SN 2017egm: 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 λ10830 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 (~-20 days) to late phases (~+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 107-108 L ⊙ 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 ≲10-3 at late phases (~100-200 days), which could help explore its close environment and central engine.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2023
- DOI:
- 10.3847/1538-4357/acc2c3
- arXiv:
- arXiv:2303.03424
- Bibcode:
- 2023ApJ...949...23Z
- Keywords:
-
- Supernovae;
- 1668;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 25 pages, 14 Figures, 4 Tables