  In this letter we report measurements of the coupling between Dirac fermion
quasiparticles (DFQs) and phonons on the (001) surface of the strong
topological insulator Bi2Se3. While most contemporary investigations of this
coupling have involved examining the temperature dependence of the DFQ
self-energy via angle-resolved photoemission spectroscopy (ARPES) measurements,
we employ inelastic helium atom scattering to explore, for the first time, this
coupling from the phonon perspective. Using a Hilbert transform, we are able to
obtain the imaginary part of the phonon self-energy associated with a
dispersive surface phonon branch identified in our previous work [1] as having
strong interactions with the DFQs. From this imaginary part of the self-energy
we obtain a branch-specific electron-phonon coupling constant of 0.43, which is
stronger than the values reported form the ARPES measurements.
