SN2017egm: A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves

Abstract

When discovered, SN~2017egm was the closest (redshift $z=0.03$) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has since been extensively observed and studied. We report spectroscopic data showing strong emission at around He~I $\lambda$10,830 and four He~I absorption lines in the optical. Consequently, we classify SN~2017egm as a member of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We also present our late-time photometric observations. By combining them with archival data, we analyze high-cadence ultra-violet, optical, and near-infrared light curves spanning from early pre-peak ($\sim -20d$) to late phases ($\sim +300d$). We obtain its most complete bolometric light curve, in which multiple bumps are identified. None of the previously proposed models can satisfactorily explain all main light-curve features, while multiple interactions between the ejecta and circumstellar material (CSM) may explain the undulating features. The prominent infrared excess with a blackbody luminosity of $10^7$--$10^8{L}_{sun}$ detected in SN~2017egm could originate from the emission of either an echo of a pre-existing dust shell, or newly-formed dust, offering an additional piece of evidence supporting the ejecta-CSM interaction model. Moreover, our analysis of deep $Chandra$ observations yields the tightest-ever constraint on the X-ray emission of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio $\lesssim 10^{-3}$ at late phases ($\sim 100-200d$), which could help explore its close environment and central engine.

25 pages, 14 Figures, 4 Tables; accepted for publication in ApJ (Mar. 2023)

References in corpus (16)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Initial Performance of the NEOWISE Reactivation Mission
• The magnetar model for Type I superluminous supernovae I: Bayesian analysis of the full multicolour light curve sample with MOSFiT
• SN 2005ap: A Most Brilliant Explosion
• A Spitzer Space Telescope Study of SN 2003gd: Still No Direct Evidence that Core-Collapse Supernovae are Major Dust Factories
• Massive stars exploding in a He-rich circumstellar medium III. SN 2006jc: IR echoes from new and old dust in the progenitor CSM
• Hydrogen-Poor Superluminous Supernovae from the Pan-STARRS1 Medium Deep Survey
• Infrared Echoes of Optical Tidal Disruption Events: ~1% Dust Covering Factor or Less at sub-parsec Scale
• Super Luminous Supernovae as standardizable candles and high redshift distance probes
• The superluminous supernova SN 2017egm in the nearby galaxy NGC 3191: a metal-rich environment can support a typical SLSN evolution
• The Hydrogen-Poor Superluminous Supernovae from the Zwicky Transient Facility Phase-I Survey: II. Light Curve Modeling and Characterization of Undulations
• Spatially resolved MaNGA observations of the host galaxy of superluminous supernova 2017egm
• SN 2018bsz: a Type I superluminous supernova with aspherical circumstellar material
• Circumstellar Interaction Models for the Bolometric Light Curve of SN 2017egm
• The Prospects of Finding Tidal Disruption Events with 2.5-Metre Wide-Field Survey Telescope (WFST) Based on Mock Observations
• A Mid-infrared Study of Superluminous Supernovae

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