Astronomy and Astrophysics, volume 489, 327-348 (2008/10-1)
XMM-Newton observations of the Small Magellanic Cloud: Be/X-ray binary pulsars active between October 2006 and June 2007.
HABERL F., EGER P. and PIETSCH W.
Abstract (from CDS):
We analysed eight XMM-Newton observations toward the Small Magellanic Cloud (SMC), performed between October 2006 and June 2007, to investigate high mass X-ray binary systems. We produced images from the European Photon Imaging Cameras (EPIC) and extracted X-ray spectra and light curves in different energy bands from sources that yielded a sufficiently high number of counts for a detailed temporal and spectral analysis. To search for periodicity we applied Fourier transformations and folding techniques and determined pulse periods using a Bayesian approach. To identify optical counterparts we produced X-ray source lists for each observation using maximum likelihood source detection techniques and correlated them with optical catalogues. The correlations were also used for astrometric boresight corrections of the X-ray source positions. We found new X-ray binary pulsars with periods of 202s (XMMUJ005929.0-723703), 342s (XMMUJ005403.8-722632), 645s (XMMUJ005535.2-722906) and 325s (XMMUJ005252.1-721715), in the latter case confirming the independent discovery in Chandra data. In addition we detected sixteen known Be/X-ray binary pulsars and six ROSAT-classified candidate high mass X-ray binaries. From one of the candidates, RXJ0058.2-7231, we discovered X-ray pulsations with a period of 291s which makes it the likely counterpart of XTEJ0051-727. From the known pulsars, we revise the pulse period of CXOUJ010206.6-714115 to 967s, and we detected the 18.37s pulsar XTEJ0055-727 (=XMMJ004911.4-724939) in outburst, which allowed us to localise the source. The pulse profiles of the X-ray pulsars show a wide variety of shapes from smooth to highly structured patterns and differing energy dependence. For all the candidate high mass X-ray binaries, optical counterparts can be identified with magnitudes and colours consistent with Be stars. Twenty of the Be/X-ray binaries were detected with X-ray luminosities in the range 1.5x1035-5.5x1036erg/s. The majority of the spectra is well represented by an absorbed power-law with an average power-law index of 0.93. The absorption (in addition to the Galactic foreground value) varies over a wide range between a few 1020cm–2 and several 1022cm–2. An overall correlation of the absorption with the total SMC HI column density suggests that the absorption seen in the X-ray spectra is often largely caused by interstellar gas.