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  • 1. Abellán, F. J.
    et al.
    Indebetouw, R.
    Marcaide, J. M.
    Gabler, M.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spyromilio, J.
    Burrows, D. N.
    Chevalier, R.
    Cigan, P.
    Gaensler, B. M.
    Gomez, H. L.
    Janka, H. -Th.
    Kirshner, R.
    Larsson, J.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Matsuura, M.
    McCray, R.
    Ng, C. -Y.
    Park, S.
    Roche, P.
    Staveley-Smith, L.
    van Loon, J. Th.
    Wheeler, J. C.
    Woosley, S. E.
    Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L24Article in journal (Refereed)
    Abstract [en]

    Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks (nickel heating). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

  • 2. Berger, E.
    et al.
    Soderberg, A. M.
    Chevalier, R. A.
    Fransson, C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Foley, R. J.
    Leonard, D. C.
    Debes, J. H.
    Diamond-Stanic, A. M.
    Dupree, A. K.
    Ivans, I. I.
    Simmerer, J.
    Thompson, I. B.
    Tremonti, C. A.
    An Intermediate Luminosity Transient in NGC 300: The Eruption of a Dust-Enshrouded Massive Star2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, p. 1850-1865Article in journal (Refereed)
    Abstract [en]

    We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

  • 3. Chakraborti, Sayan
    et al.
    Soderberg, Alicia
    Chomiuk, Laura
    Kamble, Atish
    Yadav, Naveen
    Ray, Alak
    Hurley, Kevin
    Margutti, Raffaella
    Milisavljevic, Dan
    Bietenholz, Michael
    Brunthaler, Andreas
    Pignata, Giuliano
    Pian, Elena
    Mazzali, Paolo
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bartel, Norbert
    Hamuy, Mario
    Levesque, Emily
    MacFadyen, Andrew
    Dittmann, Jason
    Krauss, Miriam
    Briggs, M. S.
    Connaughton, V.
    Yamaoka, K.
    Takahashi, T.
    Ohno, M.
    Fukazawa, Y.
    Tashiro, M.
    Terada, Y.
    Murakami, T.
    Goldsten, J.
    Barthelmy, S.
    Gehrels, N.
    Cummings, J.
    Krimm, H.
    Palmer, D.
    Golenetskii, S.
    Aptekar, R.
    Frederiks, D.
    Svinkin, D.
    Cline, T.
    Mitrofanov, I. G.
    Golovin, D.
    Litvak, M. L.
    Sanin, A. B.
    Boynton, W.
    Fellows, C.
    Harshman, K.
    Enos, H.
    von Kienlin, A.
    Rau, A.
    Zhang, X.
    Savchenko, V.
    A MISSING-LINK IN THE SUPERNOVA-GRB CONNECTION: THE CASE OF SN 2012ap2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 805, no 2, article id 187Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

  • 4. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Irwin, Christopher M.
    Soderberg, Alicia M.
    Chakraborti, Sayan
    Immler, Stefan
    Radio and x ray observations of sn 2006jd: another strongly interacting type iin supernova2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 755, no 2, p. 110-Article in journal (Refereed)
    Abstract [en]

    We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope, and Expanded Very Large Array; at X-ray wavelengths with Chandra, XMM-Newton, and Swift-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free-free absorption by cool gas mixed into the nonthermal emitting region; external free-free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density similar to 10(6) cm(-3) at a radius r similar to 2 x 10(16) cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than r(-2) because of the slow evolution of the unabsorbed emission.

  • 5. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Soderberg, Alicia M.
    X-RAY AND RADIO EMISSION FROM TYPE IIn SUPERNOVA SN 2010jl2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 810, no 1, article id 32Article in journal (Refereed)
    Abstract [en]

    We present all X-ray and radio observations of the Type IIn supernova SN 2010jl. The X-ray observations cover a period up to day 1500 with Chandra, XMM-Newton, NuSTAR, and Swift-X-ray Telescope (XRT). The Chandra observations after 2012 June, the XMM-Newton observation in 2013 November, and most of the Swift-XRT observations until 2014 December are presented for the first time. All the spectra can be fitted by an absorbed hot thermal model except for Chandra spectra on 2011 October and 2012 June when an additional component is needed. Although the origin of this component is uncertain, it is spatially coincident with the supernova and occurs when there are changes to the supernova spectrum in the energy range close to that of the extra component, indicating that the emission is related to the supernova. The X-ray light curve shows an initial plateau followed by a steep drop starting at day similar to 300. We attribute the drop to a decrease in the circumstellar density. The column density to the X-ray emission drops rapidly with time, showing that the absorption is in the vicinity of the supernova. We also present Very Large Array radio observations of SN 2010jl. Radio emission was detected from SN 2010jl from day 570 onwards. The radio light curves and spectra suggest that the radio luminosity was close to its maximum at the first detection. The velocity of the shocked ejecta derived assuming synchrotron self-absorption is much less than that estimated from the optical and X-ray observations, suggesting that free-free absorption dominates.

  • 6. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Irwin, Christopher M.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Söderberg, Alicia M.
    STRONG EVOLUTION OF X-RAY ABSORPTION IN THE TYPE IIn SUPERNOVA SN 2010jl2012In: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 750, no 1, p. L2-Article in journal (Refereed)
    Abstract [en]

    We report two epochs of Chandra-ACIS X-ray imaging spectroscopy of the nearby bright Type IIn supernova SN 2010jl, taken around two months and then a year after the explosion. The majority of the X-ray emission in both spectra is characterized by a high temperature (greater than or similar to 10 keV) and is likely to be from the forward shocked region resulting from circumstellar interaction. The absorption column density in the first spectrum is high (similar to 10(24) cm(-2)), more than three orders of magnitude higher than the Galactic absorption column, and we attribute it to absorption by circumstellar matter. In the second epoch observation, the column density has decreased by a factor of three, as expected for shock propagation in the circumstellar medium. The unabsorbed 0.2-10 keV luminosity at both epochs is similar to 7 x 10(41) erg s(-1). The 6.4 keV Fe line clearly present in the first spectrum is not detected in the second spectrum. The strength of the fluorescent line is roughly that expected for the column density of circumstellar gas, provided the Fe is not highly ionized. There is also evidence for an absorbed power-law component in both spectra, which we attribute to a background ultraluminous X-ray source.

