Microlensing of γ\gamma-Ray Burst Afterglows

The afterglow of a cosmological Gamma-Ray Burst (GRB) should appear on the sky as a narrow emission ring of radius 3x10^{16}cm(t/day)^{5/8} which expands faster than light. After a day, the ring radius is comparable to the Einstein radius of a solar mass lens at a cosmological distance. Thus, microlensing by an intervening star can modify significantly the lightcurve and polarization signal from a GRB afterglow. We show that the achromatic amplification signal of the afterglow flux can be used to determine the impact parameter and expansion rate of the source in units of the Einstein radius of the lens, and probe the superluminal nature of the expansion. If the synchrotron emission from the afterglow photosphere originates from a set of coherent magnetic field patches, microlensing would induce polarization variability due to the transient magnification of the patches behind the lens. The microlensing interpretation of the flux and polarization data can be confirmed by a parallax experiment which would probe the amplification peak at different times. The fraction of microlensed afterglows can be used to calibrate the density parameter of stellar-mass objects in the Universe.Comment: 12 pages, latex, 2 figures, submitted to ApJ

Spectral features in isolated neutron stars induced by inhomogeneous surface temperatures

The thermal X-ray spectra of several isolated neutron stars display deviations from a pure blackbody. The accurate physical interpretation of these spectral features bears profound implications for our understanding of the atmospheric composition, magnetic field strength and topology, and equation of state of dense matter. With specific details varying from source to source, common explanations for the features have ranged from atomic transitions in the magnetized atmospheres or condensed surface, to cyclotron lines generated in a hot ionized layer near the surface. Here we quantitatively evaluate the X-ray spectral distortions induced by inhomogeneous temperature distributions of the neutron star surface. To this aim, we explore several surface temperature distributions, we simulate their corresponding general relativistic X-ray spectra (assuming an isotropic, blackbody emission), and fit the latter with a single blackbody model. We find that, in some cases, the presence of a spurious 'spectral line' is required at a high significance level in order to obtain statistically acceptable fits, with central energy and equivalent width similar to the values typically observed. We also perform a fit to a specific object, RX J0806.4-4123, finding several surface temperature distributions able to model the observed spectrum. The explored effect is unlikely to work in all sources with detected lines, but in some cases it can indeed be responsible for the appearance of such lines. Our results enforce the idea that surface temperature anisotropy can be an important factor that should be considered and explored also in combination with more sophisticated emission models like atmospheres.Comment: 11 pages, 7 figures; accepted for publication in MNRA

Identifying the Environment and Redshift of GRB Afterglows from the Time-Dependence of Their Absorption Spectra

The discovery of Gamma-Ray Burst (GRB) afterglows revealed a new class of variable sources at optical and radio wavelengths. At present, the environment and precise redshift of the detected afterglows are still unknown. We show that if a GRB source resides in a compact (<100pc) gas-rich environment, the afterglow spectrum will show time-dependent absorption features due to the gradual ionization of the surrounding medium by the afterglow radiation. Detection of this time-dependence can be used to constrain the size and density of the surrounding gaseous system. For example, the MgII absorption line detected in GRB970508 should have weakened considerably during the first month if the absorption occurred in a gas cloud of size <100pc around the source. The time-dependent HI or metal absorption features provide a precise determination of the GRB redshift.Comment: 13 pages, 4 figures, submitted to ApJ

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

Population Synthesis of Isolated Neutron Stars with magneto-rotational evolution II: from radio-pulsars to magnetars

Population synthesis studies constitute a powerful method to reconstruct the birth distribution of periods and magnetic fields of the pulsar population. When this method is applied to populations in different wavelengths, it can break the degeneracy in the inferred properties of initial distributions that arises from single-band studies. In this context, we extend previous works to include $X$-ray thermal emitting pulsars within the same evolutionary model as radio-pulsars. We find that the cumulative distribution of the number of X-ray pulsars can be well reproduced by several models that, simultaneously, reproduce the characteristics of the radio-pulsar distribution. However, even considering the most favourable magneto-thermal evolution models with fast field decay, log-normal distributions of the initial magnetic field over-predict the number of visible sources with periods longer than 12 s. We then show that the problem can be solved with different distributions of magnetic field, such as a truncated log-normal distribution, or a binormal distribution with two distinct populations. We use the observational lack of isolated NSs with spin periods P>12 s to establish an upper limit to the fraction of magnetars born with B > 10^{15} G (less than 1\%). As future detections keep increasing the magnetar and high-B pulsar statistics, our approach can be used to establish a severe constraint on the maximum magnetic field at birth of NSs.Comment: 12 pages, 11 figures, 5 table

Are the therapeutic strategies in anorexia of ageing effective on nutritional status? A systematic review with meta-analysis

