The Properties of Bursts with Short Recurrence Times from the Transient X-Ray Source EXO 0748-676

Abstract

On January 13/14 1986 Exosat performed a 11.3-hr observation of the transient X-ray burst source EXO 0748-676. The source was in a low state and emitted 11 type I X-ray bursts, of which 10 were analyzed in detail. The properties of the bursts were similar to those found in previous low-state observations reported in Gottwald et al. (1986). The total energy emitted in the persistent flux between bursts divided by the total energy emitted in the following burst was about 25 with a constant apparent blackbody radius during the burst decay of 4.4 km. A regular burst pattern was identified where long and short recurrence intervals followed each other. The wait time to a burst and the total emitted energy in that burst displayed a linear relation but with an offset energy of 0.3 x 10 to the-7th ergs/sq cm at zero burst interval. This behavior is discussed in context of incomplete consumption of fuel and its subsequent reconsumption in the following bursts. The amount of unburned fuel was found to be about 10-15 percent of the total available nuclear energy.