The properties of Supernova 1997cy associated to GRB970514

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  • 18 October 1999
Abstract
The extraordinary SN 1997cy associated with GRB970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery SN 1997cy was the brightest SN observed so far (Mv<-20.1, v(hel)=19140 km/s, Ho=65 km/s Mpc^(-1)). Up to the last available observations (600 days after the GRB) the total flux was equal to or larger than that expected from the complete thermalization of the gamma-rays produced by 2.3 Msun of 56Co. However, starting already on day 60 the luminosity declines more slowly than the 56Co, indicating that the SN ejecta was interacting with a CSM. The interaction appeared to weaken around day 550. Similarly to SN 1988Z, the spectra of SN 1997cy are dominated at all epochs by Halpha emission, which shows at least 3 components of different widths. Several other lines of different widths are also visible, especially at early epochs. The entire light curve of SN 1997cy has been reproduced by a model of interaction of the very energetic (E=5x10^(52) ergs) ejecta of a massive star (25 Msun) with the CSM, without a noticable contribution from radioactive decays. Such a CSM could have been ejected with a mass-loss rate of Mdot ~ 4x10^(-4) Msun yr^(-1) by the progenitor star evolving from a BSG to a RSG about 10^4 yr before the explosion.

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