A Double-Pulsar System - A Rare Laboratory for Relativistic Gravity and   Plasma Physics
  The clock-like properties of pulsars moving in the gravitational fields of their unseen neutron-star companions have allowed unique tests of general relativity and provided evidence for gravitational radiation. We report here the detection of the 2.8-sec pulsar J0737-3039B as the companion to the 23-ms pulsar J0737-3039A in a highly-relativistic double-neutron-star system, allowing unprecedented tests of fundamental gravitational physics. We observe a short eclipse of J0737-3039A by J0737-3039B and orbital modulation of the flux density and pulse shape of J0737-3039B, probably due to the influence of J0737-3039A's energy flux upon its magnetosphere. These effects will allow us to probe magneto-ionic properties of a pulsar magnetosphere. 
A.G. Lyne, M. Burgay, M. Kramer, A. Possenti, R.N. Manchester, F.   Camilo, M.A. McLaughlin, D.R. Lorimer, N. D'Amico, B.C. ...