GLAST - LAT ICHEP 2008 - Philadelphia, PA Aug 1, 2008 R.Dubois1/21 GLAST Large Area Telescope:...

GLAST - LAT ICHEP 2008 - Philadelphia, PA Aug 1, 2008

R.Dubois 1/21

GLAST Large Area GLAST Large Area Telescope:Telescope:

Launched and Being Commissioned

Richard DuboisStanford Linear Accelerator Center

[email protected]

for the LAT Collaboration


R.Dubois 2/21


R.Dubois 3/21

25.6 Degree Orbit25.6 Degree Orbit

SAA

http://observatory.tamu.edu:8080/Trakker/

Circular orbit, 565 km altitude (96 min period), 25.6 deg inclination


R.Dubois 4/21

GLAST LAT CollaborationGLAST LAT CollaborationUnited 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. LouisFrance• IN2P3, CEA/SaclayItaly• 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 MichelsonPI: 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).


R.Dubois 5/21

• 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)

GLAST Burst Monitor (GBM)

GLAST Key Features GLAST Key Features

Spacecraft Partner: General Dynamics

Compared to EGRET: • > 100 MeV, 1 yr sensitivity x25• localization x102

• field of view x5• observing efficiency x2• deadtime x10-3

Compared to EGRET: • > 100 MeV, 1 yr sensitivity x25• localization x102

• field of view x5• observing efficiency x2• deadtime x10-3


R.Dubois 6/21

Some Questions GLAST Will AddressSome 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


R.Dubois 7/21

Experimental TechniqueExperimental Technique

• Instrument must measure the direction, energy and arrival time of gamma rays over a large energy range (~20 MeV to > 300 GeV)

e+ e– calorimeter (energy measurement)

particle tracking detectors

conversion foil

anticoincidenceshield

Pair-Conversion Telescope• 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.


R.Dubois 8/21

The GLAST ObservatoryThe GLAST Observatory

GBM Bismuth

GermanateDetector

GBM Sodium Iodide

Detector

LAT


R.Dubois 9/21

e+ e–

Overview of LATOverview of LAT

• Precision Si-strip Tracker (TKR) 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)Hodoscopic CsI Calorimeter(CAL) Array of 1536 CsI(Tl) crystals in 8 layers. Measure the photon energy; image the shower.

• Segmented Anticoincidence Detector Segmented Anticoincidence Detector (ACD)(ACD) 89 plastic scintillator tiles. Reject background of charged cosmic rays; segmentation removes self-veto effects at high energy.

• Electronics System Electronics System Includes flexible, robust hardware trigger and software filters.

Systems work together to identify and measure the flux of cosmic Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV - >300 GeV.gamma rays with energy 20 MeV - >300 GeV.

Calorimeter

Tracker

ACD [surrounds 4x4 array of TKR towers]


R.Dubois 10/21

LAT Construction: An International Effort LAT Construction: An International Effort

Tracker: US, Italy, Japan Calorimeter: US, France, Sweden

ACD: US

Integration & Data System: US


R.Dubois 11/21

GN

HEASARC

-

-

DELTA7920H •

White Sands

TDRSS SNS & Ku

LAT Instrument Science

Operations Center (SLAC)

GBM Instrument Operations Center

GRB Coordinates Network

• Telemetry 1 kbps•

-•

S

Alerts

Data, Command Loads

Schedules

Schedules

Mission Operations Center (MOC)

GLAST Science Support Center

• sec•

•

•

GLAST Spacecraft

Large Area Telescope& GBMGPS

GLAST MISSION ELEMENTS


R.Dubois 12/21

Operating modesOperating modes

• 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.

LAT sensitivity on 4 different timescales: 100 s, 1 orbit (96 mins), 1 day and 1 year


R.Dubois 13/21

In Orbit: Single Events in the LATIn 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.


R.Dubois 14/21

Calorimeter Calibration with IonsCalorimeter Calibration with Ions

Ion peaks are used for calibrations• Heavy ions probe the higher energy ranges• Peak positions stable to < 1% over days elapsed

Proton MIP

Non-Interacting Heavy Ion

C N O

FeCarbon peak vs time


R.Dubois 15/21

Vela – early returnsVela – early returns

Soup to nuts: everything works!timingbackground rejectionalignment

• precise ephemerides of many pulsars provided by Parkes, Jodrell Bank, Green bank, Nançay, Arecibo, Hartbeesthoek, Urumqi, RXTE, XMM...

• good timing of the EGRET pulsars

EGRET

• selecting on-pulse shows point source• evaluate PSF• alignment of LAT to sky (fit to several point sources)

on-pulse off-pulse


R.Dubois 16/21

Rates & DeadtimeRates & Deadtime

~2 kHz trigger rate~500 Hz downlink rate~1 Hz source photon rate26 s 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


R.Dubois 17/21

GLAST/LAT performanceGLAST/LAT performanceGLAST/LAT performanceGLAST/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 srPoint Source sens. (>100 MeV): 3x10-9 cm-2 s-1


R.Dubois 18/21

Year 1 Science Operations Timeline OverviewYear 1 Science Operations Timeline Overview

LAUNCH L+60 days

week week week week month 12 m o n t h s

spacecraftturn-on checkout

LAT, GBMturn-on check out

“first light”whole sky

initial tuning/calibrations

pointed + sky survey tuning

Start Year 1 Science Ops

Start Year 2 Science Ops

in-depth instrument studies

sky survey + ~weekly GRB repoints + extraordinary TOOs

Release Flaring and Monitored Source Info

GBM and LAT GRB Alerts

continuousrelease of newphoton data

Observatoryrenaming

GI Cycle 1 Funds Release

Fellows Year 1Start

LAT 6-monthhigh-confidencesource release, GSSC science tools advance release

GI Cycle 2Proposals LAT Year 1 photon

data release PLUSLAT Year 1 Catalogand Diffuse Model

2nd GLASTSymposium


R.Dubois 19/21

Data Release plan and operationsData 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


R.Dubois 20/21

LAT First Year Source Monitoring ListLAT 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.


R.Dubois 21/21

The LAT’s First Public Volley: 3C454.3 The LAT’s First Public Volley: 3C454.3 ATelATel


R.Dubois 22/21

OutlookOutlook• 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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