Speaker
Description
The mechanism for X-ray generation in the Gamma Cas analogues, a small group of highly variable Oe/Be stars, has been a mystery for several decades. They are characterised by their hard X-ray spectra, often including strong Fe fluorescence lines, and X-ray luminosities in the gap between those seen in similar stars and the more luminous Be/X-ray Binaries. They have also been observed to be highly variable on a range of timescales, from seconds up to several years. Competing theories for the mechanism for X-ray production include magnetic interactions between the star and its decretion disk or accretion onto a white dwarf (WD) companion. Until now the missing evidence in favour of these sources being a new population of Be+WD binaries has been the absence of persistent significant periodicities associated with potential WD companions.
We will present the results of a comprehensive review of intra-observation variability in a large sample of 89 XMM-Newton and 45 Chandra observations, using both Fourier- and time-domain techniques to search for periodicities. We will identify those sources which appear to show periodicities across several observations, and outline how the periodicities in these sources might resolve the doubt over the nature of these exotic sources.
