Swift follow-up observations of INTEGRAL sources of unknown nature

¹ Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, DAPNIA/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

Received: 6 December 2007
Accepted: 16 February 2008

Abstract

Context. Since its launch in 2002, INTEGRAL has discovered many new hard X-ray sources. A lot of them still lack sufficient positional accuracy, for finding counterparts at other wavelengths. Their true nature is, therefore, still unknown.

Aims. The goal of this study is to give an accurate X-ray position for 12 of these sources so as to further identify their counterpart at optical, infrared, and radio wavelengths, and to unveil their true nature. We also make use of the X-ray spectral parameters to tentatively distinguish between the various possible types.

Methods. We made use of X-ray observations with the X-ray telescope on-board the Swift observatory to refine the X-ray position to 3–5´´ accuracy, and performed 0.1–10 keV spectral analysis. We then searched the online catalogues (e.g. NED, SIMBAD, 2MASS, 2MASX, and NVSS) to search for counterparts at other wavelengths.

Results. For all sources, we give a refined X-ray position, provide X-ray spectral parameters, identify infrared counterparts, and give magnitudes at optical and ultra violet wavelengths seen with UVOT when observations are available. We confirm the nature of six sources formerly suspected to be AGN (IGR J02343+3229, J13149+4422, J14579-4308, J16385-2057, J18559+1535, J19378-0617). Our analysis first leads us to suggest that IGR J09523-6231 and IGR J10147-6354 are AGN. While the former has recently been confirmed as a Seyfert 1.5 AGN, we suggest the latter is a Seyfert 2. All other sources may be Galactic sources, in which case their spectral shape may suggest that they are X-ray binaries. In one case (IGR J19308+0530), the Galactic nature is confirmed through the identification of an F8 star as the counterpart. We favour a distance to the source not greater than 1 kpc. The source is likely to be a neutron star XRB or a CV. We also report the discovery of six serendipitous sources of unknown nature.