EDP Sciences
Free access
Volume 400, Number 2, March III 2003
Page(s) 643 - 647
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030011

A&A 400, 643-647 (2003)
DOI: 10.1051/0004-6361:20030011

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

D. Barret1, J. F. Olive1 and T. Oosterbroek2

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

(Received 23 October 2002 / Accepted 27 December 2002 )

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 ${\sim} 2\times10^{36}$ ergs s -1. Its broad-band energy spectrum is characterized by the presence of a hard X-ray tail extending above ${\sim} 100$ keV. It can be represented as the sum of a dominant hard Comptonized component (electron temperature of ${\sim} 36$ keV and optical depth ${\sim} 3$) and a weak soft component. The latter component which can be fitted with a blackbody of ${\sim} 0.6$ keV and equivalent radius of ${\sim} 2$ 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 ${\sim} 0.7$ Hz low frequency quasi-periodic oscillation together with three broad noise components, one of which extends above ${\sim} 200$ Hz.

Key words: accretion, accretion disks -- stars: individual 4U 1812-12 -- stars: neutron -- X-rays: bursts -- X-rays: general

Offprint request: D. Barret, Didier.Barret@cesr.fr

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© ESO 2003