Speaker
Description
In this talk, I will present a targeted search for low-frequency (144--215MHz) FRB emission from five repeating FRBs using 23.3hr of archival data taken with the Murchison Widefield Array (MWA) Voltage Capture System (VCS) between 2014 September and 2020 May. This is the first time that the MWA VCS has been used to search for FRB signals from known repeaters, which enables much more sensitive FRB searches than previously performed with the standard MWA correlator mode. We performed a standard single pulse search with a temporal and spectral resolution of 400us and 10kHz, respectively, over a 100pc cm^-3 dispersion measure (DM) range centred at the known DM of each studied repeating FRB. No FRBs exceeding a 6sigma threshold were detected. The fluence upper limits in the range of 32-1175Jy ms and 36-488Jy ms derived from 10 observations of FRB 190711A and four observations of FRB 201124A respectively, allow us to constrain the spectral indices of their bursts to >-1 if these two repeaters were active during the MWA observations. If free-free absorption is responsible for our non-detection, we can constrain the size of the absorbing medium in terms of the electron temperature T to <1.00(T/10^4K)^-1.35pc, <0.92(T/10^4K)^-1.35pc and <[0.22--2.50]*(T/10^4K)^-1.35pc for FRB 190117A, 190711A, and 201124A, respectively. However, given that the activities of these repeaters are not well characterised, our non-detections could also suggest they were inactive during the MWA observations.
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