The simultaneous low state spectral energy distribution of 1ES 2344+514 from radio to very high energies

Abstract

Context. BL Lacertae objects are variable at all energy bands on time scales down to minutes. To construct and interpret their spectral energydistribution (SED), simultaneous broad-band observations are mandatory. Up to now, the number of objects studied during such campaigns is verylimited and biased towards high flux states.Aims. We present the results of a dedicated multi-wavelength study of the high-frequency peaked BL Lacertae (HBL) object and known TeVemitter 1ES 2344+514 by means of a pre-organised campaign.Methods. The observations were conducted during simultaneous visibility windows of MAGIC and AGILE in late 2008. The measurements werecomplemented by Metsähovi, RATAN-600, KVA+Tuorla, Swift and VLBA pointings. Additional coverage was provided by the ongoing long-termF-GAMMA and MOJAVE programs, the OVRO 40-m and CrAO telescopes as well as the Fermi satellite. The obtained SEDs are modelled usinga one-zone as well as a self-consistent two-zone synchrotron self-Compton model.Results. 1ES 2344+514 was found at very low flux states in both X-rays and very high energy gamma rays. Variability was detected in the lowfrequency radio and X-ray bands only, where for the latter a small flare was observed. The X-ray flare was possibly caused by shock accelerationcharacterised by similar cooling and acceleration time scales. MOJAVE VLBA monitoring reveals a static jet whose components are stable overtime scales of eleven years, contrary to previous findings. There appears to be no significant correlation between the 15 GHz and R-band monitoringlight curves. The observations presented here constitute the first multi-wavelength campaign on 1ES 2344+514 from radio to VHE energies andone of the few simultaneous SEDs during low activity states. The quasi-simultaneous Fermi-LAT data poses some challenges for SED modelling,but in general the SEDs are described well by both applied models. The resulting parameters are typical for TeV emitting HBLs. Consequently itremains unclear whether a so-called quiescent state was found in this campaign.