Energy dependent variability as a diagnostic of the ultraluminous state: key results.
Abstract
The nature of ultraluminous X-ray sources is still the subject of much debate. However, it seems increasingly likely that many are in a new super-Eddington accretion state, and there may be some spectral state progression with increasing Eddington ratio. Here, we present some key results from a sample of ULXs observed by XMM-Newton, composed of the highest count rate EPIC data. We use this to gain new physical insights, and break some of the degeneracies inherent in spectral studies, by systematically examining the short-term, energy dependent temporal properties of ULXs. We show that the faintest ULXs typically have disc-like X-ray spectra, whilst the spectra of many brighter sources appear dominated by optically thick coronae, or a soft component consistent with a wind, with variability properties implying this latter distinction may be an inclination dependent effect.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 2013
- Bibcode:
- 2013MmSAI..84..639S