  • 7. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Circumstellar Emission from Type Ib and Ic Supernovae2006In: The Astrophysical Journal, ISSN 0004-637X, Vol. 651, no 1, p. 381-391Article in journal (Refereed)
    Abstract [sv]

    The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast, low-density winds, and the shock waves generated by the supernova interaction with the wind are not expected to be radiative at typical times of observation. The injected energy spectrum of radio-emitting electrons typically has an observed index p=3, which is suggestive of acceleration in cosmic-ray-dominated shocks. The early, absorbed part of the radio light curves can be attributed to synchrotron self-absorption, which leads to constraints on the magnetic field in the emitting region and on the circumstellar density. The range of circumstellar densities inferred from the radio emission is somewhat broader than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron emission are assumed in the extragalactic supernovae. For the observed and expected ranges of circumstellar densities to roughly overlap, a high efficiency of magnetic field production in the shocked region is required (ɛB~0.1). For the expected densities around a Wolf-Rayet star, a nonthermal mechanism is generally required to explain the observed X-ray luminosities of Type Ib/c supernovae. Inverse Compton emission is a candidate for the emission, if the observations are near optical maximum. In other cases we suggest that the mechanism is X-ray synchrotron emission in a situation in which the shock wave is cosmic-ray-dominated so that the electron energy spectrum flattens at high energy. More comprehensive X-ray observations of a Type Ib/c supernova are needed to determine whether this suggestion is correct.

  • 8. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Shock Breakout Emission from a Type Ib/c Supernova: XRT 080109/SN 2008D2008In: The Astrophysical Journal, Vol. 683, no 2, p. L135-L138Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    The X-ray transient 080109, associated with SN 2008D, can be attributed to the shock breakout emission from a normal Type Ib/c supernova. If the observed emission is interpreted as thermal emission, the temperature and radiated energy are close to expectations, considering that scattering dominates absorption processes so that spectrum formation occurs deep within the photosphere. The X-ray emission observed at ~10 days is attributed to inverse Compton scattering of photospheric photons with relativistic electrons produced in the interaction of the supernova with the progenitor wind. A simple model for the optical/ultraviolet emission from shock breakout is developed and applied to SN 1987A, SN 1999ex, SN 2008D, and SN 2006aj, all of which have optical emission observed at t~1 day. The emission from the first three can plausibly be attributed to shock breakout emission. The photospheric temperature is most sensitive to the radius of the progenitor star core and the radii in these cases are in line with expectations from stellar evolution. The early optical/ultraviolet observations of SN 2006aj cannot be accommodated by a nonrelativistic shock breakout model in a straightforward way.

  • 9. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nymark, Tanja
    Stockholm University, Faculty of Science, Department of Astronomy.
    Radio and X-Ray Emission as Probes of Type IIP Supernovae and Red Supergiant Mass Loss2006In: The Astrophysical Journal, ISSN 0004-637X, Vol. 641, no 2, p. 1029-1038Article in journal (Refereed)
    Abstract [en]

    Type IIP (plateau) supernovae are thought to come from stars with initial mass ~8-25 Msolar that end their lives as red supergiants. The expected stellar endpoints can be found from evolutionary calculations, and the corresponding mass-loss properties at these points can be estimated from typical values for Galactic stars. The mass-loss densities of observed supernovae can be estimated from observations of the thermal X-ray and radio synchrotron emission that result from the interaction of the supernova with the surrounding wind. Type IIP supernovae are expected to have energy-conserving interaction during typical times of observation. Because Type IIP supernovae have an extended period of high optical luminosity, Compton cooling could affect the radio-emitting electrons, giving rise to a relatively flat radio light curve in the optically thin regime. Alternatively, a high efficiency of magnetic field production results in synchrotron cooling of the radio-emitting electrons. Both the X-ray and radio luminosities are sensitive to the mass loss and initial masses of the progenitor stars, although the turn-on of radio emission is probably the best estimator of circumstellar density. Both the mass-loss density and the variation of density with stellar mass are consistent with expectations for the progenitor stars deduced from direct observations of recent supernovae. Current observations are consistent with mass being the only parameter; observations of supernovae in metal-poor regions could show how the mass loss depends on metallicity.

  • 10. Chomiuk, Laura
    et al.
    Soderberg, Alicia M.
    Chevalier, Roger A.
    Bruzewski, Seth
    Foley, Ryan J.
    Parrent, Jerod
    Strader, Jay
    Badenes, Carles
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kamble, Atish
    Margutti, Raffaella
    Rupen, Michael P.
    Simon, Joshua D.
    A DEEP SEARCH FOR PROMPT RADIO EMISSION FROM THERMONUCLEAR SUPERNOVAE WITH THE VERY LARGE ARRAY2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 821, no 2, article id 119Article in journal (Refereed)
    Abstract [en]

    Searches for circumstellar material around Type Ia supernovae (SNe Ia) are some of the most powerful tests of the nature of SN Ia progenitors, and radio observations provide a particularly sensitive probe of this material. Here, we report radio observations for SNe. Ia and their lower-luminosity thermonuclear cousins. We present the largest, most sensitive, and spectroscopically diverse study of prompt (Delta t less than or similar to 1 years) radio observations of 85 thermonuclear SNe, including 25 obtained by our team with the unprecedented depth of the Karl G. Jansky Very Large Array. With these observations, SN 2012cg joins SN 2011fe and SN 2014J as an SN. Ia with remarkably deep radio limits and excellent temporal coverage (six epochs, spanning 5-216 days after explosion, implying <(M)over dot>/v(w) less than or similar to 5 x 10(-9) M-circle dot yr(-1)/100 km s(-1), assuming epsilon(B) = 0.1 and epsilon(e) = 0.1). All observations yield non-detections, placing strong constraints on the presence of circumstellar material. We present analytical models for the temporal and spectral evolution of prompt radio emission from thermonuclear SNe as expected from interaction with either wind-stratified or uniform density media. These models allow us to constrain the progenitor mass loss rates, with limits in the range of <(M)over dot> less than or similar to 10(-9) - 10(-4) M-circle dot yr(-1), assuming a wind velocity of v(w) = 100 km s(-1). We compare our radio constraints with measurements of Galactic symbiotic binaries to conclude that less than or similar to 10% of thermonuclear SNe have red giant companions.

