A Non-equipartition Shock Wave Traveling in a Dense Circumstellar Environment around SN 2020oi

Full list of authors: Horesh, Assaf; Sfaradi, Itai; Ergon, Mattias; Barbarino, Cristina; Sollerman, Jesper; Moldon, Javier; Dobie, Dougal; Schulze, Steve; Pérez-Torres, Miguel; Williams, David R. A.; Fremling, Christoffer; Gal-Yam, Avishay; Kulkarni, Shrinivas R.; O'Brien, Andrew; Lundqvist, Peter; Murphy, Tara; Fender, Rob; Anand, Shreya; Belicki, Justin; Bellm, Eric C.; Coughlin, Michael W.; De, Kishalay; Golkhou, V. Zach; Graham, Matthew J.; Green, Dave A.; Hankins, Matt; Kasliwal, Mansi; Kupfer, Thomas; Laher, Russ R.; Masci, Frank J.; Miller, A. A.; Neill, James D.; Ofek, Eran O.; Perrott, Yvette; Porter, Michael; Reiley, Daniel J.; Rigault, Mickael; Rodriguez, Hector; Rusholme, Ben; Shupe, David L.; Titterington, DavidWe report the discovery and panchromatic follow-up observations of the young Type Ic supernova (SN Ic) SN 2020oi in M100, a grand-design spiral galaxy at a mere distance of 14 Mpc. We followed up with observations at radio, X-ray, and optical wavelengths from only a few days to several months after explosion. The optical behavior of the supernova is similar to those of other normal SNe Ic. The event was not detected in the X-ray band but our radio observations revealed a bright mJy source (Lν ≈ 1.2× 1027 erg s-1 Hz-1). Given the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio data set we obtained. The radio-emitting electrons initially experience a phase of inverse Compton cooling, which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of e/ B ⪆ 200, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shock wave driven by the SN ejecta into the circumstellar matter (CSM) is moving at ∼ 3× 104 km s-1. Assuming a constant mass loss from the stellar progenitor, we find that the mass-loss rate is ⊙M≈ 1.4× 10-4 M⊙ yr-1 for an assumed wind velocity of 1000 km s-1. The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard r -2. © 2020. The American Astronomical Society. All rights reserved.We thank the anonymous referee. A.H. is grateful for the support by grants from the Israel Science Foundation, the USIsrael Binational Science Foundation (BSF), and the I-CORE Program of the Planning and Budgeting Committee and the Israel Science Foundation. T.M. acknowledges the support of the Australian Research Council through grant FT150100099. D.D. is supported by an Australian Government Research Training Program Scholarship. D.R.A.W. was supported by the Oxford Centre for Astrophysical Surveys, which is funded through generous support from the Hintze Family Charitable Foundation. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). M.P.T. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and through grant PGC2018-098915-B-C21 (MCI/AEI/FEDER, UE). J.M. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). A.G.Y.'s research is supported by the EU via ERC grant No. 725161, the ISF GW excellence center, an IMOS space infrastructure grant and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Paul and Tina Gardner, Yeda-Sela and the WIS-CIT joint research grant; A.G.Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation. M.R. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement n759194-USNAC). M.W.C. acknowledges support from the National Science Foundation with grant number PHY-2010970. C.F. gratefully acknowledges support of his research by the Heising-Simons Foundation (#2018-0907). Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. Z.T.F. is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. Partly based on observations made with the Nordic Optical Telescope. SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC. We thank the staff of the Mullard Radio Astronomy Observatory for their assistance in the commissioning, maintenance, and operation of AMI, which is supported by the Universities of Cambridge and Oxford. We also acknowledge support from the European Research Council under grant ERC-2012-StG-307215 LODESTONE. This work was supported by the GROWTH project funded by the National Science Foundation under grant No. 1545949.Peer reviewe