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07-08-2018
Finding Pulsars in the LOFAR Imaging Survey
| Submitter: | Amy Tuson |
| Description: | Conventionally, pulsars have been discovered in blind, all-sky pulsation surveys. An alternative approach is to use radio continuum surveys in which pulsars show up as point sources. This proof of concept study has defined a set of selection criteria which can be used to discover new pulsars in the LOFAR Two-metre Sky Survey (LoTSS). LoTSS is an ongoing, deep, interferometric imaging survey of the Northern sky at a central frequency of 144 MHz. The survey resolution of 5" and sensitivity of 100uJy per beam will make it the deepest radio survey to date. Due to the fact pulsars are steep spectrum radio sources, with a mean spectral index of approximately -1.4+-1.0 for the known pulsar distribution, we have the unique opportunity to find pulsars missed by standard all-sky pulsation surveys. The figure above shows imaging and pulsation survey sensitivity limits and the typical range of pulsar spectral indices. Working with the LoTSS catalog of 320,000 sources, three pulsar properties can make it possible to distinguish them from other radio sources. Firstly, pulsar radio emission has a relatively high fraction of polarised flux. By searching through the preliminary catalog of 91 polarised LoTSS sources, no convincing pulsar candidates were found. Secondly is that pulsars have steep radio spectra. By computing spectral indices for LoTSS sources cross-matched to existing radio catalogs, such as WENSS, FIRST and NVSS, we found five pulsar candidates with spectral indices less than -1.5. Finally, scintillation causes variation of pulsar intensity as a function of both time and frequency. LoTSS sources were matched to sources in the TGSS catalog and we looked for those which showed a variation in total flux density. One source was measured as 6.9 times brighter in TGSS than LoTSS and this is a possible scintillating pulsar. We have been granted time with LOFAR to follow-up the six sources of interest and the search for pulsations started last week. |
| Copyright: | Amy Tuson |
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