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  • 1. Bersten, Melina C.
    et al.
    Benvenuto, Omar G.
    Nomoto, Ken'ichi
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Folatelli, Gaston
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Benetti, Stefano
    Botticella, Maria Teresa
    Fraser, Morgan
    Kotak, Rubina
    Maeda, Keiichi
    Ochner, Paolo
    Tomasella, Lina
    THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 757, no 1, article id 31Article in journal (Refereed)
    Abstract [en]

    A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R similar to 200 R-circle dot-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be approximate to 2 M-circle dot, the explosion energy to be E = (6-10) x 10(50) erg, and the Ni-56 mass to be approximately 0.06 M-circle dot. The progenitor star was composed of a helium core of 3-4 M-circle dot and a thin hydrogen-rich envelope of approximate to 0.1M(circle dot) with a main-sequence mass estimated to be in the range of 12-15 M-circle dot. Our models rule out progenitors with helium-core masses larger than 8 M-circle dot, which correspond to M-ZAMS greater than or similar to 25M(circle dot). This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

  • 2. Czekala, Ian
    et al.
    Berger, E.
    Chornock, R.
    Pastorello, A.
    Marion, G. H.
    Margutti, R.
    Botticella, M. T.
    Challis, P.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smartt, S.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Vinko, J.
    Wheeler, J. C.
    THE UNUSUALLY LUMINOUS EXTRAGALACTIC NOVA SN 2010U2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 765, no 1, p. 57-Article in journal (Refereed)
    Abstract [en]

    We present observations of the unusual optical transient SN 2010U, including spectra taken 1.03 days to 15.3 days after maximum light that identify it as a fast and luminous Fe II type nova. Our multi-band light curve traces the fast decline (t(2) = 3.5 +/- 0.3 days) from maximum light (M-V = -10.2 +/- 0.1 mag), placing SN 2010U in the top 0.5% of the most luminous novae ever observed. We find typical ejecta velocities of approximate to 1100 km s(-1) and that SN 2010U shares many spectral and photometric characteristics with two other fast and luminous Fe II type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme luminosity of this nova, the maximum magnitude versus rate of decline relationship indicates a massive white dwarf (WD) progenitor with a low pre-outburst accretion rate. However, this prediction is in conflict with emerging theories of nova populations, which predict that luminous novae from massive WDs should preferentially exhibit an alternate spectral type (He/N) near maximum light.

  • 3. Elias-Rosa, Nancy
    et al.
    Van Dyk, Schuyler D.
    Benetti, Stefano
    Cappellaro, Enrico
    Smith, Nathan
    Kotak, Rubina
    Turatto, Massimo
    Filippenko, Alexei V.
    Pignata, Giuliano
    Fox, Ori D.
    Galbany, Lluis
    González-Gaitán, Santiago
    Miluzio, Matteo
    Monard, L. A. G.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 860, no 1, article id 68Article in journal (Refereed)
    Abstract [en]

    It is well known that massive stars (M > 8M(circle dot)) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN. 2010bt, which was classified as a Type. IIn. SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L-circle dot approximate to 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (similar to 5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN. 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.

  • 4.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    SN 2011dh and the progenitors of Type IIb supernovae2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Core-collapse supernovae (SNe) are the observed events following the collapse of the core of evolved massive stars. The gravitational energy released creates a powerful shock that disrupts the star and ejects the heated material into the surrounding circumstellar medium. The observed properties depend on the mass lost by the star, e.g. through stellar winds or mass transfer in binary systems, and the subject of this thesis is the class of Type IIb SNe, which are thought to have lost most, but not all of their hydrogen envelopes. A quite unique set of observations has recently been obtained for the Type IIb SN 2011dh, which was followed to more than a thousand days after the explosion, and observed by several groups at a wide range of wavelengths. In this work, the bulk portion of the ultraviolet to mid-infrared observations, as well as pre-explosion images of the progenitor star, are presented, discussed, and analysed. Lightcurve and spectral modelling of the SN observations, presented in this and related works, all suggest a progenitor of modest initial mass (<15 solar masses) with an extended and low-mass hydrogen envelope, consistent with what is found from the pre-explosion observations. Although mass-loss rates for single stars are uncertain, they are likely too weak to expel the hydrogen envelope for stars in this mass range. Therefore, an appealing alternative is mass-loss by Roche-lobe overflow in a binary system, as was likely the case for the Type IIb SN 1993J. Post-explosion observations have revealed a blue compact companion star blended with the fading SN 1993J, and a similar result has been claimed for SN 2011dh. The fact that some SNe arise from binary systems is not surprising given the large binary fraction observed for massive stars, and in this work, a grid of hydrodynamical SN models is used to infer modest initial masses (<15 solar masses) for most Type IIb SNe documented in the literature, suggesting that binary systems actually dominate the production of Type IIb SNe.

  • 5.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Elias-Rosa, N.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Pastorello, A.
    Kotak, R.
    Taubenberger, S.
    Tomasella, L.
    Valenti, S.
    Benetti, S.
    Helou, G.
    Kasliwal, M. M.
    Maund, J.
    Smartt, S. J.
    Spyromilio, J.
    The Type IIb SN 2011dh - 2 years of observations and modelling of the lightcurvesIn: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 6.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Jerkstrand, A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Elias-Rosa, N.
    Fransson, Claes
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Fraser, M.
    Pastorello, A.
    Kotak, R.
    Taubenberger, S.
    Tomasella, L.
    Valenti, S.
    Benetti, S.
    Helou, G.
    Kasliwal, M. M.
    Maund, J.
    Smartt, S. J.
    Spyromilio, J.
    The Type IIb SN 2011dh: Two years of observations and modelling of the lightcurves2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id A142Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared (NIR) photometry and spectroscopy as well as modelling of the lightcurves of the Type IIb supernova (SN) 2011dh. Our extensive dataset, for which we present the observations obtained after day 100, spans two years, and complemented with Spitzer mid-infrared (MIR) data, we use it to build an optical-to-MIR bolometric lightcurve between days 3 and 732. To model the bolometric lightcurve before day 400 we use a grid of hydrodynamical SN models, which allows us to determine the errors in the derived quantities, and a bolometric correction determined with steady-state non-local thermodynamic equilibrium (NLTE) modelling. Using this method we find a helium core mass of 3.1(-0.)(0.7) M-circle dot for SN 2011dh, consistent within error bars with previous results obtained using the bolometric lightcurve before day 80. We compute bolometric and broad-band lightcurves between days 100 and 500 from spectral steady-state NLTE models, presented and discussed in a companion paper. The preferred 12 M-circle dot (initial mass) model, previously found to agree well with the observed spectra, shows a good overall agreement with the observed lightcurves, although some discrepancies exist. Time-dependent NLTE modelling shows that after day similar to 600 a steady-state assumption is no longer valid. The radioactive energy deposition in this phase is likely dominated by the positrons emitted in the decay of Co-56, but seems insufficient to reproduce the lightcurves, and what energy source is dominating the emitted flux is unclear. We find an excess in the K and the MIR bands developing between days 100 and 250, during which an increase in the optical decline rate is also observed. A local origin of the excess is suggested by the depth of the He I 20 581 angstrom absorption. Steady-state NLTE models with a modest dust opacity in the core (tau = 0.44), turned on during this period, reproduce the observed behaviour, but an additional excess in the Spitzer 4.5 mu m band remains. Carbon-monoxide (CO) first-overtone band emission is detected at day 206, and possibly at day 89, and assuming the additional excess to be dominated by CO fundamental band emission, we find fundamental to first-overtone band ratios considerably higher than observed in SN 1987A. The profiles of the [OI] 6300 angstrom and Mg I] 4571 angstrom lines show a remarkable similarit, suggesting that these lines originate from a common nuclear burning zone (O/Ne/Mg), and using small scale fluctuations in the line profiles we estimate a filling factor of less than or similar to 0.07 for the emitting material. This paper concludes our extensive observational and modelling work on SN 2011dh. The results from hydrodynamical modelling, steady-state NLTE modelling, and stellar evolutionary progenitor analysis are all consistent, and suggest an initial mass of similar to 12 M-circle dot for the progenitor.

