Episodic jet power extracted from a spinning black hole surrounded by a neutrino-dominated accretion flow in gamma-ray bursts

TL;DR

This paper investigates how magnetic fields in a neutrino-dominated accretion flow around a spinning black hole can power episodic jets in gamma-ray bursts through the Blandford-Znajek mechanism, explaining observed emission oscillations.

Contribution

It models magnetic field advection in NDAFs and links magnetic flux accumulation to episodic jet activity in GRBs, a novel approach.

Findings

Maximal BZ jet power ~10^53-10^54 erg/sec for extreme Kerr black holes.

Magnetic field advection is efficient with P_m=1, consistent with post-merger magnetar fields.

Episodic accretion cycles have a typical timescale of about one second.

Abstract

It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of a NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number P_m=1. The maximal BZ jet power can be ~10^53-10^54 erg/sec for an extreme Kerr black hole, if an external magnetic field with 10^14 Gauss is advected by the NDAF. This is roughly consistent with the field strength of the disk formed after a tidal disrupted magnetar. The accretion flow near the black hole horizon is arrested by the magnetic field if the accretion rate is below than a critical value for a given external field. The arrested accretion flow fails to drag the field inward and the field strength decays, and then the accretion re-starts, which leads to oscillating accretion. The typical timescale of such episodic accretion is in an order of one second. This can qualitatively explain the observed oscillation in the soft extend emission of short-type GRBs.