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Hydrodynamic simulations provide a powerful, but computationally expensive, approach to study the interplay of dark matter and baryons in cosmological structure formation. Here, we introduce the EM ulating B aryonic E n R ichment (EMBER) Deep Learning framework to predict baryon fields based on dark matter-only simulations thereby reducing computational cost. EMBER comprises two network architectures, U-Net and Wasserstein Generative Adversarial Networks (WGANs), to predict 2D gas and H  i densities from dark matter fields. We design the conditional WGANs as stochastic emulators, such that multiple target fields can be sampled from the same dark matter input. For training we combine cosmological volume and zoom-in hydrodynamical simulations from the Feedback in Realistic Environments (FIRE) project to represent a large range of scales. Our fiducial WGAN model reproduces the gas and H  i power spectra within 10 per cent accuracy down to ∼10 kpc scales. Furthermore, we investigate the capability of EMBER to predict high resolution baryon fields from low resolution dark matter inputs through upsampling techniques. As a practical application, we use this methodology to emulate high-resolution H  i maps for a dark matter simulation of a |$L=100\, \text{Mpc}\, h^{ -1}$| comoving cosmological box. The gas content of dark matter haloes and the H  i column density distributions predicted by EMBER agree well with results of large volume cosmological simulations and abundance matching models. Our method provides a computationally efficient, stochastic emulator for augmenting dark matter only simulations with physically consistent maps of baryon fields. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio μ 1 / μ 2 = 0.37 , several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction (DR) with respect to an equivalent smooth channel, and the results compared with those available for super-hydrophobic surfaces (SHS). It is found that, due to the relatively high viscosity of the liquid locked in the substrate, the drag reduction offered by LIS is substantially lower than the corresponding SHS. When reported in terms of the streamwise slip length normalized in wall units, the amount of DR obtained by LIS in the ideal case of flat interface collapses on the SHS data. The interface dynamics has a detrimental effect on the performance, that becomes particularly severe when the pitch increases. The degradation of DR is well parametrized by the log-law shift of the velocity profile, that is found to be proportional to the difference between the virtual origin of the mean flow and that experienced by the overlying turbulence. [ABSTRACT FROM AUTHOR]

Leukodystrophies are rare genetic white matter disorders that have been regarded as mainly occurring in childhood. This perception has been altered in recent years, as a growing number of leukodystrophies have been described as having an onset in adulthood. Still, many adult patients presenting with white matter changes remain without a specific molecular diagnosis. We describe a novel adult onset leukodystrophy in 16 patients from eight families carrying one of four different stop-gain or frameshift dominant variants in the CST3 gene. Clinical and radiological features differ markedly from the previously described Icelandic cerebral amyloid angiopathy found in patients carrying p.Leu68Asn substitution in CST3. The clinical phenotype consists of recurrent episodes of hemiplegic migraine associated with transient unilateral focal deficits and slowly progressing motor symptoms and cognitive decline in mid to older adult ages. In addition, in some cases acute onset clinical deterioration led to a prolonged episode with reduced consciousness and even early death. Radiologically, pathognomonic changes are found at typical predilection sites involving the deep cerebral white matter sparing a periventricular and directly subcortical rim, the middle blade of corpus callosum, posterior limb of the internal capsule, middle cerebellar peduncles, cerebral peduncles and specifically the globus pallidus. Histopathologic characterization in two autopsy cases did not reveal angiopathy, but instead micro- to macrocystic degeneration of the white matter. Astrocytes were activated at early stages and later displayed severe degeneration and loss. In addition, despite the loss of myelin, elevated numbers of partly apoptotic oligodendrocytes were observed. A structural comparison of the variants in CST3 suggests that specific truncations of cystatin C result in an abnormal function, possibly by rendering the protein more prone to aggregation. Future studies are required to confirm the assumed effect on the protein and to determine pathophysiologic downstream events at the cellular level. [ABSTRACT FROM AUTHOR]

