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   62137
   The brightest EGRET source at high Galactic latitude that remains
   unidentified is 2EG J1835+5919. Its uncertainty in position is only 9
   arc minutes, yet there are no blazar or pulsar candidates in its error
   circle, and no X-ray source was detected in a ROSAT HRI observation.
   The absence of any plausible counterpart already makes it likely that
   2EG J1835+5919 is the prototype of a new class of variable high-energy
   gamma-ray source, possibly the long-sought radio quiet or "proton
   blazar". One reason that ROSAT may have failed to detect an X-ray
   counterpart is if the source is highly absorbed. Another is if its X-
   rays are intrinsically hard or variable. A deep ASCA pointing may
   identify such a source, and reveal the nature of a new class of gamma-
   ray emitters.
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