Helium-rich Superluminous Supernovae from the Zwicky Transient Facility

October 2020 • 2020ApJ...902L...8Y

Authors • Yan, Lin • Perley, D. A. • Schulze, S. • Lunnan, R. • Sollerman, J. • De, K. • Chen, Z. H. • Fremling, C. • Gal-Yam, A. • Taggart, K. • Chen, T. -W. • Andreoni, I. • Bellm, E. C. • Cunningham, V. • Dekany, R. • Duev, D. A. • Fransson, C. • Laher, R. R. • Hankins, M. • Ho, A. Y. Q. • Jencson, J. E. • Kaye, S. • Kulkarni, S. R. • Kasliwal, M. M. • Golkhou, V. Z. • Graham, M. • Masci, F. J. • Miller, A. A. • Neill, J. D. • Ofek, E. • Porter, M. • Mróz, P. • Reiley, D. • Riddle, R. • Rigault, M. • Rusholme, B. • Shupe, D. L. • Soumagnac, M. T. • Smith, R. • Tartaglia, L. • Yao, Y. • Yaron, O.

Abstract • Helium is expected to be present in the massive ejecta of some hydrogen-poor superluminous supernovae (SLSN-I). However, until now only one event has been identified with He features in its photospheric spectra (PTF10hgi). We present the discovery of a new He-rich SLSN-I, ZTF19aawfbtg (SN2019hge), at z = 0.0866. This event has more than 10 optical spectra at phases from -41 to +103 days relative to the peak, most of which match well with that of PTF10hgi. Confirmation comes from a near-IR spectrum taken at +34 days, revealing He I features with P-Cygni profiles at 1.083 and 2.058 μm. Using the optical spectra of PTF10hgi and SN2019hge as templates, we examined 70 other SLSNe-I discovered by Zwicky Transient Facility in the first two years of operation and found five additional SLSNe-I with distinct He-features. The excitation of He I atoms in normal core-collapse supernovae requires nonthermal radiation, as proposed by previous studies. These He-rich events cannot be explained by the traditional ⁵⁶Ni mixing model because of their blue spectra, high peak luminosities, and long rise timescales. Magnetar models offer a possible solution since pulsar winds naturally generate high-energy particles, potential sources of nonthermal excitation. An alternative model is the interaction between the ejecta and dense H-poor circumstellar material, which may be supported by observed undulations in the light curves. These six SLSNe-Ib have relatively low-peak luminosities (rest frame M_g = -20.06 ± 0.16).

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IPAC Authors
(alphabetical)

Frank Masci

Senior Scientist

Ben Rusholme

Chief Engineer

Dave Shupe

Senior Scientist