Disappearance of Hard X‐Ray Emission in the Last B eppo SAX Observation of the Z Source GX 349+2

Abstract

We report on the results from two BeppoSAX observations of the Z source GX 349+2 performed in 2001 February and covering the broad energy range 0.12-200 keV. The light curve obtained from these observations shows a large flaring activity, the count rate varying from ∼130 to ∼260 counts s -1, indicating that the source was in the flaring branch during these observations. The average spectrum is well described by a soft blackbody (kTBB ∼ 0.5 keV) and a Comptonized component having a seed photon temperature of kT0 ∼ 1 keV, an electron temperature of kTe ∼ 2.7 keV, and optical depth of τ ∼ 11. To well fit the energy spectrum, three Gaussian lines are needed at 1.2, 2.6, and 6.7 keV with corresponding equivalent widths of 13, 10, and 39 eV, probably associated to L-shell emission of Fe xxiv, Lyα S xvi, and Fe xxv, respectively. These lines may be produced at different distances from the neutron star, which increase when the count rate of the source increases. An absorption edge is also needed at 9 keV with an optical depth of ∼3 7times; 10-2. From the color-color diagram (CD), we selected five zones from which we extracted the corresponding energy spectra. The temperatures of the blackbody and of the Comptonized component tend to increase when the intensity of the source increases. We discuss our results comparing them to those obtained from a previous BeppoSAX observation, performed in 2000 March, during which the source was in a similar position on its Z-track. In particular, we find that, although the source showed similar spectral states in the 2000 and the 2001 observations, a hard tail that was significantly detected in 2000 March is not observed in these recent observations.