Browsing by Author "Raiteri, C. M."

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    AGILE, Fermi, Swift, and GASP/WEBT multi-wavelength observations of the high-redshift blazar 4C +71.07 in outburst
    (EDP SCIENCES S A, 2019-01-11) Vercellone, S.; Romano, P.; Piano, G.; Vittorini, V.; Donnarumma, I.; Munar-Adrover, P.; Raiteri, C. M.; Villata, M.; Verrecchia, F.; Lucarelli, F.; Pittori, C.; Bulgarelli, A.; Fioretti, V.; Tavani, M.; Acosta-Pulido, J. A.; Agudo, I.; Arkharov, A. A.; Bach, U.; Bachev, R.; Borman, G. A.; Butuzova, M. S.; Carnerero, M. I.; Casadio, C.; Damljanovic, G.; D'Ammando, F.; Di Paola, A.; Doroshenko, V. T.; Efimova, N. V.; Ehgamberdiev, S. A.; Giroletti, M.; Gómez, J. L.; Grishina, T. S.; Järvelä, E.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Lähteenmäki, A.; Larionov, V. M.; Larionova, L. V.; Mihov, B.; Mirzaqulov, D. O.; Molina, S. N.; Morozova, D. A.; Nazarov, S. V.; Orienti, M.; Righini, S.; Savchenko, S. S.; Semkov, E.; Slavcheva-Mihova, L.; Strigachev, A.; Tornikoski, M.; Troitskaya, Y. V.; Vince, O.; Cattaneo, P. W.; Colafrancesco, S.; Longo, F.; Morselli, A.; Paoletti, F.; Parmiggiani, N.; Metsähovi Radio Observatory; Department of Electronics and Nanoengineering; Anne Lähteenmäki Group; Osservatorio Astronomico di Brera; Osservatorio Astronomico di Roma; Agenzia Spaziale Italiana; Autonomous University of Barcelona; Osservatorio Astronomico di Torino; Istituto Nazionale di Astrofisica (INAF); Università degli Studi di Roma Tor Vergata; Instituto de Astrofísica de Canarias; CSIC; RAS - Pulkovo Astronomical Observatory; Max-Planck-Institut für Radioastronomie; Bulgarian Academy of Sciences; Crimean Astrophysical Observatory; University of Belgrade; Universitá di Bologna; Lomonosov Moscow State University; Academy of Sciences of the Republic of Uzbekistan; St. Petersburg State University; Georgian National Academy of Sciences; Istituto Nazionale di Fisica Nucleare (INFN); University of the Witwatersrand, Johannesburg; Università degli studi di Trieste; Sapienza University of Rome
    Context. The flat-spectrum radio quasar 4C +71.07 is a high-redshift (z = 2.172), gamma-loud blazar whose optical emission is dominated by thermal radiation from the accretion disc. Aims. 4C +71.07 has been detected in outburst twice by the AGILE gamma-ray satellite during the period from the end of October to mid-November 2015, when it reached a gamma-ray flux of the order of F(E > 100 MeV) = (1.2 +/- 0.3) x 10(-6) photons cm (2) s(-1) and F(E > 100 MeV) = (3.1 +/- 0.6) x 10(-6) photons cm(-2) s(-1), respectively, allowing us to investigate the properties of the jet and the emission region. Methods. We investigated its spectral energy distribution by means of almost-simultaneous observations covering the cm, mm, near-infrared, optical, ultraviolet, X-ray, and gamma-ray energy bands obtained by the GASP-WEBT Consortium and the Swift, AGILE, and Fermi satellites. Results. The spectral energy distribution of the second gamma-ray flare (whose energy coverage is more dense) can be modelled by means of a one-zone leptonic model, yielding a total jet power of about 4 x 10(47) erg s(-1). Conclusions. During the most prominent gamma-ray flaring period our model is consistent with a dissipation region within the broad-line region. Moreover, this class of high-redshift, flat-spectrum radio quasars with high-mass black holes might be good targets for future gamma-ray satellites such as e-ASTROGAM.
