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Title: RADIO AND X-RAY OBSERVATIONS OF THE TYPE Ic SN 2007gr REVEAL AN ORDINARY, NON-RELATIVISTIC EXPLOSION

We present extensive radio and X-ray observations of the nearby Type Ic SN 2007gr in NGC 1058 obtained with the Very Large Array (VLA) and the Chandra X-ray Observatory and spanning 5 to 150 days after explosion. Through our detailed modeling of these data, we estimate the properties of the blast wave and the circumstellar environment. We find evidence for a freely expanding and non-relativistic explosion with an average blast wave velocity, v-bar {approx}0.2c, and a total internal energy for the radio emitting material of E {approx} 2 x 10{sup 46} erg assuming equipartition of energy between electrons and magnetic fields ({epsilon}{sub e} = {epsilon}{sub B} = 0.1). The temporal and spectral evolution of the radio emission points to a stellar wind-blown environment shaped by a steady progenitor mass loss rate of M-dot {approx}6x10{sup -7} M{sub sun} yr{sup -1} (wind velocity, v{sub w} = 10{sup 3} km s{sup -1}). These parameters are fully consistent with those inferred for other SNe Ibc and are in line with the expectations for an ordinary, homologous SN explosion. Our results are at odds with those of Paragi et al. who recently reported evidence for a relativistic blast wave in SN 2007gr based on theirmore » claim that the radio emission was resolved away in a low signal-to-noise Very Long Baseline Interferometry (VLBI) observation. Here we show that the exotic physical scenarios required to explain the claimed relativistic velocity-extreme departures from equipartition and/or a highly collimated outflow-are excluded by our detailed VLA radio observations. Moreover, we present an independent analysis of the VLBI data and propose that a modest loss of phase coherence provides a more natural explanation for the apparent flux density loss which is evident on both short and long baselines. We conclude that SN 2007gr is an ordinary Type Ibc supernova.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
  2. Max-Planck-Institute for Radio Astronomy, Auf dem Hugel 69, 53121 Bonn (Germany)
  3. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel)
  4. University of Virginia, Astronomy Department, Charlottesville, VA 22904 (United States)
  5. Hartebeesthoek Radio Observatory, P.O. Box 443, Krugersdorpa, 1740 (South Africa)
Publication Date:
OSTI Identifier:
21474392
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 725; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/725/1/922
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC GAMMA BURSTS; EMISSION; EXPLOSIONS; FLUX DENSITY; INTERFEROMETRY; MAGNETIC FIELDS; RELATIVISTIC RANGE; STELLAR WINDS; SUPERNOVAE; X RADIATION BINARY STARS; COSMIC RADIATION; ELECTROMAGNETIC RADIATION; ENERGY RANGE; ERUPTIVE VARIABLE STARS; IONIZING RADIATIONS; PRIMARY COSMIC RADIATION; RADIATIONS; STARS; STELLAR ACTIVITY; VARIABLE STARS