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

Abstract

We present the results of a BeppoSAX observation of the Z source GX 349+2 covering the energy range 0.1-200 keV. The presence of flares in the light curve indicates that the source was in the flaring branch during the BeppoSAX observation. We accumulated energy spectra separately for the nonflaring intervals and for the flares. In both cases, the continuum is well described by a soft blackbody (kTBB ∼ 0.5 keV) and a Comptonized spectrum corresponding to electron temperature kTe ∼ 2.7 keV, optical depth τ ∼ 10 (for a spherical geometry), and seed-photon temperature kTw ∼ 1 keV. All temperatures tend to increase during the flares. In the nonflaring emission, a hard tail dominates the spectrum above 30 keV. This can be fit by a power law with photon index ∼2, contributing ∼2% of the total source luminosity over the BeppoSAX energy range. A comparison with hard tails that are detected in some soft states of black hole binaries suggests that a similar mechanism could originate these components in black hole and neutron star systems.