Multi-Wavelength Monitoring and Reverberation Mapping of a Changing Look Event in the Seyfert Galaxy NGC 3516статья
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Аннотация:https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/stab1138/6246402We present the results of photometric and spectroscopic monitoring campaigns of the changinglook AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from theX-ray to the optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-mWIRO telescope, and the XRT and UVOT of S wi f t. We found that NGC 3516 brightened toa high state and could be classified as Sy1.5 during the late spring of 2020. We have measuredtime delays in the responses of the Balmer and He II 4686 lines to continuum variations. Inthe case of the best-characterized broad H-beta line, the delay to continuum variability is about 17 days in the blue wing and is clearly shorter, 9 days, in the red, which is suggestive of inflow.As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting invery asymmetric profiles with blueshifted peaks during this high state. During the outburst theX-ray flux reached its maximum on 1 April 2020 and it was the highest value ever observedfor NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, 1.8 inthe maximum on 21 Apr 2020 compared to the mean 0.7 during earlier epochs before 2020.We have found that the UV and optical variations correlated well (with a small time delayof 1–2 days) with the X-ray until the beginning of April 2020, but later, until the end of Jun.2020, these variations were not correlated. We suggest that this fact may be a consequence ofpartial obscuration by Compton-thick clouds crossing the line of sight.