Is Vela Jr. a young supernova remnant? Original Research Article

The supernova remnant RX J0852.0-4622 (or Vela Jr.) has been considered to be very young (∼680 yr) based mainly on the possible detection of a radioactive decay line of 44Ti whose lifetime is only ∼90 yr. Here, we report on expansion measurements of the northwestern rim of this remnant, based on XMM-Newton observations separated by 6.5 yr. The expansion rate is derived to be image (the first and second-term errors are responsible for statistical and systematic uncertainties, respectively). We estimate the age of this remnant to be image1000–3000 yr. Therefore, Vela Jr. turns out to be not so young as it was considered previously. The distance to this remnant is also derived to be at least ∼740 pc, assuming a high shock speed of image.