Gamma-ray Large Area Space Telescope IEEE Nuclear Science Symposium Wyndham El Conquistador Resort, Puerto Rico October 23 - 29, 2005 The Gamma Ray Large

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

IEEE Nuclear Science SymposiumWyndham El Conquistador Resort, Puerto Rico

October 23 - 29, 2005

The Gamma Ray Large Area Space Telescope:an Astro-particle Mission to Explore the High

Energy Sky

Luca BaldiniINFN - Pisa

IEEE NSS - Puerto Rico - October 25, 2005 Luca Baldini

GLASTGLAST

Launch Vehicle Delta II – 2920-10HLaunch Location Kennedy Space CenterOrbit Altitude 575 KmOrbit Inclination 28.5 degreesOrbit Period 95 MinutesLaunch Date mid 2007

Large Area Telescope (LAT)GLAST Burst Monitor (GBM)

Large Area Telescope (LAT):Large Area Telescope (LAT): Pair conversion telescope. Converter foils + tracker + calorimeter - surrounded by an anticoincidence shield. Will detect photons in the 20 MeV – 300 GeV range.GLAST Burst Monitor (GBM):GLAST Burst Monitor (GBM): Set of 14 scintillators monitoring the full sky. Energy range: 10 keV – 25 MeV. Optimize to detect GRBs.

GLAST: Gamma-ray Large Area Space Telescope


The need for a high-energy The need for a high-energy -ray detector-ray detector

Predicted sensitivity to point sources:Predicted sensitivity to point sources: EGRET, GLAST and MILAGRO: 1 year survey. Cherenkov telescopes: 50 hours observation.(from Weekes, et al. 1996 – GLAST added)

Broad spectral coverage is crucial for understanding most astrophysical sources.

Multiwavelenght campaigns: space based and ground based experiments cover complimentary energy ranges.

The improved sensitivity of GLAST will match the sensitivity of the next generation of Cherenkov telescopes filling the energy gap in between the two approaches.

Overlap for the brighter sources: cross calibration, alerts.


OutlineOutline

Talk outline:Talk outline: The scientific case for the GLAST experiment . Experimental technique and design of the Large Area Telescope. Design, construction and testing of the silicon tracker. Conclusions


The sky above 100 MeV: the EGRET surveyThe sky above 100 MeV: the EGRET survey

The heritage of EGRET:The heritage of EGRET: Diffuse extra-galactic background (~ 1.5 x 10-5 cm-2s-1sr-1 integral flux). Much larger (~ 100 times) background on the galactic plane (60% of 1.4 M). Few hundreds of point sources (both galactic and high latitude, 10% of the total photons). Essential characteristic: variability in time.


Sky mapSky map

GLAST 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)EGRET Survey: 271 sourcesEGRET Survey: 271 sources


Unidentified sourcesUnidentified sources

Counting stats not included.

170 point sources of the EGRET catalog still unidentified (no know counterpart at other wavelengths).

GLAST will provide much smaller error bars on sources location (at arc-minute level).

GLAST will be able to detect typical signatures (spectral features, flares, pulsation) allowing an easier identification with know sources.

Most of the EGRET diffuse background will be resolved into point sources.

Large effective area and good angular resolution are crucial!

Cygnus region:15o x 15o, E > 1 GeV


Active Galactic NucleiActive Galactic Nuclei

AGNs phenomenology:AGNs phenomenology: Vast amount of energy from a very compact central volume. Large fluctuations in the luminosity (with ~ hour timescale). Energetic, highly collimated, relativistic particle jets Prevailing idea: accretion onto super-massive black holes (106 – 1010 solar masses).

AGN physics AGN physics to-do-listto-do-list:: Catalogue AGN classes with a large data sample (at least ~ 3000 new AGNs) Detailed study of the high energy spectral behavior. Track flares ( ~ minutes). Large effective area and excellent spectral capabilities needed!


Gamma Ray BurstsGamma Ray Bursts

GRBs phenomenology:GRBs phenomenology: Dramatic variations in the light curve on a very short time scale. Isotropic distribution in the sky (basically from BATSE, on board CGRO, but little data @ energies > 50 MeV). Non repeating (as far as we can tell…). Spectacular energies (~ 1051 – 1052 erg).

Simulated 1 year GLAST operationSimulated 1 year GLAST operation(Assuming a various spectral index/flux.)

GRBs physics:GRBs physics: GLAST should detect ~ 200 GRBs per year above 100 MeV (a good fraction of them localized to better than 10’ in real time). The LAT will study the GeV energy range. A separate instrument on the spacecraft (the GBM) will cover the 10 keV – 25 MeV energy range. Short dead time crucial!


Experimental techniqueExperimental technique

Pair conversion telescope:Pair conversion telescope: Tracker/converter (detection planes + high Z foils): photon conversion and reconstruction of the direction (via electron/positron track reconstruction).Main L1 trigger (three x-y planes in a row hit) for GLAST. Calorimeter: energy measurements. Anti-coincidence shield: background rejection (charged cosmic rays flux typically ~104 higher than flux).

Real data collected during the integration and testing activity.

