PhD Thesis (PDF) - Department of Astronomy - University of Virginia

Chapter 4
Luminous X-Ray Flares from
Low-Mass X-Ray Binary
Candidates in the Early-Type
Galaxy NGC 4697
4.1 Introduction
Galactic X-ray binaries (XRBs) exhibit a wide-range of short-timescale variability.
X-ray bursts from XRBs were first studied in the mid-1970s (e.g., Grindlay et al. 1976;
Belian et al. 1976). Type I bursts, found in low-mass X-ray binaries (LMXBs), are due
to thermonuclear flashes on the neutron star (NS) surface with luminosities peaking
at the Eddington limit. Eight bursts lasting several hours, but otherwise like type
I bursts, have been observed (Kuulkers 2004). These superbursts are relatively rare
and appear to recur on year timescales.
116
Short-timescale variability has also been seen in high-mass X-ray binaries