UV Spectroscopy of SN 1993J and Detection of Stellar Wind Material from the Progenitor

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

[55.03] UV Spectroscopy of SN 1993J and Detection of Stellar Wind Material from the Progenitor

G. Sonneborn (NASA/GSFC), C. Fransson (Stockholm Obs.), R.P. Kirshner (CfA), P.M. Rodriguez and W. Wamsteker (ESA IUE Obs.)

Low and high resolution IUE spectra (1150-3200\AA) of SN 1993J in NGC 3031 were obtained starting on 1993 March 30.2 UT. The initially strong ultraviolet continuum faded rapidly by April 4 (a factor of 200 at $\lambda<1600$\AA); smaller decreases occurred at longer wavelengths. The time of maximum light appears to have been prior to March 30 at all UV wavelengths. The UV flux changes were initially rapid, but slowed considerably after April 2. During this period the spectrum remained devoid of significant spectral features, aside from numerous interstellar absorption lines, N V $\lambda$1240 emission, and a 2200\AA\ feature corresponding to a total extinction of $E(B-V)\sim0.1$.

A short wavelength high dispersion spectrum taken March 30 shows N V $\lambda\lambda$1238.82--1242.80 emission features. The $\lambda$1242.80 line has a red wing extending $\sim$ 200 km/sec; the $\lambda$1238.82 line is narrow, with FWHM $\sim$ 35 km/sec. The N V flux measured in the low resolution spectra has followed a light curve similar to the UV continuum, decreasing by a factor 43 between March 30.2 and April 4.5. On March 30 the N V luminosity was $L_{N V} \sim 10^6 L_{\odot}$, assuming a distance of 3.5 Mpc to NGC 3031. The properties of the N V line (narrow width, large flux, prompt appearance, rapid decay) suggest that this emission arises in slowly moving, dense material close to the progenitor, most likely a stellar wind, characteristic of late-type supergiants. The high state of ionization strongly indicates that the wind was ionized and heated by the UV and X-rays from the shock breakout and the radiation resulting from the interaction of the ejecta and circumstellar medium (e.g. Lundqvist \& Fransson, A\&A {\bf192}, 221 (1992)). The interaction of the SN ejecta with stellar wind material creates one high velocity shock and one reverse shock, producing X-ray and radio emission consistent with reported detections.

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