Pair conversion exploited (provides the information about the direction/energy and a clear signature for background rejection).


Overview of the Large Area TelescopeOverview of the Large Area Telescope

Tracker/Converter (TKR):Tracker/Converter (TKR): Silicon strip detectors (single sided, each layer is rotated by 90 degrees with respect to the previous one). W conversion foils. ~80 m2 of silicon (total). ~106 electronics chans. High precision tracking, small dead time.

Calorimeter (CAL):Calorimeter (CAL):1536 CsI crystals. 8.5 radiation lengths. Hodoscopic. Shower profile reconstruction (leakage correction)

Anti-Coincidence (ACD):Anti-Coincidence (ACD): Segmented (89 tiles). Self-veto @ high energy limited. 0.9997 detection efficiency (overall).

Overall modular design:Overall modular design: 4x4 array of identical towers - each one including a Tracker, a Calorimeter and an Electronics Module. Surrounded by an Anti-Coincidence shield (not shown in the picture).

e+ e-


Tracker designTracker design

Aggressive mechanical design:Aggressive mechanical design: Less than 2 mm spacing between x and y layers, with front-end electronics lying on the four sides of the trays. 90° pitch adapters from the front end chips to the silicon sensors. 2 mm inter-tower separation in order to minimize the inactive area.


The Silicon Tracker performanceThe Silicon Tracker performance

11500 sensors11500 sensors360 trays360 trays18 towers18 towers

~ 1M channels~ 1M channels83 m83 m22 Si surface Si surface

Construction/testing highlights:Construction/testing highlights:Average detection efficiency higher than 99.5%99.5% @ the nominal threshold setting. Single strip noise occupancy lower than 1010-6-6. Flight production completed in less than one year.


LAT statusLAT status

Current status:Current status: All the 16 towers (Tracker + Calorimeter + Electronics) integrated in the flight grid.

ACD ready to be integrated with the rest of the instrument.

Coming soon:Coming soon: Beam test of the calibration unit (2 spare TKR modules + 4 spare CAL modules). LAT environmental tests. Integration with the spacecraft. Launch.


Summary/conclusionsSummary/conclusions

GLAST has a tremendous potential of discovery. The GLAST mission will be one of the next big NASA observatories. The GLAST LAT tracker is the largest Si tracker ever built for a space application (80 m2 of active silicon surface, ~1M channels). Construction is completed, integration of the LAT is now reaching its completion. Next steps are the environmental tests of the instrument and the beam test on the calibration unit. Launch foreseen in August 2007.

RXTE launch on a DELTA II rocket.


SparesSpares


GLAST vs. EGRETGLAST vs. EGRET

ParameterParameter EGRETEGRET GLASTGLAST(design values)(design values)

DesignDesign

Energy range 20 Mev – 30 GeV ~20 MeV – 300 GeV Hodoscopic calorimeter

Peak effective area1 1500 cm2 ~10000 cm2 Factor of 4 in geometric area

Field of view 0.5 sr ~2.4 sr Favorable aspect ratio

(no TOF)

Angular resolution2 5.8º @ 100 MeV ~4.6º @ 100 MeV

~0.11º @ 1 GeV

High precision tracking (silicon vs. spark chambers)

Energy resolution3 10% ~10%

Deadtime per event 100 ms <100 s No detectors dead time

(silicon vs. spark chambers)

Source location determination4 15’ ~0.4’ PSF + Effective area

Point source sensitivity5 1x10-7 cm-2s-1 ~3x10-9 cm-2s-1 PSF + Effective area

1After background rejection.2Single photon, 68% containment, on axis.31, on axis.41 radius, high latitude source with 10-7 cm-2s-1 integral flux above 100 MeV.51 year sky survey, high latitude, above 100 MeV.


Technology impact on instrument performance IITechnology impact on instrument performance II


Technology impact on instrument performance ITechnology impact on instrument performance I


Triggering and On-board Data FlowTriggering and On-board Data Flow

xx

x

Level 1 trigger:Level 1 trigger: Hardware trigger, single-tower level. Three_in_a_row: three consecutive tracker x-y planes in a row fired. Workhorse trigger. CAL_LO: single log with E > 100 MeV (adjustable). Independent check on TKR trigger. CAL_HI: single log with E > 1 GeV (adjustable). Disengage the use of the ACD. Charged cosmic rays in the L1T! 13 kHz peak rate. Upon a L1T the LAT is read out within 20 s.

On-board processing:On-board processing: Identify candidates and reduce the data volume. Full instrument information available to the on-board processor. Use simple and robust quantities. Hierarchical process (first make the simple selections requiring little CPU and data unpacking).

Level 3 trigger:Level 3 trigger: Final L3T rate: ~ 30 Hz on average. Expected average rate: ~ few Hz( rate : cosmic rays rate = 1 : few). On-board science analysis (flares, bursts). Data transfer to the spacecraft.

Documents

Gamma-ray Large Area Space Telescope IEEE Nuclear Science Symposium Wyndham El Conquistador Resort, Puerto Rico October 23 - 29, 2005 The Gamma Ray Large