Gravitational wave observations may constrain gamma-ray burst models: the case of GW 150914 - GBM

TL;DR

This paper investigates how gravitational wave data from GW 150914 can constrain gamma-ray burst models, finding that some models are marginally consistent while others fit well, thus offering new insights into GRB physics.

Contribution

It introduces a method to use GW data to test and constrain different GRB prompt emission models, including photospheric, internal shock, and external shock scenarios.

Findings

Photospheric and internal shock models are marginally inconsistent with GBM data.

Dissipative photosphere models can explain the observations.

External shock model suggests low interstellar density and high Lorentz factor.

Abstract

The possible short gamma-ray burst (GRB) observed by {\it Fermi}/GBM in coincidence with the first gravitational wave (GW) detection, offers new ways to test GRB prompt emission models. Gravitational wave observations provide previously unaccessible physical parameters for the black hole central engine such as its horizon radius and rotation parameter. Using a minimum jet launching radius from the Advanced LIGO measurement of GW~150914, we calculate photospheric and internal shock models and find that they are marginally inconsistent with the GBM data, but cannot be definitely ruled out. Dissipative photosphere models, however have no problem explaining the observations. Based on the peak energy and the observed flux, we find that the external shock model gives a natural explanation, suggesting a low interstellar density ($\sim 10^{-3}$ cm$^{-3}$) and a high Lorentz factor ($\sim 2000$). We only speculate on the exact nature of the system producing the gamma-rays, and study the parameter space of a generic Blandford Znajek model. If future joint observations confirm the GW-short GRB association we can provide similar but more detailed tests for prompt emission models.