ASKAP discovery of a high rotation measure repeating Fast Radio Burst source with |RM| > 7000 rad m^-2

ATel #17257; Ziteng Wang (International Centre for Radio Astronomy Research, Curtin University), Apurba Bera (ICRAR, Curtin), Manisha Caleb (University of Sydney), Adam Deller (Swinburne University of Technology, SUT), Tyson Dial (SUT), Marcin Glowacki (University of Edinburgh, Curtin, IDIA), Kelly Gourdji (CSIRO Space & Astronomy), Joscha Jahns-Schindler (SUT), Ryan M. Shannon (SUT), Ben Stappers (University of Manchester), Pavan Uttarkar (SUT), Yuanming Wang (SUT) on behalf of the ASKAP/CRAFT collaboration
on 1 Jul 2025; 11:13 UT
Credential Certification: Ziteng Wang (ziteng.wang@curtin.edu.au)

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We report the discovery of the new repeating fast radio burst (FRB) source, FRB 20250613A. FRB 20250613A was first identified as a single 12sigma burst with a dispersion measure (DM) of 174.6 pc cm^-3 on 2025 June 13 at 22:22 UTC. The burst was detected during a 10-hour observation for the Evolutionary Map of the Universe survey, using the incoherent sum search mode pipeline. We localised the burst to sub-arcsec precision (R.A. 04h36m33.04(5)s, Decl. -44d31m58.6(4)s) using triggered voltage data and our post processing pipeline (Scott et al. 2023). We identified a putative host of FRB 20250613A in the Dark Energy Camera Legacy Survey. The host was measured with an r-band magnitude of 22, and a photometric redshift z=0.22(9). Together with the DM, this implies that FRB 20250613A originates from a low-luminosity dwarf galaxy, with a luminosity <~ 4x10^9 L_sun. The initial burst shows band-limited emission and has multiple components (see attached figures) with complex time-frequency structure exhibiting downwards drifting "sad trombone"-like features, which are typical features of repeating FRBs (Pleunis et al., 2021). We measure the rotation measure (RM) of -7162.3(9) rad m^-2: the fourth highest RM magnitude of all currently known FRBs. The high RM, spectro-temporal features, and dwarf host galaxy motivated prompt follow up to search for repetitions. We carried out two follow-up observations of FRB 20250613A with the MeerKAT radio telescope using the L-band (856-1712 MHz) receiving system: a 2-hour observation on 2025 June 23 starting at 05:26 UTC and a 6-hour observation on 2025 June 24 starting at 05:55 UTC, under the Director's Discretionary Time Proposal DDT-20250621-AW-01. We detected 16 additional bursts from FRB 20250613A during these observations using the real-time MeerTRAP pipeline (Rajwade et al. 2022), confirming its repeating nature. We are currently working on identifying more bursts in the data as the real time detection pipeline might have been affected by the presence of RFI. We combined the visibilities from all MeerKAT observations and performed calibration and imaging using oxkat (Heywood, 2020), and separately verified with processMeerKAT. We identified a radio source at the FRB location with a peak flux density of 24.2+/-5.1 uJy/beam. Further analysis is required to determine whether the emission originates from a persistent radio source or is associated with star formation in the host galaxy. Given that FRB 20250613A is likely still active, we encourage further observations. This work uses data obtained from Inyarrimanha Ilgari Bundara/the CSIRO Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamaji People as the Traditional Owners and native title holders of the observatory site. CSIRO's ASKAP radio telescope is part of the Australia Telescope National Facility (https://ror.org/05qajvd42). Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Research Centre. Establishment of ASKAP, Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Research Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. We would like to thank the Director and the operators of MeerKAT and the South African Radio Astronomy Observatory (SARAO) for the prompt scheduling of the observation. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.

Example of dynamic spectra from ASKAP and MeerKAT