XMM-Newton observations of the Small Magellanic Cloud: X-ray outburst of the 6.85 s pulsar XTE J0103-728*
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany e-mail: [fwh;wnp]@mpe.mpg.de
Accepted: 11 March 2008
Context. A bright X-ray transient was seen during an XMM-Newton observation in the direction of the Small Magellanic Cloud (SMC) in October 2006.
Aims. The data from the European Photon Imaging Cameras (EPIC) allow us to accurately locate the source and to investigate its temporal and spectral behaviour.
Methods. We extracted X-ray spectra covering 0.2-10 keV and pulse profiles in different energy bands from the EPIC data.
Results. The detection of 6.85 s pulsations in the EPIC-PN data unambiguously identifies the transient with XTE J0103-728, discovered as 6.85 s pulsar by the Rossi X-ray Timing Explorer. The X-ray light curve during the XMM-Newton observation shows flaring activity of the source with intensity changes by a factor of two within 10 min. Modelling of pulse-phase averaged spectra with a simple absorbed powerlaw indicates systematic residuals, which can be accounted for by a second emission component. From a model implying blackbody emission due to reprocessing by optically-thick material in the inner accretion disk, we estimate the inner disk radius to ~160 km. The photon index of the powerlaw of ~0.4 indicates a relatively hard spectrum. The 0.2-10 keV luminosity was 2 erg s-1 with a contribution of ~3% from the disk-blackbody component. A likely origin for the excess emission is reprocessing of hard X-rays from the neutron star by optically-thick material near the inner edge of an accretion disk. From a timing analysis we determine the pulse period to 6.85401(1) s, indicating an average spin-down of ~0.0017 s per year since the discovery of XTE J0103-728 in May 2003.
Conclusions. The X-ray properties and the identification with a Be star confirm XTE J0103-728 as Be/X-ray binary transient in the SMC.
Key words: Galaxy: stellar content / stars: emission-line, Be / stars: neutron / X-rays: binaries / galaxies: Magellanic Clouds
© ESO, 2008