Kapanadze, B.B.KapanadzeDorner, D.D.DornerVERCELLONE, STEFANOSTEFANOVERCELLONEROMANO, PatriziaPatriziaROMANOKapanadze, S.S.KapanadzeTabagari, L.L.Tabagari2024-01-122024-01-1220170094-243Xhttp://hdl.handle.net/20.500.12386/34528The TV-detected blazar Markarian 421 is the brightest high-energy peaked BL Lac (HBL) source in the GeV energy range, detectable with 3 sigma significance on daily timescales in medium and higher brightness states with Large Area Telescope onboard Fermi. The 0.3-300 GeV flux showed a strong variability on diverse time scales from the flares lasting a few weeks down to intraday flux fluctuations detected mostly in the flaring states. The source also exhibited a GeV spectral variability. We mostly observe a low spectral curvature in this band due to the presence of the Inverse Compton peak at the energies mainly beyond about 100 GeV. The GeV flux generally showed a significantly stronger correlation with the radio-UV fluxes than with those in the X-ray and TeV bands that confirms the hypothesis about the possible stronger connection between radio-UV and GeV emissions due the effect of Klein-Nishina suppression on the IC process, leading to the effective up-scattering of radio-UV photons at the GeV energies by the X-ray emitting electrons. <P />STAMPAenConference paper10.1063/1.4968967https://www.mpi-hd.mpg.de/hd2016/pages/news.php2017AIPC.1792e0021KFIS/05 - ASTRONOMIA E ASTROFISICA