tokens: Recent studies have focused on searching for fast radio bursts at GHz frequencies in the first few minutes of a GRB, associated with the plateau phases (Bannister et al. 2012 ), or a deeper search, ∼ Jy sensitivity, for prompt (minute to hours) radio emission from short GRBs (Kaplan et al. 2016 ; Anderson et al. 2018b ). This was followed by a catalogue of 1 d follow-up observations at 15.7 GHz with the Arcminute Microkelvin Imager which increased the number of radio detections of short and long GRBs (Staley et al. 2013 ; Anderson et al. 2018a ). The new detections spanned 0.3–33 d post-burst, meaning that coverage during the prompt emission itself remains largely unexplored. Recently, a rapid response mode was implemented for the LOw Frequency ARray (LOFAR; Van Haarlem et al. 2013 ). LOFAR operates using either its low band antenna (LBA, 10–90 MHz) or with its high band antenna (HBA, 120–240 MHz) and is capable of responding to transient alerts within 5 min of receiving the trigger notice. Rowlinson et al. ( 2019 ) outline the first LOFAR search for prompt radio emission in long GRB 180706A, beginning 4.5 min after the γ-ray trigger. By utilizing the full capability of LOFAR, the observational constraints for coherent radio emission can now reach mJy sensitivities, revolutionizing the search for this emission from many transient events. In this paper, we explore the detectability of low-frequency radio waves associated with X-ray flares, under the assumptions of a Poynting flux model for the prompt emission mechanism in which X-ray flares are a manifestation of prompt non-thermal pulses. We draw a subset of X-ray flares from an established sample, and apply the model to estimate the fraction of low-frequency waves that would have been detectable by LOFAR for a given set of observational conditions. We discuss the optimal strategy to apply to the current LOFAR triggering and data processing, to find the emission from flares expected within this framework. 2 MODEL Low-frequency waves have been postulated to arise at the shock front of a highly magnetized, relativistic wind (generated by the rotational energy of a compact object) interacting with its surroundings (Smolsky Usov 2000 ; Usov Katz 2000 ). In this model, a variable current flowing between the two media either side of the travelling shock front leads to the generation of low-frequency radio waves in the MHz regime. The radio emission should occur at a peak frequency, ν max , in the observed frame of where z is the redshift of the GRB and we adopt an observer frame value of G for the magnetic field in the wind at the radius of low-frequency wave generation (Usov Katz 2000 ), where ε B is the fraction of the total energy in the magnetic field. We note there are several assumptions embedded within equation ( 1 ), such as the properties of the magnetic wind and the deceleration radius (see Usov Katz 2000 , for further details regarding these assumptions). A delay is expected
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