INTEGRAL observations of recurrent fast X-ray transient sources

¹ School of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ, UK e-mail: sguera@astro.soton.ac.uk
² INTEGRAL Science Data Center, 1290 Versoix, Switzerland
³ IASF/CNR, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁴ IASF/CNR, via Piero Gobetti 101, 40129 Bologna, Italy

Received: 21 March 2005
Accepted: 17 August 2005

Abstract

Fast X-ray Transients (FXTs) are believed to be non-recurrent bright X-ray sources lasting less than a day and occuring at serendipitous positions, they can best be detected and discovered by instruments having a sufficiently wide field of view and high sensitivity. The IBIS/ISGRI instrument onboard INTEGRAL is particularly suited to detect new or already known fast X-ray transient sources. We report on IBIS/ISGRI detection of newly discovered outbursts of three fast transient sources located at low Galactic latitude: SAX J1818.6-1703; IGR J16479-4514; IGR J17391-302/XTE J1739-302. The reported results confirm and strengthen the very fast transient nature of these sources, given that all their newly detected outbursts have a duration less than ~3 h. Additionally, they provide the first evidence for a possible recurrent fast transient behaviour as all three sources were detected in outburst by ISGRI more than once during the last 2 years.