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The nature of the central engines of gamma-ray bursts (GRBs) and thecomposition of their relativistic jets are still under debate. If the jets arePoynting flux dominated rather than baryon dominated, a coherent radio flarefrom magnetic re-connection events might be expected with the prompt gamma-rayemission. There are two competing models for the central engines of GRBs; ablack hole or a newly formed milli-second magnetar. If the central engine is amagnetar it is predicted to produce coherent radio emission as persistent orflaring activity. In this paper, we present the deepest limits to date for thisemission following LOFAR rapid response observations of GRB 180706A. Noemission is detected to a 3$\sigma$ limit of 1.7 mJy beam$^{-1}$ at 144 MHz ina two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger.A forced source extraction at the position of GRB 180706A provides a marginallypositive (1 sigma) peak flux density of $1.1 \pm 0.9$ mJy. The data weretime-sliced into different sets of snapshot durations to search for FRB likeemission. No short duration emission was detected at the location of the GRB.We compare these results to theoretical models and discuss the implications ofa non-detection.

LOFAR early-time search for coherent radio emission from GRB 180706A