Observation of GRBs with AGILE

arXiv:0906.1446v1 [astro-ph.HE] 8 Jun 2009 PROCEEDINGS OF THE 31st ICRC, Ł ´OD´Z 2009 1 Observation of GRBs with AGILE M. Marisaldi∗, G. Barbiellini†‡, E. Costa§, S. Cutini¶, E. Del Monte§, I. Donnarumma§ Y. Evangelista§, M. Feroci§, F. Fuschino∗, M. Galli∥, A. Giuliani∗∗, C. Labanti∗, I. Lapshov§†† F. Lazzarotto§, P. Lipari‡‡x, F. Longo†, S. Mereghetti∗∗, E. Moretti†, L. Pacciani§, M. Rapisarda xi P. Soffitta§, M. Tavani§xii, M. Trifoglio∗, S. Vercellone xiii (on behalf of the AGILE Team) ∗INAF-IASF Bologna, Via Gobetti 101, I-40129 Bologna, Italy † Dipartimento di Fisica Universit`a di Trieste, via A. Valerio 2, I-34127 Trieste, Italy ‡ INFN Trieste, via A. Valerio 2, I-34127 Trieste, Italy § INAF-IASF Roma, via del Fosso del Cavaliere 100, I-00133 Roma, Italy ¶ ASI Science Data Center, Via E. Fermi 45, I-00044 Frascati (Roma), Italy ∥ENEA, via Martiri di Monte Sole 4, I-40129 Bologna, Italy ∗∗INAF-IASF Milano, via E. Bassini 15, I-20133 Milano, Italy †† IKI, Moscow, Russia ‡‡ INFN Roma “La Sapienza”, p.le Aldo Moro 2, I-00185 Roma, Italy x Dipartimento di Fisica, Universit`a La Sapienza, p.le Aldo Moro 2, I-00185 Roma, Italy xi ENEA Frascati, via Enrico Fermi 45, I-00044 Frascati(Roma), Italy xii Dipartimento di Fisica, Universit`a Tor Vergata, via della Ricerca Scientifica 1, I-00133 Roma, Italy xiii INAF-IASF Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy Abstract. Since its early phases of operation, the AGILE satellite is observing Gamma Ray Bursts (GRBs) over an energy range potentially spanning six orders of magnitude. In the hard X-ray band the SuperAGILE imager provides localization of about one GRB/month plus the detection of 1–2 GRBs per month out of its field of view. The Mini- Calorimeter detects about one GRB/week in the 350 keV–100 MeV energy range, plus several other transients at very short time scales. In fact, the on- board MCAL trigger logic, implemented for the first time on time windows as short as 300 microseconds, is particularly suitable for very short bursts detection. The Gamma-Ray Imaging Detector (GRID), sensi- tive in the 30 MeV–30 GeV range, firmly detected three GRBs (GRB 080514B, GRB 090401B and GRB 090510) plus some other candidates at a lower significance level. Moreover, all GRBs localized by other spacecrafts inside the GRID field of view are currently searched for possible detection, and upper limits are provided. In this paper we review the status of the observation of GRBs with AGILE, with particular emphasis on high energy and short time scales detections. Keywords: gamma-ray astronomy, gamma-ray bursts I. INTRODUCTION The AGILE satellite [1], an Italian space mission dedicated to high energy astrophysics launched on 23 April 2007, has the study of GRBs among its main scientific targets. The GRID (Gamma-ray Imaging De- tector) instrument is the core of the AGILE mission; it is a pair conversion telescope composed of a tungsten- silicon tracker [2] and a CsI(Tl) Mini-Calorimeter, op- erating in the 30 MeV – 30 GeV energy band, with a good sensitivity and angular resolution. Its large field of view (60◦x60◦) makes it a valuable instrument for GRB detection in the poorly explored gamma-ray energy band. SuperAGILE [3] is the hard X-ray monitor of AGILE and is a twice 1-D coded aperture instrument working in the 20 – 60 keV energy band, with a field of view of about 1 sr, an angular resolution of 3 arcmin and a dead time of 5µs. The Mini-Calorimeter (MCAL) [4] is composed of 30 CsI(Tl) scintillator bars (dimensions: 15x23x375 mm3 each) arranged in two orthogonal layers, for a total thickness of 1.5 radiation lengths. In a bar the readout of the scintillation light is accomplished by two custom PIN Photodiodes (PD) coupled one at each short side of the bar. In addition to being a subsystem of the GRID, MCAL is also equipped with a self-triggering operative mode and on-board logic making it an all-sky monitor in the 350 keV – 100 MeV energy range. The payload is surrounded and completed by a plastic anti-coincidence shield [5] for background charged particle rejection. GRBs and other X-ray transients are a primary scien- tific goal of AGILE. For this reason the Payload Data Handling Unit contains specific algorithms to trigger GRBs both in MCAL and in the SuperAGILE rateme- ters. A simultaneous GRB detection with GRID, MCAL and SuperAGILE would allow spectral coverage over six orders of magnitude. 2 M. MARISALDI et al. GRBS WITH AGILE II. GRB DETECTION WITH AGILE Table I summarizes the main AGILE GRB detection results. Since the launch, more than 120 GRBs have been detected by either of the AGILE subsystems in different energy bands, the most remarkable being those detected by the GRID above several tens of MeV. TABLE I SUMMARY OF AGILE GRB DETECTIONS UPDATED TO 10 MAY 2009. AGILE detection Number of events SuperAGILE localizations 21 MCAL detections 103 MCAL det. localized by SuperAGILE 2 MCAL det. localized by Swift 21 MCAL det. localized by Fermi-GBM 15 MCAL det. localized

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