  • Thumbnail Image
    Item
    The beamed jet and quasar core of the distant blazar 4C 71.07
    (OXFORD UNIV PRESS INC, 2019-10) Raiteri, C. M.; Villata, M.; Carnerero, M.; Acosta-Pulido, J. A.; Mirzaqulov, D. O.; Larionov, V. M.; Romano, P.; Vercellone, S.; Agudo, Ivan; Arkharov, A. A.; Bach, U.; Bachev, R.; Baitieri, S.; Borman, G. A.; Boschin, W.; Bozhilov, V.; Butuzova, M. S.; Calcidese, P.; Carosati, D.; Casadio, C.; Chen, W-P; Damljanovic, G.; Di Paola, A.; Doroshenko, V. T.; Efimova, N.; Ehgamberdiev, Sh A.; Giroletti, M.; Gomez, J. L.; Grishina, T. S.; Ibryamov, S.; Jermak, H.; Jorstad, S. G.; Kimeridze, G. N.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lahteenmaki, A.; Larionova, E. G.; Marscher, A. P.; Mihov, B.; Minev, M.; Molina, S. N.; Moody, J. W.; Morozova, D. A.; Nazarov, S.; Nikiforova, A. A.; Nikolashvili, M. G.; Ovcharov, E.; Peneva, S.; Righini, S.; Rizzi, N.; Sadun, A. C.; Samal, M. R.; Savchenko, S. S.; Semkov, E.; Sigua, L. A.; Slavcheva-Mihova, L.; Steele, I. A.; Strigachev, A.; Tornikoski, M.; Troitskaya, Yu; Troitsky, I. S.; Vince, O.; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group
    The object 4C 71.07 is a high-redshift blazar whose spectral energy distribution shows a prominent big blue bump and a strong Compton dominance. We present the results of a 2-yr multiwavelength campaign led by the Whole Earth Blazar Telescope (WEBT) to study both the quasar core and the beamed jet of this source. The WEBT data are complemented by ultraviolet and X-ray data from Swift, and by.-ray data by Fermi. The big blue bump is modelled by using optical and near-infrared mean spectra obtained during the campaign, together with optical and ultraviolet quasar templates. We give prescriptions to correct the source photometry in the various bands for the thermal contribution, in order to derive the non-thermal jet flux. The role of the intergalactic medium absorption is analysed in both the ultraviolet and X-ray bands. We provide opacity values to deabsorb ultraviolet data, and derive a best-guess value for the hydrogen column density of N-H(best) = 6.3 x 10(20) cm(-2) through the analysis of X-ray spectra. We estimate the disc and jet bolometric luminosities, accretion rate, and black hole mass. Light curves do not show persistent correlations among flux changes at different frequencies. We study the polarimetric behaviour and find no correlation between polarization degree and flux, even when correcting for the dilution effect of the big blue bump. Similarly, wide rotations of the electric vector polarization angle do not seem to be connected with the source activity.
  • Thumbnail Image
    Item
    The complex variability of blazars: Time-scales and periodicity analysis in S4 0954+65
    (OXFORD UNIV PRESS INC, 2021-07-01) Raiteri, C. M.; Villata, M.; Larionov, V. M.; Jorstad, S. G.; Marscher, A. P.; Weaver, Z. R.; Acosta-Pulido, J. A.; Agudo, I.; Andreeva, T.; Arkharov, A.; Bachev, R.; Benítez, E.; Berton, M.; Björklund, I.; Borman, G. A.; Bozhilov, V.; Carnerero, M. I.; Carosati, D.; Casadio, C.; Chen, W. P.; Damljanovic, G.; D'Ammando, F.; Escudero, J.; Fuentes, A.; Giroletti, M.; Grishina, T. S.; Gupta, A. C.; Hagen-Thorn, V. A.; Hart, M.; Hiriart, D.; Hou, W. J.; Ivanov, D.; Kim, J. Y.; Kimeridze, G. N.; Konstantopoulou, C.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.; Marchili, N.; Markovic, G.; Minev, M.; Morozova, D. A.; Myserlis, I.; Nakamura, M.; Nikiforova, A. A.; Nikolashvili, M. G.; Otero-Santos, J.; Ovcharov, E.; Pursimo, T.; Rahimov, I.; Righini, S.; Sakamoto, T.; Savchenko, S. S.; Semkov, E. H.; Shakhovskoy, D.; Sigua, L. A.; Stojanovic, M.; Strigachev, A.; Thum, C.; Tornikoski, M.; Traianou, E.; Troitskaya, Y. V.; Troitskiy, I. S.; Tsai, A.; Valcheva, A.; Vasilyev, A. A.; Vince, O.; Zaharieva, E.; Metsähovi Radio Observatory; Department of Electronics and Nanoengineering; Anne Lähteenmäki Group; National Institute for Astrophysics (INAF); St. Petersburg State University; Boston University; Instituto de Astrofísica de Canarias; CSIC; Russian Academy of Sciences; RAS - Pulkovo Astronomical Observatory; Bulgarian Academy of Sciences; Universidad Nacional Autónoma de México; Department of Electronics and Nanoengineering; Sofia University St. Kliment Ohridski; EPT Observatories; Institute of Electronic Structure and Laser; National Central University; University of Belgrade; Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna; Aryabhatta Research Institute of Observational Sciences; Korea Astronomy and Space Science Institute; Georgian National Academy of Sciences; Nordic Optical Telescope; Max Planck Institute for Radio Astronomy; Aoyama Gakuin University; Instituto de Radioastronomía Milimétrica
    Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during three observing sectors of nearly 1 month each allow us to study the fast variability in great detail. We identify several characteristic short-term time-scales, ranging from a few hours to a few days. However, these are not persistent, as they differ in the various TESS sectors. The long-term photometric and polarimetric optical and radio monitoring undertaken by the WEBT brings significant additional information, revealing that (i) in the optical, long-term flux changes are almost achromatic, while the short-term ones are strongly chromatic; (ii) the radio flux variations at 37 GHz follow those in the optical with a delay of about 3 weeks; (iii) the range of variation of the polarization degree and angle is much larger in the optical than in the radio band, but the mean polarization angles are similar; (iv) the optical long-term variability is characterized by a quasi-periodicity of about 1 month. We explain the source behaviour in terms of a rotating inhomogeneous helical jet, whose pitch angle can change in time.
  • Thumbnail Image
    Item
    The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies
    (IOP PUBLISHING LTD, 2020-02-20) Abeysekara, A. U.; Benbow, W.; Bird, R.; Brill, A.; Brose, R.; Buchovecky, M.; Buckley, J. H.; Christiansen, J. L.; Chromey, A. J.; Daniel, M. K.; Dumm, J.; Falcone, A.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; Galante, N.; Gent, A.; Gillanders, G. H.; Giuri, C.; Gueta, O.; Hassan, T.; Hervet, O.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Krennrich, F.; Kumar, S.; Lang, M. J.; Moriarty, P.; Mukherjee, R.; Nelson, T.; Nieto, D.; Nievas Rosillo, M.; O'Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Petrashyk, A.; Pichel, A.; Pohl, M.; Prado, R. R.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rovero, A. C.; Rulten, C.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Stevenson, B.; Sushch, I.; Tyler, J.; Vassiliev, V. V.; Wakely, S. P.; Weinstein, A.; Wells, R. M.; Wilcox, P.; Wilhelm, A.; Williams, D. A.; Zitzer, B.; Acciari, V. A.; Ansoldi, S.; Antonelli, L. A.; Arbet Engels, A.; Baack, D.; Babić, A.; Banerjee, B.; Barres De Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bellizzi, L.; Bernardini, E.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Busetto, G.; Carosi, R.; Ceribella, G.; Chai, Y.; Cikota, S.; Colak, S. M.; Colin, U.; Colombo, E.; Contreras, J. L.; Cortina, Juan; Covino, S.; D'Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Di Pierro, F.; Do Souto Espiñera, E.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Elsaesser, D.; Fallah Ramazani, V.; Fattorini, A.; Fernández-Barral, A.; Ferrara, G.; Fidalgo, D.; Foffano, L.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; Gallozzi, S.; García López, R. J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Godinović, N.; Green, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Herrera, J.; Hoang, J.; Hrupec, D.; Inoue, S.; Ishio, K.; Iwamura, Y.; Kubo, H.; Kushida, J.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Machado De Oliveira Fraga, B.; Maggio, C.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Masuda, S.; Mazin, D.; Miceli, D.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Morcuende, D.; Moreno, V.; Moretti, E.; Munar-Adrover, P.; Neustroev, V.; Niedzwiecki, A.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nogués, L.; Nöthe, M.; Paiano, S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Penil, P.; Peresano, M.; Persic, M.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Sahakyan, N.; Saito, T.; Satalecka, K.; Schweizer, T.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Somero, A.; Stamerra, A.; Strom, D.; Strzys, M.; Sun, S.; Surić, T.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Teshima, M.; Torres-Alba, N.; Tsujimoto, S.; Van Scherpenberg, J.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Will, Martin; Zarić, D.; Aller, H. D.; Aller, M. F.; Carini, M. T.; Horan, D.; Jordan, B.; Jorstad, S. G.