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RE: Supernova 2012cg
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Title: Strong Evidence Against A Non-Degenerate Companion in SN 2012cg
Author: B. J. Shappee, A. L. Piro, K. Z. Stanek, S. G. Patel, R. A. Margutti, V. M. Lipunov, R. W. Pogge

Even though SN 2012cg is one of the best-studied Type Ia Supernovae to date, the nature of its progenitor system has been debated in numerous studies. Specifically, it is difficult to reconcile the claims of the detection of a ~6 solar mass main-sequence companion by Marion et al. 2016 with the deep, late-time Halpha flux limits from maguire16. In this study we add three new constraints: 1) We analyse a high-signal-to-noise, nebular-phase, LBT/MODS spectrum of SN 2012cg and place an upper limit on the amount of low-velocity, solar-abundance material removed from a possible companion of <7.8 x 10^-3 solar mass. 2) We use Swift X-ray observations to constrain the preexplosion mass-loss rate to be M <10^-6 solar masses yr^-1 for vw=100kms^-1. 3) We carefully reanalyse a prediscovery MASTER image and, with published light curves of SN 2012cg, we estimate the time of first light and conservatively constrain the radius of a Roche-lobe overflowing companion to be <0.23 solar radii . These observations strongly disagree with Marion et al. 2016, and, when considered with other studies of SN 2012cg's progenitor system, essentially rule out a non-degenerate companion.

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SN 2012cg
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Title: SN~2012cg: Evidence for Interaction Between a Normal Type Ia Supernova and a Non-Degenerate Binary Companion
Author: G. H. Marion, Peter J. Brown, Jozsef Vinkó, Jeffrey M. Silverman, David J. Sand, Peter Challis, Robert P. Kirshner, J. Craig Wheeler, Perry Berlind, Warren R. Brown, Michael L. Calkins, Govinda Dhungana, Ryan J. Foley, Andrew S. Friedman, Melissa L. Graham, D. Andrew Howell, Eric Y. Hsiao, Jonathan M. Irwin, Robert Kehoe, Lucas M. Macri, Kaisey Mandel, Curtis McCully, Kenneth J. Rines, Steven Wilhelmy, Weikang Zheng

We report evidence for excess blue light from the Type Ia supernova SN~2012cg at fifteen and sixteen days before maximum B-band brightness. The emission is consistent with predictions for the impact of the supernova on a non-degenerate binary companion. This is the first evidence for emission from a companion to a normal SN~Ia. Sixteen days before maximum light, the B-V colour of SN~2012cg is 0.2 mag bluer than for other normal SN~Ia. At later times, this supernova has a typical SN~Ia light curve, with extinction-corrected M_B = -19.62 ± 0.02 mag and Delta m_{15}(B) = 0.86 ± 0.02. Our data set is extensive, with photometry in 7 filters from 5 independent sources. Early spectra also show the effects of blue light, and high-velocity features are observed at early times. Near maximum, the spectra are normal with a silicon velocity v_{Si} = -10,500 km/s. Comparing the early data with models by Kasen (2010) favours a main-sequence companion of about 6 solar masses. It is possible that many other SN Ia have main-sequence companions that have eluded detection because the emission from the impact is fleeting and faint.

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Supernova 2012cg in the galaxy NGC 4424 captured at 23:15 UT, 23rd June, 2012.
The Type Ia supernova was at ~ magnitude 12 V. 
2 minutes exposures with an 8" Reflector.
NGC 4417 (top) also captured.
No moonlight interference.



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Very early yesterday morning Herschel observed the supernova 2012cg in NGC4424. This object has been well observed by amateur astronomers and appears to have peaked at around magnitude 12 very close to the time of the Herschel observations.
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Supernova 2012cg now at magnitude 11.9



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It's official. According to AAVSO Special Notice #283 compiled by Elizabeth O. Waagen, there's a brand new, shiny supernova out there... at an observable magnitude. 
According to data taken with LOSS and reported by M. Kandrashoff, S. B. Cenko, W. Li, and A. V. Filippenko, spectra indicates a Type 1a supernova event began on approximately May 17, 2012 and has continued to brighten.

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Ed ~ Supernova 2012cg in the constellation of Virgo now at magnitude ~12.0



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Google earth file: Supernova 2012cg.kmz (1kb, kmz)



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A magnitude 16.9 Type Ia supernova, 2012cg, was discovered on the 17th May, 2012, in the Barred Spiral galaxy NGC 4424 in the constellation Virgo.
The supernova is located 17.3" East and 1.5" South from the center of the galaxy.

Position(2000): RA = 12 27 12.83 , Dec = +09 25 13.2

CBET003111

Ed ~ The supernova was reported to be at magnitude 12.9 by J. Gonzalez Carballo (Spain) on the 22nd May, 2012.



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