  • 7.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Pastorello, A.
    Taubenberger, S.
    Elias-Rosa, N.
    Bersten, M.
    Jerkstrand, A.
    Benetti, S.
    Botticella, M. T.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harutyunyan, A.
    Kotak, R.
    Smartt, S.
    Valenti, S.
    Bufano, F.
    Cappellaro, E.
    Fiaschi, M.
    Howell, A.
    Kankare, E.
    Magill, L.
    Mattila, S.
    Maund, J.
    Naves, R.
    Ochner, P.
    Ruiz, J.
    Smith, K.
    Tomasella, L.
    Turatto, M.
    Optical and near-infrared observations of SN 2011dh-The first 100 days2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A17-, article id A17Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared (NIR) photometry and spectroscopy of the Type IIb supernova (SN) 2011dh for the first 100 days. We complement our extensive dataset with Swift ultra-violet (UV) and Spitzer mid-infrared (MIR) data to build a UV to MIR bolometric lightcurve using both photometric and spectroscopic data. Hydrodynamical modelling of the SN based on this bolometric lightcurve have been presented in Bersten et al. (2012, ApJ, 757, 31). We find that the absorption minimum for the hydrogen lines is never seen below similar to 11 000 km s(-1) but approaches this value as the lines get weaker. This suggests that the interface between the helium core and hydrogen rich envelope is located near this velocity in agreement with the Bersten et al. (2012) He4R270 ejecta model. Spectral modelling of the hydrogen lines using this ejecta model supports the conclusion and we find a hydrogen mass of 0.01-0.04 M-circle dot to be consistent with the observed spectral evolution. We estimate that the photosphere reaches the helium core at 5-7 days whereas the helium lines appear between similar to 10 and similar to 15 days, close to the photosphere and then move outward in velocity until similar to 40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the gamma-rays is driving the early evolution of these lines. The Spitzer 4.5 mu m band shows a significant flux excess, which we attribute to CO fundamental band emission or a thermal dust echo although further work using late time data is needed. The distance and in particular the extinction, where we use spectral modelling to put further constraints, is discussed in some detail as well as the sensitivity of the hydrodynamical modelling to errors in these quantities. We also provide and discuss pre- and post-explosion observations of the SN site which shows a reduction by similar to 75 percent in flux at the position of the yellow supergiant coincident with SN 2011dh. The B, V and r band decline rates of 0.0073, 0.0090 and 0.0053 mag day(-1) respectively are consistent with the remaining flux being emitted by the SN. Hence we find that the star was indeed the progenitor of SN 2011dh as previously suggested by Maund et al. (2011, ApJ, 739, L37) and which is also consistent with the results from the hydrodynamical modelling.

  • 8.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, Maximilian
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hydrodynamical modelling of Type IIb SNeIn: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 9.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Challis, Peter J.
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Marion, G. H.
    Milisavljevic, Dan
    Smith, Nathan
    Bufano, Filomena
    Friedman, Andrew S.
    Kangas, Tuomas
    Larsson, Josefin
    Mattila, Seppo
    Benetti, Stefano
    Chornock, Ryan
    Czekala, Ian
    Söderberg, Alicia
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    HIGH-DENSITY CIRCUMSTELLAR INTERACTION IN THE LUMINOUS TYPE IIn SN 2010jl: THE FIRST 1100 DAYS2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 797, no 2, article id 118Article in journal (Refereed)
    Abstract [en]

    Hubble Space Telescope and ground-based observations of the Type IIn supernova (SN) 2010jl are analyzed, including photometry and spectroscopy in the ultraviolet, optical, and near-IR bands, 26-1128 days after first detection. At maximum, the bolometric luminosity was similar to 3 x 10(43) erg s(-1) and even at 850 days exceeds 10(42) erg s(-1). A near-IR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is greater than or similar to 6.5x10(50) erg, excluding the dust component. The spectral lines can be separated into one broad component that is due to electron scattering and one narrow with expansion velocity similar to 100 km s(-1) from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after similar to 50 days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large-scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an r(-2) CSM with a mass-loss rate of M similar to 0.1 M(circle dot)yr(-1). The total mass lost is greater than or similar to 3 M-circle dot. These properties are consistent with the SN expanding into a CSM characteristic of a luminous blue variable progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM that is still opaque to electron scattering.

  • 10. Fraser, M.
    et al.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Eldridge, J. J.
    Valenti, S.
    Pastorello, A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smartt, S. J.
    Agnoletto, I.
    Arcavi, I.
    Benetti, S.
    Botticella, M.-T.
    Bufano, F.
    Campillay, A.
    Crockett, R. M.
    Gal-Yam, A.
    Kankare, E.
    Leloudas, G.
    Maguire, K.
    Mattila, S.
    Maund, J. R.
    Salgado, F.
    Stephens, A.
    Taubenberger, S.
    Turatto, M.
    SN 2009md: another faint supernova from a low-mass progenitor2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 417, p. 1417-1433Article in journal (Refereed)
    Abstract [en]

    We present adaptive optics imaging of the core-collapse supernova (SN) 2009md, which we use together with archival Hubble Space Telescope data to identify a coincident progenitor candidate. We find the progenitor to have an absolute magnitude of V=-4.63+0.3-0.4 mag and a colour of V-I= 2.29+0.25-0.39 mag, corresponding to a progenitor luminosity of log L/L&sun;˜ 4.54 ± 0.19 dex. Using the stellar evolution code STARS, we find this to be consistent with a red supergiant progenitor with M= 8.5+6.5-1.5 M&sun;. The photometric and spectroscopic evolution of SN 2009md is similar to that of the class of sub-luminous Type IIP SNe; in this paper we compare the evolution of SN 2009md primarily to that of the sub-luminous SN 2005cs. We estimate the mass of 56Ni ejected in the explosion to be (5.4 ± 1.3) × 10-3 M&sun; from the luminosity on the radioactive tail, which is in agreement with the low 56Ni masses estimated for other sub-luminous Type IIP SNe. From the light curve and spectra, we show the SN explosion had a lower energy and ejecta mass than the normal Type IIP SN 1999em. We discuss problems with stellar evolutionary models, and the discrepancy between low observed progenitor luminosities (log L/L&sun;˜4.3-5 dex) and model luminosities after the second dredge-up for stars in this mass range, and consider an enhanced carbon burning rate as a possible solution. In conclusion, SN 2009md is a faint SN arising from the collapse of a progenitor close to the lower mass limit for core collapse. This is now the third discovery of a low-mass progenitor star producing a low-energy explosion and low 56Ni ejected mass, which indicates that such events arise from the lowest end of the mass range that produces a core-collapse SN (7-8 M&sun;).

  • 11. Fraser, M.
    et al.
    Maund, J. R.
    Smartt, S. J.
    Botticella, M-T
    Dall'Ora, M.
    Inserra, C.
    Tomasella, L.
    Benetti, S.
    Ciroi, S.
    Eldridge, J. J.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kotak, R.
    Mattila, S.
    Ochner, P.
    Pastorello, A.
    Reilly, E.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stephens, A.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Valenti, S.
    RED AND DEAD: THE PROGENITOR OF SN 2012aw IN M952012In: The Astrophysical Journal Letters, ISSN 2041-8205, Vol. 759, no 1, p. L13-Article in journal (Refereed)
    Abstract [en]

    Core-collapse supernovae (SNe) are the spectacular finale to massive stellar evolution. In this Letter, we identify a progenitor for the nearby core-collapse SN 2012aw in both ground-based near-infrared and space-based optical pre-explosion imaging. The SN itself appears to be a normal Type II Plateau event, reaching a bolometric luminosity of 10(42) erg s(-1) and photospheric velocities of similar to 11,000 km s(-1) from the position of the H beta P-Cygni minimum in the early SN spectra. We use an adaptive optics image to show that the SN is coincident to within 27 mas with a faint, red source in pre-explosion HST+WFPC2, VLT+ISAAC, and NTT+SOFI images. The source has magnitudes F555W = 26.70 +/- 0.06, F814W = 23.39 +/- 0.02, J = 21.1 +/- 0.2, K = 19.1 +/- 0.4, which, when compared to a grid of stellar models, best matches a red supergiant. Interestingly, the spectral energy distribution of the progenitor also implies an extinction of A(V) > 1.2 mag, whereas the SN itself does not appear to be significantly extinguished. We interpret this as evidence for the destruction of dust in the SN explosion. The progenitor candidate has a luminosity between 5.0 and 5.6 log L/L-circle dot, corresponding to a zero-age main-sequence mass between 14 and 26 M-circle dot (depending on A(V)), which would make this one of the most massive progenitors found for a core-collapse SN to date.

