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Childress M.J.,Australian National University | Scalzo R.A.,Australian National University | Sim S.A.,Australian National University | Sim S.A.,Queen's University of Belfast | And 58 more authors.
Astrophysical Journal | Year: 2013

We present 65 optical spectra of the Type Ia SN 2012fr, 33 of which were obtained before maximum light. At early times, SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II λ6355 line that can be cleanly decoupled from the lower velocity "photospheric" component. This Si II λ6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of 12,000 km s-1 until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at v 12,000 km s-1 with narrow line width and long velocity plateau, as well as an HVF beginning at v 31,000 km s-1 two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. classification scheme, and on the border between normal and high-velocity Type Ia supernovae (SNe Ia) in the Wang et al. system. Though it is a clear member of the "low velocity gradient" group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution and a key transitional event between nominal spectroscopic subclasses of SNe Ia. © 2013. The American Astronomical Society. All rights reserved..


Joyce M.,CNRS Laboratory for Nuclear and High-Energy Physics | Morand J.,CNRS Laboratory for Nuclear and High-Energy Physics | Morand J.,National Institute for Theoretical Physics NITheP | Morand J.,Stellenbosch University | And 2 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

Isolated long-range interacting particle systems appear generically to relax to nonequilibrium states ("quasistationary states" or QSSs) which are stationary in the thermodynamic limit. A fundamental open question concerns the "robustness" of these states when the system is not isolated. In this paper we explore, using both analytical and numerical approaches to a paradigmatic one-dimensional model, the effect of a simple class of perturbations. We call them "internal local perturbations" in that the particle energies are perturbed at collisions in a way which depends only on the local properties. Our central finding is that the effect of the perturbations is to drive all the very different QSSs we consider towards a unique QSS. The latter is thus independent of the initial conditions of the system, but determined instead by both the long-range forces and the details of the perturbations applied. Thus in the presence of such a perturbation the long-range system evolves to a unique nonequilibrium stationary state, completely different from its state in absence of the perturbation, and it remains in this state when the perturbation is removed. We argue that this result may be generic for long-range interacting systems subject to perturbations which are dependent on the local properties (e.g., spatial density or velocity distribution) of the system itself. © 2016 American Physical Society.


Fraser M.,Queen's University of Belfast | Inserra C.,Queen's University of Belfast | Jerkstrand A.,Queen's University of Belfast | Kotak R.,Queen's University of Belfast | And 38 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present ultraviolet, optical and near-infrared observations of the interacting transient SN 2009ip, covering the period from the start of the outburst in 2012 October until the end of the 2012 observing season. The transient reached a peak magnitude of MV =-17.7mag, with a total integrated luminosity of 1.9 × 1049 erg over the period of 2012 August-December. The light curve fades rapidly, dropping by 4.5 mag from the V-band peak in 100 d. The optical and near-infrared spectra are dominated by narrow emission lines with broad electron scattering wings, signalling a dense circumstellar environment, together with multiple components of broad emission and absorption in H and He at velocities in the range 0.5-1.2 × 104 km s-1. We see no evidence for nucleosynthesized material in SN 2009ip, even in late-time pseudonebular spectra. We set a limit of<0.02Mȯ on themass of any possible synthesized 56Ni from the late-time light curve. A simple model for the narrow Balmer lines is presented and used to derive number densities for the circumstellar medium in the range ~109-1010cm. Our near-infrared data do not show any excess at longer wavelengths, and we see no other signs of dust formation. Our last data, taken in 2012 December, show that SN 2009ip has spectroscopically evolved to something quite similar to its appearance in late 2009, albeit with higher velocities. It is possible that neither of the eruptive and high-luminosity events of SN 2009ip were induced by a core collapse. We show that the peak and total integrated luminosity can be due to the efficient conversion of kinetic energy from colliding ejecta, and that around 0.05-0.1 Mȯ of material moving at 0.5-1 × 104 km s-1 could comfortably produce the observed luminosity. We discuss the possibility that these shells were ejected by the pulsational pair instability mechanism, in which case the progenitor star may still exist, and will be observed after the current outburst fades. The long-term monitoring of SN 2009ip, due to its proximity, has given the most extensive data set yet gathered of a high-luminosity interacting transient and its progenitor. It is possible that some purported Type IIn supernovae are in fact analogues of the 2012b event and that pre-explosion outbursts have gone undetected. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Soulez F.,University of Lyon | Soulez F.,French National Center for Scientific Research | Bongard S.,CNRS Laboratory for Nuclear and High-Energy Physics | Thiebaut E.,French National Center for Scientific Research | Bacon R.,French National Center for Scientific Research
Workshop on Hyperspectral Image and Signal Processing, Evolution in Remote Sensing | Year: 2011

