MeerKAT observation of the radio magnetar candidate Swift J1818.0-1607

ATel #13562; Marcus E. Lower (Swinburne University of Technology, SUT), Sarah Buchner (South African Radio Astronomy Observatory, SARAO), Simon Johnston (CSIRO Astronomy and Space Science), Aditya Parthasarathy (Max-Planck-Institut fuer Radioastronomie), Marisa Geyer (SARAO) and Matthew Bailes (SUT) on behalf of the MeerTime collaboration
on 17 Mar 2020; 23:52 UT
Credential Certification: Marcus Lower (mlower@swin.edu.au)

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Following the reported detection and confirmation of pulsed radio emission from the magnetar candidate Swift J1818.0-1607 (GCN #27373; ATel #13553; ATel #13554), we conducted a 15 minute observation of the pulsar with the MeerKAT array at UTC 2020-03-16-09:31 as part of the MeerTime thousand-pulsar-array project (Johnston et al. 2020).

We recorded simultaneous pulsar search-mode and fold-mode data that was coherently dedispersed with a DM of 706 pc cm^-3 at a central frequency of 1283 MHz with 856 MHz bandwidth. After excising frequency channels affected by radio-frequency interference and averaging in time, frequency and polarisation, we obtain a S/N ~ 295. This corresponds to an integrated flux density of approximately 0.9 mJy at 1400 MHz.

To take into account the scatter broadening toward the bottom of the MeerKAT band, we averaged the data into 64 subbands that are independently fit by scatter broadened Gaussian templates, the centroids of which return a scatter corrected DM of 699.5 +/- 0.3 pc cm^-3, and a characteristic scattering time of 44 +/- 3 ms at 1 GHz.

We also obtain a barycentric spin frequency of 0.7334116(2) Hz at MJD 58924.398 assuming the Swift-XRT position (GCN #27373).

Diagnostic plots showing the observed pulse profiles as functions of time, frequency and total intensity are available at the attached link. Assuming there is negligible profile evolution across the band, the reduction in S/N at higher frequencies implies this magnetar candidate has a steep spectral index (consistent with what is reported in ATel #13560).

Reference: Johnston, S., et al., The Thousand-Pulsar-Array programme on MeerKAT - I. Science objectives and first results, MNRAS, 493, 3608 (2020)

MeerKAT observation of Swift J1818.0-1607