INTEGRAL observations of recurrent fast X-ray transient sources

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 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 about 3 hours. 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.