Luna, G. J. M.G. J. M.LunaMukai, K.K.MukaiSokoloski, J. L.J. L.SokoloskiNelson, T.T.NelsonKuin, P.P.KuinSEGRETO, ALBERTOALBERTOSEGRETOCUSUMANO, GIANCARLOGIANCARLOCUSUMANOJaque Arancibia, M.M.Jaque ArancibiaNuñez, N. E.N. E.Nuñez2020-10-012020-10-0120180004-6361http://hdl.handle.net/20.500.12386/27536A sudden increase in the rate at which material reaches the most internal part of an accretion disk, i.e., the boundary layer, can change its structure dramatically. We have witnessed such a change for the first time in the symbiotic recurrent nova T CrB. Our analysis of XMM-Newton, Swift Burst Alert Telescope (BAT)/X-Ray Telescope (XRT)/UltraViolet Optical Telescope (UVOT), and the American Association of Variable Stars Observers (AAVSO) V- and B-band data indicates that during an optical brightening event that started in early 2014 (∆V ≈ 1.5) the following occurred: (i) the hard X-ray emission as seen with BAT almost vanished; (ii) the XRT X-ray flux decreased significantly, while the optical flux remained high; (iii) the UV flux increased by at least a factor of 40 over the quiescent value; and (iv) the X-ray spectrum became much softer and a bright, new blackbody-like component appeared. We suggest that the optical brightening event, which could be a similar event to that observed about 8 years before the most recent thermonuclear outburst in 1946, is due to a disk instability.STAMPAenArticle10.1051/0004-6361/2018337472-s2.0-85056506893000449724800001https://www.aanda.org/articles/aa/abs/2018/11/aa33747-18/aa33747-18.html2018A&A...619A..61LFIS/05 - ASTRONOMIA E ASTROFISICA