In this paper we present a method for hyper-spectral image restoration for integral field spectrographs (IFS) data. It takes advantage of all the spectral and spatial correlations in the observed scene to enhance the spatial resolution. We illustrate this method with simulations coming from the Multi Unit Spectroscopic Explorer (MUSE) instrument. It shows the clear increase of the spatial resolution provided by our method as well as its denoising capability. © 2011 IEEE.


Labini F.S.,Centro Studi e Ricerche Enrico Fermi | Labini F.S.,CNR Institute for Complex Systems | Benhaiem D.,Centro Studi e Ricerche Enrico Fermi | Benhaiem D.,CNR Institute for Complex Systems | Joyce M.,CNRS Laboratory for Nuclear and High-Energy Physics
Monthly Notices of the Royal Astronomical Society | Year: 2015

Initially cold and spherically symmetric self-gravitating systems may give rise to a virial equilibrium state which is far from spherically symmetric, and typically triaxial. We focus here on how the degree of symmetry breaking in the final state depends on the initial density profile. We note that the most asymmetric structures result when, during the collapse phase, there is a strong injection of energy preferentially into the particles which are localized initially in the outer shells. These particles are still collapsing when the others, initially located in the inner part, are already re-expanding; the motion of particles in a time varying potential allow them to gain kinetic energy - in some cases enough to be ejected from the system. We show that this mechanism of energy gain amplifies the initial small deviations from perfect spherical symmetry due to finite N fluctuations. This amplification is more efficient when the initial density profile depends on radius, because particles have a greater spread of fall times compared to a uniform density profile, for which very close to symmetric final states are obtained. These effects lead to a distinctive correlation of the orientation of the final structure with the distribution of ejected mass, and also with the initial (very small) angular fluctuations. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Benetti S.,National institute for astrophysics | Nicholl M.,Queen's University of Belfast | Cappellaro E.,National institute for astrophysics | Pastorello A.,National institute for astrophysics | And 28 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present optical photometry and spectra of the superluminous Type II/IIn supernova (SN) CSS121015:004244+132827 (z = 0.2868) spanning epochs from -30 d (rest frame) to more than 200 d after maximum. CSS121015 is one of the more luminous SNe ever found and one of the best observed. The photometric evolution is characterized by a relatively fast rise to maximum (~40 d in the SN rest frame), and by a linear post-maximum decline. The light curve shows no sign of a break to an exponential tail. A broad Hα is first detected at ~+40 d (rest frame). Narrow, barely resolved Balmer and [O iii] 5007 Å lines, with decreasing strength, are visible along the entire spectral evolution. The spectra are very similar to other superluminous supernovae (SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes considered Type Ia interacting with H-rich circumstellar medium. The spectra are also similar to a subsample of H-deficient SLSNe. We propose that the properties of CSS121015 are consistent with the interaction of the ejecta with a massive, extended, opaque shell, lost by the progenitor decades before the final explosion, although a magnetar-powered model cannot be excluded. Based on the similarity of CSS121015 with other SLSNe (with and without H), we suggest that the shocked-shell scenario should be seriously considered as a plausible model for both types of SLSN. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Gabrielli A.,CNR Institute for Complex Systems | Gabrielli A.,University of Rome La Sapienza | Joyce M.,CNRS Laboratory for Nuclear and High-Energy Physics | Morand J.,CNRS Laboratory for Nuclear and High-Energy Physics
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We explore the conditions on a pair interaction for the validity of the Vlasov equation to describe the dynamics of an interacting N-particle system in the large N limit. Using a coarse graining in phase space of the exact Klimontovich equation for the N-particle system, we evaluate, neglecting correlations of density fluctuations, the scalings with N of the terms describing the corrections to the Vlasov equation for the coarse-grained one-particle phase space density. Considering a generic interaction with radial pair force F(r), with F(r)∼1/rγ at large scales, and regulated to a bounded behavior below a "softening" scale, we find that there is an essential qualitative difference between the cases γd, i.e., depending on the the integrability at large distances of the pair force. In the former case, the corrections to the Vlasov dynamics for a given coarse-grained scale are essentially insensitive to the softening parameter , while for γ>d the amplitude of these terms is directly regulated by , and thus by the small scale properties of the interaction. This corresponds to a simple physical criterion for a basic distinction between long-range (γ≤d) and short-range (γ>d) interactions, different from the canonical one (γ≤d+1 or γ>d+1) based on thermodynamic analysis. This alternative classification, based on purely dynamical considerations, is relevant notably to understanding the conditions for the existence of so-called quasistationary states in long-range interacting systems. © 2014 American Physical Society.


