GLAST Mission: Status and Science Opportunities Peter F. Michelson Stanford University Gamma-ray Large Area Space Telescope

Outline GLAST: An International Science Mission – Large Area Telescope (LAT) – GLAST Burst Monitor (GBM) Mission Operations Plan highlights of science opportunities schedule highlights

The GLAST Observatory two GLAST instruments: LAT: 20 MeV – >300 GeV GBM: 10 keV – 25 MeV Large Area Telescope (LAT) GLAST Burst Monitor (GBM)

GLAST is an International Mission NASA - DoE Partnership on LAT LAT is being built by an international team (PI: P. Michelson, Stanford University) Si Tracker: UCSC, Italy, Japan, Stanford/SLAC CsI Calorimeter: NRL, France, Sweden Anticoincidence: GSFC Data Acquisition System: Stanford/SLAC, NRL GBM is being built by US and Germany (PI: C. Meegan, NASA/MSFC) Detectors: MPE Data Acquisition System: MSFC Spacecraft and integration - Spectrum Astro Mission Management: NASA/GSFC ( K. Grady, Project Manager; S. Ritz, Project Scientist) Germany France Sweden Italy USA Japan

 e+e+ e–e– calorimeter (energy measurement) particle tracking detectors conversion foil anticoincidence shield Pair-Conversion Telescope LAT: experimental technique instrument must measure the direction, energy, and arrival time of high energy photons (from approximately 20 MeV to greater than 300 GeV): - photon interactions with matter in GLAST energy range dominated by pair conversion: determine photon direction clear signature for background rejection Energy loss mechanisms: - limitations on angular resolution (PSF) low E: multiple scattering => many thin layers high E: hit precision & lever arm must detect  -rays with high efficiency and reject the much larger (~10 4 :1) flux of background cosmic-rays, etc.; energy resolution requires calorimeter of sufficient depth to measure buildup of the EM shower. Segmentation useful for resolution and background rejection.

Overview of LAT Precision Si-strip Tracker (TKR) 18 XY tracking planes. Single-sided silicon strip detectors (228  m 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. Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV - >300 GeV. e+e+ e–e–  Calorimeter Tracker ACD [surrounds 4x4 array of TKR towers]

Huge FOV (~20% of sky) Broadband (4 decades in energy, including unexplored region > 10 GeV) Unprecedented PSF for gamma rays (factor > 3 better than EGRET for E>1 GeV) Large effective area (factor > 4 better than EGRET) Results in factor > improvement in sensitivityResults in factor > improvement in sensitivity No expendables long mission without degradation GLAST LAT High Energy Capabilities

8 High energy source sensitivity: all-sky scan mode 100 sec * 1 orbit * ^ 1 day^ ^“rocking” all-sky scan: alternating orbits point above/below the orbit plane EGRET Fluxes - GRB (100sec) - PKS flare - 3C279 flare - Vela Pulsar - Crab Pulsar - 3EG (SNR  Cygni?) - 3EG C279 lowest 5  detection - 3EG (AGN) - Mrk Weakest 5  EGRET source During the all-sky survey, GLAST will have sufficient sensitivity after O(1) day to detect (5  ) the weakest EGRET sources. *zenith-pointed

GBM Detector (12) Sodium Iodide (NaI) Scintillation Detectors Major Purposes –Provide low-energy spectral coverage in the typical GRB energy regime over a wide FoV (10 keV – 1 MeV) –Provide rough burst locations over a wide FoV Bismuth Germanate (BGO) Scintillation Detector Major Purpose –Provide high-energy spectral coverage (150 keV – 25 MeV) to overlap LAT range over a wide FoV LAT

Roles of the GBM provides spectra for bursts from 10 keV to 25 MeV, connecting frontier LAT high-energy measurements with more familiar energy domain; provides wide sky coverage (8 sr) -- enables autonomous repoint requests for exceptionally bright bursts that occur outside LAT FOV for high-energy afterglow studies (an important question from EGRET); GLAST observatory provides burst alerts to the ground. Simulated GBM and LAT response to time-integrated flux from bright GRB Spectral model parameters from CGRO wide-band fit 1 NaI (14º) and 1 BGO (30º)

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

The GLAST Science Support Center located in Goddard’s Laboratory for High Energy Astrophysics SSC responsible for: –supporting the guest investigator program –the mission timeline (includes support for TOOs, commands) –providing data & analysis software to the scientific community –archiving data & software in the HEASARC –supporting (logistically & scientifically) the Project Scientist, the Science Working Group, and the Users’ Committee instrument teams and SSC define and develop the analysis software together –instrument teams manage the software development, but SSC staff assists

GLAST addresses a broad science menu GLAST draws the interest of both the High Energy Particle Physics and High Energy Astrophysics communities. Systems with supermassive black holes & relativistic jets Gamma-ray bursts (GRBs) Pulsars Solar physics Origin of Cosmic Rays Probing the era of galaxy formation Solving the mystery of the high-energy unidentified sources Discovery! Particle Dark Matter? Other relics from the Big Bang? Testing Lorentz invariance. New source classes

EGRET all-sky survey (E>100 MeV) diffuse extra-galactic background (flux ~ 1.5x10 -5 cm -2 s -1 sr -1 ) galactic diffuse (flux ~O(100) times larger) high latitude (extra-galactic) point sources (typical flux from EGRET sources O( ) cm -2 s -1 galactic sources (pulsars, un-ID’d) An essential characteristic: VARIABILITY in time! field of view, and the ability to repoint, important for study of transients. Features of the gamma-ray sky

3 rd EGRET Catalog GLAST Survey: ~300 sources (2 days) GLAST Survey: ~10,000 sources (2 years) AGN - blazars unidentified pulsars LMC

photons with E>10 GeV are attenuated by the diffuse field of UV-Optical- IR extragalactic background light (EBL)  +   e + + e - a dominant factor in determining the EBL is the time of galaxy formation Chen & Ritz, ApJ (2000) Salamon & Stecker, ApJ 493, 547 (1998) opaque No significant attenuation below 10 GeV Constraints on extragalactic background light (EBL) from  -ray blazars

172 of the 271 sources in the EGRET 3 rd catalog are “unidentified” Cygnus region (15x15 deg) Unidentified Sources EGRET source position error circles are ~0.5°, resulting in counterpart confusion. GLAST will provide much more accurate positions, with ~30 arcsec - ~5 arcmin localizations, depending on brightness.

EGRET detected very high energy emission associated with bursts, including a 20 GeV photon ~75 minutes after the start of a burst: Future Prospects: GLAST will provide definitive information about the high energy behavior of bursts: LAT and GBM together will measure emission over >7 decades of energy. Hurley et al., 1994 GRBs are now confirmed to be at cosmological distances. The question persists : What are they?? Gamma-Ray Bursts

GRBs and instrument deadtime Time between consecutive arriving photons Distribution for the 20 th brightest burst in a year (Norris et al) LAT will open a wide window on the study of the high energy behavior of bursts.

recent analysis by Gonzalez, et al. Compare data from EGRET and BATSE: Distinct high- energy component has different time behavior! What is the high-energy break and total luminosity? Need GLAST data! -18 to 14 sec 14 to 47 sec 47 to 80 sec sec sec GRB

GLAST Master Schedule Launch: February 2007 First flight hardware deliveries to SLAC for I&T: August 2004 Observatory I&T starts: December 2005 LAT ready for Environmental Test: July 2005 GBM I&T starts: September 2004

22 ` launch: February 2007 GLAST: Exploring Nature’s Highest Energy Processes