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

TL;DR

This paper reports the observation and analysis of a rare long X-ray burst from XTE J1701-407, including spectral evolution, flux decay, and implications for accreted material composition.

Contribution

It provides detailed spectral and flux analysis of a rare long X-ray burst and discusses its implications for neutron star accretion and thermonuclear burning.

Findings

Upper limit on source distance: 6.1 kpc

Total burst fluence: 3.5×10^{-6} erg/cm^2

Flux decay follows a power law with index ~1.6

Abstract

XTE J1701-407 is a new transient X-ray source discovered on June 8th, 2008. More than one month later it showed a rare type of thermonuclear explosion: a long type I X-ray burst. We report herein the results of our study of the spectral and flux evolution during this burst, as well as the analysis of the outburst in which it took place. We find an upper limit on the distance to the source of 6.1 kpc by considering the maximum luminosity reached by the burst. We measure a total fluence of 3.5*10^{-6} erg/cm^2 throughout the ~20 minutes burst duration and a fluence of 2.6*10^{-3} erg/cm^2 during the first two months of the outburst. We show that the flux decay is best fitted by a power law (index ~1.6) along the tail of the burst. Finally, we discuss the implications of the long burst properties, and the presence of a second and shorter burst detected by Swift ten days later, for the composition of the accreted material and the heating of the burning layer.