NS and Asteroids/Comets

From FRB Theory Wiki
Jump to navigation Jump to search

Summary Table
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
Collision/ Interaction NS and Asteroids/ Comets Single Mag. reconnection Curv. Yes -- -- -- -- Yes (probably too faint to detect) Yes (probably too faint to detect) -- -- http://adsabs.harvard.edu/abs/2015ApJ...809...24G None

Definitions: LF Radio (3 MHz to 3 GHz); HF Radio (3 GHz to 30 GHz); Microwave (30 to 300 GHz)

Model Description

A small body, such as a comet or asteroid, captured by the gravitational potential of a NS will free-fall toward it, becoming radially elongated until it exceeds its Roche limit and breaks apart. The fragments are compressed by the gravitational acceleration and the magnetic field of the NS, resulting in leading and lagging portions with the same velocity. In order to nullify the effects evaporation and ionisation may have, the body must have a sufficiently large mass and shear, and is thus predicted to be of Fe-Ni composition. Infalling matter would be confined to the poles of the NS by strong magnetic stresses, creating an accretion column. If the accretion column travels through a region where electrostatic equilibrium has been disturbed, particles are accelerated to yield γ-ray emission. When the matter impacts the NS, an expanding plasmoid fireball will be launched along the magnetic field lines. Magnetic reconnection at the collision site accelerates e+/e− pairs within the plasma-fan to ultra-relativistic speeds, resulting in coherent curvature emission.

Observational Constraints

The event rate associated with such a theory has been shown to be consistent with the other predictions and, notably, the impact timescale between the leading and tailing fragments is roughly consistent with the brevity of FRB signals. The model predicts X-ray emission and γ-ray emission from inverse Compton scattering, however these are probably too faint to be observed.