Unusual flaring activity in the blazar PKS 1424−418 during 2008−2011
Istituto Nazionale di Fisica Nucleare, Sezione di Padova,
2 Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, 35131 Padova, Italy
3 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, 34127 Trieste, Italy
4 Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
5 Department of Physics, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
6 The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, 106 91 Stockholm, Sweden
7 Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden
8 Agenzia Spaziale Italiana (ASI) Science Data Center, via del Politecnico, 00133 Roma, Italy
9 Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Roma, 00040 Monte Porzio Catone, Roma, Italy
10 Space Science Division, Naval Research Laboratory, Washington DC 20375-5352, USA
11 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
12 INAF Istituto di Radioastronomia, 40129 Bologna, Italy
13 Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
14 Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
15 Landessternwarte, Universitat Heidelberg, Konigstuhl, 69117 Heidelberg, Germany
16 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
17 The Catholic University of America, 620 Michigan Ave., N.E. Washington, DC 20064, USA
18 Institut für Theoretische Physik and Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
19 Dr. Remeis-Sternwarte Bamberg, Sternwartstrasse 7, 96049 Bamberg, Germany
20 Erlangen Centre for Astroparticle Physics, 91058 Erlangen, Germany
21 Universities Space Research Association (USRA), Columbia, MD 21044, USA
22 CSIRO Astronomy and Space Science, ATNF, Locked Bag 194, Narrabri NSW 2390, Australia
23 School of Mathematics & Physics, Private Bag 37, University of Tasmania, Hobart TAS 7001, Australia
24 CSIRO Astronomy and Space Science, ATNF, PO Box 76, Epping NSW 1710, Australia
25 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
26 Space Science Institute, Boulder, CO, USA
27 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Accepted: 28 June 2014
Context. Blazars are a subset of active galactic nuclei (AGN) with jets that are oriented along our line of sight. Variability and spectral energy distribution (SED) studies are crucial tools for understanding the physical processes responsible for observed AGN emission.
Aims. We report peculiar behavior in the bright γ-ray blazar PKS 1424−418 and use its strong variability to reveal information about the particle acceleration and interactions in the jet.
Methods. Correlation analysis of the extensive optical coverage by the ATOM telescope and nearly continuous γ-ray coverage by the Fermi Large Area Telescope is combined with broadband, time-dependent modeling of the SED incorporating supplemental information from radio and X-ray observations of this blazar.
Results. We analyse in detail four bright phases at optical-GeV energies. These flares of PKS 1424−418 show high correlation between these energy ranges, with the exception of one large optical flare that coincides with relatively low γ-ray activity. Although the optical/γ-ray behavior of PKS 1424−418 shows variety, the multiwavelength modeling indicates that these differences can largely be explained by changes in the flux and energy spectrum of the electrons in the jet that are radiating. We find that for all flares the SED is adequately represented by a leptonic model that includes inverse Compton emission from external radiation fields with similar parameters.
Conclusions. Detailed studies of individual blazars like PKS 1424−418 during periods of enhanced activity in different wavebands are helping us identify underlying patterns in the physical parameters in this class of AGN.
Key words: galaxies: active / radiation mechanisms: non-thermal / quasars: individual: PKS 1424-418 / gamma rays: galaxies / galaxies: jets
© ESO, 2014