TY - JOUR

T1 - SN 2017egm

T2 - A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves

AU - Zhu, Jiazheng

AU - Jiang, Ning

AU - Dong, Subo

AU - Filippenko, Alexei V.

AU - Rudy, Richard J.

AU - Pastorello, A.

AU - Ashall, Christopher

AU - Bose, Subhash

AU - Post, R. S.

AU - Bersier, D.

AU - Benetti, Stefano

AU - Brink, Thomas G.

AU - Chen, Ping

AU - Dou, Liming

AU - Elias-Rosa, N.

AU - Lundqvist, Peter

AU - Mattila, Seppo

AU - Russell, Ray W.

AU - Sitko, Michael L.

AU - Somero, Auni

AU - Stritzinger, M. D.

AU - Wang, Tinggui

AU - Brown, Peter J.

AU - Cappellaro, E.

AU - Fraser, Morgan

AU - Kankare, Erkki

AU - Moran, S.

AU - Prentice, Simon

AU - Pursimo, Tapio

AU - Reynolds, T. M.

AU - Zheng, WeiKang

PY - 2023/5/1

Y1 - 2023/5/1

N2 - 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 10830 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 ultraviolet, optical, and near-infrared light curves spanning from early pre-peak (similar to-20 days) to late phases (similar to+300 days). 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 (circle dot) 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 less than or similar to 10(-3) at late phases (similar to 100-200 days), which could help explore its close environment and central engine.

AB - 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 10830 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 ultraviolet, optical, and near-infrared light curves spanning from early pre-peak (similar to-20 days) to late phases (similar to+300 days). 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 (circle dot) 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 less than or similar to 10(-3) at late phases (similar to 100-200 days), which could help explore its close environment and central engine.

U2 - 10.3847/1538-4357/acc2c3

DO - 10.3847/1538-4357/acc2c3

M3 - Journal article

VL - 949

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 23

ER -