  • 11. Chomiuk, Laura
    et al.
    Söderberg, Alicia M.
    Moe, Maxwell
    Chevalier, Roger A.
    Rupen, Michael P.
    Badenes, Carles
    Margutti, Raffaella
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fong, Wen-fai
    Dittmann, Jason A.
    EVLA OBSERVATIONS CONSTRAIN THE ENVIRONMENT AND PROGENITOR SYSTEM OF Type Ia SUPERNOVA 2011fe2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 750, no 2, p. 164-Article in journal (Refereed)
    Abstract [en]

    We report unique Expanded Very Large Array observations of SN 2011fe representing the most sensitive radio study of a Type Ia supernova to date. Our data place direct constraints on the density of the surrounding medium at radii similar to 10(15)-10(16) cm, implying an upper limit on the mass loss rate from the progenitor system of (M) over dot less than or similar to 6x10(-10) M-circle dot yr(-1) (assuming a wind speed of 100 km s(-1)) or expansion into a uniform medium with density n(CSM) less than or similar to 6 cm(-3). Drawing from the observed properties of non-conservative mass transfer among accreting white dwarfs, we use these limits on the density of the immediate environs to exclude a phase space of possible progenitor systems for SN 2011fe. We rule out a symbiotic progenitor system and also a system characterized by high accretion rate onto the white dwarf that is expected to give rise to optically thick accretion winds. Assuming that a small fraction, 1%, of the mass accreted is lost from the progenitor system, we also eliminate much of the potential progenitor parameter space for white dwarfs hosting recurrent novae or undergoing stable nuclear burning. Therefore, we rule out much of the parameter space associated with popular single degenerate progenitor models for SN 2011fe, leaving a limited phase space largely inhabited by some double degenerate systems, as well as exotic single degenerates with a sufficient time delay between mass accretion and SN explosion.

  • 12. Clocchiatti, Alejandro
    et al.
    Wheeler, J. Craig
    Kirshner, Robert P.
    Branch, David
    Challis, Peter
    Chevalier, Roger A.
    Filippenko, Alexei V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Garnavich, Peter
    Leibundgut, Bruno
    Panagia, Nino
    Phillips, Mark M.
    Suntzeff, Nicholas B.
    Hoeflich, Peter A.
    Gallardo, Jose
    Late-time HST photometry of SN1994I: Hints of positron annihilation energy deposition2008In: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 120, no 865, p. 290-300Article in journal (Refereed)
    Abstract [en]

    We present multicolor Hubble Space Telescope ( HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained similar to 280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the gamma-rays produced by the radioactive decay of Co-56 diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.

  • 13.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dickinson, Hugh
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. 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).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy2011In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 32, no 3, p. 193-316Article in journal (Refereed)
    Abstract [en]

    Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

  • 14.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dickinson, Hugh J.
    Stockholm University, Faculty of Science, Department of Physics.
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. University of Geneva, Switzerland.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics.
    Introducing the CTA concept2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 3-18Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.

  • 15. Dahlen, Tomas
    et al.
    Melinder, J.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mencia Trinchant, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, S.
    Ostlin, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    The Stockholm Vimos Supernova Survey (SVISS) - First Results From An Intermediate Redshift Sn Survey2009Conference paper (Refereed)
    Abstract [en]

    The aim of the Stockholm VIMOS Supernova Survey is to find and characterize supernovae in the redshift range 0.1 to 1.2 and to derive accurate supernova rate densities for this redshift range. A preliminary analysis show that we have 14 prime SN candidates and an additional 23 less secure detections in one of our search fields. A sample of R+I light curves for the prime candidates will be presented. We will also show some results from testing of our supernova search pipeline and our supernova typing method.

  • 16.
    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)
  • 17.
    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.

  • 18.
    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.

  • 19.
    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)
  • 20. Fox, Ori D.
    et al.
    Bostroem, K. Azalee
    Van Dyk, Schuyler D.
    Filippenko, Alexei V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Matheson, Thomas
    Cenko, S. Bradley
    Chandra, Poonam
    Dwarkadas, Vikram
    Li, Weidong
    Parker, Alex H.
    Smith, Nathan
    UNCOVERING THE PUTATIVE B-STAR BINARY COMPANION OF THE SN 1993J PROGENITOR2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 790, no 1, p. 17-Article in journal (Refereed)
    Abstract [en]

    The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22M(circle dot) and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.

  • 21. France, Kevin
    et al.
    McCray, Richard
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, Josefin
    Frank, Kari A.
    Burrows, David N.
    Challis, Peter
    Kirshner, Robert P.
    Chevalier, Roger A.
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Smith, Nathan
    Sonneborn, George
    MAPPING HIGH-VELOCITY H alpha AND Ly alpha EMISSION FROM SUPERNOVA 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L16Article in journal (Refereed)
    Abstract [en]

    We present new Hubble Space Telescope images of high-velocity H alpha and Ly alpha emission in the outer debris of SN 1987 A. The Ha images are dominated by emission from hydrogen atoms crossing the reverse shock (RS). For the first time we observe emission from the RS surface well above and below the equatorial. ring (ER), suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H alpha imaging, we measure the mass flux of hydrogen atoms crossing the RS front, in the velocity intervals (-7500 < V-obs < -2800 km s(-1)) and (1000 < V-obs < 7500 km s(-1)), (M)(H) over dot = 1.2 x 10(-3) M-circle dot yr(-1). We also present the first Ly alpha imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Ly alpha and X-ray emission, we observe that the majority of the high-velocity Ly alpha emission originates interior to the ER. The observed Ly alpha/H alpha photon ratio, < R(L alpha/H alpha)> approximate to 17, is significantly higher than the theoretically predicted ratio of approximate to 5 for neutral atoms crossing the RS front. We attribute this excess to Ly alpha emission produced by X-ray heating of the outer debris. The spatial orientation of the Ly alpha and X-ray emission suggests that X-ray heating of the outer debris is the dominant Ly alpha production mechanism in SN 1987 A at this phase in its evolution.

