XMM-Newton Observations of Two Unusual Binary Pulsars

In a recent radio survey of unidentified EGRET sources, we discovered two veryunusual binary pulsars: PSRs J16142230 and J17443922. The first source, a3.15ms binary pulsar with a companion too massive for standard binary evolutionscenarios, may become the second known gammaray pulsar. The second source, a172 ms pulsar in a tight 4.6 hr orbit around a lowmass companion, is likelyunrelated to the coincident EGRET source. However, it displays bizarre radioemission behavior that may indicate transient accretion. This could be thelongsought missing link between accretionpowered and rotationpoweredneutron stars. Here we propose to test both hypotheses using brief XMMNewtonsnapshots. Xray detection of either source would be very exciting. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]