  The gamma-ray annihilation and decay products of very heavy dark matter
particles can undergo attenuation through pair production, leading to the
development of electromagnetic cascades. This has a significant impact not only
on the spectral shape of the gamma-ray signal, but also on the angular
distribution of the observed photons. Such phenomena are particularly important
in light of the new HAWC experiment, which provides unprecedented sensitivity
to multi-TeV photons and thus to very heavy dark matter particles. In this
study, we focus on dark matter in the 100 TeV-100 PeV mass range, and calculate
the spectral and angular distribution of gamma-rays from dwarf galaxies and
from nearby galaxy clusters in this class of models.