  • 22. France, Kevin
    et al.
    McCray, Richard
    Heng, Kevin
    Kirshner, Robert P.
    Challis, Peter
    Bouchet, Patrice
    Crotts, Arlin
    Dwek, Eli
    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, Peter M.
    Larsson, Josefin
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lawrence, Stephen S.
    Lundqvist, Peter
    Panagia, Nino
    Pun, Chun S. J.
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Stocke, John T.
    Wang, Lifan
    Wheeler, J. Craig
    Observing Supernova 1987A with the Refurbished Hubble Space Telescope2010In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 329, no 5999, p. 1624-1627Article in journal (Refereed)
    Abstract [en]

    Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Ly alpha and H alpha lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Ly alpha, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v lambda lambda 1239, 1243 angstrom line emission, but only to the red of Ly alpha. The profiles of the N v lines differ markedly from that of H alpha, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.

  • 23. France, Kevin
    et al.
    McCray, Richard
    Penton, Steven V.
    Kirshner, Robert P.
    Challis, Peter
    Laming, J. Martin
    Bouchet, Patrice
    Chevalier, Roger
    Garnavich, Peter M.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Heng, Kevin
    Larsson, Josefin
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lawrence, Stephen
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Panagia, Nino
    Pun, Chun S. J.
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Sugerman, Ben
    Wheeler, J. Craig
    HST-COS Observations of Hydrogen, Helium, Carbon, and Nitrogen Emission from the SN 1987A Reverse Shock2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, no 2, p. 186-Article in journal (Refereed)
    Abstract [en]

    We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (Δv ~ 300 km s-1) emission lines from the circumstellar ring, broad (Δv ~ 10-20 × 103 km s-1) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise ratio (>40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350 Å can be explained by H I two-photon (2s 2 S 1/2-1s 2 S 1/2) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ± 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (Te /Tp ≈ 0.14-0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  • 24.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Challis, Peter M.
    Chevalier, Roger A.
    Filippenko, Alexei V.
    Kirshner, Robert P.
    Kozma, Cecilia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leonard, Douglas C.
    Matheson, Thomas
    Baron, E.
    Garnavich, Peter
    Jha, Saurabh
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pun, C. S. J.
    Wang, Lifan
    Wheeler, J. Craig
    Hubble Space Telescope and Ground-based Observations of SN 1993J and SN 1998S: CNO Processing in the Progenitors2005In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 622, p. 991-1007Article in journal (Refereed)
    Abstract [en]

    Ground-based and Hubble Space Telescope observations are presented for SN 1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar emission lines of N III-V and C III-IV, as well as broad lines from the ejecta. Both the broad ultraviolet and optical lines in SN 1998S indicate an expansion velocity of ~7000 km s-1. The broad emission components of Lyα and Mg II are strongly asymmetrical after day 72 past the explosion and differ in shape from Hα. Different models based on dust extinction from dust in the ejecta or shock region, in combination with Hα from a circumstellar torus, are discussed. It is concluded, however, that the double-peaked line profiles are more likely to arise as a result of optical depth effects in the narrow, cool, dense shell behind the reverse shock than in a torus-like region. The ultraviolet lines of SN 1993J are broad, with a boxlike shape, coming from the ejecta and a cool, dense shell. The shapes of the lines are well fitted by a shell with inner velocity ~7000 km s-1 and outer velocity ~10,000 km s-1. For both SN 1993J and SN 1998S a strong nitrogen enrichment is found, with N/C~12.4 in SN 1993J and N/C~6.0 in SN 1998S. From a compilation of all supernovae with determined CNO ratios, we discuss the implications of these observations for the structure of the progenitors of Type II supernovae. Based in part on observations obtained with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  • 25.
    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.

  • 26.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gröningsson, Per
    Stockholm University, Faculty of Science, Department of Astronomy.
    Twenty Years of Supernova 1987A2007In: The Messenger, Vol. 127, no 44Article in journal (Other (popular science, discussion, etc.))
  • 27.
    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).
    Jerkstrand, Anders
    RECONCILING THE INFRARED CATASTROPHE AND OBSERVATIONS OF SN 2011fe2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    The observational effects of the Infrared Catastrophe are discussed in view of the very late observations of the Type Ia SN 2011fe. Our model spectra at 1000 days take non-local radiative transfer into account and find that this has a crucial impact on the spectral formation. Although rapid cooling of the ejecta to a few 100 K occurs also in these models, the late-time optical/NIR flux is brighter by 1-2 mag due to redistribution of UV emissivity, resulting from non-thermal excitation and ionization. This effect brings models into better agreement with late-time observations of SN 2011fe, and other SNe Ia, and offers a solution to the long-standing discrepancy between models and observations. The models show that spectral formation shifts from Fe II and Fe III at 300 days to Fe I at 1000 days, which explains the apparent wavelength shifts seen in SN 2011fe. We discuss the effects of time dependence and energy input from Co-57, finding both to be important at 1000 days.

  • 28.
    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).
    Larsson, Josefin
    Migotto, Katia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pesce, Dominic
    Challis, Peter
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    McCray, Richard
    Spyromilio, Jason
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, Anders
    Mattila, Seppo
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wheeler, J. Craig
    Crotts, Arlin
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Panagia, Nino
    Pun, Chun S. J.
    Sonneborn, George
    Sugerman, Ben
    THE DESTRUCTION OF THE CIRCUMSTELLAR RING OF SN 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 806, no 1, article id L19Article in journal (Refereed)
    Abstract [en]

    We present imaging and spectroscopic observations with Hubble Space Telescope and Very Large Telescope of the ring of SN 1987A from 1994 to 2014. After an almost exponential increase of the shocked emission from the hotspots up to day similar to 8000 (similar to 2009), both this and the unshocked emission are now fading. From the radial positions of the hotspots we see an acceleration of these up to 500-1000 km s(-1), consistent with the highest spectroscopic shock velocities from the radiative shocks. In the most recent observations (2013 and 2014), we find several new hotspots outside the inner ring, excited by either X-rays from the shocks or by direct shock interaction. All of these observations indicate that the interaction with the supernova ejecta is now gradually dissolving the hotspots. We predict, based on the observed decay, that the inner ring will be destroyed by similar to 2025.

