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.

12 pages, 3 figures, 4 tables, accepted by ApJ

References in corpus (7)

• A Catalog of Multiplicity among Bright Stellar Systems
• An Eccentric Binary Millisecond Pulsar in the Galactic Plane
• Population synthesis of ultracompact X-ray binaries in the Galactic Bulge
• Swift observations of SAX J1808.4-3658: monitoring the return to quiescence
• Disk reflection and a possible disk wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058
• Outbursts in ultracompact X-ray binaries
• On the triple nature of the X-ray source 4U2129+47 (= V1727 Cyg)

Cited by in corpus (5)

• 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
• Constraining the nature of the accreting binary in CXOGBS J174623.5-310550