The broad band X–ray spectrum of the black hole candidate GRS 1758–258

Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Milano “G. Occhialini" – CNR via Bassini 15, 20133 Milano, Italy

Corresponding author: L. Sidoli, sidoli@ifctr.mi.cnr.it

Received: 11 February 2002
Accepted: 8 April 2002

Abstract

We present the results of a BeppoSAX observation of the black hole candidate GRS 1758–258 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  keV and optical depth (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  eV has been marginally detected. The 0.1–200 keV luminosity is  erg s^-1 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.