The LOFAR pilot surveys for pulsars and fast radio transients

We have conducted two pilot surveys for radio pulsarsand fast transients with the Low-Frequency Array ( LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burstlimit and the discovery of two new pulsars. The first survey, the LOFARPilot PulsarSurvey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times. Each observation covered ~75 sq. deg using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFARTied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR"Superterp" stations, we formed 19 tied-array beams, together covering 4 sq. deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFARor any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFARcan efficiently carry out all-sky surveys for pulsarsand fast transients, and they set the stage for further surveying efforts using LOFARand the planned low-frequency component of the Square KilometerArray.