ON THE EXPANSION RATE, AGE, AND DISTANCE OF THE SUPERNOVA REMNANT G266.2−1.2 (Vela Jr.)

An analysis of Chandra ACIS data for two relatively bright and narrow portions of the northwestern rim of G266.2−1.2 (a.k.a. RX J0852.0–4622 or Vela Jr.) reveal evidence of a radial displacement of 2.40 ± 0.56 arcsec between 2003 and 2008. The corresponding expansion rate (0.42 ± 0.10 arcsec yr−1 or 13.6% ± 4.2% kyr−1) is about half the rate reported for an analysis of XMM-Newton data from a similar, but not identical, portion of the rim over a similar, but not identical, time interval (0.84 ± 0.23 arcsec yr−1). If the Chandra rate is representative of the remnant as a whole, then the results of a hydrodynamic analysis suggest that G266.2−1.2 is between 2.4 and 5.1 kyr old if it is expanding into a uniform ambient medium (whether or not it was produced by a Type Ia or Type II event). If the remnant is expanding into the material shed by a steady stellar wind, then the age could be as much as 50% higher. The Chandra expansion rate and a requirement that the shock speed be greater than or equal to 1000 km s−1 yields a lower limit on the distance of 0.5 kpc. An analysis of previously published distance estimates and constraints suggests G266.2−1.2 is no further than 1.0 kpc. This range of distances is consistent with the distance to the nearer of two groups of material in the Vela Molecular Ridge (0.7 ± 0.2 kpc) and to the Vel OB1 association (0.8 kpc).