A three-dimensional high-fidelity numerical simulation of a small-scale solid rocket motor is carried out adopting the implicit large-eddy simulation (ILES) approach to investigate the coupling between vortex shedding and the acoustic modes of the motor chamber. The ONERA C1xb laboratory-scale model is considered at a firing time close to ignition, corresponding to a 3-mm-grain burned layer. The analysis focuses on the characterization of the unsteady pressure signature on the motor wall, with emphasis on the role played by turbulence on the level of pressure oscillations. It is found that the root mean square of the wall-pressure fluctuations obtained by ILES along the motor wall is in excellent agreement with the experimental data, which is contrary to the prediction of axisymmetric simulations. Fourier spectral analysis reveals that, for this grain geometry, the first three longitudinal modes are weakly excited at the motor head end and most of the energy is concentrated in the shear layer detaching from the grain edge, whose development in the motor chamber is characterized by the rollers breakup with subsequent transition to fine-scale turbulence. The spectrum highlights that the coupling between vortex shedding and pressure oscillations is locked on the third acoustic mode, in agreement with previous experimental observations and with the frequency predicted by a simple acoustic feedback loop model. [ABSTRACT FROM AUTHOR]

The joint observation of GW170817 and GRB170817A proved that binary neutron star (BNS) mergers are progenitors of short gamma-ray bursts (SGRBs): this established a direct link between the still unsettled SGRB central engine and the outcome of BNS mergers, whose nature depends on the equation of state (EOS) and on the masses of the NSs. We propose a novel method to probe the central engine of SGRBs based on this link. We produce an extended catalogue of BNS mergers by combining recent theoretically predicted BNS merger rate as a function of redshift and the NS mass distribution inferred from measurements of Galactic BNSs. We use this catalogue to predict the number of BNS systems ending as magnetars (stable or supramassive NS) or BHs (formed promptly or after the collapse of a hypermassive NS) for different EOSs, and we compare these outcomes with the observed rate of SGRBs. Despite the uncertainties mainly related to the poor knowledge of the SGRB jet structure, we find that for most EOSs the rate of magnetars produced after BNS mergers is sufficient to power all the SGRBs, while scenarios with only BHs as possible central engine seem to be disfavoured. [ABSTRACT FROM AUTHOR]

SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a Sino-French space mission dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade, capable to detect and localise the GRB emission, and to follow its evolution in the high-energy and X-ray domains, and in the visible and NIR bands. The satellite carries two wide-field high-energy instruments: a coded-mask gamma-ray imager (ECLAIRs; 4-150 keV), and a gamma-ray spectrometer (GRM; 15-5500 keV) that, together, will characterise the GRB prompt emission spectrum over a wide energy range. In this paper we describe the performances of the ECLAIRs and GRM system with different populations of GRBs from existing catalogues, from the classical ones to those with a possible thermal component superimposed to their non-thermal emission. The combination of ECLAIRs and the GRM will provide new insights also on other GRB properties, as for example the spectral characterisation of the subclass of short GRBs showing an extended emission after the initial spike. [ABSTRACT FROM AUTHOR]

From a comprehensive statistical analysis of Swift X-ray light curves of gamma-ray bursts (GRBs) collected from 2004 December to the end of 2010, we found a three-parameter correlation between the isotropic energy emitted in the rest-frame 1-104 keV energy band during the prompt emission (Eγ,iso), the rest-frame peak of the prompt emission energy spectrum (Epk), and the X-ray energy emitted in the rest-frame 0.3-30 keV observed energy band (EX,iso), computed excluding the contribution of the flares. In this paper, we update this correlation with the data collected until 2014 June, expanding the sample size with ~35 per cent more objects, where the number of short GRBs doubled. With this larger sample, we confirm the existence of a universal correlation that connects the prompt and afterglow properties of long and short GRBs. We show that this correlation does not depend on the X-ray light-curve morphology and that further analysis is necessary to firmly exclude possible biases derived by redshift measurements. In addition, we discuss about the behaviour of the peculiar objects as ultra-long GRBs and we propose the existence of an intermediate group between long and short GRBs. Interestingly, two GRBs with uncertain classification fall into this category. Finally, we discuss the physics underlying this correlation, in the contest of the efficiency of conversion of the prompt gamma-ray emission energy into the kinetic energy of the afterglow, the photospheric model, and the cannonball model. [ABSTRACT FROM AUTHOR]

