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MAXI Discovers Bright Black Hole X-ray Transient "MAXI J1820+070"

Last Updated: May 9, 2019

Japan Aerospace Exploration Agency
Ehime University


The black hole X-ray transient MAXI J1820+070 (J1820 for short) was discovered with the Monitor of All-sky X-ray Image (MAXI), an X-ray camera installed on the Exposed Facility of the Japanese Experiment Module "Kibo" aboard the International Space Station (ISS), by the MAXI research group of Megumi Shidatsu, assistant professor at Ehime University, Satoshi Nakahira, JAXA visiting researcher from RIKEN, and researchers from other institutes in Japan. The over eight-month monitoring of its transient activity has continued after this discovery, using JAXA's MAXI and other Japanese optical and near-infrared telescopes. In November 2018, the discovery of J1820 appeared in the Astrophysical Journal, an American scientific journal of astronomy and astrophysics, and afterward the result of the subsequent monitoring observations was released in the April 5, 2019 issue of the journal.

Following the discovery in constellation Ophiuchus on March 11, 2018, J1820 rapidly brightened by 50 times only in 2 weeks and then gradually decreased its brightness over three and a half months. At the end of June 2018, however, it started a dramatic increase in its brightness again. In July, it reached twice the brightness of the Crab Nebula, and thus became the second brightest X-ray object next to Scorpius X-1 in the whole sky. Such two-step brightening is unusual in black hole X-ray transients. A similar behavior was observed in XTE J1752-223, which was discovered also with the MAXI in 2009, but no other similar sources had been reported ever since.

MAXI's discovery triggered extensive follow-up observations of J1820 by X-ray observatories, including the NASA's Neutron star Interior Composition Explorer (NICER) also aboard the ISS and X-ray telescope (XRT) of the orbiting satellite Swift. The transient was frequently observed in visual light, infrared, and radio with ground-based telescopes as well. Roughly 60 observations have been reported to the Astronomer's Telegram. During the first four months in particular until the peak of the X-ray brightness, the source exhibited rapid variations of its brightness several times in a few seconds or less, in X-rays and visual light. The X-ray flux variation was likely generated at the inner parts of the accretion disk formed around the black hole, while the visible light variation was mainly observed in jets launched near the black hole. Megumi Shidatsu and the team also conducted X-ray, optical, and near-infrared observations with MAXI and Japanese telescopes, in collaboration with the Japanese universities' research team, called OISTER (Optical and Infrared Synergetic Telescopes for Education and Research). They successfully detected emissions from the accretion disk and the jets simultaneously, and found that the base of the jets is likely to have a strong magnetic field. The series of observations demonstrates that MAXI's rapid detection of X-ray sources offers astronomers around the world opportunities to observe transients and greatly contributes to a better understanding of high energy phenomena in black hole X-ray transients.

*Black hole X-ray transient
A black hole X-ray transient is a binary star system consisting of a stellar-mass black hole and a companion star orbiting around each other. Gravitational and magnetic forces of the stellar black hole can siphon gas from the nearby companion star, forming a gas disk around the black hole, called an accretion disk. The inner parts of the disk closer to the black hole glow in higher energy X-rays. Collimated outflows called the jets sometimes emit perpendicularly to the accretion disk near the black hole.

Research paper information

Discovery of MAXI J1820+070 and observations in the first four months after the discovery

Journal: The Astrophysical Journal

Article: X-Ray, Optical, and Near-infrared Monitoring of the New X-Ray Transient MAXI J1820+070 in the Low/Hard State


Authors: Megumi Shidatsu, Satoshi Nakahira, Satoshi Yamada, Taiki Kawamuro, Yoshihiro Ueda, Hitoshi Negoro, Katsuhiro L. Murata, Ryosuke Itoh, Yutaro Tachibana, Ryo Adachi, Yoichi Yatsu, Nobuyuki Kawai, Hidekazu Hanayama, Takashi Horiuchi, Hiroshi Akitaya, Tomoki Saito, Masaki Takayama, Tomohito Ohshima, Noriyuki Katoh, Jun Takahashi, Takahiro Nagayama, Masayuki Yamanaka, Miho Kawabata, Tatsuya Nakaoka, Seiko Takagi, Tomoki Morokuma, Kumiko Morihana, Hiroyuki Maehara, and Kazuhiro Sekiguchi

Monitoring over the entire brightening period

Journal: The Astrophysical Journal

Article: X-Ray and Optical Monitoring of State Transitions in MAXI J1820+070

DOI: 10.3847/1538-4357/ab09ff

Authors: Megumi Shidatsu, Satoshi Nakahira, Katsuhiro L. Murata, Ryo Adachi, Nobuyuki Kawai, Yoshihiro Ueda, and Hitoshi Negoro

Related link

MAXI's discovery and 200-day observation of MAXI J1535-571, one of the brightest X-ray novae of this century, are published in the astronomical journal of Japan! (November 2, 2018)

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