Exploring the spectral characteristics of the periodic burster 4U 1323-62: Type-I X-ray burst and persistent emission

TL;DR

This study analyzes NuSTAR observations of the periodic burster 4U 1323-62, revealing spectral features, burst characteristics, and the interaction between bursts and persistent emission, providing insights into the neutron star's environment and burst mechanisms.

Contribution

First detailed spectral and temporal analysis of 4U 1323-62's bursts and persistent emission using NuSTAR, highlighting burst-disc interactions and neutron star properties.

Findings

Detection of an absorption edge at 7.42 keV indicating nearby absorbing material.

Observation of six Type-I X-ray bursts with a recurrence time of ~4.52 hours.

Estimation of neutron star radius within 1.5-3.5 km and evidence of short bursts from mixed hydrogen-helium fuel.

Abstract

We report on the results obtained by the analysis of persistent and type-I thermonuclear X-ray burst emission observed from the periodic burster 4U 1323-62. These analyses are based on the NuSTAR observation performed on 2024 August 7 for a total exposure of around 90 ks. The persistent emission is well described by an absorbed thermal Comptonization model. An absorption edge is also detected at an energy of approximately 7.42 keV, which indicates the presence of absorbing material in the vicinity of this system. Six bursts have been observed during this observation, wherein we find the burst recurrence time to be approximately 4.52 hr. All the bursts exhibit the characteristics of a sharp rise and exponential decay. We perform the time-resolved spectroscopy of the burst spectra described by a model consisting of thermal emission from the neutron star surface and a varying persistent emission component to study the evolution of burst parameters. The enhancement of the persistent emission during burst exposure is characterized by the scaling parameter f a, which reflects the increasing strength of the burst-disc interaction with burst intensity, likely driven by Poynting-Robertson drag. The spectral analysis of bursts estimate the average apparent blackbody emitting radius of the neutron star to lie within 1.5-3.5 km. The ignition depths computed from the burst parameters indicate short Type-I thermonuclear bursts from a mixed hydrogen-helium fuel layer.