Evidence of two spectral breaks in the prompt emission of gamma ray bursts

The long-lasting tension between the observed spectra of gamma ray bursts (GRBs) and the predicted synchrotron emission spectrum might be solved if electrons do not completely cool. Evidence for incomplete cooling was recently found in Swift GRBs with prompt observations down to 0.1 keV and in one bright Fermi burst, GRB 160625B. Here we systematically search for evidence of incomplete cooling in the spectra of the ten brightest short and long GRBs observed by Fermi. We find that in 8/10 long GRBs there is compelling evidence of a low energy break (below the peak energy) and good agreement with the photon indices of the synchrotron spectrum (respectively -2/3 and -3/2 below the break and between the break and the peak energy). Interestingly, none of the ten short GRBs analysed shows a break but the low energy spectral slope is consistent with -2/3. In a standard scenario, these results imply a very low magnetic field in the emission region (B' ~ 10 G in the comoving frame), at odd with expectations.Comment: 14 pages, 15 figures, in press, accepted for publication in A&

Exact ground state Monte Carlo method for Bosons without importance sampling

Generally ``exact'' Quantum Monte Carlo computations for the ground state of many Bosons make use of importance sampling. The importance sampling is based, either on a guiding function or on an initial variational wave function. Here we investigate the need of importance sampling in the case of Path Integral Ground State (PIGS) Monte Carlo. PIGS is based on a discrete imaginary time evolution of an initial wave function with a non zero overlap with the ground state, that gives rise to a discrete path which is sampled via a Metropolis like algorithm. In principle the exact ground state is reached in the limit of an infinite imaginary time evolution, but actual computations are based on finite time evolutions and the question is whether such computations give unbiased exact results. We have studied bulk liquid and solid 4He with PIGS by considering as initial wave function a constant, i.e. the ground state of an ideal Bose gas. This implies that the evolution toward the ground state is driven only by the imaginary time propagator, i.e. there is no importance sampling. For both the phases we obtain results converging to those obtained by considering the best available variational wave function (the Shadow wave function) as initial wave function. Moreover we obtain the same results even by considering wave functions with the wrong correlations, for instance a wave function of a strongly localized Einstein crystal for the liquid phase. This convergence is true not only for diagonal properties such as the energy, the radial distribution function and the static structure factor, but also for off-diagonal ones, such as the one--body density matrix. From this analysis we conclude that zero temperature PIGS calculations can be as unbiased as those of finite temperature Path Integral Monte Carlo.Comment: 11 pages, 10 figure

Novel substrates for Helium adsorption: Graphane and Graphene-Fluoride

The discovery of fullerenes has stimulated extensive exploration of the resulting behavior of adsorbed films. Our study addresses the planar substrates graphene-fluoride (GF) and graphane (GH) in comparison to graphene. We present initial results concerning the potential energy, energy bands and low density behavior of 4He and 3He films on such different surfaces. For example, while graphene presents an adsorption potential that is qualitatively similar to that on graphite, GF and GH yield potentials with different symmetry, a number of adsorption sites double that on graphene/graphite and a larger corrugation for the adatom. In the case of GF, the lowest energy band width is similar to that on graphite but the He atom has a significantly larger effective mass and the adsorption energy is about three time that on graphite. Implications concerning the monolayer phase diagram of 4He are explored with the exact path integral ground state method. A commensurate ordered state similar to the sqrt{3} x sqrt{3} R30^o state on graphite is found the be unstable both on GF and on GH. The ground states of submonolayer 4He on both GF and GH are superfluids with a Bose Einstein condensate fraction of about 10%.Comment: 6 pages, 3 figures, LT26 proceedings, accepted for publication in Journal of Physics: Conference Serie

Long Gamma-Ray Bursts as standard candles

As soon as it was realized that long GRBs lie at cosmological distances, attempts have been made to use them as cosmological probes. Besides their use as lighthouses, a task that presents mainly the technological challenge of a rapid deep high resolution follow-up, researchers attempted to find the Holy Grail: a way to create a standard candle from GRB observables. We discuss here the attempts and the discovery of the Ghirlanda correlation, to date the best method to standardize the GRB candle. Together with discussing the promises of this method, we will underline the open issues, the required calibrations and how to understand them and keep them under control. Even though GRB cosmology is a field in its infancy, ongoing work and studies will clarify soon if and how GRBs will be able to keep up to the promises.Comment: To appear in the proceedings of the 16th Annual October Astrophysics Conference in Maryland "Gamma Ray Bursts in the Swift Era", eds. S. Holt, N. Gehrels & J. Nouse

T-violation in Kμ3K_{\mu3} decay in a general two-Higgs doublet model

We calculate the transverse muon polarization in the $K^+_{\mu3}$ process arising from the Yukawa couplings of charged Higgs boson in a general two-Higgs doublet model where spontaneous violation of CP is presentComment: 6 pages, latex, accepted for publication in Phys. Rev.

Continuous H2O2 production sustained by anodic O2 for the destruction of the antibiotic ampicillin by photoelectro-Fenton process in a rotating cylinder electrode reactor

Complete degradation of the antibiotic ampicillin (AMP) by photoelectro-Fenton (PEF) process has been addressed for the first time. Once produced from water oxidation at six Ti|IrO2 anodic plates, O2 was quickly transported by forced convection toward the central RCE, which consisted of a 316 stainless-steel cylinder covered with a (C-PTFE)-coated carbon cloth, thus ensuring the continuous production of H2O2 from the twoelectron O2 reduction reaction (ORR). The accumulated H2O2 reached a concentration of 83.3 mg L-1 H2O2 after 60 min in a 50 mM Na2SO4 solution at pH 3, operating at an RCE peripheral velocity U = 79.6 cm s-1 and fixed cathodic potential of Ecath = - 0.45 V vs. SHE. Furthermore, the optimum PEF conditions led to the complete destruction of 10 mg L-1 AMP in only 10 min upon addition of 0.4 mM Fe2+ as catalyst under UVA light irradiation, with a low electrolytic energy consumption of 0.211 kWh (g TOC)-1. In addition, the evolution of final carboxylic acids and inorganic ions over the electrolysis time was monitored by chromatographic and spectrophotometric techniques. PEF treatment clearly outperformed the anodic oxidation with (AO-H2O2) and the electro-Fenton (EF) processes, which opens the door to a sustainable and powerful electrochemical technology with no need for an air compressor for H2O2 production and viable under limitless sunlight irradiation

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO was determined by the flash-photolysis resonance fluorescence method to be 7.5 plus or minus 0.9 (2 sigma) times 10 to the minus 11th power cu cm/molecule sec at 298 K and to have a negligible temperature dependence. This rate which is more than 2000 times faster than the rate of Cl + CH4 indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratosphere ozone than previously believed. Ambient stratospheric ozone will depend less on the ambient chlorine amount and the predicted response to chlorine perturbations will be lessened. One-dimensional eddy-diffusion photochemical model calculations indicate a factor of 1.1 less sensitivity to chlorine than recently reported. For a steady-state CFM release at 1975 rates (750,000 tons/year) the eventual ozone depletion is now calculated to be 14%