The Type II-Plateau Supernova 2017eaw in NGC 6946 and Its Red Supergiant Progenitor

Creators: Van Dyk, Schuyler D.; Zheng, WeiKang; Maund, Justyn R.; Brink, Thomas G.; Srinivasan, Sundar; Andrews, Jennifer E.; Smith, Nathan; Leonard, Douglas C.; Morozova, Viktoriya; Filippenko, Alexei V.; Conner, Brody; Milisavljevic, Dan; Jaeger, Thomas de; Long, Knox S.; Isaacson, Howard; Crossfield, Ian J. M.; Kosiarek, Molly R.; Howard, Andrew W.; Fox, Ori D.; Kelly, Patrick L.; Piro, Anthony L.; Littlefair, Stuart P.; Dhillon, Vik S.; Wilson, Richard; Butterley, Timothy; Yunus, Sameen; Channa, Sanyum; Jeffers, Benjamin T.; Falcon, Edward; Ross, Timothy W.; Hestenes, Julia C.; Stegman, Samantha M.; Zhang, Keto; Kumar, Sahana

Abstract

We present extensive optical photometric and spectroscopic observations, from 4 to 482 days after explosion, of the Type II-plateau (II-P) supernova (SN) 2017eaw in NGC 6946. SN 2017eaw is a normal SN II-P intermediate in properties between, for example, SN 1999em and SN 2012aw and the more luminous SN 2004et, also in NGC 6946. We have determined that the extinction to SN 2017eaw is primarily due to the Galactic foreground and that the SN site metallicity is likely subsolar. We have also independently confirmed a tip-of-the-red-giant-branch (TRGB) distance to NGC 6946 of 7.73 ± 0.78 Mpc. The distances to the SN that we have also estimated via both the standardized candle method and expanding photosphere method corroborate the TRGB distance. We confirm the SN progenitor identity in pre-explosion archival Hubble Space Telescope (HST) and Spitzer Space Telescope images, via imaging of the SN through our HST Target of Opportunity program. Detailed modeling of the progenitor's spectral energy distribution indicates that the star was a dusty, luminous red supergiant consistent with an initial mass of ~15 M_⊙.

