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    A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign
    (Basel : MDPI, 2016) Zola, S.; Valtonen, M.; Bhatta, G.; Goyal, A.; Debski, B.; Baran, A.; Krzesinski, J.; Siwak, M.; Ciprini, S.; Gopakumar, A.; Jermak, H.; Nilsson, K.; Reichart, D.; Matsumoto, K.; Sadakane, K.; Gazeas, K.; Kidger, M.; Piirola, V.; Alicavus, F.; Baliyan, K.; Berdyugin, A.; Boyd, D.; Campas Torrent, M.; Campos, F.; Carrillo Gómez, J.; Caton, D.; Chavushyan, V.; Dalessio, J.; Dimitrov, D.; Drozdz, M.; Er, H.; Erdem, A.; Escartin Pérez, A.; Fallah Ramazani, V.; Filippenko, A.; Garcia, F.; Gómez Pinilla, F.; Gopinathan, M.; Haislip, J.; Harmanen, J.; Hudec, R.; Hurst, G.; Ivarsen, K.; Jelinek, M.; Joshi, A.; Kagitani, M.; Kaur, N.; Keel, W.; LaCluyze, A.; Lee, B.; Lindfors, E.; Lozano de Haro, J.; Moore, J.; Mugrauer, M.; Naves Nogues, R.; Neely, A.; Nelson, R.; Ogloza, W.; Okano, S.; Pandey, J.; Perri, M.; Pihajoki, P.; Poyner, G.; Provencal, J.; Pursimo, T.; Raj, A.; Reinthal, R.; Sadegi, S.; Sakanoi, T.; Sameer, null; Salto González, J.-L.; Schweyer, T.; Soldán Alfaro, F.; Karaman, N.; Sonbas, E.; Steele, I.; Stocke, J.; Strobl, J.; Takalo, L.; Tomov, T.; Tremosa Espasa, L.; Valdes, J.; Valero Pérez, J.; Verrecchia, F.; Webb, J.; Yoneda, M.; Zejmo, M.; Zheng, W.; Telting, J.; Saario, J.; Reynolds, T.; Kvammen, A.; Gafton, E.; Karjalainen, R.; Blay, P.
    We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.
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    A Transient “Changing-look” Active Galactic Nucleus Resolved on Month Timescales from First-year Sloan Digital Sky Survey V Data
    (London : Institute of Physics Publ., 2022) Zeltyn, Grisha; Trakhtenbrot, Benny; Eracleous, Michael; Runnoe, Jessie; Trump, Jonathan R.; Stern, Jonathan; Shen, Yue; Hernández-García, Lorena; Bauer, Franz E.; Yang, Qian; Dwelly, Tom; Ricci, Claudio; Green, Paul; Anderson, Scott F.; Assef, Roberto J.; Guolo, Muryel; MacLeod, Chelsea; Davis, Megan C.; Fries, Logan; Gezari, Suvi; Grogin, Norman A.; Homan, David; Koekemoer, Anton M.; Krumpe, Mirko; LaMassa, Stephanie; Liu, Xin; Merloni, Andrea; Martínez-Aldama, Mary Loli; Schneider, Donald P.; Temple, Matthew J.; Brownstein, Joel R.; Ibarra-Medel, Hector; Burke, Jamison; Pellegrino, Craig; Kollmeier, Juna A.
    We report the discovery of a new “changing-look” active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z = 0.2603, identified through repeat spectroscopy from the fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020-2021 shows a dramatic dimming of Δg ≈ 1 mag, followed by a rapid recovery on a timescale of several months, with the ≲2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011-2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve.