Narrow Results

A theoretical attempt to identify the physical process responsible for the afterglow emission of Gamma-Ray Bursts (GRBs) is presented, leading to the occurrence of thermal emission in the comoving frame of the shock wave which gives rise to the bursts. The determination of the luminosities and spectra involves integration over an infinite number of Planckian spectra, weighted by appropriate relativistic transformations, each one corresponding to a different viewing angle in the past light cone of the observer. The relativistic transformations have been computed using the equations of motion of GRBs within our theory, giving special attention to the determination of the equitemporal surfaces. The only free parameter of the present theory is the "effective emitting area" in the shock wave front. A self-consistent model for the observed hard-to-soft transition in GRBs is also presented. When applied to GRB 991216 a precise fit (χ²≃1.078) of the observed luminosity in the 2–10 keV band is obtained. Similarly, detailed estimates of the observed luminosity in the 50–300 keV and in the 10–50 keV bands are obtained.

Spectral line profiles produced in an outflow near a neutron star or a black hole can be strongly influenced by gravitational redshifting and by Doppler shifting due to a global motion of plasma. We consider a scenario in which a resonant absorption in a spectral line takes place in the outflowing plasma within several tens of Schwarzschild radii from a compact object. The main goal of this work is to show that under certain conditions a combination of the gravitational redshifting and Doppler blue/redshifting may produce line profiles which can be considered as "fingerprints" of the gravitational field of the compact object, much as P-Cygni profiles are "fingerprints" of stellar winds.

Modeling implications of recent VERITAS discoveries of Intermediate BL Lac Objects (IBLs) are presented. Leptonic jet models for the IBLs W Comae (z = 0.102) and 3C 66A (z = 0.444) are, in principle, viable with only synchrotron and synchrotron self-Compton (SSC) components, but more plausible parameters can be achieved including an external infrared radiation field as source for Compton upscattering to produce the observed VHE gamma-ray emission. The unknown redshift of PKS 1424+240 makes a theoretical interpretation difficult. A pure SSC model seems to be sufficient to represent its SED, and modeling results favor a low redshift of z ≲ 0.1.

The origin of gamma-ray burst (GRB) prompt emission, bursts of γ-rays lasting from shorter than one second to thousands of seconds, remains not fully understood after more than 40 years of observations. The uncertainties lie in several open questions in the GRB physics, including jet composition, energy dissipation mechanism, particle acceleration mechanism and radiation mechanism. Recent broad-band observations of prompt emission with Fermi sharpen the debates in these areas, which stimulated intense theoretical investigations invoking very different ideas. I will review these debates, and argue that the current data suggest the following picture: A quasi-thermal spectral component originating from the photosphere of the relativistic ejecta has been detected in some GRBs. Even though in some cases (e.g. GRB 090902B) this component dominates the spectrum, in most GRBs, this component either forms a sub-dominant "shoulder" spectral component in the low energy spectral regime of the more dominant "Band" component, or is not detectable at all. The main "Band" spectral component likely originates from the optically thin region due to synchrotron radiation. The diverse magnetization in the GRB central engine is likely the origin of the observed diverse prompt emission properties among bursts.

High energy transients make up a diverse and exotic class of objects, from terrestrial lightning to $\gamma$-ray bursts at cosmological distances. In this review, we provide a detailed look at some of the more exciting transients observed over the last few years by Swift and other high energy missions.

We present the first results obtained in the elaboration of a complete model of a microquasar where the donor star is from Population III. These stars do not produce stellar winds so we consider that the mass loss is due exclusively to matter overflowing the Roche lobe towards the compact object, a maximally rotating black hole. The rate of accretion is extremely super-Eddington, with an intense mass loss from the system in the form of winds and jets. We calculate the relativistic particle content of the jet and the corresponding spectral energy distribution (SED) considering a lepto-hadronic model. Prospects for the cosmological implications of these objects are briefly discussed.

