Browsing by Author "Gal-Yam, A."

Now showing 1 - 9 of 9
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    Early observations of the nearby Type Ia supernova SN 2015F
    (2017) Cartier, R.; Sullivan, M.; Firth, R. E.; Pignata, G.; Mazzali, P.; Maguire, K.; Childress, M. J.; Arcavi, I.; Ashall, C.; Bassett, B.; Crawford, S. M.; Frohmaier, C.; Galbany, L.; Gal-Yam, A.; Hosseinzadeh, G.; Howell, D. A.; Inserra, C.; Johansson, J.; Kasai, E. K.; McCully, C.; Prajs, S.; Prentice, S.; Schulze, S.; Smartt, S. J.; Smith, K. W.; Smith, M.; Valenti, S.; Young, D. R.
    We present photometry and time series spectroscopy of the nearby Type Ia supernova (SN Ia) SN 2015F over -16 d to +80 d relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2015F is a slightly sub-luminous SN Ia with a decline rate of Delta m15(B) = 1.35 +/- 0.03 mag, placing it in the region between normal and SN 1991bg-like events. Our densely sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II lambda 6580 absorption until -4 days, and high-velocity Ca II is particularly strong at <-10 d at expansion velocities of 23 000 km s(-1). At early times, our spectral modelling with SYN++ shows strong evidence for iron-peak elements ( Fe (II), Cr (II), Ti (II), and V-II) expanding at velocities > 14 000 km s(-1), suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including VII in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at similar to 6800 angstrom that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity CII material could also be responsible. In both cases, the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 feature is weakly present in other normal SN Ia events and common in the SN 1991bg-like sub-class.
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    Interacting supernovae and supernova impostors. LSQ13zm : an outburst heralds the death of a massive star
    (2016) Tartaglia, L.; Pastorello, A.; Sullivan, M.; Baltay, C.; Rabinowitz, D.; Nugent, P.; Drake, A. J.; Djorgovski, S. G.; Gal-Yam, A.; Bauer, Franz Erik; Barsukova, E. A.; Goranskij, V. P.; Valeev, A. F.; Fatkhullin, T.; Schulze, S.; Mehner, A.; Fabrika, S.; Taubenberger, S.; Nordin, J.; Valenti, S.
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    LSQ14bdq: A TYPE Ic SUPER-LUMINOUS SUPERNOVA WITH A DOUBLE-PEAKED LIGHT CURVE
    (2015) Nicholl, M.; Smartt, S. J.; Jerkstrand, A.; Sim, S. A.; Inserra, C.; Anderson, J. P.; Baltay, C.; Benetti, S.; Chambers, K.; Chen, T. -W.; Elias-Rosa, N.; Feindt, U.; Flewelling, H. A.; Fraser, M.; Gal-Yam, A.; Galbany, L.; Huber, M. E.; Kangas, T.; Kankare, E.; Kotak, R.; Kruehler, T.; Maguire, K.; McKinnon, R.; Rabinowitz, D.; Rostami, S.; Schulze, S.; Smith, K. W.; Sullivan, M.; Tonry, J. L.; Valenti, S.; Young, D. R.
    We present data for LSQ14bdq, a hydrogen-poor super-luminous supernova (SLSN) discovered by the La Silla QUEST survey and classified by the Public ESO Spectroscopic Survey of Transient Objects. The spectrum and light curve are very similar to slow-declining SLSNe such as PTF12dam. However, detections within similar to 1 day after explosion show a bright and relatively fast initial peak, lasting for similar to 15 days, prior to the usual slow rise to maximum light. The broader, main peak can be fit with either central engine or circumstellar interaction models. We discuss the implications of the precursor peak in the context of these models. It is too bright and narrow to be explained as a normal Ni-56-powered SN, and we suggest that interaction models may struggle to fit the two peaks simultaneously. We propose that the initial peak may arise from the post-shock cooling of extended stellar material, and reheating by a central engine drives the second peak. In this picture, we show that an explosion energy of similar to 2 X 10(52) erg and a progenitor radius of a few hundred solar radii would be required to power the early emission. The competing engine models involve rapidly spinning magnetars (neutron stars) or fallback onto a central black hole. The prompt energy required may favor the black hole scenario. The bright initial peak may be difficult to reconcile with a compact Wolf-Rayet star as a progenitor since the inferred energies and ejected masses become unphysical.
