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  • 2013  (41)
  • 1
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    Compacted tunable split-ring resonators (2013)
    American Institute of Physics
    Details
    Publication Date: 2013-10-14
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 2
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    Berkeley Supernova Ia Program - V. Late-time spectra of Type Ia Supernovae (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-02
    Description: In this work, we analyse late-time ( t  〉 100 d) optical spectra of low-redshift ( z  〈 0.1) Type Ia supernovae (SNe Ia) which come mostly from the Berkeley Supernova Ia Program (BSNIP) data set. We also present spectra of SN 2011 by for the first time. The BSNIP sample studied consists of 34 SNe Ia with 60 nebular spectra, to which we add nebular spectral feature measurements of 20 SNe Ia from previously published work (Maeda et al. and Blondin et al.), representing the largest set of late-time SN Ia spectra ever analysed. The full width at half-maximum intensity and velocities of the [Fe  iii ] 4701, [Fe  ii ] 7155 and [Ni  ii ] 7378 emission features are measured in most observations of spectroscopically normal objects where the data have signal-to-noise ratios 20 pixel –1 and are older than 160 d past maximum brightness. The velocities of all three features are seen to be relatively constant with time, increasing only a few to ~20 km s –1 d –1 . The nebular velocity ( v neb , calculated by taking the average of the [Fe  ii ] 7155 and [Ni  ii ] 7378 velocities) is correlated with the near-maximum-brightness velocity gradient and early-time ejecta velocity. Nearly all high velocity gradient objects have redshifted nebular lines while most low velocity gradient objects have blueshifted nebular lines. No correlation is found between v neb and m 15 ( B ), and for a given light-curve shape there is a large range of observed nebular velocities. The data also indicate a correlation between observed ( B  – V ) max and v neb .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    High-velocity features in Type Ia supernova spectra (2013)
    Oxford University Press
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    Publication Date: 2013-12-06
    Description: We use a sample of 58 low-redshift ( z  ≤ 0.03) Type Ia supernovae (SNe Ia) having well-sampled light curves and spectra near maximum light to examine the behaviour of high-velocity features (HVFs) in SN Ia spectra. We take advantage of the fact that Si ii 6355 is free of HVFs at maximum light in all SNe Ia, while HVFs are still strong in the Ca ii near-infrared feature in many SNe, allowing us to quantify the strength of HVFs by comparing the structure of these two lines. We find that the average HVF strength increases with decreasing light-curve decline rate, and rapidly declining SNe Ia ( m 15 ( B ) ≥ 1.4 mag) show no HVFs in their maximum-light spectra. Comparison of HVF strength to the light-curve colour of the SNe Ia in our sample shows no evidence of correlation. We find a correlation of HVF strength with the velocity of Si ii 6355 at maximum light ( v Si ), such that SNe Ia with lower v Si have stronger HVFs, while those SNe Ia firmly in the ‘high-velocity’ (i.e. v Si  ≥ 12 000 km s –1 ) subclass exhibit no HVFs in their maximum-light spectra. While v Si and m 15 ( B ) show no correlation in the full sample of SNe Ia, we find a significant correlation between these quantities in the subset of SNe Ia having weak HVFs. In general, we find that slowly declining (low m 15 ( B )) SNe Ia, which are more luminous and more energetic than average SNe Ia, tend to produce either high photospheric ejecta velocities (i.e. high v Si ) or strong HVFs at maximum light, but not both. Finally, we examine the evolution of HVF strength for a sample of SNe Ia having extensive pre-maximum spectroscopic coverage and find significant diversity of the pre-maximum HVF behaviour.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    An outburst from a massive star 40 days before a supernova explosion (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-02-08
    Description: Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae, as do several models. Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a mass-loss event detected 40 days before the explosion of the type IIn supernova SN 2010mc (also known as PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 x 10(47) erg of energy and releasing about 10(-2) solar masses of material at typical velocities of 2,000 km s(-1). The temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model, and disfavour alternative suggestions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ofek, E O -- Sullivan, M -- Cenko, S B -- Kasliwal, M M -- Gal-Yam, A -- Kulkarni, S R -- Arcavi, I -- Bildsten, L -- Bloom, J S -- Horesh, A -- Howell, D A -- Filippenko, A V -- Laher, R -- Murray, D -- Nakar, E -- Nugent, P E -- Silverman, J M -- Shaviv, N J -- Surace, J -- Yaron, O -- England -- Nature. 2013 Feb 7;494(7435):65-7. doi: 10.1038/nature11877.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel. eran@astro.caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23389540" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Evidence for two distinct populations of type Ia supernovae (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-03-09
