We describe our monitoring strategy which best exploits the sensitivity and flexibility of Swift to study the long-term behaviour of Supergiant Fast X-ray Transients (SFXTs). We present observations of the recent outbursts from two objects of this class. IGR J16479-4514, underwent an outburst on 2008 March 19, reaching a peak luminosity of about 6×1037 erg s-1 (0.5-100 keV; at a distance of 4.9 kpc). We obtained a simultaneous broad-band spectrum (0.3-100 keV), the first for the SFXT class, which is fit with a heavily absorbed (column density 5×1022 cm-2) hard power-law with a high energy cut-off at about 7 keV. This spectrum shows properties similar to the ones of accreting pulsars, although no X-ray pulsations were found. IGR J11215-5952, one of the only two periodic SFXT known to date, was observed with Swift several times, first with an intense 23-day long monitoring campaign around the 2007 February 9 outburst; then with a 26-day long monitoring around the unexpected July 24 outburst; finally with a deep exposure during the 2008 June 16 outburst. We present the whole dataset, which also includes observations which allowed us to firmly establish the outburst period at P ∼ 165 days. Thanks to our combined observations common characteristics to this class of objects are emerging, i.e., outburst lengths well in excess of hours, often with a multiple peaked structure, dynamic range ∼ 3 orders of magnitude, and periodicities are starting to be found.
|Original language||English (US)|
|Journal||Proceedings of Science|
|State||Published - 2008|
|Event||7th INTEGRAL Workshop - An INTEGRAL View of Compact Objects, INTEGRAL 2008 - Copenhagen, Denmark|
Duration: Sep 8 2008 → Sep 11 2008
All Science Journal Classification (ASJC) codes