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The Distance to the Isolated Neutron Star RX J0720.4-3125

D. L. Kaplan·M. H. van Kerkwijk·J. Anderson
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Abstract

We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4-3125. At each of eight epochs over two years, we used the High Resolution Camera of the Advanced Camera for Surveys to measure the position of the B=26.6 target to a precision of ~2 mas (~0.07 pix) relative to 22 other stars. From these data we measure a parallax of pi=2.8+/-0.9 mas (for a distance of 360+170-90 pc) and a proper motion of mu=107.8+/-1.2 mas/yr. Exhaustive testing of every stage of our analysis suggests that it is robust, with a maximum systematic uncertainty on the parallax of 0.4 mas. The distance is compatible with earlier estimates made from scaling the optical emission of RX J0720.4-3125 relative to the even closer neutron star RX J1856.5-3754. The distance and proper motion imply a transverse velocity of 180+90-40 km/s, comparable to velocities observed for radio pulsars. The speed and direction suggest an origin for RX J0720.4-3125 in the Trumpler 10 OB association ~0.7 Myr ago, with a possible range of 0.5-1.0 Myr given by the uncertainty in the distance.

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D. L. Kaplan, M. H. van Kerkwijk, J. Anderson. 2007-03-13. The Distance to the Isolated Neutron Star RX J0720.4-3125. https://doi.org/10.1086/513309

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