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

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 similar to2 x 10 36 ergs s(-1). Its broad-band energy spectrum is characterized by the presence of a hard X-ray tail extending above similar to100 keV. It can be represented as the sum of a dominant hard Comptonized component (electron temperature of similar to36 keV and optical depth similar to3) and a weak soft component. The latter component which can be fitted with a blackbody of similar to0.6 keV and equivalent radius of similar to2 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 similar to0.7 Hz low frequency quasi-periodic oscillation together with three broad noise components, one of which extends above similar to200 Hz.