An Ultrasoft Transient X-Ray Source in the Norma Region Discovered with Ginga

Abstract

Abstract A new X-ray source was discovered in the Norma region with Ginga in 1988 April. The source position, derived from one-dimensional scan data, and its spectral properties are presented. The X-ray emission was dominant below $\sim 6 \,\mathrm{keV}$ and not found in other observations. Thus, it is thought to be an ultrasoft transient X-ray source. The X-ray spectrum, constructed by a scan fit technique, was well represented by either blackbody, thermal bremsstrahlung, power-law, or multicolor disk models. Although all of the spectral models were acceptable from a statistical point of view, the ultrasoft nature of the spectrum and the transient behavior suggest that this source is a candidate source of black hole binaries.