A new mechanism of neutron star radiation
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abstract
We find a new mechanism of neutron star radiation wherein radiation is produced by the stellar interior. The source of radiation is oscillating neutron vortices in the superfluid core of a rotating neutron star. Thermally excited helical waves of vortices generate fast magnetosonic waves at the stellar crust. Near the crust bottom such waves reduce to a collisionless zero sound in an electron liquid, while near the stellar surface they behave as electromagnetic waves in a medium. The magnetosonic waves propagate across the crust and transform into electromagnetic radiation at the surface. The vortex contribution has the spectral index -0.45 and can explain nonthermal radiation of middle-aged pulsars observed in infrared, optical and hard X-ray bands. Detection of vortex radiation allows direct determination of the core temperature. Comparing the theory with available spectra observations we find that the core temperature of the Vela pulsar is T=8*10^8K, while the core temperature of PSR B0656+14 exceeds 2*10^8K. This is the first measurement of the temperature of a neutron star core. The temperature estimate rules out equation of states incorporating Bose condensations of pions or kaons and quark matter in these objects. In principle, zero sound can also be emitted by other mechanisms, rather than vortices, which opens a perspective of direct spectroscopic study of superdense matter in the neutron star interiors.
