A Novel View of AGN Accretion Flows Revealed by X-ray and Optical Monitoring

Kazuo Makishima, Hirofumi Noda, Takeo Minezaki, Mitsuru Kokubo, Tomoki Morokuma, Mamoru Doi, Yuki Moritani, Kazuhiro Nakazawa, Makoto Watanabe, Hikaru Nakao, Masataka Imai, Kenji Kawaguchi, Katsutoshi Takagi, Koji S. Kawabata, Tatsuya Nakaoka, Miho Kawabata, Makoto Uemura, Yasushi Fukazawa, Michitoshi Yoshida, Kumiko Morihana, Yoich Itoh, Yuhei Takagi, Akira Arai, Ryosuke Itoh, Yoshihiko Saito, and Shin'ya Yamada

The Seyfert galaxy NGC 3516 was monitored for about a year, with Suzaku and five Japanese optical telescopes (Pirka, Kiso Schmidt, Nayuta, MITSuME, and Kanata). In both X-rays and optical, NGC 3516 remained in its very faint state. The source meantime varied in X-rays by a factor of ∼ 20, and in the optical B-band by a similar amount in the flux difference. A tight correlation was detected between the two bands, with an optical delay by 2.0+0.6−0.7 days. The optical change is hence due to X-ray reprocessing, but the lag is too large for the standard “lamppost” X-ray source illuminating an accretion disk that is not truncated. The results are successfully explained by a hot accretion flow inside a truncated disk.

7 years of MAXI: monitoring X-ray Transients

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