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Date and Time of the Query: 2019-08-23 T06:55:51 PDT
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For refcode 2006ApJ...651.1005S:
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Copyright by American Astronomical Society. Reproduced by permission
2006ApJ...651.1005S The Radio and X-Ray Luminous SN 2003bg and the Circumstellar Density Variations around Radio Supernovae A. M. Soderberg, R. A. Chevalier, S. R. Kulkarni, and D. A. Frail Abstract. We report extensive radio and X-ray observations of SN 2003bg, whose spectroscopic evolution shows a transition from a broad-lined Type Ic to a hydrogen-rich Type II, and later to a typical hydrogen-poor Type Ibc. We show that the extraordinarily luminous radio emission is well described by a self-absorption-dominated synchrotron spectrum, while the observed X-ray emission at t~30 days is adequately fit by inverse Compton scattering of the optical photons off of the synchrotron-emitting electrons. Our radio model implies a subrelativistic ejecta velocity, v^bar^~0.24c, at t_0_~10 days after the explosion, which emphasizes that broad optical absorption lines do not imply relativistic ejecta. We find that the total energy of the radio-emitting region evolves as E~7.3x10^48^(t/t_0_)^0.4^ ergs, assuming equipartition of energy between relativistic electrons and magnetic fields ({epsilon}_e_={epsilon}_B_=0.1). The circumstellar density is well described by a stellar wind profile, with modest (factor of ~2) episodic density enhancements that produce abrupt achromatic flux variations. We estimate an average mass-loss rate of M^dot^~3x10^-4^ M_sun_ yr^-1^ (assuming a wind velocity of v_w_=10^3^ km s^-1^) for the progenitor, consistent with the observed values for Galactic Wolf-Rayet stars. Comparison with other events reveals that ~50% of radio supernovae show similar short-timescale flux variations, attributable to circumstellar density irregularities. Specifically, the radio light curves of SN 2003bg are strikingly similar to those of the Type IIb SN 2001ig, suggestive of a common progenitor evolution for these two events. Based on the relative intensity of the inferred density enhancements, we conclude that the progenitors of SNe 2003bg and 2001ig experienced quasi-periodic mass-loss episodes just prior to the SN explosion. Finally, this study emphasizes that abrupt radio light-curve variations cannot be used as a reliable proxy for an engine-driven explosion, including off-axis gamma-ray bursts. Key words: Radiation Mechanisms: Nonthermal, Radio Continuum: General, supernovae: individual (SN 2003bg)
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