Kapanadze, B.B.KapanadzeDorner, D.D.DornerVERCELLONE, STEFANOSTEFANOVERCELLONEROMANO, PatriziaPatriziaROMANOKapanadze, S.S.KapanadzeMdzinarishvili, T.T.Mdzinarishvili2020-06-012020-06-0120160035-8711http://hdl.handle.net/20.500.12386/25877We present an X-ray flaring activity of 1ES 1959+650 in 2015 August-2016 January, which was the most powerful and prolonged during the 10.75 yr period since the start of its monitoring with X-ray Telescope onboard Swift. A new highest historical 0.3-10 keV count rate was recorded three times that makes this object the third BL Lacertae source exceeding the level of 20 counts s<SUP>-1</SUP>. Along with the overall variability by a factor of 5.7, this epoch was characterized by fast X-ray flares by a factor of 2.0-3.1, accompanied with an extreme spectral variability. The source also shows a simultaneous flaring activity in the optical - UV and 0.3-100 GeV bands, although a fast γ-ray flare without significant optical - X-ray counterparts is also found. In contrast to the X-ray flares in the previous years, the stochastic acceleration seems be less important for the electrons responsible for producing X-ray emission during this flare that challenges the earlier suggestion that the electrons in the jets of TeV-detected BL Lacertae objects should undergo an efficient stochastic acceleration resulting in a lower X-ray spectral curvature.STAMPAenArticle10.1093/mnrasl/slw0542-s2.0-84982286514000383269900006https://academic.oup.com/mnrasl/article/461/1/L26/25895002016MNRAS.461L..26KFIS/05 - ASTRONOMIA E ASTROFISICA