# Unveiling the nature of compact object in the LMXB MAXI J1957+032 using Swift-XRT

## TL;DR

This study analyzes Swift-XRT data of the transient LMXB MAXI J1957+032, revealing spectral softening during outbursts and suggesting the compact object is a neutron star based on spectral evolution.

## Contribution

It provides new spectral analysis results that support the neutron star hypothesis for MAXI J1957+032, clarifying its nature.

## Key findings

- Spectral softening observed as luminosity decreases.
- Power-law index increases from ~1.8 to 2.5 during outbursts.
- Evidence supports a neutron star as the compact object.

## Abstract

MAXI J1957+032 is a transient Low-mass X-ray binary (LMXB) that underwent four short outbursts in 1.5 years since its discovery in 2015. The nature of the compact object in MAXI J1957+032 is not clear, but it was proposed to be a neutron star based on the short-duration of its outbursts. Here, we report the results obtained after performing spectral analysis using data obtained with the X-ray telescope aboard the Neil Gehrels Swift satellite. When describing the spectrum with an absorbed power law, we found that the spectra softens (the power-law index increases from $\sim$ 1.8 to 2.5) as the luminosity decreases. Near the end of its outbursts the observed value of power-law index ($\Gamma$) is $\sim$ 2.5. To identify the nature of the compact object in this system, we used $\Gamma$ as a tracer of the spectral evolution with luminosity. We found that for the distance of 4 kpc, our results suggest that the source harbours a neutron star.