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

Abstract

An analysis of Chandra ACIS data for two relatively bright and narrow\nportions of the northwestern rim of G266.2-1.2 (a.k.a. RX J0852.0-4622 or Vela\nJr.) reveal evidence of a radial displacement of 2.40 +/- 0.56 arcsec between\n2003 and 2008. The corresponding expansion rate (0.42 +/- 0.10 arcsec/yr or\n13.6 +/- 4.2%/kyr) is about half the rate reported for an analysis of\nXMM-Newton data from a similar, but not identical, portion of the rim over a\nsimilar, but not identical, time interval (0.84 +/- 0.23 arcsec/yr, Katsuda et\nal. 2008a). If the Chandra rate is representative of the remnant as a whole,\nthen the results of a hydrodynamic analysis suggest that G266.2-1.2 is between\n2.4 and 5.1 kyr old if it is expanding into a uniform ambient medium (whether\nor not it was produced by a Type Ia or Type II event). If the remnant is\nexpanding into the material shed by a steady stellar wind, then the age could\nbe as much as 50% higher. The Chandra expansion rate and a requirement that the\nshock speed be greater than or equal to 1000 km/s yields a lower limit on the\ndistance of 0.5 kpc. An analysis of previously-published distance estimates and\nconstraints suggests G266.2-1.2 is no further than 1.0 kpc. This range of\ndistances is consistent with the distance to the nearer of two groups of\nmaterial in the Vela Molecular Ridge (0.7 +/- 0.2 kpc, Liseau et al. 1992) and\nto the Vel OB1 association (0.8 kpc, Eggen 1982).\n