Discovery of a Photoionization Precursor in Tycho's Supernova Remnant

Details Discovery of a Photoionization Precursor in Tycho's Supernova Remnant Discovery of a Photoionization Precursor in Tycho's Supernova Remnant

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.4308g&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #43.08; Bulletin of the American Astronomical Society, Vol. 31, p.1432

Astronomy and Astrophysics

Astronomy

Scientific paper

We report optical spectroscopy and imaging of Tycho's supernova remnant which suggest the presence of a He II λ 304 photoionization precursor associated with the blast wave. In longslit spectra of the eastern rim, we find diffuse Hα emission extending ≳ 1' ahead of Knot g, a bright nonradiative shock propagating at velocity 2000 km s-1. In addition to the hydrogen lines, the diffuse spectrum also exhibits [SII] λ λ 6716, 6731, [NII] λ 6583 and weak [OIII] λ 5007 emission. Narrow band imagery of Tycho's SNR shows that the diffuse emission extends ahead of most of the Balmer-dominated optical filaments, and drops sharply in the remnant interior, suggesting that the diffuse gas is overrun by the supernova shock. We compare the line ratios of the diffuse gas with predictions from a simple He II λ 304 photoionization precursor model. The models predict that the radiative transfer of He II photons in the precursor produces spatially distinct ionization layers of H0, He0- He+, N0- N++, O0- O++ and S+- S3+ ahead of the shock. The models suggest that the diffuse emission arises from collisional excitation in mostly neutral gas which has been heated to a temperature 12,000 K.

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