XMM-Newton observations of the Small Magellanic Cloud: Be/X-ray binary pulsars active between October 2006 and June 2007*
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany e-mail: email@example.com
Accepted: 25 June 2008
Aims. 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.
Methods. 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.
Results. We found new X-ray binary pulsars with periods of 202 s (XMMU J005929.0-723703), 342 s (XMMU J005403.8-722632), 645 s (XMMU J005535.2-722906) and 325 s (XMMU J005252.1-721715), 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, RX J0058.2-7231, we discovered X-ray pulsations with a period of 291 s which makes it the likely counterpart of XTE J0051-727. From the known pulsars, we revise the pulse period of CXOU J010206.6-714115 to 967 s, and we detected the 18.37 s pulsar XTE J0055-727 (=XMM J004911.4-724939) 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 1.5 1035–5.5 1036 erg s-1. 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 1020 cm-2 and several 1022 cm-2. An overall correlation of the absorption with the total SMC H I column density suggests that the absorption seen in the X-ray spectra is often largely caused by interstellar gas.
Key words: galaxies: individual: Small Magellanic Cloud / galaxies: stellar content / stars: emission-line, Be / stars: neutron / X-rays: binaries
© ESO, 2008