- SN 1993J
SN 1993J is asupernova observed in the galaxyM81 . It was discovered on 28 March 1993 by F. Garcia in Spaincite journal
author=J. Ripero, F. Garcia, D. Rodriguez, P. Pujol, A. V. Filippenko, R. R. Treffers, Y. Paik, M. Davis, D. Schlegel, F. D. A. Hartwick, D. D. Balam, D. Zurek, R. M. Robb, P. Garnavich, B. A. Hong
title=Supernova 1993J in NGC 3031
journal=IAU Circular
year=1993
volume=5731
url=http://adsabs.harvard.edu/abs/1993IAUC.5731....1R] . At the time, it was the second brightest supernova observed in the twentieth centurycite journal
author=B. P. Schmidt, R. P. Kirshner, R. G. Eastman, R. Grashuis, I. dell'Antonio, N. Caldwell, C. Foltz, J. P. Huchra, A. A. E. Milone
title=The unusual supernova SN1993J in the galaxy M81
journal=Nature
year=1993
volume=364
pages=600–602
url=http://adsabs.harvard.edu/abs/1993Natur.364..600S
doi=10.1038/364600a0] .The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernova formed by the explosion of a giant star) with strong
hydrogen spectral line emission, but later the hydrogen lines faded and stronghelium spectral lines appeared, making the supernova look more like a type Ibcite journal
author=A. V. Filippenko, T. Matheson, L. C. Ho
title=The "Type IIb" Supernova 1993J in M81: A Close Relative of Type Ib Supernovae
journal=Astrophysical Journal Letters
year=1993
volume=415
pages=L103–L106
url=http://adsabs.harvard.edu/abs/1993ApJ...415L.103F
doi=10.1086/187043] . Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovaecite journal
author=P. J. Benson, W. Herbst, J. J> Salzer, G. Vinton, G. J. Hanson, S. J. Ratcliff, P. F. Winkler, D. M. Elmegreen, F. Chromey, C. Strom, T. J. Balonek, B. G. Elmegreen
title=Light curves of SN 1993J from the Keck Northeast Astronomy Consortium
journal=Astronomical Journal
year=1994
volume=107
pages=1453–1460
url=http://adsabs.harvard.edu/abs/1994AJ....107.1453B
doi=10.1086/116958] cite journal
author=J. C. Wheeler, E. Barker, R. Benjamin, J. Boisseau, A. Clocchiatti, G. de Vaucouleurs, N. Gaffney, R. P. Harkness, A. M. Khokhlov, D. F. Lester, B. J> Smith, V. V. Smith, J. Tomkin
title=Early Observations of SN 1993J in M81 at McDonald Observatory
journal=Astrophysical Journal
year=1993
volume=417
pages=L71–L74
url=http://adsabs.harvard.edu/abs/1993ApJ...417L..71W
doi=10.1086/187097] but did resemble the variations observed in type Ib supernovaecite journal
author=M. W. Richmond, R. R. Treffers, A. V. Filippenko, Y. Palik, B. Leibundgut, E. Schulman, C. V. Cox
title=UBVRI photometry of SN 1993J in M81: The first 120 days
journal=Astronomical Journal
year=1994
volume=107
pages=1022–1040
url=http://adsabs.harvard.edu/abs/1994AJ....107.1022R
doi=10.1086/116915] . Hence, the supernova has been classified as a "type IIb", a transitory class between type II and type Ib. The scientific results from this supernova suggested that type Ib and Ic supernovae were actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovaecite journal
author=A. V. Filippenko, T. Matheson, A. J. Barth
title=The peculiar type II supernova 1993J in M81: Transition to the nebular phase
journal=Astronomical Journal
year=1994
volume=108
pages=2220–2225
url=http://adsabs.harvard.edu/abs/1994AJ....108.2220F
doi=10.1086/117234] . The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81.Light echo s from the explosion have subsequently been detected. [cite paper|title=Multiple Light Echoes from Supernova 1993J|url=http://arxiv.org/abs/astro-ph/0207497|author=Sugerman, Ben and Crotts, Arlin|date=November 8, 2002|publisher=Columbia University]References
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