Soft X-ray observations of the binary sigma σ Cr B with HEAO-1

A new soft X-ray source H 1613 + 33 has been detected with the Low Energy Detector 1 (LED1) of the HEAO A-2 experiment. The binary a Corona Borealis (σ Cr B), the primary star (HD 143631) of which is a spectroscopic binary of period 1.1 day, lies near the centre of the error box of the source. On the bases of positional coincidence and the resemblance of the optical characteristics of HD 146361 with those of a RS CVn binary, we propose identification of H 1613 + 33 with HD 146361. The observed energy spectrum of the source is consistent with thermal emission from a hot plasma at a temperature of $(6.3_{+9.5}^{-2.3})\times \,{10}^{6}\text{K}$. The observed energy flux of $1.7\,\times {10}^{-10}\text{erg}\,\text{cm}^{-2}\text{s}^{-1}$ in the 0.15–2 keV band corresponds to a luminosity of $1.6\,\times {10}^{31}\,\text{erg}\,\text{s}^{-1}$ for a distance of 23 pc. The characteristicsof HD146361 are compared with those of other X-ray emitting RS CVn binaries. It is suggested that the soft X-rays are probably of coronal origin.