Relativistic X-ray reflection and highly ionized absorption in the spectrum of NS LMXB 1A 1744-361

TL;DR

This study analyzes the X-ray spectrum of the neutron star binary 1A 1744-361, revealing relativistic reflection and highly ionized absorption features, constraining disk properties, magnetic field strength, and disc wind characteristics.

Contribution

First detailed spectral analysis of 1A 1744-361 showing relativistic reflection and ionized absorption, constraining disk radius, magnetic field, and disc wind properties.

Findings

Inner disk radius estimated at 8.4-14.9 km.

Magnetic field strength constrained to less than 0.94×10^9 G.

Detection of highly ionized disc wind with outflow velocity of 6300 km/s.

Abstract

We present the results from the spectral and timing analysis of the accreting neutron star 1A~1744-361 from the \nustar{} observation performed in its 2022 outbursts. The unabsorbed bolometric X-ray luminosity during this observation in the energy band $0.1-100\kev{}$ is $3.9\times 10^{37}$ erg~s$^{-1}$, assuming a distance of $9$ kpc. During this observation, the source was in the banana branch of the atoll track. The source spectrum exhibits relativistic disc reflection and clear absorption features when an absorbed blackbody and cut-off power-law model describes the continuum emission. The $3-50\kev{}$ source spectrum is well fitted using a model combination consisting of an absorbed single-temperature blackbody and a reflection model along with the addition of a warm absorber component. The inner-disk radius, $R_{in}$, obtained from the reflection fit is $\sim(1.61-2.86)R_{ISCO}=(8.4-14.9)R_{g}$ ($17.6-31.2$ km for a $1.4\Msun$ NS). This measurement allowed us to further constrain the magnetic field strength to $B\lesssim 0.94\times 10^{9}$G. The strong absorption features $\sim 6.91\kev{}$ and $\sim 7.99\kev{}$ imply the presence of highly ionized absorbing material with a column density $N_{H}$ of $\sim 3\times 10^{22}$ cm$^{-2}$, emanating from the accretion disk in the form of disc wind with an outflow velocity of $v_{out}\simeq 0.021c\simeq 6300$ km s$^{-1}$.