Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources GX 3+1 and Ser X-1

We have obtained spectral and timing data on GX 3+1 and Ser X-1. Both sourc es were observed simultaneously with BeppoSAX and RXTE. The RXTE data is us ed to provide power spectra and colour-colour diagrams ill order to constra in the state (and thus track M) the sources are in. The BeppoSAX data provi de the broad-band spectra. The spectra of both sources are reasonably well- fit using a model consisting of a disk-blackbody, a comptonized component a nd a Fe line, absorbed by interstellar absorption. The electron temperature (kT(e)) of the Comptonizing plasma is in both cases similar to2.5 keV. Thi s implies that no strong high-energy tail from the Comptonized component is present in either of the sources. We discuss the similarities between thes e burst sources and the luminous X-ray sources located in globular clusters . We find that the spectral parameters of the comptonized component provide information about the mass-accretion rate, which agrees well with estimate s from the timing and spectral variations.