Rapid and multiband variability of the TeV bright active nucleus of the galaxy IC 310

• Published in: Astronomy and astrophysics (Berlin) Vol. 563; pp. A91 - np
• Main Authors: Aleksić, J., Babic, A., Becerra González, J., Berger, K., Bernardini, E., Blanch, O., Boller, A., Bonnefoy, S., Borracci, F., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., Delgado Mendez, C., De Lotto, B., Doert, M., Domínguez, A., Dominis Prester, D., Dorner, D., Doro, M., Eisenacher, D., Farina, E., Font, L., Fruck, C., García López, R. J., Garczarczyk, M., Garrido Terrats, D., Giavitto, G., González Muñoz, A., Hadamek, A., Hadasch, D., Häfner, D., Herrero, A., Idec, W., Knoetig, M. L., Krause, J., Kushida, J., López-Oramas, A., Lorenz, E., Maneva, G., Mankuzhiyil, N., Marcote, B., Mariotti, M., Martínez, M., Masbou, J., Mazin, D., Meucci, M., Miranda, J. M., Moldón, J., Munar-Adrover, P., Nilsson, K., Nowak, N., Orito, R., Overkemping, A., Palatiello, M., Paoletti, R., Persic, M., Prandini, E., Preziuso, S., Puljak, I., Rhode, W., Ribó, M., Rügamer, S., Saggion, A., Saito, K., Saito, T. Y., Salvati, M., Satalecka, K., Scapin, V., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamatescu, V., Stamerra, A., Steinke, B., Sun, S., Surić, T., Tavecchio, F., Temnikov, P., Terzić, T., Tibolla, O., Torres, D. F., Toyama, T., Treves, A., Uellenbeck, M., Vogler, P., Weitzel, Q., Zandanel, F., Fortin, P., Kadler, M., Wilbert, S., Wilms, J.
• Format: Journal Article
• Language: English
• Published: United States EDP Sciences 01.03.2014; Springer Verlag
• Subjects: Active galaxies; Astrofísica; Astronomia de raigs gamma; Astronomia de raigs X; Astrophysics; Cosmic rays; Cosmology and Extra-Galactic Astrophysics; Emission analysis; Flux; Galactic Astrophysics; galaxies: active; galaxies: individual: IC 310; Galàxies actives; Gamma ray astronomy; gamma rays: galaxies; High Energy Astrophysical Phenomena; High Energy Physics - Experiment; Instrumentation and Methods for Astrophysic; Integrated circuits; Luminosity; Nuclei; Physics; Radio galaxies; Raigs còsmics; Spectral energy distribution; X-ray astronomy; X-rays; X-rays: galaxies
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201321938

Context. The radio galaxy IC 310 has recently been identified as a γ-ray emitter based on observations at GeV energies with Fermi-LAT and at very high energies (VHE, E > 100 GeV) with the MAGIC telescopes. Originally classified as a head-tail radio galaxy, the nature of this object is subject of controversy since its nucleus shows blazar-like behavior. Aims. To understand the nature of IC 310 and the origin of the VHE emission, we studied the spectral and flux variability of IC 310 from the X-ray band to the VHE γ-ray regime. Methods. The light curve of IC 310 above 300 GeV has been measured with the MAGIC telescopes from 2009 October to 2010 February. Contemporaneous Fermi-LAT data (2008−2011) in the 10−500 GeV energy range were also analyzed. In the X-ray regime, archival observations from 2003 to 2007 with XMM-Newton, Chandra, and Swift-XRT in the 0.5−10 keV band were studied. Results. The VHE light curve reveals several high-amplitude and short-duration flares. Day-to-day flux variability is clearly present (>5σ). The photon index between 120 GeV and 8 TeV remains at the value Γ ~ 2.0 during both low and high flux states. The VHE spectral shape does not show significant variability, whereas the flux at 1 TeV changes by a factor of ~7. Fermi-LAT detected only eight γ-ray events in the energy range 10 GeV–500 GeV in three years of observation. The measured photon index of Γ = 1.3 ± 0.5 in the Fermi-LAT range is very hard. The X-ray measurements show strong variability in both flux and photon index. The latter varied from 1.76 ± 0.07 to 2.55 ± 0.07. Conclusions. The rapid variability measured in γ-rays and X-rays confirms the blazar-like behavior of IC 310. The multi-TeV γ-ray emission seems to originate from scales of less than 80 Schwarzschild radii (for a black hole mass of 2 × 108 M⊙) within the compact core of its FR I radio jet with orientation angle 10°−38°. The spectral energy distribution resembles that of an extreme blazar, albeit the luminosity is more than two orders of magnitude lower.