How much radioactive nickel does ASASSN-15lh require?

The discovery of the most luminous supernova ASASSN-15lh triggered a shock-wave in the supernova community. The three possible mechanisms proposed for the majority of other superluminous supernovae do not produce a realistic physical model for this particular supernova. In the present study we show the limiting luminosity available from a nickel-powered pair-instability supernova. We computed a few exotic nickel-powered explosions with a total mass of nickel up to 1500 solar masses. We used the hydrostatic configurations prepared with the GENEVA and MESA codes, and the STELLA radiative-transfer code for following the explosion of these models. We show that 1500 solar masses of radioactive nickel is needed to power a luminosity of 2x10^45 erg/s. The resulting light curve is very broad and incompatible with the shorter ASASSN-15lh time-scale. This rules out a nickel-powered origin of ASASSN-15lh. In addition, we derive a simple peak luminosity - nickel mass relation from our data, which may serve to estimate of nickel mass from observed peak luminosities.Comment: accepted for publication in MNRAS Letter

Assessment of foam fracture in sandwich beams using thermoelastic stress analysis

Thermoelastic Stress Analysis (TSA) has been well established for determining crack-tip parameters in metallic materials. This paper examines its ability to determine accurately the crack-tip parameters for PVC foam used in sandwich structures

Local reionizations histories with merger tree of HII regions

We constrain the initial stage of the reionization process around progenitors of galaxies, such as the extent of the initial HII region before its fusion with the UV background and the duration of its propagation. We use a set of reionisation simulations with different resolutions and ionizing source recipes. A catalog of the HII regions properties is built thanks to a merger tree of HII regions. We draw local reionization histories as a function of time and investigate variations according to the halo mass progenitors of the regions. We then extrapolate the halo mass inside the region from high z to z=0 to make predictions about the reionization histories of z=0 galaxies. We found that the later an HII region appears, the smaller will be its related lifetime and volume before it sees the global UV background. Quantitatively the duration and the extent of the initial growth of an HII region is strongly dependent on the mass of the inner halo and can be as long as 50 % of the reionization epoch. We found that the most massive is a halo today, the earlier it appears and the larger are the extension and the duration of propagation of its HII region. Quantitative predictions differ depending on the box size or the source model: small simulated volumes are affected by proximity effects between HII regions and halo-based source models predict smaller regions and slower I-front expansion than in models using star particles as ionizing sources. Our results suggests that Milky Way-type halos have a maximal extent of 1.1 Mpc/h for the initial HII region that established itself in 150-200$\pm 20$ Myrs. This is consistent with prediction made using constrained Local Group simulation. Considering halos with masses comparable to those of the Local Group (MW+M31), our result suggests that statistically it has not been influenced by an external front coming from a Virgo-like cluster.Comment: 16 pages, 9 figures, Accepted for publication in A&

Systematic Derivation of Amplitude Equations and Normal Forms for Dynamical Systems

We present a systematic approach to deriving normal forms and related amplitude equations for flows and discrete dynamics on the center manifold of a dynamical system at local bifurcations and unfoldings of these. We derive a general, explicit recurrence relation that completely determines the amplitude equation and the associated transformation from amplitudes to physical space. At any order, the relation provides explicit expressions for all the nonvanishing coefficients of the amplitude equation together with straightforward linear equations for the coefficients of the transformation. The recurrence relation therefore provides all the machinery needed to solve a given physical problem in physical terms through an amplitude equation. The new result applies to any local bifurcation of a flow or map for which all the critical eigenvalues are semisimple i.e. have Riesz index unity). The method is an efficient and rigorous alternative to more intuitive approaches in terms of multiple time scales. We illustrate the use of the method by deriving amplitude equations and associated transformations for the most common simple bifurcations in flows and iterated maps. The results are expressed in tables in a form that can be immediately applied to specific problems.Comment: 40 pages, 1 figure, 4 tables. Submitted to Chaos. Please address any correspondence by email to [email protected]

Search for composite and exotic fermions at LEP 2

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermio

A study of simulated histories of reionization with merger trees of HII regions

We describe a new methodology to analyze the reionization process in numerical simulations: the chronology and the geometry of reionization is investigated by means of merger histories of individual HII regions. From the merger tree of ionized patches, one can track the individual evolution of the regions properties such as e.g. their size, or the intensity of the percolation process by looking at the formation rate, the frequency of mergers and the number of individual HII regions involved in the mergers. We apply the merger tree technique to simulations of reionization with three different kinds of ionizing source models and two resolutions. Two of them use star particles as ionizing sources. In this case we confront two emissivity evolutions for the sources in order to reach the reionization at z ~ 6. As an alternative we built a semi-analytical model where the dark matter halos extracted from the density fields are assumed as ionizing sources. We then show how this methodology is a good candidate to quantify the impact of the adopted star formation on the history of the observed reionization. The semi-analytical model shows a homogeneous reionization history with 'local' hierarchical growth steps for individual HII regions. On the other hand auto-consistent models for star formation tend to present fewer regions with a dominant region in size which governs the fusion process early in the reionization at the expense of the 'local' reionizations. The differences are attenuated when the resolution of the simulation is increased.Comment: Accepted for publication in A&

Analysis of Fermi gamma-ray burst duration distribution

Two classes of GRBs, short and long, have been determined without any doubts, and are usually prescribed to different physical scenarios. A third class, intermediate in $T_{90}$ durations, has been reported to be present in the datasets of BATSE, Swift, RHESSI and possibly BeppoSAX. The latest release of $>1500$ GRBs observed by Fermi gives an opportunity to further investigate the duration distribution. The aim of this paper is to investigate whether a third class is present in the $\log T_{90}$ distribution, or is it described by a bimodal distribution. A standard $\chi^2$ fitting of a mixture of Gaussians is applied to 25 histograms with different binnings. Different binnings give various values of the fitting parameters, as well as the shape of the fitted curve. Among five statistically significant fits none is trimodal. Locations of the Gaussian components are in agreement with previous works. However, a trimodal distribution, understood in the sense of having three separated peaks, is not found for any binning. It is concluded that the duration distribution in Fermi data is well described by a mixture of three log-normal distributions, but it is intrinsically bimodal, hence no third class is present in the $T_{90}$ data of Fermi. It is suggested that the log-normal fit may not be an adequate model.Comment: 6 pages, 3 figures; matches the version to be publishe