Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES~2344+514

A&A 682, A114 (2024) The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $\nu_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional multi-year observing campaigns are requir...

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Main Authors:	Agudo, I, Aniello, T, Ansoldi, S, Antonelli, L. A, Engels, A. Arbet, Artero, M, Asano, K, Baack, D, Baquero, A, Bernardini, E, Bernete, J, Besenrieder, J, Bigongiari, C, Blanch, O, Bonnoli, G, Bošjak, Ž, Busetto, G, Campoy-Ordaz, A, Carosi, R, Castro-Tirado, A. J, Cikota, S, Contreras, J. L, Covino, S, De Lotto, B, Del Popolo, A, Delgado, J, Depaoli, D, Di Venere, L, Prester, D. Dominis, Elsaesser, D, Escudero, J, Font, L, López, R. J. García, Gasparyan, S, Grau, R, Green, J. G, Herrera, J, Hrupec, D, Martínez, I. Jiménez, Kerszberg, D, Kluge, G. W, Lezáun, M. Láinez, Leone, F, Lindfors, E, Linhoff, L, Lombardi, S, Longo, F, López-Moya, M, Loporchio, S, Lorini, A, Mang, N, Mas-Aguilar, A, Mazin, D, Mender, S, Morcuende, D, Nanci, C, Neustroev, V, Nigro, C, Ekoume, T. Njoh, Okumura, A, Paiano, S, Palatiello, M, Paneque, D, Paoletti, R, Pavlović, D, Persic, M, Moroni, P. G. Prada, Principe, G, Priyadarshi, C, Rhode, W, Saito, T, Satalecka, K, Saturni, F. G, Schleicher, B, Schubert, J. L, Stamerra, A, Strišović, J, Takeishi, R, Terzić, T, Teshima, M, Truzzi, S, Ventura, S, Vitale, V, Wunderlich, C, Leto, T. Yamamoto M. Perri F. Verrecchia C, Chatterjee, R, Raiteri, C. M, Bachev, R, Strigachev, A, Stojanovic, M, Larionova, E. G, Hou, W. J, Lin, C. S, Tsai, A, Weaver, Z. R, Acosta-Pulido, J. A, Carosati, D, Ivanidze, R. Z, Gazeas, K, Kiehlmann, S
Format:	Journal Article
Language:	English
Published:	05-10-2023
Subjects:	Physics - High Energy Astrophysical Phenomena
Online Access:	Get full text
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Summary:	A&A 682, A114 (2024) The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $\nu_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to VHE performed so far, focusing on a systematic characterisation of the intermittent extreme states. While our results confirm that 1ES 2344+514 typically exhibits $\nu_{synch,p}>$1keV 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 of the electron acceleration efficiency without a change in the electron injection luminosity. We also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of $\nu_{synch,p}$. 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. 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 contribute significantly 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 0.3-2keV band. Using a time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model.
DOI:	10.48550/arxiv.2310.03922