A Strong X‐Ray Burst from the Low‐Mass X‐Ray Binary EXO 0748−676

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 5.2 × 10 -8 ergs cm -2 s -1 , 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.