Discovery of black hole spindown in the BATSE catalogue of long GRBs

TL;DR

This study analyzes the BATSE catalogue of long GRBs to find evidence of black hole spindown, using matched filtering of light curves, and suggests gravitational-wave emission from inner disk instabilities as a key process.

Contribution

It provides the first evidence linking black hole spindown signatures in GRB light curves to gravitational-wave emitting instabilities at the ISCO.

Findings

Consistent match between observed light curves and black hole spindown model.

Spindown against matter at the ISCO fits data better than alternative models.

Potential gravitational-wave signals lasting tens of seconds are predicted.

Abstract

The BATSE catalogue is searched for evidence of spindown of black holes or proto-neutron stars (PNS) by extracting normalized light curves (nLC). The nLC are obtained by matched filtering, to suppress intermediate time scales such as due to the shock break-out of GRB jets through a remnant stellar envelope. We find consistency within a few percent of the nLC and the model template for spindown of an initially extremal black hole against high-density matter at the ISCO. The large BATSE size enables a study of the nLC as a function of durations $T_{90}$. The resulting $\chi^2_{red}$ is within a $2.35\sigma$ confidence interval for durations $T_{90}>20$ s, which compares favorably with the alternative of spindown against matter further out and spindown of a PNS, whose $\chi^2$ fits are, respectively, outside the 4$\sigma$ and 12$\sigma$ confidence intervals. We attribute spindown against matter at the ISCO to cooling by gravitational-wave emission from non-axisymmetric instabilities in the inner disk or torus as the result of a Hopf bifurcation in response to energetic input from the central black hole. This identification gives an attractive outlook for chirps in quasi-periodic gravitational waves lasting tens of seconds of interest to LIGO, Virgo and the LCGT.