title: Spectral properties of the nonspherically decaying radiation generated by a rotating superluminal source.
abstract: The focusing of the radiation generated by a polarization current with a superluminally rotating distribution pattern is of a higher order in the plane of rotation than in other directions. Consequently, our previously published [J. Opt. Soc. Am. A24, 2443 (2007)] asymptotic approximation to the value of this field outside the equatorial plane breaks down as the line of sight approaches a direction normal to the rotation axis, i.e., is nonuniform with respect to the polar angle. Here we employ an alternative asymptotic expansion to show that, though having a rate of decay with frequency (mu) that is by a factor of order mu(2/3) slower, the equatorial radiation field has the same dependence on distance as the nonspherically decaying component of the generated field in other directions: It, too, diminishes as the inverse square root of the distance from its source. We also briefly discuss the relevance of these results to the giant pulses received from pulsars: The focused, nonspherically decaying pulses that arise from a superluminal polarization current in a highly magnetized plasma have a power-law spectrum (i.e., a flux density S infinity mu(alpha)) whose index (alpha) is given by one of the values -2/3, -2, -8/3, or -4.
authors.affiliation: Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: Houshang
authors.initials: H
authors.lastname: Ardavan
authors.forename: Arzhang
authors.initials: A
authors.lastname: Ardavan
authors.forename: John
authors.initials: J
authors.lastname: Singleton
authors.forename: Joseph
authors.initials: J
authors.lastname: Fasel
authors.forename: Andrea
authors.initials: A
authors.lastname: Schmidt