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  • 1. Bulla, M.
    et al.
    Sim, S. A.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Polarization spectral synthesis for Type Ia supernova explosion models2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 1, p. 967-981Article in journal (Refereed)
    Abstract [en]

    We present a Monte Carlo radiative transfer technique for calculating synthetic spectropolarimetry for multidimensional supernova explosion models. The approach utilizes 'virtual-packets' that are generated during the propagation of the Monte Carlo quanta and used to compute synthetic observables for specific observer orientations. Compared to extracting synthetic observables by direct binning of emergent Monte Carlo quanta, this virtual-packet approach leads to a substantial reduction in the Monte Carlo noise. This is not only vital for calculating synthetic spectropolarimetry (since the degree of polarization is typically very small) but also useful for calculations of light curves and spectra. We first validate our approach via application of an idealized test code to simple geometries. We then describe its implementation in the Monte Carlo radiative transfer code ARTIS and present test calculations for simple models for Type Ia supernovae. Specifically, we use the well-known one-dimensional W7 model to verify that our scheme can accurately recover zero polarization from a spherical model, and to demonstrate the reduction in Monte Carlo noise compared to a simple packet-binning approach. To investigate the impact of aspherical ejecta on the polarization spectra, we then use ARTIS to calculate synthetic observables for prolate and oblate ellipsoidal models with Type Ia supernova compositions.

  • 2. Bulla, M.
    et al.
    Sim, S. A.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seitenzahl, I. R.
    Fink, M.
    Ciaraldi-Schoolmann, F.
    Röpke, K.
    Hillebrandt, W.
    Pakmor, R.
    Ruiter, A. J.
    Taubenberger, S.
    Predicting polarization signatures for double-detonation and delayed-detonation models of Type Ia supernovae2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, no 1, p. 1039-1056Article in journal (Refereed)
    Abstract [en]

    Calculations of synthetic spectropolarimetry are one means to test multidimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M-circle dot white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a 2D double-detonation model and a 3D delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels (<1 per cent) for both explosion models. Polarization in the continuum peaks at similar to 0.1-0.3 per cent and decreases aftermaximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si II lambda 6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O I lambda 7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.

  • 3. Bulla, M.
    et al.
    Sim, S. A.
    Pakmor, R.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taubenberger, S.
    Röpke, F. K.
    Hillebrandt, W.
    Seitenzahl, I. R.
    Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs: polarization signatures2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 455, no 1, p. 1060-1070Article in journal (Refereed)
    Abstract [en]

    The violent merger of two carbon-oxygen white dwarfs has been proposed as a viable progenitor for some Type Ia supernovae. However, it has been argued that the strong ejecta asymmetries produced by this model might be inconsistent with the low degree of polarization typically observed in Type Ia supernova explosions. Here, we test this claim by carrying out a spectropolarimetric analysis for the model proposed by Pakmor et al. for an explosion triggered during the merger of a 1.1 and 0.9 M-circle dot carbon-oxygen white dwarf binary system. Owing to the asymmetries of the ejecta, the polarization signal varies significantly with viewing angle. We find that polarization levels for observers in the equatorial plane are modest (less than or similar to 1 per cent) and show clear evidence for a dominant axis, as a consequence of the ejecta symmetry about the orbital plane. In contrast, orientations out of the plane are associated with higher degrees of polarization and departures from a dominant axis. While the particular model studied here gives a good match to highly polarized events such as SN 2004dt, it has difficulties in reproducing the low polarization levels commonly observed in normal Type Ia supernovae. Specifically, we find that significant asymmetries in the element distribution result in a wealth of strong polarization features that are not observed in the majority of currently available spectropolarimetric data of Type Ia supernovae. Future studies will map out the parameter space of the merger scenario to investigate if alternative models can provide better agreement with observations.

  • 4. Diehl, Roland
    et al.
    Siegert, Thomas
    Hillebrandt, Wolfgang
    Grebenev, Sergei A.
    Greiner, Jochen
    Krause, Martin
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Maeda, Keiichi
    Roepke, Friedrich
    Taubenberger, Stefan
    Early Ni-56 decay gamma rays from SN2014J suggest an unusual explosion2014In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 345, no 6201, p. 1162-1165Article in journal (Refereed)
    Abstract [en]

    Type Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 solar mass of radioactive Ni-56. The Ni-56 is commonly believed to be buried deeply in the expanding supernova cloud. In SN2014J, we detected the lines at 158 and 812 kiloelectron volts from Ni-56 decay (time similar to 8.8 days) earlier than the expected several-week time scale, only similar to 20 days after the explosion and with flux levels corresponding to roughly 10% of the total expected amount of Ni-56. Some mechanism must break the spherical symmetry of the supernova and at the same time create a major amount of Ni-56 at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event.

