The first GRB survey of the IBIS/PICsIT archive^⋆

¹ INAF/IASF-Bologna, via Gobetti 101, 40129 Bologna, Italy
e-mail: bianchin@iasfbo.inaf.it
² INAF/IASF-Milano, via Bassini 15, 20133 Milano, Italy
³ Dipartimento di Fisica, Università di Ferrara, via Saragat 1, 44100 Ferrara, Italy
⁴ INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
⁵ W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, CA 94305 Stanford, USA

Received: 19 May 2011
Accepted: 18 September 2011

Abstract

Context. The multi-purpose INTEGRAL mission is continuously contributing to Gamma Ray Burst (GRB) science, thanks to the performances of its two main instruments, IBIS and SPI, operating in the hard X-ray / soft γ-ray domain.

Aims. We investigate the possibilities offered to the study of GRBs by PICsIT, the high-energy detector of the IBIS instrument.

Methods. We searched for transient episodes in the PICsIT light curves archive from May 2006 to August 2009, using stringent criteria optimized for the detection of long events. In the time interval under examination PICsIT provides an energy coverage from 208 to 2600 keV, resolved in eight energy channels, combined with a fine time resolution of 16 ms.

Results. PICsIT successfully observes GRBs in the 260–2600 keV energy range with an incoming direction spread over half the sky for the brightest events. We compiled a list of 39 bursts, most of which are confirmed GRBs or simultaneous to triggers from other satellites/instruments. We produced light curves with a time sampling down to 0.25 s in three energy intervals for all events. Because an adequate response matrix is not yet available for the PICsIT burst sample, we obtained a calibration coefficient in three selected energy bands by comparing instrumental counts with physical fluences inferred from observations with different satellites. The good time resolution provided by the PICsIT data allows a spectral variability study of our sample through the hardness ratio.