Strongly Bipolar Inner Ejecta of the Normal Type IIP Supernova ASASSN-16at
Abstract
We report distinctly double-peakedH-alpha and H-beta emission lines in the late-time, nebular-phase spectra (>~200 d) of the otherwise normal at early phases (<~ 100 d) Type IIP supernova ASASSN-16at (SN 2016X). Such distinctly double-peaked nebular Balmer lines have never been observed for a Type II SN. The nebular-phase Balmer emission is driven by the radioactive Co56 decay, so the observed line-profile bifurcation suggests a strong bipolarity in the Ni56 distribution or in the line-forming region of the inner ejecta. The strongly bifurcated blue- and red-shifted peaks are separated by ~3x10^3 km/s and are roughly symmetrically positioned with respect to the host-galaxy rest frame, implying that the inner ejecta are composed of two almost detached blobs. The red peak progressively weakens relative to the blue peak, and disappears in the 740 d spectrum. One possible reason for the line-ratio evolution is increasing differential extinction from continuous formation of dust within the envelope, which is also supported by the near-infrared flux excess that develops after ~100 d.
Cite
@article{arxiv.1810.12304,
title = {Strongly Bipolar Inner Ejecta of the Normal Type IIP Supernova ASASSN-16at},
author = {Subhash Bose and Subo Dong and N. Elias-Rosa and B. J. Shappee and David Bersier and Stefano Benetti and M. D. Stritzinger and D. Grupe and C. S. Kochanek and J. L. Prieto and Ping Chen and H. Kuncarayakti and Seppo Mattila and Antonia Morales-Garoffolo and Nidia Morrell and F. Onori and Thomas M Reynolds and A. Siviero and Auni Somero and K. Z. Stanek and Giacomo Terreran and Todd A. Thompson and L. Tomasella and C. Ashall and Christa Gall and M. Gromadzki and T. W. -S. Holoien},
journal= {arXiv preprint arXiv:1810.12304},
year = {2019}
}
Comments
Published in ApJL