A Missing-Link in the Supernova-GRB Connection: The Case of SN 2012ap

Chakraborti, Sayan and Soderberg, Alicia and Chomiuk, Laura and Kamble, Atish and Yadav, Naveen and Ray, Alak and Hurley, Kevin and Margutti, Raffaella and Milisavljevic, Dan and Bietenholz, Michael and Brunthaler, Andreas and Pignata, Giuliano and Pian, Elena and Mazzali, Paolo and Fransson, Claes and Bartel, Norbert and Hamuy, Mario and Levesque, Emily and MacFadyen, Andrew and Dittmann, Jason and Krauss, Miriam and Briggs, M. S. and Connaughton, V. and Yamaoka, K. and Takahashi, T. and Ohno, Masanori and Fukazawa, Y. and Tashiro, M. and Terada, Y. and Murakami, T. (2015) A Missing-Link in the Supernova-GRB Connection: The Case of SN 2012ap. ASTROPHYSICAL JOURNAL, 805 (2). ISSN 1538-4357

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Abstract

Gamma Ray Bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However supernovae, with heavy ejecta, can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. Yet the ejecta from SN 2009bb was baryon loaded, and in nearly-free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB, but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than a sixth of the fluence from GRB 980425. This shows for the first time that central engines in type Ic supernovae, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

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