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P.M. Garnavich (ND), R.P. Kirshner, P. Challis, S. Jha (CfA), D. Branch (U.Okla.), R. Chevalier (U.Va.), A.V. Filippenko, W. Li (UCB), C. Fransson, P. Lundqvist (Stockholm), R. McCray (U.Col.), N. Panagia (STScI), M.M. Phillips (Carnegie), C.S.J. Pun, G. Sonneborn, B.P. Schmidt (GSFC), N.B. Suntzeff (CTIO), J.C. Wheeler (U.Tex.), Supernova INtensive Study (SINS) Collaboration
We resolve the light echos produced by the type~Ia supernova 1998bu using the Hubble Space Telescope (HST) Wide Field Planetary Camera 2. An echo results when light emitted near supernova maximum is redirected toward the earth by dust scattering and delayed by the increased path length. SN~1987A and SN~1991T are the only other supernovae to have detected echos. The HST data was taken 762 days after SN~1998bu reached maximum brightness. The image exhibits two echos, an outer ring with radius of 0.24''±0.01'' and a inner component with a full width at half maximum of 0.14''±0.01''. The inner echo is shifted by 0.04'' from the center of the ring which suggests that the outer dust sheet is highly inclined to our line-of-sight or the inner dust is not distributed uniformly near the supernova. The total brightness of the echos is V=21.4 with approximately two thirds of the flux coming from the outer ring. Using a Cepheid distance to M96 of 10.5~Mpc, we find that the dust producing the outer ring is at an average distance of 120±15~parsec from the supernova and this may correspond to the distance between the supernova and the disk of M96. The inner echo comes from dust which is no more than 10~parsec from the explosion and which may have surrounded the progenitor.
The author(s) of this abstract have provided an email address for comments about the abstract: pgarnavi@nd.edu