  • 29.
    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).
    Larsson, Josefin
    Spyromilio, Jason
    Chevalier, Roger
    Gröningsson, Per
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Leibundgut, Bruno
    McCray, Richard
    Challis, Peter
    Kirshner, Robert P.
    Kjaer, Karina
    Lundqvist, Peter
    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).
    LATE SPECTRAL EVOLUTION OF THE EJECTA AND REVERSE SHOCK IN SN 1987A2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 768, no 1, p. 88-Article in journal (Refereed)
    Abstract [en]

    We present observations with the Very Large Telescope and Hubble Space Telescope (HST) of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 February until 2012 January (days 4381-9100 after explosion). We detect broad lines from H alpha, H beta, Mg I], Na I, [O I], [Ca II], and a feature at similar to 9220 angstrom. We identify the latter line with Mg II lambda lambda 9218, 9244, which is most likely pumped by Ly alpha fluorescence. H alpha and H beta both have a centrally peaked component extending to similar to 4500 km s(-1) and a very broad component extending to greater than or similar to 11,000 km s(-1), while the other lines have only the central component. The low-velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar environment, whereas the very broad component comes from faster ejecta passing through the reverse shock, created by the collision with the circumstellar ring. The flux in H alpha from the reverse shock has increased by a factor of four to six from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in the optical lines from the shocked ring. The core component seen in H alpha, [Ca II], and Mg II has experienced a similar increase, which is consistent with that found from HST photometry. The energy deposition of the external X-rays is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. The external X-ray illumination also explains the edge-brightened morphology of the ejecta seen in the HST images. We finally discuss evidence for dust in the ejecta from line asymmetries.

  • 30.
    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).
    Larsson, Josefin
    Spyromilio, Jason
    Leibundgut, Bruno
    McCray, Richard
    Jerkstrand, Anders
    DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 821, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    Both CO and SiO have been observed at early and late phases in SN 1987A. H-2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here, we report the detection of NIR lines from H-2 at 2.12 and 2.40 mu m in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the SN in contrast to Ha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H-2 luminosities, we favor excitation resulting from the Ti-44 decay.

  • 31. Graves, Genevieve J. M.
    et al.
    Challis, Peter M.
    Chevalier, Roger A.
    Crotts, Arlin
    Filippenko, Alexei V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Garnavich, Peter
    Kirshner, Robert P.
    Li, Weidong
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    McCray, Richard
    Panagia, Nino
    Phillips, Mark M.
    Pun, Chun J. S.
    Schmidt, Brian P.
    Sonneborn, George
    Suntzeff, Nicholas B.
    Wang, Lifan
    Wheeler, J. Craig
    Limits from the Hubble Space Telescope on a Point Source in SN 1987A2005In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 629, p. 944-959Article in journal (Refereed)
    Abstract [en]

    We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. Our spectral observations cover ultraviolet (UV) and optical wavelengths from 1140 to 10266 Å, and our imaging observations cover UV and optical wavelengths from 2900 to 9650 Å. No point source is observed in the remnant. We obtain a limiting flux of Fopt<=1.6×10-14 ergs s-1 cm-2 in the wavelength range 2900-9650 Å for any continuum emitter at the center of the supernova remnant (SNR). This corresponds to an intrinsic luminosity of Lopt<=5×1033 ergs s-1. It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of ~35% due to dust absorption in the SNR. Correcting for this level of dust absorption would increase our upper limit on the luminosity of a continuum source by a factor of 1.54. Taking into account dust absorption in the remnant, we find a limit of Lopt<=8×1033 ergs s-1. We compare this upper bound with empirical evidence from point sources in other supernova remnants and with theoretical models for possible compact sources. We show that any survivor of a possible binary system must be no more luminous than an F6 main-sequence star. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Other nonplerionic X-ray point sources have luminosities similar to the limits on a point source in SN 1987A; RCW 103 and Cas A are slightly brighter than the limits on SN 1987A, while Pup A is slightly fainter. Of the young pulsars known to be associated with SNRs, those with ages <=5000 yr are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 1010 cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant. It will not be easy to improve substantially on our optical-UV limit for a point source in SN 1987A, although we can hope that a better understanding of the thermal infrared emission will provide a more complete picture of the possible energy sources at the center of SN 1987A.

  • 32.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Challis, Peter
    Chevalier, Roger
    Spyromilio, Jason
    Time evolution of the line emission from the inner circumstellar ring of SN 1987A and its hot spots2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 492, no 2, p. 481-491Article in journal (Refereed)
    Abstract [en]

    We present seven epochs between October 1999 and November 2007 of high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A.
The fluxes of most of the narrow lines from the unshocked gas decreased by a factor of 2-3 during this period, consistent with the decay from the initial ionization by the shock break-out. However, [O III] in particular shows an increase up to day ~6800. This agrees with radiative shock models where the pre-shocked gas is heated by the soft X-rays from the shock. The evolution of the [O III] line ratio shows a decreasing temperature of the unshocked ring gas, consistent with a transition from a hot, low density component which was heated by the initial flash ionization to the lower temperature in the pre-ionized gas ahead of the shocks.
The line emission from the shocked gas increases rapidly as the shock sweeps up more gas. We find that the neutral and high ionization lines follow the evolution of the Balmer lines roughly, while the intermediate ionization lines evolve less rapidly. Up to day ~6800, the optical light curves have a similar evolution to that of the soft X-rays. The break between day 6500 and day 7000 for [O III] and [Ne III] is likely due to recombination to lower ionization levels. Nevertheless, the evolution of the [Fe XIV] line, as well as the lines from the lowest ionization stages, continue to follow that of the soft X-rays, as expected.
There is a clear difference in the line profiles between the low and intermediate ionization lines, and those from the coronal lines at the earlier epochs. This shows that these lines arise from regions with different physical conditions, with at least a fraction of the coronal lines coming from adiabatic shocks. At later epochs the line widths of the low ionization lines, however, increase and approach those of the high ionization lines of [ Fe X-XIV] . The H line profile can be traced up to ~500 km s-1 at the latest epoch. This is consistent with the cooling time of shocks propagating into a density of (1-4) 104 cm-3. This means that these shocks are among the highest velocity radiative shocks observed.

  • 33.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leibundgut, Bruno
    Spyromilio, Jason
    Chevalier, Roger A.
    Gilmozzi, Roberto
    Kjær, Karina
    Mattila, Seppo
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    High resolution spectroscopy of the line emission from the inner circumstellar ring of SN 1987A and its hot spots2007Report (Other academic)
    Abstract [en]

    We discuss high resolution VLT/UVES observations (FWHM ~ 6 km/s) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (1.5-5.0)E3 cm-3 and temperatures of 6.5E3-2.4E4 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4E6-1E7 cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X-XIV], with the latter extending up to ~ -390 km/s in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~ -260 km/s. For H-alpha a faint extension up to ~ -450 km/s can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool down, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~ 510 km/s. We expect the maximum width of especially the low ionization lines to increase with time.

