Letter to the Editor

First simultaneous multi-wavelength observations of the black hole candidate IGR J17091−3624

ATCA, INTEGRAL, Swift, and RXTE views of the 2011 outburst^⋆

¹ Laboratoire AIM, CEA/IRFU, CNRS/INSU, Université Paris Diderot, CEA DSM/IRFU/SAp, 91191 Gif-sur-Yvette, France
e-mail: jrodriguez@cea.fr
² Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA
³ Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia
⁴ Istituto Nazionale di Astrofisica, INAF-IASF, via Bassini 15, 20133 Milano, Italy
⁵ ESAC, ISOC, Villañueva de la Cañada, Madrid, Spain

Received: 17 June 2011
Accepted: 31 July 2011

Abstract

We present the results of the first four (quasi-)simultaneous radio (ATCA), X-ray (Swift, RXTE), and γ-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_⊙, we estimate a distance to the source between  ~11 and  ~17 kpc, compatible with the radio behaviour of the source.