Swift follow-up observations of 13 INTEGRAL sources

¹ Laboratoire AIM, CEA/IRFU - CNRS/INSU - Université Paris Diderot, CEA DSM/IRFU/SAp, Centre de Saclay, 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: 24 December 2009
Accepted: 13 March 2010

Abstract

The various IBIS/ISGRI catalogues contain a large population of hard X-ray sources whose nature is still unknown. Even if the >20 keV positional uncertainty provided by ISGRI is unprecedented, it is still too large to pinpoint the counterpart at other wavelengths, which is the only secure way of obtaining a source identification. We continue the work of trying to reveal the nature of these hard X-ray sources, starting with analysis of X-ray data collected via focusing X-ray telescopes, in order to obtain arcsec accurate X-ray positions. We can then identify counterparts at infrared and optical wavelengths and try to unveil the nature of the sources. We analysed data from observations of 13 INTEGRAL sources made with the Swift satellite. The X-ray images obtained by the X-Ray Telescope instrument allowed us to find possible counterparts to the IGR sources with a positional accuracy of a few arcsec. We then browsed the online catalogues (e.g., NED, SIMBAD, 2MASS, 2MASX, USNO B1.0) to search for counterparts at other wavelengths. We also made use of the X-ray spectral parameters in trying to identify the nature of those objects. For the 13 objects, we found possible counterparts at X-ray energies and identified the IR/optical and/or UV counterparts as seen with Swift/UVOT. We also discuss the likelihood of association of the X-ray and INTEGRAL source in each case. We confirm the previously proposed classification of IGR J02524–0829 (Sey 2 AGN), J08023–6954 (RS CVn star), and J11457–1827 (Sey 1 AGN). For 7 of these sources we give the first identification of their nature: IGR J02086–1742, J12060+3818, J12070+2535, J13042–1020, and J13412+3022 are AGN, and J14488–5942 is a probable X-ray binary. For J03184–0014, although we question the association of the IGR and Swift sources, we classify the latter as an AGN. We suggest that IGR J15283–4443 is a Galactic source, but we cannot classify the source further. Finally, we question the association of IGR J11457–1827 and J23130+8608 with the X-ray sources we found, and go on to question the genuineness of the former IGR source.