  • 5. Fink, Michael
    et al.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Seitenzahl, Ivo R.
    Ciaraldi-Schoolmann, Franco
    Roepke, Friedrich K.
    Sim, Stuart A.
    Pakmor, Ruediger
    Ruiter, Ashley J.
    Hillebrandt, Wolfgang
    Three-dimensional pure deflagration models with nucleosynthesis and synthetic observables for Type Ia supernovae2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 2, p. 1762-1783Article in journal (Refereed)
    Abstract [en]

    We investigate whether pure deflagration models of Chandrasekhar-mass carbon-oxygen white dwarf stars can account for one or more subclass of the observed population of Type Ia supernova (SN Ia) explosions. We compute a set of 3D full-star hydrodynamic explosion models, in which the deflagration strength is parametrized using the multispot ignition approach. For each model, we calculate detailed nucleosynthesis yields in a post-processing step with a 384 nuclide nuclear network. We also compute synthetic observables with our 3D Monte Carlo radiative transfer code for comparison with observations. For weak and intermediate deflagration strengths (energy release E-nuc less than or similar to 1.1 x 10(51) erg), we find that the explosion leaves behind a bound remnant enriched with 3 to 10 per cent (by mass) of deflagration ashes. However, we do not obtain the large kick velocities recently reported in the literature. We find that weak deflagrations with E-nuc similar to 0.5 x 10(51) erg fit well both the light curves and spectra of 2002cx-like SNe Ia, and models with even lower explosion energies could explain some of the fainter members of this subclass. By comparing our synthetic observables with the properties of SNe Ia, we can exclude the brightest, most vigorously ignited models as candidates for any observed class of SN Ia: their B - V colours deviate significantly from both normal and 2002cx-like SNe Ia and they are too bright to be candidates for other subclasses.

  • 6. Foley, Ryan J.
    et al.
    Fox, O. D.
    McCully, C.
    Phillips, M. M.
    Sand, D. J.
    Zheng, W.
    Challis, P.
    Filippenko, A. V.
    Folatelli, G.
    Hillebrandt, W.
    Hsiao, E. Y.
    Jha, S. W.
    Kirshner, R. P.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marion, G. H.
    Nelson, M.
    Pakmor, R.
    Pignata, G.
    Roepke, F. K.
    Seitenzahl, I. R.
    Silverman, J. M.
    Skrutskie, M.
    Stritzinger, M. D.
    Extensive HST ultraviolet spectra and multiwavelength observations of SN 2014J in M82 indicate reddening and circumstellar scattering by typical dust2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 443, no 4, p. 2887-2906Article in journal (Refereed)
    Abstract [en]

    SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 yr and perhaps in 410 yr. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A(V) = 2.0 +/- 0.1 mag. But this picture, with R-V = 1.6 +/- 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/Space Telescope Imaging Spectrograph (STIS) ultraviolet through near-infrared spectroscopy with HST/Wide Field Camera 3 (WFC3), Katzman Automatic Imaging Telescope, and FanCam photometry from the optical to the infrared and nine epochs of high-resolution TRES (Tillinghast Reflection Echelle Spectrograph) spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B - V) = 0.45 mag and R-V = 2.6) and roughly half by scattering off Large Magellanic Cloud-like dust in the circumstellar environment of SN 2014J.

  • 7. Gall, E. E. E.
    et al.
    Kotak, R.
    Leibundgut, B.
    Taubenberger, S.
    Hillebrandt, W.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 592, article id A129Article in journal (Refereed)
    Abstract [en]

    Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq, we present a comparative study of commonly used distance determination methods based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z = 0.041 +/- 0.001) prompted us to investigate the implications of the difference between angular and luminosity distances within the framework of the expanding photosphere method (EPM) that relies upon a relation between flux and angular size to yield a distance. Following a re-derivation of the basic equations of the EPM for SNe at non-negligible redshifts, we conclude that the EPM results in an angular distance. The observed flux should be converted into the SN rest frame and the angular size, theta, has to be corrected by a factor of (1 + z)(2). Alternatively, the EPM angular distance can be converted to a luminosity distance by implementing a modification of the angular size. For SN 2013eq, we find EPM luminosity distances of D-L = 151 +/- 18 Mpc and D-L = 164 +/- 20 Mpc by making use of different sets of dilution factors taken from the literature. Application of the standardized candle method for Type II-P SNe results in an independent luminosity distance estimate (D-L = 168 +/- 16 Mpc) that is consistent with the EPM estimate.

  • 8. Gall, E. E. E.
    et al.
    Kotak, R.
    Leibundgut, B.
    Taubenberger, S.
    Hillebrandt, W.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Heidelberger Institut für Theoretische Studien, Germany; Institut für Theoretische Astrophysik, Germany.
    Burgett, W. S.
    Chambers, K.
    Flewelling, H.
    Huber, M. E.
    Kaiser, N.
    Kudritzki, R. P.
    Magnier, E. A.
    Metcalfe, N.
    Smith, K.
    Tonry, J. L.
    Wainscoat, R. J.
    Waters, C.
    An updated Type II supernova Hubble diagram2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 611, article id A25Article in journal (Refereed)
    Abstract [en]

    We present photometry and spectroscopy of nine Type II-P/L supernovae (SNe) with redshifts in the 0.045 less than or similar to z less than or similar to 0.335 range, with a view to re-examining their utility as distance indicators. Specifically, we apply the expanding photosphere method (EPM) and the standardized candle method (SCM) to each target, and find that both methods yield distances that are in reasonable agreement with each other. The current record-holder for the highest-redshift spectroscopically confirmed supernova (SN) II-P is PS1-13bni (z = 0.335(-0 .012)(+ 0.009)), and illustrates the promise of Type II SNe as cosmological tools. We updated existing EPM and SCM Hubble diagrams by adding our sample to those previously published. Within the context of Type II SN distance measuring techniques, we investigated two related questions. First, we explored the possibility of utilising spectral lines other than the traditionally used Fe II lambda 5169 to infer the photospheric velocity of SN ejecta. Using local well-observed objects, we derive an epoch-dependent relation between the strong Balmer line and Fe II lambda 5169 velocities that is applicable 30 to 40 days post-explosion. Motivated in part by the continuum of key observables such as rise time and decline rates exhibited from II-P to II-L SNe, we assessed the possibility of using Hubble-flow Type II-L SNe as distance indicators. These yield similar distances as the Type II-P SNe. Although these initial results are encouraging, a significantly larger sample of SNe II-L would be required to draw definitive conclusions.

