Unveiling the nature of compact object in the LMXB MAXI J1957+032 using Swift-XRT
Abstract
MAXI J1957+032 is a transient low-mass X-ray binary (LMXB) that underwent four short outbursts in 1.5 yr 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 (NS) 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 ∼1.8 to 2.5) as the luminosity decreases. Near the end of its outbursts the observed value of power-law index (Γ) is ∼2.5. To identify the nature of the compact object in this system, we used Γ 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 NS.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2019
- DOI:
- 10.1093/mnras/stz938
- arXiv:
- arXiv:1904.00914
- Bibcode:
- 2019MNRAS.486.1620B
- Keywords:
-
- binaries: spectroscopic;
- stars: neutron;
- X-rays: binaries;
- X-rays: individual: MAXI J1957+032;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, Accepted for publication in MNRAS