Discovery of Five Binary Radio Pulsars

We report on five binary pulsars discovered in the Parkes multibeam Galactic plane survey. All of the pulsars are old, with characteristic ages (1-11) × 109 yr, and have relatively small inferred magnetic fields, (5-90) × 108 G. The orbital periods range from 1.3 to 15 days. As a group these objects differ from the usual low-mass binary pulsars (LMBPs): their spin periods of 9-88 ms are relatively long; their companion masses, 0.2-1.1 M☉, are, in at least some cases, suggestive of CO or more massive white dwarfs; and some of the orbital eccentricities, 10-5 ≲ e ≲ 0.002, are unexpectedly large. We argue that these observed characteristics reflect binary evolution that is significantly different from that of LMBPs. We also note that intermediate-mass binary pulsars apparently have a smaller scale height than LMBPs.