  • 9.
    Goobar, Ariel
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Siverd, R.
    Stassun, K. G.
    Pepper, J.
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, 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).
    CONSTRAINTS ON THE ORIGIN OF THE FIRST LIGHT FROM SN 2014J2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 799, no 1, p. 106-Article in journal (Refereed)
    Abstract [en]

    We study the very early light curve of supernova 2014J (SN 2014J) using the high-cadence broad-band imaging data obtained by the Kilodegree Extremely Little Telescope, which fortuitously observed M 82 around the time of the explosion, starting more than 2 months prior to detection, with up to 20 observations per night. These observations are complemented by observations in two narrow-band filters used in an Ha survey of nearby galaxies by the intermediate Palomar Transient Factory that also captured the first days of the brightening of the supernova. The evolution of the light curves is consistent with the expected signal from the cooling of shock heated material of large scale dimensions, greater than or similar to 1R(circle dot). This could be due to heated material of the progenitor, a companion star or pre-existing circumstellar environment, e.g., in the form of an accretion disk. Structure seen in the light curves during the first days after explosion could also originate from radioactive material in the outer parts of an exploding white dwarf, as suggested from the early detection of gamma-rays. The model degeneracy translates into a systematic uncertainty of +/- 0.3 days on the estimate of the first light from SN 2014J.

  • 10. Inserra, C.
    et al.
    Sim, S. A.
    Wyrzykowski, L.
    Smartt, S. J.
    Fraser, M.
    Nicholl, M.
    Shen, K. J.
    Jerkstrand, A.
    Gal-Yam, A.
    Howell, D. A.
    Maguire, K.
    Mazzali, P.
    Valenti, S.
    Taubenberger, S.
    Benitez-Herrera, S.
    Bersier, D.
    Blagorodnova, N.
    Campbell, H.
    Chen, T. -W
    Elias-Rosa, N.
    Hillebrandt, W.
    Kostrzewa-Rutkowska, Z.
    Kozllowski, S.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lyman, J. D.
    Polshaw, J.
    Roepke, F. K.
    Ruiter, A. J.
    Smith, K.
    Spiro, S.
    Sullivan, M.
    Yaron, O.
    Young, D.
    Yuan, F.
    OGLE-2013-SN-079: A LONELY SUPERNOVA CONSISTENT WITH A HELIUM SHELL DETONATION2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 799, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of z = 0.07 implies an absolute magnitude in the rest-frame I-band of M-1 similar to -17.6 mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths <5000 angstrom. To date, this is the only reported SN showing Ti-dominated spectra. The data are broadly consistent with existing models for the pure detonation of a helium shell around a low-mass CO white dwarf and double-detonation models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.

  • 11. Kosenko, D.
    et al.
    Hillebrandt, W.
    Kromer, Markus
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy. Max-Planck-Institut für Astrophysik, Germany.
    Blinnikov, S. I.
    Pakmor, R.
    Kaastra, J. S.
    Oxygen emission in remnants of thermonuclear supernovae as a probe for their progenitor system2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 449, no 2, p. 1441-1448Article in journal (Refereed)
    Abstract [en]

    Recent progress in numerical simulations of thermonuclear supernova explosions brings up a unique opportunity in studying the progenitors of Type Ia supernovae. Coupling state-of-the-art explosion models with detailed hydrodynamical simulations of the supernova remnant evolution and the most up-to-date atomic data for X-ray emission calculations makes it possible to create realistic synthetic X-ray spectra for the supernova remnant phase. Comparing such spectra with high-quality observations of supernova remnants could allow us to constrain the explosion mechanism and the progenitor of the supernova. The present study focuses in particular on the oxygen emission line properties in young supernova remnants, since different explosion scenarios predict a different amount and distribution of this element. Analysis of the soft X-ray spectra from supernova remnants in the Large Magellanic Cloud and confrontation with remnant models for different explosion scenarios suggest that SNR 0509-67.5 could originate from a delayed detonation explosion and SNR 0519-69.0 from an oxygen-rich merger.

  • 12.
    Kromer, Markus
    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).
    Pakmor, R.
    Taubenberger, S.
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cenko, S. B.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Leloudas, G.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Roepke, F. K.
    Seitenzahl, I. R.
    Sim, S. 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).
    The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 459, no 4, p. 4428-4439Article in journal (Refereed)
    Abstract [en]

    iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system, where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multidimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 M-aS (TM), respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10 d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circumstellar medium and surface radioactivity from an He-ignited merger that may be able to account for the early UV emission in violent merger models.

