| The movie shows an image of the entire sky using only the super-terp LOFAR stations. Data from one 7 minute snapshot of the MSSS HBA survey were used to generate a movie frame every 3.5 seconds. The integration time of MSSS is 2 seconds, and in each frame multiple airy patterns can be seen, across the entire sky.
The KNMI archive shows the meteorological conditions above the Netherlands at the time of the observation. We can see that a large storm was in progress, with multiple recorded lightning events. Since they are in the near field of LOFAR, the discharges (which generate radio waves) show up as de-focused radio sources. Multiple events are visible in the image; since a lightning lasts a fraction of a second, LOFAR detects many of them in 2 seconds of integration. Some events persist in the image for longer than a second.
A time-frequency view of one super-terp baseline shows the events; they are detected on all the baselines of the observing run, varying in intensity.
Much can be deduced from data-sets like this. Paralactic determination of the distance to the point in the cloud which generated the lightning is possible (by near-field imaging for example) and consequently a 3D model of the storm front can be produced based on that distribution. Details about the physics and how it is related to what an interferometer detects are also intriguing; are we seeing single events, or multiple reflections of a single one? Or, do we detect the ionization trail of the lightning events? LOFAR is capable of higher time resolution observations. Correlating and imaging those data sets may be of use. Also, our data archives certainly contain more events like the one presented here and are worth exploring.
LOFAR is a multi-faceted radio astronomy toolkit with many possibilities we can exploit.
Credit: Aleksandar Shulevski, Wilfred Frieswijk, the LOFAR Science Support group, Michiel Brentjens, the MSSS team (Heald et al. 2015)