Non-detection at 1.26 GHz of persistent radio source associated with the repeating FRB 20230607A
ATel #17230; D. Pelliciari (IRA-INAF), L. Bruno (IRA-INAF), Y. Bhusare (NCRA-TIFR), G. Bernardi (IRA-INAF), A. Kumar (NCRA-TIFR), B. Lal (NCRA-TIFR), Y. Maan (NCRA-TIFR)
on 16 Jun 2025; 09:29 UT
Credential Certification: Davide Pelliciari (d.pelliciari@ira.inaf.it)
Subjects: Radio, Transient, Fast Radio Burst
We report on follow-up radio observations to search for a possible persistent radio source (PRS) associated with FRB 20230607A. The latter is a repeater for which an intense bursting activity has been recently reported in Zhou et al. 2025 (arXiv: 2504.11173). Moreover, the bursts from this source presented a rotation measure (RM) of approximately −1.2 × 104 rad m-2 (Zhou et al. 2025). Given the large RM values and the expected relation between the RM and the persistent radio luminosity of a possible persistent counterpart associated with the FRB (Yang et al. 2022, Bruni et al. 2023), this source represents an ideal candidate to search for a PRS.
We observed the field of FRB 20230607A with the upgraded Giant Meterwave Radio Telescope (uGMRT) using the band-5 (1050-1450 MHz) for a total of 4.3 h on 2025 May 27. The total bandwidth was splitted into 4096 channels, each of 97.7 kHz. The sources 3C48 and 2130+050 were used as absolute flux scale and phase calibrators, respectively. We carried out a standard interferometric data reduction using the Common Astronomy Software Applications (CASA; McMullin et al. 2007) package. We then iteratively performed flagging of RFI, bandpass, amplitude and phase calibration. We finally performed a round of phase self-calibration. Imaging was carried out with WSClean (Offringa et al. 2014) by using various weighting schemes. We achieved a final noise level of 15 μJy beam-1 at an angular resolution of 2.5'' × 1.7'' (briggs weighting with robust 0).
We searched for a compact continuum source around the fiducial localization coordinates of FRB 20230607A, being R.A. (J2000) = 21h53m35.0s, Dec. (J2000) = 11∘17'04.20 '' (Zhou et al. 2025), within the 90% confidence level (C.L.) localization uncertainties, using σR.A. = 44.1'' and σDec. = 66.8'' (Zhou et al. 2025). We didn't detect any possible PRS for a S/N > 3 within the 90% C.L. localization region. Instead, there is a compact radio source within the 99% C.L. region having ≈ 100 ± 15 μJy flux density. Its coordinates are R.A. (J2000) = 21h53m33.556s ± 0.005s, Dec. (J2000) = 11∘16'11.83'' ± 0.04 ''. Given that the FRB has not yet been associated with any host galaxy we cannot claim that this is the PRS of the source. Considering a non-detection, our flux density limit of 45 μJy beam-1 converts to an upper limit on the persistent radio luminosity at 1.26 GHz of 5.9 × 1028 erg s-1 Hz-1, when considering z = 0.22 as the redshift of FRB 20230607A (as estimated from the DM of FRB 20230607A, Zhou et al. 2025). Our 3σ luminosity limit is a factor of 2 deeper than the radio power of confirmed PRSs associated with FRBs 20121102A (Chatterjee et al. 2017) and 20190520B (Niu et al. 2022); nevertheless, the candidate PRS associated with FRB 20201124A (Bruni et al. 2023) has a radio power which is a factor 10 lower than our limit. The implications of our non-detection will be discussed in an upcoming paper.
The link below shows the optical i-filter field of FRB 20230607A obtained with the Dark Energy Spectroscopic Instrument (DESI) via the DESI Legacy Imaging Surveys, with overlaid 1.26 GHz radio contours from our uGMRT observations.
Optical and radio image of the FRB 20230607A field