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lahteenmaki, Anne; Larionov, V. M.; Larionova, E. G.; Madejski, G.; Marscher, A. P.; Max-Moerbeck, W.; Moody, J. Ward; Morozova, D. A.; Nikolashvili, M. G.; Raiteri, C. M.; Readhead, A. C.S.; Richards, J. L.; Sadun, A. C.; Sakamoto, T.; Sigua, L. A.; Smith, P. S.; Talvikki, H.; Tammi, Joni; Tornikoski, Merja; Troitsky, I. S.; Villata, M.; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; University of Utah; Harvard University; University of California, Los Angeles; Columbia University; University of Potsdam; Washington University St. Louis; California Polytechnic State University, San Luis Obispo; Iowa State University; University of Minnesota Twin Cities; Pennsylvania State University; Purdue University; California State University, East Bay; Georgia Institute of Technology; National University of Ireland, Galway; German Electron Synchrotron; University of California, Santa Cruz; University of Delaware; University of Iowa; DePauw University; McGill University; Complutense University of Madrid; University College Dublin; University of Wisconsin-Madison; Universidad de Buenos Aires; Cork Institute of Technology; University of Alabama; University of Chicago; Instituto de Astrofísica de Canarias; University of Udine; Osservatorio Astronomico di Roma; Swiss Federal Institute of Technology Zurich; TU Dortmund University; University of Rijeka; Saha Institute of Nuclear Physics; Centro Brasileiro de Pesquisas Físicas; University of Łódź; University of Siena; National Institute for Nuclear Physics; Max Planck Institute for Physics; Institute for High Energy Physics; University of Padova; University of Pisa; University of Würzburg; Autonomous University of Barcelona; University of Barcelona; National Academy of Sciences of the Republic of Armenia; University of Tokyo; University of Turku; Bulgarian Academy of Sciences; Fudan University; University of Michigan, Ann Arbor; Western Kentucky University; CNRS; Dublin Institute for Advanced Studies; Boston University; Ilia State University; St. Petersburg State University; United States Department of Energy; Universidad de Chile; Brigham Young University; California Institute of Technology; University of Colorado Denver; Aoyama Gakuin University; University of Arizona
    We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.
  • Thumbnail Image
    Item
    Long-term Swift and Metsähovi monitoring of SDSS J164100.10+345452.7 reveals multi-wavelength correlated variability
    (EDP Sciences, 2023-05-01) Romano, P.; Lähteenmäki, A.; Vercellone, S.; Foschini, L.; Berton, M.; Raiteri, C. M.; Braito, V.; Ciroi, S.; Järvelä, E.; Baitieri, S.; Varglund, I.; Tornikoski, M.; Suutarinen, S.; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; Osservatorio Astronomico di Brera; National Institute for Astrophysics (INAF); University of Padova; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; European Southern Observatory Santiago; Urbanización Villafranca Del Castillo
    We report on the first multi-wavelength Swift monitoring campaign performed on SDSS J164100.10+345452.7, a nearby narrow-line Seyfert 1 galaxy that had formerly been considered to be radio-quiet. It has, however, more recently been detected both in the radio (at 37 GHz) and in the γ-ray, a behaviour that hints at the presence of a relativistic jet. During our 20-month Swift campaign, while pursuing the primary goal of assessing the baseline optical/UV and X-ray properties of SDSS J164100.10+345452.7, we observed two radio flaring episodes, namely, one each year. Our strictly simultaneous multi-wavelength data closely match the radio flare and allow us to unambiguously link the jetted radio emission of SDSS J164100.10+345452.7. Indeed, for the X-ray spectra preceding and following the radio flare, a simple absorbed power-law model does not offer an adequate description and, thus, an extra absorption component is required. The average spectrum of SDSS J164100.10+345452.7 can best be described by an absorbed power-law model with a photon index Σ = 1.93 ± 0.12, modified by a partially covering neutral absorber with a covering fraction of f = 0.91-0.03+0.02. On the contrary, the X-ray spectrum closest to the radio flare does not require any such extra absorber and it is much harder (Σflare ∼0.7 ± 0.4), thus implying the emergence of an additional, harder spectral component. We interpret this as the jet emission emerging from a gap in the absorber. The fractional variability we derived in the optical/UV and X-ray bands is found to be lower than the typical values reported in the literature because our observations of SDSS J164100.10+345452.7 are dominated by the source being in a low state, as opposed to the literature, where the observations were generally taken as a follow-up of bright flares in other energy bands. Based on the assumption that the origin of the 37 GHz radio flare is the emergence of a jet from an obscuring screen also observed in the X-ray, the derived total jet power is Pjettot = 3.5 × 1042 erg s-1. This result is close to the lowest values measured in the literature.
