Fall-back crust around a quark-nova compact remnant II: The degenerate torus case with applications to AXPs

TL;DR

This paper models a degenerate, Keplerian torus formed from quark-nova ejecta with angular momentum, applying it to explain various observed phenomena in AXPs, including luminosity, temperature, and timing irregularities.

Contribution

It introduces a new model of a degenerate torus around quark-nova remnants, explaining multiple observational features of AXPs not previously accounted for.

Findings

The degenerate torus remains stable over its lifetime.

The model explains quiescent luminosity and temperature during different phases.

It accounts for burst decay, glitches, and optical/infrared emissions in AXPs.

Abstract

In the first paper of this series we explored the case where a quark-nova ejecta forms a degenerate shell, supported by the star's magnetic field. Herein, we consider the case where the ejecta has sufficient angular momentum to form a Keplerian torus, and we show that the density and temperature of the torus are such that it will remain degenerate throughout it's lifetime. We go on to discuss the evolution of such a torus and apply it to two AXPs, namely 1E2259$+$586 and 4U0142$+$615. As it turns out, using our model we can account for many of the observations of these objects including the quiescent phase luminosity, and blackbody temperatures during quiescence and bursting phases. Furthermore, for 1E2259$+$586 our model explains the steep and slow decay components seen in the burst lightcurve, as well as the rotation period glitches and enhanced spin-down rate. We also estimate the mass of the degenerate torus to be of the order of $10^{-6}M_{\odot}$, and speculate that the observed optical/infrared emission from 4U0142$+$615 might be a signature of the thin degenerate torus we describe here.