2008A&A...484..451H

A bright X-ray transient was seen during an XMM-Newton observation in the direction of the Small Magellanic Cloud (SMC) in October 2006. The data from the European Photon Imaging Cameras (EPIC) allow us to accurately locate the source and to investigate its temporal and spectral behaviour. We extracted X-ray spectra covering 0.2-10keV and pulse profiles in different energy bands from the EPIC data. The detection of 6.85s pulsations in the EPIC-PN data unambiguously identifies the transient with XTEJ0103-728, discovered as 6.85s 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 10min. 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 ∼160km. The photon index of the powerlaw of ∼0.4 indicates a relatively hard spectrum. The 0.2-10keV luminosity was 2x10³⁷erg/s 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 ∼0.0017s per year since the discovery of XTEJ0103-728 in May 2003. The X-ray properties and the identification with a Be star confirm XTEJ0103-728 as Be/X-ray binary transient in the SMC.