High-redshift gamma-ray bursts (GRBs) offer several advantages when studying the distant Universe, providing unique information about the structure and properties of the galaxies in which they exploded. Spectroscopic identification with large ground-based telescopes has improved our knowledge of this kind of distant events. We present the multi-wavelength analysis of the high-z Swift GRB GRB 140515A (z = 6.327). The best estimate of the neutral hydrogen fraction of the intergalactic medium towards the burst is xHI ≤ 0.002. The spectral absorption lines detected for this event are the weakest lines ever observed in GRB afterglows, suggesting that GRB 140515A exploded in a very low-density environment. Its circum-burst medium is characterised by an average extinction (AV ~ 0.1) that seems to be typical of z ≥ 6 events. The observed multi-band light curves are explained either with a very hard injected spectrum (p = 1.7) or with a multi-component emission (p = 2.1). In the second case a long-lasting central engine activity is needed in order to explain the late time X-ray emission. The possible origin of GRB 140515A in a Pop III (or in a Pop II star with a local environment enriched by Pop III) massive star is unlikely. [ABSTRACT FROM AUTHOR]

We investigated the rest-frame spectral lags of two complete samples of bright long (50) and short (6) gamma-ray bursts (GRB) detected by Swift. We analysed the Swift/Burst Alert Telescope data through a discrete cross-correlation function fittedwith an asymmetric Gaussian function to estimate the lag and the associated uncertainty. We find that half of the long GRBs have a positive lag and half a lag consistent with zero. All short GRBs have lags consistent with zero. The distributions of the spectral lags for short and long GRBs have different average values. Limited by the small number of short GRBs, we cannot exclude at more than 2σ significance level that the two distributions of lags are drawn from the same parent population. If we consider the entire sample of long GRBs, we do not find evidence for a lag-luminosity correlation, rather the lag-luminosity plane appears filled on the left-hand side, thus suggesting that the lag-luminosity correlation could be a boundary. Short GRBs are consistent with the long ones in the lag-luminosity plane. [ABSTRACT FROM AUTHOR]

We investigate the scaling relation between the observed amount of absorption in the X-ray spectra of gamma-ray burst afterglows and the absorber redshift. Through dedicated numerical simulations of an ideal instrument, we establish that this dependence has a power-law shape with index 2.4. However, for real instruments, this value depends on their low-energy cut-off, spectral resolution and on the detector spectral response in general. We thus provide appropriate scaling laws for specific instruments. Finally, we discuss the possibility to measure the absorber redshift from X-ray data alone. We find that 105-106 counts in the 0.3–10 keV band are needed to constrain the redshift with 10 per cent accuracy. As a test case, we discuss the XMM–Newton observation of GRB 090618 at z = 0.54. We are able to recover the correct redshift of this burst with the expected accuracy. [ABSTRACT FROM AUTHOR]

Aims. We present a comprehensive analysis of the optical and X-ray light curves (LCs) and spectral energy distributions (SEDs) of a large sample of gamma-ray burst (GRB) afterglows to investigate the relationship between the optical and X-ray emission after the prompt phase. We consider all data available in the literature, which where obtained with different instruments. Methods. We collected the optical data from the literature and determined the shapes of the optical LCs. Then, using previously presented X-ray data, we modeled the optical/X-ray SEDs.We studied the SED parameter distributions and compared the optical and X-ray LC slopes and shapes. Results. The optical and X-ray spectra become softer as a function of time while the gas-to-dust ratios of GRBs are higher than the values calculated for the Milky Way and the Large and Small Magellanic Clouds. For 20% of the GRBs the difference between the optical and X-ray slopes is consistent with 0 or 1/4 within the uncertainties (we did it not consider the steep decay phase), while in the remaining 80% the optical and X-ray afterglows show significantly different temporal behaviors. Interestingly, we find an indication that the onset of the forward shock in the optical LCs (initial peaks or shallow phases) could be linked to the presence of the X-ray flares. Indeed, when X-ray flares are present during the steep decay, the optical LC initial peak or end plateau occurs during the steep decay; if instead the X-ray flares are absent or occur during the plateau, the optical initial peak or end plateau takes place during the X-ray plateau. Conclusions. The forward-shock model cannot explain all features of the optical (e.g. bumps, late re-brightenings) and X-ray (e.g. flares) LCs. However, the synchrotron model is a viable mechanism for GRBs at late times. In particular, we found a relationship between the presence of the X-ray flares and the shape of the optical LC that indicates a link between the prompt emission and the optical afterglow. [ABSTRACT FROM AUTHOR]

