Simultaneous BeppoSAX and Rossi X-ray timing explorer observations of 4U 1812–12

¹ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 04, France
² ESA-ESTEC, Science Operations & Data Systems Division, SCI-SDG, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

Corresponding author: D. Barret, Didier.Barret@cesr.fr

Received: 23 October 2002
Accepted: 27 December 2002

Abstract

4U 1812–12 is a faint persistent and weakly variable neutron star X-ray binary. It was observed by BeppoSAX between April 20th and 21st, 2000 in a hard spectral state with a bolometric luminosity of  ergs s^-1. Its broad-band energy spectrum is characterized by the presence of a hard X-ray tail extending above keV. It can be represented as the sum of a dominant hard Comptonized component (electron temperature of keV and optical depth ) and a weak soft component. The latter component which can be fitted with a blackbody of keV and equivalent radius of km is likely to originate from the neutron star surface. We also report on the first measurement of the power density spectrum of the source rapid X-ray variability, as recorded during a simultaneous snapshot observation performed by the Rossi X-ray Timing Explorer. As expected for a neutron star system in such a hard spectral state, its power density spectrum is characterized by the presence of a Hz low frequency quasi-periodic oscillation together with three broad noise components, one of which extends above Hz.