    Description: Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here, we report that the spectral diversity of SNe Ia is tied to their birthplace environments. We found that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than do normal-velocity SNe Ia and are restricted to galaxies with substantial chemical evolution.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Xiaofeng -- Wang, Lifan -- Filippenko, Alexei V -- Zhang, Tianmeng -- Zhao, Xulin -- New York, N.Y. -- Science. 2013 Apr 12;340(6129):170-3. doi: 10.1126/science.1231502. Epub 2013 Mar 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Tsinghua University, Beijing, China. wang_xf@mail.tsinghua.edu.cn〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23470733" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Constraints on dark energy with the LOSS SN Ia sample (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-14
    Description: We present a cosmological analysis of the Lick Observatory Supernova Search (LOSS) Type Ia supernova (SN Ia) photometry sample introduced by Ganeshalingam et al. These supernovae (SNe) provide an effective anchor point to estimate cosmological parameters when combined with data sets at higher redshift. The data presented by Ganeshalingam et al. have been rereduced in the natural system of the Katzman Automatic Imaging Telescope (KAIT) and Nickel telescopes to minimize systematic uncertainties. We have run the light-curve-fitting software salt2 on our natural-system light curves to measure light-curve parameters for LOSS light curves and available SN Ia data sets in the literature. We present a Hubble diagram of 586 SNe in the redshift range z  = 0.01–1.4 with a residual scatter of 0.176 mag. Of the 226 low- z SNe Ia in our sample, 91 objects are from LOSS, including 45 without previously published distances. Assuming a flat Universe, we find that the best fit for the dark energy equation-of-state parameter w = –0.86 $^{+0.13}_{-0.16}$ (stat) ±0.11 (sys) from SNe alone, consistent with a cosmological constant. Our data prefer a Universe with an accelerating rate of expansion with 99.999 per cent confidence. When looking at Hubble residuals as a function of host-galaxy morphology, we do not see evidence for a significant trend, although we find a somewhat reduced scatter in Hubble residuals from SNe residing within a projected distance 〈10 kpc of the host-galaxy nucleus ( = 0.156 mag). Similar to the results of Blondin, Mandel and Kirshner and Silverman et al., we find that Hubble residuals do not correlate with the expansion velocity of Si ii 6355 measured in optical spectra near maximum light. Our data are consistent with no presence of a local ‘Hubble bubble.’ Improvements in cosmological analyses within low- z samples can be achieved by better constraining calibration uncertainties in the zero-points of photometric systems.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The unprecedented 2012 outburst of SN 2009ip: a luminous blue variable star becomes a true supernova (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-16
    Description: Some reports of supernova (SN) discoveries turn out not to be true core-collapse explosions. One such case was SN 2009ip, which was recognized to be the eruption of a luminous blue variable (LBV) star. This source had a massive (50–80 M ), hot progenitor star identified in pre-explosion data; it had documented evidence of pre-outburst variability and it was subsequently discovered to have a second outburst in 2010. In 2012, the source entered its third known outburst. Initial spectra showed the same narrow-line profiles as before, suggesting another LBV-like eruption. We present new photometry and spectroscopy of SN 2009ip, indicating that the 2012 outburst transitioned into a genuine SN explosion. The most striking aspect of these data is that unlike any previous episodes, the spectrum developed Balmer lines with very broad P-Cygni profiles characteristic of normal Type II supernovae (SNe II), in addition to overlying narrow emission components. The emission lines exhibit unprecedented (for any known non-terminal LBV-like eruption) full width at half-maximum intensity values of ~8000 km s –1 , while the absorption components seen just before the main brightening had blue wings extending out to –13 000 km s –1 . These velocities are typical of core-collapse SN explosions, but have never been associated with emission lines from a non-terminal LBV-like eruption. SN 2009ip is the first object to have both a known massive blue progenitor star and LBV-like eruptions with accompanying spectra observed a few years prior to becoming a SN. Immediately after the broad lines first appeared, the peak absolute magnitude of M V  –14.5 was fainter than that of normal SNe II. However, after a brief period of fading, the source quickly brightened again to M R  = –17.5 mag in ~2 d, suggesting a causal link to the prior emergence of the broad-line spectrum. Once the bright phase began, the broad lines mostly disappeared, and the spectrum resembled the early optically thick phases of luminous SNe IIn. The source reached a peak brightness of –18 mag about 2 weeks later, after which broad emission lines again developed in the spectrum as the source faded. We conclude that the most recent 2012 outburst of SN 2009ip was the result of a true core-collapse SN IIn that occurred when the progenitor star was in an LBV-like outburst phase, and where the SN was initially faint and then rapidly brightened due to interaction with circumstellar material. The pulsational pair instability, LBV-like eruptions or other instabilities due to late nuclear burning phases in massive stars may have caused the multiple pre-SN eruptions.