On the Angular Resolution of the AGILE Gamma-Ray Imaging Detector
Journal
Date Issued
2015
Author(s)
Sabatini, S.
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Donnarumma, I.
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Barbiellini, G.
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Cattaneo, P. W.
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Chen, A.
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Longo, F.
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Morselli, A.
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Description
We acknowledge several discussions with our colleagues of the Fermi Team. The AGILE mission is funded by the Italian Space Institute (ASI), with scientific and programmatic participation by the Italian Institute of Astrophysics (INAF) and the Italian Institute of Nuclear Physics (INFN). Our research is partially supported by ASI grants I/042/10/0, I/028/12/0, and I/028/12/02. We would like to thank the referee for the careful review and for providing valuable comments that helped to improve the contents of this paper.
Abstract
We present a study of the angular resolution of the AGILE gamma-ray imaging detector (GRID) that has been operational in space since 2007 April. The AGILE instrument is made of an array of 12 planes that are each equipped with a tungsten converter and silicon microstrip detectors, and is sensitive in the energy range 50 MeV-10 GeV. Among the space instruments devoted to gamma-ray astrophysics, AGILE uniquely exploit an analog readout system with dedicated electronics coupled with silicon detectors. We show the results of Monte Carlo simulations carried out to reproduce the gamma-ray detection by the GRID and we compare them to in-flight data. We use the Crab (pulsar + Nebula) system for discussion of real data performance, since its {E}-2 energy spectrum is representative of the majority of gamma-ray sources. For Crab-like spectrum sources, the GRID angular resolution (FWHM of ̃ 4^\circ at 100 MeV; ̃ 0\buildrel{\circ}\over{.} 8 at 1 GeV; ̃ 0\buildrel{\circ}\over{.} 9 integrating the full energy band from 100 MeV to tens of GeV) is stable across a large field of view, characterized by a flat response up to 30^\circ off-axis. A comparison of the angular resolution obtained by the two operational gamma-ray instruments, AGILE/GRID and Fermi/LAT (Large Area Telescope), is interesting in view of future gamma-ray missions, which are currently under study. The two instruments exploit different detector configurations that affect the angular resolution: the former is optimized in the readout and track reconstruction, especially in the low-energy band, the latter is optimized in terms of converter thickness and power consumption. We show that despite these differences, the angular resolution of both instruments is very similar, between 100 MeV and a few GeV.
Volume
809
Issue
1
Start page
60
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...809...60S
Rights
open.access
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