MAXI detection of X-ray brightening from the black hole X-ray binary V4641 Sgr
ATel #17581; M. Nakajima, H. Negoro, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U)
on 7 Jan 2026; 10:49 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Black Hole, Quasar, Transient
The MAXI/GSC nova alert system triggered an X-ray brightening from the black hole X-ray binary V4641 Sgr on January 6, 2026 (MJD 61046). It is a galactic microquasar discovered in 1999. The last outburst detected with MAXI was in September 2024 (ATel #16804, #16811, #16819, #16852, #16916). During the 16 years of the MAXI/GSC monitoring, the source exhibited major outbursts roughly once every two years. The latest 2-4 and 4-10 keV fluxes are 30 ± 4 and 19 ± 4 mCrab, respectively, on January 6, 2026. Since the source region was in the vicinity of the Sun until January 3, 2026 (MJD 61043), the onset date of the outburst is unclear. Compared with the early phases of previous outbursts, the flux in the present outburst is rising a few times more rapidly than previously observed ones with MAXI/GSC (ATel #5803, #7858, #11931, #14968, #16804). Follow-up observations are encouraged.
Trigger Information about V4641 Sgr