  • 13.
    Kromer, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ohlmann, S. T.
    Pakmor, R.
    Ruiter, A. J.
    Hillebrandt, W.
    Marquardt, K. S.
    Roepke, F. K.
    Seitenzahl, I. R.
    Sim, S. A.
    Taubenberger, S.
    Deflagrations in hybrid CONe white dwarfs: a route to explain the faint Type Iax supernova 2008ha2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 3, p. 3045-3053Article in journal (Refereed)
    Abstract [en]

    Stellar evolution models predict the existence of hybrid white dwarfs (WDs) with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with masses similar to 1.1 M-aS (TM), hybrid WDs in a binary system may easily approach the Chandrasekhar mass (M-Ch) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-M-Ch hybrid WD under the assumption that nuclear burning only occurs in carbon-rich material. Performing hydrodynamics simulations of the explosion and detailed nucleosynthesis post-processing calculations, we find that only 0.014 M-aS (TM) of material is ejected while the remainder of the mass stays bound. The ejecta consist predominantly of iron-group elements, O, C, Si and S. We also calculate synthetic observables for our model and find reasonable agreement with the faint Type Iax SN 2008ha. This shows for the first time that deflagrations in near-M-Ch WDs can in principle explain the observed diversity of Type Iax supernovae. Leaving behind a near-M-Ch bound remnant opens the possibility for recurrent explosions or a subsequent accretion-induced collapse in faint Type Iax SNe, if further accretion episodes occur. From binary population synthesis calculations, we find the rate of hybrid WDs approaching M-Ch to be of the order of 1 per cent of the Galactic SN Ia rate.

  • 14.
    Kromer, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Astrophysik, Germany.
    Pakmor, R.
    Taubenberger, S.
    Pignata, G.
    Fink, M.
    Röpke, F. K.
    Seitenzahl, I. R.
    Sim, S. A.
    Hillebrandt, W.
    SN 2010LP-A TYPE IA SUPERNOVA FROM A VIOLENT MERGER OF TWO CARBON-OXYGEN WHITE DWARFS2013In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 778, no 1, article id L18Article in journal (Refereed)
    Abstract [en]

    SN 2010lp is a subluminous Type Ia supernova (SN Ia) with slowly evolving lightcurves. Moreover, it is the only subluminous SN Ia observed so far that shows narrow emission lines of [O I] in late-time spectra, indicating unburned oxygen close to the center of the ejecta. Most explosion models for SNe Ia cannot explain the narrow [O I] emission. Here, we present hydrodynamic explosion and radiative transfer calculations showing that the violent merger of two carbon-oxygen white dwarfs of 0.9 and 0.76 M-circle dot adequately reproduces the early-time observables of SN 2010lp. Moreover, our model predicts oxygen close to the center of the explosion ejecta, a pre-requisite for narrow [O I] emission in nebular spectra as observed in SN 2010lp.

  • 15. Latour, M.
    et al.
    Heber, U.
    Irrgang, A.
    Schaffenroth, V.
    Geier, S.
    Hillebrandt, W.
    Röpke, F. K.
    Taubenberger, S.
    Kromer, Markus
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Fink, M.
    Quantitative spectral analysis of the sdB star HD188112: A helium-core white dwarf progenitor2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 585, article id A115Article in journal (Refereed)
    Abstract [en]

    Context. HD 188112 is a bright (V = 10 : 2 mag) hot subdwarf B (sdB) star with a mass too low to ignite core helium burning and is therefore considered a pre-extremely low-mass (ELM) white dwarf (WD). ELM WDs (M less than or similar to 0.3 M-circle dot) are He-core objects produced by the evolution of compact binary systems. Aims. We present in this paper a detailed abundance analysis of HD188112 based on high-resolution Hubble Space Telescope (HST) near-and far-ultraviolet spectroscopy. We also constrain the mass of the star's companion. Methods. We use hybrid non-LTE model atmospheres to fit the observed spectral lines, and to derive the abundances of more than a dozen elements and the rotational broadening of metallic lines. Results. We confirm the previous binary system parameters by combining radial velocities measured in our UV spectra with the previously published values. The system has a period of 0.60658584 days and a WD companion with M >= 0.70 M-circle dot. By assuming a tidally locked rotation combined with the projected rotational velocity (v sin i = 7.9 +/- 0.3 km s(-1)), we constrain the companion mass to be between 0.9 and 1.3 M-circle dot. We further discuss the future evolution of the system as a potential progenitor of an underluminous type Ia supernova. We measure abundances for Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Ni, and Zn, and for the trans-iron elements Ga, Sn, and Pb. In addition, we derive upper limits for the C, N, O elements and find HD188112 to be strongly depleted in carbon. We find evidence of non-LTE e ff ects on the line strength of some ionic species such as Si II and Ni II. The metallic abundances indicate that the star is metal-poor, with an abundance pattern most likely produced by diffusion effects.

  • 16.
    Lundqvist, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nyholm, Anders
    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).
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kozma, Cecilia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundqvist, N.
    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).
    Garnavich, P. M.
    Kromer, Marcus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Shappee, B. J.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    No trace of a single-degenerate companion in late spectra of supernovae 2011fe and 2014J2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, article id A39Article in journal (Refereed)
    Abstract [en]