Abstract: We perform finite-difference numerical simulations of turbulent channel flow in stationary and moving reference frames. The flow statistics computed in the stationary frame exhibit significant discrepancies with respect to reference spectral data in terms of energy spectra and convection velocity of disturbances, especially in the near-wall region. On the other hand, simulations performed in a reference frame moving with the bulk flow velocity suffer from this shortcoming to a much lesser extent. We propose an explanation of these observations by assuming the scalar Burgers’ equation as working model. The analysis highlights the lack of Galilean invariance of finite-difference schemes, which exhibit a leading dispersive error in the presence of bulk advection. The numerically computed energy spectra exhibit the same features as the channel spectra, supporting the notion that dispersive effects are responsible for the blockage of the mechanism of energy cascade to high wavenumbers. [Copyright &y& Elsevier]

ABSTRACT The comprehensive statistical analysis of Swift X-ray light curves, collecting data from six years of operation, revealed the existence of a universal scaling among the isotropic energy emitted in the rest-frame 1 - 104 keV energy band during the prompt emission ( [ABSTRACT FROM AUTHOR]

Aims. We present the analysis of a large sample of gamma-ray burst (GRB) X-ray light curves in the rest frame to characterise their intrinsic properties in the context of different theoretical scenarios. Methods. We determine the morphology, timescales, and energetics of 64 long GRBs observed by Swift/XRT without flaring activity. We furthermore provide a one-to-one comparison to the properties of GRBs with X-ray flares. Results. We find that the steep decay morphology and its connection with X-ray flares favour a scenario in which a central engine origin. We show that this scenario can also account for the shallow decay phase, provided that the GRB progenitor star has a selfsimilar structure with a constant envelope-to-core mass ratio ∼0.02-0.03. However, difficulties arise for very long duration (tp ≳ 104 s) shallow phases. Alternatively, a spinning-down magnetar whose emitted power refreshes the forward shock can quantitatively account for the shallow decay properties. In particular we demonstrate that this model can account for the plateau luminosity vs. end time anticorrelation. [ABSTRACT FROM AUTHOR]

Observations of Gamma-ray Bursts (GRBs) put forward in the recent years have revealed, with increasing evidence, that the historical classification between long and short bursts has to be revised. Within the Fireshell scenario, both short and long bursts are canonical bursts, consisting of two different phases. First, a Proper-GRB (P-GRB), that is the emission of photons at the transparency of the fireshell. Then, the Extended Afterglow, multiwavelength emission due to the interacion of the baryonic remnants of the fireshell with the CircumBurst Medium (CBM). We discriminate between long and short bursts by the amount of energy stored in the first phase with respect to the second one. Within the Fireshell scenario, we have introduced a third intermediate class: the disguised GRBs. They appear like short bursts, because their morphology is characterized by a first, short, hard episode and a following deflated tail, but this last part - coincident with the peak of the afterglow - is energetically predominant. The origin of this peculiar kind of sources is inferred to a very low average density of the environment (of the order of 10-3). After GRB 970228 and GRB 060614, we find in GRB 071227 a third example of disguised burst. [ABSTRACT FROM AUTHOR]

