Highly absorbed X-ray binaries in the Small Magellanic Cloud

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, which hampers their detection at the softest X-ray energies. We have undertaken a search for highly-absorbed X-ray sources in the Small Magellanic Cloud (SMC) with a systematic analysis of 62 XMM-Newton SMC observations. We obtained a sample of 30 sources showing evidence for an equivalent hydrogen column density larger than 3x10^23 cm^-2. Five of these sources are clearly identified as HMXRBs: four were already known (including three X-ray pulsars) and one, XMM J005605.8-720012, 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 of them 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.

10 pages, 4 figures, 4 tables. Accepted for publication by Astronomy & Astrophysics

References in corpus (10)

• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• Star formation history and X-ray binary populations: the case of the Small Magellanic Cloud
• A Long Look at the Be/X-Ray Binaries of the Small Magellanic Cloud
• Spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud
• Very Long-term Optical Variability of High Mass X-ray Binaries in the SMC
• XMM-Newton observations of the Small Magellanic Cloud: Be/X-ray binary pulsars active between October 2006 and June 2007
• The Chandra Small Magellanic Cloud Wing Survey - the search for X-ray Binaries
• High Mass X-ray Binaries and Recent Star Formation History of the Small Magellanic Cloud
• XMM-Newton observations of the Small Magellanic Cloud: XMMU J004814.1-731003, a 25.55 s Be/X-ray binary pulsar
• New Galactic High Mass X-ray Binaries discovered with INTEGRAL

Cited by in corpus (7)

• High-Mass X-ray binaries in the Small Magellanic Cloud
• The XMM-Newton survey of the Small Magellanic Cloud: The X-ray point-source catalogue
• The XMM-Newton survey of the Small Magellanic Cloud
• Optical spectra of 5 new Be/X-ray Binaries in the Small Magellanic Cloud and the link of the supergiant B[e] star LHA 115-S 18 with an X-ray source
• eROSITA calibration and performance verification phase: High-mass X-ray binaries in the Magellanic Clouds
• Confirmation of six Be X-ray binaries in the Small Magellanic Cloud
• Suzaku Observations of Spectral Variations of the Ultra Luminous X-ray Source Holmberg IX X-1