A MILLISECOND INTERFEROMETRIC SEARCH FOR FAST RADIO BURSTS WITH THE VERY LARGE ARRAY

Abstract

Draft version May 8, 2015 Preprint typeset using L A TEX style emulateapj v. 12/16/11 A MILLISECOND INTERFEROMETRIC SEARCH FOR FAST RADIO BURSTS WITH THE VERY LARGE ARRAY Casey J. Law 1 , Geoffrey C. Bower 2 , Sarah Burke-Spolaor 3,4 , Bryan Butler 4 , Earl Lawrence 5 , T. Joseph W. Lazio 3 , Chris A. Mattmann 3 , Michael Rupen 6 , Andrew Siemion 1 , and Scott VanderWiel 5 Draft version May 8, 2015 ABSTRACT We report on the first millisecond timescale radio interferometric search for the new class of tran- sient known as fast radio bursts (FRBs). We used the Very Large Array (VLA) for a 166-hour, millisecond imaging campaign to detect and precisely localize an FRB. We observed at 1.4 GHz and produced visibilities with 5 ms time resolution over 256 MHz of bandwidth. Dedispersed images were searched for transients with dispersion measures from 0 to 3000 pc cm −3 . No transients were detected in observations of high Galactic latitude fields taken from September 2013 though October 2014. Ob- servations of a known pulsar show that images typically had a thermal-noise limited sensitivity of 120 mJy beam −1 (8σ; Stokes I) in 5 ms and could detect and localize transients over a wide field of view. Our nondetection limits the FRB rate to less than 7 × 10 4 sky −1 day −1 (95% confidence) above a fluence limit of 1.5 Jy ms. The VLA rate limit is consistent with past estimates when published flux limits are recalculated with a homogeneous definition that includes effects of primary beam attenua- tion, dispersion, pulse width, and sky brightness. This calculation revises the FRB rate downward by a factor of 2, giving the VLA observations a roughly 50% chance of detecting a typical FRB, assuming a pulse width of 3 ms. A 95% confidence constraint would require 600 hours of similar VLA observ- ing. Our survey also limits the repetition rate of an FRB to 2 times less than any known repeating millisecond radio transient. 1. INTRODUCTION Large radio pulsar surveys have revealed a new class of transient: the “fast radio burst” (FRB; Thornton et al. 2013). Several FRBs have now been detected in multi- beam pulsar surveys at the Parkes and Arecibo obser- vatories with a temporal width of 3 ms (Lorimer et al. 2007; Keane et al. 2011; Spitler et al. 2014; Ravi et al. 2014; Petroff et al. 2014a). FRBs are distinguished by their large dispersion measures (DMs). Observed DMs for FRBs range from 300 to 1100 pc cm −3 , which exceeds the expected Galactic value along their line of sight by as much as an order of magnitude. One possibility is that the large DM is induced by low density ionized plasma in the intergalactic medium (IGM), implying that they originate at distances up to and beyond redshifts of 1. Models for extragalactic FRBs must account for ra- dio luminosities higher than 10 12 Jy kpc 2 , far beyond that of Galactic neutron star transients (McLaughlin & Cordes 2003). Despite their unusual luminosity, their oc- currence rate is 10 4 sky −1 day −1 for fluences of ∼ 3 Jy ms (Thornton et al. 2013), which is about as frequent as core-collapse supernovae within roughly 1 Gpc. Sev- eral kinds of cataclysmic events have been proposed to produce FRBs, such as the births of black holes (Falcke & Rezzolla 2014) and the mergers of binary degenerate objects (Totani 2013; Kashiyama et al. 2013). Rapid 1 Dept of Astronomy and Radio Astronomy Lab, Univ. of California, Berkeley, CA 2 Academia Sinica Institute of Astronomy and Astrophysics, 645 N. A’ohoku Place,Hilo, HI 96720, USA 3 Jet Propulsion Laboratory, California Institute of Technol- ogy, Pasadena, CA 4 National Radio Astronomy Observatory, Socorro, NM 5 Los Alamos National Laboratory, Los Alamos, NM 6 NRC Herzberg, Penticton, BC, Canada radio follow-up of gamma-ray bursts have found no ev- idence for an association with FRBs (Bannister et al. 2012; Palaniswamy et al. 2014). Very rare repeating sources, such as extremely energetic pulses from neutron stars, may also be detectable at extragalactic distances (Cordes & Wasserman 2015; Pen & Connor 2015). If in fact extragalactic, FRBs have huge potential in understanding the intergalactic medium and measuring cosmological parameters. The dispersion of an extra- galactic transient measures the electron column density, a good proxy for baryonic mass. For FRBs of known dis- tance, the measured DM will make novel measurements of the IGM properties and test models of galaxy forma- tion (Macquart & Koay 2013; McQuinn 2014). Even in the local universe, the dispersion measure of any pulses from outside our Galaxy would measure the baryon con- tent in the diffuse halo to potentially solve the “missing baryon problem” (Bregman 2007; Fang et al. 2013). At cosmological distances, FRBs could test models for dark energy in a new way (Deng & Zhang 2014). The story of the FRB is complicated by the concur- rent discovery of a new class of terrestrial interference known as perytons (Burke-Spolaor et al. 2011). Pery- tons are impulsive radio transients with a width of tens of ms and an apparent DM of a few hundred, partially overlapping with characteristics expected of extragalac- tic radio transients (Kocz et al. 2012; Bagchi et al. 2012). Recently, Petroff et al. (2015) showed that perytons de- tected at the Parkes observatory are most likely caused by a microwave oven at the visitor’s center. That work presents a very specific physical model for perytons that cannot explain known FRBs detected at Parkes. How- ever, it also highlights the difficulty in interpreting the signal from a single-dish telescope. Kulkarni et al. (2014) notes that an interferometer like the VLA can more eas-