First simultaneous multi-wavelength observations of the black hole candidate IGR J17091-3624: ATCA, INTEGRAL, Swift, and RXTE views of the 2011 outburst

Abstract: We present the results of the first four (quasi-)simultaneous radio (ATCA), X-ray (Swift, RXTE), and Gamma-ray (INTEGRAL) observations of the black hole candidate IGR J17091-3624, performed in February and March 2011. The X-ray analysis shows that the source was in the hard state, and then it transited to a soft intermediate state. We study the correlated radio/X-ray behaviour of this source for the first time. The radio counterpart to IGR J17091-3624 was detected during all four observations with the ATCA. In the hard state, the radio spectrum is typical of optically thick synchrotron emission from a self-absorbed compact jet. In the soft intermediate state, the detection of optically thin synchrotron emission is probably due to a discrete ejection event associated with the state transition. The position of IGR J17091-3624 in the radio versus X-ray luminosity diagram (aka fundamental plane) is compatible with that of the other black hole sources for distances greater than 11 kpc. IGR J17091-3624 also appears as a new member of the few sources that show a strong quenching of radio emission after the state transition. Using the estimated luminosity at the spectral transition from the hard state, and for a typical mass of 10 M_sun, we estimate a distance to the source between ~11 and ~17 kpc, compatible with the radio behaviour of the source.