Long tails on thermonuclear X-ray bursts from neutron stars: a signature of inward heating?

TL;DR

This paper reports the discovery of long-lasting X-ray burst tails from neutron stars, attributed to inward heat conduction and cooling of deeper layers, revealing insights into neutron star thermal processes.

Contribution

It introduces the observation of extended X-ray burst tails and proposes a model involving inward heat conduction and cooling of neutron star layers.

Findings

Detection of one-hour long tails in X-ray bursts from multiple neutron stars.

Tails are due to cooling of deeper neutron star layers heated during bursts.

The neutron star surface is already hot, affecting tail characteristics.

Abstract

We report the discovery of one-hour long tails on the few-minutes long X-ray bursts from the `clocked burster' GS 1826-24. We propose that the tails are due to enduring thermal radiation from the neutron star envelope. The enduring emission can be explained by cooling of deeper NS layers which were heated up through inward conduction of heat produced in the thermonuclear shell flash responsible for the burst. Similar, though somewhat shorter, tails are seen in bursts from EXO 0748-676 and 4U 1728-34. Only a small amount of cooling is detected in all these tails. This is either due to compton up scattering of the tail photons or, more likely, to a NS that is already fairly hot due to other, stable, nuclear processes.