Early-Time Spectroscopy of SN1993J

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Session 55 -- SN 1993J; High Energy Astrophysics
Oral presentation, Wednesday, 10:30-12:00, Dwinelle 145 Room

[55.02] Early-Time Spectroscopy of SN1993J

T.Matheson, A.V. Filippenko (UCB)

We present high quality optical to near-infrared spectra of SN 1993J in M81. The initial spectrum, obtained on March 30.3 UT, two days after discovery, is featureless on large scales, but contains many broad peaks and valleys with relative amplitudes of approximately 2-8\%. The largest bump occurs at 5360 \AA, with others near 4500, 5610, and 6450 \AA. The emission feature at 6450 \AA~has a corresponding absorption trough with a minimum at 6270 \AA, which may be a weak P-Cygni profile. If this is H$\alpha$, the expansion velocity derived from the minimum of the trough would be 13,000 km s$^{-1}$, with an emission peak blueshifted by 5000 km~s$^{-1}$. In addition to the broad features, SN 1993J exhibited several narrow emission lines at this early stage. One is at 6560 \AA, and is identified with H$\alpha$. Another is He~II $\lambda$4686 at 4684 \AA, and a line at 6371 \AA~that is possibly [Fe~X] $\lambda$6374. The high-excitation emission could be the result of ionization of circumstellar gas by the ultraviolet radiation from the stellar surface after the supernova shockwave has broken out. There are also several interstellar absorption lines, including 3735 \AA, which might be Al~II $\lambda$3735, 3933~\AA~(Ca~II~K), 3968 \AA~(Ca~II~H), and 5893 \AA~(Na~I~D, blended). We will also discuss several spectra obtained in the weeks following discovery as the supernova evolved. We hope to have fairly complete coverage of the day-to-day development of the spectra, and to correlate this with daily photometry of the supernova (Paik, et al. 1993, this meeting).

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