FRB20221128A found by UTMOST-NS

ATel #15783; A. Mandlik (Swinburne University of Technology, "SUT"), M. Bailes (SUT), A. Deller (SUT), C. Flynn (SUT), V. Gupta (CSIRO), A. Jameson (SUT), T. Bateman (SUT), M. Caleb (University of Sydney, "USyd"), D. Campbell-Wilson (USyd), C. Day (McGill), L. Dunn (University of Melbourne, "UMelb"), W. Farah (University of California, Berkeley), A. J. Green (USyd), G. Howitt (UMelb), Y. S. C. Lee (UMelb), M. E. Lower (CSIRO), A. Melatos (UMelb), P. Meyers (UMelb), D. C. Price (Curtin), R. Sekhri (Alphington Grammar School), A. Sutherland (USyd), G. Torr (SUT), G. Urquhart (SUT), V. Venkatraman Krishnan (Max-Planck-Institut fuer Radioastronomie)
on 1 Dec 2022; 04:54 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Chris Flynn (cflynn@swin.edu.au)

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At UTC 2022-11-28-17:02:22.72 (2022-11-28.70999), we discovered a Fast Radio Burst (FRB) with the revamped North-South arm ("UTMOST-NS") of the Molonglo Observatory Synthesis Telescope (owned and operated by the University of Sydney).

UTMOST-NS is a 1.6 km long North-South array, restored to full operations in 2019-2021 (Deller and Flynn, 2020). It has 45 MHz of usable bandwidth contained within a 50 MHz of sampled band split into 512 channels and centred on 835.25 MHz. There are 66 dual polarisation stations spread across the arm, of which 36 were operational at the time of detection. It was operating in drift-scan mode with pointing centred on the meridian at the time of detection. Due to the one-dimensional nature of the detector, localisation precision is high in Declination (~1 arcmin at 1-sigma) but low in Right Ascension (~2 deg at 1-sigma) (Mandlik et al 2022 in prep).

FRB20221128A was identified during a blind FRB search programme in real-time using an automated GPU-accelerated search pipeline, which makes use of a novel Convolutional Neural Network-based, spatially-aware pipeline ("Adjacent Beam Classifier", or ABC) to distinguish real astrophysical signals from radio frequency interference in real time. This triggered a voltage dump within 12 sec of the FRB arrival time, enabling 1.3 seconds of raw voltage data centred on the FRB to be recorded from each station for offline processing. This saved voltage data completely contains the dispersed FRB signal (which is spread across ~362 ms from the top to the bottom of the band).

The optimal dispersion measure (DM) that maximises the signal-to-noise ratio is 505.6 +/- 1.8 pc cm^-3. The NE2001 model (Cordes and Lazio, 2002) predicts a total Milky Way DM along this sight-line of ~400 pc cm^-3, while the YMW16 model (Yao, Manchester, and Wang, 2017) predicts ~250 pc cm^-3. If, in line with typical practice, we assume a contribution from the Milky Way halo of 50 pc cm^-3 and a further 50 pc cm^-3 contribution from the FRB host galaxy, the predicted intergalactic excess DM could thus range from ~0 to ~150 pc cm^-3, making FRB20221128A likely to originate from a relatively nearby galaxy.

An early estimate (lower limit) of the event's apparent fluence is ~130 +/- 30 Jy ms (corrected for attenuation of the primary beam in the NS direction, but not in the EW direction), width ~5.5 +/- 0.7 ms, with a detection signal-to-noise ratio = 9.0.

The most likely position is RA = 07:30(10), DEC = -41:32(1), J2000 which corresponds to Galactic coordinates: Gl = 177.1 deg, Gb = 24.45 deg.

For the dynamic spectrum of the FRB, follow this link

The UTMOST team acknowledges the generous support of the Mount Cuba Astronomical Foundation which contributed to the UTMOST-NS upgrade. This research was supported by Australian Research Council grants CE110001020, FT150100415 and FL150100148.

References

Cordes and Lazio, 2002, arXiv:0207156
Deller and Flynn, 2020, Nature Astronomy, 4, 292
Yao, Manchester, and Wang, 2017, 835, 29