e.g. thermal control) but will be complete for CDR. Robert P. Johnson SpacePart

21 LAT Schedule Calendar Years I-CDR (Joint DOE/NASA Review) SRR PDR NAR M-CDR Begin LAT-S/C Integration Launch Formulation Implementation Ops. 1 st Joint DOE/NASA Review of GLAST LAT Build & Test Engineering Models Baseline Review Build & Test Flight Units Inst. I&T Schedule Reserve Observatory I&T Robert P. Johnson SpacePart

22 Conclusions The LAT is quickly moving towards flight-instrument fabrication. GLAST will address many important questions: How do Nature s most powerful accelerators work? What is the source of galactic cosmic rays? What is going on around black holes? What are the unidentified sources found by EGRET? What is the origin of the extragalactic diffuse background? What is the high energy behavior of gamma-ray bursts? What are gamma-ray bursts? What else out there is shining gamma rays? Are there further surprises in the poorly measured energy region? When did galaxies form? What is the nature of the dark matter? Large discovery potential! Robert P. Johnson SpacePart

23 Science Performance Requirements Summary Parameter Peak Effective Area (in range 1-10 GeV) Energy Resolution 100 MeV on-axis Energy Resolution 10 GeV on-axis Energy Resolution GeV on-axis Energy Resolution GeV off-axis (>60º) PSF 68% 100 MeV on-axis PSF 68% 10 GeV on-axis PSF 95/68 ratio PSF 55º/normal ratio Field of View Background rejection (E>100 MeV) Point Source Sensitivity(>100MeV) Source Location Determination GRB localization SRD Value >8000 cm 2 <10% <10% <20% <6% <3.5 <0.15 <3 <1.7 >2sr <10% diffuse <6x10-9 cm -2 s -1 <0.5 arcmin <10 arcmin Present Design Value 10,000 cm 2 at 10 GeV 9% 8% <15% <4.5% 3.37 (front), 4.64 (total) (front), (total) 2.1 front, 2.6 back (100 MeV) sr 6% diffuse (adjustable) 3x10-9 cm -2 s -1 <0.4 arcmin (ignoring BACK info) 5 arcmin (ignoring BACK info) Robert P. Johnson SpacePart

24 Beam Test Results Using beams of positrons, tagged photons and hadrons: Published in NIM A474(2001)19. Point-spread function Data system, trigger Hit multiplicities in front and back tracker sections Tracker efficiency, noise occupancy, power, time-over-threshold Calorimeter response with prototype electronics. Upper limit on neutron component of ACD backsplash Hadron tagging and first look at response Robert P. Johnson SpacePart

25 Simulations of Background Rejection 50 Million generated MC events Residual background is 5% of the diffuse. Below 100 MeV, without any retuning of cuts for low energy, the fraction rises to 14%. Peak effective area: 10,000 cm 2 (at ~10 GeV). Extragalactic diffuse flux, after cuts, scaled to generated background log(e) corrected (MeV) 100 MeV 1 GeV 10 GeV 100 GeV Robert P. Johnson SpacePart