Search and detection of low frequency radio transients
Johannes Norbertus Spreeuw · UvA-DARE (University of Amsterdam) · 2010
Chapter 1 Figure 1.1:Low Band Antennas as they are presently deployed.Netherlands, is presently (2010) being completed.There will be at least 18 core stations, 18 remote stations (in the Netherlands) and 8 international stations.These and other planned but yet not (fully) funded international stations are depicted in figure 1.4.The research plan for my Ph.D. position was written down in 2004 when only prototype stations, such as ITS (Wijnholds et al. 2004) and THEA, the Thousand Element Array (Bij de Vaate et al. 2003), were deployed.At that time it was anticipated that the roll-out of LO-FAR would be completed by the end of 2006.Originally, I would spend the first two years of my thesis (2005, 2006) on the development of code for the detection of transient sources and apply this code in the last two years (2007, 2008) to actual LOFAR data.The LOFAR science case (De Bruyn et al. 2002) mentioned the search for variable sources and "LOFAR as an All-Sky Monitor".Fast radio transients were to be discovered by processing visibilities and/or maps from short integrations in real time.Those maps would together cover a large patch of the sky.They could, in fact, be image cubes, with frequency as a third dimension.All data were to be recorded in full Stokes, so in principle four maps could be made from any integration.The message was clear: the datastream was huge and only conpressed forms of data could be stored indefinitely.Any code written to find transient sources in the LOFAR datastream would have to be fast, efficient and fully automated, performing only tasks that were obviously necessary.Although these requirements were well understood, essential directions were unclear at thend -image is the extension module to numarray written at STScI.The first command selects all pixels above the threshold and gives them the value 1.The second labels groups of pixels based on connectivity.By connectivity we mean the level of contiguity.By default we use 4-connectivity which means that groups of pixels only connected at corners are considered separate.This is not the case when one uses 8-connectivity.The last command uses 1 see www.lofar.org