Multiwavelength observations of the black hole X-ray binary MAXI J1820+070 in the rebrightening phase. (3rd June 2022)

• Record Type: Journal Article
• Authors: Yoshitake, Tomohiro; Shidatsu, Megumi; Ueda, Yoshihiro; Mineshige, Shin; Murata, Katsuhiro L; Adachi, Ryo; Maehara, Hiroyuki; Nogami, Daisaku; Negoro, Hitoshi; Kawai, Nobuyuki; Niwano, Masafumi; Hosokawa, Ryohei; Saito, Tomoki; Oasa, Yumiko; Takarada, Takuya; Shigeyoshi, Takumi
• Is Part Of: Publications of the Astronomical Society of Japan. Volume 74:Number 4(2022)
• Page Start: 805
• Page End: 814
• Publication Date: 2022-06-03
• Subjects: accretion, accretion disks -- black hole physics -- X-rays: individual (MAXI J1820+070) -- X-rays: binaries; Astronomy -- Periodicals; 520.5
• DOI: 10.1093/pasj/psac038
• Languages: English
• ISSNs: 0004-6264

Abstract

Abstract: We report the results of quasi-simultaneous multiwavelength (near-infrared, optical, UV, and X-ray) observations of the Galactic X-ray black hole binary MAXI J1820+070 performed in 2019 May 10–13, ∼60 d after the onset of the first rebrightening phase. It showed a much larger optical-to-X-ray luminosity ratio (∼8) than in the initial outburst epoch. The primary components of the spectral energy distribution (SED) can be best interpreted by a radiatively inefficient accretion flow (RIAF) spectrum showing a luminosity peak in the optical band. By comparison with theoretical calculations, we estimate the mass accretion rate to be $\dot{M}/(8 L_{\rm Edd}/c^2) \sim 10^{-3}$, where c is the light speed and L Edd is the Eddington luminosity. In addition to the RIAF emission, a blue power-law component is detected in the optical–UV SED, which is most likely synchrotron radiation from the jet. The optical spectrum taken at the Seimei telescope shows a weak and narrow Hα emission line, the emitting region of which is constrained to be ≳2 × 10 4 times the gravitational radius. We suggest that the entire disk structure cannot be described by a single RIAF solution but cooler material responsible for the Hα emission must exist at the outermost region.