K. Asai, T. Dotani, H. Kunieda and N. Kawai

Abstract

We observed the Rapid Burster in quiescence and detected a significant X-ray flux for the first time. Neither a type-I nor type-II burst was observed during the observation. The luminosity was estimated to be (3(+2}_{-1) )times 10(33) erg s(-1) ( 2--10 keV), assuming a power-law with a photon index of 2 and a distance of 10 kpc. This luminosity is comparable to that of neutron-star transients in quiescence. If mass accretion is responsible for the X-ray emission, we can constrain the magnetic-field strength and spin period of the neutron star. A highly magnetized, rapidly rotating neutron star may be excluded.