LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole

A. J. Stewart (1) , R. P. Fender (2) , J. W. Broderick (2) , T. E. Hassall (3) , T. Muñoz-Darias (4) , A. Rowlinson (5) , J. D. Swinbank (6) , T. D. Staley (7) , G. J. Molenaar (6) , B. Scheers (6) , T. L. Grobler (8) , M. Pietka (9) , G. Heald (5) , J. P. Mckean (5) , M. E. Bell (10) , A. Bonafede (11) , R. P. Breton (3) , D. Carbone (12) , Y. Cendes (6) , A. O. Clarke (3) , Stéphane Corbel (13, 14) , F. De gasperin (15) , J. Eislöffel (16) , H. Falcke (17, 5) , C. Ferrari (18) , Jean-Mathias Griessmeier (14, 19) , M. J. Hardcastle (20) , V. Heesen (4) , J. W. T. Hessels (12) , A. Horneffer (21) , M. Iacobelli (22) , P. Jonker (23) , A. Karastergiou (9) , G. Kokotanekov (6) , V. I. Kondratiev (5) , M. Kuniyoshi (21) , C. J. Law (6) , J. Van leeuwen (5) , S. Markoff (6) , J. C. A. Miller-Jones (24) , D. Mulcahy (3) , E. Orru (5) , M. Pandey-Pommier (25) , L. Pratley (26) , E. Rol (6) , H. J. A. Röttgering (22) , A. M. M. Scaife (4) , A. Shulevski (27) , C. A. Sobey (21) , B. W. Stappers (3) , C. Tasse (28, 29) , A. J. Van der horst (30) , S. Van velzen (17) , R. J. Van weeren (31) , R. A. M. J. Wijers (32) , R. Wijnands (6) , M. Wise (6, 5) , P. Zarka (33, 34, 14) , A. Alexov (5) , J. Anderson (35) , A. Asgekar (5) , I. M. Avruch (36) , M. J. Bentum (5) , G. Bernardi (37) , P. Best (38) , F. Breitling (39) , M. Brüggen (11) , H. R. Butcher (5) , B. Ciardi (40) , J. E. Conway (41) , A. Corstanje (17) , E. De geus (5) , A. Deller (5) , S. Duscha (5) , W. Frieswijk (5) , M. A. Garrett (22, 5) , A. W. Gunst (5) , M. P. Van haarlem (5) , M. Hoeft (16) , J. Hörandel (17) , E. Juette (42) , G. Kuper (5) , M. Loose (5) , P. Maat (5) , R. Mcfadden (5) , D. Mckay-Bukowski (43) , J. Moldon (5, 44) , H. Munk (5) , M. J. Norden (5) , H. Paas (45) , A. G. Polatidis (5) , D. Schwarz (46) , J. Sluman (5) , O. Smirnov (8) , M. Steinmetz (47) , S. Thoudam (17) , M. C. Toribio (48) , R. Vermeulen (5) , C. Vocks (39) , S. J. Wijnholds (5) , O. Wucknitz (49) , S. Yatawatta (5)

1 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
2 University of Southampton
3 Jodrell Bank Centre for Astrophysics
4 School of Physics and Astronomy [Southampton]
5 ASTRON - Netherlands Institute for Radio Astronomy
6 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
7 Oxford Astrophysics
8 Rhodes University, Grahamstown
9 Oxford Astrophysics
10 CSIRO Astronomy and Space Science
11 Jacobs University [Bremen]
12 UvA - University of Amsterdam [Amsterdam]
13 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
14 USN - Unité Scientifique de la Station de Nançay
15 UHH - Universität Hamburg
16 TLS - Thüringer Landessternwarte Tautenburg
17 Radboud University [Nijmegen]
18 Département de Géologie
19 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
20 UH - University of Hertfordshire [Hatfield]
21 MPIFR - Max-Planck-Institut für Radioastronomie
22 Leiden Observatory [Leiden]
23 IMAPP - Institute for Mathematics, Astrophysics and Particle Physics
24 Curtin University [Perth]
25 CRAL - Centre de Recherche Astrophysique de Lyon
26 Victoria University of Wellington
27 Kapteyn Astronomical Institute [Groningen]
28 SKA South Africa
29 GEPI - Galaxies, Etoiles, Physique, Instrumentation
30 GW - Department of Mathematics [George Washington University]
31 CfA - Harvard-Smithsonian Center for Astrophysics
32 Anton Pannekoek Institute for Astronomy
33 OP - Observatoire de Paris - Site de Paris
34 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
35 Institute for Mathematics Applied to Geoscience
36 SRON - SRON Netherlands Institute for Space Research
37 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
38 University of Edinburgh
39 AIP - Leibniz-Institut für Astrophysik Potsdam
40 Max Planck Institute for Astrophysics
41 Onsala Space Observatory, Dept. of Radio and Space Science, Chalmers University of Technology
42 Ruhr-Universität Bochum [Bochum]
43 University of Oulu
44 Departament d'Astronomia i Meteorologia [Barcelona]
45 Center for Information Technology CIT
46 Interactions Son Musique Mouvement
47 DSMZ - Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures
48 Finca El Encin
49 AlfA - Argelander-Institut für Astronomie

We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-minute snapshots, each covering 175 deg^2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15-25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of 3.9 (+14.7, -3.7) x 10^-4 day^-1 deg^-2, and a transient surface density of 1.5 x 10^-5 deg^-2, at a 7.9-Jy limiting flux density and ~10-minute time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration.

Keywords: instrumentation: interferometers – techniques: image processing – radio continuum: general.

Domains: Sciences of the Universe [physics]

A. J. Stewart, R. P. Fender, J. W. Broderick, T. E. Hassall, T. Muñoz-Darias, et al.. LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole. Monthly Notices of the Royal Astronomical Society, 2016, 456 (3), pp.2321-2342. ⟨10.1093/mnras/stv2797⟩. ⟨insu-01321898⟩