A model for giant flares in soft gamma repeaters

TL;DR

This paper proposes a model where giant flares in soft gamma repeaters result from core conversion in neutron stars with fallback disks, explaining observed flare characteristics through neutrino emission and quark matter formation.

Contribution

It introduces a novel mechanism linking fallback disk accretion to core conversion and gamma-ray flares in SGRs, providing explanations for observed flare features.

Findings

Explains the spike and tail energies of SGR 1806-20 flare.

Accounts for timescales and spectra of the giant flare.

Links core conversion to gamma-ray emission in neutron stars.

Abstract

We argue that giant flares in SGRs can be associated to the core conversion of an isolated neutron star having a subcritical magnetic field $\sim 10^{12}$ G and a fallback disk around it. We show that, in a timescale of $\lesssim 10^5$ yrs, accretion from the fallback disk can increase the mass of the central object up to the critical mass for the conversion of the core of the star into quark matter. A small fraction of the neutrino-antineutrino emission from the just-converted quark-matter hot core annihilates into $e^+e^-$ pairs above the neutron star surface originating the gamma emission of the spike while the further cooling of the heated neutron star envelope originates the tail of the burst. We show that several characteristics of the giant flare of the SGR 1806-20 of 27 December 2004 (spike and tail energies, timescales, and spectra) can be explained by this mechanism.