  • 12. Fraser, M.
    et al.
    Maund, J. R.
    Smartt, S. J.
    Kotak, R.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    A low mass red supergiant progenitor candidate for SN 2012aw2012Report (Other academic)
    Abstract [en]

    We obtained an unfiltered image of the Type IIP SN 2012aw (CBET 3054) from the Nordic Optical Telescope + ALFOSC on 2012 March 19.9 UT, under excellent (~0.5") seeing conditions. 6 sources were identified in both the the ALFOSC image, and a pre-explosion HST+WFPC2 F555W mosaic of M95 retrieved (together with F439W and F814W-filter images) from the Hubble Legacy Archive. Using a geometric transformation derived from the position of the fiducial sources in both images, SN 2012aw was located in the WFPC2 image to an accuracy of 0.24". We find SN 2012aw to be coincident with a faint, red source in the pre-explosion WFPC data, which is the probable progenitor.

  • 13. Fraser, M.
    et al.
    Takáts, K.
    Pastorello, A.
    Smartt, S. J.
    Mattila, S.
    Botticella, M.-T.
    Valenti, S.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Arcavi, I.
    Benetti, S.
    Bufano, F.
    Crockett, R. M.
    Danziger, I. J.
    Gal-Yam, A.
    Maund, J. R.
    Taubenberger, S.
    Turatto, M.
    On the Progenitor and Early Evolution of the Type II Supernova 2009kr2010In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 714, p. L280-L284Article in journal (Refereed)
    Abstract [en]

    We identify a source coincident with SN 2009kr in Hubble Space Telescope pre-explosion images. The object appears to be a single point source with an intrinsic color V - I = 1.1 ± 0.25 and MV = -7.6 ± 0.6. If this is a single star, it would be a yellow supergiant of log L/L sun ~ 5.1 and a mass of 15+5 -4 M sun. The spatial resolution does not allow us yet to definitively determine if the progenitor object is a single star, a binary system, or a compact cluster. We show that the early light curve is similar to a Type IIL SN, but the prominent Hα P-Cygni profiles and the signature of the end of a recombination phase are reminiscent of a Type IIP. The evolution of the expanding ejecta will play an important role in understanding the progenitor object.

  • 14.
    Fremling, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). California Institute of Technology, USA.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, M. M.
    Kulkarni, S. R.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Arcavi, I
    Cenko, S. B.
    Clubb, K.
    De Cia, A.
    Duggan, G.
    Filippenko, A.
    Gal-Yam, A.
    Graham, M. L.
    Horesh, A.
    Hosseinzadeh, G.
    Howell, D. A.
    Kuesters, D.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). California Institute of Technology, USA.
    Matheson, T.
    Nugent, P. E.
    Perley, D. A.
    Quimby, R. M.
    Saunders, C.
    Oxygen and helium in stripped-envelope supernovae2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 618, article id A37Article in journal (Refereed)
    Abstract [en]

    We present an analysis of 507 spectra of 173 stripped-envelope (SE) supernovae (SNe) discovered by the untargeted Palomar Transient Factory (PTF) and intermediate PTF (iPTF) surveys. Our sample contains 55 Type IIb SNe (SNe 45 Type Ib SNe (SNe IIb), 56 Type Ic SNe (SNe Ic), and 17 Type Ib/c SNe (SNe Ib/c). We have compared the SE SN subtypes via measurements of the pseudo-equivalent widths (pEWs) and velocities of the He I lambda lambda 5876, 7065 and O I lambda 7774 absorption lines. Consistent with previous work, we find that SNe Ic show higher pEWs and velocities in O I lambda 7774 compared to SNe IIb and Ib. The pEWs of the He I lambda lambda 5876, 7065 lines are similar in SNe Ib and IIb after maximum light. The He I lambda lambda 5876, 7065 velocities at maximum light are higher in SNe Ib compared to SNe IIb. We identify an anticorrelation between the He I lambda 7065 pEW and O I lambda 7774 velocity among SNe IIb and Ib. This can be interpreted as a continuum in the amount of He present at the time of explosion. It has been suggested that SNe Ib and Ic have similar amounts of He, and that lower mixing could be responsible for hiding He in SNe Ic. However, our data contradict this mixing hypothesis. The observed difference in the expansion rate of the ejecta around maximum light of SNe Ic (V-m root 2E(k)/M-ej approximate to 15 000 km s(-1)) and SNe Ib (V-m approximate to 9000 km s(-1)) would imply an average He mass difference of similar to 1.4 M-circle dot, if the other explosion parameters are assumed to be unchanged between the SE SN subtypes. We conclude that SNe Ic do not hide He but lose He due to envelope stripping.

  • 15.
    Fremling, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    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, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pian, E.
    Smartt, S.
    PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 58062016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, article id A68Article in journal (Refereed)
    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.

  • 16.
    Fremling, Christoffer
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Valenti, S.
    Arcavi, I.
    Ben-Ami, S.
    Cao, Y.
    Cenko, S. B.
    Filippenko, A. V.
    Gal-Yam, A.
    Howell, D. A.
    The rise and fall of the Type Ib supernova iPTF13bvn Not a massive Wolf-Rayet star2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 565, article id A114Article in journal (Refereed)
    Abstract [en]

    Context. We investigate iPTF13bvn, a core-collapse (CC) supernova (SN) in the nearby spiral galaxy NGC 5806. This object was discovered by the intermediate Palomar Transient Factory (iPTF) very close to the estimated explosion date and was classified as a stripped-envelope CC SN, likely of Type Ib. Furthermore, a possible progenitor detection in pre-explosion Hubble Space Telescope (HST) images was reported, making this the only SN Ib with such an identification. Based on the luminosity and color of the progenitor candidate, as well as on early-time spectra and photometry of the SN, it was argued that the progenitor candidate is consistent with a single, massive Wolf-Rayet (WR) star. Aims. We aim to confirm the progenitor detection, to robustly classify the SN using additional spectroscopy, and to investigate if our follow-up photometric and spectroscopic data on iPTF13bvn are consistent with a single-star WR progenitor scenario. Methods. We present a large set of observational data, consisting of multi-band light curves (UBVRI, g' r' i' z') and optical spectra. We perform standard spectral line analysis to track the evolution of the SN ejecta. We also construct a bolometric light curve and perform hydrodynamical calculations to model this light curve to constrain the synthesized radioactive nickel mass and the total ejecta mass of the SN. Late-time photometry is analyzed to constrain the amount of oxygen. Furthermore, image registration of pre- and post-explosion HST images is performed. Results. Our HST astrometry confirms the location of the progenitor candidate of iPTF13bvn, and follow-up spectra securely classify this as a SN Ib. We use our hydrodynamical model to fit the observed bolometric light curve, estimating the total ejecta mass to be 1.9 M-circle dot and the radioactive nickel mass to be 0.05 M-circle dot. The model fit requires the nickel synthesized in the explosion to be highly mixed out in the ejecta. We also find that the late-time nebular r'-band luminosity is not consistent with predictions based on the expected oxygen nucleosynthesis in very massive stars. Conclusions. We find that our bolometric light curve of iPTF13bvn is not consistent with the previously proposed single massive WR-star progenitor scenario. The total ejecta mass and, in particular, the late-time oxygen emission are both significantly lower than what would be expected from a single WR progenitor with a main-sequence mass of at least 30 M-circle dot.

  • 17. Inserra, C.
    et al.
    Smartt, S. J.
    Chambers, K. C.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Leloudas, Georgios
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesca
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Waters, C.
    Young, D.
    SUPER-LUMINOUS TYPE Ic SUPERNOVAE: CATCHING A MAGNETAR BY THE TAIL2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 770, no 2, article id 128Article in journal (Refereed)
    Abstract [en]

    We report extensive observational data for five of the lowest redshift Super-Luminous Type Ic Supernovae (SL-SNe Ic) discovered to date, namely, PTF10hgi, SN2011ke, PTF11rks, SN2011kf, and SN2012il. Photometric imaging of the transients at +50 to +230 days after peak combined with host galaxy subtraction reveals a luminous tail phase for four of these SL-SNe. A high-resolution, optical, and near-infrared spectrum from xshooter provides detection of a broad He I lambda 10830 emission line in the spectrum (+50 days) of SN2012il, revealing that at least some SL-SNe Ic are not completely helium-free. At first sight, the tail luminosity decline rates that we measure are consistent with the radioactive decay of Co-56, and would require 1-4 M-circle dot of Ni-56 to produce the luminosity. These Ni-56 masses cannot be made consistent with the short diffusion times at peak, and indeed are insufficient to power the peak luminosity. We instead favor energy deposition by newborn magnetars as the power source for these objects. A semi-analytical diffusion model with energy input from the spin-down of a magnetar reproduces the extensive light curve data well. The model predictions of ejecta velocities and temperatures which are required are in reasonable agreement with those determined from our observations. We derive magnetar energies of 0.4 less than or similar to E(10(51) erg) less than or similar to 6.9 and ejecta masses of 2.3 less than or similar to M-ej(M-circle dot) less than or similar to 8.6. The sample of five SL-SNe Ic presented here, combined with SN 2010gx-the best sampled SL-SNe Ic so far-points toward an explosion driven by a magnetar as a viable explanation for all SL-SNe Ic.

