The Swift capture of a long X-ray burst from XTE J1701-407

Abstract

XTE J1701-407 is a new transient X-ray source discovered on 2008 June 8. More than onemonth later, it showed a rare type of thermonuclear explosion: a long type I X-ray burst. Wereport herein the results of our study of the spectral and flux evolution during this burst, as wellas the analysis of the outburst in which it took place. We find an upper limit on the distanceto the source of 6.1 kpc by considering the maximum luminosity reached by the burst. Wemeasure a total fluence of 3.5 × 10-6 erg cm-2 throughout the ~20 min burst duration and afluence of 2.6 × 10-3 erg cm-2 during the first two months of the outburst. We show that theflux decay is best fitted by a power law (index ~1.6) along the tail of the burst. Finally, wediscuss the implications of the long burst properties, and the presence of a second and shorterburst detected by Swift ten days later, for the composition of the accreted material and theheating of the burning layer.