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Hydrogen-poor Superluminous Supernovae with Late-time H alpha Emission: Three Events From the Intermediate Palomar Transient Factory

Yan, L, Lunnan, R, Perley, DA, Gal-Yam, A, Yaron, O, Roy, R, Quimby, R, Sollerman, J, Fremling, C, Leloudas, G, Cenko, SB, Vreeswijk, P, Graham, ML, Howell, DA, De Cia, A, Ofek, EO, Nugent, P, Kulkarni, SR, Hosseinzadeh, G, Masci, F , McCully, C, Rebbapragada, UD and Wozniak, P (2017) Hydrogen-poor Superluminous Supernovae with Late-time H alpha Emission: Three Events From the Intermediate Palomar Transient Factory. Astrophysical Journal, 848 (1). ISSN 0004-637X

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We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time Hα emission with line luminosities of $(1\mbox{--}3)\times {10}^{41}$ erg s−1 and velocity widths of (4000–6000) km s−1. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ~1016 cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O ii absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower [O i] 6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10 M ⊙). The blueshifted Hα emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ~22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society; IOP Publishing
Related URLs:
Date Deposited: 21 Feb 2018 12:26
Last Modified: 21 Feb 2018 12:26
DOI or Identification number: 10.3847/1538-4357/aa8993
URI: http://researchonline.ljmu.ac.uk/id/eprint/8098

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