Did we observe the supernova shock breakout in GRB 060218?

TL;DR

This paper investigates whether the early optical and X-ray black-body emissions in GRB 060218 can be attributed to a supernova shock breakout, analyzing the energetics, luminosity, and possible interpretations of the observed data.

Contribution

The study provides new limits on the bolometric luminosity and energetics of the black-body component in GRB 060218, and discusses alternative interpretations beyond shock breakout.

Findings

Lower limits on bolometric luminosity and energetics are around 10^51 erg.

The X-ray black-body emission suggests a nearly constant temperature with a slowly increasing surface area.

An alternative explanation involves late dissipation of the fireball's kinetic energy with a small Lorentz factor.

Abstract

If the early optical data of GRB 060218 up to 1e5 s are interpreted as the black-body flux associated with the supernova shock breakout, we can derive lower limits to the bolometric luminosity and energetics of this black-body component. These limits are more severe for the very early data that imply energetics of order of 1e51 erg. These values, puzzlingly large, are rather independent of the assumed time profile of the emitting surface, provided that the corresponding radius does not increase superluminally. Another concern is the luminosity of the black-body component observed in the X-rays, that is large and appears to be produced by an approximately constant temperature and a surface area increasing only slowly in time. Although it has been suggested that the long X-ray black-body duration is consistent with the supernova shock breakout if anisotropy is assumed, the nearly constant emitting surface requires some fine tuning, allowing and suggesting an alternative interpretation, i.e. emission from late dissipation of the fireball bulk kinetic energy. This in turn requires a small value of the bulk Lorentz factor.