  Angle resolved photoemission on underdoped Bi2Sr2CaCu2O8 reveals that the
magnitude and d-wave anisotropy of the superconducting state energy gap are
independent of temperature all the way up to Tc. This lack of T variation of
the entire k-dependent gap is in marked contrast to mean field theory. At Tc
the point nodes of the d-wave gap abruptly expand into finite length ``Fermi
arcs''. This change occurs within the width of the resistive transition, and
thus the Fermi arcs are not simply thermally broadened nodes but rather a
unique signature of the pseudogap phase.