BACKGROUND: Anorexia of ageing (AA) may be considered as a risk factor for frailty and has an important impact on quality of life, morbidity and mortality. METHODS: A systematic review and a meta-analysis were performed to summarise the results from several trials on the effectiveness of treatments in AA, as associated with depression, sensory impairment of taste and smell, decreased appetite or early satiety, and disability. Eligible studies were required to report baseline and follow-up values, the mean change (∆-change) from baseline, and/or the mean difference among intervention groups versus control group, concerning food intake (kcal/daily) and/or nutritional outcomes, such as body weight, body mass index, albumin and Mini Nutritional Assessment. RESULTS: The systematic review included 20 papers based on different therapeutic approaches concerning food intake and/or nutritional outcomes. The results of the meta-analysis indicate that the interventions for AA have an important impact on body weight [+1.59 kg; 95% confidence interval (CI) = 1.48-+1.71 kg; P &lt; 0.001) and on energy intake (+56.09 kcal; 95% CI = -54.05 to +166.25 kcal; P = 0.32). Regarding secondary outcomes, it was not possible to meta-analyse the limited amount of data availab le. CONCLUSIONS: The different variants of AA need to be defined because diverse therapeutic approaches are available. A more precise definition of the functional impairments associated with AA may allow a more correct decision about the most appropriate therapy to be prescribed. Moreover, this may allow for a more effective performance of the different therapeutic approaches once they are better targeted to the different scenarios of AA

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

Magnetars vs. high magnetic field pulsars: a theoretical interpretation of the apparent dichotomy

Highly magnetized neutron stars (NSs) are characterized by a bewildering range of astrophysical manifestations. Here, building on our simulations of the evolution of magnetic stresses in the NS crust and its ensuing fractures (Perna & Pons 2011), we explore in detail, for the middle-age and old NSs, the dependence of starquake frequency and energetics on the relative strength of the poloidal (B_p) and toroidal (B_tor) components. We find that, for B_p >~10^{14}G, since a strong crustal toroidal field B_tor B_p is quickly formed on a Hall timescale, the initial toroidal field needs to be B_tor >> B_p to have a clear influence on the outbursting behaviour. For initial fields B_p <~ 10^{14}G, it is very unlikely that a middle-age (t~10^5 years) NS shows any bursting activity. This study allows us to solve the apparent puzzle of how NSs with similar dipolar magnetic fields can behave in a remarkably different way: an outbursting 'magnetar' with a high X-ray luminosity, or a quiet, low-luminosity, "high-$B$" radio pulsar. As an example, we consider the specific cases of the magnetar 1E2259+586 and the radio pulsar PSRJ1814-1744, which at present have a similar dipolar field ~6x10^{13}G. We determine for each object an initial magnetic field configuration that reproduces the observed timing parameters at their current age. The same two configurations also account for the differences in quiescent X-ray luminosity and for the 'magnetar/outbursting' behaviour of 1E2259+586 but not of PSRJ1814-1744. We further use the theoretically predicted surface temperature distribution to compute the light-curve for these objects. In the case of 1E2259+586, for which data are available, our predicted temperature distribution gives rise to a pulse profile whose double-peaked nature and modulation level is consistent with the observations.Comment: 8 pages emulateapj, 5 figures, accepted to Ap

Spectral variability on primitive asteroids of the Themis and Beagle families: space weathering effects or parent body heterogeneity?

Themis is an old and statistically robust asteroid family populating the outer main belt, and resulting from a catastrophic collision that took place 2.5$\pm$1.0 Gyr ago. Within the old Themis family a young sub-family, Beagle, formed less than 10 Myr ago, has been identified. We present the results of a spectroscopic survey in the visible and near infrared range of 22 Themis and 8 Beagle families members. The Themis members investigated exhibit a wide range of spectral behaviors, while the younger Beagle family members look spectrally bluer with a smaller spectral slope variability. The best meteorite spectral analogues found for both Themis and Beagle families members are carbonaceous chondrites having experienced different degrees of aqueous alteration, prevalently CM2 but also CV3 and CI, and some of them are chondrite samples being unusual or heated. We extended the spectral analysis including the data available in the literature on Themis and Beagle families members, and we looked for correlations between spectral behavior and physical parameters using the albedo and size values derived from the WISE data. The analysis of this larger sample confirm the spectral diversity within the Themis family and that Beagle members tend to be bluer and to have an higher albedo. The differences between the two family may be partially explained by space weathering processes, which act on these primitive surfaces in a similar way than on S-type asteroids, i.e. producing reddening and darkening. However we see several Themis members having albedos and spectral slopes similar to the young Beagle members. Alternative scenarios are proposed including heterogeneity in the parent body having a compositional gradient with depth, and/or the survival of projectile fragments having a different composition than the parent body.Comment: Manuscript pages: 40; Figures: 15 ; Tables: 4 Icarus (2016),in pres