MAXI J1957+032: an accreting neutron star possibly in a triple system

Abstract

I present an optical characterization of the Galactic X-ray transient source MAXI J1957$+$032. This system flares by a factor of $\gtrsim 10^4$ every few-hundred days, with each flare lasting $\sim 5$ days. I identify its quiescent counterpart to be a late-K/early-M dwarf star at a distance of $5\pm 2$ kpc. This implies that the peak $0.5-10$ keV luminosity of the system is $10^{36.4\pm 0.4}$ erg s${}^{-1}$. As found by Mata Sanchez et al., the outburst properties of MAXI J1957$+$032 are most consistent with the sample of accreting millisecond pulsars. However, the low inferred accretion rate, and the lack of evidence for a hydrogen-rich accretion flow, are difficult to reconcile with the late-K/early-M dwarf counterpart being the mass donor. Instead, the observations are best described by a low-mass hydrogen- and possibly helium-poor mass donor, such as a carbon-oxygen white dwarf, forming a tight interacting binary with a neutron star. The observed main-sequence counterpart would then likely be in a wide orbit around the inner binary.

arXiv comment12 pages, 3 figures, 4 tables, accepted by ApJ

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Cited by in corpus (6)

• UltraCompCAT: a comprehensive Catalogue of Ultra-Compact and Short Orbital Period X-ray Binaries
• MAXI J1957+032: a new accreting millisecond X-ray pulsar in an ultra-compact binary
• Catalog of outbursts of neutron star LMXBs
• Unveiling the nature of compact object in the LMXB MAXI J1957+032 using Swift-XRT
• Quiescent NIR and optical counterparts to candidate black hole X-ray binaries
• Constraining the nature of the accreting binary in CXOGBS J174623.5-310550