Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514
Covino, S.; Antonelli, L. A.; D'Elia, V.; Zheng, W.; Filippenko, A. V.; Schmidt, K.; Chen, W. P.; Prada Moroni, P. G.; Fukazawa, Y.; Giglietto, N.; Giordano, F.; Hadasch, D.; Longo, F.; Paneque, D.; Vitale, V.; Okumura, A.; Villata, M.; Tavecchio, F.; Walter, R.; Hütten, M.; Carnerero, M. I.; Raiteri, C. M.; Damljanovic, G.; Bošnjak, Ž.; Leone, F.; Stamerra, A.; Larionov, V. M.; Acosta-Pulido, J. A.; Bachev, R.; Carosati, D.; Grishina, T. S.; Ibryamov, S.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Larionova, E. G.; Liodakis, I.; Morozova, D. A.; Savchenko, S. S.; Semkov, E.; Strigachev, A.; Vasilyev, A. A.; Vince, O.; Readhead, A. C. S.; Castro-Tirado, A. J.; Gazeas, K.; Perri, M.; Biland, A.; Gaug, M.; Teshima, M.; Paredes, J. M.; D'Ammando, F.; Di Venere, L.; Agudo, I.; Jorstad, S. G.; Ansoldi, S.; Arcaro, C.; Barres de Almeida, U.; Becerra González, J.; Bernardini, E.; Berti, A.; Blanch, O.; Bonnoli, G.; Carosi, R.; Carosi, A.; Colombo, E.; Contreras, J. L.; Cortina, J.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Di Pierro, F.; Dominis Prester, D.; Dorner, D.; Doro, M.; Elsaesser, D.; Fallah Ramazani, V.; Font, L.; García López, R. J.; Hahn, A.; Herrera, J.; Hrupec, D.; Kubo, H.; Kushida, J.; Lindfors, E.; Lombardi, S.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Mariotti, M.; Martínez, M.; Mazin, D.; Mirzoyan, R.; Moralejo, A.; Neustroev, V.; Nishijima, K.; Noda, K.; Paiano, S.; Palatiello, M.; Paoletti, R.; Persic, M.; Prandini, E.; Rhode, W.; Ribó, M.; Rico, J.; Saito, T.; Satalecka, K.; Schweizer, T.; Sitarek, J.; Temnikov, P.; Terzić, T.; MAGIC Collaboration; Hovatta, T.; Verrecchia, F.; Nakamori, T.; Tajima, H.; Leto, C.; Lamastra, A.; Acciari, V. A.; Arbet Engels, A.; Baack, D.; Babić, A.; Besenrieder, J.; Bigongiari, C.; Busetto, G.; Chai, Y.; Cikota, S.; Delfino, M.; Delgado, J.; Depaoli, D.; Fattorini, A.; Foffano, L.; Fukami, S.; Gasparyan, S.; Inada, T.; Ishio, K.; Kerszberg, D.; López-Oramas, A.; Loporchio, S.; Machado de Oliveira Fraga, B.; Miceli, D.; Miranda, J. M.; Molina, E.; Morcuende, D.; Nigro, C.; Nozaki, S.; Righi, C.; Sahakyan, N.; Strom, D.; Suda, Y.; Tosti, L.; van Scherpenberg, J.; Vigorito, C. F.; Asano, K.; Saturni, F. G.; Delgado Mendez, C.; Kiehlmann, S.; Jormanainen, J.; Del Popolo, A.; Principe, G.; Jordan, B.; Weaver, Z. R.; Stojanovic, M.; Emery, G.; Carretero-Castrillo, M.; Tutone, A.; Tsai, A.; Abe, H.; Abe, S.; Aniello, T.; Artero, M.; Baquero, A.; Batković, I.; Baxter, J.; Bernete, J.; Burelli, I.; Campoy-Ordaz, A.; Cifuentes, A.; D'Amico, G.; Escudero, J.; Fariña, L.; Giesbrecht Paiva, J. G.; Gliwny, P.; Grau, R.; Green, J. G.; Heckmann, L.; Imazawa, R.; Iotov, R.; Jiménez Martínez, I.; Kluge, G. W.; Kobayashi, Y.; Kouch, P. M.; Láinez Lezáun, M.; Linhoff, L.; López-Moya, M.; Lorini, A.; Mang, N.; Martínez-Chicharro, M.; Mas-Aguilar, A.; Menchiari, S.; Mender, S.; Miener, T.; Molero González, M.; Mondal, H. A.; Nanci, C.; Nikolić, L.; Njoh Ekoume, T.; Ohtani, Y.; Otero-Santos, J.; Pavlović, D.; Pihet, M.; Pirola, G.; Podobnik, F.; Priyadarshi, C.; Schleicher, B.; Schmuckermaier, F.; Schubert, J. L.; Sciaccaluga, A.; Spolon, A.; Strišković, J.; Takeishi, R.; Terauchi, K.; Truzzi, S.; Ubach, S.; Ventura, S.; Verguilov, V.; Viale, I.; Wunderlich, C.; Yamamoto, T.; Multi-wavelength Collaborators; Das, S.; Chatterjee, R.; Jovanovic, M. D.; Troitskiy, I. S.; Troitskaya, Y. V.; Hou, W. J.; Lin, C. S.; Ivanidze, R. Z.; Vrontaki, K.
Japan, Spain, Italy, Germany, Croatia, Brazil, Switzerland, Norway, Austria, Armenia, Poland, Finland, India, Bulgaria, Serbia, Russia, Taiwan, United States, Georgia, Ireland, Greece
Abstract
Aims: The BL Lac 1ES 2344+514 is known for temporary extreme properties characterised by a shift of the synchrotron spectral energy distribution (SED) peak energy νsynch, p above 1 keV. While those extreme states have only been observed during high flux levels thus far, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to very high energy (VHE) performed so far, focussing on a systematic characterisation of the intermittent extreme states.
Methods: We organised a monitoring campaign covering a 3-year period from 2019 to 2021. More than ten instruments participated in the observations in order to cover the emission from radio to VHE. In particular, sensitive X-ray measurements by XMM-Newton, NuSTAR, and AstroSat took place simultaneously with multi-hour MAGIC observations, providing an unprecedented constraint of the two SED components for this blazar.
Results: While our results confirm that 1ES 2344+514 typically exhibits νsynch, p > 1 keV during elevated flux periods, we also find periods where the extreme state coincides with low flux activity. A strong spectral variability thus happens in the quiescent state, and is likely caused by an increase in the electron acceleration efficiency without a change in the electron injection luminosity. On the other hand, we also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of νsynch, p. During this particular flare, the X-ray spectrum is among the softest of the campaign. It unveils complexity in the spectral evolution, where the common harder-when-brighter trend observed in BL Lacs is violated. By combining Swift-XRT and Swift-UVOT measurements during a low and hard X-ray state, we find an excess of the UV flux with respect to an extrapolation of the X-ray spectrum to lower energies. This UV excess implies that at least two regions significantly contribute to the infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC, XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly associated with the 10 GHz radio core may explain such an excess. Finally, we investigate a VHE flare, showing an absence of simultaneous variability in the 0.3−2 keV band. Using time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model.