A new population of radio transient neutron stars

Abstract

The small fields-of-view of radio telescopes and the short observation times of most radio surveys mean that the transient radio sky is relatively unexplored compared to other regions of the electromagnetic spectrum ( Cordes et al., 2004b). In the largest-scale search ever performed for transient radio sources, we have discovered a new class of neutron stars ( McLaughlin et al., 2006). The eleven new sources are characterized by single dispersed radio bursts with durations between 2 and 30 ms, 1400 MHz peak flux densities from 0.1 to 3.6 Jy and average intervals between events ranging from 4 min to 3 h. So far, no periodicities have been detected in their emission using standard search techniques ( Lorimer and Kramer, 2005), and radio emission is only detectable from these objects for a total of typically less than 1 s per day. However, through an arrival-time analysis of the bursts, we have identified periodicities in the range of 0.4–7 s for ten of the eleven sources. Period derivatives have been measured for three sources; one with a spin period of 4.3 s has an inferred surface dipole magnetic field strength of 5 × 10 13 G, perhaps indicating a close relationship between this source and the high-energy magnetars ( Woods and Thompson, 2006). Because of the unique properties of this new population, we call them Repeating RAdio Transients, or RRATs. Our discoveries pose challenges to standard models of pulsar emission physics, substantially increase the estimated population of active Galactic neutron stars and highlight the rich variety of radio transient sources that will be discovered by future large-scale transient searches with instruments such as the Square Kilometer Array ( Carilli and Rawlings, 2004).