  The prompt emission in long gamma-ray bursts arises from within relativistic
outflows created during the collapse of massive stars, and the mechanism by
which radiation is produced may be either magnetically- or matter-dominated. In
this work we suggest an observational test of a magnetically-dominated Poynting
flux model that predicts both gamma-ray and low-frequency radio pulses. A
common feature among early light curves of long gamma-ray bursts are X-ray
flares, which have been shown to arise from sites internal to the jet.
Ascribing these events to the prompt emission, we take an established Swift XRT
flare sample and apply a magnetically-dominated wind model to make predictions
for the timing and flux density of corresponding radio pulses in the ~100-200
MHz band observable with radio facilities such as LOFAR. We find that 44 per
cent of the X-ray flares studied would have had detectable radio emission under
this model, for typical sensitivities reached using LOFAR's rapid response mode
and assuming negligible absorption and scattering effects in the interstellar
and intergalactic medium. We estimate the rate of Swift gamma-ray bursts
displaying X-ray flares with detectable radio pulses, accessible to LOFAR, of
order seven per year. We determine that LOFAR triggered observations can play a
key role in establishing the long debated mechanism responsible for gamma-ray
burst prompt emission.
