The 1998 outburst of the X–ray transient XTE J2012+381 as observed with BeppoSAX

¹ Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (Lecco), Italy
² Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
³ Istituto di Fisica Cosmica e Applicazioni all'Informatica, C.N.R., via La Malfa 153, 90146 Palermo, Italy
⁴ Università di Ferrara, Dipartimento di fisica, via Paradiso 12, 44100 Ferrara, Italy
⁵ Istituto Tecnologie e Studio Radiazioni Extraterrestri, C.N.R., via Gobetti 101, 40129 Bologna, Italy

Corresponding author: S. Campana, campana@mera te.mi.astro.it

Received: 8 November 2001
Accepted: 14 December 2001

Abstract

We report on the results of a series of X–ray observations of the transient black hole candidate XTE J2012+381 during the 1998 outburst performed with the BeppoSAX satellite. The observed broad-band energy spectrum can be described by the superposition of an absorbed disk black body, with an iron line plus a high energy component, modelled with either a power law or a Comptonisation tail. The source showed pronounced spectral variability between our five observations. While the soft component in the spectrum remained almost unchanged throughout our campaign, we detected a hard spectral tail which extended to 200 keV in the first two observations, but became barely detectable up to 50 keV in the following two. A further re-hardening is observed in the final observation. The transition from a hard to a soft and then back to a hard state occurred around an unabsorbed 0.1–200 keV luminosity of (at 10 kpc). This indicates that state transitions in XTE 2012+281 are probably not driven only by mass accretion rate, but additional physical parameters must play a role in the evolution of the outburst.