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Title:
Hubble Space Telescope Observations of High-Velocity Lyα and Hα Emission from Supernova Remnant 1987A: The Structure and Development of the Reverse Shock
Authors:
Michael, Eli; McCray, Richard; Chevalier, Roger; Filippenko, Alexei V.; Lundqvist, Peter; Challis, Peter; Sugerman, Ben; Lawrence, Stephen; Pun, C. S. J.; Garnavich, Peter; Kirshner, Robert; Crotts, Arlin; Fransson, Claes; Li, Weidong; Panagia, Nino; Phillips, Mark; Schmidt, Brian; Sonneborn, George; Suntzeff, Nicholas; Wang, Lifan; Wheeler, J. Craig
Affiliation:
AA(JILA, University of Colorado, Campus Box 440, Boulder, CO 80309-0440 .), AB(JILA, University of Colorado, Campus Box 440, Boulder, CO 80309-0440 .), AC(Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818.), AD(Department of Astronomy, University of California, Berkeley, CA 94720-3411.), AE(SCFAB, Stockholm Observatory, Department of Astronomy, SE-10691 Stockholm, Sweden.), AF(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.), AG(Department of Physics and Astronomy, 151 Hofstra University, Hempstead, NY 11590.), AH(Department of Physics and Astronomy, 151 Hofstra University, Hempstead, NY 11590.), AI(Laboratory for Astronomy and Space Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt, MD 20771.; Current address: Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong.), AJ(Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556.), AK(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.), AL(Department of Physics and Astronomy, 151 Hofstra University, Hempstead, NY 11590.), AM(SCFAB, Stockholm Observatory, Department of Astronomy, SE-10691 Stockholm, Sweden.), AN(Department of Astronomy, University of California, Berkeley, CA 94720-3411.), AO(STScI, 3700 San Martin Drive, Baltimore, MD 21218; on assignment from the Space Science Department of ESA.), AP(Carnegie Institution of Washington, Las Campanas Observatory, Casilla 601, Chile.), AQ(Mount Stromlo and Siding Spring Observatories, Private Bag, Weston Creek P.O., ACT 2611, Australia.), AR(Laboratory for Astronomy and Space Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt, MD 20771.), AS(Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile.), AT(Institute for Nuclear and Particle Astrophysics, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA 94720.), AU(Department of Astronomy, University of Texas, Austin, TX 78712.)
Publication:
The Astrophysical Journal, Volume 593, Issue 2, pp. 809-830. (ApJ Homepage)
Publication Date:
08/2003
Origin:
UCP
ApJ Keywords:
Shock Waves, Stars: Supernovae: Individual: Alphanumeric: SN 1987A, ISM: Supernova Remnants
DOI:
10.1086/376725
Bibliographic Code:
2003ApJ...593..809M

Abstract

We present two-dimensional line profiles of high-velocity (~+/-12,000 km s-1) Lyα and Hα emission from supernova remnant 1987A obtained with the Space Telescope Imaging Spectrograph between 1997 September and 2001 September (days 3869-5327 after the explosion). This emission comes from hydrogen in the debris that is excited and ionized as it passes through the remnant's reverse shock. We use these profiles to measure the geometry and development of the reverse-shock surface. The observed emission is confined within ~+/-30° about the remnant's equatorial plane. At the equator, the reverse shock has a radius of ~75% of the distance to the equatorial ring. We detect marginal differences (6%+/-3%) between the location of the reverse-shock front in the northeast and southwest parts of the remnant. The radius of the reverse shock surface increases for latitudes above the equator, a geometry consistent with a model in which the supernova debris expands into a bipolar nebula. Assuming that the outer supernova debris has a power-law density distribution, we can infer from the reverse-shock emission light curve an expansion rate (in the northeast part of the remnant) of 3700+/-900kms-1, consistent with the expansion velocities determined from observations in radio (Manchester et al.) and X-ray (Park et al.; Michael et al.) wavelengths. However, our most recent observation (at day 5327) suggests that the rate of increase of mass flux across the northeast sector of the reverse shock has accelerated, perhaps because of deceleration of the reverse shock caused by the arrival of a reflected shock created when the blast wave struck the inner ring. Resonant scattering within the supernova debris causes Lyα photons created at the reverse shock to be directed preferentially outward, resulting in a factor of ~5 difference in the observed brightness of the reverse shock in Lyα between the near and far sides of the remnant. Accounting for this effect, we compare the observed reverse-shock Lyα and Hα fluxes to infer the amount of interstellar extinction by dust as E(B-V)=0.17+/-0.01 mag. We also notice extinction by dust in the equatorial ring with E(B-V)~0.02-0.08 mag, which implies dust-to-gas ratios similar to that of the LMC. Since Hα photons are optically thin to scattering, the observed asymmetry in brightness of Hα from the near and far sides of the remnant represents a real asymmetry in the mass flux through the reverse shock of ~30%. We discuss future observational strategies that will permit us to further investigate the reverse-shock dynamics and resonant scattering of the Lyα line and to constrain better the extinction by dust within and in front of the remnant.
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