  • 18. Jerkstrand, A.
    et al.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smartt, S. J.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taubenberger, S.
    Bersten, M.
    Spyromilio, J.
    Late-time spectral line formation in Type IIb supernovae, with application to SN 1993J, SN 2008ax, and SN 2011dh2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 573, article id A12Article in journal (Refereed)
    Abstract [en]

    We investigate line formation processes in Type IIb supernovae (SNe) from 100 to 500 days post-explosion using spectral synthesis calculations. The modelling identifies the nuclear burning layers and physical mechanisms that produce the major emission lines, and the diagnostic potential of these. We compare the model calculations with data on the three best observed Type IIb SNe to-date - SN 1993J, SN 2008ax, and SN 2011dh. Oxygen nucleosynthesis depends sensitively on the main-sequence mass of the star and modelling of the [O I] lambda lambda 6300, 6364 lines constrains the progenitors of these three SNe to the M-ZAMS = 12-16 M-circle dot range (ejected oxygen masses 0.3-0.9 M-circle dot), with SN 2011dh towards the lower end and SN 1993J towards the upper end of the range. The high ejecta masses from M-ZAMS greater than or similar to 17 M-circle dot progenitors give rise to brighter nebular phase emission lines than observed. Nucleosynthesis analysis thus supports a scenario of low-to-moderate mass progenitors for Type IIb SNe, and by implication an origin in binary systems. We demonstrate how oxygen and magnesium recombination lines may be combined to diagnose the magnesium mass in the SN ejecta. For SN 2011dh, a magnesium mass of 0.02-0.14 M-circle dot is derived, which gives a Mg/O production ratio consistent with the solar value. Nitrogen left in the He envelope from CNO burning gives strong [N II] lambda lambda 6548, 6583 emission lines that dominate over Ha emission in our models. The hydrogen envelopes of Type IIb SNe are too small and dilute to produce any noticeable H alpha emission or absorption after similar to 150 days, and nebular phase emission seen around 6550 angstrom is in many cases likely caused by [N II] lambda lambda 6548, 6583. Finally, the influence of radiative transport on the emergent line profiles is investigated. Significant line blocking in the metal core remains for several hundred days, which affects the emergent spectrum. These radiative transfer effects lead to early-time blueshifts of the emission line peaks, which gradually disappear as the optical depths decrease with time. The modelled evolution of this effect matches the observed evolution in SN 2011dh.

  • 19.
    Jerkstrand, A.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Maguire, K.
    Smartt, S.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spyromilio, J.
    The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modeling2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 546, p. A28-Article in journal (Refereed)
    Abstract [en]

    SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a progenitor detection as well as good photometric and spectroscopic observational coverage well into the nebular phase. Based on nucleosynthesis from stellar evolution/explosion models we apply spectral modeling to analyze its 140-700 day evolution from ultraviolet to mid-infrared. We find a M-ZAMS = 15 M-circle dot progenitor star (with an oxygen mass of 0.8 M-circle dot) to satisfactorily reproduce [Oi] lambda lambda 6300, 6364 and other emission lines of carbon, sodium, magnesium, and silicon, while 12 M-circle dot and 19 M-circle dot models under-and overproduce most of these lines, respectively. This result is in fair agreement with the mass derived from the progenitor detection, but in disagreement with hydrodynamical modeling of the early-time light curve. From modeling of the mid-infrared iron-group emission lines, we determine the density of the Ni-bubble to rho(t) similar or equal to 7 x 10(-14) x (t/100 d)(-3) g cm(-3), corresponding to a filling factor of f = 0.15 in the metal core region (V = 1800 km s(-1)). We also confirm that silicate dust, CO, and SiO emission are all present in the spectra.

  • 20.
    Jerkstrand, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Maguire, Kate
    Smartt, Stephen
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    Spyromilio, Jason
    The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modelingManuscript (preprint) (Other academic)
  • 21. Kankare, E.
    et al.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bufano, F.
    Spyromilio, J.
    Mattila, S.
    Chugai, N. N.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pastorello, A.
    Kotak, R.
    Benetti, S.
    Botticella, M. -T
    Cumming, R. J.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Leloudas, Georgios
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Miluzio, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, M.
    Turatto, M.
    Valenti, S.
    SN 2009kn-the twin of the Type IIn supernova 1994W2012In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 424, no 2, p. 855-873Article in journal (Refereed)
    Abstract [en]

    We present an optical and near-infrared photometric and spectroscopic study of supernova (SN) 2009kn spanning similar to 1.5 yr from the discovery. The optical spectra are dominated by the narrow (full width at half-maximum similar to 1000 km s-1) Balmer lines distinctive of a Type IIn SN with P Cygni profiles. Contrarily, the photometric evolution resembles more that of a Type IIP SN with a large drop in luminosity at the end of the plateau phase. These characteristics are similar to those of SN 1994W, whose nature has been explained with two different models with different approaches. The well-sampled data set on SN 2009kn offers the possibility to test these models, in the case of both SN 2009kn and SN 1994W. We associate the narrow P Cygni lines with a swept-up shell composed of circumstellar matter and SN ejecta. The broad emission line wings, seen during the plateau phase, arise from internal electron scattering in this shell. The slope of the light curve after the post-plateau drop is fairly consistent with that expected from the radioactive decay of 56Co, suggesting an SN origin for SN 2009kn. Assuming radioactivity to be the main source powering the light curve of SN 2009kn in the tail phase, we infer an upper limit for 56Ni mass of 0.023 M?. This is significantly higher than that estimated for SN 1994W, which also showed a much steeper decline of the light curve after the post-plateau drop. We also observe late-time near-infrared emission which most likely arises from newly formed dust produced by SN 2009kn. As with SN 1994W, no broad lines are observed in the spectra of SN 2009kn, not even in the late-time tail phase.

  • 22. Maund, J. R.
    et al.
    Arcavi, I.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Eldridge, J. J.
    Georgy, C.
    Cenko, S. B.
    Horesh, A.
    Izzard, R. G.
    Stancliffe, R. J.
    Did the progenitor of SN 2011dh have a binary companion?2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, no 3, p. 2580-2585Article in journal (Refereed)
    Abstract [en]

    We present late-time Hubble Space Telescope ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, similar to 1164 days post-explosion. At the supernova (SN) location, we observe a point source that is visible at all wavelengths, which is significantly fainter than the spectral energy distribution (SED) of the yellow supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with an SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star cannot be ruled out.

  • 23. Maund, J. R.
    et al.
    Fraser, M.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pastorello, A.
    Smartt, S. J.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Benetti, S.
    Botticella, M-T
    Bufano, F.
    Danziger, I. J.
    Kotak, R.
    Magill, L.
    Stephens, A. W.
    Valenti, S.
    THE YELLOW SUPERGIANT PROGENITOR OF THE TYPE II SUPERNOVA 2011dh IN M512011In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 739, no 2, article id L37Article in journal (Refereed)
    Abstract [en]

    We present the detection of the putative progenitor of the Type IIb SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the supernova (SN) in the pre-explosion images was determined to within 23 mas. The progenitor candidate is consistent with an F8 supergiant star (logL/L(circle dot) = 4.92 +/- 0.20 and T(eff) = 6000 +/- 280 K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M(ZAMS) = 13 +/- 3 M(circle dot). The possibility of the progenitor source being a cluster is rejected, on the basis of: (1) the source not being spatially extended, (2) the absence of excess H alpha emission, and (3) the poor fit to synthetic cluster spectral energy distributions (SEDs). It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest that the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion. Late-time observations will reveal if the yellow supergiant or the putative companion star were responsible for this SN explosion.

  • 24. Maund, Justyn R.
    et al.
    Fraser, Morgan
    Reilly, Emma
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, Seppo
    Whatever happened to the progenitors of supernovae 2008cn, 2009kr and 2009md?2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 447, no 4, p. 3207-3217Article in journal (Refereed)
    Abstract [en]

    We present new late-time, high-resolution observations of the sites of supernovae (SNe) 2008cn, 2009kr and 2009md, acquired with the Hubble Space Telescope. In all instances, significant flux from the SNe is still recovered at late times. We show that the previous identification of the progenitor of SN 2008cn was actually a blend of two sources, whose locations are resolved in these new observations. We suggest that the progenitor of SN 2008cn was actually a red supergiant with M-init < 16 M-circle dot. In the late-time observations of SN 20091cr, we find that the pre-explosion source (previously thought to be a yellow supergiant) is most probably a small compact cluster with mass similar to 6000 M-circle dot. In late-time F814W observations of the site of SN 2009md, we find a single point source with identical brightness to the pre-explosion source, suggesting some caution in assuming that the pre-explosion source was the progenitor.

