We report Fermi Large Area Telescope (LAT) observations and broadband spectral modeling of the radio-loud active galaxy 4C +55.17 (z = 0.896), formally classified as a flat-spectrum radio quasar. ...Using 19 months of all-sky survey Fermi-LAT data, we detect a Delta *g-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of Delta *g-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady Delta *g-ray emission, where we re-examine the common classification of 4C +55.17 as a quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broadband spectrum. Second, we show that the Delta *g-ray spectrum may be formally extrapolated into the very high energy (VHE, >=100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light within LAT energies and features the source as a promising candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.
In the frame of the collapsar model for long gamma-ray bursts (GRBs), we investigate the formation of a torus around a spinning black hole (BH), and we check what rotational properties a progenitor ...star must have in order to sustain torus accretion over relatively long activity periods. We also study the time evolution of the BH spin parameter. We take into account the coupling between BH mass, its spin parameter, and the critical specific angular momentum of accreting gas needed for the torus to form. The large BH spin reduces the critical angular momentum which in turn can increase the GRB duration with respect to the Schwarzschild BH case. We quantify this effect and estimate the GRB durations in three cases: when a hyperaccreting torus operates or a BH spins very fast or both. We show under what conditions a given progenitor star produces a burst that can last as short as several seconds and as long as several hundred of seconds. Our models indicate that it is possible for a single collapse to produce three kinds of jets: (1) a very short, lasting between a fraction of a second and a few seconds, 'precursor' jet, powered only by a hyperaccreting torus before the BH spins up, (2) an 'early' jet, lasting several tens of seconds and powered by both hyperaccretion and BH rotation, and (3) a 'late' jet, powered only by the spinning BH.
We present a description of our numerical code BLAZAR. This code calculates spectra and light curves of blazars during outbursts. The code is based on a model in which the non-thermal flares in ...blazars are produced in thin shells propagating down a conical jet with relativistic velocities. Such shells may represent layers of a shocked plasma, enclosed between the forward and reverse fronts of an internal shock. In the model adopted by us, the production of non-thermal radiation is assumed to be dominated by electrons and positrons which are accelerated directly, rather then injected by pair cascades. The code includes synchrotron emission and inverse-Compton process as the radiation mechanisms. Both synchrotron photons and external photons are included as the seed photons for Comptonization. At the present stage, the code is limited to treat the inverse Compton process only within the Thomson limit and is specialized to model radiation production in the flat spectrum radio quasars. As an example, we present the results of modeling an outburst in 3C 279 – the most extensively monitored γ-ray – bright quasar.
The Carina arm region, containing the supernova remnant SNRG284.3-1.8, the high-energy (HE; E > 100 MeV) binary 1FGL J1018.6-5856 and the energetic pulsar PSRJ1016-5857 and its nebula, has been ...observed with the H.E.S.S. telescope array. The observational coverage of the region in very-high-energy (VHE; E > 0.1TeV) ...-rays benefits from deep exposure (40 h) of the neighboring open clusterWesterlund 2. The observations have revealed a new extended region of VHE ...-ray emission. The characteristics of this thermal emission are used to estimate the plasma density in the region as n ... 0.5 cm...3 (2.9 kpc/d)... The position of XMMUJ101855.4-58564 is compatible with the position reported by the Fermi-LAT collaboration for the binary system 1FGL J1018.6-5856 and the variable Swift XRT source identified with it.
PDF
