A 106 Day Period in the Nuclear Source X-8 in M33

摘要

We present here new and archival ROSAT observations of X-8 spread over 6 yr that show variability and a periodicity of ～106 days. This implies that (most of) the emission from M33 X-8 arises from a single object, perhaps a binary system with a black hole primary of ～10 M. We suggest that the companion is a giant orbiting with a period of ～10 days and that the observed modulation is "superorbital," analogous to that seen in Cyg X-2 and X1820-30.