Repetitive patterns in rapid optical variations in the nearby black-hole binary V404 Cygni

Mariko Kimura, Keisuke Isogai, Taichi Kato, Yoshihiro Ueda, Satoshi Nakahira, Megumi Shidatsu, Teruaki Enoto, Takafumi Hori, Daisaku Nogami, Colin Littlefield, Ryoko Ishioka, Ying Tung Chen, Sun Kun King, Chih Yi Wen, Shiang Yu Wang, Matthew J. Lehner, Megan E. Schwamb, Jen Hung Wang, Zhi Wei Zhang, Charles AlcockTim Axelrod, Federica B. Bianco, Yong Ik Byun, Wen Ping Chen, Kem H. Cook, Dae Won Kim, Typhoon Lee, Stuart L. Marshall, Elena P. Pavlenko, Oksana I. Antonyuk, Kirill A. Antonyuk, Nikolai V. Pit, Aleksei A. Sosnovskij, Julia V. Babina, Aleksei V. Baklanov, Alexei S. Pozanenko, Elena D. Mazaeva, Sergei E. Schmalz, Inna V. Reva, Sergei P. Belan, Raguli Ya Inasaridze, Namkhai Tungalag, Alina A. Volnova, Igor E. Molotov, Enrique De Miguel, Kiyoshi Kasai, William L. Stein, Pavol A. Dubovsky, Seiichiro Kiyota, Ian Miller, Michael Richmond, William Goff, Maksim V. Andreev, Hiromitsu Takahashi, Naoto Kojiguchi, Yuki Sugiura, Nao Takeda, Eiji Yamada, Katsura Matsumoto, Nick James, Roger D. Pickard, Tamás Tordai, Yutaka Maeda, Javier Ruiz, Atsushi Miyashita, Lewis M. Cook, Akira Imada, Makoto Uemura

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)


How black holes accrete surrounding matter is a fundamental yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disk, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. In fact, such oscillations have been observed only in sources with a high mass-accretion rate, such as GRS 1915+105 (refs 2, 3). These large-amplitude, relatively slow timescale, phenomena are thought to have physical origins distinct from those of X-ray or optical variations with small amplitudes and fast timescales (less than about 10 seconds) often observed in other black-hole binaries - for example, XTE J1118+480 (ref. 4) and GX 339â '4 (ref. 5). Here we report an extensive multi-colour optical photometric data set of V404 Cygni, an X-ray transient source containing a black hole of nine solar masses (and a companion star) at a distance of 2.4 kiloparsecs (ref. 8). Our data show that optical oscillations on timescales of 100 seconds to 2.5 hours can occur at mass-accretion rates more than ten times lower than previously thought. This suggests that the accretion rate is not the critical parameter for inducing inner-disk instabilities. Instead, we propose that a long orbital period is a key condition for these large-amplitude oscillations, because the outer part of the large disk in binaries with long orbital periods will have surface densities too low to maintain sustained mass accretion to the inner part of the disk. The lack of sustained accretion - not the actual rate - would then be the critical factor causing large-amplitude oscillations in long-period systems.

Original languageEnglish
Pages (from-to)54-58
Number of pages5
Issue number7584
Publication statusPublished - 2016 Jan 6

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