An X-Ray Flare from a B9+ Post--T Tauri Star System in the Field of the Seyfert Galaxy III ZW 2

Abstract

We report the serendipitous discovery by EXOSAT of a flaring X-ray source in the field of the Seyfert type I galaxy III Zw 2. In contrast to an earlier report that attributed the variability observed by the medium energy experiment to III Zw 2, we show that the variability was entirely due to the serendipitous source. We identify this source with the visual binary HD 560 (B9V+G5Ve) and we argue that virtually all of the observed X-ray flux from the binary, including the flare, came from its late-type component. These X-ray observations bring support to the optical classification of HD 560 B as a post-T Tauri star.