  A quantum-optics approach is used to study the nature of the acceleration
radiation due to a random atomic cloud falling freely into a generalized
Schwarzschild black hole through a Boulware vacuum. The properties of this
horizon brightened acceleration radiation (HBAR) are analyzed with a master
equation that is fully developed in a multimode format. A scheme for the
coarse-graining average for an atomic cloud is considered, with emphasis on the
random injection scenario, which is shown to generate a thermal state. The role
played by conformal quantum mechanics (CQM) is shown to be critical for
detailed balance via a Boltzmann factor governed by the near-horizon physics,
with the unique selection of the Hawking temperature. The HBAR thermal state is
the basis for a thermodynamic framework that parallels black hole
thermodynamics.
