XMM-Newton and INTEGRAL observations of the black hole candidate XTE J1817-330

Abstract

Aims:The galactic black hole candidate XTE J1817-330 was discovered in outburst by RXTE in January 2006. We present here the results of an XMM-Newton target of opportunity observation, performed on 13 March 2006 (44 days after the maximum), and an INTEGRAL observation performed on 15-18 February 2006 (18 days after the maximum).
Methods: The EPIC-pn camera on-board XMM-Newton was used in the fast read-out burst mode to avoid photon pile-up, while the RGS was used in spectroscopy high count rate mode. We fit both the XMM-Newton and the INTEGRAL spectra with a two-component model consisting of a thermal accretion disk (represented by diskbb or diskpn models) and a comptonizing hot corona (represented by a power-law or the compTT model).
Results: The soft X-ray spectrum is dominated by an accretion disk component, with a maximum temperature decreasing from 0.96±0.04 keV at the time of the INTEGRAL observation to 0.70±0.01 keV on 13 March. The optical monitors on board INTEGRAL and XMM-Newton showed the source with magnitudes V:11.3-11.4, U:15.0-15.1 and UVW1:14.7-14.8. The soft X-ray spectrum, together with the optical and UV data, show a low hydrogen column density towards the source, and several absorption lines, most likely of interstellar origin, are detected in the RGS spectrum: OIKα, OIKβ, OII, OIII and OVII, which trace both cold and hot components of the interstellar medium. The soft X-ray spectrum indicates the presence of a black hole, with an estimate for the upper limit of the mass of 6.0^+4.0_-2.5 M_⊙.

Based on observations obtained with XMM-Newton, an ESA science mission with

instruments and contributions directly funded by ESA Member States and NASA; and with INTEGRAL,

an ESA project with instruments and science data center funded by ESA member states

(especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain),

Czech Republic and Poland, and with the participation of Russia and the USA.