The analysis of various Gamma-Ray Bursts (GRBs) having a low energetics (an isotropic energy Eiso ≲ 1053 ergs) within the fireshell model has shown how the N(E) spectrum of their prompt emission can be reproduced in a satisfactory way by a convolution of thermal spectra. Nevertheless, from the study of very energetic bursts (Eiso ≳ 1054 ergs) such as, for example, GRB 080319B, some discrepancies between the numerical simulations and the observational data have been observed. We investigate a different spectrum of photons in the comoving frame of the fireshell in order to better reproduce the spectral properties of GRB prompt emission within the fireshell model. We introduce a phenomenologically modified thermal spectrum: a thermal spectrum characterized by a different asymptotic power-law index in the low energy region. Such an index depends on a free parameter α, so that the pure thermal spectrum corresponds to the case α = 0. We test this spectrum by comparing the numerical simulations with the observed prompt emission spectra of various GRBs. From this analysis it has emerged that the observational data can be correctly reproduced by assuming a modified thermal spectrum with α = -1.8. [ABSTRACT FROM AUTHOR]

Sjögren–Larsson syndrome (SLS) is an autosomal recessively inherited neurocutaneous disorder characterized by the triad of congenital ichthyosis, mental deficiency, and spastic diplegia or tetraplegia. Less common features are retinal changes, short stature, kyphoscoliosis, preterm birth, photophobia, reduction of visual acuity, seizures, and delayed speech. SLS is characterized by a genetic block in the oxidation of fatty alcohol to fatty acid because of deficient activity of fatty aldehyde dehydrogenase (FALDH), a component of the fatty alcohol: NAD oxidoreductase enzyme complex. As in other rare multisystem diseases, the diagnosis of SLS is often delayed. The definitive test for SLS is considered the measurement of FALDH or fatty alcohol: NAD oxidoreductase in cultured skin fibroblasts. Nevertheless, if specific FALDH activity test or DNA FALDH gene mutation tests are not available (as in our country), a reliable diagnosis of SLS is also possible when it is based on the matching of peculiar clinical, histologic and ultrastructural, laboratoristic, and imaging features. The simultaneous presence of cutaneous histologic features including hyperkeratosis, orthokeratosis, thickening of granular layer, abnormal lamellar inclusions in the cytoplasm of granular and horny cells (demonstrated by light and electron microscopy) in a child with ichthyosis, and typical neurologic abnormalities is highly suggestive of SLS. We describe the case of a young Moroccan boy presenting with ichthyosis, mental retardation, spastic diplegia, and peculiar skin histologic findings. [ABSTRACT FROM AUTHOR]

The future of cancer research is no longer limited to epidemiological data and clinical management, but rather encompasses a new dimension of understanding, that involves genetics of the tumors themselves. This has been exemplified most prominently in hematological tumors where alterations at the DNA level have been found to play key roles in the pathophysiology, diagnosis, monitoring and prognosis of these tumors. It has been shown over the last 20 years that recurrent chromosomal rearrangements are strongly associated with the activation of oncogenes, acquisition of drug resistance and loss of tumor suppressor gene function. Chromosomal alterations have also been shown to characterize many solid tumors, including epithelial ovarian cancer [Cancer Res. 62 (2002) 3466; Cancer 91 (2001) 534; Genes Chromosomes Cancer 25 (1999) 290]. Despite these findings, however, there are currently few examples of specific cytogenetic studies that have contributed to the clinical management of solid tumors such as ovarian cancer. The limiting factor to date is the resolution of available techniques. With time, as the technology improves, so will our ability to focus on specific findings that may be applicable to future clinical management. The intention of this report is to familiarize the reader with the evolution of cytogenetic and molecular cytogenetic techniques used in the study of ovarian cancer, the early formulations from these studies and their use in answering specific clinical questions such as association with pathologic subtype, the relevance of drug resistance, the impact of BRCA mutations, and finally to guide the reader into the future of this ever growing field. [Copyright &y& Elsevier]

Examines the design of a preisolator stage for the VIRGO superattenuator. Specifications; Forces required to move the superattenuator acting on the inverted pendulum; Suitability for the active control of mirror suspension.

Presents information on a study which explored the effects of postweaning feeding of female rabbits on the performance and energy balance. Apparent digestibility and nutritive value of the experimental diets; Data collection and analysis; Results and discussion.

