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

Journal
Date Issued
2019
Author(s)
Bose, Subhash
•
Dong, Subo
•
•
Shappee, B. J.
•
Bersier, David
•
•
Stritzinger, M. D.
•
Grupe, D.
•
Kochanek, C. S.
•
Prieto, J. L.
•
Chen, Ping
•
Kuncarayakti, H.
•
Mattila, Seppo
•
Morales-Garoffolo, Antonia
•
Morrell, Nidia
•
•
Reynolds, Thomas M.
•
Siviero, A.
•
Somero, Auni
•
Stanek, K. Z.
•
Terreran, Giacomo
•
Thompson, Todd A.
•
•
Ashall, C.
•
Gall, Christa
•
Gromadzki, M.
•
Holoien, T. W. -S.
DOI
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.
Volume
873
Issue
1
Start page
L3
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2019ApJ...873L...3B
Rights
open.access
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