Magnetar wind-driven shock breakout emission after double neutron star mergers: The effect of the anisotropy of the merger ejecta

TL;DR

This paper studies how the anisotropic structure of merger ejecta influences shock breakout emission from a magnetar wind after double neutron star mergers, proposing SBO light curves as a probe of ejecta geometry.

Contribution

It introduces the impact of ejecta anisotropy on SBO emission, highlighting its potential to reveal ejecta structure through light curve analysis.

Findings

SBO emission can be broadened due to ejecta anisotropy.

The SBO light curve profile depends on ejecta structure.

SBO observations can probe merger ejecta geometry.

Abstract

A rapidly rotating and highly magnetized remnant neutron star (NS; magnetar) could survive from a merger of double NSs and drive a powerful relativistic wind. The early interaction of this wind with the previous merger ejecta can lead to shock breakout (SBO) emission mainly in ultraviolet and soft X-ray bands, which provides an observational signature for the existence of the remnant magnetar. Here we investigate the effect of an anisotropic structure of the merger ejecta on the SBO emission. It is found that bolometric light curve of the SBO emission can be broadened, since the SBO can occur at different times for different directions. In more detail, the profile of the SBO light curve can be highly dependent on the ejecta structure and, thus, we can in principle use the SBO light curves to probe the structure of the merger ejecta in future.