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The composition of relativistic gamma-ray burst (GRB) jets and their emissionmechanisms are still debated, and they could be matter or magneticallydominated. One way to distinguish these mechanisms arises because a Poyntingflux dominated jet may produce low-frequency radio emission during theenergetic prompt phase, through magnetic reconnection at the shock front. Wepresent a search for radio emission coincident with three GRB X-ray flares withthe LOw Frequency ARray (LOFAR), in a rapid response mode follow-up of long GRB210112A (at z~2) with a 2 hour duration, where our observations began 511seconds after the initial swift-BAT trigger. Using timesliced imaging at120-168 MHz, we obtain upper limits at 3 sigma confidence of 42 mJy averagingover 320 second snapshot images, and 87 mJy averaging over 60 second snapshotimages. LOFAR's fast response time means that all three potential radiocounterparts to X-ray flares are observable after accounting for dispersion atthe estimated source redshift. Furthermore, the radio pulse in the magneticwind model was expected to be detectable at our observing frequency and fluxdensity limits which allows us to disfavour a region of parameter space forthis GRB. However, we note that stricter constraints on redshift and thefraction of energy in the magnetic field are required to further test jetcharacteristics across the GRB population.

A LOFAR prompt search for radio emission accompanying X-ray flares in GRB 210112A