AstroNote 2021-76

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DRAFT
2021-02-23 11:00:13
Type: Object/s-Discovery/Classification
Introducing a new Supernova classification type: SN Icn
Authors: Avishay Gal-Yam, Ofer Yaron (WIS), Andrea Pastorello (INAF), Stefan Taubenberger (MPA), Morgan Fraser (UCD), Daniel Perley (LJMU)
Keywords: Supernova
Abstract:
Motivated by recent discovery and classification reports of transients with spectra showing prominent narrow emission lines of carbon and/or oxygen, but lacking lines of hydrogen and helium, we propose to use a new spectroscopic SN type - SN Icn - to refer to such objects.

Motivated by recent discovery and classification reports of transients with spectra showing strong narrow (<~1000 km/s) emission lines (including potential narrow P-Cygni profiles) of carbon and/or oxygen, but lacking lines of hydrogen and helium, we propose to use a new spectroscopic SN type - SN Icn - to refer to such objects, following the current SN classification as implemented in types IIn and Ibn (events with narrow lines of hydrogen and helium, respectively).   

Fiducially we propose that events showing spectra with strong emission lines of CNO elements but lacking prominent lines of H and He (in particular the He II 4686) would be classified as SNe Icn. Several relevant example are listed in the table below, including recent reports by Perley et al. (AstroNote 2021-62; 2021TNSAN..62....1P), Pastorello et al. (AstroNote 2021-71; 2021TNSAN..71....1P) and the classification of the earlier SN 2019hgp (Class. report 90022021TNSCR.547....1G). A potentially related object could be SN 2010mb where Ben-Ami et al. 2014 (2014ApJ...785...37B) reported transient narrow emission lines of oxygen, though that object appears to differ photometrically and spectroscopically from the recently reported events.

We propose that should transitional events between types Ibn (prominent He lines, no C/O lines) and Icn (prominent C/O, no/weak He) appear, i.e., events whose spectra show narrow C/N/O and He lines with comparable strengths, those events should be classified as Ibn/Icn.

Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2019hgp [ZTF19aayejww]15:36:12.874+39:44:00.56SN Icn0.064115:36:12.874+39:44:00.56SN Icn0.0641
TNS2010mb16:00:23.100+37:44:57.01SN Ic0.1325Anon.16:00:23.100+37:44:57.01SN Ic
TNS2021csp [ZTF21aakilyd]14:26:22.120+05:51:33.17SN Icn0.08314:26:22.120+05:51:33.17SN Icn0.083
TNS2021ckj [ZTF21aajbgol]09:05:51.083-08:35:07.57SN Icn0.14309:05:51.083-08:35:07.57SN Icn0.143