PSR J2229+6114: Discovery of an energetic young pulsar in the error box of the EGRET source 3EG J2227+6122

We report the detection of radio and X-ray pulsations at a period of 51.6 ms from the X-ray source RX/AX J2229.0+6114 in the error box of the EGRET source 3EG J2227+6122. An ephemeris derived from a single ASCA observation and multiple epochs at 1412 MHz from Jodrell Bank indicates steady spin-down with P = 7.83 × 10^-14 s s^-1. From the measured P and Ṗ, we derive spin-down power Ė = 2.2 × 10³⁷ ergs s^-1, magnetic field B_p = 2.0 × 10¹² G, and characteristic age P/2Ṗ = 10,460 yr. An image from the Chandra X-Ray Observatory reveals a point source surrounded by centrally peaked diffuse emission that is contained within an incomplete radio shell. We assign the name G106.6+2.9 to this new supernova remnant, which is evidently a pulsar wind nebula. For a distance of 3 kpc estimated from X-ray absorption, the ratio of X-ray luminosity to spin-down power is ≈8 × 10^-5, smaller than that of most pulsars but similar to the Vela pulsar. If PSR J2229+6114 is the counterpart of 3EG J2227+6122, then its efficiency of γ-ray production, if isotropic, is 0.016 (d/3 kpc)². It obeys an established trend of γ-ray efficiency among known γ-ray pulsars, which, in combination with the demonstrated absence of any other plausible counterpart for 3EG J2227+6122, makes the identification compelling. If confirmed, this identification bolsters the pulsar model for unidentified Galactic EGRET sources.