A MeerKAT search for persistent radio sources towards twenty-five localised Fast Radio Bursts

TL;DR

We investigate whether persistent radio sources (PRSs) co-locate with fast radio bursts (FRBs) by conducting a sub-arcsecond MeerKAT survey at 1.28 GHz toward 25 well-localised FRBs. The study detects 14 radio sources and places 3σ upper limits for 17 non-detections, with 13 optical associations and one plausible X-ray counterpart; RO-ratio analysis indicates the detected emission is typically consistent with star formation rather than compact PRSs, though high-resolution follow-up with e-MERLIN is required to rule out faint PRSs embedded in host emission. The results imply either an absence of PRSs in this sample or PRSs that are below MeerKAT's resolution, underscoring the need for higher angular resolution and broader samples to constrain FRB progenitor environments. These findings provide flux benchmarks and identify targets for future high-resolution, multi-wavelength follow-up to refine models of FRB engines and their surroundings.

Abstract

The discovery of persistent radio sources (PRSs) associated with repeating fast radio bursts (FRBs) has shed light on the immediate environments and possible progenitors of these FRBs. The confirmed PRSs may support the theory that FRB progenitors are compact central engines, whilst the non-detections suggest diversity of FRB's local environment. We perform a subarcsecond-resolution MeerKAT search at 1.28 GHz on 25 well-localised FRB positions provided by ASKAP and MeerTRAP. We detect 14 radio sources and provide flux upper limits for 12 non-detections (both these numbers include a source that was detected during two epochs of observation, and not detected during one epoch, adding up to 26). One radio source shows variability as seen in flux variations over three epochs of observation. Archival optical data reveal excesses in the direction of 13 detected radio sources. Similarly for four sources in the X-ray band, with one possibly being a high-energy signature of a radio galaxy core. Since we cannot definitively classify our detected radio sources as PRSs, future high-resolution observations with e-MERLIN will be required to resolve the radio emission and pronounce on the presence of compact PRSs associated with the 14 detected sources presented here.

Figures (8)

• Figure 1: Non-detections by MeerKAT. The cyan circle indicates the position of the ASKAP/MeerTRAP FRB. White contours corresponding to $3,6,12,24$ times the rms of the image represent non-associated continuum radio emission. The black circle in the bottom left corner represents the beam size of MeerKAT in each case. For sources that were observed for more than one epoch, we indicate the epoch as part of the FRB name.
• Figure 2: Non-detections by MeerKAT. The cyan circle indicates the position of the ASKAP/MeerTRAP FRB. White contours corresponding to $3,6,12,24$ times the rms of the image represent non-associated continuum radio emission. The black circle in the bottom left corner represents the beam size of MeerKAT in each case. For sources that were observed for more than one epoch, we indicate the epoch as part of the FRB name.
• Figure 3: MeerKAT images of various FRB sources at different angular scales. The cyan circle indicates the position of the FRB. White contours corresponding to 3, 6, 12, 24 $\times$ the respective rms (see Table \ref{['tab:info1']}) of the images represent continuum radio emission coincident with the FRB position. The black circle in the bottom left corner represents the beam size of MeerKAT. For sources that were observed for more than one epoch, we indicate the epoch as part of the FRB name.
• Figure 4: MeerKAT images of various FRB sources at different angular scales. The cyan circle indicates the position of the FRB. White contours corresponding to 3, 6, 12, 24 $\times$ the respective rms (see Table \ref{['tab:info1']}) of the images represent continuum radio emission coincident with the FRB position. The black circle in the bottom left corner represents the beam size of MeerKAT. For sources that were observed for more than one epoch, we indicate the epoch as part of the FRB name.
• Figure 5: Optical fields with the MeerKAT radio contours overlaid. The background is the DESI-Legacy survey $grz$-band optical flux and the white contours represent the MeerKAT radio emission corresponding to $3,6,12,24$ times the rms of the image. The magenta triangle is the position of the FRB and black circle in the bottom left corner represents the size of the MeerKAT beam.