2005ApJ...632.1099W

We have observed an unusually strong X-ray burst as a part of our regular eclipse timing observations of the low-mass binary system EXO 0748-676. The burst peak flux was 5.2x10^–8 ergs/cm2/s, approximately 5 times the normal peak X-ray burst flux observed from this source by RXTE. Spectral fits to the data strongly suggest that photospheric radius expansion occurred during the burst. In this paper we examine the properties of this X-ray burst, which is the first example of a radius expansion burst from EXO 0748-676 observed by RXTE. We find no evidence for coherent burst oscillations. Assuming that the peak burst luminosity is the Eddington luminosity for a 1.4 M_☉neutron star, we derive a distance to EXO 0748-676 of 7.7 kpc for a helium-dominated burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.