Evidence of spreading layer emission in thermonuclear superbursts
Abstract
When a neutron star accretes matter from a companion star in a low-mass X-ray binary, the accreted gas settles onto the stellar surface through a boundary/spreading layer. On rare occasions the accumulated gas undergoes a powerful thermonuclear superburst powered by carbon burning deep below the neutron star atmosphere. In this paper, we apply the non-negative matrix factorization spectral decomposition technique to show that the spectral variations during a superburst from 4U 1636-536 can be explained by two distinct components: 1) the superburst emission characterized by a variable temperature black body radiation component, and 2) a quasi-Planckian component with a constant, 2.5 keV, temperature varying by a factor of 15 in flux. The spectrum of the quasi-Planckian component is identical in shape and characteristics to the frequency-resolved spectra observed in the accretion/persistent spectrum of neutron star low-mass X-ray binaries, and agrees well with the predictions of the spreading layer model by Inogamov & Sunyaev (1999). Our result is yet another observational evidence that superbursts - and possibly also normal X-ray bursts - induce changes in the disc-star boundary.
Keywords
Cite
@article{arxiv.1606.00595,
title = {Evidence of spreading layer emission in thermonuclear superbursts},
author = {K. I. I. Koljonen and J. J. E. Kajava and E. Kuulkers},
journal= {arXiv preprint arXiv:1606.00595},
year = {2016}
}
Comments
8 pages, 8 figures. Accepted for publication in ApJ