Search for spectral features in PRE bursts
Thermonuclear bursts that show photospheric radius-expansion (PRE) are pretty rare in most sources, so much so that Chandra has only observed a few of them in a decade of observations. In 2006 we made an observation of a prolific PRE burster, 4U 1728-34, to try to catch some bursts and search for spectral features near the peak. We got plenty of bursts, but only 4 of them were likely PRE, and we saw no features. But, we did find evidence for an extremely weak periodic variation in the X-ray intensity, which if orbital in nature, means the neutron star orbits its mass donor once every 10.77 minutes! Our paper was just accepted by ApJ, and is available at arXiv:1009.2296.