Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution
Abstract
New observations of the supernova SN 1980K made with the VLA at 20 cm and 6 cm from 1994 April through 1996 October show that it has undergone a significant change in its radio emission evolution, dropping by a factor of ~2 below the flux density S ~ t-0.73 power-law decline with time t observed earlier. However, although S at all observed frequencies has decreased significantly, its current spectral index of α = -0.42 +/- 0.15 (S ~ ν+α) is consistent with the previous spectral index of α = -0.60+0.04-0.07.
It is suggested that this decrease in emission may be due to the supernova (SN) shock entering a new region of the circumstellar material that has a lower density than that expected for a constant speed (w), constant mass-loss rate (Ṁ) wind from the progenitor. If such an interpretation is correct, the difference in wind and shock speeds appears to indicate a significant evolution in the mass-loss history of the SN progenitor ~104 yr before explosion, with a change in circumstellar density (~Ṁ/w) occurring over a time span of <~4 kyr. Such features could be explained in terms of a fast ``blue-loop'' evolutionary phase of a relatively massive pre-SN progenitor star. If so, we may, for the first time, provide a stringent constraint on the mass of the SN progenitor based solely on the SN's radio emission.- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1998
- DOI:
- 10.1086/306261
- arXiv:
- arXiv:astro-ph/9802296
- Bibcode:
- 1998ApJ...506..874M
- Keywords:
-
- RADIO CONTINUUM: STARS;
- STARS: EVOLUTION;
- STARS: SUPERNOVAE: INDIVIDUAL: ALPHANUMERIC: SN 1980K;
- Radio Continuum: Stars;
- Stars: Evolution;
- Stars: Supernovae: Individual: Alphanumeric: SN 1980K;
- Astrophysics
- E-Print:
- 22 pages, 3 figures, to appear in ApJ