GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole

TL;DR

This paper proposes that the unusual gamma-ray burst GRB060218 and associated supernova can be explained by a tidal disruption event where a white dwarf is torn apart by an intermediate mass black hole, leading to observable emissions.

Contribution

It introduces a novel explanation for GRB060218 involving WD tidal disruption by an IMBH, supported by multiwavelength spectral fitting and independent IMBH mass estimates.

Findings

IMBH mass estimated at about 10^4 solar masses

Soft X-ray spectrum fits Comptonized blackbody emission from jet photosphere

High rate of such tidal disruptions in dwarf galaxies aligns with observations

Abstract

A highly unusual pair of a gamma-ray burst (GRB) GRB060218 and an associated supernova SN2006aj has puzzled theorists for years. A supernova shock breakout and a jet from a newborn stellar mass compact object were put forward to explain its multiwavelength signature. We propose that the source is naturally explained by another channel, a tidal disruption of a white dwarf (WD) by an intermediate mass black hole (IMBH). The tidal disruption is accompanied by a tidal pinching, which leads to the ignition of a WD and a supernova. Some debris falls back onto the IMBH, forms a disk, which quickly amplifies the magnetic field, and launches a jet. We successfully fit soft X-ray spectrum with the Comptonized blackbody emission from a jet photosphere. The optical/UV emission is consistent with self-absorbed synchrotron from the expanding jet front. The accretion rate temporal dependence Mdot(t) in a tidal disruption provides a good fit to soft X-ray lightcurve. The IMBH mass is found to be about 10^4Msun in three independent estimates: (1) fitting tidal disruption Mdot(t) to soft X-ray lightcurve; (2) computing the jet base radius in a jet photospheric emission model; (3) inferring the central BH mass based on a host dwarf galaxy stellar mass. The supernova position is consistent with the center of the host galaxy, while low supernova ejecta mass is consistent with a WD mass. High expected rate of tidal disruptions in dwarf galaxies is consistent with one source observed by Swift satellite over several years at GRB060218 distance of 150Mpc. The encounters with the WDs provide a lot of fuel for IMBH growth.