Electromagnetic Waves Generated by Null Cosmic Strings Passing Pulsars

TL;DR

This paper analyzes how null cosmic strings passing near pulsars generate electromagnetic waves, potentially causing observable luminosity variations that could serve as signatures of such strings in the universe.

Contribution

The authors develop an analytic approximation for electromagnetic wave asymptotics caused by null cosmic strings and calculate radiation fluxes for different source types.

Findings

Radiation flux depends on magnetic moment orientation.

Peak power can be significant near pulsars and magnetars.

Luminosity variations may serve as observational signatures.

Abstract

Null cosmic strings disturb electromagnetic (EM) fields of charged sources and sources with magnetic moments. As has been recently shown by the authors, these perturbations result in a self-force acting on the sources and create EM waves outgoing from the sources. We develop an analytic approximation for asymptotic of the EM waves at the future null infinity and calculate radiation fluxes for sources of the both types. For magnetic-dipole-like sources the radiation flux depends on orientation of the magnetic moment with respect to the string. Estimates show that the peak power of the radiation can be quite large for null strings moving near pulsars and considerably large in case of magnetars. The string generated variations of the luminosities of the stars can be used as a potential experimental signature of null cosmic strings.