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    Massive stars exploding in a He-rich circumstellar medium - V. Observations of the slow-evolving SN Ibn OGLE-2012-SN-006
    (2015) Pastorello, A.; Wyrzykowski, L.; Valenti, S.; Prieto, J. L.; Kozlowski, S.; Udalski, A.; Elias-Rosa, N.; Morales-Garoffolo, A.; Anderson, J. P.; Benetti, S.; Bersten, M.; Botticella, M. T.; Cappellaro, E.; Fasano, G.; Fraser, M.; Gal-Yam, A.; Gillone, M.; Graham, M. L.; Greiner, J.; Hachinger, S.; Howell, D. A.; Inserra, C.; Parrent, J.; Rau, A.; Schulze, S.; Smartt, S. J.; Smith, K. W.; Turatto, M.; Yaron, O.; Young, D. R.; Kubiak, M.; Szymanski, M. K.; Pietrzynski, G.; Soszynski, I.; Ulaczyk, K.; Poleski, R.; Pietrukowicz, P.; Skowron, J.; Mroz, P.
    We present optical observations of the peculiar Type Ibn supernova (SN Ibn) OGLE-2012-SN-006, discovered and monitored by the Optical Gravitational Lensing Experiment-IV survey, and spectroscopically followed by Public ESO Spectroscopic Survey of Transient Objects (PESSTO) at late phases. Stringent pre-discovery limits constrain the explosion epoch with fair precision to JD = 245 6203.8 +/- 4.0. The rise time to the I-band light-curve maximum is about two weeks. The object reaches the peak absolute magnitude M-I = -19.65 +/- 0.19 on JD = 245 6218.1 +/- 1.8. After maximum, the light curve declines for about 25 d with a rate of 4 mag (100 d)(-1). The symmetric I-band peak resembles that of canonical Type Ib/c supernovae (SNe), whereas SNe Ibn usually exhibit asymmetric and narrower early-time light curves. Since 25 d past maximum, the light curve flattens with a decline rate slower than that of the Co-56-Fe-56 decay, although at very late phases it steepens to approach that rate. However, other observables suggest that the match with the Co-56 decay rate is a mere coincidence, and the radioactive decay is not the main mechanism powering the light curve of OGLE-2012-SN-006. An early-time spectrum is dominated by a blue continuum, with only a marginal evidence for the presence of He I lines marking this SN type. This spectrum shows broad absorptions bluewards than 5000 angstrom, likely O II lines, which are similar to spectral features observed in superluminous SNe at early epochs. The object has been spectroscopically monitored by PESSTO from 90 to 180 d after peak, and these spectra show the typical features observed in a number of SN 2006jc-like events, including a blue spectral energy distribution and prominent and narrow (v(FWHM) approximate to 1900 km s(-1)) He I emission lines. This suggests that the ejecta are interacting with He-rich circumstellar material. The detection of broad (10(4) km s(-1)) O I and Ca II features likely produced in the SN ejecta (including the [OI] lambda lambda 6300,6364 doublet in the latest spectra) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event.
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    On the diversity of superluminous supernovae : ejected mass as the dominant factor
    (2015) Nicholl, M.; Smartt, S.; Jerkstrand, A.; Inserra, C.; Sim, S.; Chen, T.; Benetti, S.; Fraser, M.; Bauer, Franz Erik; Schulze, S; Maguire, K.; Smith, K.; Sullivan, M.; Valenti, S.; Young, D.; Gal-Yam, A.; Kankare, E.
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    On the nature of hydrogen-rich superluminous supernovae
    (2018) Inserra, C.; Smartt, S. J.; Gall, E. E. E.; Leloudas, G.; Chen, T-W.; Schulze, S.; Jerkstrand, A.; Nicholl, M.; Anderson, J. P.; Arcavi, I.; Benetti, S.; Cartier, R. A.; Childress, M.; Della Valle, M.; Flewelling, H.; Fraser, M.; Gal-Yam, A.; Gutierrez, C. P.; Hosseinzadeh, G.; Howell, D. A.; Huber, M.; Kankare, E.; Kruehler, T.; Magnier, E. A.; Maguire, K.; McCully, C.; Prajs, S.; Primak, N.; Scalzo, R.; Schmidt, B. P.; Smith, M.; Smith, K. W.; Tucker, B. E.; Valenti, S.; Wilman, M.; Young, D. R.; Yuan, F.