It's an incredibly important moment to focus on work-family scholarship – and to consider research related to 'just' work and care in unsettling and challenging times. Against this backdrop, the 2022 WFRN theme was established. The conference gathered members from around the world toward building impactful scholarship for practices and policy. In this Voices piece, we draw upon WFRN presidential panelists' voices. The first plenary, 'The Meanings of Work-Family Justice', provided opportunities for panelists to consider different ways to conceptualize and expand this idea as labor markets, workplaces, and many aspects of people's lives are in flux, with new understandings about how to think expansively about creating 'work-family justice', The second plenary – 'Work-Family Justice on the Ground' – featured panelists from leading non-profits who discuss how they've met challenges and succeeded in implementing and building policies that create a more just world of work and care. They discuss barriers and some ideas for overcoming difficulties. We conclude by considering the evolving meanings and practices of work-family justice. In all, the voices presented here help us focus on creating more 'just' worlds of work and care – a distinct and vital – if sometimes precarious – possibility in this moment. [ABSTRACT FROM AUTHOR]

Aerothermodynamics of space launchers operating at high altitudes (above 100 km) is characterized by complex physical processes that are related to the substantially higher air rarefaction with respect to lower altitudes. Consequently, the use of continuum methods to numerically simulate such flow conditions is questionable. In this study, the problem of proper assessment of the aerothermodynamic behavior of space launchers operating at high altitudes is analyzed considering Vega in its ascent flight, an actual space launcher that has already performed a number of successful flights. The direct simulation Monte Carlo molecular method is used to carry out the simulations. After a convergence analysis of the adopted numerical approach, a comparison of different air models is presented to highlight the effect of chemical reactions and molecules vibrational excitation. Then, a comparison of the flowfield around the Vega launcher is reported at two altitudes (113 and 127 km), where the third stage of the space launcher is not propelled. The analysis describes the effects of the atmospheric air rarefaction, which has significant repercussions on the bow-shock structure and the drag coefficient. Finally, the achieved solutions are compared with computational fluid dynamics (CFD) continuum solutions to show that a standard CFD approach is not able to represent the physical phenomenon under examination, due to the model's breakdown caused by the effects of rarefaction. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented regarding the case of a 67-year-old man who had itchy skin eruption, and was diagnosed to have mycosis fungoides.

This work investigates the self-excited shock-wave oscillations in a three-dimensional planar overexpanded nozzle turbulent flow by means of detached-eddy simulations. Time-resolved wall pressure measurements are used as primary diagnostics. The statistical analysis reveals that the shock unsteadiness has common features in terms of the standard deviation of the pressure fluctuations with other classical shock-wave/boundary-layer interactions, like compression ramps and incident shocks on a flat plate. The Fourier transform and the continuous wavelet transform are used to conduct the spectral analysis. The results of the former indicate that the pressure in the shock region is characterized by a broad low-frequency content, without any resonant tone. The wavelet analysis, which is well suited to study non stationary process, reveals that the pressure signal is characterized by an amplitude and a frequency modulation in time. [ABSTRACT FROM AUTHOR]

The observation of GRB 080319B, with an isotropic energy Eiso = 1.32 × 1054 erg, and GRB 050904, with Eiso = 1.04 × 1054 erg, offers the possibility of studying the spectral properties of the prompt radiation of two of the most energetic gamma-ray bursts (GRBs). This allows us to probe the validity of the fireshell model for GRBs beyond 1054 erg, well outside the energy range where it has been successfully tested up to now (1049-1053 erg). We find that in the low-energy region, the prompt emission spectra observed by Swift Burst Alert Telescope (BAT) reveals more power than theoretically predicted. The opportunities offered by these observations to improve the fireshell model are outlined in this paper. One of the distinguishing features of the fireshell model is that it relates the observed GRB spectra to the spectrum in the comoving frame of the fireshell. Originally, a fully radiative condition and a comoving thermal spectrum were adopted. An additional power law in the comoving thermal spectrum is required due to the discrepancy of the theoretical and observed light curves and spectra in the fireshell model for GRBs 080319B and 050904. A new phenomenological parameter α is correspondingly introduced in the model. We perform numerical simulations of the prompt emission in the Swift BAT bandpass by assuming different values of α within the fireshell model. We compare them with the GRB 080319B and GRB 050904 observed time-resolved spectra, as well as with their time-integrated spectra and light curves. Although GRB 080319B and GRB 050904 are at very different redshifts (z = 0.937 and z = 6.29, respectively), a value of α = –1.8 for both of them leads to a good agreement between the numerical simulations and the observed BAT light curves, time-resolved and time-integrated spectra. Such a modified spectrum is also consistent with the observations of previously analyzed less energetic GRBs and reasons for this additional agreement are given. Perspectives for future low-energy missions are outlined. [ABSTRACT FROM AUTHOR]

