Abstract
SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN), showing no narrow features in its early-time spectra, and therefore, its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 d after explosion. Only broad H α emission is detected in a Gemini spectrum at 288 d. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, an NIR excess with blackbody temperature ∼1500 K and radius ∼1016 cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with ∼2–3 M☉ of circumstellar material (CSM) and ∼10–20 M☉ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius ∼1015 cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount (≲0.4 M☉) of 56Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 3783-3793 |
| Number of pages | 11 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 488 |
| Issue number | 3 |
| DOIs | |
| State | Published - Sep 21 2019 |
Funding
Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank J. M. Silverman for assistance with some of the Keck observations and D. A. Perley for obtaining some of the Keck I/LRIS images. We thank M. Kasliwal for obtaining the P200/COSMIC images. Also, this research has made use of the KOA, which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. KB and RC acknowledge support from National Aeronautics and Space Administration (NASA) grant 80NSSC18K0665. Support for AVF’s SN research has been provided by the NSF, the TABASGO Foundation, the Christopher R. Redlich Fund, and the Miller Institute for Basic Research in Science (U.C. Berkeley). AVF’s work was conducted in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611; he thanks the centre for its hospitality during the supermassive black holes workshop in 2018 June and July. This study is based on observations obtained at the Gemini Observatory (Program ID GN-2009A-Q-48, PI Miller), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovac¸ão (Brazil). KB and RC acknowledge support from National Aeronautics and Space Administration (NASA) grant 80NSSC18K0665. Support for AVF?s SN research has been provided by the NSF, the TABASGO Foundation, the Christopher R. Redlich Fund, and the Miller Institute for Basic Research in Science (U.C. Berkeley). AVF?s work was conducted in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611; he thanks the centre for its hospitality during the supermassive black holes workshop in 2018 June and July. This study is based on observations obtained at the Gemini Observatory (Program ID GN-2009A-Q-48, PI Miller), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnolog?a e Innovaci?n Productiva (Argentina), and Minist?rio da Ci?ncia, Tecnologia e Inova??o (Brazil). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank J. M. Silverman for assistance with some of the Keck observations and D. A. Perley for obtaining some of the Keck I/LRIS images. We thank M. Kasliwal for obtaining the P200/COSMIC images. Also, this research has made use of the KOA, which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Keywords
- Circumstellar matter
- Supernovae: individual (SN 2008es)
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science