A peculiar type-I X-ray burst from GRS 1747-312

¹ SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
² Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
³ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
⁴ Dept. of Astronomy, University of Maryland, College Park, MD 20742, USA

Corresponding author: J. J. M. in 't Zand, jeanz@sron.nl

Received: 19 May 2003
Accepted: 3 July 2003

Abstract

We report the serendipitous detection with the Rossi X-ray Timing Explorer of a long and peculiar X-ray burst whose position is consistent with one known X-ray burster (GRS 1747-312) and which occurred when that source was otherwise quiescent. The peculiar feature concerns a strong radius expansion of the neutron star photosphere, which occurred not within a few seconds from the start of the burst, as is standard in radius-expansion bursts, but 20 s later. This suggests that two different layers of the neutron star may have undergone thermonuclear runaways: a hydrogen-rich and a hydrogen-poor layer. The reason for the delay may be related to the source being otherwise quiescent.