PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 5806

Creators: Fremling, C.; Sollerman, J.; Taddia, F.; Ergon, M.; Fraser, M.; Karamehmetoglu, E.; Valenti, S.; Jerkstrand, A.; Arcavi, I.; Bufano, F.; Elias-Rosa, N.; Filippenko, A. V.; Fox, D.; Gal-Yam, A.; Howell, D. A.; Kotak, R.; Mazzali, P.; Milisavljevic, D.; Nugent, P. E.; Nyholm, A.; Pian, E.; Smartt, S.

Abstract

Context. We investigate two stripped-envelope supernovae (SNe) discovered in the nearby galaxy NGC 5806 by the (intermediate) Palomar Transient Factory [(i)PTF]. These SNe, designated PTF12os/SN 2012P and iPTF13bvn, exploded within ~520 days of one another at a similar distance from the host-galaxy center. We classify PTF12os as a Type IIb SN based on our spectral sequence; iPTF13bvn has previously been classified as Type Ib having a likely progenitor with zero age main sequence (ZAMS) mass below ~17 M_⊙. Because of the shared and nearby host, we are presented with a unique opportunity to compare these two SNe. Aims. Our main objective is to constrain the explosion parameters of iPTF12os and iPTF13bvn, and to put constraints on the SN progenitors. We also aim to spatially map the metallicity in the host galaxy, and to investigate the presence of hydrogen in early-time spectra of both SNe. Methods. We present comprehensive datasets collected on PTF12os and iPTF13bvn, and introduce a new automatic reference-subtraction photometry pipeline (FPipe) currently in use by the iPTF. We perform a detailed study of the light curves (LCs) and spectral evolution of the SNe. The bolometric LCs are modeled using the hydrodynamical code HYDE. We analyze early spectra of both SNe to investigate the presence of hydrogen; for iPTF13bvn we also investigate the regions of the Paschen lines in infrared spectra. We perform spectral line analysis of helium and iron lines to map the ejecta structure of both SNe. We use nebular models and late-time spectroscopy to constrain the ZAMS mass of the progenitors. We also perform image registration of ground-based images of PTF12os to archival HST images of NGC 5806 to identify a potential progenitor candidate. Results. We find that our nebular spectroscopy of iPTF13bvn remains consistent with a low-mass progenitor, likely having a ZAMS mass of ~12M_⊙. Our late-time spectroscopy of PTF12os is consistent with a ZAMS mass of ~15M⊙. We successfully identify a source in pre-explosion HST images coincident with PTF12os. The colors and absolute magnitude of this object are consistent between pre-explosion and late-time HST images, implying it is a cluster of massive stars. Our hydrodynamical modeling suggests that the progenitor of PTF12os had a compact He core with a mass of 3.25^(+0.77)_(-0.56)M_⊙ at the time of the explosion, which had a total kinetic energy of 0.54^(+0.41)_(-0.25) ×10^(51) erg and synthesized 0.063^(+0.020)_(-0.011)M_⊙ of strongly mixed ^(56)Ni. Spectral comparisons to the Type IIb SN 2011dh indicate that the progenitor of PTF12os was surrounded by a thin hydrogen envelope with a mass lower than 0.02M_⊙. We also find tentative evidence that the progenitor of iPTF13bvn could have been surrounded by a small amount of hydrogen prior to the explosion. This result is supported by possible weak signals of hydrogen in both optical and infrared spectra.

Additional Information

© 2016 ESO. Article published by EDP Sciences. Received 8 February 2016; Accepted 26 May 2016; Published online 22 September 2016. We gratefully acknowledge support from the Knut and Alice Wallenberg Foundation. The Oskar Klein Centre is funded by the Swedish Research Council. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231. We acknowledge help from Rob Fesen, Craig Wheeler, and Shazrene Mohamed with the SALT data, as well as Jeffrey Silverman for help with the Keck data. We thank Alastair Bruce for assistance with the WHT observing and data reduction. We especially thank Shri Kulkarni, Mansi Kasliwal, Yi Cao, Anna-Lisa de Cia, Jerod Parrent, Assaf Horesh, Tom Matheson, Melissa Graham, Dan Perley, Eric Bellm, Ofer Yaron, Yen-Chen Pan and Kelsey Clubb for help with observations and/or reductions within the PTF effort. We also acknowledge observers, organizers, and data reducers who participated in the BLP 2012P campaign, in particular Andrea Pastorello, Max Stritzinger, Cosimo Inserra, Flora Cellier-Holzem, Luca Borsato, Valerio Nascimbeni, Stefano Benetti, and Stefan Taubenberger. We thank Doug Leonard for discussions regarding complementary MLO data. This work is partly based on observations obtained with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain. We acknowledge the exceptional support we received from the NOT staff throughout this campaign. Also based in part on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofısica de Canarias, in the island of La Palma. This work is based in part on observations from the LCOGT network. 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. Research at Lick Observatory is partially supported by a generous gift from Google. CAFOS, AFOSC, and EFOSC2 data were taken within the European supernova collaboration involved in the ESO-NTT large programme 184.D-1140 led by Stefano Benetti. Partially based on observations collected at Copernico telescope (Asiago, Italy) of the INAF − Osservatorio Astronomico di Padova, and the 2.2 m Telescope of the Centro Astronomico Hispano-Aleman, Calar Alto, Spain. Based in part on observations obtained at the Gemini Observatory, 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 National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). The Hobby-Eberly Telescope (HET) is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). This paper is partly based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Partially based on observations obtained with the Apache Point Observatory 3.5-m telescope, which is owned and operated by the Astrophysical Research Consortium. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Based in part on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme 093.D-0199(A). We are grateful for the assistance of the staff members at all observatories where we obtained data.A.G.-Y. is supported by the EU/FP7 via ERC grant No. 307260, the Quantum Universe I-Core program by the Israeli Committee for Planning and Budgeting; by Minerva and ISF grants; by the Weizmann-UK making connections program; and by Kimmel and ARCHES awards. A.V.F.'s research is supported by NASA/HST grant AR-14295 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; additional financial assistance was provided by the Christopher R. Redlich Fund, the TABASGO Foundation, and NSF grant AST-1211916. N.E.R. is supported by the PRIN-INAF 2014 with the project: Transient Universe: unveiling new types of stellar explosions with PESSTO. This work was partly supported by the European Union FP7 program though ERC grant number 320360. We acknowledge funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement n° [291222].

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