Joyce M.,CNRS Laboratory for Nuclear and High-Energy Physics | Morand J.,CNRS Laboratory for Nuclear and High-Energy Physics | Sicard F.,University Paul Sabatier | Viot P.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review Letters | Year: 2014

Hamiltonian systems with long-range interactions give rise to long-lived out-of-equilibrium macroscopic states, so-called quasistationary states. We show here that, in a suitably generalized form, this result remains valid for many such systems in the presence of dissipation. Using an appropriate mean-field kinetic description, we show that models with dissipation due to a viscous damping or due to inelastic collisions admit "scaling quasistationary states," i.e., states that are quasistationary in rescaled variables. A numerical study of one-dimensional self-gravitating systems confirms the relevance of these solutions and gives indications of their regime of validity in line with theoretical predictions. We underline that the velocity distributions never show any tendency to evolve towards a Maxwell-Boltzmann form. © 2014 American Physical Society.


PubMed | CNRS Laboratory for Nuclear and High-Energy Physics and CNRS Laboratory of Theoretical Physics and Condensed Matter
Type: Journal Article | Journal: Physical review. E | Year: 2016

Isolated long-range interacting particle systems appear generically to relax to nonequilibrium states (quasistationary states or QSSs) which are stationary in the thermodynamic limit. A fundamental open question concerns the robustness of these states when the system is not isolated. In this paper we explore, using both analytical and numerical approaches to a paradigmatic one-dimensional model, the effect of a simple class of perturbations. We call them internal local perturbations in that the particle energies are perturbed at collisions in a way which depends only on the local properties. Our central finding is that the effect of the perturbations is to drive all the very different QSSs we consider towards a unique QSS. The latter is thus independent of the initial conditions of the system, but determined instead by both the long-range forces and the details of the perturbations applied. Thus in the presence of such a perturbation the long-range system evolves to a unique nonequilibrium stationary state, completely different from its state in absence of the perturbation, and it remains in this state when the perturbation is removed. We argue that this result may be generic for long-range interacting systems subject to perturbations which are dependent on the local properties (e.g., spatial density or velocity distribution) of the system itself.


PubMed | CNRS Laboratory for Nuclear and High-Energy Physics, CNRS Laboratory of Theoretical Physics and Condensed Matter and CNRS Laboratory for Theoretical Physics
Type: Journal Article | Journal: Physical review letters | Year: 2014

Hamiltonian systems with long-range interactions give rise to long-lived out-of-equilibrium macroscopic states, so-called quasistationary states. We show here that, in a suitably generalized form, this result remains valid for many such systems in the presence of dissipation. Using an appropriate mean-field kinetic description, we show that models with dissipation due to a viscous damping or due to inelastic collisions admit scaling quasistationary states, i.e., states that are quasistationary in rescaled variables. A numerical study of one-dimensional self-gravitating systems confirms the relevance of these solutions and gives indications of their regime of validity in line with theoretical predictions. We underline that the velocity distributions never show any tendency to evolve towards a Maxwell-Boltzmann form.

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