  • 25. Morales-Garoffolo, A.
    et al.
    Elias-Rosa, N.
    Bersten, M.
    Jerkstrand, A.
    Taubenberger, S.
    Benetti, S.
    Cappellaro, E.
    Kotak, R.
    Pastorello, A.
    Bufano, F.
    Dominguez, R. M.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Gao, X.
    Garcia, E.
    Howell, D. A.
    Isern, J.
    Smartt, S. J.
    Tomasella, L.
    Valenti, S.
    SN 2011fu: a type IIb supernova with a luminous double-peaked light curve2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, no 1, p. 95-114Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared observations of the type IIb supernova (SN) 2011fu from a few days to similar to 300 d after explosion. The SN presents a double-peaked light curve (LC) similar to that of SN 1993J, although more luminous and with a longer cooling phase after the primary peak. The spectral evolution is also similar to SN 1993J's, with hydrogen dominating the spectra to similar to 40 d, then helium gaining strength, and nebular emission lines appearing from similar to 60 d post-explosion. The velocities derived from the P-Cygni absorptions are overall similar to those of other type IIb SNe. We have found a strong similarity between the oxygen and magnesium line profiles at late times, which suggests that these lines are forming at the same location within the ejecta. The hydrodynamical modelling of the pseudo-bolometric LC and the observed photospheric velocities suggest that SN 2011fu was the explosion of an extended star (R similar to 450 R-circle dot), in which 1.3 x 10(51) erg of kinetic energy were released and 0.15 M-circle dot of Ni-56 were synthesized. In addition, a better reproduction of the observed early pseudo-bolometric LC is achieved if a more massive H-rich envelope than for other type IIb SNe is considered (0.3 M-circle dot). The hydrodynamical modelling of the LC and the comparison of our late-time spectra with nebular spectral models for type IIb SNe, point to a progenitor for SN 2011fu with a Zero Age Main Sequence (ZAMS) mass of 13-18 M-circle dot.

  • 26. Moriya, Takashi J.
    et al.
    Pruzhinskaya, Maria V.
    Ergon, Mattias
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Blinnikov, Sergei I.
    On the nature of rapidly fading Type II supernovae2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 455, no 1, p. 423-430Article in journal (Refereed)
    Abstract [en]

    It has been suggested that Type II supernovae with rapidly fading light curves (a.k.a. Type IIL supernovae) are explosions of progenitors with low-mass hydrogen-rich envelopes which are of the order of 1M(circle dot.) We investigate light-curve properties of supernovae from such progenitors. We confirm that such progenitors lead to rapidly fading Type II supernovae. We find that the luminosity of supernovae from such progenitors with the canonical explosion energy of 10(51) erg and Ni-56 mass of 0.05 M-circle dot can increase temporarily shortly before all the hydrogen in the envelope recombines. As a result, a bump appears in their light curves. The bump appears because the heating from the nuclear decay of Ni-56 can keep the bottom of hydrogen-rich layers in the ejecta ionized, and thus the photosphere can stay there for a while. We find that the light-curve bump becomes less significant when we make explosion energy larger (greater than or similar to 2 x 10(51) erg), Ni-56 mass smaller (less than or similar to 0.01 M-circle dot), Ni-56 mixed in the ejecta, or the progenitor radius larger. Helium mixing in hydrogen-rich layers makes the light-curve decline rates large but does not help reducing the light-curve bump. Because the light-curve bump we found in our light-curve models has not been observed in rapidly fading Type II supernovae, they may be characterized by not only low-mass hydrogen-rich envelopes but also higher explosion energy, larger degrees of Ni-56 mixing, and/or larger progenitor radii than slowly fading Type II supernovae, so that the light-curve bump does not become significant.

  • 27. Pastorello, A.
    et al.
    Benetti, S.
    Brown, P. J.
    Tsvetkov, D. Y.
    Inserra, C.
    Taubenberger, S.
    Tomasella, L.
    Fraser, M.
    Rich, D. J.
    Botticella, M. T.
    Bufano, F.
    Cappellaro, E.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gorbovskoy, E. S.
    Harutyunyan, A.
    Huang, F.
    Kotak, R.
    Lipunov, V. M.
    Magill, L.
    Miluzio, M.
    Morrell, N.
    Ochner, P.
    Smartt, S. J.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spiro, S.
    Stritzinger, M. D.
    Turatto, M.
    Valenti, S.
    Wang, X.
    Wright, D. E.
    Yurkov, V. V.
    Zampieri, L.
    Zhang, T.
    Massive stars exploding in a He-rich circumstellar medium - IV. Transitional Type Ibn supernovae2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 449, no 2, p. 1921-1940Article in journal (Refereed)
    Abstract [en]

    We present ultraviolet, optical and near-infrared data of the Type Ibn supernovae (SNe) 2010al and 2011hw. SN 2010al reaches an absolute magnitude at peak of M-R = -18.86 +/- 0.21. Its early light curve shows similarities with normal SNe Ib, with a rise to maximum slower than most SNe Ibn. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni He I lines indicating the presence of a slow-moving, He-rich circumstellar medium. At later epochs, the spectra well match those of the prototypical SN Ibn 2006jc, although the broader lines suggest that a significant amount of He was still present in the stellar envelope at the time of the explosion. SN 2011hw is somewhat different. It was discovered after the first maximum, but the light curve shows a double peak. The absolute magnitude at discovery is similar to that of the second peak (M-R = -18.59 +/- 0.25), and slightly fainter than the average of SNe Ibn. Though the spectra of SN 2011hw are similar to those of SN 2006jc, coronal lines and narrow Balmer lines are clearly detected. This indicates substantial interaction of the SN ejecta with He-rich, but not H-free, circumstellar material. The spectra of SN 2011hw suggest that it is a transitional SN Ibn/IIn event similar to SN 2005la. While for SN 2010al the spectrophotometric evolution favours a H-deprived Wolf-Rayet progenitor (of WN-type), we agree with the conclusion of Smith et al. that the precursor of SN 2011hw was likely in transition from a luminous blue variable to an early Wolf-Rayet (Ofpe/WN9) stage.

  • 28. Pastorello, A.
    et al.
    Cappellaro, E.
    Inserra, C.
    Smartt, S. J.
    Pignata, G.
    Benetti, S.
    Valenti, S.
    Fraser, M.
    Takats, K.
    Benitez, S.
    Botticella, M. T.
    Brimacombe, J.
    Bufano, F.
    Cellier-Holzem, F.
    Costado, M. T.
    Cupani, G.
    Curtis, I.
    Elias-Rosa, N.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fynbo, J. P. U.
    Hambsch, F. -J
    Hamuy, M.
    Harutyunyan, A.
    Ivarson, K. M.
    Kankare, E.
    Martin, J. C.
    Kotak, R.
    LaCluyze, A. P.
    Maguire, K.
    Mattila, S.
    Maza, J.
    McCrum, M.
    Miluzio, M.
    Norgaard-Nielsen, H. U.
    Nysewander, M. C.
    Ochner, P.
    Pan, Y. -C
    Pumo, M. L.
    Reichart, D. E.
    Tan, T. G.
    Taubenberger, S.
    Tomasella, L.
    Turatto, M.
    Wright, D.
    INTERACTING SUPERNOVAE AND SUPERNOVA IMPOSTORS: SN 2009ip, IS THIS THE END?2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 767, no 1, p. 1-Article in journal (Refereed)
    Abstract [en]

    We report the results of a three-year-long dedicated monitoring campaign of a restless luminous blue variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper, we present the full historical data set from 2009 to 2012 with multi-wavelength dense coverage of the two high-luminosity events between 2012 August and September. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting similar to 50 days) with a peak of 3x10(41) erg s(-1), and the 2012b event (14 day rise time, still ongoing) with a peak of 8 x 1042 erg s(-1). The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (similar to 13,000 km s(-1)) in 2011 September, one year before the current SN-like event. This implies that the detection of such high-velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.

