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

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 -. 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 ~10 16 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. Lastly, 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.
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [3] ;  [4] ; ORCiD logo [5] ; ORCiD logo [4] ; ORCiD logo [4] ; ORCiD logo [6] ; ORCiD logo [7] ; ORCiD logo [3] ; ORCiD logo [8] ; ORCiD logo [9] ; ORCiD logo [10] ; ORCiD logo [3] ; ORCiD logo [11] ; ORCiD logo [1] ; ORCiD logo [9] ; ORCiD logo [1] more »; ORCiD logo [9] ; ORCiD logo [1] ;  [12] « less
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. Univ. of Copenhagen, Copenhagen (Denmark); Liverpool John Moores Univ., Liverpool (United Kingdom)
  3. Weizmann Institute of Science, Rehovot (Israel)
  4. Stockholm Univ., Stockholm (Sweden)
  5. San Diego State Univ., San Diego, CA (United States); The Univ. of Tokyo, Chiba (Japan)
  6. Univ. of Copenhagen, Copenhagen (Denmark); Weizmann Institute of Science, Rehovot (Israel)
  7. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
  8. Univ. of Washington, Seattle, WA (United States); Univ. of California, Berkeley, CA (United States)
  9. Las Cumbres Observatory, Goleta, CA (United States); Univ. of California, Santa Barbara, CA (United States)
  10. Weizmann Institute of Science, Rehovot (Israel); European Southern Observatory, Garching bei Munchen (Germany)
  11. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  12. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 848; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; stars: massive; supernovae: individual (iPTF13ehe, iPTF15esb, iPTF16bad)
OSTI Identifier:
1421822