New possible class of rapidly rotating neutron stars

Mar 28, 2014, 4:50 PM


Andrey Chugunov (I)


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 ~10^9 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. This work was partially supported by RF president programme (grant MK-506.2014.2), by RFBR (grant 14-02-31616-mol-a), by the Dynasty Foundation, and by the Ministry of Education and Science of Russian Federation (Agreement No.\ 8409, 2012).

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