  • 34.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leibundgut, Bruno
    Spyromilio, Jason
    Chevalier, Roger
    Gilmozzi, Roberto
    Kjaer, Karina
    Mattila, Seppo
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    High resolution spectroscopy of the inner ring of SN 1987A2008In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 479, no 3, p. 761-777Article in journal (Refereed)
    Abstract [en]

    We discuss high resolution VLT/UVES observations (FWHM similar to 6 kms(-1)) from October 2002 (day similar to 5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (similar to 1.5 - 5.0) x 10(3) cm(-3) and temperatures of similar to 6.5 x 10(3) - 2.4 x 104 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [FeXIV]. From a nebular analysis we find that the density in the low ionization region is 4 x 10(6) - 10(7) cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X - XIV], with the latter extending up to similar to- 390 km s(-1) in the blue wing for [Fe XIV], while the low ionization lines extend to typically similar to- 260 km s(-1). For H alpha a faint extension up to similar to- 450 km s(-1) can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are similar to 510 km s(-1). We expect the maximum width of especially the low ionization lines to increase with time.

  • 35.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nymark, Tanja
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Chevalier, R.
    Leibundgut, B.
    Spyromilio, J.
    Coronal emission from the shocked circumstellar ring of SN 1987A2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 456, no 2, p. 581-589Article in journal (Refereed)
    Abstract [en]

    High resolution spectra with UVES/VLT of SN 1987A from December 2000 until November 2005 show a number of high ionization lines from gas with velocities of ± 350 km s-1, emerging from the shocked gas formed by the ejecta-ring collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which have increased by a factor of 20 during the observed period. The evolution of the lines is similar to that of the soft X-rays, indicating that they arise in the same component. The line ratios are consistent with those expected from radiative shocks with velocity 310{-}390 km s-1, corresponding to a shock temperature of (1.6{-}2.5)× 106 K. A fraction of the coronal emission may, however, originate in higher velocity adiabatic shocks.

  • 36. Heng, Kevin
    et al.
    McCray, Richard
    Zhekov, Svetozar A.
    Challis, Peter M.
    Chevalier, Roger A.
    Crotts, Arlin P. S.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Garnavich, Peter
    Kirshner, Robert P.
    Lawrence, Stephen S.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Panagia, Nino
    Pun, C. S. J.
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Wang, Lifan
    Evolution of the Reverse Shock Emission from SNR 1987A2006In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 644, p. 959-970Article in journal (Refereed)
    Abstract [en]

    We present new (2004 July) G750L and G140L Space Telescope Imaging Spectrograph (STIS) data of the Hα and Lyα emission from supernova remnant (SNR) 1987A. With the aid of earlier data, from 1997 October to 2002 October, we track the local evolution of Lyα emission and both the local and global evolution of Hα emission. The most recent observations allow us to directly compare the Hα and Lyα emission from the same slit position and at the same epoch. Consequently, we find clear evidence that, unlike Hα, Lyα is reflected from the debris by resonant scattering. In addition to emission that we can clearly attribute to the surface of the reverse shock, we also measure comparable emission, in both Hα and Lyα, that appears to emerge from supernova debris interior to the surface. New observations taken through slits positioned slightly eastward and westward of a central slit show a departure from cylindrical symmetry in the Hα surface emission. Using a combination of old and new observations, we construct a light curve of the total Hα flux, F, from the reverse shock, which has increased by a factor of ~4 over about 8 yr. However, due to large systematic uncertainties, we are unable to discern between the two limiting behaviors of the flux: F~t (self-similar expansion) and F~t5 (halting of the reverse shock). Such a determination is important for constraining the rate of hydrogen atoms crossing the shock, which is relevant to the question of whether the reverse shock emission will vanish in <~7 yr. Future deep, low- or moderate-resolution spectra are essential for accomplishing this task.

  • 37. Indebetouw, R.
    et al.
    Matsuura, M.
    Dwek, E.
    Zanardo, G.
    Barlow, M. J.
    Baes, M.
    Bouchet, P.
    Burrows, D. N.
    Chevalier, R.
    Clayton, G. C.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gaensler, B.
    Kirshner, R.
    Lakicevic, M.
    Long, K. S.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Marti-Vidal, I.
    Marcaide, J.
    McCray, R.
    Meixner, M.
    Ng, C. -Y
    Park, S.
    Sonneborn, G.
    Staveley-Smith, L.
    Vlahakis, C.
    van Loon, J.
    DUST PRODUCTION AND PARTICLE ACCELERATION IN SUPERNOVA 1987A REVEALED WITH ALMA2014In: The Astrophysical Journal Letters, ISSN 2041-8205, Vol. 782, no 1, p. L2-Article in journal (Refereed)
    Abstract [en]

    Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 mu m, 870 mu m, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M-circle dot). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.

  • 38. Iping, Rosina C.
    et al.
    Sonneborn, George
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Search for O VI Emission from the Shocked Circumstellar Ring of SN 1987A2007In: SUPERNOVA 1987A: 20 YEARS AFTER: Supernovae and Gamma-Ray Bursters, 2007, p. 182-184Conference paper (Other academic)
    Abstract [en]

    A search for O VI 1032-38 Å emission from the circumstellar shock interaction zones of SN 1987A was made with the FUSE satellite. The shock interaction of supernova ejecta with the dense inner ring began in the mid-1990s. Broad (FWHM ~300 km s−1) emission from optical coronal lines (e.g. [Fe X], [Fe XI], and [Fe XIV]) has emerged and increased exponentially in strength. O VI emission is expected to track the coronal lines and is expected to be the primary cooling transition for the million-degree shocked gas. In the most recent FUSE observation of SN 1987A, June 2004, a weak broad O VI feature may be present. An upper limit on the intrinsic O VI flux is ~1×10−13 erg cm−2 s−1 (corrected for foreground Galactic and LMC extinction). A follow-up observation of planned for mid-2007.

  • 39. 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.

  • 40.
    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.

