Transient study using LoTSS – framework development and preliminary results

Monthly Notices of the Royal Astronomical Society, vol. 531, pp. 4805–4822

Abstract

ABSTRACT We present a search for transient radio sources on time-scales of seconds to hours at 144 MHz using the LOFAR Two-metre Sky Survey (LoTSS). This search is conducted by examining short time-scale images derived from the LoTSS data. To allow imaging of LoTSS on short time-scales, a modern imaging procedure and fast filtering strategy are introduced. This includes sky model source subtraction, no cleaning or primary beam correction, a simple source finder, fast filtering schemes, and source catalogue matching. This new strategy is first tested by injecting simulated transients, with a range of flux densities and durations, into the data. We find the limiting sensitivity to be 113 and 6 mJy for 8 s and 1 h transients, respectively. The new imaging and filtering strategies are applied to 58 fields of the LoTSS survey, corresponding to LoTSS-DR1 (2 per cent of the survey). One transient source is identified in the 8 s and 2 min snapshot images. The source shows 1 min duration flare in the 8 h observation. Our method puts the most sensitive constraints on/estimates of the transient surface density at low frequencies at time-scales of seconds to hours; <4.0 × 10−4 deg−2 at 1 h at a sensitivity of 6.3 mJy; 5.7 × 10−7 deg−2 at 2 min at a sensitivity of 30 mJy; and 3.6 × 10−8 deg−2 at 8 s at a sensitivity of 113 mJy. In the future, we plan to apply the strategies presented in this paper to all LoTSS data.

Authors 6

1. Iris de Ruiter corresponding

   University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

2. Z.S. Meyers

   Friedrich-Alexander-Universität Erlangen-Nürnberg · Deutsches Elektronen-Synchrotron DESY

   Affiliation as printed

   Deutsches Elektronen-Synchrotron DESY , Platanenallee 6, D-15738 Zeuthen , Germany

   Erlangen Center for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nuremberg , D-91058 Erlangen , Germany

3. A. Rowlinson

   University of Amsterdam · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, the Netherlands Institute for Radio Astronomy , Postbus 2, NL-7990 AA Dwingeloo , the Netherlands

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

4. T. W. Shimwell Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, the Netherlands Institute for Radio Astronomy , Postbus 2, NL-7990 AA Dwingeloo , the Netherlands

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

5. David Ruhe

   University of Amsterdam

   Affiliation as printed

   AI4Science (AMLab), Informatics Institute, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

6. Ralph A. M. J. Wijers

   University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands