Photospheric radius expansion X-ray bursts as standard candles

We examined the maximum bolometric peak luminosities during type I X-ray bursts from the persistent or transient luminous X-ray sources in globular clusters. We show that for about two thirds of the sources the maximum peak luminosities during photospheric radius expansion X-ray bursts extend to a critical value of erg s-1, assuming the total X-ray burst emission is entirely due to black-body radiation and the recorded maximum luminosity is the …