  • 41. Jerkstrand, A.
    et al.
    Smartt, S. J.
    Fraser, M.
    Fransson, Claes
    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.
    Kotak, R.
    The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 439, no 4, p. 3694-3703Article in journal (Refereed)
    Abstract [en]

    We present nebular-phase optical and near-infrared spectroscopy of the Type IIP supernova SN 2012aw combined with non-local thermodynamic equilibrium radiative transfer calculations applied to ejecta from stellar evolution/explosion models. Our spectral synthesis models generally show good agreement with the ejecta from a M-ZAMS = 15 M-circle dot progenitor star. The emission lines of oxygen, sodium, and magnesium are all consistent with the nucleosynthesis in a progenitor in the 14-18 M-circle dot range. We also demonstrate how the evolution of the oxygen cooling lines of [O i] lambda 5577, [O i] lambda 6300, and [O i] lambda 6364 can be used to constrain the mass of oxygen in the non-molecularly cooled ashes to < 1 M-circle dot, independent of the mixing in the ejecta. This constraint implies that any progenitor model of initial mass greater than 20 M-circle dot would be difficult to reconcile with the observed line strengths. A stellar progenitor of around M-ZAMS = 15 M-circle dot can consistently explain the directly measured luminosity of the progenitor star, the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We conclude that there is still no convincing example of a Type IIP supernova showing the nucleosynthesis products expected from an M-ZAMS > 20 M-circle dot progenitor.

  • 42. Jerkstrand, A.
    et al.
    Smartt, S. J.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Inserra, C.
    Fraser, M.
    Spyromilio, J.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Chen, T. -W
    Barbarino, C.
    Dall'Ora, M.
    Botticella, M. T.
    Della Valle, M.
    Gal-Yam, A.
    Valenti, S.
    Maguire, K.
    Mazzali, P.
    Tomasella, L.
    Supersolar Ni/Fe production in the Type IIP SN 2012ec2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 448, no 3, p. 2482-2494Article in journal (Refereed)
    Abstract [en]

    SN 2012ec is a Type IIP supernova (SN) with a progenitor detection and comprehensive photospheric phase observational coverage. Here, we present Very Large Telescope and Public ESO Spectroscopic Survey of Transient Objects observations of this SN in the nebular phase. We model the nebular [O I] lambda lambda 6300, 6364 lines and find their strength to suggest a progenitor main-sequence mass of 13-15 M-circle dot. SN2012ec is unique among hydrogen-rich SNe in showing a distinct line of stable nickel [Ni II] lambda 7378. This line is produced by Ni-58, a nuclear burning ash whose abundance is a sensitive tracer of explosive burning conditions. Using spectral synthesis modelling, we use the relative strengths of [Ni II] lambda 7378 and [Fe II] lambda 7155 (the progenitor of which is Ni-56) to derive a Ni/Fe production ratio of 0.20 +/- 0.07 (by mass), which is a factor 3.4 +/- 1.2 times the solar value. High production of stable nickel is confirmed by a strong [Ni II] 1.939 mu m line. This is the third reported case of a core-collapse SN producing a Ni/Fe ratio far above the solar value, which has implications for core-collapse explosion theory and galactic chemical evolution models.

  • 43. Jerkstrand, A.
    et al.
    Timmes, F. X.
    Magkotsios, G.
    Sim, S. 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).
    Spyromilio, J.
    Mueller, B.
    Heger, 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.
    CONSTRAINTS ON EXPLOSIVE SILICON BURNING IN CORE-COLLAPSE SUPERNOVAE FROM MEASURED Ni/Fe RATIOS2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 807, no 1, article id 110Article in journal (Refereed)
    Abstract [en]

    Measurements of explosive nucleosynthesis yields in core-collapse supernovae provide tests for explosion models. We investigate constraints on explosive conditions derivable from measured amounts of nickel and iron after radioactive decays using nucleosynthesis networks with parameterized thermodynamic trajectories. The Ni/Fe ratio is for most regimes dominated by the production ratio of Ni-58/(Fe-54 + Ni-56), which tends to grow with higher neutron excess and with higher entropy. For SN 2012ec, a supernova (SN) that produced a Ni/Fe ratio of 3.4 +/- 1.2 times solar, we find that burning of a fuel with neutron excess eta approximate to 6 x 10(-3) is required. Unless the progenitor metallicity is over five times solar, the only layer in the progenitor with such a neutron excess is the silicon shell. SNe producing large amounts of stable nickel thus suggest that this deep-lying layer can be, at least partially, ejected in the explosion. We find that common spherically symmetric models of M-ZAMS less than or similar to 13 M-circle dot stars exploding with a delay time of less than one second (M-cut < 1.5 M-circle dot) are able to achieve such silicon-shell ejection. SNe that produce solar or subsolar Ni/Fe ratios, such as SN 1987A, must instead have burnt and ejected only oxygen-shell material, which allows a lower limit to the mass cut to be set. Finally, we find that the extreme Ni/Fe value of 60-75 times solar derived for the Crab cannot be reproduced by any realistic entropy burning outside the iron core, and neutrino-neutronization obtained in electron capture models remains the only viable explanation.

  • 44.
    Jerkstrand, Anders
    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).
    Kozma, Cecilia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The 44Ti-powered spectrum of SN 1987A2011In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 530, p. A45-Article in journal (Refereed)
    Abstract [en]

    SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Owing to the rich chemical structure, the multitude of physical processes involved and extensive radiative transfer effects, detailed modeling is needed to interpret the emission from this and other supernovae. In this paper, we analyze the late-time (about eight years) Hubble Space Telescope spectrum of the SN 1987A ejecta, where 44Ti is the dominant power source. Based on an explosion model for a 19 Msun progenitor, we compute a model spectrum by calculating the degradation of positrons and gamma-rays from the radioactive decays, solving the equations governing temperature, ionization balance and NLTE level populations, and treating the radiative transfer with a Monte Carlo technique. We obtain a UV/optical/NIR model spectrum that reproduces most of the lines in the observed spectrum with good accuracy. We find non-local radiative transfer in atomic lines to be an important process also at this late stage of the supernova, with 30% of the emerging flux in the optical and NIR coming from scattering/fluorescence. We investigate the question of where the positrons deposit their energy, and favor the scenario where they are locally trapped in the Fe/He clumps by a magnetic field. Energy deposition into these largely neutral Fe/He clumps makes Fe I lines prominent in the emerging spectrum. With the best available estimates for the dust extinction, we determine the amount of 44Ti produced in the explosion to be 1.5+-0.5 Msun.

