THE ORBIT AND COMPANION OF PROBABLE γ-RAY PULSAR J2339-0533

We have measured dramatic flux and spectral variations through the 0.193 day orbit of the optical counterpart of the unidentified gamma-ray source 0FGL J2339.8-0530. This compact object companion is strongly heated, with T-eff varying from similar to 6900 K (superior conjunction) to <3000 K at minimum. A combined fit to the light curve and radial velocity amplitudes imply M-1 approximate to 0.075 M-circle dot, M-2 approximate to 1.4 M-circle dot, and inclination i approximate to 57 degrees. Thus, this is a likely black widow system with a (E)over dot approximate to 10(34-34.5) erg s(-1) pulsar driving companion mass loss. This wind, also suggested by the X-ray light curve, may prevent radio pulse detection. Our measurements constrain the pulsar's reflex motion, increasing the possibility of a pulse detection in the gamma-ray signal.