The Rrat Trap: Interferometric Localization of Radio Pulses From J0628+0909

Abstract

We present the first blind interferometric detection and imaging of a millisecond radio transient with an observation of transient pulsar J0628+0909. We developed a special observing mode of the Karl G. Jansky Very Large Array (VLA) to produce correlated data products (i.e., visibilities and images) on a time scale of 10 ms. Correlated data effectively produce thousands of beams on the sky that can localize sources anywhere over a wide field of view. We used this new observing mode to find and image pulses from the rotating radio transient (RRAT) J0628+0909, improving its localization by two orders of magnitude. Since the location of the RRAT was only approximately known when first observed, we searched for transients using a wide-field detection algorithm based on the bispectrum, an interferometric closure quantity. Over 16 minutes of observing, this algorithm detected one transient offset roughly 1 ′ from its nominal location; this allowed us to image the RRAT to localize it with an accuracy of 1. ′′ 6. With a priori knowledge of the RRAT location, a traditional beamforming search of the same data found two, lower significance pulses. The refined RRAT position excludes all potential multiwavelength counterparts, limiting its optical luminosity to L i ′ < 1.1 × 10 31 erg s −1 and excluding its association with a young, luminous neutron star.

Science with the Murchison Widefield Array

“…They do appear as repeating transients and so many of the techniques required will be similar to those for other transients (Lorimer et al 2007; Keane et al 2012). We will also explore the bispectrum techniques of Law & Bower (2012), which enable computationally simple searches for dispersed pulses at the expense of S/N, although the small area of each antenna leads to a low S/N on each baseline, making such searches (Law et al 2012) significantly less sensitive than traditional beamforming.…”