[Paper Review] SuperNova IDentification spectral templates of 70 stripped-envelope core-collapse supernovae

Yuqian Liu, M. Modjaz|arXiv (Cornell University)|May 6, 2014

Gamma-ray bursts and supernovae12 citations

TL;DR

This paper presents 56 new spectral templates for stripped-envelope core-collapse supernovae (SESNe), significantly expanding the SNID database by 160% in template count and 100% in spectrum count. Using 640 high-quality, continuum-removed, and de-redshifted spectra from the CfA survey, the authors improve classification accuracy by introducing a new SNID subtype (Ib-n) and refining type and phase information for 6 SNe, enhancing reliability for low signal-to-noise ratio spectra.

ABSTRACT

We constructed 70 SuperNova IDentification (SNID; Blondin & Tonry 2007) supernova (SN) templates using 640 spectra of stripped-envelope core-collapse SNe (SESNe) published by Modjaz et al. (2014). Fifty-six SN templates which are constructed from 458 spectra are brand new, increasing the number of SESNe and the number of SESNe spectra in the current SNID database by a factor of 2.6 and 2.0, respectively. We also made some type and phase refinements to templates in the current SNID database.

Motivation & Objective

• Address the imbalance in SNID database templates between Type Ia and stripped-envelope SNe (SESNe), which increases misclassification risk for low-S/N spectra.
• Improve SN classification accuracy by expanding the number of SESNe templates and enhancing their phase and type information.
• Introduce a new SNID subtype (Ib-n) to better represent supernovae with narrow He I lines due to circumstellar interaction.
• Refine existing SNID templates by correcting type and phase assignments based on updated analysis of CfA spectra.
• Provide a publicly accessible, high-fidelity set of CfA spectral templates to enhance the SNID code's performance for SESNe.

Proposed method

• Collected 640 high-quality, continuum-removed, and de-redshifted spectra of 70 SESNe from the M14 CfA survey, excluding low-S/N or ambiguous cases.
• Created 56 new SNID-compatible spectral templates using the logwave software to ensure format consistency with templates-2.0.
• Introduced the Ib-n subtype in SNID by modifying the code's typeinfo.f file, enabling better classification of SNe with narrow He I lines.
• Updated type and phase information for 6 existing SNID templates based on M14's re-analysis, including corrected dates of maximum light and revised classifications.
• Removed telluric lines and corrected for H II region emission lines via interpolation during data reduction.
• Provided recommendations for SNID users on whether to adopt new templates or retain original ones, especially when original templates combine multiple data sources.

Experimental results

Research questions

• RQ1 How can the SNID database be improved to reduce misclassification of stripped-envelope SNe with low signal-to-noise spectra?
• RQ2 What is the impact of increasing the number and quality of SESNe spectral templates on SN classification accuracy?
• RQ3 Can a new SNID subtype (Ib-n) be effectively implemented to better represent SNe with narrow He I lines from circumstellar interaction?
• RQ4 To what extent do updated type and phase assignments for existing SN templates improve classification reliability?
• RQ5 How do the new CfA spectral templates compare in quality and consistency to existing SNID templates?

Key findings

• The study introduces 56 new SNID spectral templates, increasing the number of SESNe templates in the SNID database by 160%.
• The number of SESNe spectra in the SNID database increases by 100%, now totaling 640 spectra from 70 unique SNe.
• The authors successfully implemented the Ib-n subtype in SNID, enabling better classification of SNe with narrow He I lines due to circumstellar interaction.
• Six existing SNID templates were updated with corrected types and/or revised dates of maximum light, including SN 1995F (Ic-norm → Ib-norm) and SN 2008D (Ib-pec → Ib-norm, MJD max from 54492.9 to 54494.1).
• For 14 SNe, the original SNID templates are recommended over the new ones due to inclusion of multiple data sources, but users are advised to update type or phase information if using the original templates.
• The new templates are publicly available via the SNYU webpage, enhancing accessibility and reproducibility for the broader astronomical community.