TP-20

Fireballs from collapse of neutron stars induced by primordial black holes

E.V. Derishev, V.V. Kocharovsky, Vl.V. Kocharovsky (Institute of Applied Physics of the Russian Academy of Science)

We show that primordial black holes (PBHs) captured in the very first (Population III) stars may be responsible for Gamma-Ray Bursts (GRBs) even if PBHs constitute only 10^-9-10^-8 fraction of the critical density of the Universe, which is consistent with the non-detection of hard gamma-ray emission from evaporating black holes.

We find that a typical PBH with initial mass $\sim 5\cdot10^{14}$g swallows the entire NS in a time period $\sim 4\cdot10^{6}$ years. This is much shorter than the Hubble timescale, so that the present-day rate of such events is defined by PBHs falling down to NSs from close orbits under the influence of gravitational radiation and tidal friction. The final stage of the PBH-induced collapse of a NS lasts only few milliseconds and is accompanied by a powerful pulse of neutrino emission from hot quark-gluon plasma formed in the inner part of accretion flow in the NS core. The energy is transferred by degenerate neutrinos to the star's surface, where neutrinos annihilate into an electron-positron plasma and produce an inverted temperature layer that preserves a fireball from undue baryonic pollution. We describe quantitatively all stages of the corresponding scenario up to the formation of a relativistic fireball and propose specific observational tests.

A PBH heavier than $\sim 10^{17}$g can cause collapse of white dwarfs, normal stars and brown dwarfs within the limits of the Hubble time, resulting in unusual supernovae characterized by significantly larger energy release and faster increase of luminosity as compared with ordinary ones.

The observed GRB rate taken in comparison with the rate of the above-mentioned unusual supernovae may place a stronger limit on the PBH number density than the present-day one.