  • Thumbnail Image
    Item
    Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio
    (OXFORD UNIV PRESS INC, 2020-03-01) Larionov, V. M.; Jorstad, S. G.; Marscher, A. P.; Villata, M.; Raiteri, C. M.; Smith, P. S.; Agudo, Ivan; Savchenko, S. S.; Morozova, D. A.; Acosta-Pulido, J. A.; Aller, M. F.; Aller, H. D.; Andreeva, T. S.; Arkharov, A. A.; Bachev, R.; Bonnoli, G.; Borman, G. A.; Bozhilov, V.; Calcidese, P.; Carnerero, M.; Carosati, D.; Casadio, C.; Chen, W-P; Damljanovic, G.; Dementyev, A.; Di Paola, A.; Frasca, A.; Fuentes, A.; Gomez, J. L.; Gonzalez-Morales, P.; Giunta, A.; Grishina, T. S.; Gurwell, M. A.; Hagen-Thorn, V. A.; Hovatta, Talvikki; Ibryamov, S.; Joshi, M.; Kiehlmann, S.; Kim, J-Y; Kimeridze, Givi N.; Kopatskaya, E. N.; Kovalev, Yu A.; Kovalev, Y.; Kurtanidze, O. M.; Kurtanidze, Sofia O.; Lahteenmaki, Anne; Lazaro, C.; Larionova, L.; Larionova, E. G.; Leto, G.; Marchini, A.; Matsumoto, K.; Mihov, B.; Minev, M.; Mingaliev, M. G.; Mirzaqulov, D.; Dimitrova, R. V. Munoz; Myserlis, I.; Nikiforova, A. A.; Nikolashvili, M. G.; Nizhelsky, N. A.; Ovcharov, E.; Pressburger, L. D.; Rakhimov, I. A.; Righini, S.; Rizzi, N.; Sadakane, K.; Sadun, A. C.; Samal, M. R.; Sanchez, R. Z.; Semkov, E.; Sergeev, S. G.; Sigua, L. A.; Slavcheva-Mihova, L.; Sola, P.; Sotnikova, Yu; Strigachev, A.; Thum, C.; Traianou, Efthalia; Troitskaya, Yu; Troitsky, I. S.; Tsybulev, P. G.; Vasilyev, A. A.; Vince, O.; Weaver, Z. R.; Williamson, K. E.; Zhekanis, G.; Metsähovi Radio Observatory; Department of Electronics and Nanoengineering; Anne Lähteenmäki Group; St. Petersburg State University; Boston University; Istituto Nazionale di Astrofisica (INAF); University of Arizona; Instituto de Astrofísica de Andalucía; University of La Laguna; University of Michigan; Russian Academy of Sciences; RAS - Pulkovo Astronomical Observatory; Bulgarian Academy of Sciences; University of Siena; Crimean Astrophysical Observatory; Technical University of Sofia; Osservatorio Astronomico della Regione Autonoma Valle d'Aosta; INAF - Osservatorio Astrofisico di Torino; EPT Observatories; Max-Planck-Institut für Radioastronomie; National Central University; Astronomical Observatory Belgrade; Osservatorio Astronomico di Roma; INAF - Osservatorio Astrofisico di Catania; Italian Space Agency; Harvard University; Konstantin Preslavsky University of Shumen; Abastumani Observatory; Lebedev Physical Institute; Osaka Kyoiku University; Kazan Federal University; Academy of Sciences of the Republic of Uzbekistan; INAF - Istituto di Radioastronomia; Osservatorio Astronomico Sirio; University of Colorado Denver; Instituto de Astrofísica de Canarias; Instituto de Radioastronomía Milimétrica; Special Astrophysical Observatory of the Russian Academy of Sciences; California Institute of Technology
    We report the results of decade-long (2008-2018) γ -ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ -ray light curves correlate well, with no delay ≳ 3 h, implying general cospatiality of the emission regions. The γ -ray-optical flux-flux relation changes with activity state, ranging from a linear to amore complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz Very Long Baseline Array images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ -ray variability on very short time-scales. The MgII emission line flux in the 'blue' and 'red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands, we find progressive delays of the most prominent light-curve maxima with decreasing frequency, as expected from the frequency dependence of the τ= 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.