  • 29. Pastorello, A.
    et al.
    Pumo, M. L.
    Navasardyan, H.
    Zampieri, L.
    Turatto, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kankare, E.
    Mattila, S.
    Nicolas, J.
    Prosperi, E.
    San Segundo Delgado, A.
    Taubenberger, S.
    Boles, T.
    Bachini, M.
    Benetti, S.
    Bufano, F.
    Cappellaro, E.
    Cason, A. D.
    Cetrulo, G.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Germany, L.
    Harutyunyan, A.
    Howerton, S.
    Hurst, G. M.
    Patat, F.
    Stritzinger, Maximilian
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
    Strolger, L.-G.
    Wells, W.
    SN 2009E: a faint clone of SN 1987A2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 537, article id A141Article in journal (Refereed)
    Abstract [en]

    Context. 1987A-like events form a rare sub-group of hydrogen-rich core-collapse supernovae that are thought to originate from the explosion of blue supergiant stars. Although SN 1987A is the best known supernova, very few objects of this group have been discovered and, hence, studied. Aims. In this paper we investigate the properties of SN 2009E, which exploded in a relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest 1987A-like supernova discovered so far. We also attempt to characterize this subgroup of core-collapse supernovae with the help of the literature and present new data for a few additional objects. Methods. The lack of early-time observations from professional telescopes is compensated by frequent follow-up observations performed by a number of amateur astronomers. This allows us to reconstruct a well-sampled light curve for SN 2009E. Spectroscopic observations which started about 2 months after the supernova explosion, highlight significant differences between SN 2009E and the prototypical SN 1987A. Modelling the data of SN 2009E allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 1987A and 1998A. Results. The light curve of SN 2009E is less luminous than that of SN 1987A and the other members of this class, and the maximum light curve peak is reached at a slightly later epoch than in SN 1987A. Late-time photometric observations suggest that SN 2009E ejected about 0.04 M-circle dot of Ni-56, which is the smallest Ni-56 mass in our sample of 1987A-like events. Modelling the observations with a radiation hydrodynamics code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an initial radius of similar to 7x10(12) cm and an ejected mass of similar to 19 M-circle dot. The photospheric spectra show a number of narrow (v approximate to 1800 km s(-1)) metal lines, with unusually strong Ba II lines. The nebular spectrum displays narrow emission lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively strong compared to the [Ca II] doublet. The overall spectroscopic evolution is reminiscent of that of the faint Ni-56-poor type II-plateau supernovae. This suggests that SN 2009E belongs to the low-luminosity, low Ni-56 mass, low-energy tail in the distribution of the 1987A-like objects in the same manner as SN 1997D and similar events represent the faint tail in the distribution of physical properties for normal type II-plateau supernovae.

  • 30. Quadri, U.
    et al.
    Strabla, L.
    Girelli, R.
    Quadri, A.
    Itoh, R.
    Ui, T.
    Siviero, A.
    Tomasella, L.
    Pastorello, A.
    Benetti, S.
    Munari, U.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy.
    Barisevicius, G.
    Supernova 2012aw in M95 = Psn J10435372+11401772012Report (Other academic)
    Abstract [en]

    CBET 3054 available at Central Bureau for Astronomical Telegrams.

  • 31.
    Roy, Rupak
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Silverman, J. M.
    Pastorello, A.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Drake, A.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kankare, E.
    Kumar, B.
    Cappellaro, E.
    Bose, S.
    Benetti, S.
    Filippenko, A. V.
    Valenti, S.
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sutaria, F.
    Kumar, B.
    Pandey, S. B.
    Nicholl, M.
    Garcia-Alvarez, D.
    Tomasella, L.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Migotto, Katia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SN 2012aa: A transient between Type Ibc core-collapse and superluminous supernovae2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A67Article in journal (Refereed)
    Abstract [en]

    Context. Research on supernovae (SNe) over the past decade has confirmed that there is a distinct class of events which are much more luminous (by similar to 2 mag) than canonical core-collapse SNe (CCSNe). These events with visual peak magnitudes less than or similar to-21 are called superluminous SNe (SLSNe). The mechanism that powers the light curves of SLSNe is still not well understood. The proposed scenarios are circumstellar interaction, the emergence of a magnetar after core collapse, or disruption of a massive star through pair production. Aims. There are a few intermediate events which have luminosities between these two classes. They are important for constraining the nature of the progenitors of these two different populations and their environments and powering mechanisms. Here we study one such object, SN 2012aa. Methods. We observed and analysed the evolution of the luminous Type Ic SN 2012aa. The event was discovered by the Lick Observatory Supernova Search in an anonymous galaxy (z approximate to 0.08). The optical photometric and spectroscopic follow-up observations were conducted over a time span of about 120 days. Results. With an absolute V-band peak of similar to-20 mag, the SN is an intermediate-luminosity transient between regular SNe Ibc and SLSNe. SN 2012aa also exhibits an unusual secondary bump after the maximum in its light curve. For SN 2012aa, we interpret this as a manifestation of SN-shock interaction with the circumstellar medium (CSM). If we assume a Ni-56-powered ejecta, the quasi-bolometric light curve requires roughly 1.3 M-circle dot of Ni-56 and an ejected mass of similar to 14 M-circle dot. This also implies a high kinetic energy of the explosion, similar to 5.4 x 10(51) erg. On the other hand, the unusually broad light curve along with the secondary peak indicate the possibility of interaction with CSM. The third alternative is the presence of a central engine releasing spin energy that eventually powers the light curve over a long time. The host of SN 2012aa is a star-forming Sa/Sb/Sbc galaxy. Conclusions. Although the spectral properties of SN 2012aa and its velocity evolution are comparable to those of normal SNe Ibc, its broad light curve along with a large peak luminosity distinguish it from canonical CCSNe, suggesting that the event is an intermediate-luminosity transient between CCSNe and SLSNe at least in terms of peak luminosity. In comparison to other SNe, we argue that SN 2012aa belongs to a subclass where CSM interaction plays a significant role in powering the SN, at least during the initial stages of evolution.

  • 32.
    Sollerman, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy.
    Inserra, C.
    Valenti, S.
    Wilson, P. A.
    Jon Juliusson, S.
    Holma, H.
    Ingemyr, M.
    Saxen, O.
    Haukanes, L.
    Supernova 2009md in NGC 33892009In: Central Bureau Electronic Telegrams, Vol. 2068, p. 1-Article in journal (Other academic)
    Abstract [en]

    CBET 2068 available at Central Bureau for Astronomical Telegrams.

  • 33.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Corsi, A.
    Gal-Yam, A.
    Karamehmetoglu, Emir
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lunnan, R.
    Bue, B.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, M.
    Vreeswijk, P. M.
    Wozniak, P. R.
    iPTF15dtg: a double-peaked Type Ic supernova from a massive progenitor2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 592, article id A89Article in journal (Refereed)
    Abstract [en]

    Context. Type Ic supernovae (SNe Ic) arise from the core-collapse of H-(and He-) poor stars, which could either be single Wolf-Rayet (WR) stars or lower-mass stars stripped of their envelope by a companion. Their light curves are radioactively powered and usually show a fast rise to peak (similar to 10-15 d), without any early (in the first few days) emission bumps (with the exception of broad-lined SNe Ic) as sometimes seen for other types of stripped-envelope SNe (e.g., Type IIb SN 1993J and Type Ib SN 2008D). Aims. We have studied iPTF15dtg, a spectroscopically normal SN Ic with an early excess in the optical light curves followed by a long (similar to 30 d) rise to the main peak. It is the first spectroscopically-normal double-peaked SN Ic to be observed. Our aim is to determine the properties of this explosion and of its progenitor star. Methods. Optical photometry and spectroscopy of iPTF15dtg was obtained with multiple telescopes. The resulting light curves and spectral sequence are analyzed and modeled with hydrodynamical and analytical models, with particular focus on the early emission. Results. iPTF15dtg is a slow rising SN Ic, similar to SN 2011bm. Hydrodynamical modeling of the bolometric properties reveals a large ejecta mass (similar to 10 M-circle dot) and strong Ni-56 mixing. The luminous early emission can be reproduced if we account for the presence of an extended (greater than or similar to 500 R-circle dot), low-mass (greater than or similar to 0.045 M-circle dot) envelope around the progenitor star. Alternative scenarios for the early peak, such as the interaction with a companion, a shock-breakout (SBO) cooling tail from the progenitor surface, or a magnetar-driven SBO are not favored. Conclusions. The large ejecta mass and the presence of H-and He-free extended material around the star suggest that the progenitor of iPTF15dtg was a massive (greater than or similar to 35 M-circle dot) WR star that experienced strong mass loss.

