XMM-Newton and INTEGRAL observations of new absorbed supergiant high-mass X-ray binaries

Abstract

Context. During the first year in operation, INTEGRAL, the European Space Agency's γ-ray observatory, has detected more than 28 new bright sources in the galactic plane which emit the bulk of their emission above 10 keV. Aims. To understand the nature of those sources we have obtained follow-up observations in the X-ray band with XMM-Newton. Methods. We derive accurate X-ray positions, propose infrared counterparts and study the source high energy long and short term variability and spectra. Results. 70% of the sources are strongly absorbed (NH ≥ 1023 atom cm-2). More than half of these absorbed sources show pulsations with periods ranging from 139 to 1300 s, i.e., they are slow X-ray pulsars. The candidate infrared counterparts are not as strongly absorbed demonstrating that part of the absorbing matter is local to the sources. Conclusions. Many of these new sources are supergiant high-mass X-ray binaries (HMXB) in which the stellar wind of the companion star is accreted onto the compact object. The large local absorption in these new sources can be understood if the compact objects are buried deep in their stellar winds. These new objects represent half of the population of supergiant HMXB. © ESO 2006.