标题： 使用Swift-XRT揭示MAXI J1957+032中致密天体的性质 显示英文标题

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

摘要： MAXI J1957+032 是一个瞬变的低质量 X 射线双星（LMXB），自 2015 年发现以来，在 1.5 年内经历了四次短暂的爆发。 MAXI J1957+032 中致密天体的性质尚不清楚，但根据其爆发持续时间较短，曾提出它可能是一颗中子星。 在这里，我们报告了使用尼尔·盖勒斯·斯威夫特卫星上的 X 射线望远镜获得的数据进行光谱分析的结果。 当用吸收幂律模型描述光谱时，我们发现随着光度的降低，光谱变软（幂律指数从$\sim$1.8 增加到 2.5）。 在爆发接近尾声时，观测到的幂律指数（$\Gamma$）为$\sim$2.5。 为了确定该系统中致密天体的性质，我们使用$\Gamma$作为光度变化的光谱演化示踪器。 我们发现，对于距离为 4 kpc 的情况，我们的结果表明该源包含一颗中子星。 显示英文摘要

摘要： 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.