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Ultrahigh resolution angle-resolved photoemission spectroscopy with low-energy photons is used to study the detailed momentum dependence of the well-known nodal ‘kink’ dispersion anomaly of Bi _2 Sr _2 CaCu _2 O _8+ _δ . We find that the kink's location transitions smoothly from a maximum binding energy of about 65 meV at the node of the d -wave superconducting gap to 55 meV roughly one-third of the way to the antinode. Meanwhile, the self-energy spectrum corresponding to the kink dramatically sharpens and intensifies beyond a critical point in momentum space. We discuss the possible bosonic spectrum in energy and momentum space that can couple to the k -space dispersion of the electronic kinks.