THE TWO INTEGRAL X-RAY TRANSIENTS IGR J17091–3624 AND IGR J17098–3628: A MULTIWAVELENGTH LONG-TERM CAMPAIGN

IGR J17091−3624 and IGR J17098−3628 are two X-ray transients discovered by INTEGRAL and classified as possible black hole candidates. We present here the results obtained from the analysis of multiwavelength data sets collected by different instruments from 2005 until the end of 2007 on both sources. IGR J17098−3628 has been regularly detected by INTEGRAL and RXTE over the entire period of the observational campaign; it was also observed with pointed observations by XMM-Newton and Swift /X-ray Telescope (XRT) in 2005 and 2006 and exhibited flux variations not linked with the change of any particular spectral features. IGR J17091 − 3624 was initially in quiescence (after a period of activity between 2003 April and 2004 April) and it was then detected again in outburst in the XRT field of view during a Swift observation of IGR J17098−3628 on 2007 July 9. The observations during quiescence provide an upper limit to the 0.2–10 keV luminosity, while the observations in outburst cover the transition from the hard to the soft state. Moreover, we obtain a refined X-ray position for IGR J17091−3624 from the Swift /XRT observations during the outburst in 2007. The new position is inconsistent with the previously proposed radio counterpart. We identify in VLA archive data a compact radio source consistent with the new X-ray position and propose it as the radio counterpart of the X-ray transient.