Cosmological and astrophysical surveys in various wavebands, in particular from the radio to the far-infrared, offer a unique view of the universe’s properties and the formation and evolution of its structures. After a preamble on the so-called tension problem, which occurs when different types of data are used to determine cosmological parameters, we discuss the role of fast radio bursts in cosmology, in particular for the missing baryon problem, and the perspectives from the analysis of the 21 cm redshifted line from neutral hydrogen. We then describe the Planck Legacy Archive, its wealth of scientific information and next developments, and the promising perspectives expected from higher resolution observations, in particular for the analysis of the thermal Sunyaev–Zel’dovich effect. Three cosmological results of the Planck mission are presented next: the implications of the map of Comptonization fluctuations, the dipole analysis from cross-correlating cosmic microwave background anisotropy and Comptonization fluctuation maps, and the constraints on the primordial tensor-to-scalar perturbation ratio. Finally, we discuss some future perspectives and alternative scenarios in cosmology, such as the study of the Lorentz invariance violation with the cosmic microwave background polarization, the introduction of new gravitational degrees of freedom to solve the dark matter problem, and the exploitation of the magnification bias with high-redshift sub-millimeter galaxies to constrain cosmological parameters.

The radiation of relativistic electrons in random and small-scale magnetic field is called jitter radiation. We apply jitter process to study the polarization feature of GRB prompt emission. A two-dimensional compressed slab which contains stochastic magnetic field is applied in our model. If jitter condition is satisfied, the high degree polarization can be achieved when the angle between line-of-sight and slab plane is small. Moreover, micro-emitters with mini-jet structure and jet off-axis effect are considered.

The recent associations of neutrino events with blazars (e.g. TXS 0506+056, 3HSP J095507.9+355101) provided a unique opportunity to study the possible physical connection between the multiwavelength electromagnetic and neutrino emissions. We present SOPRANO, a new conservative implicit kinetic code which follows the time evolution of the isotropic distribution functions of protons, neutrons and the secondaries produced in photo-pion and photo-pair interactions, alongside with the evolution of photon and electron/positron distribution functions. In the current work, we apply SOPRANO to model the broadband spectrum of TXS 0506+056, 3HSP J095507.9+355101 and 3C 279 blazars. It was possible to constrain main physical parameters within both a pure hadronic and lepto-hadronic scenarios.

Cosmological and astrophysical surveys in various wavebands, in particular from the radio to the far-infrared, offer a unique view of the universe’s properties and the formation and evolution of its structures. After a preamble on the so-called tension problem, which occurs when different types of data are used to determine cosmological parameters, we discuss the role of fast radio bursts in cosmology, in particular for the missing baryon Bologna, Italy problem, and the perspectives from the analysis of the 21 cm redshifted line from neutral hydrogen. We then describe the Planck Legacy Archive, its wealth of scientific information and next developments, and the promising perspectives expected from higher resolution observations, in particular for the analysis of the thermal Sunyaev-Zel’dovich effect. Three cosmological results of the Planck mission are presented next: the implications of the map of Comptonization fluctuations, the dipole analysis from cross-correlating cosmic microwave background anisotropy and Comptonization fluctuation maps, and the constraints on the primordial tensor-to-scalar perturbation ratio. Finally, we discuss some future perspectives and alternative scenarios in cosmology, such as the study of the Lorentz invariance violation with the cosmic microwave background polarization, the introduction of new gravitational degrees of freedom to solve the dark matter problem, and the exploitation of the magnification bias with high-redshift sub-millimeter galaxies to constrain cosmological parameters.

High energy transients make up a diverse and exotic class of objects, from terrestrial lightning to γ-ray bursts at cosmological distances. In this review, we provide a detailed look at some of the more exciting transients observed over the last few years by Swift and other high energy missions.

We put accent on a relation linking lag and duration and name reduced lag the ratio between them. We then show two arguments in favor of the reduced lag, as an interesting quantity for exploring correlated properties in GRBs.

Amati-like relations are the most discussed relations in the physics of GRBs. The question raised is if these relations are intrinsic or consequences of the instruments selection. Furthermore, the analyses of the GRB samples with known redshifts and spectral properties report that these relations have large dispersions. In this work we study the Amati and Yonetoku relations by using a Monte-Carlo method to generate a population of synthetic GRBs. We discuss about the parameters characterizing these two relations.