New possible class of neutron stars: hot and fast non-accreting rotators

Abstract

A new class of neutron stars (NSs) -- hot rapidly rotating non-accreting NSs, which we propose to call HOFNARs (HOt and Fast Non-Accreting Rotators) or "hot widows" (in analogy with "black widow" pulsars) -- is suggested. We argue that such stars should originate from the low-mass X-ray binaries (LMXBs) provided that they were unstable with respect to excitation of $r$-modes at the end of accretion epoch (when their low-mass companions ceased to fill the Roche lobe). High temperature of "hot widows"/HOFNARs is maintained by $r$-mode dissipation rather than by accretion. We analyse observational properties of "hot widows"/HOFNARs and demonstrate that these objects form a specific separate class of neutron stars. In particular, some of the most stable X-ray sources among the candidates to quiescent LMXB systems (qLMXBs), can, in fact, belong to that new class. We formulate observational criteria which allow to distinguish "hot widows"/HOFNARs from qLMXB systems, and argue that available observations of X-ray sources 47 Tuc X5 and X7 satisfy (or, at least, do not contradict) these criteria. In addition, we discuss indirect evidences in favor of "hot widows"/HOFNARs existence, following from the analysis of observations and predictions of population synthesis theories. If that new class of NSs does exist, it would prove the possibility to emit gravitational waves by mass-current multipole. Various applications of our results, such as prospects for constraining superdense matter properties with hot widows"/HOFNARs, are analyzed.

8 pages, 1 figure, accepted for publication in MNRAS

References in corpus (14)

• Shapiro delay measurement of a two solar mass neutron star
• A Massive Pulsar in a Compact Relativistic Binary
• A Radio Pulsar/X-ray Binary Link
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• eROSITA Science Book: Mapping the Structure of the Energetic Universe
• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• Faint X-ray Sources in the Globular Cluster Terzan 5
• Spin-Down of Radio Millisecond Pulsars at Genesis
• Thermal X-rays from Millisecond Pulsars: Constraining the Fundamental Properties of Neutron Stars
• Rotational evolution of young pulsars due to superfluid decoupling
• Spin frequency distributions of binary millisecond pulsars
• Studying Millisecond Pulsars in X-rays
• Resistive relaxation of a magnetically confined mountain on an accreting neutron star
• Joule heating in high magnetic field pulsars

Cited by in corpus (9)

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• Spectral analysis of the quiescent low-mass X-ray binary in the globular cluster M30
• Radiation driven instability of rapidly rotating relativistic stars: criterion and evolution equations via multipolar expansion of gravitational waves
• Observability of HOFNARs with SRG/eROSITA
• Magnetic field amplification by the r-mode instability
• Constraints on r-modes and mountains on millisecond neutron stars in binary systems