    Aims. This study aims at constraining the origin of the nearby Type Ia supernovae (SNe), 2011fe and 2014J. The two most favoured scenarios for triggering the explosion of the white dwarf supernova progenitor is either mass loss from a non-degenerate companion or merger with another white dwarf. In the former, there could be a significant amount of leftover material from the companion at the centre of the supernova. Detecting such material would therefore favour the single-degenerate scenario. Methods. The left-over material from a possible non-degenerate companion can reveal itself after about one year, and in this study such material was searched for in the spectra of SN 2011fe (at 294 days after the explosion) using the Large Binocular Telescope and for SN 2014J using the Nordic Optical Telescope (315 days past explosion). The observations were interpreted using numerical models simulating the expected line emission from ablated material from the companion star. The spectral lines sought for are H alpha, [O I] lambda 6300, and [Ca II] lambda lambda 7291,7324, and the expected width of these lines is similar to 1000 km s(-1), which in the case of the [Ca II] lines blend to a broader feature. Results. No signs of H alpha, [O I] lambda 6300, or [Ca II] lambda lambda 7291, 7324 could be traced for in any of the two supernovae. When systematic uncertainties are included, the limits on hydrogen-rich ablated gas are 0 : 003 M-circle dot in SN 2011fe and 0 : 0085 M-circle dot in SN 2014J, where the limit for SN 2014J is the second lowest ever, and the limit for SN 2011fe is a revision of a previous limit. Limits are also put on helium-rich ablated gas, and here limits from [O I] lambda 6300 provide the upper mass limits 0 : 002 M-circle dot and 0 : 005 M-circle dot for SNe 2011fe and 2014J, respectively. These numbers are used in conjunction with other data to argue that these supernovae can stem from double-degenerate systems or from single-degenerate systems with a spun-up/spun-down super-Chandrasekhar white dwarf. For SN 2011fe, other types of hydrogen-rich donors can very likely be ruled out, whereas a main-sequence donor system with large intrinsic separation is still possible for SN 2014J. Helium-rich donor systems cannot be ruled out for any of the two supernovae, but the expected short delay time for such progenitors makes this possibility less likely, especially for SN 2011fe. Published data for SNe 1998bu, 2000cx, 2001el, 2005am, and 2005cf are used to constrain their origin. We emphasise that the results of this study depend on the sought-after lines emerging unattenuated from the central regions of the nebula. Detailed radiative transfer calculations with longer line lists than are presently used are needed to confirm that this is, in fact, true. Finally, the broad lines of SNe 2011fe and 2014J are discussed, and it is found that the [Ni II] lambda 7378 emission is redshifted by similar to+ 1300 km s(-1), as opposed to the known blueshift of similar to-1100 km s(-1) for SN 2011fe. [Fe II] lambda 7155 is also redshifted in SN 2014J. SN 2014J belongs to a minority of SNe Ia that both have a nebular redshift of [Fe II] lambda 7155 and [Ni II] lambda 7378, and a slow decline of the Si II lambda 6355 absorption trough just after B-band maximum.

  • 17. Magee, M. R.
    et al.
    Kotak, R.
    Sim, S. A.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rabinowitz, D.
    Smartt, S. J.
    Baltay, C.
    Campbell, H. C.
    Chen, T. -W.
    Fink, M.
    Gal-Yam, A.
    Galbany, L.
    Hillebrandt, W.
    Inserra, C.
    Kankare, E.
    Le Guillou, L.
    Lyman, J. D.
    Maguire, K.
    Pakmor, R.
    Ropke, F. K.
    Ruiter, A. J.
    Seitenzahl, I. R.
    Sullivan, M.
    Valenti, S.
    Young, D. R.
    The type Iax supernova, SN 2015H A white dwarf deflagration candidate2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 589, article id A89Article in journal (Refereed)
    Abstract [en]

    We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M-r = 17.27 +/- 0.07, and a (Delta m(15))(r) = 0.69 +/- 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of similar to 0.2 M-circle dot of material containing similar to 0.07 M-circle dot of Ni-56. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that less than or similar to 0.6 M-circle dot of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.

  • 18. Marquardt, Kai S.
    et al.
    Sim, Stuart A.
    Ruiter, Ashley J.
    Seitenzahl, Ivo R.
    Ohlmann, Sebastian T.
    Kromer, Markus
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Pakmor, Rüdiger
    Röpke, Friedrich K.
    Type Ia supernovae from exploding oxygen-neon white dwarfs2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id A118Article in journal (Refereed)
    Abstract [en]

    Context: The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M-Ch, WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor.

    Aims: We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia.

    Methods: We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M-Ch), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the number of SNe Ia involving ONe WDs relative to the number of other promising progenitor channels.

    Results: The ejecta structures of our simulated detonations in sub-M-Ch, ONe WDs are similar to those from CO WDs. There are, however, small systematic deviations in the mass fractions and the ejecta velocities. These lead to spectral features that are systematically less blueshifted. Nevertheless, the synthetic observables of our ONe WD explosions are similar to those obtained from CO models.

    Conclusions: Our binary evolution calculations show that a significant fraction (3-10%) of potential progenitor systems should contain an ONe WD. The comparison of our ONe models with our CO models of comparable mass (similar to 1.2 M-circle dot) shows that the less blueshifted spectral features fit the observations better, although they are too bright for normal SNe Ia.

  • 19. Ohlmann, Sebastian T.
    et al.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Fink, Michael
    Pakmor, Ruediger
    Seitenzahl, Ivo R.
    Sim, Stuart A.
    Roepke, Friedrich K.
    The white dwarf's carbon fraction as a secondary parameter of Type la supernovae2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 572, p. A57-Article in journal (Refereed)
    Abstract [en]

    Context. Binary stellar evolution calculations predict that Chandrasekhar-mass carbon/oxygen white dwarfs (WDs) show a radially varying profile for the composition with a carbon depleted core. Many recent multi-dimensional simulations of Type Ia supernovae (SNe Ia), however, assume the progenitor WD has a homogeneous chemical composition. Aims. In this work, we explore the impact of different initial carbon profiles of the progenitor WD on the explosion phase and on synthetic observables in the Chandrasekhar-mass delayed detonation model. Spectra and light curves are compared to observations to judge the validity of the model. Methods. The explosion phase is simulated using the finite volume supernova code LEAFS, which is extended to treat different compositions of the progenitor WD. The synthetic observables are computed with the Monte Carlo radiative transfer code ARTIS. Results. Differences in binding energies of carbon and oxygen lead to a lower nuclear energy release for carbon depleted material; thus, the burning fronts that develop are weaker and the total nuclear energy release is smaller. For otherwise identical conditions, carbon depleted models produce less Ni-56. Comparing different models with similar Ni-56 yields shows lower kinetic energies in the ejecta for carbon depleted models, but only small differences in velocity distributions and line velocities in spectra. The light curve width-luminosity relation (WLR) obtained for models with differing carbon depletion is roughly perpendicular to the observed WLR, hence the carbon mass fraction is probably only a secondary parameter in the family of SNe Ia.

