Examinando por Autor "Ergon, M."
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Ítem Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions(EDP Sciences, 2021-10-01) Cai, Y.-Z.; Pastorello, A.; Fraser, M.; Botticella, M. T.; Elias-Rosa, N.; Wang, L.-Z.; Kotak, R.; Benetti, S.; Cappellaro, E.; Turatto, M.; Reguitti, A.; Mattila, S.; Smartt, S. J.; Ashall, C.; Benitez, S.; Chen, T.-W.; Harutyunyan, A.; Kankare, E.; Lundqvist, P.; Mazzali, P. A.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Prentice, S. J.; Reynolds, T. M.; Shu, X.-W.; Stritzinger, M. D.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Valenti, S.; Valerin, G.; Wang, G.-J.; Wang, X.-F.; Borsato, L.; Callis, E.; Cannizzaro, G.; Chen, S.; Congiu, E.; Ergon, M.; Galbany, L.; Gal-Yam, A.; Gao, X.; Gromadzki, M.; Holmbo, S.; Huang, F.; Inserra, C.; Itagaki, K.; Kostrzewa-Rutkowska, Z.; Maguire, K.; Margheim, S.; Moran, S.; Onori, F.; Sagués Carracedo, A.; Smith, K. W.; Sollerman, J.; Somero, A.; Wang, B.; Young, D. R.We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between-11.5 and-14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5-9.0 × 1040 erg s-1 and their total radiated energies are on the order of (0.3-3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10-4 to 10-3 M⊙. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s-1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.Ítem Massive stars exploding in a He-rich circumstellar medium - IV. Transitional type Ibn supernovae(Oxford University Press, 2015-05) Pastorello, A.; Benetti, S.; Brown, P.J.; Tsvetkov, D.Y.; Inserra, C.; Taubenberger, S.; Tomasella, L.; Fraser, M.; Rich, D.J.; Botticella, M.T.; Bufano, F.; Cappellaro, E.; Ergon, M.; Gorbovskoy, E.S.; Harutyunyan, A.; Huang, F.; Kotak, R.; Lipunov, V.M.; Magill, L.; Miluzio, M.; Morrell, N.; Ochner, P.; Smartt, S.J.; Sollerman, J.; Spiro, S.; Stritzinger, M.D.; Turatto, M.; Valenti, S.; Wang, X.; Wright, D.E.; Yurkov, V.V.; Zampieri, L.; Zhang, L.We present ultraviolet, optical and near-infrared data of the Type Ibn supernovae (SNe) 2010al and 2011hw. SN 2010al reaches an absolute magnitude at peak of MR = -18.86 ± 0.21. Its early light curve shows similarities with normal SNe Ib, with a rise to maximum slower than most SNe Ibn. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni He I lines indicating the presence of a slow-moving, He-rich circumstellar medium. At later epochs, the spectra well match those of the prototypical SN Ibn 2006jc, although the broader lines suggest that a significant amount of He was still present in the stellar envelope at the time of the explosion. SN 2011hw is somewhat different. It was discovered after the first maximum, but the light curve shows a double peak. The absolute magnitude at discovery is similar to that of the second peak (MR = -18.59 ± 0.25), and slightly fainter than the average of SNe Ibn. Though the spectra of SN 2011hw are similar to those of SN 2006jc, coronal lines and narrow Balmer lines are clearly detected. This indicates substantial interaction of the SN ejecta with He-rich, but not H-free, circumstellar material. The spectra of SN 2011hw suggest that it is a transitional SN Ibn/IIn event similar to SN 2005la. While for SN 2010al the spectrophotometric evolution favours a H-deprived Wolf-Rayet progenitor (of WN-type), we agree with the conclusion of Smith et al. that the precursor of SN 2011hw was likely in transition from a luminous blue variable to an early Wolf-Rayet (Ofpe/WN9) stage. © 2015 The Authors.Ítem Optical and near-infrared observations of SN 2011dh-The first 100 days(EDP Sciences, 2014-02) Ergon, M.; Sollerman, J.; Fraser, M.; Pastorello, A.; Taubenberger, S.; Elias-Rosa, N.; Bersten, M.; Jerkstrand, A.; Benetti, S.; Botticella, M.T.; Fransson, C.; 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.