Hyperaccreting Neutron-Star Disks, Magnetized Disks and Gamma-Ray Bursts

TL;DR

This thesis investigates hyperaccreting neutron-star disks and magnetized accretion flows, revealing their potential to produce higher neutrino luminosities than black hole disks, with implications for gamma-ray burst central engines.

Contribution

It introduces a detailed analysis of neutron-star hyperaccretion disks, including their structure, neutrino emission, and the effects of magnetic fields, expanding understanding of GRB central engine models.

Findings

Neutron-star disks cool more efficiently than black hole disks.

Neutron-star disks produce higher neutrino and annihilation luminosities.

Magnetic fields influence accretion flow dynamics and neutrino emission.

Abstract

This thesis focuses on the study of the hyperaccreting neutron-star disks and magnetized accretion flows. It is usually proposed that hyperaccreting disks surrounding stellar-mass black holes with a huge accretion rate are central engines of gamma-ray bursts (GRBs). However, hyperaccretion disks around neutron stars may exist in some GRB formation scenarios. We study the structure and neutrino emission of a hyperaccretion disk around a neutron star. We consider a steady-state hyperaccretion disk, and as a reasonable approximation, divide it into two regions, the inner and outer disks. The outer disk is similar to that of a black hole. The inner disk has a self-similar structure, such as the entropy-conservation or the advection structure, depending on the energy transfer and emission in the disk. We see that the neutron star disk can cool more efficiently, produce much higher neutrino luminosity and neutrino annihilation luminosity than a black hole disk. The neutrino emission from the neutron star surface boundary layer could increase the neutrino annihilation luminosity. Moreover, we study the effects of a global magnetic field on viscously-rotating and vertically-integrated accretion disks around compact objects using a self-similar treatment, and use two methods to study magnetized flows with convection. We also give a review on GRB progenitors, central engines and an outlook in this thesis.