Jets in GRBs: Tests and Predictions for the Structured Jet Model

The two leading interpretations of achromatic breaks that are observed in the light curves of GRBs afterglow are (i) the manifestation of the edge of a jet, which has a roughly uniform energy profile and a sharp edge and (ii) a line of sight effect in jets with a variable energy profile. The first scenario requires the inner engine to produce a jet with a different opening angle each explosion, while the latter requires a standard engine. The physical structure of the jet is a crucial factor in understanding GRB progenitors, and therefore discriminating the two jet scenarios is particularly relevant. In the structured jet case, specific predictions can be made for the distribution of observed break angles $\theta_{\rm break}$, while that distribution is arbitrary in the first scenario. We derive the theoretical distribution for the structured jet model. Specifically, we predict the most common angle to be about 0.12 rad, in rough agreement with the sample. If this agreement would hold as the sample size increases, it would strengthen the case for the standard jet hypothesis. We show that a prediction of this model is that the average viewing angle is an increasing function of the survey sensitivity, and in particular that a mission like {\em Swift} will find the typical viewing angle to be about 0.3 rad. The local event rate predicted by this model is $R_{\rm GRB}(z=0)\sim 0.5$ Gpc$^{-3}$ yr$^{-1}$.Comment: 14 pages, 3 figures; accepted to Ap

A Self-Similar Solution for the Propagation of a Relativistic Shock in an Exponential Atmosphere

We derive a fully relativistic, self-similar solution to describe the propagation of a shock along an exponentially decreasing atmosphere, in the limit of very large Lorentz factor. We solve the problem in planar symmetry and compute the acceleration of the shock in terms of the density gradient crossed during its evolution. We apply our solution to the acceleration of shocks within the atmosphere of a HyperNova, and show that velocities consistent with the requirements of GRB models can be achieved with exponential atmospheres spanning a wide density range.Comment: ApJL in pres

Refereeing the Referees: The Continuing Procedural Muddle in Cases of General Reference Pursuant to Ohio Rule of Civil Procedure 53

The judicial reference device set out in Rule 53 of the Ohio Rules of Civil Procedure was touted in 1974 as a procedure capable of relieving the problem of justice delayed by easing the increasing judicial burden on a besieged judiciary. While judicial reference is certainly no panacea for the problem (if numbers alone are a valid indicator), it is difficult to refute claims that the reference device contributes to a more efficient and speedy administration of justice

Deep VLT infrared observations of X-ray Dim Isolated Neutron Stars

X-ray observations have unveiled the existence of a family of radio-quiet Isolated Neutron Stars whose X-ray emission is purely thermal, hence dubbed X-ray Dim Isolated Neutron Stars (XDINSs). While optical observations have allowed to relate the thermal emission to the neutron star cooling and to build the neutron star surface thermal map, IR observations are critical to pinpoint a spectral turnover produced by a so far unseen magnetospheric component, or by the presence of a fallback disk. The detection of such a turnover can provide further evidence of a link between this class of isolated neutron stars and the magnetars, which show a distinctive spectral flattening in the IR. Here we present the deepest IR observations ever of five XDINSs, which we use to constrain a spectral turnover in the IR and the presence of a fallback disk. The data are obtained using the ISAAC instrument at the VLT. For none of our targets it was possible to identify the IR counterpart down to limiting magnitudes H = 21.5 - 22.9. Although these limits are the deepest ever obtained for neutron stars of this class, they are not deep enough to rule out the existence and the nature of a possible spectral flattening in the IR. We also derive, by using disk models, the upper limits on the mass inflow rate in a fallback disk. We find the existence of a putative fallback disk consistent (although not confirmed) with our observations.Comment: 6 pages, 2 figures, accepted by A&A on 26-06-200

UVES/VLT high resolution absorption spectroscopy of the GRB080330 afterglow: a study of the GRB host galaxy and intervening absorbers

We study the Gamma Ray Burst (GRB) environment and intervening absorbers by analyzing the optical absorption features produced by gas surrounding the GRB or along its line of sight. We analyzed high resolution spectroscopic observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which has at least four components in the main absorption system. We detect strong FeII, SiII, and NiII excited absorption lines associated with the bluemost component only. In addition to the host galaxy, at least two more absorbers lying along the line of sight to the afterglow have been detected in the redshift range 0.8 < z < 1.1, each exhibiting MgII absorption. For the bluemost component in the host galaxy, we derive information about its distance from the site of the GRB explosion. We do so by assuming that the excited absorption lines are produced by indirect UV pumping, and compare the data with a time dependent photo-excitation code. The distance of this component is found to be 280+40-50 pc, which is lower than found for other GRBs (1 - 6 kpc). We identify two additional MgII absorbers, one of them with a rest frame equivalent width larger than 1A. The distance between the GRB and the absorber measured in this paper confirms that the power of the GRB radiation can influence the conditions of the interstellar medium up to a distance of at least several hundred pc. For the intervening absorbers, we confirm the trend that on average one strong intervening system is found per afterglow, as has been noted in studies exhibiting an excess of strong MgII absorbers along GRB sightlines compared to quasars.Comment: 8 Pages, 7 ps figures, A&A in pres

Assessing energy efficiency: econometric evidence and implications for Italian energy policy

Energy efficiency represents one of the key objectives of the Clean Energy Package. In this context, EU member countries determine the optimal policies for energy efficiency. This papers aims to develop econometric evidence on country-level energy efficiency performance based on stochastic frontier analysis, with a specific focus on Italy’s efficiency levels. The analysis is based on data for a sample of 17 European companies over the period 1996-2016. Overall, Italy’s historical efficiency and performance ranking is consistently above the sample average and is on an increasing path since 2012. However, efficiency benchmarking shows that there may be scope for efficiency savings above and beyond the 2030 targets in the set out in the National Energy Plan. Disaggregate econometric analysis shows that part of these additional efficiency savings may stem from the industrial and residential sectors. To the authors’ knowledge, this is the first attempt to directly compare the efficiency assumptions in a National Action Plan using econometric benchmarking approaches

performance analysis of integrated systems based on mhd generators

Abstract Magnetohydrodynamic (MHD) power generation is considered an interesting energy conversion system because converts thermal energy into electrical energy without mechanically moving parts. In an MHD generator, a thermal plasma is moving across a magnetic field generating electric power. The heat source required to produce the high-speed gas flow can be supplied by the combustion of a fossil fuel or by using renewable source such as solar energy. The MHD efficiency is usually less than the conventional energy conversion systems (i.e. gas turbine combined cycle, steam power plant) but the availability of thermal power at high temperature can allow plant configurations with high overall efficiency. In this paper two plant configurations based on open-cycle MHD generators fed with coal are presented. The first one is a conventional configuration in which the plasma gas is the products of direct combustion of coal. The second one can be considered an advanced type because the working fluid is the combustion exhausts of syngas generated from coal gasification. In order to evaluate the energy suitability of the proposed systems, a performance analysis has been carried out by means of numerical modeling. Therefore, the operating conditions and the plant configurations for an efficient recovery of the thermal energy available from the MHD exhausts have been defined by a sensitivity analysis carried out varying the preheating temperature of air (or enriched air) sent to the combustion chamber. Results show that high system efficiencies (up to 60%) can be achieved by using the syngas due to a better heat recovery in the high temperature region