The unexpected, long-lasting, UV rebrightening of the superluminous supernova ASASSN-15lh
- The Ohio State University, Columbus, OH (United States)
- Peking University, Beijing (China)
- Peking University, Beijing (China). Kavli Institute for Astronomy and Astrophysics
- Universidad Diego Portales, Santiago (Chile); Millennium Institute of Astrophysics, Santiago (Chile)
- Carnegie Observatories, Pasadena, CA (United States)
- Rutgers University, Piscataway, NJ (United States)
- University of California, Santa Cruz, CA (United States)
- University of Illinois at Urbana-Champaign, IL (United States)
- Morehead State University, Morehead, KY (United States
Given its peak luminosity and early-time spectra, ASASSN-15lh was classified as the most luminous supernova ever discovered. Here, we report a UV rebrightening of ASASSN-15lh observed with Swift during our follow-up campaign. The rebrightening began at t ≃ 90 d (observer frame) after the primary peak and was followed by a p120-d long plateau in the bolometric luminosity, before starting to fade again at t ≃ 210 d. ASASSN-15lh rebrightened in the Swift UV bands by ΔmUVW2 ≃ -1.75 mag, ΔmUVM2 ≃ -1.25 mag and ΔmUVW1 ≃ -0.8 mag, but did not rebrighten in the optical bands. Throughout its initial decline, subsequent rebrightening and renewed decline, the spectra did not show evidence of interactions between the ejecta and circumstellar medium such as narrow emission lines. There are hints of weak Hα emission at late-times, but Margutti et al. have shown that it is narrow line emission consistent with star formation in the host nucleus. By fitting a blackbody, we find that during the rebrightening, the effective photospheric temperature increased from TBB ≃ 11 000 K to TBB ≃ 18 000 K. Over the ~ 550 d since its detection, ASASSN-15lh has radiated ~1.7 -1.9 × 1052 erg. Although its physical nature remains uncertain, the evolution of ASASSN-15lh's photospheric radius, its radiated energy and the implied event rate, are all more similar to those of H-poor superluminous supernovae than to tidal disruption events.
- Research Organization:
- Krell Institute, Ames, IA (United States); The Ohio State University, Columbus, OH (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); Chinese Academy of Sciences; National Fund for Scientific and Technological Development (FONDECYT); National Aeronautics and Space Administration (NASA); Alfred P. Sloan Foundation; David and Lucile Packard Foundation
- Grant/Contract Number:
- FG02-97ER25308; AST-1515927; AST-0908816; XDB09000000; 11 XDB09000000; 1151445; IC120009; HF-51348.001; NAS 5-26555; AST-1518052; PHY-1404311
- OSTI ID:
- 1535669
- Journal Information:
- Monthly Notices of the Royal Astronomical Society, Vol. 466, Issue 2; ISSN 0035-8711
- Publisher:
- Oxford University PressCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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