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

Abstract

Extreme High-frequency BL~Lacs (EHBL) feature their synchrotron peak of the broadband spectral energy distribution (SED) at $\hat{I}{½}_{\mathrm{s}}\ge$10${}^{17}$\,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 August 2016, 1ES~2344+514 was detected with the ground-based ${\hat{I}}^3$-ray telescope FACT during a high ${\hat{I}}^3$-ray state, triggering multi-wavelength (MWL) observations. We studied the MWL light curves of 1ES~2344+514 during the 2016 flaring state, using data from radio to VHE ${\hat{I}}^3$ rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, \textit{Swift}-UVOT, \textit{Swift}-XRT, \textit{Fermi}-LAT, FACT and MAGIC. With simultaneous observations of the flare, we built the broadband SED and studied it in the framework of a leptonic and an hadronic model. The VHE ${\hat{I}}^3$-ray observations show a flux level of 55\% of the Crab Nebula flux above 300\,GeV, similar to the historical maximum of 1995. The combination of MAGIC and \textit{Fermi}-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The $\hat{I}“$ index of the intrinsic spectrum in the VHE ${\hat{I}}^3$-ray band is $2.04\pm 0.12_{\mathrm{stat}}\pm 0.15_{\mathrm{sys}}$. We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to $10^{18}$\,Hz

Accepted in MNRAS. Corresponding authors: M. Manganaro, A. Arbet Engels, D. Dorner