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PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 5806
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, A68Article in journal (Refereed) Published
Abstract [en]

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+ 0.77-0.56M at the time of the explosion, which had a total kinetic energy of 0.54+ 0.41-0.25 × 1051 erg and synthesized 0.063+ 0.020-0.011M of strongly mixed  56Ni. 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.

Place, publisher, year, edition, pages
2016. Vol. 593, A68
Keyword [en]
supernovae: general, supernovae: individual: PTF12os, galaxies: individual: NGC 5806, techniques: image processing, supernovae: individual: iPTF13bvn
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-135750DOI: 10.1051/0004-6361/201628275ISI: 000385820100054OAI: oai:DiVA.org:su-135750DiVA: diva2:1048671
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-12-14Bibliographically approved
In thesis
1. PTF12os and iPTF13bvn: Two stripped-envelope supernovae discovered by the Palomar Transient Factory
Open this publication in new window or tab >>PTF12os and iPTF13bvn: Two stripped-envelope supernovae discovered by the Palomar Transient Factory
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on research made by the intermediate Palomar Transient Factory [(i)PTF], and it is particularly closely tied to the still ongoing research on the stripped-envelope (SE) supernova (SN), iPTF13bvn (Type Ib), that occurred in the nearby galaxy NGC 5806. This SN was initially thought to have been the explosion of a very massive Wolf-Rayet (WR) star, but I have shown that this is very likely not the case. I suggest instead that the most likely scenario is that iPTF13bvn originated from a binary system where the envelope was stripped off from the SN progenitor by tidal forces from a companion star, in a similar way as for the very well studied Type IIb SN 2011dh. I have also investigated another SE SN, PTF12os (Type IIb), that occurred in the same galaxy as iPTF13bvn, with the conclusion that PTF12os and iPTF13bvn are very similar amongst themselves, and that both of them are also remarkably similar to SN 2011dh, in terms of all of the available observations (light-curves, spectra). Hydrodynamical models have been used to constrain the explosion parameters of iPTF13bvn, PTF12os and SN 2011dh; finding 56Ni masses in the range 0.063 − 0.075 M⊙, ejecta masses in the range 1.85 − 1.91 M⊙. Using the 56Ni-masses derived from our hydrodynamical modeling in combination with nebular models and late-time spectroscopy we were able to constrain the Zero-Age Main Sequence (ZAMS) mass to ∼ 12 M⊙ for iPTF13bvn and ≲ 15 M⊙ for PTF12os. In current stellar evolution models, stars with these masses on the ZAMS cannot lose their hydrogen envelopes and become SE SNe without binary interactions.

Place, publisher, year, edition, pages
Stockholm: Stockholm University, 2016. 64 p.
Keyword
sovernovae
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:su:diva-135752 (URN)
Presentation
2016-11-08, Albanova, 19:42 (English)
Opponent
Supervisors
Available from: 2016-11-22 Created: 2016-11-21 Last updated: 2016-11-22Bibliographically approved

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Fremling, ChristofferSollerman, JesperTaddia, FrancescoErgon, MattiasKaramehmetoglu, EmirNyholm, Anders
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