GLAST Mission:GLAST Mission: Status and Science Status and Science OpportunitiesOpportunities

Peter F. MichelsonStanford University

peterm@stanford.edu

Gamma-ray Large Area Gamma-ray Large Area Space TelescopeSpace Telescope

OutlineOutline

• 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 The GLAST Observatory

two GLAST instruments:

LAT: 20 MeV – >300 GeV

GBM: 10 keV – 25 MeVLarge Area Telescope (LAT)

GLAST Burst Monitor (GBM)

GLAST is an International MissionGLAST is an International MissionNASA - 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, SwedenAnticoincidence: GSFCData 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

FranceSweden Italy

USA Japan

e+ e– calorimeter (energy measurement)

particle tracking detectors

conversion foil

anticoincidenceshield

Pair-Conversion Telescope

LAT: experimental techniqueLAT: 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 (~104:1) 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 LATOverview 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–

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 > 30-100 improvement in sensitivityResults in factor > 30-100 improvement in sensitivity

• No expendables long mission without degradation

GLAST LAT High Energy CapabilitiesGLAST LAT High Energy Capabilities

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High energy source sensitivity: all-sky scan modeHigh energy source sensitivity: all-sky scan mode

100 sec

1 orbit**

1 day^̂

^“rocking” all-sky scan: ^“rocking” all-sky scan: alternating orbits point alternating orbits point above/below the orbit planeabove/below the orbit plane

EGRET Fluxes

- GRB940217 (100sec)- PKS 1622-287 flare- 3C279 flare- Vela Pulsar

- Crab Pulsar- 3EG 2020+40 (SNR Cygni?)

- 3EG 1835+59- 3C279 lowest 5 detection- 3EG 1911-2000 (AGN)- Mrk 421- 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 *zenith-pointed

GBM DetectorGBM 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 GBMRoles 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 940217

Spectral model parameters from CGRO wide-band fit

1 NaI (14º) and 1 BGO (30º)

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GLAST MISSION ELEMENTSGLAST MISSION ELEMENTS

GN

HEASARCGSFC

-

-

DELTA7920H •

White Sands

TDRSS SNS & Ku

LAT Instrument Operations Center

GBM Instrument Operations Center

GRB Coordinates Network

• Telemetry 1 kbps•

-•

S

Alerts

Data, Command Loads

Schedules

Schedules

ArchiveMission Operations Center (MOC)

GLAST Science Support Center

• sec•

•

•

GLAST Spacecraft

Large Area Telescope& GBMGPS

GLAST MISSION ELEMENTS

The GLAST Science Support CenterThe 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 menuGLAST addresses a broad science menu

GLAST draws the interest of both the High Energy Particle Physics GLAST draws the interest of both the High Energy Particle Physics and High Energy Astrophysics communities.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-2s-1sr-1)

galactic diffuse (flux ~O(100) times larger)

high latitude (extra-galactic) point sources (typical flux from EGRET sources O(10-7 - 10-6) cm-2s-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 skyFeatures of the gamma-ray sky

33rdrd EGRET Catalog EGRET CatalogGLAST Survey: ~300 sources (2 days)GLAST Survey: ~300 sources (2 days) GLAST Survey: ~10,000 sources (2 years)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 Constraints on extragalactic background light (EBL) from light (EBL) from -ray blazars-ray blazars

172 of the 271 sources in the EGRET 3rd catalog are “unidentified”

Cygnus region (15x15 deg)

Unidentified SourcesUnidentified 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 BurstsGamma-Ray Bursts

GRBs and instrument deadtimeGRBs and instrument deadtime

Time between consecutive arriving photons

Distribution for the 20th 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

80-113 sec

113-211 sec

GRB 941017GRB 941017

GLAST Master ScheduleGLAST Master Schedule

Launch: Launch: February 2007February 2007

First flight hardware First flight hardware deliveries to SLAC for deliveries to SLAC for I&T: August 2004I&T: August 2004

Observatory I&T Observatory I&T starts: December 2005starts: December 2005

LAT ready for LAT ready for Environmental Test: Environmental Test: July 2005July 2005

GBM I&T starts: GBM I&T starts: September 2004September 2004

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launch: February 2007

GLAST: Exploring Nature’s Highest Energy Processes