  • Thumbnail Image
    Item
    The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An analysis of the enigmatic synchrotron emission
    (2015-11) Raiteri, C. M.; Stamerra, A.; Villata, M.; Larionov, V. M.; Acosta-Pulido, J. A.; Arévalo, M. J.; Arkharov, A. A.; Bachev, R.; Benítez, E.; Bozhilov, V. V.; Borman, G. A.; Buemi, C. S.; Calcidese, P.; Carnerero, M. I.; Carosati, D.; Chigladze, R. A.; Damljanovic, G.; Di Paola, A.; Doroshenko, V. T.; Efimova, N. V.; Ehgamberdiev, Sh. A.; Giroletti, M.; González-Morales, P. A.; Grinon-Marin, A. B.; Grishina, T. S.; Hiriart, D.; Ibryamov, S.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Kurtenkov, A. A.; Larionova, L. V.; Larionova, E. G.; Lázaro, C.; Lähteenmäki, A.; Leto, P.; Markovic, G.; Mirzaqulov, D. O.; Mokrushina, A. A.; Morozova, D. A.; Mújica, R.; Nazarov, S. V.; Nikolashvili, M. G.; Ohlert, J. M.; Ovcharov, E. P.; Paiano, S.; Pastor Yabar, A.; Prandini, E.; Ramakrishnan, V.; Sadun, A. C.; Semkov, E.; Sigua, L. A.; Strigachev, A.; Tammi, J.; Tornikoski, M.; Trigilio, C.; Troitskaya, Yu. V.; Troitsky, I. S.; Umana, G.; Velasco, S.; Vince, O.; Department of Radio Science and Engineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; INAF - Osservatorio Astrofisico di Torino; Istituto Nazionale di Fisica Nucleare (INFN); Isaac Newton Institute of Chile, St Petersburg Branch; University of La Laguna; Pulkovo Observatory; Bulgarian Academy of Sciences; Universidad Nacional Autónoma de México; Sofia University St. Kliment Ohridski; Crimean Astrophysical Observatory; INAF - Osservatorio Astrofisico di Catania; Osservatorio Astronomico della Regione Autonoma Valle d'Aosta; Fundación Galileo Galilei; Abastumani Observatory; Astronomical Observatory Belgrade; Osservatorio Astronomico di Roma; Lomonosov Moscow State University; Ulugh Beg Astronomical Institute; INAF - Istituto di Radioastronomia; St. Petersburg State University; Kazan Federal University; University of Belgrade; Instituto Nacional de Astrofísica, Óptica y Electrónica; Michael Adrian Observatory; INAF - Osservatorio Astronomico di Padova; ISDC - Science Data Center for Astrophysics; University of Colorado Denver
    A multifrequency campaign on the BL Lac object PG 1553+113 was organized by the Whole Earth Blazar Telescope (WEBT) in 2013 April-August, involving 19 optical, two near-IR, and three radio telescopes. The aim was to study the source behaviour at low energies during and around the high-energy observations by the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes in April-July. We also analyse the UV and X-ray data acquired by the Swift and XMM-Newton satellites in the same period. The WEBT and satellite observations allow us to detail the synchrotron emission bump in the source spectral energy distribution (SED). In the optical, we found a general bluer-when-brighter trend. The X-ray spectrum remained stable during 2013, but a comparison with previous observations suggests that it becomes harder when the X-ray flux increases. The long XMM-Newton exposure reveals a curved X-ray spectrum. In the SED, the XMM-Newton data show a hard near-UV spectrum, while Swift data display a softer shape that is confirmed by previous Hubble Space Telescope/Cosmic Origins Spectrograph and International Ultraviolet Explorer observations. Polynomial fits to the optical-X-ray SED show that the synchrotron peak likely lies in the 4-30 eV energy range, with a general shift towards higher frequencies for increasing X-ray brightness. However, the UV and X-ray spectra do not connect smoothly. Possible interpretations include: (i) orientation effects, (ii) additional absorption, (iii) multiple emission components, and (iv) a peculiar energy distribution of relativistic electrons. We discuss the first possibility in terms of an inhomogeneous helical jet model.