The identity of the persistent EGRET sources in the Galactic plane is largely a mystery .
For one of these , 3EG J2227+6122 , our complete census of X-ray and radio sources in its error circle reveals a remarkable superposition of an incomplete radio shell with a flat radio spectrum , and a compact , power-law X-ray source with photon index \Gamma = 1.5 and with no obvious optical counterpart .
The radio shell is polarized at a level of \simeq 25 \% .
The anomalous properties of the radio source prevent us from deriving a completely satisfactory theory as to its nature .
Nevertheless , using data from ROSAT , ASCA , the VLA , and optical imaging and spectroscopy , we argue that the X-ray source may be a young pulsar with an associated wind-blown bubble or bow shock nebula , and an example of the class of radio-quiet pulsars which are hypothesized to comprise the majority of EGRET sources in the Galaxy .
The distance to this source can be estimated from its X-ray absorption as 3 kpc .
At this distance , the X-ray and \gamma -ray luminosities would be \approx 1.7 \times 10 ^ { 33 } and \approx 3.7 \times 10 ^ { 35 } erg s ^ { -1 } , respectively , which would require an energetic pulsar to power them .

If , on the contrary , this X-ray source is not the counterpart of 3EG J2227+6122 , then by process of elimination the X-ray luminosity of the latter must be less than 10 ^ { -4 } of its \gamma -ray luminosity , a condition not satisfied by any established class of \gamma -ray source counterpart .
This would require the existence of at least a quantitatively new type of EGRET source , as has been suggested in studies of other EGRET fields .