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تسجيل مستخدم جديدThe Evolution of Late-time Optical Emission from SN 1986J
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We present late-time optical images and spectra of the Type IIn supernova SN 1986J. HST ACS/WFC images obtained in February 2003 show it to be still relatively bright with m(F606W) = 21.4 and m(F814W) = 20.0 mag. Compared against December 1994 HST WFPC2 images, SN 1986J shows a decline of only <1 mag in brightness over eight years. Ground-based spectra taken in 1989, 1991 and 2007 show a 50% decline in Halpha emission between 1989-1991 and an order of magnitude drop between 1991-2007, along with the disappearance of He I line emissions during the period 1991-2007. The objects [O I] 6300, 6364, [O II] 7319, 7330 and [O III] 4959, 5007 emission lines show two prominent peaks near -1000 km/s and -3500 km/s, with the more blueshifted component declining significantly in strength between 1991 and 2007. The observed spectral evolution suggests two different origins for SN 1986Js late-time optical emission: dense, shock-heated circumstellar material which gave rise to the initially bright Halpha, He I, and [N II] 5755 lines, and reverse-shock heated O-rich ejecta on the facing expanding hemisphere dominated by two large clumps generating two blueshifted emission peaks of [O I], [O II], and [O III] lines.
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Optical spectra of the bright Type II-L supernova SN 1979C obtained in April 2008 with the 6.5 m MMT telescope are compared with archival late-time spectra to follow the evolution of its optical emission over the age range of 11 to 29 years. We estim
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determined age. In contrast to the strongly blueshifted emission line profiles observed for all other late-time CCSNe thought to be due to dust extinction of rear hemisphere ejecta, SN 1941Cs spectrum exhibits stronger redshifted than blueshifted emissions of [O I] 6300, 6364 A, [O II] 7319, 7330 A, and [O III] 4959, 5007 A. The oxygen emissions exhibit rest frame expansion velocities of -2200 to +4400 km/s. No other significant broad line emissions were detected including Halpha emission. We discuss possible causes for this unusual spectrum and compare SN 1941Cs optical and X-ray luminosities to other evolved CCSNe.
Ground-based optical spectra and Hubble Space Telescope images of ten core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. Ne
w observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor stars circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in Halpha/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the 330 yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as clumps or blobs of ejecta may instead be linked with large-scale rings of SN debris.
We report on VLA measurements between 1 and 45 GHz of the evolving radio spectral energy distribution (SED) of SN 1986J, made in conjunction with VLBI imaging. The SED of SN 1986J is unique among supernovae, and shows an inversion point and a high-fr
equency turnover. Both are due to the central component seen in the VLBI images, and both are progressing downward in frequency with time. The optically-thin spectral index of the central component is almost the same as that of the shell. We fit a simple model to the evolving SED consisting of an optically-thin shell and a partly-absorbed central component. The evolution of the SED is consistent with that of a homologously expanding system. Both components are fading, but the shell more rapidly. We conclude that the central component is physically inside the expanding shell, and not a surface hot-spot central only in projection. Our observations are consistent with the central component being due to interaction of the shock with the dense and highly-structured circumstellar medium that resulted from a period of common-envelope evolution of the progenitor. However a young pulsar-wind nebula or emission from an accreting black hole can also not be ruled out at this point.
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