Additional Information

© 2019 The American Astronomical Society. Received 2018 November 21; revised 2019 March 9; accepted 2019 March 12; published 2019 April 24. We are grateful to Patrick Wiggins for providing his discovery and pre-discovery images and to Andrew Drake for providing the CRTS pre-discovery images. Daniel Huber kindly donated some observing time for us to obtain the Keck HIRES spectrum. We appreciate useful discussions with Shoko Sakai, Insung Jang, and Myung Gyoon Lee regarding TRGB distance estimates, Matt Nicholl regarding use of superbol, Jim Fuller about pre-SN outbursts, and Luc Dessart concerning EPM distance estimates. We also appreciate Xiaofeng Wang giving us permission to include the spectrum their team posted to TNS. Andrew G. Halle, Costas Q. Soler, Nick Choksi, Kevin Tang, Jeffrey D. Molloy, Goni Halevy, and Ben Stahl helped with some of the Lick observations. We thank the Lick and Keck Observatory staffs for their expert assistance. This work is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under National Aeronautics and Space Administration (NASA) contract NAS5-26555. Support for programs GO-14645 and GO-15166 was provided by NASA through grants from STScI. This work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by an award issued by JPL/Caltech. This research has made use of NED, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The research of J.R.M. is supported through a Royal Society University Research Fellowship. S.S. acknowledges grant MOST104-2628-M-001-004-MY3 from the Taiwan Ministry of Science and Technology. Partial support for N.S.'s supernova and transient research group at the University of Arizona was provided by NSF grant AST-1515559. M.R.K. acknowledges support from the NSF Graduate Research Fellowship, grant No. DGE 1339067. Support for A.V.F.'s supernova research group at U.C. Berkeley has been provided by NSF grant AST-1211916, the TABASGO Foundation, the Christopher R. Redlich Fund, Gary and Cynthia Bengier, and the Miller Institute for Basic Research in Science (U.C. Berkeley), and NASA/HST grant AR-14295 from STScI. A.L.P. acknowledges financial support for this research from a Scialog award made by the Research Corporation for Science Advancement. PyRAF is a product of the Space Telescope Science Institute, which is operated by AURA for NASA. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory was made possible through generous gifts from the Heising-Simons Foundation, as well as William and Marina Kast. Research at Lick Observatory is partially supported by a generous gift from Google. We also greatly appreciate contributions from numerous individuals, including Charles Baxter and Jinee Tao, Firmin Berta, Marc and Cristina Bensadoun, Frank and Roberta Bliss, Eliza Brown and Hal Candee, Kathy Burck and Gilbert Montoya, Alan and Jane Chew, David and Linda Cornfield, Michael Danylchuk, Jim and Hildy DeFrisco, William and Phyllis Draper, Luke Ellis and Laura Sawczuk, Jim Erbs and Shan Atkins, Alan Eustace and Kathy Kwan, David Friedberg, Harvey Glasser, Charles and Gretchen Gooding, Alan Gould and Diane Tokugawa, Thomas and Dana Grogan, Alan and Gladys Hoefer, Charles and Patricia Hunt, Stephen and Catherine Imbler, Adam and Rita Kablanian, Roger and Jody Lawler, Kenneth and Gloria Levy, Peter Maier, DuBose and Nancy Montgomery, Rand Morimoto and Ana Henderson, Sunil Nagaraj and Mary Katherine Stimmler, Peter and Kristan Norvig, James and Marie O'Brient, Emilie and Doug Ogden, Paul and Sandra Otellini, Jeanne and Sanford Robertson, Stanley and Miriam Schiffman, Thomas and Alison Schneider, Ajay Shah and Lata Krishnan, Alex and Irina Shubat, the Silicon Valley Community Foundation, Mary-Lou Smulders and Nicholas Hodson, Hans Spiller, Alan and Janet Stanford, the Hugh Stuart Center Charitable Trust, Clark and Sharon Winslow, Weldon and Ruth Wood, and many others. The pt5m is a collaborative effort between the Universities of Durham and Sheffield. The telescope is kindly hosted by the Isaac Newton Group of Telescopes, La Palma. The Roque de los Muchachos Observatory is operated by the Instituto de Astrofísica de Canarias. Financial contributions from the University of Sheffield Alumni Foundation are gratefully acknowledged. We also thank the Science and Technology Facilities Council for financial support in the form of grant ST/P000541/1. 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. 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. Facilities: HST (ACS - , WFC3) - , Spitzer (IRAC - , MIPS) - , KAIT - , Nickel - , Shane (Kast Spectrograph) - , MMT (Blue Channel spectrograph) - , Keck:I (HIRES) - , MAST. - Software: AstroDrizzle (http://drizzlepac.stsci.edu/; Hack et al. 2012), Dolphot (Dolphin 2016), DAOPHOT (Stetson 1987), IRAF (Tody 1986, 1993), PyRAF (http://www.stsci.edu/institute/software_hardware/pyraf), MOPEX/APEX (Makovoz & Khan 2005; Makovoz & Marleau 2005; Makovoz et al. 2006), astrometry.net (http://astrometry.net), swarp (https://www.astromatic.net/software/swarp; Bertin et al. 2002), SExtractor (https://www.astromatic.net/software/sextractor; Bertin & Arnouts 1996), superbol (https://github.com/mnicholl/astro-scripts/blob/master/superbol.py3; Nicholl 2018), SNID (https://people.lam.fr/blondin.stephane/software/snid/; Blondin & Tonry 2007), GELATO (https://gelato.tng.iac.es/; Harutyunyan et al. 2008), extinction (https://doi.org/10.5281/zenodo.804967), pysynphot (https://github.com/spacetelescope/pysynphot; STScI Development Team 2013).

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