# Radio emission of SN1993J: the complete picture. I. Re-analysis of all the available VLBI data - Astrophysics > High Energy Astrophysical Phenomena

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Abstract: We have performed a complete re-calibration and re-analysis of all theavailable VLBI observations of supernova SN1993J, following an homogeneous andwell-defined methodology. Observations of SN1993J at 69 epochs, spanning 13years, were performed by two teams, which used different strategies andanalysis tools. The results obtained by each group are similar, but theirconclusions on the supernova expansion and the shape and evolution of theemitting region differ significantly. From our analysis of the combined set ofobservations, we have obtained an expansion curve with unprecedented timeresolution and coverage. We find that the data from both teams are compatiblewhen analyzed with the same methodology. One expansion index $m 3 = 0.87 \pm0.02$ is enough to model the expansion observed at 1.7\,GHz, while twoexpansion indices $m 1 = 0.933\pm0.010$ and $m 2 = 0.796\pm0.005$, separatedby a break time, $t {br} = 390\pm30$ days, are needed to model the data, atfrequencies higher than 1.7\,GHz, up to day 4000 after explosion. We thusconfirm the wavelength dependence of the size of the emitting region reportedby one of the groups. We also find that all sizes measured at epochs later thanday 4000 after explosion are systematically smaller than our model predictions.We estimate the fractional shell width $0.31 \pm 0.02$, average of all epochsand frequencies and the level of opacity to the radio emission by the ejecta.We find evidence of a spectral-index radial gradient in the supernova shell,which is indicative of a frequency-dependent ejecta opacity. Finally, we studythe distribution and evolution of the azimuthal anisotropies hot spots foundaround the radio shell during the expansion. These anisotropies haveintensities of $\sim 20$% of the mean flux density of the shell, and appear tosystematically evolve during the expansion.

Autor: I. Marti-Vidal, J.M. Marcaide, A. Alberdi, J.C. Guirado, M.A. Perez-Torres, E. Ros

Fuente: https://arxiv.org/