A Direct Measurement of Sense of Rotation of PSR J0737-3039A

We apply the algorithm published by Liang et al. to describe the Double Pulsar system J0737-3039 and extract the sense of rotation of the first born recycled pulsar PSR J0737-3039A. We find that this pulsar is rotating prograde in its orbit. This is the first direct measurement of the sense of rotation of a pulsar with respect to its orbit and a direct confirmation of the rotating lighthouse model for pulsars. This result confirms that the spin angular momentum vector is closely aligned with the orbital angular momentum, suggesting that the kick of the supernova producing the second born pulsar J0737-3039B was small.