Radio light curve of the afterglow of GRB 151027B at 5.5 and 9 GHz, with the ALMA 97.5 GHz 2σ upper limitoverplotted (lower panel). The upper panel shows the measured fluxes of selected brighter (130–500 μJy) sources. While their nature or intrinsic variability is not known, their <20% flux variation demonstrates that the strong fluctuations seen for the GRB 151027B afterglow (which would correspond to an amplitude between 0.2 and 2 in this graph) is not an instrumental artifact.