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Published December 1, 2013 | Published + Submitted
Journal Article Open

An early and comprehensive millimetre and centimetre wave and X-ray study of SN 2011dh: a non-equipartition blast wave expanding into a massive stellar wind


Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3–12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (ϵ_e/ϵ_B ∼ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R^(−2). Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s^(−1), contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (∼1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ϵ_e/ϵ_B.

Additional Information

© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 August 30. Received 2013 August 30; in original form 2013 June 5. Published: 26 September 2013. We thank the EVLA and CARMA staff for promptly scheduling this target of opportunity. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Support for CARMA construction was derived from the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the James S. McDonnell Foundation, the Associates of the California Institute of Technology, the University of Chicago, the states of California, Illinois and Maryland, and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities. This work made use of data supplied by the UK SSDC. PTF is a fully automated, wide-field survey aimed at a systematic exploration of explosions and variable phenomena in optical wavelengths. The participating institutions are Caltech, Columbia University, Weizmann Institute of Science, Lawrence Berkeley Laboratory, Oxford and University of California at Berkeley. The programme is centred on a 12K × 8K, 7.8 deg2 CCD array (CFH12K) re-engineered for the 1.2-m Oschin Telescope at the Palomar Observatory by Caltech Optical Observatories. Photometric follow-up is undertaken by the automated Palomar 1.5-m telescope. Research at Caltech is supported by grants from NSF and NASA. The Weizmann PTF partnership is supported in part by the Israeli Science Foundation via grants to AG. The Weizmann–Caltech collaboration is supported by a grant from the BSF to AG and SRK. AG further acknowledges the Lord Sieff of Brimpton Foundation. CS is supported by the NASA Wisconsin Space Grant Consortium. FB acknowledges support from CONICYT, Chile, under grants FONDECYT 1101024 and FONDAP-CATA 15010003, Programa de Financiamiento Basal, the Iniciativa Cientifica Milenio through the Millennium Center for Supernova Science grant P10-064-F, and Chandra X-ray Center grants SAO GO9-0086D and GO0-11095A. MMK acknowledges support from the Hubble Fellowship and the Carnegie–Princeton Fellowship. NP acknowledges partial support by STScI-DDRF grant D0001.82435. Research at the Naval Research Laboratory is supported by funding from the Office of Naval Research. SBC acknowledges generous financial assistance from Gary & Cynthia Bengier, the Richard & Rhoda Goldman Fund, the Sylvia & Jim Katzman Foundation, the Christopher R. Redlich Fund, the TABASGO Foundation, and NSF grants AST-0908886 and AST-1211916. We thank the anonymous referee for his constructive comments.

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