  • 20. Pan, Y. -C
    et al.
    Foley, R. J.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fox, O. D.
    Zheng, W.
    Challis, P.
    Clubb, K. I.
    Filippenko, A. V.
    Folatelli, G.
    Graham, M. L.
    Hillebrandt, W.
    Kirshner, R. P.
    Lee, W. H.
    Pakmor, R.
    Patat, F.
    Phillips, M. M.
    Pignata, G.
    Roepke, F.
    Seitenzahl, I.
    Silverman, J. M.
    Simon, J. D.
    Sternberg, A.
    Stritzinger, M. D.
    Taubenberger, S.
    Vinko, J.
    Wheeler, J. C.
    500 days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 452, no 4, p. 4307-4325Article in journal (Refereed)
    Abstract [en]

    SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to similar to 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with Hubble Space Telescope/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (Delta m(15)(B)= 0.92 mag), shallow Si II lambda 6355 absorption, and a low velocity gradient. We detect strong C II in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of 10.0(-3.8)(+4.8) x 10(42) erg s(-1). We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.

  • 21. Polshaw, J.
    et al.
    Kotak, R.
    Chambers, K. C.
    Smartt, S. J.
    Taubenberger, S.
    Kromer, Markus
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Gall, E. E. E.
    Hillebrandt, W.
    Huber, M.
    Smith, K. W.
    Wainscoat, R. J.
    A supernova distance to the anchor galaxy NGC 42582015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id L15Article in journal (Refereed)
    Abstract [en]

    The fortuitous occurrence of a type II-Plateau (IIP) supernova, SN 2014bc, in a galaxy for which distance estimates from a number of primary distance indicators are available provides a means with which to cross-calibrate the standardised candle method (SCM) for type IIP SNe. By applying calibrations from the literature we find distance estimates in line with the most precise measurement to NGC 4258 based on the Keplerian motion of masers (7.6 +/- 0.23 Mpc), albeit with significant scatter. We provide an alternative local SCM calibration by only considering type IIP SNe that have occurred in galaxies for which a Cepheid distance estimate is available. We find a considerable reduction in scatter (sigma(I) = 0.16 mag), but note that the current sample size is limited. Applying this calibration, we estimate a distance to NGC 4258 of 7.08 +/- 0.86 Mpc.

  • 22. Sasdelli, Michele
    et al.
    Hillebrandt, W.
    Aldering, G.
    Antilogus, P.
    Aragon, C.
    Bailey, S.
    Baltay, C.
    Benitez-Herrera, S.
    Bongard, S.
    Buton, C.
    Canto, A.
    Cellier-Holzem, F.
    Chen, J.
    Childress, M.
    Chotard, N.
    Copin, Y.
    Fakhouri, H. K.
    Feindt, U.
    Fink, M.
    Fleury, M.
    Fouchez, D.
    Gangler, E.
    Guy, J.
    Ishida, E. E. O.
    Kim, A. G.
    Kowalski, M.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Lombardo, S.
    Mazzali, P. A.
    Nordin, J.
    Pain, R.
    Pecontal, E.
    Pereira, R.
    Perlmutter, S.
    Rabinowitz, D.
    Rigault, M.
    Runge, K.
    Saunders, C.
    Scalzo, R.
    Smadja, G.
    Suzuki, N.
    Tao, C.
    Taubenberger, S.
    Thomas, R. C.
    Tilquin, A.
    Weaver, B. A.
    A metric space for Type Ia supernova spectra2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 447, no 2, p. 1247-1266Article in journal (Refereed)
    Abstract [en]

    We develop a new framework for use in exploring Type Ia supernovae (SNe Ia) spectra. Combining principal component analysis (PCA) and partial least square (PLS) analysis we are able to establish correlations between the principal components (PCs) and spectroscopic/photometric SNe Ia features. The technique was applied to similar to 120 SN and similar to 800 spectra from the Nearby Supernova Factory. The ability of PCA to group together SNe Ia with similar spectral features, already explored in previous studies, is greatly enhanced by two important modifications: (1) the initial data matrix is built using derivatives of spectra over the wavelength, which increases the weight of weak lines and discards extinction, and (2) we extract time evolution information through the use of entire spectral sequences concatenated in each line of the input data matrix. These allow us to define a stable PC parameter space which can be used to characterize synthetic SN Ia spectra by means of real SN features. Using PLS, we demonstrate that the information from important previously known spectral indicators (namely the pseudo-equivalent width of Si II 5972 angstrom/Si II 6355 angstrom and the line veloci of S II 5640 angstrom/Si II 6355 angstrom) at a given epoch is contained within the PC space and can be determined through a linear combination of the most important PCs. We also show that the PC space encompasses photometric features like B/V magnitudes, B - V colours and SALT2 parameters c and x(1). The observed colours and magnitudes, which are heavily affected by extinction, cannot be reconstructed using this technique alone. All the above-mentioned applications allowed us to construct a metric space for comparing synthetic SN Ia spectra with observations.

