Kavli Affiliate: Kiyoshi W. Masui
| First 5 Authors: Utkarsh Giri, Bridget C. Andersen, Pragya Chawla, Alice P. Curtin, Emmanuel Fonseca
| Summary:
The bright millisecond-duration radio burst from the Galactic magnetar SGR
1935+2154 in 2020 April was a landmark event, demonstrating that at least some
fast radio burst (FRB) sources could be magnetars. The two-component burst was
temporally coincident with peaks observed within a contemporaneous short X-ray
burst envelope, marking the first instance where FRB-like bursts were observed
to coincide with X-ray counterparts. In this study, we detail five new radio
burst detections from SGR 1935+2154, observed by the CHIME/FRB instrument
between October 2020 and December 2022. We develop a fast and efficient
Bayesian inference pipeline that incorporates state-of-the-art Markov chain
Monte Carlo techniques and use it to model the intensity data of these bursts
under a flexible burst model. We revisit the 2020 April burst and corroborate
that both the radio sub-components lead the corresponding peaks in their
high-energy counterparts. For a burst observed in 2022 October, we find that
our estimated radio pulse arrival time is contemporaneous with a short X-ray
burst detected by GECAM and HEBS, and Konus-Wind and is consistent with the
arrival time of a radio burst detected by GBT. We present flux and fluence
estimates for all five bursts, employing an improved estimator for bursts
detected in the side-lobes. We also present upper limits on radio emission for
X-ray emission sources which were within CHIME/FRB’s field-of-view at trigger
time. Finally, we present our exposure and sensitivity analysis and estimate
the Poisson rate for FRB-like events from SGR 1935+2154 to be
$0.005^{+0.082}_{-0.004}$ events/day above a fluence of $10~mathrm{kJy~ms}$
during the interval from 28 August 2018 to 1 December 2022, although we note
this was measured during a time of great X-ray activity from the source.
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