The nature of the X-ray binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift observations

¹ Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot (UMR 7158), CEA Saclay, DSM/IRFU/SAp, 91191 Gif-sur-Yvette, France e-mail: jrodriguez@cea.fr
² Space Science Laboratory, 7 Gauss Way, University of California, Berkeley, C1 94720-7450, USA
³ INAF-IASF, Sezione di Milano, via Bassini 15, 20133 Milano, Italy

Received: 22 June 2009
Accepted: 9 October 2009

Abstract

We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+1816. The Swift/XRT data allow us to refine the position of the source to = = +18° 18′38.4″ (±3.5″), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Γ ~ 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic absorption in this source. We detected a strong (%) pulsation at 12.43781 (±0.00003) s that we interpret as the spin period of a pulsar. All these results, coupled with the possible 117 day orbital period, point to IGR J19294+1816 being an HMXB with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI 18-40 keV light curve shows that the source spends most of its time in an undetectable state, we detect occurrences of short (~ s) and intense flares that are more typical of supergiant fast X-ray transients. We therefore cannot make firm conclusions on the type of system, and we discuss the possible implications of IGR J19294+1816 being an SFXT.