Shock Breakout Driven by the Remnant of a Neutron Star Binary Merger: An X-Ray Precursor of Mergernova Emission
Abstract
A supra-massive neutron star (NS) spinning extremely rapidly could survive from a merger of an NS-NS binary. The spin-down of this remnant NS that is highly magnetized could power the isotropic merger ejecta to produce a bright mergernova emission in the ultraviolet/optical bands. Before the mergernova, the early interaction between the NS wind and the ejecta could drive a forward shock propagating outward into the ejecta. As a result, a remarkable amount of heat can be accumulated behind the shock front and the final escape of this heat could produce a shock breakout emission. We describe the dynamics and thermal emission of this shock with a semi-analytical model. It is found that a few hours after the merger, by leading the mergernova emission as a precursor, sharp and luminous breakout emission appears mainly in soft X-rays, with a luminosity of ∼ {10}45 {erg} {{{s}}}-1. Therefore, the detection of such an X-ray precursor could provide evidence for identifying NS-powered mergernovae and distinguishing them from radioactivity-powered novae (I.e., kilonovae or macronovae). The discovery of NS-powered mergernovae could finally help to confirm the gravitational wave signals due to the mergers and the existence of supra-massive NSs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2016
- DOI:
- 10.3847/0004-637X/819/2/120
- arXiv:
- arXiv:1511.01229
- Bibcode:
- 2016ApJ...819..120L
- Keywords:
-
- gamma-ray burst: general;
- stars: neutron;
- supernovae: general;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 7 pages, 4 figures, accepted by ApJ