INTEGRAL observations of the peculiar BeX System SAX J2103.5+4545

Abstract

We present an INTEGRAL data analysis of the X-ray transient SAX J2103.5+4545 during two outbursts detected in December 2002. The INTEGRAL coordinates and error circle agree with the position of the recently proposed optical counterpart. A power-law plus cut-off model provided a good fit to the 4-150 keV spectrum yielding a photon index of 1.0±0.1, a cut-off energy E_cut=7.6±2.0 keV and a folding energy E_fold=30.9±2.5 keV. The X-ray luminosity in the 4-150 keV energy range was found to be 6.0× 10³⁶ erg s^-1, assuming a distance of 6.5 kpc. This luminosity, together with the derived photon index, indicate that the source is in a bright state. A 354.9±0.5 second pulse period is measured. This value is significantly smaller than previous measurements, indicating a long-term spin-up episode.