ON THE NATURE OF THE X-RAY-EMISSION FROM 1E-1024.0-5732/WACK-2134 - THE 1ST X-RAY-SELECTED WOLF-RAYET STAR

We report on a ROSAT PSPC observation of the X-ray source 1E 1024.0-5732. The optical identification with the emission-line star Wackerling 2134 is confirmed, but we do not find any evidence of the periodic pulsations at 61 ms which were previously reported in its X-ray flux. On the basis of the new timing and spectral results, a reexamination of the old X-ray and optical data, and a new optical spectrum, we propose that this source is a new Wolf-Rayet star of type WN6. The high level of X-ray emission hints at the presence of a binary companion to Wack 2134. This could be either an accreting compact object or a massive OB star, in which case the X-rays would be produced in the colliding winds of the two stars. The small equivalent widths of the Wolf-Rayet star emission lines strongly support the 0-star companion hypothesis. If this scenario is confirmed, Wack 2134 would be the first case of an X-ray-selected Wolf-Rayet star.