|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||WD-BH||Single||Maser||Synch.||--||--||--||--||--||Yes (transient accretion disk)||--||--||--||http://adsabs.harvard.edu/abs/2018RAA....18...61L||None|
Definitions: LF Radio (3 MHz to 3 GHz); HF Radio (3 GHz to 30 GHz); Microwave (30 to 300 GHz)
During the merger of a BH and a WD, a transient accretion disk is expected to form around the BH, which could power a high speed wind around the entire BH-accretion disk system, forming a corona. Closed magnetic field lines, emerging continuously between the accretion disk and the corona, are twisted by the turbulence in the system, leading to the formation of rope-like flux structures in the corona. When the threshold for mass equilibrium is exceeded, the rope is thrust outward as an episodic jet of relativistic magnetized plasma; a so-called "magnetic blob". Before the accretion disk is exhausted, 2 - 3 magnetic blobs could be ejected at different speeds and will collide at a time after ejection. The collision causes catastrophic magnetic reconnection, and the release of magnetic energy is propagated through the magnetized cold plasma of the blob, and converted to particle kinetic energy. The resulting synchrotron maser could power a non-repeating FRB. Note that the accretion disk is advection-dominated. If the disk has a neutron-dominated accretion flow, only a single blob can be ejected within the lifetime of the accretion disk, and thus no collision will take place. X-ray emission from the accretion disk is expected, which will last only as long as the transient disk itself.
The expected duration, frequency and energetics in this scenario are consistent with FRBs, and the event rate of BH-WD mergers is compatible with that expected for non-repeating FRBs.