  • 45.
    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)
  • 46. Kamble, Atish
    et al.
    Margutti, Raffaella
    Soderberg, Alicia M.
    Chakraborti, Sayan
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Chevalier, Roger
    Powell, Diana
    Milisavljevic, Dan
    Parrent, Jerod
    Bietenholz, Michael
    PROGENITORS OF TYPE IIb SUPERNOVAE IN THE LIGHT OF RADIO AND X-RAYS FROM SN 2013df2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 818, no 2, article id 111Article in journal (Refereed)
    Abstract [en]

    We present radio and X-ray observations of the nearby SN IIb 2013df in NGC 4414 from 10 to 250 days after the explosion. The radio emission showed a peculiar steep-to-shallow spectral evolution. We present a model in which inverse Compton cooling of synchrotron emitting electrons can account for the observed spectral and light curve evolution. A significant mass-loss rate, (M) over dot approximate to 8 x 10(-5) M-circle dot yr(-1) for a wind velocity of 10 km s(-1), is estimated from the detailed modeling of radio and X-ray emission, which are primarily due to synchrotron and bremsstrahlung, respectively. We show that SN 2013df is similar to SN 1993J in various ways. The shock wave speed of SN 2013df was found to be average among the radio supernovae; v(sh)/c similar to 0.07. We did not find any significant deviation from smooth decline in the light curve of SN 2013df. One of the main results of our self-consistent multiband modeling is the significant deviation from energy equipartition between magnetic fields and relativistic electrons behind the shock. We estimate epsilon(e) = 200 epsilon(B). In general for SNe IIb, we find that the presence of bright optical cooling envelope emission is linked with free-free radio absorption and bright thermal X-ray emission. This finding suggests that more extended progenitors, similar to that of SN 2013df, suffer from substantial mass loss in the years before the supernova.

  • 47. Kamble, Atish
    et al.
    Soderberg, Alicia M.
    Chomiuk, Laura
    Margutti, Raffaella
    Medvedev, Mikhail
    Milisavljevic, Dan
    Chakraborti, Sayan
    Chevalier, Roger
    Chugai, Nikolai
    Dittmann, Jason
    Drout, Maria
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nakar, Ehud
    Sanders, Nathan
    RADIO OBSERVATIONS REVEAL A SMOOTH CIRCUMSTELLAR ENVIRONMENT AROUND THE EXTRAORDINARY TYPE Ib SUPERNOVA 2012au2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 797, no 1, p. 2-Article in journal (Refereed)
    Abstract [en]

    We present extensive radio and X-ray observations of SN 2012au, an energetic, radio-luminous supernova of Type Ib that exhibits multi-wavelength properties bridging subsets of hydrogen-poor superluminous supernovae, hypernovae, and normal core-collapse supernovae. The observations closely follow models of synchrotron emission from a shock-heated circumburst medium that has a wind density profile (rho alpha r(-2)). We infer a sub-relativistic velocity for the shock wave v approximate to 0.2 c and a radius of r approximate to 1.4 x 10(16) cm at 25 days after the estimated date of explosion. For a wind velocity of 1000 km s(-1), we determine the mass-loss rate of the progenitor to be M = 3.6 x 10(-6) M-circle dot yr(-1), consistent with the estimates from X-ray observations. We estimate the total internal energy of the radio-emitting material to be E approximate to 10(47) crg, which is intermediate to SN 1998bw and SN 2002ap. The evolution of the radio light curve of SN 2012au is in agreement with its interaction with a smoothly distributed circumburst medium and the absence of stellar shells ejected from previous outbursts out to r approximate to 10(17) cm from the supernova site. We conclude that the bright radio emission from SN 2012au was not dissimilar from other core-collapse supernovae despite its extraordinary optical properties, and that the evolution of the SN 2012au progenitor star was relatively quiet, marked with a steady mass loss, during the final years preceding explosion.

  • 48. Kamenetzky, J.
    et al.
    McCray, R.
    Indebetouw, R.
    Barlow, M. J.
    Matsuura, M.
    Baes, M.
    Blommaert, J. A. D. L.
    Bolatto, A.
    Decin, L.
    Dunne, L.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Glenn, J.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Hopwood, R.
    Kirshner, R. P.
    Lakicevic, M.
    Marcaide, J.
    Marti-Vidal, I.
    Meixner, M.
    Royer, P.
    Soderberg, A.
    Sonneborn, G.
    Staveley-Smith, L.
    Swinyard, B. M.
    Van de Steene, G.
    van Hoof, P. A. M.
    van Loon, J. Th.
    Yates, J.
    Zanardo, G.
    CARBON MONOXIDE IN THE COLD DEBRIS OF SUPERNOVA 1987A2013In: ASTROPHYS J LETT, ISSN 2041-8205, Vol. 773, no 2, p. L34-Article in journal (Refereed)
    Abstract [en]

    We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M-circle dot of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at similar to 2000 km s(-1). Moreover, we locate the emission within 1 '' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.

  • 49. 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.

  • 50. Kerzendorf, W. E.
    et al.
    McCully, C.
    Taubenberger, S.
    Jerkstrand, A.
    Seitenzahl, I.
    Ruiter, A. J.
    Spyromilio, J.
    Long, K. S.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Extremely late photometry of the nearby SN 2011fe2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, no 3, p. 2534-2542Article in journal (Refereed)
    Abstract [en]

    Type Ia supernovae are widely accepted to be the outcomes of thermonuclear explosions in white dwarf stars. However, many details of these explosions remain uncertain (e.g. the mass, ignition mechanism and flame speed). Theory predicts that at very late times (beyond 1000 d) it might be possible to distinguish between explosion models. Few very nearby supernovae can be observed that long after the explosion. The Type Ia supernova SN 2011fe located in M101 and along a line of sight with negligible extinction, provides us with the once-in-a-lifetime chance to obtain measurements that may distinguish between theoretical models. In this work, we present the analysis of photometric data of SN2011fe taken between 900 and 1600 d after explosion with Gemini and HST. At these extremely late epochs theory suggests that the light-curve shape might be used to measure isotopic abundances which is a useful model discriminant. However, we show in this work that there are several currently not well constrained physical processes introducing large systematic uncertainties to the isotopic abundance measurement. We conclude that without further detailed knowledge of the physical processes at this late stage one cannot reliably exclude any models on the basis of this data set.

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