Detection of a Hard Tail in the X‐Ray Spectrum of the Z Source GX 349+2

We present the results of a BeppoSAX observation of the Z source GX 349+2covering the energy range 0.1-200 keV. The presence of flares in the lightcurve indicates that the source was in the flaring branch during the BeppoSAXobservation. We accumulated energy spectra separately for the non-flaringintervals and the flares. In both cases the continuum is well described by asoft blackbody ($k T_{BB} \sim 0.5$ keV) and a Comptonized spectrumcorresponding to an electron temperature of $k T_e \sim 2.7$ keV, optical depth$\tau \sim 10$ (for a spherical geometry), and seed photon temperature of $kT_W \sim 1$ keV. All temperatures tend to increase during the flares. In thenon-flaring emission a hard tail dominates the spectrum above 30 keV. This canbe fit by a power law with photon index $\sim 2$, contributing $\sim 2%$ of thetotal source luminosity over the BeppoSAX energy range. A comparison with hardtails detected in some soft states of black hole binaries suggests that asimilar mechanism could originate these components in black hole and neutronstar systems.Comment: 15 pages, including 8 figures, to appear in Ap