  • 23. Seitenzahl, I. R.
    et al.
    Summa, A.
    Krauss, F.
    Sim, S. A.
    Diehl, R.
    Elsaesser, D.
    Fink, M.
    Hillebrandt, W.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max Planck Society, Germany.
    Maeda, K.
    Mannheim, K.
    Pakmor, R.
    Roepke, F. K.
    Ruiter, A. J.
    Wilms, J.
    5.9-keV Mn K-shell X-ray luminosity from the decay of Fe-55 in Type Ia supernova models2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 447, no 2, p. 1484-1490Article in journal (Refereed)
    Abstract [en]

    We show that the X-ray line flux of the Mn Ka line at 5.9 keV from the decay of Fe-55 is a promising diagnostic to distinguish between Type Ia supernova (SN Ia) explosion models. Using radiation transport calculations, we compute the line flux for two three-dimensional explosion models: a near-Chandrasekhar mass delayed detonation and a violent merger of two (1.1 and 0.9 M-circle dot) white dwarfs. Both models are based on solar metallicity zero-age main-sequence progenitors. Due to explosive nuclear burning at higher density, the delayed-detonation model synthesizes similar to 3.5 times more radioactive Fe-55 than the merger model. As a result, we find that the peak Mn K alpha line flux of the delayed-detonation model exceeds that of the merger model by a factor of similar to 4.5. Since in both models the 5.9-keV X-ray flux peaks five to six years after the explosion, a single measurement of the X-ray line emission at this time can place a constraint on the explosion physics that is complementary to those derived from earlier phase optical spectra or light curves. We perform detector simulations of current and future X-ray telescopes to investigate the possibilities of detecting the X-ray line at 5.9 keV. Of the currently existing telescopes, XMM-Newton/pn is the best instrument for close (less than or similar to 1-2 Mpc), non-background limited SNe Ia because of its large effective area. Due to its low instrumental background, Chandra/ACIS is currently the best choice for SNe Ia at distances above similar to 2 Mpc. For the delayed-detonation scenario, a line detection is feasible with Chandra up to similar to 3 Mpc for an exposure time of 10(6) s. We find that it should be possible with currently existing X-ray instruments (with exposure times less than or similar to 5 x 10(5) s) to detect both of our models at sufficiently high S/N to distinguish between them for hypothetical events within the Local Group. The prospects for detection will be better with future missions. For example, the proposed Athena/X-IFU instrument could detect our delayed-detonation model out to a distance of similar to 5 Mpc. This would make it possible to study future events occurring during its operational life at distances comparable to those of the recent supernovae SN 2011 fe (similar to 6.4 Mpc) and SN 2014J (similar to 3.5 Mpc).

  • 24. Seitenzahl, Ivo R.
    et al.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ohlmann, Sebastian T.
    Ciaraldi-Schoolmann, Franco
    Marquardt, Kai
    Fink, Michael
    Hillebrandt, Wolfgang
    Pakmor, Ruediger
    Roepke, Friedrich K.
    Ruiter, Ashley J.
    Sim, Stuart A.
    Taubenberger, Stefan
    Three-dimensional simulations of gravitationally confined detonations compared to observations of SN 1991T2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 592, article id A57Article in journal (Refereed)
    Abstract [en]

    The gravitationally confined detonation (GCD) model has been proposed as a possible explosion mechanism for Type Ia supernovae in the single-degenerate evolution channel. It starts with ignition of a deflagration in a single off-centre bubble in a near-Chandrasekhar-mass white dwarf. Driven by buoyancy, the deflagration flame rises in a narrow cone towards the surface. For the most part, the main component of the flow of the expanding ashes remains radial, but upon reaching the outer, low-pressure layers of the white dwarf, an additional lateral component develops. This causes the deflagration ashes to converge again at the opposite side, where the compression heats fuel and a detonation may be launched. We first performed five three-dimensional hydrodynamic simulations of the deflagration phase in 1.4 M-circle dot carbon/oxygen white dwarfs at intermediate-resolution (256(3) computational zones). We confirm that the closer the initial deflagration is ignited to the centre, the slower the buoyant rise and the longer the deflagration ashes takes to break out and close in on the opposite pole to collide. To test the GCD explosion model, we then performed a high-resolution (512(3) computational zones) simulation for a model with an ignition spot offset near the upper limit of what is still justifiable, 200 km. This high-resolution simulation met our deliberately optimistic detonation criteria, and we initiated a detonation. The detonation burned through the white dwarf and led to its complete disruption. For this model, we determined detailed nucleosynthetic yields by post-processing 10(6) tracer particles with a 384 nuclide reaction network, and we present multi-band light curves and time-dependent optical spectra. We find that our synthetic observables show a prominent viewing-angle sensitivity in ultraviolet and blue wavelength bands, which contradicts observed SNe Ia. The strong dependence on the viewing angle is caused by the asymmetric distribution of the deflagration ashes in the outer ejecta layers. Finally, we compared our model to SN 1991T. The overall flux level of the model is slightly too low, and the model predicts pre-maximum light spectral features due to Ca, S, and Si that are too strong. Furthermore, the model chemical abundance stratification qualitatively disagrees with recent abundance tomography results in two key areas: our model lacks low-velocity stable Fe and instead has copious amounts of high-velocity Ni-56 and stable Fe. We therefore do not find good agreement of the model with SN 1991T.

