Low-frequency follow-up of SGR 1935+2154 with the uGMRT

ATel #14946; Shubham Singh (NCRA-TIFR), Jayanta Roy (NCRA-TIFR)
on 30 Sep 2021; 05:31 UT
Credential Certification: Jayanta Roy (jroy@ncra.tifr.res.in)

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Following multiple triggers from Fermi Gamma-Ray Burst Monitor (GBM) over a period of 2021 September 6 to 10 (ATel #14907) and detection of 20 burst candidates with The Neutron star Interior Composition Explorer (NICER) on 2021 September 11 and 12 (ATel #14916) from Galactic magnetar SGR 1935+2154, we observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) on 2021 September 17. During the 2020 April episodes of X-ray flares, radio millisecond bursts from this source were detected with the CHIME (CHIME/FRB Collaboration 2020), STARE2 (Bochenek et al. 2020) and FAST ((Zhang et al. 2020). We observed SGR 1935+2154 with the uGMRT simultaneously in band-3 (300-500 MHz) and band-4 (550-750 MHz) on 2021 September 17 for a duration of two hours (17:54:17 - 18:34:49 UT and 18:45:57 - 20:07:49 UT). The full array was divided into two sub-arrays with 8 and 14 antennas each in band-3 and band-4 respectively. In band-4 filterbank was recorded with 8192 channels over 200 MHz band-width sampled at 327.68 micro-second time-resolution. The band-3 data was coherently dedispersed at a DM of 332.7 pc cm^-3 producing a filterbank having 2048 channels over 200 MHz at a time-resolution of 40.96 micro-second. We dedispersed the data at the magnetar DM and performed periodicity search using Fast Folding Algorithm (FFA, Morello et al. 2020) and single pulse search using PRESTO (Ransom et al. 2001). We did not find any radio emission, either pulsation (with periodicity of 3.24s, Israel et al. 2014) or burst above a significance of 7-sigma. We use a nearby known pulsar J1954+2923 to calibrate the gain of the phased array beam in band-3 and band-4 observations to estimate the noise. The 7-sigma upper limit of flux density for periodic signal is 0.4 mJy for both band-3 and band-4 (assuming 5% duty-cycle). For burst events, 7-sigma upper limit on fluence is around 3 Jy-ms for band-3 and band-4. We thank the staff of the GMRT who have made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.