Coronal Neutrino Emission in Hypercritical Accretion Flows

TL;DR

This paper investigates how a disk corona in hypercritical accretion flows onto black holes affects neutrino emission and energy deposition, finding a modest enhancement in efficiency that depends on the corona's properties.

Contribution

It provides a detailed model of the disk corona's impact on neutrino spectra and energy release in hypercritical accretion flows, clarifying the limited enhancement effect.

Findings

Neutrino spectra show two peaks from disk and corona emissions.

Corona can increase energy release efficiency by about 1.5 times.

Efficiency enhancement depends on the corona's height relative to the disk.

Abstract

Hypercritical accretion flows onto stellar mass black holes (BHs) are commonly considered as a promising model of central engines of gamma-ray bursts (GRBs). In this model a certain fraction of gravitational binding energy of accreting matter is deposited to the energy of relativistic jets via neutrino annihilation and/or magnetic fields. However, some recent studies have indicated that the energy deposition rate by neutrino annihilation is somewhat smaller than that needed to power a GRB. To overcome this difficulty, Ramirez-Ruiz & Socrates (2005) proposed that high energy neutrinos from hot corona above the accretion disk might enhance the efficiency of energy deposition. We elucidate the disk corona model in the context of hypercritical accretion flows. From the energy balance in the disk and the corona, we can calculate the disk and coronal temperature, Td and Tc, and neutrino spectra, taking into account the neutrino cooling processes by neutrino-electron scatterings and neutrino pair productions. The calculated neutrino spectra consist of two peaks; one by the neutrino emission from the disk and the other by that from the corona. We find that the disk corona can enhance the efficiency of energy release but only by a factor of 1.5 or so, unless the height of the corona is very small, H<<r. This is because the neutrino emission is very sensitive to the temperature of emitting region, and then the ratio Tc/Td cannot be so large.