X-ray bursts as a probe of the corona: the case of XRB 4U 1636-536

TL;DR

This study analyzes 114 X-ray bursts from 4U 1636-536 to explore how soft X-ray bursts may cool the corona, revealing a time-lagged flux shortage at high energies indicative of corona cooling mechanisms.

Contribution

It provides observational evidence of corona cooling during X-ray bursts and measures the time lag between soft and hard X-ray flux changes, informing models of corona location.

Findings

Detected a flux shortage at 30--50 keV during bursts

Observed a time lag of approximately 2.4 seconds between soft and hard X-ray flux changes

Suggests soft X-ray bursts can cool the corona in neutron star systems

Abstract

To investigate the possible cooling of the corona by soft X-rays bursts, we have studied 114 bursts embedded in the known X-ray evolution of 4U 1636-536. We have grouped these bursts according to the ratio of the flux in the 1.5--12 keV band with respect to that in the 15--50 keV band, as monitored by RXTE/ASM and Swift/BAT, respectively. We have detected a shortage at hard X-rays while bursting. This provides hints for a corona cooling process driven by soft X-rays fed by the bursts that occurred on the surface of neutron star. The flux shortage at 30--50 keV has a time lag of 2.4$\pm$1.5 seconds with respect to that at 2--10 keV, which is comparable to that of 0.7$\pm$0.5 seconds reported in bursts of IGR 17473-2721. We comment on the possible origin of these phenomena and on the implications for the models on the location of the corona.