Browsing Faculty of Natural and Agricultural Sciences by Subject "galaxies: jets"

Now showing items 1-10 of 19

    • The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT 

      Raiteri, C.M.; Böttcher, M.; Villata, M.; D'Ammando, F.; Larionov, V.M. (Oxford University Press, 2013)
      Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved ...

    • Hadronic models of blazars require a change of the accretion paradigm 

      Zdziarski, Andrzej A.; Böttcher, Markus (Oxford University Press, 2015)
      We study hadronic models of broad-band emission of jets in radio-loud active galactic nuclei, and their implications for the accretion in those sources. We show that the models that account for broad-band spectra of blazars ...

    • HESS and Fermi-LAT discovery of γ-rays from the blazar 1ES 1312-423 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (Oxford Univ Press, 2013)
      A deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of γ-rays from the blazar 1ES 1312−423, 2° away from the radio galaxy. With a differential flux at ...

    • How gravitational lensing helps y-ray photons avoid y-y absorption 

      Barnacka, Anna; Böttcher, Markus; Sushch, Iurii (IOP Publishing, 2014)
      We investigate potential γ – γ absorption of γ-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess γ – γ ...

    • Leptonic and hadronic modeling of Fermi-detected blazars 

      Böttcher, M.; Reimer, A.; Sweeney, K.; Prakash, A. (IOP Science, 2013)
      We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in active galactic nuclei in a temporary steady state. For the leptonic model, a temporary equilibrium between ...

    • Long-term monitoring of PKS2155-304 with ATOM and H.E.S.S.: investigation of optical/y-ray correlations in different spectral states 

      Abramowski, A.; Böttcher, M.; Davids, I.D.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Spanier, F.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2014)
      In this paper we report on the analysis of all the available optical and very high-energy y-ray (>200 GeV) data for the BL Lac object PKS 2155-304, collected simultaneously with the ATOM and H.E.S.S. telescopes from ...

    • Magnetic field amplification and flat spectrum radio quasars 

      Chen, Xuhui; Böttcher, Markus; Chatterjee, Ritaban; Zhang, Haocheng; Pohl, Martin (Oxford University Press, 2014)
      We perform time-dependent, spatially resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts ...

    • Multi-band implications of external-IC flares 

      Richter, Stephan; Spanier, Felix (Elsevier, 2015)
      Very fast variability on scales of minutes is regularly observed in Blazars. The assumption that these flares are emerging from the dominant emission zone of the very high energy (VHE) radiation within the jet challenges ...

    • Nature of intranight optical variability of BL Lacertae 

      Gaur, Haritma; Böttcher, M.; Gupta, Alok C.; Bachev, R.; Strigachev, A. (Oxford University Press, 2015)
      We present the results of extensive multiband intranight optical monitoring of BL Lacertae during 2010–2012. BL Lacertae was very active in this period and showed intense variability in almost all wavelengths. We extensively ...

    • Particle diffusion and localized acceleration in inhomogeneous AGN jets. I. Steady-state spectra 

      Chen, Xuhui; Böttcher, Markus; Pohl, Martin (Oxford University Press, 2015)
      We study the acceleration, transport, and emission of particles in relativistic jets. Localized stochastic particle acceleration, spatial diffusion, and synchrotron as well as synchrotron self-Compton (SSC) emission are ...