  We present the extensive follow-up campaign on the afterglow of GRB 110715A
at 17 different wavelengths, from X-ray to radio bands, starting 81 seconds
after the burst and extending up to 74 days later. We performed for the first
time a GRB afterglow observation with the ALMA observatory. We find that the
afterglow of GRB 110715A is very bright at optical and radio wavelengths. We
use optical and near infrared spectroscopy to provide further information about
the progenitor's environment and its host galaxy. The spectrum shows weak
absorption features at a redshift z = 0.8225, which reveal a host galaxy
environment with low ionization, column density and dynamical activity. Late
deep imaging shows a very faint galaxy, consistent with the spectroscopic
results. The broadband afterglow emission is modelled with synchrotron
radiation using a numerical algorithm and we determine the best fit parameters
using Bayesian inference in order to constrain the physical parameters of the
jet and the medium in which the relativistic shock propagates. We fitted our
data with a variety of models, including different density profiles and energy
injections. Although the general behaviour can be roughly described by these
models, none of them are able to fully explain all data points simultaneously.
GRB 110715A shows the complexity of reproducing extensive multi-wavelength
broadband afterglow observations, and the need of good sampling in wavelength
and time and more complex models to accurately constrain the physics of GRB
afterglows.
