Properties of the CHIME/FRB 2020 October 8 detections of SGR 1935+2154

ATel #14080; Ziggy Pleunis (McGill University) for the CHIME/FRB Collaboration
on 9 Oct 2020; 21:45 UT
Credential Certification: Shriharsh Tendulkar (shriharsh@physics.mcgill.ca)

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We report on refined burst parameters for three radio bursts from Galactic magnetar SGR 1935+2154 detected by CHIME/FRB and announced in ATel #14074.

Refined arrival times of the three bursts are 02:23:41.976, 02:23:43.922 and 02:23:44.871 UTC on 2020 October 8. These arrival times are referenced at the CHIME/FRB location (topocentric) and at a frequency of 400.1953125 MHz. The DM constant used is k_DM = 1.0 / 2.41e-4 MHz^-2 pc cm^-3 s^-1. A preliminary model of the first, and brightest, burst of the three was obtained from fitting a Gaussian profile convolved with an exponential scattering tail to the intensity data (see, e.g., CHIME/FRB Collaboration 2019 Nature, 566, 230--234, for details). This results in a preliminary best-fit DM of 332.658+/-0.002 pc cm^-3, an intrinsic width of 0.26+/-0.01 ms and a scattering timescale of 0.64+/-0.02 ms (at 600 MHz). We have fixed these best-fit DM and scattering timescale values for all three bursts to calculate the times-of-arrival. The uncertainties on the arrival times are approximately 1 ms.

The 400--800-MHz fluences of the three bursts are 900+/-160, 9.2+/-1.6, 6.4+/-1.1 Jy ms, respectively. Fluences were calculated using the saved intensity data from the beam closest to the known position of the magnetar, and scaled from a calibrator source (Tau A) to the radio bursts using the CHIME/FRB beam model. The fluences were then corrected by a factor 1.06 to account for the spectral leakage that was missed in the fluence calculation (see CHIME/FRB Collaboration et al. 2020, arXiv:2005.10324). Uncertainties are derived from applying different calibrators to each other (see, e.g., CHIME/FRB Collaboration et al. 2019 Nature, 566, 235-238, for details). These fluences are consistent with the upper limits derived from non-detections of the same bursts with the STARE2 telescope, as reported in ATel #14077.

Full details of burst modelling of these bursts will be presented in a forthcoming paper.