Insight-HXMT observation on 4U~1608--52: evolving spectral properties of a bright type-I X-ray burst

TL;DR

This study uses Insight-HXMT observations to analyze a bright type-I X-ray burst from 4U 1608-52, revealing spectral evolution and excess soft X-ray emission likely due to enhanced persistent emission or Comptonization effects.

Contribution

First detailed spectral analysis of a PRE burst from 4U 1608-52 with broad energy coverage, identifying excess soft X-ray emission and its possible origins.

Findings

Excess soft X-ray emission not caused by disk reflection.

Burst plus persistent emission exceeds Eddington luminosity by ~40%.

Enhanced emission may originate beyond PRE radius or from Comptonization.

Abstract

The evidences for the influence of thermonuclear (type-I) X-ray bursts upon the surrounding environments in neutron star low-mass X-ray binaries (LMXB) were detected previously via spectral and timing analyses. Benefitting from a broad energy coverage of Insight-HXMT, we analyze one photospheric radius expansion (PRE) burst, and find an emission excess at soft X-rays. Our spectral analysis shows that, such an excess is not likely relevant to the disk reflection induced by the burst emission and can be attributed to an enhanced pre-burst/persistent emission. We find that the burst and enhanced persistent emissions sum up to exceed Eddington luminosity by $\sim$ 40 percentages. We speculate that the enhanced emission is from a region beyond the PRE radius, or through the Comptonization of the corona.