  Gamma-Ray Bursts (GRBs) are the most explosive phenomena in the Universe
after the Big Bang. A large fraction of GRB lightcurves (LCs) shows X-ray
plateaus. We perform the most comprehensive analysis of all GRBs (with known
and unknown redshifts) with plateau emission observed by The Neil Gehrels Swift
Observatory from its launch until August 2019. We fit 455 LCs showing a plateau
and explore whether these LCs follow closure relations, relations between the
temporal and spectral indices of the afterglow, corresponding to 2 distinct
astrophysical environments and cooling regimes within the external forward
shock (ES) model, and find that the ES model works for the majority of cases.
The most favored environments are a constant density interstellar or wind
medium with slow cooling. We also confirm the existence of the fundamental
plane relation between the rest-frame time and luminosity at the end of the
plateau emission and the peak prompt luminosity for this enlarged sample, and
test this relation on groups corresponding to the astrophysical environments of
our known redshift sample. The plane becomes a crucial discriminant
corresponding to these environments in terms of the best fitting parameters and
dispersions. Most GRBs for which the closure relations are fulfilled with
respect to astrophysical environments have an intrinsic scatter sigma
compatible within 1 sigma of that of the Gold GRBs, a subset of long GRBs with
relatively flat plateaus. We also find that GRBs satisfying closure relations
indicating a fast cooling regime have a lower sigma than ever previously found
in literature.
