Suzaku and multi-wavelength observations of OJ 287 during the periodic optical outburst in 2007

Hiromi Seta, Naoki Isobe, Makoto S. Tashiro, Yuichi Yaji, Akira Arai, Masayuki Fukuhara, Kotaro Kohno, Kouichiro Nakanishi, Mahito Sasada, Yoshito Shimajiri, Tomoka Tosaki, Makoto Uemura, Hans Anderhub, Lucio Angelo Antonelli, Pedro Antoranz, Michael Backes, Carmen Baixeras, Silvia Balestra, Juan Abel Barrio, Denis BastieriJosefa Becerra González, Julia K. Becker, Włodzimierz Bednarek, Karsten Berger, Elisa Bernardini, Adrian Biland, Rudolf K. Bock, Giacomo Bonnoli, Pol Bordas, Daniela Borla Tridon, Valenti Bosch-Ramon, Debanjan Bose, Isabel Braun, Thomas Bretz, Ilia Britvitch, Miguel Camara, Emiliano Carmona, Sebastian Commichau, José Luis Contreras, Juan Cortina, Ma Teresa Costado Dios, Stefano Covino, Valentin Curtef, Francesco Dazzi, Alessandro De Angelis, Elsa De Cea Del Pozo, Raquel De Los Reyes, Barbara De Lotto, Michela De Maria, Francesco De Sabata, Carlos Delgado Méndez, Alberto Domínguez, Daniela Dorner, Michele Doro, Dominik Elsaesser, Manel Errando, Daniela Ferenc, Enrique Fernandez, Roger Firpo, Maria Victoria Fonseca, Lluis Font, Nicola Galante, Ramon J.García López, Markus Garczarczyk, Markus Gaug, Florian Goebel, Daniela Hadasch, Masaaki Hayashida, Artemio Herrero, Dorothée Hildebrand, Daniel Höhne-Mönch, Jürgen Hose, Ching Cheng Hsu, Tobias Jogler, Daniel Kranich, Antonio La Barbera, Alvin Laille, Elvira Leonardo, Elina Llndfors, Saverio Lombardi, Francesco Longo, Donatella López, Eckart Lorenz, Pratik Majumdar, Galina Maneva, Nijil Mankuzhiyil, Karl Mannheim, Laura Maraschi, Mosé Mariotti, Manel Martínez, Daniel Mazin, Mario Meucci, Markus Meyer, Jose Miguel Miranda, Razmick Mirzoyan, Hiroko Miyamoto, Javier Moldón, Mariano Moles, Abelardo Moralejo, Daniel Nieto

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25 Citations (Scopus)

Abstract

Suzaku observations of the blazar OJ 287 were performed in 2007 April 10-13 and November 7-9. They correspond to a quiescent and a flaring state, respectively. The X-ray spectra of the source can be well-described with single power-law models in both exposures. The derived X-ray photon index and the flux density at 1 keV were found to be Γ = 1.65 ± 0.02 and S 1 keV = 215 ± 5 nJy in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum (Γ = 1.50±0.01) with a nearly doubled X-ray flux density of S1 keV = 404 +6-5nJy. Moreover, significant hard X-ray signals were detected up to ∼27 keV. In cooperation with Suzaku, simultaneous radio, optical, and very-high-energy γ-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04±0.46 Jy and 8.93 ± 0.05 mJy at 86.75 Hz and in the V-band, respectively) were found to be higher by a factor of 2-3 than those in the quiescent state (1.73 ± 0.26 Jy and 3.03 ± 0.01 mJy at 86.75 Hz and in the V-band, respectively). No notable γ-ray events were detected in either observation. The spectral energy distribution of OJ 287 indicated that the X-ray spectrum was dominated by inverse Compton radiation in both observations, while synchrotron radiation exhibited a spectral cutoff at around the optical frequency. Furthermore, no significant difference in the synchrotron cutoff frequency was found between the quiescent and flaring states. According to a simple synchrotron self-Compton model, the change of the spectral energy distribution is due to an increase in the energy density of electrons with small changes of both the magnetic field strength and the maximum Lorentz factor of electrons. © 2009. Astronomical Society of Japan.
Original languageEnglish
Pages (from-to)1011-1022
JournalPublications of the Astronomical Society of Japan
Volume61
Issue number5
DOIs
Publication statusPublished - 1 Jan 2009

Keywords

  • Galaxies: BL lacertae objects: general
  • Galaxies: BL lacertae objects: individual (OJ 287)
  • Radiation mechanisms: non-thermal
  • X-rays: galaxies

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