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GLAST Italian meetingFrancesco Longo & Carlotta Pittori

Udine 11 marzo 2004V. Cocco, A.Giuliani, P.Lipari,

A. Pellizzoni, M.Prest, M.Tavani. E.Vallazza

AGILE on-board BKG AGILE on-board BKG rejectionrejection

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DETECTOR DESCRIPTIONDETECTOR DESCRIPTION

• Top AnticoincidenceTop Anticoincidence• Lateral AnticoincidencesLateral Anticoincidences• SuperAGILESuperAGILE • Silicon TrackerSilicon Tracker• Mini-CalorimeterMini-Calorimeter• Mechanical structure Mechanical structure (not shown in the figure)(not shown in the figure)

40 cm

5 cm

22 c

m15

cm

15 c

m

54 cm

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Expected particle/albedo-photon Expected particle/albedo-photon background for an Equatorial background for an Equatorial

OrbitOrbit

• Particle flux from SAS-2 and BeppoSAX data (~0.3 cm-2 s-1 for Ekin 1 MeV )

• 3 main components: e+, e-, p • Spectral data from AMS and Marya• Assumptions: 1) isotropic distribution for e+, e-, and low

energy protons 2) sky-incidence for high energy p (Ekin

7 GeV )

Albedo photons from the Earth (from SAS-2 data)

[Thompson et al. 1981]

Longo, Cocco & Tavani (2002)

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Albedo PhotonsAlbedo Photons

[Thompson et al. 1981]

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Event GenerationEvent Generation

• Particle/Albedo-photon Background

• Astrophysical point sources

Particle/photon tracks originating on a spherical surface

Montecarlo methods for the generation of the distribution functions

AGILE Payload

AGILE SatelliteLongo, Cocco & Tavani (2002)

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Trigger LevelsTrigger Levels

Level-1

Level-2

Hardware Implementation Information from Silicon Tracker and AC

panels Track topology at the ‘chip’ level

Software Implementation Analog Information on the released charge

in the Si-microstrips Track topology at the ‘cluster’ level 3D-reconstruction to reject albedo photons

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L1 - TRIGGERL1 - TRIGGER

R trigger concept

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L1- TRIGGERL1- TRIGGER

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Charge deposition Charge deposition

Optimal spatial resolution: ~40 mfor a broad range of incidence angles (0-50)

50 MeV gamma-ray, ~50

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Monte Carlo Simulations:

Simulated Gamma-Ray Simulated Gamma-Ray (E=100 MeV, (E=100 MeV, =30º)=30º)

Simulated background Simulated background proton event:proton event:

It can be rejected by the on-board trigger because of the crucial use of the analog signal from the Si-microstrips providing information on cluster charges.

direction from 3-D AGILE REconstruction Method (AREM) integrated with Kalman filter algorithms (Pittori-Tavani NIM 2002)

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On-board GRID Background Rejection:

Particle background rates :- e+/e-: reduced by a factor ~ 100

- Protons: reduced by a factor ~ 1000

- Earth albedo -ray flux : reduced by a factor ~ 30

The GRID on-board background rejection is quite efficient, reducing the total charged-particle rate from ~ 2000 Hz to ~ 20 Hz.

Cocco, Longo & Tavani (2002)

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• Expected total rate of particle/albedo-photon entering into the Tracker volume 2-3 KHz

• Level-1Trigger cut 100 Hz

• Level-2 processing cut 20-30 Hz

On-board Background Rejection : ~10-2

SUMMARY OF ON-BOARD SUMMARY OF ON-BOARD BACKGROUND REJECTIONBACKGROUND REJECTION

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Effective AreaEffective Area

Science with AGILE (2003)