The X-ray spectrum of the black hole candidate GX339-4 in a low state

¹ IASF-CNR, Sezione di Milano “G. Occhialini”, via Bassini 15, 20133 Milano, Italy
² Dipartimento di Scienze Fisiche, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
³ INAF – Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, strada 54, 09012 Capoterra, Italy
⁴ Dipartimento di Scienze, Università dell'Insubria/Como, via Valleggio 11, 22100 Como, Italy
⁵ Dipartimento di Fisica, Università di Milano Bicocca, piazza delle Scienze 3, 20126 Milano, Italy
⁶ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy

Corresponding author: A. Corongiu, corongiu@ca.astro.it

Received: 22 April 2003
Accepted: 12 June 2003

Abstract

We report on four observations of the black hole candidate GX 339-4 collected in the spectral range 0.4-140 keV with the BeppoSAX satellite during 1997. All our spectra are typical of a black hole candidate in its low-hard state, i.e. are dominated by the hard tail of the emission from the corona. Although the direct emission from the accretion disk in the soft X-ray range is weak, spectra are well described only with models that take into consideration the Compton reflection of hard X-rays from the corona onto the surface of an accretion disk of non negligible extent.