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 nu(synch.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. Morethan 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 nu(synch.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 e fficiency 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 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. 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.
Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514 / Null, N., Abe, H., Abe, S., Acciari, V.A., Agudo, I., Aniello, T., Ansoldi, S., Antonelli, L.A., Arbet Engels, A., Arcaro, C., Artero, M., Asano, K., Baack, D., Babić, A., Baquero, A., Barres de Almeida, U., Batković, I., Baxter, J., Becerra González, J., Bernardini, E., et al.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - 682:(2024). [10.1051/0004-6361/202347845]
Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514
Giglietto, N.Membro del Collaboration Group
;Loporchio, S.Membro del Collaboration Group
;
2024
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 nu(synch.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. Morethan 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 nu(synch.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 e fficiency 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 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. 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
