The broad band X-ray spectrum of the black hole candidate GRS1758-258

Abstract

We present the results of a BeppoSAX observation of the black hole candidate GRS1758-258 carried out in 1997, while the source was in its low/hard state. The X-ray spectrum, simultaneously observed over the broad energy range from 0.1 to 200 keV, can be well described by a Comptonized emission model with electron temperature kT_e = 31.4 keV and optical depth of 4.0 (spherical geometry), although a cut-off power-law and a reflection model cannot be excluded. Additionally, a broad iron line at 6.4 keV with equivalent width EW = 67 eV has been marginally detected. The 0.1-200 keV luminosity is 1.4x10^37 erg/s for an assumed distance of 8 kpc. The soft and hard luminosities are such that the source falls inside the so-called "burster box". No evidence for a soft excess is present.