Parkes ultra-wideband observations of SGR 1935+2154 during recent epochs of high activity
ATel #15172; M. E. Lower (CSIRO Space and Astronomy), R. M. Shannon (Swinburne University of Technology) and P. Kumar (Swinburne University of Technology)
on 21 Jan 2022; 05:04 UT
Credential Certification: Marcus Lower (mlower@swin.edu.au)
Subjects: Radio, Gamma Ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar, Magnetar
Following reports of renewed high-energy activity of magnetar SGR 1935+2154 in September 2021 (GCN #30806) and January 2022 (GCN #31445), we conducted 10425 s and 9416 s target of opportunity observations of the source starting at UTC 2021-09-11-09:04:54 and UTC 2022-01-14-01:09:33 respectively, with the CSIRO Parkes 64-m radio telescope (Murriyang). We recorded pulsar search-mode data via the Medusa backend using the Ultra-Wideband Low receiver system (central frequency of 2368 MHz, 3328 MHz of bandwidth; Hobbs et al. 2020) with 0.5 MHz-wide frequency channels and 64 microsecond sampling. These data were coherently dedispersed at a DM of 332.72 pc/cc.
The data were searched for single pulses and fast radio bursts using the Heimdall (Barsdell 2012) and Fetch (Agarwal et al. 2020) packages over a DM range of 100-1100 pc/cm^3, employing a tiered sub-band strategy as described in Kumar et al. (2021). No significant single-pulse candidates of astrophysical origin were identified in either observation. Hence, we constrain the the fluence of 1 ms wide single pulses down to be less than ~0.15 Jy ms for broadband (3.3 GHz bandwidth) pulses or ~1 Jy ms for narrowband (64 MHz bandwidth) pulses during our observations.
We note that two high-energy bursts were recorded by Fermi Gamma-Ray Burst Monitor at UTC 2021-09-11-10:42:51.85 and UTC 2021-09-11-11:53:57.29 (GCN #30831), both of which overlap with our first Parkes observation. Neither burst appears to have been accompanied by a radio counterpart.
We also searched for signs of low-level pulsed emission by folding the data at the magnetar rotation period. No evidence for a periodic signal was found in a search spanning +/- 1 ms from the nominal period of the magnetar and +/- 25 pc/cc around its previously reported dispersion measure. Using the radiometer equation with an assumed 10 percent duty cycle and limiting S/N of 7, we place upper limits on the 2368 MHz flux of SGR 1935+2154 of 4.9 uJy on 2021-09-11 and 5.2 uJy on 2022-01-14.
We would like to thank the ATNF staff, in particular James Green, for allocating the observation time.
References:
Agarwal, D., et al., FETCH: A deep-learning based classifier for fast transient classification, MNRAS, 479, 1661 (2020)
Barsdell, B. R., Advanced Architectures for Astrophysical Supercomputing PhD thesis, Swinburne Univ. Technology (2012)
Hobbs, G., et al., An ultra-wide bandwidth (704 to 4032 MHz) receiver for the Parkes radio telescope, PASA, 37, e012 (2020)
Kumar, P., et al., Extremely band-limited repetition from a fast radio burst source, MNRAS, 500, 2525 (2021)
