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N. R. Robba, T. Di Salvo (Dipartimento di Scienze Fisiche ed Astronomiche di Palermo), L. Burderi (Osservatorio Astronomico di Monteporzio - Roma), R. Iaria, A. La Barbera (Dipartimento di Scienze Fisiche ed Astronomiche di Palermo)
We present the results of a broad band (0.1-200 keV) spectral analysis of a BeppoSAX observation of the Z source GX349+2. The source was in the flaring branch of the color-color diagram during our observation. We produced energy spectra out and during the flares. The soft spectral continuum, both during and out of the flare, is well described by a blackbody and a Comptonization model . In addition, a hard power-law component, with photon index ~2, is needed to fit the spectrum out of the flare. This component does not significantly improve the fit during the flare.
Similar hard components have been detected in the spectra of other Z sources, such as GX 17+2 and GX 5-1, and in Cir X-1. In each case the power-law intensity seems to decrease with increasing mass accretion rate. A possible origin of these components is scattering of soft photons by the electrons of a hot corona or a jet emission.