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 bolo metric 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 ∼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 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 ∼10 and ∼15 days, close to the photosphere and then move outward in velocity until ∼40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the γ-rays is driving the early evo lution of these lines. The Spitzer 4.5 µm 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 ∼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.Ítem SN 2009ib: A Type II-P supernova with an unusually long plateau(Oxford University Press, 2015-05) Takáts, K.; Pignata, G.; Pumo, M.L.; Paillas, E.; Zampieri, L.; Elias-Rosa, N.; Benetti, S.; Bufano, F.; Cappellaro, E.; Ergon, M.; Fraser, M.; Hamuy, M.; Inserra, C.; Kankare, E.; Smartt, S.J.; Stritzinger, M.D.; Van Dyk, S.D.; Haislip, J.B.; LaCluyze, A.P.; Moore, J.P.; Reichart, D.We present optical and near-infrared photometry and spectroscopy of SN 2009ib, a Type II-P supernova in NGC 1559. This object has moderate brightness, similar to those of the intermediate-luminosity SNe 2008in and 2009N. Its plateau phase is unusually long, lasting for about 130 d after explosion. The spectra are similar to those of the subluminous SN 2002gd, with moderate expansion velocities.We estimate the 56Ni mass produced as 0.046±0.015M⊙. We determine the distance to SN 2009ib using both the expanding photosphere method (EPM) and the standard candle method. We also apply EPM to SN 1986L, a Type II-P SN that exploded in the same galaxy. Combining the results of different methods, we conclude the distance to NGC 1559 as D = 19.8 ± 3.0 Mpc. We examine archival, pre-explosion images of the field taken with the Hubble Space Telescope, and find a faint source at the position of the SN, which has a yellow colour [(V - I)0 = 0.85 mag]. Assuming it is a single star, we estimate its initial mass as MZAMS = 20M⊙. We also examine the possibility, that instead of the yellow source the progenitor of SN 2009ib is a red supergiant star too faint to be detected. In this case, we estimate the upper limit for the initial zero-age main sequence (ZAMS) mass of the progenitor to be ~14-17M⊙. In addition, we infer the physical properties of the progenitor at the explosion via hydrodynamical modelling of the observables, and estimate the total energy as ~0.55 × 1051 erg, the pre-explosion radius as ~400 R⊙, and the ejected envelope mass as ~15M⊙, which implies that the mass of the progenitor before explosion was ~16.5-17M⊙. © 2015 The Authors.Ítem SN 2009jf: a slow-evolving stripped-envelope core-collapse supernova(2011) Valenti, S.; Fraser, M.;; Benetti, S.; Pignata, G.; Sollerman, J.; Inserra, C.; Cappellaro, E.; Pastorello, A.; Smartt, S. J.; Ergon, M.; Botticella, M. T.; Brimacombe, J.; Bufano, F.; Crockett, M.; Eder, I.; Fugazza, D.; Haislip, J. B.; Hamuy, M.; Ivarsen, K. M.; Kankare, E.; Kotak, R.; LaCluyze, A. P.; Magill, L.; Mattila, S.; Maza, J.; Mazzali, P. A.; Reichart, D. E.; Taubenberger, S.; Turatto, M.; Zampieri, L.; Harutyunyan, K.M.We present an extensive set of photometric and spectroscopic data for SN 2009jf, a nearby Type Ib supernova, spanning from 20 days before B-band maximum to one year after maximum. We show that SN 2009jf is a slowly evolving and energetic stripped-envelope SN and is likely from a massive progenitor (25-30 solar masses). The large progenitor’s mass allows us to explain the complete hydrogen plus helium strip- ping without invoking the presence of a binary companion. The supernova occurred close to a young cluster, in a crowded environment with ongoing star-formation. The specroscopic similarity with the He-poor Type Ic SN 2007gr suggests a common pro- genitor for some supernovae Ib and Ic. The nebular spectra of SN 2009jf are consistent with an asymmetric explosion, with an off-center dense core. We also find evidence that He-rich Ib supernovae have a rise time longer than other stripped-envelope su- pernovae, however confirmation of this result and further observations are needed.