Electromagnetic Transients Powered by Nuclear Decay in the Tidal Tails of Coalescing Compact Binaries

TL;DR

This paper models optical transients powered by radioactive decay in tidal tails from merging compact objects, predicting observable signals that can test merger models and their connection to short gamma-ray bursts.

Contribution

It provides a detailed, realistic simulation of electromagnetic transients from merger ejecta, combining hydrodynamics, nuclear synthesis, and radiative transfer to predict observable signatures.

Findings

Ejected debris can produce detectable optical transients.

Transient properties depend on binary mass ratio and orientation.

Estimated detection rates suggest observability in transient surveys.

Abstract

The possibility that long tidal tails formed during compact object mergers may power optical transients through the decay of freshly synthesized r-process material is investigated. Precise modeling of the merger dynamics allows for a realistic determination of the thermodynamic conditions in the ejected debris. The results of hydrodynamic and full nuclear network calculations are combined to calculate the resultant r-process abundances and the heating of the material by their decays. The subsequent homologous structure is mapped into a radiative transfer code to synthesize emergent model light curves and determine how their properties (variability and color evolution) depend on the mass ratio and orientation of the merging binary. The radiation emanating from the ejected debris, though less spectacular than a typical supernova, should be observable in transient surveys and we estimate the associated detection rates. The case for (or against) compact object mergers as the progenitors of short gamma-ray bursts can be tested if such electromagnetic transients are detected (or not) in coincidence with some bursts, although they may be obscured by on-axis afterglows.