Detection of Ne VIII in an Intervening Multi-Phase Absorption System
  Towards 3C 263
  We report on the detection of Ne VIII in an intervening multiphase absorption
line system at z=0.32566 in the FUSE spectrum of the quasar 3C 263. The Ne VIII
770 A line 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 (+0.10,-0.13) and b = 49.8
+/- 5.5 km/s. 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 multi-phase 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 et al.
(2005). 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.
