The Orbital Evolution and Proper Motion of PSR J2051−0827

We have carried out high-precision timing observations of the eclipsing binary PSR J2051−0827 in the 3.3 years since its discovery. These data indicate that the orbital period is decreasing at a rate of Ṗb = (−11±1)×10. If secular, this orbital period derivative implies a decay time for the orbit of only 25 Myr which is much shorter than the expected timescale for ablation of the companion. We have also measured the proper motion of the pulsar to be 5±3 mas yr. Assuming the pulsar is at the dispersionmeasure distance this implies a very slow transverse velocity vt=(30±20) km s. This combination of low velocity and short orbital period argue against formation of the system in the standard manner and we discuss the implications for its evolutionary history. 1Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, ANU, Private Bag, Weston Creek, ACT 2611, Australia. 2Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, Victoria, 3122, Australia. 3Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia. 4California Institute of Technology, MS 105-24, Pasadena, CA 91125. 5Physics Department, University of Melbourne, Parkville, Vic 3052, Australia.