The Transitional Stripped-Envelope SN 2008ax: Spectral Evolution and Evidence for Large Asphericity - Astrophysics > Solar and Stellar AstrophysicsReportar como inadecuado




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Abstract: Supernova SN 2008ax in NGC 4490 was discovered within hours after shockbreakout, presenting the rare opportunity to study a core-collapse SN beginningwith the initial envelope-cooling phase immediately following shock breakout.We present an extensive sequence of optical and near-infrared spectra, as wellas three epochs of optical spectropolarimetry. Our initial spectra, taken twodays after shock breakout, are dominated by hydrogen Balmer lines at highvelocity. However, by maximum light, He I lines dominated the optical andnear-infrared spectra, which closely resembled those of normal Type Ibsupernovae SNe Ib such as SN 1999ex. This spectroscopic transition definesType IIb supernovae, but the strong similarity of SN 2008ax to normal SNe Ibbeginning near maximum light, including an absorption feature near 6270A due toH-alpha at high velocities, suggests that many objects classified as SNe Ib inthe literature may have ejected similar amounts of hydrogen as SN 2008ax,roughly a few x 0.01 M sun. Early-time spectropolarimetry 6 and 9 days aftershock breakout revealed strong line polarization modulations of 3.4% acrossH-alpha, indicating the presence of large asphericities in the outer ejecta.The continuum shares a common polarization angle with the hydrogen, helium, andoxygen lines, while the calcium and iron absorptions are oriented at differentangles. This is clear evidence of deviations from axisymmetry even in the outerejecta. Intrinsic continuum polarization of 0.64% only nine days after shockbreakout shows that the outer layers of the ejecta were quite aspherical. Asingle epoch of late-time spectropolarimetry, as well as the shapes of thenebular line profiles, demonstrate that asphericities extended from theoutermost layers all the way down to the center of this SN. Abridged



Autor: R. Chornock, A. V. Filippenko, W. Li, G. H. Marion, R. J. Foley, M. Modjaz, M. Rafelski, G. D. Becker, W. H. de Vries, P. Garnavi

Fuente: https://arxiv.org/



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