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EDP Sciences, Astronomy & Astrophysics, (532), p. A153, 2011

DOI: 10.1051/0004-6361/201116997

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Highly absorbed X-ray binaries in the Small Magellanic Cloud

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Data provided by SHERPA/RoMEO

Abstract

Many of the high mass X-ray binaries (HMXRBs) discovered in recent years in our Galaxy are characterized by a high absorption, most likely intrinsic to the system, that can impede their detection at the softest X-ray energies. Exploiting the good coverage obtained with sensitive XMM-Newton observations, we have undertaken a search for highly absorbed X-ray sources in the Small Magellanic Cloud (SMC), which is known to contain a large number of HMXRBs. After a systematic analysis of 62 XMM-Newton SMC observations, we obtained a sample of 30 sources with evidence of an equivalent hydrogen column density larger than 3 × 10 23 cm -2. Five of these sources are clearly identified as HMXRBs, four being previously known (including three X-ray pulsars) and one, XMMU J005605.8-720012, being reported here for the first time. For the latter, we present optical spectroscopy confirming the association with a Be star in the SMC. The other sources in our sample have optical counterparts fainter than magnitude ∼16 in the V band, and many have possible NIR counterparts consistent with highly reddened early-type stars in the SMC. While their number is broadly consistent with the expected population of background highly absorbed active galactic nuclei, a few of them could be HMXRBs in which an early-type companion is severely reddened by local material. © 2011 ESO.