At UTC 2021-06-30-12:48:11.2 (2021-03-30.533462963), we found a fast radio burst as part of the ongoing search program at the Molonglo telescope (UTMOST).

Molonglo is a 1.6 km long East-West array (Bailes et al 2017, PASA, 34, 45) and was operating in drift-scan mode, pointing at the meridian at the time of detection. Source localisation is excellent in Right Ascension (5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma) (see Caleb et al 2017 MNRAS 468, 3746).

FRB20210630A was found during a blind FRB search programme in real-time using an automated GPU-accelerated/machine learning-based pipeline and the raw voltages were recorded for offline processing.

The optimal dispersion measure (DM) that maximizes the signal-to-noise ratio is: 943.7 pc cm^-3. The DM estimate of NE2001 model is ~78.7 pc cm^-3, and YMW16 model is ~59.7 pc cm^-3 at this position, resulting in an intergalactic excess of ~865  pc cm^-3. The upper limit on the DM-inferred redshift is thus z ~ 0.87.

An early estimate (lower limit) of the event’s apparent fluence is ~60 Jy ms (corrected for attenuation of the primary beam in the RA direction, but not in the Dec direction) with a detection signal-to-noise ratio = 10.

The most likely position is RA = 17:23:07.4, DEC=+07:51:42, J2000, Galactic: Gl = 29.9356 deg, Gb = 23.1882 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours, deg):

17.384378 5.300861
17.384511 5.661528
17.384650 6.022194
17.384789 6.382861
17.384933 6.743556
17.385078 7.104222
17.385225 7.464889
17.385375 7.825556
17.385531 8.186222
17.385686 8.546889
17.385844 8.907556
17.386006 9.268222
17.386169 9.628917
17.386336 9.989583
17.386506 10.35025

A formula describing the localisation arc is:

RA = 17.385376 + 4.22212*e-4(DEC – 7.825551) + 1.024401e-5*(DEC – 7.825551)**2

where RA is in hours, Dec is in deg, and is valid in the range Dec= [5.3, 10.35]

Follow-up observations of the FRB are encouraged.