English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., ashift of the synchrotron SED peak energy $\nu_{synch,p}$ above 1keV). Whilethose extreme states were so far observed only during high flux levels,additional multi-year observing campaigns are required to achieve a coherentpicture. Here, we report the longest investigation of the source from radio toVHE performed so far, focusing on a systematic characterisation of theintermittent extreme states. While our results confirm that 1ES 2344+514typically exhibits $\nu_{synch,p}>$1keV during elevated flux periods, we alsofind periods where the extreme state coincides with low flux activity. A strongspectral variability thus happens in the quiescent state, and is likely causedby an increase of the electron acceleration efficiency without a change in theelectron injection luminosity. We also report a strong X-ray flare (among thebrightest 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 thecampaign. It unveils complexity in the spectral evolution, where the commonharder-when-brighter trend observed in BL Lacs is violated. During a low andhard X-ray state, we find an excess of the UV flux with respect to anextrapolation of the X-ray spectrum to lower energies. This UV excess impliesthat at least two regions contribute significantly to theinfrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC,XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possiblyassociated with the 10 GHz radio core may explain such an excess. Finally, weinvestigate a VHE flare, showing an absence of simultaneous variability in the0.3-2keV band. Using a time-dependent leptonic modelling, we show that thisbehaviour, in contradiction to single-zone scenarios, can instead be explainedby a two-component model.

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