Tracking spectral variability with luminosity in the ultraluminous state
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A substantial body of evidence suggests that most ultraluminous Xray sources(ULXs) are stellar remnant black holes accreting at superEddington rates, in anew ultraluminous. accretion state. Little is known of the astrophysics of thisputative state to date. Gladstone et al. (2009) propose a sequence of threespectral regimes that ULXs may progress through as their accretion rateincreases; but no evidence for this progression from an individual source hasyet been seen. Here, we propose three observations of a highly variable ULX inNGC 5907, triggered at different flux levels by Swift monitoring data. Thesewill investigate whether large amplitude luminosity variation in a ULX isaccompanied by transitions through these ultraluminous state regimes. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]
