ASKAP/CRACO and Murriyang detection of a new repeating fast radio burst source FRB20261031B

ATel #18153; Pavan Uttarkar (Max Planck Institute for Radio Astronomy, MPIfR), Ryan Shannon (Swinburne University of Technology, SUT), Alexa Gordon (Caltech), Ziteng Wang (International Centre for Radio Astronomy Research, Curtin University), Apurba Bera (ASTRON), Wen-fai Fong (Northwestern/CIERA), Adam Deller (SUT), Kelly Gourdji (CSIRO Space & Astronomy), Marcin Glowacki (University of Edinburgh, Curtin, IDIA), Joscha Jahns-Schindler (SUT), Marcus E. Lower (SUT), Pravir Kumar (MPIfR), Adarsh Bathula (SUT), on behalf of the ASKAP/CRAFT collaboration
on 11 Nov 2026; 19:14 UT
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Credential Certification: Pravir Kumar (pkumar@mpifr-bonn.mpg.de)

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We report on the discovery of a repeating fast radio burst (FRB) source, FRB 20261031B. The source was discovered using CRAft COherent (ASKAP/CRACO) backend as part of the Commensal Real-time ASKAP Fast Transient Survey. A repeat burst was detected in observations ~1 hr after the initial burst. The source was detected at a dispersion measure (DM) of 581.4 pc cm^-3. These bursts (listed as B1 and B2 below) were detected at an S/N of 14 and 11, respectively, at a central frequency of 943 MHz. The bursts were detected commensally in a 10 hr Evolutionary Map of the Universe observation.

The source was localised to sub-arcsec precision (R.A. = 01:15:25.41(6), DEC = -80:39:18.6(6), J2000) using voltages triggered by CRACO and processed with the CRAFT Effortless Localisation and Enhanced Burst Inspection Pipeline (CELEBI). We identified the putative host of FRB 20261031B in the Dark Energy Camera Legacy Survey DR11 (RA=01:15:24.85 Dec=-80:39:18.5; see Figure 1). The host has a catalogued r-band magnitude of 23.2, and a photometric redshift z=0.6+/-0.1 (median and 68% CI). If the photo-z is accurate, it would indicate that FRB 20261031B is a repeating FRB with the highest known redshift.

Motivated by the discovery of a repeating source, we triggered follow up observations with Murriyang, the 64-m Parkes radio telescope, using the Ultra-Wideband Low receiver (UWL). Search-mode data from UWL were recorded at 128 microsecond temporal resolution and 0.5 MHz spectral bandwidth, covering 3328 MHz bandwidth, with full Stokes polarimetry. The data were searched for FRBs using a Heimdall-FETCH based multi-tiered sub-banded search pipeline to search for single pulses. We observed the source for a total of ~11 hours, spread equally between two observing sessions on 3rd and 5th November 2026. We detected a repeat burst (listed as B3 below) on 5th November 2026 with an S/N of 61.4, confirming that the source has remained active. We measure the rotation measure (RM) of the UWL-detected burst to be 22.1 +/- 0.1 rad m^-2 using the brute force method in rmfit.

The dynamic spectra of the discovery burst from ASKAP/CRACO and Murriyang are shown in Figures 2 and 3, respectively. The topocentric arrival times of the bursts from ASKAP and Murriyang are:

B1: 61344.45576415 MJD / 2026-10-31 10:56:18.023 UTC (ASKAP/CRACO)
B2: 61344.50033871 MJD / 2026-10-31 12:00:29.265 UTC (ASKAP/CRACO)
B3: 61349.42206845 MJD / 2026-11-05 10:07:46.714 UTC (Murriyang)

We thank the Murriyang System Scientist and staff for the prompt scheduling and coordination of the observation.

Host galaxy and localisation of FRB20261031B