Strongly Bipolar Inner Ejecta of the Normal Type IIP Supernova ASASSN-16at

Bose, Subhash and Dong, Subo and Elias-Rosa, N. and Shappee, B. J. and Bersier, David and Benetti, Stefano and Stritzinger, M. D. and Grupe, D. and Kochanek, C. S. and Prieto, J. L. and Chen, Ping and Kuncarayakti, H. and Mattila, Seppo and Morales-Garoffolo, Antonia and Morrell, Nidia and Onori, F. and Reynolds, Thomas M and Siviero, A. and Somero, Auni and Stanek, K. Z. and Terreran, Giacomo and Thompson, Todd A. and Tomasella, L. and Ashall, C. and Gall, Christa and Gromadzki, M. and Holoien, T. W.-S. (2019) Strongly Bipolar Inner Ejecta of the Normal Type IIP Supernova ASASSN-16at. The Astrophysical Journal, 873 (1). L3. ISSN 2041-8213

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Abstract

We report distinctly double-peaked Hα and Hβ emission lines in the late-time, nebular-phase spectra (≳200 days) of the otherwise normal at early phases (≲100 days) 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 56Co decay, so the observed line profile bifurcation suggests a strong bipolarity in the 56Ni distribution or in the line-forming region of the inner ejecta. The strongly bifurcated blueshifted and redshifted peaks are separated by ∼3 × 103 km s−1 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 days 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 days.

Item Type: Article
Subjects: Science Repository > Physics and Astronomy
Depositing User: Managing Editor
Date Deposited: 06 Jun 2023 05:47
Last Modified: 06 Nov 2023 03:56
URI: http://research.manuscritpub.com/id/eprint/2363

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