Suzaku and Multi-Wavelength Observations of OJ 287 during the Periodic Optical Outburst in 2007
Authors: Seta Hiromi , Isobe Naoki , Tashiro Makoto S. , Yaji Yuichi , Arai Akira , Fukuhara Masayuki , Kohno Kotaro , Nakanishi Kouichiro , Sasada Mahito , Shimajiri Yoshito , Tosaki Tomoka , Uemura Makoto , Anderhub Hans , Antonelli Lucio Angelo , Antoranz Pedro , Backes Michael , Baixeras Carmen , Balestra Silvia , Barrio Juan Abel , Bastieri Denis , González Josefa Becerra , Becker Julia K. , Bednarek Wodzimierz , Berger Karsten , Bernardini Elisa , Biland Adrian , Bock Rudolf K. , Bonnoli Giacomo , Bordas Pol , Tridon Daniela Borla , Bosch-Ramon Valenti , Bose Debanjan , Braun Isabel , Bretz Thomas , Britvitch Ilia , Camara Miguel , Carmona Emiliano , Commichau Sebastian , Contreras José Luis , Cortina Juan , Dios Ma Teresa Costado , Covino Stefano , Curtef Valentin , Dazzi Francesco , DeAngelis Alessandro , DelPozo Elsa De Cea , DelosReyes Raquel , DeLotto Barbara , DeMaria Michela , DeSabata Francesco , Méndez Carlos Delgado , Domínguez Alberto , Dorner Daniela , Doro Michele , Elsaesser Dominik , Errando Manel , Ferenc Daniela , Fernández Enrique , Firpo Roger , Fonseca Maria Victoria , Font Lluis , Galante Nicola , GarcíaLópez Ramon J. , Garczarczyk Markus , Gaug Markus , Goebel Florian , Hadasch Daniela , Hayashida Masaaki , Herrero Artemio , Hildebrand Dorothée , Höhne-Mönch Daniel , Hose Jürgen , Hsu Ching Cheng , Jogler Tobias , Kranich Daniel , Barbera Antonio La , Laille Alvin , Leonardo Elvira , Lindfors Elina , Lombardi Saverio , Longo Francesco , López Donatella , Lorenz Eckart , Majumdar Pratik , Maneva Galina , Mankuzhiyil Nijil , Mannheim Karl , Maraschi Laura , Mariotti Mosé , Martínez Manel , Mazin Daniel , Meucci Mario , Meyer Markus , Miranda Jose Miguel , Mirzoyan Razmick , Miyamoto Hiroko , Moldón Javier , Moles Mariano , Moralejo Abelardo , Nieto Daniel , Nilsson Kari , Ninkovic Jelena , Otte Nepomuk , Oya Igor , Paoletti Riccardo , Paredes Josep M. , Pasanen Mikko , Pascoli Donatella , Pauss Felicitas , Pegna Raffaello G. , Perez-Torres Miguel A. , Persic Massimo , Peruzzo Luigi , Prada Francisco , Prandini Elisa , Puchades Neus , Reichardt Ignasi , Rhode Wolfgang , Ribó Marc , Rico Javier , Rissi Michael , Robert Arnau , Rügamer Stefan , Saggion Antonio , Saito Takayuki Y. , Salvati Marco , Sánchez-Conde Miguel , Satalecka Konstancja , Scalzotto Villi , Scapin Valeria , Schweizer Thomas , Shayduk Maxim , Shore Steve N. , Sidro Nuria , Sierpowska-Bartosik Agnieszka , Sillanpää Aimo , Sitarek Julian , Sobczynska Dorota , Spanier Felix , Stamerra Antonio , Schneebeli Luisa Sabrina Stark , Takalo Leo , Tavecchio Fabrizio , Temnikov Petar , Tescaro Diego , Teshima Masahiro , Tluczykont Martin , Torres Diego F. , Turini Nicola , Vankov Hristofor , Wagner Robert M. , Wittek Wolfgang , Zabalza Victor , Zandanel Fabio , Zanin Roberta , Zapatero Jordi 
Published: March 2014

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 $\Gamma$$=$ 1.65$ \pm $0.02 and $S_{\rm 1 keV}$$=$ 215$ \pm $5 nJy in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum ($\Gamma$$=$ 1.50$ \pm $0.01) with a nearly doubled X-ray flux density of $S_{\rm 1 keV}$$=$ 404$^{+6}_{-5} $nJy. Moreover, significant hard X-ray signals were detected up to $\sim $27 keV. In cooperation with Suzaku, simultaneous radio, optical, and very-high-energy $\gamma $-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04$ \pm $0.46 Jy and 8.93$ \pm $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$ \pm $0.26 Jy and 3.03$ \pm $0.01 mJy at 86.75 Hz and in the $V$-band, respectively). No notable $\gamma $-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.