GLAST:GLAST:Status and Science Status and Science ProspectsProspects

Peter F. MichelsonStanford University

peterm@stanford.edu

GammaGamma--ray Large Area ray Large Area Space TelescopeSpace Telescope

Joint GLAST LAT-SWG Symposium, September 30, 2004

2

Outline Outline

LAT: 20 LAT: 20 MeVMeV –– >300 >300 GeVGeV

GBM: 10 GBM: 10 keVkeV –– 25 25 MeVMeV

Large Area Telescope (LAT)

GLAST Burst Monitor (GBM)

launch: February 2007

• GLAST: An International Science Mission –– Large Area Telescope (LAT)Large Area Telescope (LAT)–– GLAST Burst Monitor (GBM)GLAST Burst Monitor (GBM)

• science opportunities: the need for multi-wavelength observations

• schedule highlights

3

GLAST is an International MissionGLAST is an International MissionNASA – Department of Energy Partnership on LATLAT is being built by an international team

Stanford University (SLAC & HEPL, Physics)Goddard Space Flight CenterNaval Research LaboratoryUniversity of California, Santa CruzUniversity of WashingtonOhio State UniversityCEA/Saclay & IN2P3 (France)ASI & INFN (Italy)Hiroshima University, ISAS, RIKEN (Japan)Royal Inst. of Technology & Stockholm Univ. (Sweden)

GBM is being built by US and GermanyMPE, Garching (Germany)Marshall Space Flight Center

Spacecraft and integration - Spectrum AstroMission Management: NASA/GSFC

Germany

FranceSweden Italy

USA Japan

4

GLAST addresses a broad science menuGLAST addresses a broad science menu

•• Systems with Systems with supermassivesupermassive black holes & relativistic jetsblack holes & relativistic jets•• GammaGamma--ray bursts (ray bursts (GRBsGRBs))•• PulsarsPulsars•• Solar physicsSolar physics•• Origin of Cosmic RaysOrigin of Cosmic Rays•• Probing the era of galaxy formationProbing the era of galaxy formation•• Solving the mystery of the highSolving the mystery of the high--energy unidentified sources energy unidentified sources •• Discovery! Particle Dark Matter? Other relics from the Big BDiscovery! Particle Dark Matter? Other relics from the Big Bang? ang?

Testing Testing LorentzLorentz invariance. New source classesinvariance. New source classes

5

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!

wide field of view, and the ability to repoint, important for study of transients.

Features of the gammaFeatures of the gamma--ray skyray sky

6

Overview of GLAST Large Area TelescopeOverview of GLAST Large Area Telescope

• Precision Si-strip Tracker (TKR)18 XY tracking planes. Single-sided silicon strip detectors (228 µm 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–

γ

Calorimeter

Tracker

ACD [surrounds 4x4 array of TKR towers]

7

• 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 (9x larger than EGRET @ 1 GeV)

•• Results in factor > 30Results in factor > 30--100 improvement in sensitivity100 improvement in sensitivity

• much smaller deadtime per event (25 µsec factor 4,000 better than EGRET)

• No expendables long mission without degradation

GLAST LAT High Energy CapabilitiesGLAST LAT High Energy Capabilities

8

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

GLAST MISSION ELEMENTSGLAST MISSION ELEMENTS

GN

-

-

DELTA7920H •

White Sands

TDRSS SNS & Ku

• Telemetry 1 kbps•

-•

S

• µsec•

•

HEASARCGSFC

LAT Instrument Operations Center

GBM Instrument Operations Center

GRB Coordinates Network Alerts

Data, Command Loads

Schedules

Schedules

ArchiveMission Operations Center (MOC)

GLAST Science Support Center

•

GLAST Spacecraft

Large Area Telescope& GBMGPS

GLAST MISSION ELEMENTS

10

Science Mission ElementsScience Mission Elements•Science Working Group (chair, S. Ritz, Project Scientist)

–membership includes Interdisciplinary Scientists, instrument team PIs and instrument team representatives–bi-monthly telecons and ~bi-annual sit-down meetings, along with science symposia to engage the community.