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    SN 2011ht: confirming a class of interacting supernovae with plateau light curves (Type IIn-P) (2013)
    Oxford University Press
    Details
    Publication Date: 2013-04-26
    Description: We present photometry and spectroscopy of the Type IIn supernova (SN) 2011ht, identified previously as a possible SN impostor. The light curve exhibits an abrupt transition from a well-defined ~120 d plateau to a steep bolometric decline, plummeting 4–5 mag in the optical and 2–3 mag in the infrared in only ~10 d. Leading up to peak brightness ( M V  = –17.4 mag), a hot emission-line spectrum exhibits strong signs of interaction with circumstellar material (CSM), in the form of relatively narrow P-Cygni features of H i and He i superimposed on broad Lorentzian wings. For the latter half of the plateau phase, the spectrum exhibits strengthening P-Cygni profiles of Fe ii , Ca ii and Hα. By day 147, after the plateau has ended, the SN entered the nebular phase, heralded by the appearance of forbidden transitions of [O i ], [O ii ] and [Ca ii ] over a weak continuum. At this stage, the light curve exhibits a low optical luminosity that is comparable to that of the most subluminous Type II-P supernovae, and a relatively fast visual wavelength decline that appeared to be significantly steeper than the 56 Co decay rate. However, the total pseudo-bolometric decline, including the infrared luminosity, is consistent with 56 Co decay, and implies a low 56 Ni mass in the range 0.006–0.01 M , near the lower end of the range exhibited by SNe II-P. We therefore characterize SN 2011ht as a core-collapse SN very similar to the peculiar SNe IIn 1994W and 2009kn. These three SNe appear to define a subclass, which are Type IIn based on their spectrum, but that also exhibit well-defined plateaus and produce low 56 Ni yields. We therefore suggest Type IIn-P as a name for this subclass. The absence of observational signatures of high-velocity material from SNe IIn-P could be the result of an opaque shell at the shocked SN-CSM interface, which remains optically thick longer than the time-scale for the inner ejecta to cool and become transparent. Possible progenitors of SNe IIn-P, consistent with the available data, include 8–10 M stars, which undergo core collapse as a result of electron capture after a brief phase of enhanced mass loss, or more massive ( M 25 M ) progenitors, which experience substantial fallback of the metal-rich radioactive ejecta. In either case, the energy radiated by these three SNe during their plateau (2–3  x 10 49  erg for SN 2011ht) must be dominated by CSM interaction, and the subluminous tail is the result of low 56 Ni yield.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Nebular spectroscopy of the nearby Type IIb supernova 2011dh (2013)
    Oxford University Press
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    Publication Date: 2013-11-30
    Description: We present nebular spectra of the nearby Type IIb supernova (SN) 2011dh taken between 201 and 678 d after core collapse. At these late times, SN 2011dh exhibits strong emission lines including a broad and persistent Hα feature. New models of the nebular spectra confirm that the progenitor of SN 2011dh was a low-mass giant ( M 13–15 M ) that ejected ~ 0.07 M of 56 Ni and ~ 0.27 M of oxygen at the time of explosion, consistent with the recent disappearance of a candidate yellow supergiant progenitor. We show that light from the SN location is dominated by the fading SN at very late times (~ 2 yr) and not, for example, by a binary companion or a background source. We present evidence for interaction between the expanding SN blast wave and a circumstellar medium at late times and show that the SN is likely powered by positron deposition 1 yr after explosion. We also examine the geometry of the ejecta and show that the nebular line profiles of SN 2011dh indicate a roughly spherical explosion with aspherical components or clumps.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    A HIGH-RESOLUTION SPECTROSCOPIC SEARCH FOR THE REMAINING DONOR FOR TYCHO'S SUPERNOVA (2013)
    Institute of Physics
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    Publication Date: 2013-08-21
    Print ISSN: 0004-637X
    Electronic ISSN: 1538-4357
    Topics: Physics
    Published by Institute of Physics
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