MAXI J1957+032: a new accreting millisecond X-ray pulsar in an ultra-compact binary

Abstract

The detection of coherent X-ray pulsations at ~314 Hz (3.2 ms) classifies MAXI J1957+032 as a fast-rotating, accreting neutron star. We present the temporal and spectral analysis performed using NICER observations collected during the latest outburst of the source. Doppler modulation of the X-ray pulsation revealed the ultra-compact nature of the binary system characterised by an orbital period of ~1 hour and a projected semi-major axis of 14 lt-ms. The neutron star binary mass function suggests a minimum donor mass of 1.7e-2 Msun, assuming a neutron star mass of 1.4 Msun and a binary inclination angle lower than 60 degrees. This assumption is supported by the lack of eclipses or dips in the X-ray light curve of the source. We characterised the 0.5-10 keV energy spectrum of the source in outburst as the superposition of a relatively cold black-body-like thermal emission compatible with the emission from the neutron star surface and a Comptonisation component with photon index consistent with a typical hard state. We did not find evidence for iron K-alpha lines or reflection components.

arXiv comment5 pages, 4 figures. Accepted for publication in MNRAS

References in corpus (35)

• On the Absorption of X-rays in the Interstellar Medium
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Gravitational Radiation and Rotation of Accreting Neutron Stars
• An Empirical Background Model for the NICER X-ray Timing Instrument
• White Dwarf Donors in Ultracompact Binaries: The Stellar Structure of Finite Entropy Objects
• The XMM-Newton/Chandra monitoring campaign of the Galactic center region: Description of the program and preliminary results
• Physics of accretion in the millisecond pulsar XTE J1751-305
• The mass-radius relationship from solar-type stars to terrestrial planets: a review
• A model for the waveform behavior of accreting millisecond pulsars: Nearly aligned magnetic fields and moving emission regions
• Discovery of a Second Transient Low-Mass X-ray Binary in the Globular Cluster NGC 6440
• INTEGRAL spectroscopy of the accreting millisecond pulsar XTE J1807-294 in outburst
• The magnetic field strengths of accreting millisecond pulsars
• Accreting Millisecond X-Ray Pulsars
• Timing of the Accreting Millisecond Pulsar XTE J1814-338
• An in-depth study of a neutron star accreting at low Eddington rate: On the possibility of a truncated disk and an outflow
• Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658
• Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704
• XMM-Newton observation of the 5.25 ms transient millisecond pulsar XTE J1807-294 in outburst
• Spin up and phase fluctuations in the timing of the accreting millisecond pulsar XTE J1807-294
• Timing of the accreting millisecond pulsar SAX J1748.9-2021 during its 2015 outburst
• Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808
• Accretion torques and motion of the hot spot on the accreting millisecond pulsar XTE J1807-294
• XMM-Newton Spectroscopy of the Accretion-Driven Millisecond X-ray Pulsar XTE J1751-305 in Outburst
• Spectral and timing properties of IGR J00291+5934 during its 2015 outburst
• Accretion onto Stars with Octupole Magnetic Fields: Matter Flow, Hot Spots and Phase Shifts
• NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar
• On the nature of pulse profile variations and timing noise in accreting millisecond pulsars
• NICER Discovery of Millisecond X-ray Pulsations and an Ultracompact Orbit in IGR J17494-3030
• SWIFT J1756.9-2508: spectral and timing properties of its 2018 outburst
• Swift and SALT observations of the Multiple Outbursts of MAXI J1957+032
• Unveiling the nature of compact object in the LMXB MAXI J1957+032 using Swift-XRT
• On the peculiar long-term orbital evolution of the eclipsing accreting millisecond X-ray pulsar SWIFT J1749.4-2807
• Disappearance of the Fe K$\alpha$ emission line in Ultra Compact X-ray Binaries 4U 1543-624 and Swift J1756.9-2508
• MAXI J1957+032: an accreting neutron star possibly in a triple system

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