  We have identified an optical binary with orbital period P_b=4488s as the
probable counterpart of the Fermi source 2FGL J1653.6-0159. Although pulsations
have not yet been detected, the source properties are consistent with an
evaporating millisecond pulsar binary; this P_b=75min is the record low for a
spin-powered system. The heated side of the companion shows coherent radial
velocity variations, with amplitude K=666.9+/-7.5 km/s for a large mass
function of f(M)=1.60+/-0.05 M_sun. This heating suggests a pulsar luminosity
~3x10^34 erg/s. The colors and spectra show additional hard emission dominating
at binary minimum. Its origin is, at present, unclear. This system is similar
to PSR J1311-3430, with a low mass H-depleted companion, a dense shrouding wind
and, likely, a large pulsar mass.

High Energy Astrophysical Phenomena;Solar and Stellar Astrophysics