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

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$^{-1}$.