1. Gamma-ray Large Area Space Telescope IEEE Nuclear Science Symposium Wyndham 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 Baldini INFN - Pisa

2. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini GLAST Launch VehicleDelta II – 2920-10H Launch LocationKennedy Space Center Orbit Altitude575 Km Orbit Inclination28.5 degrees Orbit Period95 Minutes Launch Datemid 2007 Large Area Telescope (LAT) GLAST Burst Monitor (GBM) 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): 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

3. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini The need for a high-energy  -ray detector 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.

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

5. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini The sky above 100 MeV: the EGRET survey The heritage of EGRET: Diffuse extra-galactic background (~ 1.5 x 10 -5 cm -2 s -1 sr -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.

6. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Sky map GLAST Survey: ~300 sources (2 days) GLAST Survey: ~300 sources (2 days) GLAST Survey: ~10,000 sources (2 years) EGRET Survey: 271 sources

7. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Unidentified 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: 15 o x 15 o, E > 1 GeV

8. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Active Galactic Nuclei 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 (10 6 – 10 10 solar masses). AGN physics to-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!

9. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Gamma Ray Bursts 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 (~ 10 51 – 10 52 erg). Simulated 1 year GLAST operation (Assuming a various spectral index/flux.) 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!

10. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Experimental technique 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 ~10 4 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).

11. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Overview of the Large Area Telescope 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 m 2 of silicon (total). ~10 6 electronics chans. High precision tracking, small dead time. Calorimeter (CAL): 1536 CsI crystals. 8.5 radiation lengths. Hodoscopic. Shower profile reconstruction (leakage correction) Anti-Coincidence (ACD): Segmented (89 tiles). Self-veto @ high energy limited. 0.9997 detection efficiency (overall). 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+ e-e-

12. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Tracker 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.

13. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini The Silicon Tracker performance 11500 sensors 360 trays 18 towers ~ 1M channels 83 m 2 Si surface Construction/testing highlights: 99.5% Average detection efficiency higher than 99.5% @ the nominal threshold setting. 10 -6 Single strip noise occupancy lower than 10 -6. Flight production completed in less than one year.

14. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini LAT 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: Beam test of the calibration unit (2 spare TKR modules + 4 spare CAL modules). LAT environmental tests. Integration with the spacecraft. Launch.

15. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Summary/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 m 2 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.

16. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Spares

17. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini GLAST vs. EGRET ParameterEGRETGLAST (design values) Design Energy range20 Mev – 30 GeV~20 MeV – 300 GeVHodoscopic calorimeter Peak effective area 1 1500 cm 2 ~10000 cm 2 Factor of 4 in geometric area Field of view0.5 sr~2.4 srFavorable aspect ratio (no TOF) Angular resolution 2 5.8º @ 100 MeV~4.6º @ 100 MeV ~0.11º @ 1 GeV High precision tracking (silicon vs. spark chambers) Energy resolution 3 10%~10% Deadtime per event100 ms <100  s No detectors dead time (silicon vs. spark chambers) Source location determination 4 15’~0.4’PSF + Effective area Point source sensitivity 5 1x10 -7 cm -2 s -1 ~3x10 -9 cm -2 s -1 PSF + Effective area 1 After background rejection. 2 Single photon, 68% containment, on axis. 3 1 , on axis. 4 1  radius, high latitude source with 10 -7 cm -2 s -1 integral flux above 100 MeV. 5 1 year sky survey, high latitude, above 100 MeV.

18. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Technology impact on instrument performance II

19. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Technology impact on instrument performance I

20. IEEE NSS - Puerto Rico - October 25, 2005Luca Baldini Triggering and On-board Data Flow x x x 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: 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: 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.