|Category||Progenitor||Type||Energy Mechanism||Emission Mechanism||Counterparts||References||Brief Comments|
|LF Radio||HF Radio||Microwave||Terahertz||Optical/IR||X-rays||Gamma-rays||Gravitational Waves||Neutrinos|
|Merger/Collapse||Magnetars Born in BNS Mergers and WD Collapse||Repeat||Maser||Synch.||Yes||Afterglow||--||--||Possible SN||Afterglow||sGRB||Yes||--||https://arxiv.org/pdf/1907.00016.pdf||Same mechanisms as flares, but magnetars born in mergers or collapse as opposed in to SLSNe or LGRBs.|
Definitions: LF Radio (3 MHz to 3 GHz); HF Radio (3 GHz to 30 GHz); Microwave (30 to 300 GHz)
The localization of FRB 180924 to the outskirts of a massive early-type host galaxy suggests FRBs may be from magnetars born in binary neutron star (BNS) mergers and accretion induced WD collapse. The FRBs themselves are formed by the same mechanism as that of giant flare FRB theories.
sGRBs are expected in BNS mergers. The accretion-induced collapse of a WD has yet to be observed but might produce a SN Type Ia-like transient. Persistent synchrotron radio emission may be observable with timescales of months to years from the nebula or on longer timescales when the merger ejecta interacts with the ISM, but is shorter than for the SLSNe/LGRBs. BNS mergers are expected in all galaxy types and may be spatially offset from their birth sites or host galaxies.
Consistency with Observations
Using FRB 121102 to calibrate the model, the expected DM, RM and persistent radio emission is consistent with the upper limits of FRB 180924. The host galaxy and offset of FRB 180924 from the center are consistent with distributions of SGRBs and Type Ia SNe. It may be more difficult to detect persistent nebular radio emission from known FRB positions than in the SLSN/LGRB case because of high ejecta velocity and low ejecta mass: the emission peaks at early times and the ejecta become transparent to free-free absorption earlier. This is consistent with the non-detection of persistent emission from FRB 180924 and could explain its lower RM.