Publications associated with Four Pi Sky

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 Oxford University Press 456 (2016) 2321-2342

TE Hassall, T Muñoz-Darias, A Rowlinson, JD Swinbank, TD Staley, GJ Molenaar, B Scheers, M Pietka, G Heald, JP McKean, RP Breton, C Ferrari, J-M Grießmeier, V Heesen, M Iacobelli, P Jonker, G Kokotanekov, D Mulcahy, E Orru, M Pandey-Pommier, L Pratley, E Rol, HJA Röttgering, AMM Scaife, A Shulevski

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-min 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 -3.7 +14.7 × 10 -4 d -1 deg -2 , and a transient surface density of 1.5 × 10 -5 deg -2 , at a 7.9-Jy limiting flux density and ~10-min 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 60MHz as a function of observation duration.

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