XMM-Newton and INTEGRAL observations of the very faint X-ray transient IGRJ17285-2922/XTEJ1728-295 during the 2010 outburst

Abstract

We report the first broad-band (0.5-150keV) simultaneous X-ray observations of the very faint X-ray transient IGRJ17285-2922/XTEJ1728-295 performed with the XMM-Newton and INTEGRAL satellites during its last outburst, started on 2010 August 28. XMM-Newton observed the source on 2010 September 9-10 for 22 ks. INTEGRAL observations were part of the publicly available Galactic bulge program, and overlapped with the times covered by XMM-Newton. The broad-band spectroscopy resulted in a best fit with an absorbed power law displaying a photon index Γ of 1.61 ± 0.01, an absorbing column density NH of (5.10 ± 0.05) × 1021cm-2 and a flux of 2.4 × 10-10erg cm-2s-1 (1-100keV), corrected for the absorption. The data did not require either a spectral cut-off (Ec > 50keV) or an additional soft component. The slopes of the power law fitting the XMM-Newton and INTEGRAL separate spectra were compatible, within the uncertainties. The timing analysis does not show evidence either for X-ray pulsations or for type I X-ray bursts. The broad-band X-ray spectrum as well as the power-density spectrum is indicative of a low-hard state in a low-mass X-ray binary, although nothing conclusive can be said about the nature of the compact object (neutron star or black hole). The results we report here allow us to conclude that IGRJ17285-2922 is a low-mass X-ray binary, located at a distance greater than 4kpc. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.