•Users Committee (chair: J. Grindlay)–independent of the SWG. External review/feedback on science tools planning and progress.–includes members from both the astrophysics and high-energy particle physics communities who are likely users of GLAST data.

•GLAST Science Support Center (GSSC)–located at Goddard. Supports guest observer program, provides training workshops, provides data and software to community, archives to HEASARC, joint software development with Instrument Teams.

11

• After the initial on-orbit checkout, verification, and calibrations, the first year of science operations will be an all-sky survey. – first year data used for detailed instrument characterization,

refinement of the alignment, and key projects (source catalog, diffuse background models, etc.) needed by the community

– data on transients will be released, with caveats– repoints for bright bursts and burst alerts enabled– extraordinary ToO’s supported– limited first-year guest observer program– workshops for guest observers on science tools and mission

characteristics for proposal preparation

• Observing plan in subsequent years driven by guest observer proposal selections by peer review. All data released through the science support center (GSSC).

Operations PhasesOperations Phases

12

The next-generation ground-based and space-based experiments are well matched.

Complementary capabilitiesground-based space-basedACT EAS Pair

angular resolution good fair goodduty cycle low high higharea large large smallfield of view small large large+can reorient

energy resolution good fair good, w/ smaller systematic uncertainties

GammaGamma--ray Observatoriesray Observatories

(credit: A. Morselli et al.)

13

AnticenterAnticenter RegionRegion

GemingaIC 443

Crab

PKS 0528+134

14

33rdrd EGRET CatalogEGRET CatalogGLAST Survey: ~10,000 sources (2 years)GLAST Survey: ~10,000 sources (2 years)

AGN - blazarsunidentified

pulsarsLMC

15

GammaGamma--ray Sources: Inherently ray Sources: Inherently MultiwavelengthMultiwavelength

• Nature rarely produces monoenergetic particle beams. Broad range of particle energies leads to broad range of photon energies.

–– Example: Example: ππo o productionproduction

• Charged particles rarely interact by only one process. Different processes radiate in different energy bands.

–– Example: synchrotronExample: synchrotron--Compton processesCompton processes

• High-energy particles needed to produce γ-rays can radiate in lower-energy bands as they lose energy.

–– Contrast: Contrast: nonthermalnonthermal XX--ray ray source can have highsource can have high--energy energy cutoffcutoff

In the In the MeVMeV range and above, sources are nonrange and above, sources are non--thermal: thermal: ⇒⇒ produced by interactions of energetic particlesproduced by interactions of energetic particles

GLAST LAT Multiwavelength Coordinator: Dave Thompson

16

GLAST ScheduleGLAST Schedule

• Launch February 2007–– Kennedy Space Flight CenterKennedy Space Flight Center

• Science operation begins May 2007

Delta II launch

17

MW Approaches for GLAST SourcesMW Approaches for GLAST Sources

Two broad areas:Two broad areas:1. Identification for known

source classes; discovery of new classes. “What are they?”

2. Exploration of identified sources. “What can we learn from them?”

?0Clusters of galaxies

?0Starburst galaxies

?1 likely1 possible

X-ray binaries/microquasars

?1 likely1 possible

Radio galaxies

>101 likely~5 possible

Supernova remnants/plerions

?170Unidentified sources

>5005Gamma-ray bursts

4-52Normal galaxies

>200080 definite50 possible

Blazars

100-5006 definite3 possible

Rotation-powered pulsars

Number anticipated with GLAST

Number seen by EGRET

Source Class

18

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.

19

ussource Eγ lower

ussource Eγ higher

eVETeV

≈

131ε

AGN, the EBL, and CosmologyAGN, the EBL, and CosmologyIFIF AGN spectra can be understood well enough, they may providea means to probe the era of galaxy formation:(Stecker, De Jager & Salamon; Madau & Phinney; MacMinn & Primack)

If γγ c.m. energy > 2mec2, pair creation attenuates flux. For flux of γ-rays with energy, E, this cross-section is maximized when the partner, ε, is

For 10 GeV- TeV γ-rays, this corresponds to a partner photon energy in the optical - UV range. Density is sensitive to time of galaxy formation.

eVETeV

≈

131ε

source Eγ lower

source Eγ higher

Salamon & Stecker, ApJ 493, 547 (1998)

opaque

No significant attenuation below 10 GeV

20

• GLAST will see thousands of blazars - instead of peculiarities of individual sources, look for systematic effects vs redshift.

