A uGMRT search for low-frequency persistent radio emission and afterglow from SGR 1935+2154

ATel #13773; Apurba Bera (NCRA-TIFR), Surajit Mondal (NCRA-TIFR), Poonam Chandra (NCRA-TIFR), Shriharsh Tendulkar (McGill University) and Jayanta Roy (NCRA-TIFR)
on 1 Jun 2020; 19:12 UT
Credential Certification: Apurba Bera ([email protected])

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The galactic magnetar SGR 1935+2154 is currently known to be in an active state and has shown flaring activity in the X-ray bands in recent past (Palmer et al., ATEL #13675; Younes et al., ATEL #13678; Barthelmy et al., GCN #27657; Nakahira et al., GCN #27661). Millisecond-duration bursts of radio emission were also observed from this magnetar by the CHIME, STARE2 and FAST telescopes (Scholz et al., ATEL #13681; Bochenek et al., ATEL #13684; Zhang et al., ATEL #13699). One of these radio bursts was nearly comparable to the fast radio bursts in intrinsic brightness.

We observed SGR 1935+2154 with the upgraded Giant Metrewave Radio Telescope (uGMRT) using the band-4 (550-750 MHz) and band-5 (1250-1450 MHz) systems to search for possible low-frequency radio afterglow or an associated persistent compact radio source similar to, albeit far fainter than, what has been observed for the repeating FRB 121102 (Chatterjee et al., Nature 541 (7635), 58-61). The observations were carried out during 2020 May 26, 10:30 UT — 2020 May 27, 02:30 UT (band-4) and 2020 May 28, 10:30 UT — 2020 May 29, 02:30 UT (band-5) with approximately 3 hours of on-source time in each observing session.

The radio images were made at high angular resolution, excluding the short baselines, to resolve out the extended emission coming from the supernova remnant SNR G057.2+00.8. The FWHM of the synthesized beams were ~4" in band-4 and ~2" in band-5. No compact radio emission was detected at the location of SGR 1935+2154, in either of the observing frequency bands. The 3σ upper limits on the flux densities of a possible associated compact source are ≈60 μJy at 0.65 GHz and ≈78 μJy at 1.37 GHz, as obtained from our observations.

Cut-outs (~15" × 15") of the images around the target (in PNG format) can be found at the link given below.

Link to image cut-outs