A Hard Tail in the Broadband Spectrum of the Dipper XB 1254−690

We report on the results of spectral analysis of the dipping source XB1254-690 observed by the BeppoSAX satellite. We find that the X-ray dips arenot present during the BeppoSAX observation, in line with recent RXTE results.The broad band (0.1-100 keV) energy spectrum is well fitted by athree-component model consisting of a multicolor disk blackbody with an innerdisk temperature of ~0.85 keV, a comptonized spectrum with an electrontemperature of ~2 keV, and a bremsstrahlung at a temperature of ~20 keV.Adopting a distance of 10 kpc and taking into account a spectral hardeningfactor of ~1.7 (because of electron scattering which modifies the blackbodyspectrum emitted by the disk) we estimated that the inner disk radius is$R_{\rm in} \sqrt{\cos i} \sim 11$ km, where i is the inclination angle of thesystem with respect to the line of sight. The comptonized component couldoriginate in a spherical corona or boundary layer, surrounding the neutronstar, with optical depth ~19. The bremsstrahlung emission, contributing ~4% ofthe total luminosity, probably originates in an extended accretion disk coronawith radius $\sim 10^{10}$ cm. In this scenario we calculated that the opticaldepth of this region is ~0.71 and its mean electron density is $N_e \sim 2.7\times 10^{14}$ cm$^{-3}$. This last component might also be present in otherlow mass X-ray binaries, but, because of its low intrinsic luminosity, it isnot easily observable. We also find an absorption edge at ~1.27 keV with anoptical depth of ~0.15. Its energy could correspond to the L-edge of Fe XVII,or K-edge of Ne X or neutral Mg.Comment: 13 pages, 3 figures, Accepted by Ap