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Title:
Location of the Optical Reverse Shock in the Cassiopeia A Supernova Remnant
Authors:
Morse, Jon A.; Fesen, Robert A.; Chevalier, Roger A.; Borkowski, Kazimierz J.; Gerardy, Christopher L.; Lawrence, Stephen S.; van den Bergh, Sidney
Affiliation:
AA(Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309.; Current address: Department of Physics and Astronomy, Arizona State University, Box 871504, Tempe, AZ 85287-1504 .), AB(Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755.), AC(Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903.), AD(Department of Physics, North Carolina State University, Raleigh, NC 27695.), AE(McDonald Observatory, 1 University Station, C1402, Austin, TX 78712-0259.), AF(Department of Physics and Astronomy, Hofstra University, Hempstead, NY 11549.), AG(Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada.)
Publication:
The Astrophysical Journal, Volume 614, Issue 2, pp. 727-736. (ApJ Homepage)
Publication Date:
10/2004
Origin:
UCP
ApJ Keywords:
ISM: Individual: Name: Cassiopeia A, ISM: Kinematics and Dynamics, ISM: Supernova Remnants
DOI:
10.1086/423709
Bibliographic Code:
2004ApJ...614..727M

Abstract

We use two epochs of Hubble Space Telescope WFPC2 images separated by 2 yr to determine the location and propagation of the reverse shock (RS) in the young supernova remnant Cassiopeia A (Cas A). The images trace optical line emission from fast-moving knots and filaments of highly processed ejecta as they cross the RS, become heated and compressed, and radiatively cool. At numerous positions around the optical shell, new emission features are seen in the 2002 images that were not yet visible in the 2000 exposures. In a few instances emission features seen in the first epoch have completely disappeared in the second epoch. We concentrate on two regions along the rim of the main emission shell in Cas A for close inspection: one in the northwestern part of the shell and another along the southwestern part of it. In these regions the RS is viewed almost edge-on, and its precise position has been measured. The RS is coherent in these regions over arcminute (~1 pc) scales but is highly distorted perpendicular to the direction of expansion. We find the RS to be generally expanding at 50%-60% of the ~5500 km s-1 bulk velocity of the optical ejecta. We present shock models for the ejecta that are consistent with the high densities and short cooling times observed in the optical knots of the Cas A remnant.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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