The last stages of evolution of close binaries composed of compact companions

TL;DR

This paper investigates the final stages of close binary systems with compact objects, particularly black hole-neutron star mergers, and presents observational evidence of high-frequency oscillations supporting their role in short gamma-ray bursts.

Contribution

It provides the first observational detection of high-frequency oscillations and chirp phenomena in short gamma-ray bursts consistent with black hole-neutron star merger predictions.

Findings

Detection of high-frequency oscillations in short GRBs

Frequencies and durations match theoretical predictions

Supports BH-NS mergers as short GRB progenitors

Abstract

Gamma-ray bursts (GRB) are the most powerful transient phenomena in the Universe. Nowadays dozens of speculations on the origin of GRB were undertaken, but so far a single model for the origin of, in particular, short GRBs does not exist. The black hole (BH) - neutron star (NS) coalescence is a promising candidate source for short GRBs. Most of binary mergers numerical simulations were carried out with the purpose of investigating the emission of gravitational waves. Such a scenario consists of an inspiral, merging and ringdown phase. In this paper we present the comparison of the observational results and analytical predictions for a test particle in a quasicircular orbit around the BH. The emission of gravitational waves causes a rapid decrease of the orbital radius and a rise of a {\it chirp} of radiation. Matter orbiting the black hole would be expected to produce high-frequency oscillations (HFO). Timescales of the coalescence process are of the order of milliseconds and oscillation frequencies of hundreds Hz for a system with a solar mass BH companion. We report on the detection of HFO in two short gamma-ray bursts in this paper. The frequencies and durations of the oscillations are in agreement with the predicted values. A {\it chirp} phenomenon is identified also. We therefore argue in favor of BH-NS mergers as a scenario for the production of short gamma-ray bursts.