  Photoemission and phonon spectroscopies have yielded widely varying estimates
of the electron-phonon coupling constant \lambda\ on the surfaces of
topological insulators, even for a particular material and technique. We
connect the results of these experiments by determining the Dirac fermion
quasiparticle spectral function using information from measured spectra of a
strongly-interacting, low-lying optical surface phonon band. The manifest
spectral features resulting from the coupling are found to vary on energy
scales < 1 meV, and are distinct from those traditionally observed in the case
of acoustic phonons in metals. We explore different means of determining
\lambda\ from the electron perspective and identify definitions that yield
values consistent with phonon spectroscopy.
