An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state

Acciari, V. A.; Ansoldi, S.; Antonelli, L. A.; Arbet Engels, A.; Babic, A.; Banerjee, B.; Barres de Almeida, U.; Barrio, J. A.; Becerra Gonzalez, J.; Bednarek, W.; Bellizzi, L.; Bernardini, E.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Blanch, O.; Bonnoli, G.; Bosnjak, Z.; Busetto, G.; Carosi, R.; Ceribella, G.; Cerruti, M.; Chai, Y.; Chilingaryan, A.; Cikota, S.; Colak, S. M.; Colin, U.; Colombo, E.; Contrera, J. L.; Cortina, J.; Covino, S.; D'Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Depaoli, D.; Di Pierro, F.; Di Venere, L.; Do Souto Espineira, E.; Dominis Prester, D.; Donini, A.; Doro, M.; Elsaesser, D.; Fallah Ramazani, V.; Fattorini, A.; Ferrara, G.; Foffano, L.; Fonsec, M. V.; Font, L.; Fruck, C.; Fukami, S.; Garcia Lopez, R. J.; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Giglietto, N.; Giordano, F.; Godinovic, N.; Gliwny, P.; Green, D.; Hadasch, D.; Hahn, A.; Herrera, J.; Hoang, J.; Hrupec, D.; Hutten, M.; Inada, T.; Inoue, S.; Ishio, K.; Iwamura, Y.; Jouvin, L.; Kajiwara, Y.; Kerszberg, D.; Kobayashi, Y.; Kubo, H.; Kushida, J.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; Lopez, M.; Lopez-Coto, R.; Lopez-Oramas, A.; Loporchio, S.; Machado de Oliveira Fraga, B.; Maggio, C.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Maneva, G.; Manganaro, M.; Maraschi, L.; Mariotti, M.; Martinez, M.; Mazin, D.; Mender, S.; Micanovic, S.; Miceli, D.; Miener, T.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Morcuende, D.; Moreno, V.; Moretti, E.; Munar-Adrover, P.; Neustroev, V.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nogues, L.; Nozaki, S.; Ohtani, Y.; Oka, T.; Otero-Santos, J.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Parede, J. M.; Pavletic, L.; Penil, P.; Peresano, M.; Persic, M.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Ribo, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Sahakyan, N.; Saito, T.; Sakurai, S.; Satalecka, K.; Schleicher, B.; Schmidt, K.; Schweizer, T.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spolon, A.; Stamerra, A.; Strom, D.; Strzys, M.; Suda, Y.; Suric, T.; Takahashi, M.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Teshima, M.; Torres-Alba, N.; Tosti, L.; Van Scherpenberg, J.; Vanzo, G.; Vazquez Acosta, M.; Ventura, S.; Verguilov, V.; Vigorito, C. F.; Vitale, V.; Vovk, I.; Will, M.; Zaric, D.; Baack, D.; Balbo, M.; Beck, M.; Biederbeck, N.; Biland, A.; Blank, M.; Bretz, T.; Bruegge, K.; Bulinski, M.; Buss, J.; Doerr, M.; Dorner, D.; Hildebrand, D.; Iotov, R.; Klinger, M.; Mannheim, K.; Achim Mueller, S.; Neise, D.; Neronov, A.; Nothe, M.; Paravac, A.; Rhode, W.; Schleicher, B.; Sedlaczek, K.; Shukla, A.; Sliusar, V.; Tani, L.; Theissen, F.; Walter, R.; Acosta Pulido, J.; Filippenko, A. V.; Hovatta, T.; Kiehlmann, S.; Larionov, V. M.; Max-Moerbeck, W.; Raiteri, C. M.; Readhead, A. C. S.; Segon, M.; Villata, M.; Zheng, W.

doi:10.1093/mnras/staa1702

Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at vs ≥ 1017 Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state without showing any extreme behaviours. In 2016 August, 1ES 2344+514 was detected with the groundbased γ -ray telescope FACT during a high γ -ray state, triggering multiwavelength (MWL) observations. We studied the MWL light curves of 1ES 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (VHE) γ -rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, Swift-UVOT, Swift-XRT, Fermi-LAT, FACT, and MAGIC. With simultaneous observations of the flare, we built the broad-band SED and studied it in the framework of a leptonic and a hadronic model. The VHE γ -ray observations show a flux level of 55 per cent of the Crab Nebula flux above 300 GeV, similar to the historical maximum of 1995. The combination of MAGIC and Fermi-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The _ index of the intrinsic spectrum in the VHE γ -ray band is 2.04 ± 0.12stat ± 0.15sys.We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 Hz.