    We present two hydrogen-rich superluminous supernovae (SLSNe): SN2103hx and PS 15br. These objects, together with SN2008es, are the only SLSNe showing a distinct, broad H alpha feature during the photospheric phase; also, they show no sign of strong interaction between fast moving ejecta and circumstellar shells in their early spectra. Despite the fact that the peak luminosity of PS 15br is fainter than that of the other two objects, the spectrophotometric evolution is similar to SN2103hx and different from any other supernova in a similar luminosity space. We group all of them as SLSNe II and hence they are distinct from the known class of SLSN IIn. Both transients show a strong, multicomponent H alpha emission after 200 d past maximum, which we interpret as an indication of the interaction of the ejecta with an asymmetric, clumpy circumstellar material. The spectra and photometric evolution of the two objects are similar to Type II supernovae, although they have much higher luminosity and evolve on slower time-scales. This is qualitatively similar to how SLSNe I compare with normal type Ic, in that the former are brighter and evolve more slowly. We apply a magnetar and an interaction semi-analytical code to fit the light curves of our two objects and SN2008es. The overall observational data set would tend to favour the magnetar, or central engine, model as the source of the peak luminosity, although the clear signature of late-time interaction indicates that interaction can play a role in the luminosity evolution of SLSNe II at some phases.
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    PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
    (2015) Smartt, S. J.; Valenti, S.; Fraser, M.; Inserra, C.; Young, D. R.; Sullivan, M.; Bauer, Franz Erik; Clocchiatti, Alejandro; Romero Cañizales, Cristina; Schulze, S.; Pastorello, A.; Benetti, S.; Gal-Yam, A.; Knapic, C.; Molinaro, M.; Smareglia, R.; Smith, K. W.; Taubenberger, S.; Yaron, O.; Anderson, J. P.; Ashall, C.; Balland, C.; Baltay, C.; Barbarino, C.; Baumont, S.; Bersier, D.; Blagorodnova, N.; Bongard, S.; Botticella, M. T.; Bufano, F.; Bulla, M.; Cappellaro, E.; Campbell, H.; Cellier-Holzem, F.; Chen, T. W.; Childress, M. J.; Contreras, C.; Dall’Ora, M.; Danziger, J.; de Jaeger, T.; De Cia, A.; Della Valle, M.; Dennefeld, M.; Elias Rosa, N.; Elman, N.; Feindt, U.; Fleury, M.; Gall, E.; González Gaitan, S.; Galbany, L.; Morales Garoffolo, A.; Greggio, L.; Guillou, L. L.; Hachinger, S.; Hadjiyska, E.; Hage, P. E.; Hillebrandt, W.; Hodgkin, S.; Hsiao, E. Y.; James, P. A.; Jerkstrand, A.; Kangas, T.; Kankare, E.; Kotak, R.; Kromer, M.; Kuncarayakti, H.; Leloudas, G.; Lundqvist, P.; Lyman, J. D.; Hook, I. M.; Maguire, K.; Manulis, I.; Margheim, S. J.; Mattila, S.; Maund, J. R.; Mazzali, P. A.; McCrum, M.; McKinnon, R.; Moreno Raya, M. E.; Nicholl, M.; Nugent, P.; Pain, R.; Pignata, Giuliano; Phillips, M. M.; Polshaw, J.; Pumo, M. L.; Rabinowitz, D.; Reilly, E.; Scalzo, R.; Schmidt, B.; Sim, S.; Sollerman, J.; Taddia, F.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Turatto, M.; Walker, E.; Walton, N. A.; Wyrzykowski, L.; Yuan, F.; Zampieri, L.
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    The delay of shock breakout due to circumstellar material evident in most type II supernovae
    (2018) Forster, F.; Moriya, T. J.; Maureira, J. C.; Anderson, J. P.; Blinnikov, S.; Bufano, F.; Cabrera Vives, G.; Clocchiatti, Alejandro; De Jaeger, T.; Estevez, P. A.; Galbany, L.; González -Gaitán, S.; Grafener, G.; Hamuy, M.; Hsiao, E. Y.; Huentelemu, P.; Huijse, P.; Kuncarayakti, H.; Martínez, J.; Medina, G.; Olivares, F.; Pignata, Giuliano; Razza, A.; Reyes, I.; San Martín, J.; Smith, R. C.; Vera, E.; Vivas, A. K.; Postigo, A. D.; Yoon, S. C.; Ashall, C.; Fraser, M.; Gal-Yam, A.; Kankare, E.; Le Guillou, L.; Mazzali, P. A.; Walton, N. A.; Young, D. R.
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    The young and nearby normal type Ia supernova 2018gv : UV-optical observations and the earliest spectropolarimetry
    (2020) Yang, Y.; Hoeflich, P.; Baade, D.; Maund J. R.; Wang, L.; Brown, P. J.; Stevance, H. F.; Arcavi, I.; Burke, J.; Clocchiatti, Alejandro; Cikota, A.; Gal-Yam, A.; Graham, M. L.; Hiramatsu, D.; Hosseinzadeh, G.; Howell, D. A.; Jha, S. W.; McCully, C.; Patat, F.; Sand, D. J.; Schulze, S.; Spyromilio, J.; Valenti, S.; Vinkó, J.; Wang, X.; Wheeler, J. C.; Yaron, O.; Zhang, J.