1. SN 2017egm : A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves
- Author
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Zhu, Jiazheng, Jiang, Ning, Dong, Subo, Filippenko, Alexei V., Rudy, Richard J., Pastorello, A., Ashall, Christopher, Bose, Subhash, Post, R. S., Bersier, D., Benetti, Stefano, Brink, Thomas G., Chen, Ping, Dou, Liming, Elias-Rosa, N., Lundqvist, Peter, Mattila, Seppo, Russell, Ray W., Sitko, Michael L., Somero, Auni, Stritzinger, M. D., Wang, Tinggui, Brown, Peter J., Cappellaro, E., Fraser, Morgan, Kankare, Erkki, Moran, S., Prentice, Simon, Pursimo, Tapio, Reynolds, T. M., Zheng, WeiKang, Zhu, Jiazheng, Jiang, Ning, Dong, Subo, Filippenko, Alexei V., Rudy, Richard J., Pastorello, A., Ashall, Christopher, Bose, Subhash, Post, R. S., Bersier, D., Benetti, Stefano, Brink, Thomas G., Chen, Ping, Dou, Liming, Elias-Rosa, N., Lundqvist, Peter, Mattila, Seppo, Russell, Ray W., Sitko, Michael L., Somero, Auni, Stritzinger, M. D., Wang, Tinggui, Brown, Peter J., Cappellaro, E., Fraser, Morgan, Kankare, Erkki, Moran, S., Prentice, Simon, Pursimo, Tapio, Reynolds, T. M., and Zheng, WeiKang
- 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 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.
- Published
- 2023
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