Spectral study of neutron star low mass X-ray binary source 1A 1744-361

TL;DR

This paper analyzes X-ray spectral data from the 2022 outburst of neutron star LMXB 1A 1744-361, revealing spectral features and variability in the soft state using joint NuSTAR and NICER observations.

Contribution

First detailed spectral analysis of 1A 1744-361 during its 2022 outburst, identifying iron and nickel absorption features and their variability.

Findings

Detection of broad iron Kα emission line.

Identification of absorption lines at 6.92 keV and 7.98 keV.

Spectral variability observed over time.

Abstract

We present X-ray observations of the recent outburst of 2022 from the neutron star low mass X-ray binary (LMXB) source 1A 1744-361. Spectral properties of the source have been analyzed using joint NuSTAR and NICER observations. During our observations, the source happens to be in the banana state (soft state) of the hardness intensity diagram (HID). In addition to a power-law with a high energy cutoff, the spectrum is found to exhibit broad iron $K_{\alpha}$ emission along with distinct absorption features. A prominent absorption feature observed at 6.92 keV may be interpreted as $K_{\alpha}$ absorption line from hydrogen-like iron. The absorption feature observed at 7.98 keV may be interpreted as a blend of Fe XXV and Ni XXVII transitions. We have summarized the evidence of variability of the spectral features observed in the X-ray continuum by time-resolved spectroscopy.