The MAXI/GSC Nova-Alert System and results of its first 68 months

Hitoshi Negoro, Mitsuhiro Kohama, Motoko Serino, Hiroki Saito, Tomonori Takahashi, Sho Miyoshi, Hiroshi Ozawa, Fumitoshi Suwa, Masato Asada, Kosuke Fukushima, Satoshi Eguchi, Nobuyuki Kawai, Jamie Kennea, Tatehiro Mihara, Mikio Morii, Satoshi Nakahira, Yuji Ogawa, Aya Sugawara, Hiroshi Tomida, Shiro UenoMasaki Ishikawa, Naoki Isobe, Taiki Kawamuro, Masashi Kimura, Takahiro Masumitsu, Yujin E. Nakagawa, Motoki Nakajima, Takanori Sakamoto, Megumi Shidatsu, Mutsumi Sugizaki, Juri Sugimoto, Kazuhiko Suzuki, Toshihiro Takagi, Kazuki Tanaka, Yohko Tsuboi, Hiroshi Tsunemi, Yoshihiro Ueda, Kazutaka Yamaoka, Makoto Yamauchi, Atsumasa Yoshida, Masaru Matsuoka

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Various transient phenomena on a timescale ranging from seconds to days appear at unexpected sky positions in X-rays. MAXI, Monitor of All-sky X-ray Image, on the International Space Station has been monitoring about 95% of the sky a day and has detected transient objects since 2009 August. Here, we describe quasi-real-time data processing systems of MAXI and a subsequent nova-alert system to find transient objects, and present the capabilities for the nova-alert system to detect transient events with excess fluxes from ≥80 mCrab in a single scan transit to ≥8 mCrab for 4 d, and to send prompt alert information to the world in less than 30 s after the onboard detection of a burst, making the best use of the International Space Station (ISS) real-time network. We also report on highlights of scientific results obtained with the system until the end of the first extended mission phase, 2015 March. Including 15 X-ray novae solely or independently discovered, we have reported on 177 transient phenomena, such as X-ray bursts, outbursts, and state transitions of X-ray binaries and X-ray flares from active stars and blazars, via the Astronomer's Telegram, and on 63 burst phenomena of other types via the Gamma-ray Coordinates Network. We summarize the results of these transient sources and phenomena focusing on the detections with the nova-alert system, and some new transients yet unpublished or requiring attention.

Original languageEnglish (US)
Article numberS1
JournalPublications of the Astronomical Society of Japan
StatePublished - Jun 1 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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