• key energy range for cosmological distances (TeV-IR attenuation more local due to opacity).

GLAST Can Probe the OpticalGLAST Can Probe the Optical--UV EBLUV EBL

• How many blazars have intrinsic roll-offs in this energy range (10-100 GeV)? (An important question by itself for GLAST!) Power of statistics is the key.

• Must measure the redshifts for a large sample of these blazars!

Caveats

Primack & Bullock

Salamon & Stecker

No EBL

Chen, Reyes, and Ritz, ApJ, in press

effect is model-dependent (this is good):

21

MW Planning Group RecommendationsMW Planning Group Recommendations

• Complete a southern hemisphere catalog of flat spectrum radio sources out to 8.4 GHz or higher frequencies, at least down to 100 mJy, and preferably to 30 mJy.

• Complete a program of optical identifications and redshiftmeasurements for all known flat-spectrum radio sources brighter than 100 mJy at 8 GHz.

• Use pulsar models to develop a prioritized list of radio pulsars to be monitored. Start the timing program before the GLAST launch.

• Sponsor observations with the CfA telescope of special directions such as tangent directions of spiral arms. Encourage observations of the Galactic center region and a search for southern intermediate-latitude clouds.

Pre-launch MW Planning:

22

MW Planning Group RecommendationsMW Planning Group Recommendations

• Plan campaigns with Chandra, XMM, Astro E2, and (if selected) NuSTAR for high-energy X-ray studies of unidentified gamma-ray source error boxes.

• Plan pulsar search proposals for X-ray telescopes

• Plan coordinated proposals with optical and radio observatories for follow-on observations of LAT sources.

• The LAT blazar program should collaborate with existing blazar study groups wherever possible, for both Target of Opportunity campaigns and pre-planned MW campaigns.

• Plan a dedicated radio timing program for the pulsars expected to be brightest and most interesting GLAST sources.

• Plan follow-on proposals for radio, optical, or X-ray telescope time for LAT sources identified as pulsars in order to develop the most complete MW picture possible for these pulsars.

MW Activities starting early in the Post-launch Phase:

MW Activities throughout the GLAST Mission:

23

SummarySummary

•• BEFORE LAUNCHBEFORE LAUNCH – expand the list of known blazars, start radio timing program for pulsars

•• EARLY IN THE MISSIONEARLY IN THE MISSION – radio and X-ray observations, in particular, to help identify gamma-ray sources.

•• THROUGHOUT THE MISSIONTHROUGHOUT THE MISSION – monitoring and coordinated MW campaigns for flaring sources, regular timing for pulsars

GLAST science will be maximized by multi-wavelength observations

24

photons with E>10 GeV are attenuated by the diffuse field of UV-Optical-IR extragalactic background light (EBL) γ + γ → 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 Constraints on extragalactic background light (EBL) from (EBL) from γγ--ray ray blazarsblazars

25

GammaGamma--ray Observatoriesray Observatories

“sensitivity”

26

High energy source sensitivity: allHigh energy source sensitivity: all--sky scan modesky scan mode

100 sec

1 orbit**

1 day^̂

^̂““rockingrocking”” allall--sky scan: alternating sky scan: alternating orbits point above/below the orbit planeorbits point above/below the orbit plane

EGRET Fluxes

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

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

- 3EG 1835+59- 3C279 lowest 5σ detection- 3EG 1911-2000 (AGN)- Mrk 421- Weakest 5σ EGRET source

During the all-sky survey, GLAST will have sufficient sensitivity after O(1) day to detect (5σ) the weakest EGRET sources.

*zenith*zenith--pointed pointed