DISCOVERY OF MORE CHANGING LOOK EVENTS IN NGC 1566

摘要

We summarize a study of optical,UV and X-ray light curves of the nearby changinglook active galactic nucleus in the galaxy NGC 1566obtained with the Neil Gehrels Swift Observatory andthe MASTER Global Robotic Network over the period2007-2019. We also report on optical spectroscopyusing the South African Astronomical Observatory1.9-m telescope between Aug. 2018 and Mar. 2019. Asubstantial increase in X-ray flux by 1.5 orders of mag-nitude was observed following the brightening in theUV and optical bands during the first half of 2018 year.After a maximum was reached at the beginning ofJuly 2018, the fluxes in all bands decreased with somefluctuations. The most remarkable re-brightenings inof the light curve following the decline from the brightphase were observed at MJD range 58440-58494 and58603-58654. The amplitude of the flux variabilityis strongest in the X-ray band and decreases withincreasing wavelength. Low-resolution spectra (Aug2018) reveal a dramatic strengthening of the broademission as well as high-ionization [FeX]6374 lines.These lines were not detected so strongly in the pastpublished spectra. The change in the type of the opti-cal spectrum was accompanied by a significant changein the X-ray spectrum. For the last optical spectra (31Nov. 2018 – 28 Mar. 2019) we see dramatic changescompared to 2 Aug 2018, accompanied by the fadingof broad emission lines and high-ionization [FeX]6374line. Effectively, two changing look (CL) cases wereobserved for this object: changing to Sy1.2 type andthen returning to the low state as Sy 1.8–Sy1.9 type.Some possible explanations of the observed dramaticchanges are discussed.