6533b7d4fe1ef96bd1263432
RESEARCH PRODUCT
MAXI J1957+032: a new accreting millisecond X-ray pulsar in an ultra-compact binary
A SannaP BultM NgP S RayG K JaisawalL BurderiT Di SalvoA RiggioD AltamiranoT E StrohmayerA MancaK C GendreauD ChakrabartyW IwakiriR Iariasubject
High Energy Astrophysical Phenomena (astro-ph.HE)general–stars:neutron [Binaries]FOS: Physical sciencesAstronomy and Astrophysicsaccretion discsbinaries:generalX-rays:binariesSettore FIS/05 - Astronomia E AstrofisicaaccretionSpace and Planetary Sciencebinaries [X-rays]stars:neutronAstrophysics - High Energy Astrophysical PhenomenaAstrophysics - Instrumentation and Methods for AstrophysicsInstrumentation and Methods for Astrophysics (astro-ph.IM)accretion disks [Accretion]description
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.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2022-01-01 |