Chandra X-ray Observation of a Mature Cloud-Shock Interaction in the Bright Eastern Knot Region of Puppis A

We present Chandra X-ray images and spectra of the most prominent cloudshock interaction region in the Puppis A supernova remnant. The Bright Eastern Knot (BEK) has two main morphological components: (1) a bright compact knot that lies directly behind the apex of an indentation in the eastern X-ray boundary and (2) lying 1 westward behind the shock, a curved vertical structure (bar) that is separated from a smaller bright cloud (cap) by faint diffuse emission. Based on hardness images and spectra, we identify the bar and cap as a single shocked interstellar cloud. Its morphology strongly resembles the “voided sphere” structures seen at late times in Klein et al.’s experimental simulations of cloud-shock interactions, when the crushing of the cloud by shear instabilities is well underway. We infer an interaction time of roughly 3 cloud-crushing timescales, which translates to 2000-4000 years, based on the X-ray temperature, physical size, and estimated expansion of the shocked cloud. This is the first X-ray identified example of a cloud-shock interaction in this advanced phase. Closer to the shock front, the X-ray emission of the compact knot in the eastern part of the BEK region implies a recent interaction with relatively denser gas, some of which lies in front of the remnant. The complex spatial relationship of the X-ray emission of the compact knot to optical [O III] emission suggests that there are multiple cloud interactions occurring along the line of sight. Subject headings: instabilities; ISM:clouds; ISM: supernova remants; X-rays: individual (Puppis A) NASA Goddard Space Flight Center, Code 662, Greenbelt MD 20771; [email protected] Department of Physics and Astronomy, The Johns Hopkins University, 3400 Charles St, Baltimore MD 21218 Kavli Institute for Astrophysics and Space Research, MIT, 77 Massachussetts Ave, Cambridge MA 02139