An ultra-soft X-ray source (RX 215319-1514) and discovery of a narrow line Seyfert 1 galaxy

Abstract

Two optical candidates - a galaxy and a star, are found within the error circle of the X-ray source position of an ultra-soft X-ray source discovered with ROSAT. Optical spectroscopy of the two candidates reveals that a) the galaxy is a narrow-line Seyfert type 1 galaxy, and b) the star is a late A-type or an early F-type. The Fx/Fopt ratio is too high for the star to be the counterpart of the X-ray source, but consistent with that for an active galaxy. Although higher resolution X-ray imaging of the region is needed to definitely settle the question of the counterpart of the X-ray source, the narrow-line Seyfert 1 galaxy is the best candidate. The spectral properties of the newly discovered narrow-line Seyfert 1 galaxy are also presented, including its extreme X-ray power law spectral (photon) index > 4.