  • 34.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Migotto, Katia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, A.
    Armen, S.
    Duggan, G.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Filippenko, A. V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hosseinzadeh, G.
    Kasliwal, M. M.
    Laher, R. R.
    Leloudas, G.
    Leonard, D. C.
    Lunnan, R.
    Masci, F. J.
    Moon, D. -S.
    Silverman, J. M.
    Wozniak, P. R.
    Long-rising Type II supernovae from Palomar Transient Factory and Caltech Core-Collapse Project2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 588, article id A5Article in journal (Refereed)
    Abstract [en]

    Context. Supernova (SN) 1987A was a peculiar hydrogen-rich event with a long-rising (similar to 84 d) light curve, stemming from the explosion of a compact blue supergiant star. Only a few similar events have been presented in the literature in recent decades. Aims. We present new data for a sample of six long-rising Type II SNe (SNe II), three of which were discovered and observed by the Palomar Transient Factory (PTF) and three observed by the Caltech Core-Collapse Project (CCCP). Our aim is to enlarge this small family of long-rising SNe II, characterizing their differences in terms of progenitor and explosion parameters. We also study the metallicity of their environments. Methods. Optical light curves, spectra, and host-galaxy properties of these SNe are presented and analyzed. Detailed comparisons with known SN 1987A-like events in the literature are shown, with particular emphasis on the absolute magnitudes, colors, expansion velocities, and host-galaxy metallicities. Bolometric properties are derived from the multiband light curves. By modeling the early-time emission with scaling relations derived from the SuperNova Explosion Code (SNEC) models of MESA progenitor stars, we estimate the progenitor radii of these transients. The modeling of the bolometric light curves also allows us to estimate other progenitor and explosion parameters, such as the ejected Ni-56 mass, the explosion energy, and the ejecta mass. Results. We present PTF12kso, a long-rising SN II that is estimated to have the largest amount of ejected Ni-56 mass measured for this class. PTF09gpn and PTF12kso are found at the lowest host metallicities observed for this SN group. The variety of early light-curve luminosities depends on the wide range of progenitor radii of these SNe, from a few tens of R-circle dot (SN 2005ci) up to thousands (SN 2004ek) with some intermediate cases between 100 R-circle dot (PTF09gpn) and 300 R-circle dot (SN 2004em). Conclusions. We confirm that long-rising SNe II with light-curve shapes closely resembling that of SN 1987A generally arise from blue supergiant (BSG) stars. However, some of them, such as SN 2004em, likely have progenitors with larger radii (similar to 300 R-circle dot, typical of yellow supergiants) and can thus be regarded as intermediate cases between normal SNe IIP and SN 1987A-like SNe. Some extended red supergiant (RSG) stars such as the progenitor of SN 2004ek can also produce long-rising SNe II if they synthesized a large amount of Ni-56 in the explosion. Low host metallicity is confirmed as a characteristic of the SNe arising from compact BSG stars.

  • 35.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Fremling, Christoffer
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Pastorello, A.
    Leloudas, G.
    Fransson, Claes
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Nyholm, Anders
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Stritzinger, M. D.
    Ergon, Mattias
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Roy, Rupak
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Migotto, Katia
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Metallicity at the explosion sites of interacting transients2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id A131Article in journal (Refereed)
    Abstract [en]

    Context: Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored.

    Aims: Our goal is to gain insight into the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. Methods. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs) via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes, and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties.

    Results: We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (which may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the normalized cumulative rank (NCR) values, which quantifies the SN association to HII regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower.

    Conclusions: The difference in metallicity between SNe IIn and SN IMs indicates that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though line-driven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients.

  • 36.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Razza, Alessandro
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gafton, Emanuel
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pastorello, A.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, M. D.
    Leloudas, Georgios
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A metallicity study of 1987A-like supernova host galaxies2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 558, article id UNSP A143Article in journal (Refereed)
    Abstract [en]

    Context. The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A has long been debated, along with the role that its sub-solar metallicity played. We now have a sample of SN 1987A-like events that arise from the rare core collapse (CC) of massive (similar to 20 M-circle dot) and compact (less than or similar to 100 R-circle dot) BSGs. Aims. The metallicity of the explosion sites of the known BSG SNe is investigated, as well as the association of BSG SNe to star-forming regions. Methods. Both indirect and direct metallicity measurements of 13 BSG SN host galaxies are presented, and compared to those of other CC SN types. Indirect measurements are based on the known luminosity-metallicity relation and on published metallicity gradients of spiral galaxies. In order to provide direct metallicity measurements based on strong line diagnostics, we obtained spectra of each BSG SN host galaxy both at the exact SN explosion sites and at the positions of other H II regions. We also observed these hosts with narrow H alpha and broad R-band filters in order to produce continuum-subtracted H alpha images. This allows us to measure the degree of association between BSG SNe and star-forming regions, and to compare it to that of other SN types. Results. BSG SNe are found to explode either in low-luminosity galaxies or at large distances from the nuclei of luminous hosts. Therefore, their indirectly measured metallicities are typically lower than those of SNe IIP and Ibc. This result is confirmed by the direct metallicity estimates, which show slightly sub-solar oxygen abundances (12 + log (O/H) similar to 8.3-8.4 dex) for the local environments of BSG SNe, similar to that of the Large Magellanic Cloud (LMC), where SN 1987A exploded. However, we also note that two objects of our sample (SNe 1998A and 2004em) were found at near solar metallicity. SNe IIb have a metallicity distribution similar to that of our BSG SNe. Finally, we find that the degree of association to star-forming regions is similar among BSG SNe, SNe IIP and IIn. Conclusions. Our results suggest that LMC metal abundances play a role in the formation of some 1987A-like SNe. This would naturally fit in a single star scenario for the progenitors. However, the existence of two events at nearly solar metallicity suggests that also other channels, e.g. binarity, contribute to produce BSG SNe.

  • 37.
    Taddia, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, Maximilian D.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Copenhagen, Denmark.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Phillips, M. M.
    Anderson, J. P.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Folatelli, G.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Freedman, W.
    Hamuy, M.
    Morrell, N.
    Pastorello, A.
    Persson, S. E.
    Gonzalez, S.
    The Type II supernovae 2006V and 2006au: two SN 1987A-like events2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 537, article id A140Article in journal (Refereed)
    Abstract [en]

    Context. Supernova 1987A revealed that a blue supergiant (BSG) star can end its life as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose progenitors are believed to be red supergiants (RSGs). Similarities among 1987A-like events include a long rise to maximum, early luminosity fainter than that of normal Type IIP SNe, and radioactivity acting as the primary source powering the light curves.

    Aims. We present and analyze two SNe monitored by the Carnegie Supernova Project that are reminiscent of SN 1987A.

    Methods. Optical and near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and 2006au are presented. These observations are compared to those of SN 1987A, and are used to estimate properties of their progenitors.

    Results. Both objects exhibit a slow rise to maximum and light curve evolution similar to that of SN 1987A. At the earliest epochs, SN 2006au also displays an initial dip which we interpret as the signature of the adiabatic cooling phase that ensues shock break-out. SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN 1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and other normal Type II objects, although both consistently exhibit expansion velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR light curve of each object from which physical properties of the progenitors are estimated. This yields ejecta mass estimates of Mej ≈ 20 M, explosion energies of E ≈ 2−3 × 1051 erg s-1, and progenitor radii of R ≈ 75−100 R for both SNe.

    Conclusions. The progenitors of SNe 2006V and 2006au were most likely BSGs with a larger explosion energy as compared to that of SN 1987A.

  • 38. Takats, K.
    et al.
    Pignata, G.
    Pumo, M. L.
    Paillas, E.
    Zampieri, L.
    Elias-Rosa, N.
    Benetti, S.
    Bufano, F.
    Cappellaro, E.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Hamuy, M.
    Inserra, C.
    Kankare, E.
    Smartt, S. J.
    Stritzinger, M. D.
    Van Dyk, S. D.
    Haislip, J. B.
    LaCluyze, A. P.
    Moore, J. P.
    Reichart, D.
    SN 2009ib: a Type II-P supernova with an unusually long plateau2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 3, p. 3137-3154Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared photometry and spectroscopy of SN 2009ib, a Type II-P supernova in NGC 1559. This object has moderate brightness, similar to those of the intermediate-luminosity SNe 2008in and 2009N. Its plateau phase is unusually long, lasting for about 130 d after explosion. The spectra are similar to those of the subluminous SN 2002gd, with moderate expansion velocities. We estimate the Ni-56 mass produced as 0.046 +/- A 0.015 M-aS (TM). We determine the distance to SN 2009ib using both the expanding photosphere method (EPM) and the standard candle method. We also apply EPM to SN 1986L, a Type II-P SN that exploded in the same galaxy. Combining the results of different methods, we conclude the distance to NGC 1559 as D = 19.8 +/- A 3.0 Mpc. We examine archival, pre-explosion images of the field taken with the Hubble Space Telescope, and find a faint source at the position of the SN, which has a yellow colour [(V - I)(0) = 0.85 mag]. Assuming it is a single star, we estimate its initial mass as M-ZAMS = 20 M-aS (TM). We also examine the possibility, that instead of the yellow source the progenitor of SN 2009ib is a red supergiant star too faint to be detected. In this case, we estimate the upper limit for the initial zero-age main sequence (ZAMS) mass of the progenitor to be similar to 14-17 M-aS (TM). In addition, we infer the physical properties of the progenitor at the explosion via hydrodynamical modelling of the observables, and estimate the total energy as similar to 0.55 x 10(51) erg, the pre-explosion radius as similar to 400 R-aS (TM), and the ejected envelope mass as similar to 15 M-aS (TM), which implies that the mass of the progenitor before explosion was similar to 16.5-17 M-aS (TM).

