Regular, mixed H/He thermonuclear bursts have long served as valuable comparisons for numerical ignition models. Such bursts are observed only from a few systems, and it remains a mystery why this mode of bursting is so rare. GS 1826-24 is well-known for it's consistently regular bursts, but similarly regular bursts have also been observed from the long-duration (now quiescent) transient KS 1731-26. These bursts may also serve as important test-cases for understanding the burst X-ray spectrum and how it may be used to constrain the neutron star EOS.
Recently Nathanael Lampe & I published a paper examining the consistency of radius measurements from samples of highly consistent, regular bursts. We found that the blackbody normalisation (from which the radius can be determined) can vary significantly between burst epochs. This may partly be attributed to variations in the spectral correction factor f_c during some bursts.
In parallel, Michael Zamfir and Andrew Cumming developed a way to constrain the surface redshift, and hence the neutron star mass and radius based on these bursts. (I had done something similar on the bursts from KS 1731-26 a few years ago with a 3rd-year student at Monash, Richard Linossi, but Michael & Andrew took this approach much further). There remains a lot of uncertainty about how best to extract meaningful measurements from bursts, but we are beginning to better understand the systematics that affect this approach. This is also timely as other groups have already derived mass and radius constraints from KS 1731-26 (Özel et al. 2012).

Galloway & Lampe 2012 (ApJ 747, #75)
Zamfir et al. 2012 (ApJ 749, #69)

Labels: 2012, /neutron star EOS