Ítem SN 2016gsd: An unusually luminous and linear Type II supernova with high velocities(Oxford University Press, 2020-04) Reynolds, T.M.; Fraser, M.; Mattila, S.; Ergon, M.; Dessart, L.; Lundqvist, P.; Dong, S.; Elias-Rosa, N.; Galbany, L.; Gutierrez, C.P.; Kangas, T.; Kankare, E.; Kotak, R.; Kuncarayakti, H.; Pastorello, A.; Rodriguez, O.; Smartt, S.J.; Stritzinger, M.; Tomasella, L.; Chen, P.; Harmanen, J.; Hosseinzadeh, G.; Howell, D.A.; Inserra, C.; Nicholl, M.; Nielsen, M.; Smith, K.; Somero, A.; Tronsgaard, R.; Young, D.R.We present observations of the unusually luminous Type II supernova (SN) 2016gsd. With a peak absolute magnitude of V = -19.95 ± 0.08, this object is one of the brightest Type II SNe, and lies in the gap of magnitudes between the majority of Type II SNe and the superluminous SNe. Its light curve shows little evidence of the expected drop from the optically thick phase to the radioactively powered tail. The velocities derived from the absorption in H α are also unusually high with the blue edge tracing the fastest moving gas initially at 20 000 km s-1, and then declining approximately linearly to 15 000 km s-1 over ∼100 d. The dwarf host galaxy of the SN indicates a low-metallicity progenitor which may also contribute to the weakness of the metal lines in its spectra. We examine SN 2016gsd with reference to similarly luminous, linear Type II SNe such as SNe 1979C and 1998S, and discuss the interpretation of its observational characteristics. We compare the observations with a model produced by the jekyll code and find that a massive star with a depleted and inflated hydrogen envelope struggles to reproduce the high luminosity and extreme linearity of SN 2016gsd. Instead, we suggest that the influence of interaction between the SN ejecta and circumstellar material can explain the majority of the observed properties of the SN. The high velocities and strong H α absorption present throughout the evolution of the SN may imply a circumstellar medium configured in an asymmetric geometry. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem SN 2020acat: an energetic fast rising Type IIb supernova(Oxford University Press, 2022-07-01) Medler, K.; Mazzali, P.A.; Teffs, J.; Ashall, C.; Anderson, J.P.; Arcavi, I.; Benetti, S.; Bostroem, K.A.; Burke, J.; Cai, Y.-Z.; Charalampopoulos, P.; Elias Rosa, N.; Ergon, M.; Galbany, L.; Gromadzki, M.; Hiramatsu, D.; Howell, D.A.; Inserra, C.; Lundqvist, P.; McCully, C.; Müller Bravo, T.; Newsome, M.; Nicholl, M.; Gonzalez, E. Padilla; Paraskeva, E.; Pastorello, A.; Pellegrino, C.; Pessi, P.J.; Reguitti, A.; Reynolds, T.M.; Roy, R.; Terreran, G.; Tomasella, L.; Young, D.R.The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of Log10(L) = 42.49 ± 0.17 erg s-1 in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of MNi = 0.13 ± 0.03 M⊙, with an ejecta mass of Mej = 2.3 ± 0.4 M⊙ and a kinetic energy of Ek = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900 Å that cannot be solely accounted for by the presence of the Fe ii 5018 line. We suggest that the Fe ii feature was augmented by He i 5016 and possibly by the presence of N ii 5005. From both photometric and spectroscopic analysis, we inferred that the progenitor of SN 2020acat was an intermediate-mass compact star with an MZAMS of 15-20 M⊙. © 2022 The Author(s).Ítem The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst(Institute of Physics Publishing, 2018) Elias-Rosa, N.; Van Dyk, S.D.; Benetti, S.; Cappellaro, E.; Smith, N.; Kotak, R.; Turatto, M.; Filippenko, A.V.; Pignata, G.; Fox, O.D.; Galbany, L.; González-Gaitán, S.; Miluzio, M.; Monard, L.A.G.; Ergon, M.It is well known that massive stars (M > 8 M ) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN 2010bt, which was classified as a Type IIn SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L ≈ 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (∼5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor. © 2018. The American Astronomical Society. All rights reserved.