Hot widows/HOFNARs: a new possible class of rapidly rotating neutron stars

A.I. Chugunov, M.E. Gusakov, E.M. Kantor

Ioffe Physical-Tekhnical Institute, Politekhnicheskaya 26, St. Petersburg, 194021, Russia

We discuss a new hypothetical class of neutron stars dubbed "HOFNARs" (HOt and Fast Non-Accreting Rotators) or "hot widows" (similar to "black widow" pulsars) which are hot and fast-rotating, but do not accrete matter. These sources are unstable with respect to r-modes and are formed in low-mass X-ray binaries (LMXBs), after exhausting the low-mass companion. Their high temperatures are maintained by r-mode dissipation; as we show they can stay hot during a very long period of time ∼109 yrs. "Hot widows"/HOFNARs can be observed as X-ray sources with purely thermal neutron star atmosphere spectrum, which perfectly matches spectral identification criteria for quiescent LMXBs (qLMXBs) candidates in globular clusters. This means that some of X-ray sources known as qLMXB candidates can in fact be "Hot widows"/HOFNARs. An existence of "Hot widows"/HOFNARs might allow
(i) to explain overproduction of millisecond pulsars in population synthesis models of globular clusters;
(ii) to lower estimates of recurrence time for qLMXB candidates in globular clusters to theoretically predicted value.
We discuss identification criteria for "Hot widows"/HOFNARs and analyze a variety of possibilities, which they give to constrain dense matter properties.
Russian abstract
Russian
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