DETECTION OF Ne VIII IN AN INTERVENING MULTIPHASE ABSORPTION SYSTEM TOWARD 3C 263

We report the detection of Ne VIII in an intervening multiphase absorption line system at z = 0.32566 in the Far Ultraviolet Spectroscopic Explorer spectrum of the quasar 3C 263 (z(em) = 0.646). The Ne VIII gamma 770 angstrom detection has a 3.9 sigma significance. At the same velocity, we also find absorption lines from C IV, O III, O IV, and N IV. The line parameter measurements yield log [N(Ne VIII) cm(-2)] = 13.98(-0.13)(+0.10) b = 49.8 +/- 5.5 km s(-1). We find that the ionization mechanism in the gas phase giving rise to the Ne VIII absorption is inconsistent with photoionization. The absorber has a multiphase structure, with the intermediate ions produced in cool photoionized gas and the Ne VIII most likely in a warm collisionally ionized medium in the temperature range (0.5-1.0) x 10(6) K. This is the second ever detection of an intervening Ne VIII absorption system. Its properties resemble the previous Ne VIII absorber reported by Savage and colleagues. Direct observations of H I and O VI are needed to better constrain the physical conditions in the collisionally ionized gas phase of this absorber.