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Helium-rich Superluminous Supernovae from the Zwicky Transient Facility

Yan, L, Perley, DA, Schulze, S, Lunnan, R, Sollerman, J, De, K, Chen, ZH, Fremling, C, Gal-Yam, A, Taggart, K, Chen, T-W, Andreoni, I, Bellm, EC, Cunningham, V, Dekany, R, Duev, DA, Fransson, C, Laher, RR, Hankins, M, Ho, AYQ , Jencson, JE, Kaye, S, Kulkarni, SR, Kasliwal, MM, Golkhou, VZ, Graham, M, Masci, FJ, Miller, AA, Neill, JD, Ofek, E, Porter, M, Mroz, P, Reiley, D, Riddle, R, Rigault, M, Rusholme, B, Shupe, DL, Soumagnac, MT, Smith, R, Tartaglia, L, Yao, Y and Yaron, O (2020) Helium-rich Superluminous Supernovae from the Zwicky Transient Facility. The Astrophysical Journal Letters, 902 (1). ISSN 2041-8205

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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 Mg = −20.06 ± 0.16).

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
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Date Deposited: 30 Mar 2021 12:05
Last Modified: 30 Mar 2021 12:15
DOI or Identification number: 10.3847/2041-8213/abb8c5
URI: https://researchonline.ljmu.ac.uk/id/eprint/14725

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