  • 25. Smartt, S. J.
    et al.
    Chambers, K. C.
    Smith, K. W.
    Huber, M. E.
    Young, D. R.
    Chen, T. -W.
    Inserra, C.
    Wright, D. E.
    Coughlin, M.
    Denneau, L.
    Flewelling, H.
    Heinze, A.
    Jerkstrand, A.
    Magnier, E. A.
    Maguire, K.
    Mueller, B.
    Rest, A.
    Sherstyuk, A.
    Stalder, B.
    Schultz, A. S. B.
    Stubbs, C. W.
    Tonry, J.
    Waters, C.
    Wainscoat, R. J.
    Della Valle, M.
    Dennefeld, M.
    Dimitriadis, G.
    Firth, R. E.
    Fraser, M.
    Frohmaier, C.
    Gal-Yam, A.
    Harmanen, J.
    Kankare, E.
    Kotak, R.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mandel, I.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gibson, B.
    Primak, N.
    Willman, M.
    A SEARCH FOR AN OPTICAL COUNTERPART TO THE GRAVITATIONAL-WAVE EVENT GW1512262016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 827, no 2, article id L40Article in journal (Refereed)
    Abstract [en]

    We present a search for an electromagnetic counterpart of the gravitational-wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i(P1) filter, starting 11.5 hr after the LIGO information release and lasting for an additional 28 days. The first observations started 49.5 hr after the time of the GW151226 detection. We typically reached sensitivity limits of i(P1) = 20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m similar or equal to 19. We found 49 extragalactic transients (that are not obviously active galactic nuclei), including a faint transient in a galaxy at 7 Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226, that evolved into a type Ibn supernova. The redshift of the transient is secure at z = 0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS-NS mergers producing kilonovae at D-L less than or similar to 100 Mpc, which is promising for future LIGO/Virgo searches.

  • 26. Smartt, S. J.
    et al.
    Valenti, S.
    Fraser, M.
    Inserra, C.
    Young, D. R.
    Sullivan, M.
    Pastorello, A.
    Benetti, S.
    Gal-Yam, A.
    Knapic, C.
    Molinaro, M.
    Smareglia, R.
    Smith, K. W.
    Taubenberger, S.
    Yaron, O.
    Anderson, J. P.
    Ashall, C.
    Balland, C.
    Baltay, C.
    Barbarino, C.
    Bauer, F. E.
    Baumont, S.
    Bersier, D.
    Blagorodnova, N.
    Bongard, S.
    Botticella, M. T.
    Bufano, F.
    Bulla, M.
    Cappellaro, E.
    Campbell, H.
    Cellier-Holzem, F.
    Chen, T. -W.
    Childress, M. J.
    Clocchiatti, A.
    Contreras, C.
    Dall'Ora, M.
    Danziger, J.
    de Jaeger, T.
    De Cia, A.
    Della Valle, M.
    Dennefeld, M.
    Elias-Rosa, N.
    Elman, N.
    Feindt, U.
    Fleury, M.
    Gall, E.
    Gonzalez-Gaitan, S.
    Galbany, L.
    Morales Garoffolo, A.
    Greggio, L.
    Guillou, L. L.
    Hachinger, S.
    Hadjiyska, E.
    Hage, P. E.
    Hillebrandt, W.
    Hodgkin, S.
    Hsiao, E. Y.
    James, P. A.
    Jerkstrand, A.
    Kangas, T.
    Kankare, E.
    Kotak, R.
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kuncarayakti, H.
    Leloudas, G.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lyman, J. D.
    Hook, I. M.
    Maguire, K.
    Manulis, I.
    Margheim, S. J.
    Mattila, S.
    Maund, J. R.
    Mazzali, P. A.
    McCrum, M.
    McKinnon, R.
    Moreno-Raya, M. E.
    Nicholl, M.
    Nugent, P.
    Pain, R.
    Pignata, G.
    Phillips, M. M.
    Polshaw, J.
    Pumo, M. L.
    Rabinowitz, D.
    Reilly, E.
    Romero-Canizales, C.
    Scalzo, R.
    Schmidt, B.
    Schulze, S.
    Sim, 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).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tartaglia, L.
    Terreran, G.
    Tomasella, L.
    Turatto, M.
    Walker, E.
    Walton, N. A.
    Wyrzykowski, L.
    Yuan, F.
    Zampieri, L.
    PESSTO: survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 579, article id A40Article in journal (Refereed)
    Abstract [en]

    Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January - April and August - December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5(m) for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 angstrom between 3345-9995 angstrom. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 mu m and resolutions 23-33 angstrom) and imaging with broadband JHK(s) filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012-2013). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically similar to 15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHK(s) imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey.

  • 27. Taubenberger, S.
    et al.
    Elias-Rosa, N.
    Kerzendorf, W. E.
    Hachinger, S.
    Spyromilio, 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).
    Kromer, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ruiter, A. J.
    Seitenzahl, I. R.
    Benetti, S.
    Cappellaro, E.
    Pastorello, A.
    Turatto, M.
    Marchetti, A.
    Spectroscopy of the Type Ia supernova 2011fe past 1000 d2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 448, no 1, p. L48-L52Article in journal (Refereed)
    Abstract [en]

    In this Letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and Local Group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 angstrom - has entirely faded away, suggesting a significant change in the ionization state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 angstrom has newly developed at 1034 d, which we tentatively identify with Fe I lambda 6359, [Fe I] lambda lambda 6231, 6394 or [O I] lambda lambda 6300, 6364. Interestingly, the features in the 1034 d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement.

1 - 27 of 27
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