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Title: Detection of Broad Hα Emission Lines in the Late-Time Spectra of a Hydrogen-Poor Superluminous Supernova

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83–148 days to reach a peak bolometric luminosity of ~1.3 × 10 44 erg s -1, then decays slowly at 0.015 mag day -1. The measured ejecta velocity is ~ 13,000 km s -1. The inferred explosion characteristics, such as the ejecta mass (70–220 M ), and the total radiative and kinetic energy (E rad ~ 10 51 erg, E kin ~ 2 × 10 53 erg), are typical of slow-evolving H-poor SLSN events. However, the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ~4500 km s -1 and a ~300 km s -1 blueward shift relative to the narrow component. In this paper, we interpret this broad Hα emission with a luminosity of ~2 × 10 41 erg s -1 as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ~4 × 10 16 cm frommore » the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M . Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M H-shell, ejected from a progenitor star with an initial mass of (95–150) M about 40 years ago. Finally, we estimate that at least ~15% of all SLSNe-I may have late-time Balmer emission lines.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [3] ; ORCiD logo [4] ; ORCiD logo [5] ;  [3] ; ORCiD logo [6] ;  [3] ; ORCiD logo [1] ; ORCiD logo [7] ; ORCiD logo [1] ; ORCiD logo [1] ;  [8] ;  [1] ;  [9] ;  [3]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. San Diego State Univ., CA (United States); Univ. of Tokyo, Kashiwa (Japan)
  3. Weizmann Inst. of Science, Rehovot (Israel)
  4. Liverpool John Moores Univ., Liverpool (United Kingdom); Max Planck Inst. for Astrophysics, Garching (Germany)
  5. California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Copenhagen (Denmark)
  6. Weizmann Inst. of Science, Rehovot (Israel); Univ. of Copenhagen (Denmark)
  7. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
  8. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  9. 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: 814; Journal Issue: 2; 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); LANL Laboratory Directed Research and Development (LDRD) Program; National Aeronautic and Space Administration (NASA); Israel Science Foundation (ISF)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; supernovae; iPTF13ehe; SN2007bi; PTF12dam
OSTI Identifier:
1392978