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Recently, very high-energy photons above 100 GeV were reported to be detectedfrom GRB~190114C and GRB~180720B at, respectively, 100-1000 s and 10 hoursafter the burst. We model the available broad-band data of both GRBs with thesynchrotron plus synchrotron self-Compton (SSC) emission of the afterglowshocks. We find that the sub-TeV emission of GRB~180720B can be interpreted asthe SSC emission from afterglow shocks expanding in a constant densitycircum-burst medium. The SSC emission of GRB~190114C dominates over thesynchrotron component from GeV energies at $\sim100$ s, which can explain thepossible hard spectrum of the GeV emission at this time. The extrapolated fluxof this SSC component to sub-TeV energies can explain the high-significancedetection of GRB~190114C by the MAGIC telescope. The parameter values (such asthe circum-burst density and shock microphysical parameters) in the modelingare not unusual for both GRBs, implying that the detection of sub-TeV photonsfrom these two bursts should be attributed to their large burst energies andlow redshifts.

Synchrotron self-Compton emission from external shocks as the origin of the sub-TeV emission in GRB 180720B and GRB 190114C