Do CRAFT Fast Radio Bursts repeat?
Do any of the CRAFT Fast Radio Bursts repeat?
We have been using the 64-m Parkes radio telescope and the 110-m Green Bank Telescope (GBT) to search for repeated emission from ASKAP-detected fast radio bursts. The greater sensitivities of Parkes and the GBT enable searches for faint repetitions from sources known to emit intrinsically bright bursts (if they repeat), or place strong constraints on repetition from one-off FRBs.
At Parkes, the first searches used the 20-cm multibeam receiver and the BPSR backend to conduct real-time searches. We are now commissioning FRB search algorithms for use with the new ultra-wide band low system (700 MHz – 4.2 GHz) which will open up new ways to search for and study repeating burst sources. At the Green Bank telescope, we have been primarily using the 800 MHz system, motivated by its cleaner RFI environment and the opportunity to search for FRBs where they may (or may not) be brighter.
Project highlights and publications:
Prompt follow up of ASKAP-detected bursts: Our search strategy has enabled prompt follow up of many of our ASKAP detections. Motivated by intermittency in the first repeating FRB source (121102), which shows active periods of days to weeks, fast follow up enables us to constrain repetitions when a putative source is active. Fast follow up was used to constrain activity for both the fly’s eye FRBs (Shannon et al. 2018, Nature) and the first localized ASKAP FRB (180924, Bannister et al. 2019, Science).
Discovery of faint repetitions from FRB 171019: A major breakthrough came with the discovery of faint repetitions from one of the brightest ASKAP fly’s eye FRBs. The repetitions, detected at the GBT, were 600 time fainter than the initial ASKAP detections. The discovery shows that at least some bright FRBs repeat. By combining ASKAP, GBT, and Parkes observations of the field we are able to place strong constraints on burst repetition rate and spectral energy distributions and motivate a follow localization campaign with the Very Large Array. The discovery was published in a student-led publication (Kumar et al. 2019, ApJL). Repetitions from the source have also been detected by the CHIME telescope.
Which FRBs repeat? We have also undertaken a statistical analysis of the follow up campaigns with the Parkes multibeam and GBT, combining the detection of repetitions from FRB 171019 with the non-detections from the remaining burst sources. The results show that at most 20% of ASKAP FRBs repeat like FRB 121102 (James et al. 2019, submitted to MNRAS).