  • 39. Takats, K.
    et al.
    Pumo, M. L.
    Elias-Rosa, N.
    Pastorello, A.
    Pignata, G.
    Paillas, E.
    Zampieri, L.
    Anderson, J. P.
    Vinko, J.
    Benetti, S.
    Botticella, M-T
    Bufano, F.
    Campillay, A.
    Cartier, R.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Folatelli, G.
    Foley, R. J.
    Foerster, F.
    Hamuy, M.
    Hentunen, V-P
    Kankare, E.
    Leloudas, Georgios
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Morrell, N.
    Nissinen, M.
    Phillips, M. M.
    Smartt, S. J.
    Stritzinger, M.
    Taubenberger, S.
    Valenti, S.
    Van Dyk, S. D.
    Haislip, J. B.
    LaCluyze, A. P.
    Moore, J. P.
    Reichart, D.
    SN 2009N: linking normal and subluminous Type II-P SNe2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 1, p. 368-387Article in journal (Refereed)
    Abstract [en]

    We present ultraviolet, optical, near-infrared photometry and spectroscopy of SN 2009N in NGC 4487. This object is a Type II-P supernova with spectra resembling those of subluminous II-P supernovae, while its bolometric luminosity is similar to that of the intermediate-luminosity SN 2008in. We created SYNOW models of the plateau phase spectra for line identification and to measure the expansion velocity. In the near-infrared spectra we find signs indicating possible weak interaction between the supernova ejecta and the pre-existing circumstellar material. These signs are also present in the previously unpublished near-infrared spectra of SN 2008in. The distance to SN 2009N is determined via the expanding photosphere method and the standard candle method as D = 21.6 +/- 1.1 Mpc. The produced nickel-mass is estimated to be similar to 0.020 +/- 0.004 M-circle dot. We infer the physical properties of the progenitor at the explosion through hydrodynamical modelling of the observables. We find the values ofthe total energy as similar to 0.48 x 10(51) erg, the ejected mass as similar to 11.5 M-circle dot, and the initial radius as similar to 287 R-circle dot.

  • 40. Taubenberger, S.
    et al.
    Benetti, S.
    Childress, M.
    Pakmor, R.
    Hachinger, S.
    Mazzali, P. A.
    Stanishev, V.
    Elias-Rosa, N.
    Agnoletto, I.
    Bufano, F.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harutyunyan, A.
    Inserra, C.
    Kankare, E.
    Kromer, M.
    Navasardyan, H.
    Nicolas, J.
    Pastorello, A.
    Prosperi, E.
    Salgado, F.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, Maximilian
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Turatto, M.
    Valenti, S.
    Hillebrandt, W.
    High luminosity, slow ejecta and persistent carbon lines: SN 2009dc challenges thermonuclear explosion scenarios2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 412, no 4, p. 2735-2762Article, review/survey (Refereed)
    Abstract [en]

    Extended optical and near-IR observations reveal that SN 2009dc shares a number of similarities with normal Type Ia supernovae (SNe Ia), but is clearly overluminous, with a (pseudo-bolometric) peak luminosity of log (L) = 43.47 (erg s-1). Its light curves decline slowly over half a year after maximum light [delta m(15)(B)(true) = 0.71], and the early-time near-IR light curves show secondary maxima, although the minima between the first and the second peaks are not very pronounced. The bluer bands exhibit an enhanced fading after similar to 200 d, which might be caused by dust formation or an unexpectedly early IR catastrophe. The spectra of SN 2009dc are dominated by intermediate-mass elements and unburned material at early times, and by iron-group elements at late phases. Strong C ii lines are present until similar to 2 weeks past maximum, which is unprecedented in thermonuclear SNe. The ejecta velocities are significantly lower than in normal and even subluminous SNe Ia. No signatures of interaction with a circumstellar medium (CSM) are found in the spectra. Assuming that the light curves are powered by radioactive decay, analytic modelling suggests that SN 2009dc produced similar to 1.8 M(circle dot) of 56Ni assuming the smallest possible rise time of 22 d. Together with a derived total ejecta mass of similar to 2.8 M(circle dot), this confirms that SN 2009dc is a member of the class of possible super-Chandrasekhar-mass SNe Ia similar to SNe 2003fg, 2006gz and 2007if. A study of the hosts of SN 2009dc and other superluminous SNe Ia reveals a tendency of these SNe to explode in low-mass galaxies. A low metallicity of the progenitor may therefore be an important prerequisite for producing superluminous SNe Ia. We discuss a number of possible explosion scenarios, ranging from super-Chandrasekhar-mass white-dwarf progenitors over dynamical white-dwarf mergers and Type I<file name=mnr_18107_mu1.gif type=gif/> SNe to a core-collapse origin of the explosion. None of the models seems capable of explaining all properties of SN 2009dc, so that the true nature of this SN and its peers remains nebulous.

  • 41. Valenti, S.
    et al.
    Fraser, M.
    Benetti, S.
    Pignata, G.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Inserra, C.
    Cappellaro, E.
    Pastorello, A.
    Smartt, S. J.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Botticella, M. T.
    Brimacombe, J.
    Bufano, F.
    Crockett, M.
    Eder, I.
    Fugazza, D.
    Haislip, J. B.
    Hamuy, M.
    Harutyunyan, A.
    Ivarsen, K. M.
    Kankare, E.
    Kotak, R.
    LaCluyze, A. P.
    Magill, L.
    SUBMattila, S.
    Maza, J.
    Mazzali, P. A.
    Reichart, D. E.
    Taubenberger, S.
    Turatto, M.
    Zampieri, L.
    SN 2009jf: a slow-evolving stripped-envelope core-collapse supernova2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 416, no 4, p. 3138-3159Article in journal (Refereed)
    Abstract [en]

    We present an extensive set of photometric and spectroscopic data for SN 2009jf, a nearby Type Ib supernova (SN), spanning from similar to 20 d before B-band maximum to 1 yr after maximum. We show that SN 2009jf is a slowly evolving and energetic stripped-envelope SN and is likely from a massive progenitor (25-30 M(circle dot)). The large progenitor's mass allows us to explain the complete hydrogen plus helium stripping without invoking the presence of a binary companion. The SN occurred close to a young cluster, in a crowded environment with ongoing star formation. The spectroscopic similarity with the He-poor Type Ic SN 2007gr suggests a common progenitor for some SNe Ib and Ic. The nebular spectra of SN 2009jf are consistent with an asymmetric explosion, with an off-centre dense core. We also find evidence that Herich Ib SNe have a rise time longer than other stripped-envelope SNe, however confirmation of this result and further observations are needed.

  • 42. Valenti, Stefano
    et al.
    Taubenberger, Stefan
    Pastorello, Andrea
    Aramyan, Levon
    Botticella, Maria Teresa
    Fraser, Morgan
    Benetti, Stefano
    Smartt, Stephen J.
    Cappellaro, Enrico
    Elias-Rosa, Nancy
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Magill, Lindsay
    Magnier, Eugene
    Kotak, Rubina
    Price, Paul A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Tomasella, Lina
    Turatto, Massimo
    Wright, Darryl E.
    A SPECTROSCOPICALLY NORMAL TYPE Ic SUPERNOVA FROM A VERY MASSIVE PROGENITOR2012In: The Astrophysical Journal Letters, ISSN 2041-8205, Vol. 749, no 2, p. L28-Article in journal (Refereed)
    Abstract [en]

    We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was similar to 40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of similar to 7-17 foe and a total ejected mass of similar to 7-17 M-circle dot, 5-10 M-circle dot of which is oxygen and 0.6-0.7 M-circle dot is Ni-56. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 M-circle dot. The profile of the forbidden oxygen lines in the nebular spectra shows no evidence of a bi-polar geometry in the ejected material.

1 - 42 of 42
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