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 characterized by an orbital period of ∼1 h and a projected semimajor axis of 14 lt-ms. The neutron star binary mass function suggests a minimum donor mass of 1.7 × 10−2 M⊙, assuming a neutron star mass of 1.4 M⊙ and a binary inclination angle lower than 60 deg. This assumption is supported by the lack of eclipses or dips in the X-ray light curve of the source. We characterized 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 Comptonization component with photon index consistent with a typical hard state. We did not find evidence for iron K α lines or reflection components.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Aug 16, 2022
- Source ID
- 10.1093/mnrasl/slac093
Entities
People
- A Manca
- Alessandro Riggio
- Andrea Sanna
- Deepto Chakrabarty
- Diego Altamirano
- Gaurava Kumar Jaisawal
- Keith C. Gendreau
- Luciano Burderi
- Mason Ng
- Paul S Ray
- Peter Bult
- R. Iaria
- Tiziana Di Salvo
- Tod E. Strohmayer
- W. Iwakiri
Organizations
- Chuo University
- DTU Space
- Goddard Space Flight Center
- Institute of Space Astrophysics and Cosmic Physics in Palermo
- Massachusetts Institute of Technology
- National Aeronautics and Space Administration
- United States Naval Research Laboratory
- University of Cagliari
- University of Maryland
- University of Palermo
- University of Southampton