Research Note

Gamma-ray burst detection with the AGILE mini-calorimeter

¹ INAF – IASF Bologna, via Gobetti 101, 40129 Bologna, Italy e-mail: marisaldi@iasfbo.inaf.it
² ENEA, via Martiri di Monte Sole 4, 40129 Bologna, Italy
³ INAF – IASF Roma, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁴ Dipartimento di Fisica Università di Trieste, via A. Valerio 2, 34127 Trieste, Italy
⁵ INFN Trieste, via A. Valerio 2, 34127 Trieste, Italy
⁶ INFN Pavia, via Bassi 6, 27100 Pavia, Italy
⁷ Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, via Bassi 6, 27100 Pavia, Italy
⁸ INAF – IASF Milano, via E. Bassini 15, 20133 Milano, Italy
⁹ CIFS Torino, via le Settimio Severo 63, 10133 Torino, Italy
¹⁰ Dipartimento di Fisica, Università Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹¹ Dipartimento di Fisica, Università di Torino, Torino, Italy
¹² Dipartimento di Fisica, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy
¹³ INFN Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁴ IKI, Moscow, Russia
¹⁵ INFN Roma “La Sapienza”, p.le Aldo Moro 2, 00185 Roma, Italy
¹⁶ Dipartimento di Fisica, Università La Sapienza, p.le Aldo Moro 2, 00185 Roma, Italy
¹⁷ CNR-IMIP, Area della Ricerca di Montelibretti, Roma, Italy
¹⁸ INFN Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁹ ENEA Frascati, via Enrico Fermi 45, 00044 Frascati, Roma, Italy
²⁰ ASI Science Data Center, via E. Fermi 45, 00044 Frascati, Roma, Italy
²¹ Agenzia Spaziale Italiana, viale Liegi 26, 00198 Roma, Italy

Received: 10 July 2008
Accepted: 13 August 2008

Abstract

Context. The mini-calorimeter (MCAL) instrument on-board the AGILE satellite is a non-imaging gamma-ray scintillation detector sensitive in the 300 keV–100 MeV energy range with a total on-axis geometrical area of 1400 cm². Gamma-ray bursts (GRBs) are one of the main scientific targets of the AGILE mission and the MCAL design as an independent self-triggering detector makes it a valuable all-sky monitor for GRBs. Furthermore MCAL is one of the very few operative instruments with microsecond timing capabilities in the MeV range.

Aims. In this paper the results of GRB detections with MCAL after one year of operation in space are presented and discussed.

Methods. A flexible trigger logic implemented in the AGILE payload data-handling unit allows the on-board detection of GRBs. For triggered events, energy and timing information are sent to telemetry on a photon-by-photon basis, so that energy and time binning are limited by counting statistics only. When the trigger logic is not active, GRBs can be detected offline in ratemeter data, although with worse energy and time resolution.

Results. Between the end of June 2007 and June 2008 MCAL detected 51 GRBs, with a detection rate of about 1 GRB/week, plus several other events at a few milliseconds timescales. Since February 2008 the on-board trigger logic has been fully active. Comparison of MCAL detected events and data provided by other space instruments confirms the sensitivity and effective area estimations. MCAL also joined the 3rd Inter-Planetary Network, to contribute to GRB localization by means of triangulation.