  GRB 190114C was a bright burst that occurred in the local Universe (z=0.425).
It was the first gamma-ray burst (GRB) ever detected at TeV energies, thanks to
MAGIC. We characterize the ambient medium properties of the host galaxy through
the study of the absorbing X-ray column density. Joining Swift, XMM-Newton, and
NuSTAR observations, we find that the GRB X-ray spectrum is characterized by a
high column density that is well in excess of the expected Milky Way value and
decreases, by a factor of ~2, around ~$10^5$ s. Such a variability is not
common in GRBs. The most straightforward interpretation of the variability in
terms of photoionization of the ambient medium is not able to account for the
decrease at such late times, when the source flux is less intense. Instead, we
interpret the decrease as due to a clumped absorber, denser along the line of
sight and surrounded by lower-density gas. After the detection at TeV energies
of GRB 190114C, two other GRBs were promptly detected. They share a high value
of the intrinsic column density and there are hints for a decrease of the
column density, too. We speculate that a high local column density might be a
common ingredient for TeV-detected GRBs.