We present a carefully selected sample of short gamma-ray bursts (SGRBs) observed by the Swift satellite up to 2013 June. Inspired by the criteria we used to build a similar sample of bright long GRBs (the BAT6 sample), we selected SGRBs with favourable observing conditions for the redshift determination on ground, ending up with a sample of 36 events, almost half of which with a redshift measure. The redshift completeness increases up to about 70 per cent (with an average redshift value of z = 0.85) by restricting to those events that are bright in the 15–150 keV Swift Burst Alert Telescope energy band. Such flux-limited sample minimizes any redshift-related selection effects, and can provide a robust base for the study of the energetics, redshift distribution and environment of the Swift bright population of SGRBs. For all the events of the sample, we derived the prompt and afterglow emission in both the observer and (when possible) rest frame and tested the consistency with the correlations valid for long GRBs. The redshift and intrinsic X-ray absorbing column density distributions we obtain are consistent with the scenario of SGRBs originated by the coalescence of compact objects in primordial binaries, with a possible minor contribution (∼10–25 per cent) of binaries formed by dynamical capture (or experiencing large natal kicks). This sample is expected to significantly increase with further years of Swift activity. [ABSTRACT FROM AUTHOR]

We present a comprehensive statistical analysis of Swift X-ray light curves of gamma-ray bursts (GRBs) collecting data from more than 650 GRBs discovered by Swift and other facilities. The unprecedented sample size allows us to constrain the rest-frame X-ray properties of GRBs from a statistical perspective, with particular reference to intrinsic time-scales and the energetics of the different light-curve phases in a common rest-frame 0.3-30 keV energy band. Temporal variability episodes are also studied and their properties constrained. Two fundamental questions drive this effort: (i) Does the X-ray emission retain any kind of 'memory' of the prompt Ɣ-ray phase? (ii) Where is the dividing line between long and short GRB X-ray properties? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs in the X-rays, but are interestingly characterized by similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt Ɣ-ray parameters in long GRBs; short GRBs are outliers of the majority of these two-parameter relations. However and more importantly, we report on the existence of a universal three-parameter scaling that links the X-ray and the Ɣ-ray energy to the prompt spectral peak energy of both long and short GRBs: EX,iso Ey,iso1.00±0.06 ∞ /Epk0.60±0.10. [ABSTRACT FROM AUTHOR]

We revisit the Polish doughnut model of accretion discs providing a comprehensive analytical description of the Polish doughnut structure. We describe a perfect fluid circularly orbiting around a Schwarzschild black hole, source of gravitational field, by the effective potential approach for the exact gravitational and centrifugal effects. This analysis leads to a detailed, analytical description of accretion disc, its toroidal surface, the thickness and the distance from the source. We determine the variation of these features with the effective potential and the fluid angular momentum. Many analytical formulas are given. In particular it turns out that the distance from the source of the inner surface of the torus increases with increasing fluid angular momentum but decreases with increasing energy function defined as the value of the effective potential for that momentum. The location of torus maximum thickness moves towards the external regions of the surface with increasing angular momentum, until it reaches a maximum and then decreases. Assuming a polytropic equation of state we investigate some specific cases. [ABSTRACT FROM PUBLISHER]