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Following the GRB 170817A prompt emission lasting a fraction of a second, 1 0 8 s of data in the X-rays, optical, and radio wavelengths have been acquired. We here present a model that fits the spectra, flux, and time variability of all these emissions, based on the thermal and synchrotron cooling of the expanding matter ejected in a binary white dwarf merger. The 1 0 − 3 M ⊙ of ejecta, expanding at velocities of 1 0 9 cm s − 1 , are powered by the newborn massive, fast rotating, magnetized white dwarf with a mass of 1. 3 M ⊙ , a rotation period of ≳ 1 2 s, and a dipole magnetic field ∼ 1 0 1 0 G, born in the merger of a 1. 0 + 0. 8 M ⊙ white dwarf binary. Therefore, the long-lasting mystery of the GRB 170817A nature is solved by the merger of a white dwarf binary that also explains the prompt emission energetics. [ABSTRACT FROM AUTHOR]

Important information on the evolution of a jet can be obtained by comparing the physical state of the plasma at its propagation through the broad-line region (where the jet is most likely formed) into the intergalactic medium, where it starts to decelerate significantly. This approach can be fruitfully applied to sources having a large-scale jet long enough to be resolved by Chandra telescope. This is why, from the Fermi Large Area Telescope (Fermi LAT) third source catalog we have selected radio galaxies that have a knot or hot-spot structure in their large-scale jet. We compare the constraints on the physical parameters in the innermost ( < pc) and outer ( > kpc) regions of the same jet by means of a detailed multiwavelength analysis and theoretical modeling of the broadband spectra of M87, Pictor A, 3C 303, 3C 275.1, NGC 6251, 3C 207, 3C 111 and 3C 120. [ABSTRACT FROM AUTHOR]

The discovery of very-high-energy gamma-ray emission from Flat Spectrum Radio Quasars (FSRQs) by ground-based Cherenkov telescopes (HESS, MAGIC, VERITAS) provides a new view of blazar emission processes. The available data from multiwavelength observations of FSRQs, allow us to constrain the size (possibly also location) of the emitting region, magnetic field, electron energy distribution, etc., which are crucial for the understanding of the jet properties. We investigate the origin of emission from FSRQs (PKS 1510-089, PKS 1222+216 and 3C 279) by modeling the broadband spectral energy distribution in their quiescent and flaring states, using estimation of the parameter space that describes the underlying particle distribution responsible for the emission through the Markov Chain Monte Carlo (MCMC) technique. [ABSTRACT FROM AUTHOR]

The recent observations by Fermi large area telescope (Fermi-LAT) showed that in addition to the radio galaxies and blazars, Narrow-Line Seyfert 1 (NLSy1) galaxies are also γ -rays emitters. NLSy1 are AGNs with optical spectral properties similar to those of Seyfert 1 galaxies, except for having narrow Balmer lines and strong optical lines. They also exhibit strong X-ray variability, steep X-ray spectra and relatively high luminosity. The multiwavelength emission properties of 1H 0323+342, SBS 0846+513 and PMN J0948+0022 are discussed, using the γ -ray data from the last 8.8 years Fermi-LAT observations as well as available Swift(UVOT/XRT) data. It is shown that one-zone synchrotron/synchrotron self-Compton (SSC) model can satisfactorily reproduce their observed broadband spectra. [ABSTRACT FROM AUTHOR]

Short and long-duration gamma-ray bursts (GRBs) have been recently sub-classified into seven families according to the binary nature of their progenitors. For short GRBs, mergers of neutron star binaries (NS-NS) or neutron star-black hole binaries (NS-BH) are proposed. For long GRBs, the induced gravitational collapse (IGC) paradigm proposes a tight binary system composed of a carbon-oxygen core (CO) and a NS companion. The explosion of the CO as supernova (SN) triggers a hypercritical accretion process onto the NS companion which might reach the critical mass for the gravitational collapse to a BH. Thus, this process can lead either to a NS-BH or to NS-NS depending on whether or not the accretion is sufficient to induce the collapse of the NS into a BH. We shall discuss for the above compact object binaries: (1) the role of the NS structure and the equation-of-state on their final fate; (2) their occurrence rates as inferred from the X and gamma-ray observations; (3) the expected number of detections of their gravitational wave (GW) emission by the Advanced LIGO interferometer. [ABSTRACT FROM AUTHOR]