MAXI/GSC detection of a onset of the X-ray outburst from the Be/X-ray binary pulsar XTE J1858+034

ATel #17923; Y. Kawakubo (AGU), M. Nakajima, H. Negoro, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, 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), S. Ogawa (TUS)
on 24 Jul 2026; 09:17 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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The MAXI/GSC nova alert system triggered on an X-ray brightening from the Be/X-ray binary pulsar XTE J1858+034 on 2026 July 23. The latest X-ray flux in 4-10 keV band, averaged over 12 scan transits between 21:22 UT on July 22 (MJD 61243) and 19:03 UT on July 23 (MJD 61244), was 29 ± 4 mCrab. This exceeds the peak flux of its previous X-ray activity in 2025 (∼19 mCrab; ATel #17260), suggesting that the current event may develop into a major outburst. Multi-wavelength follow-up observations are encouraged.

the MAXI alert information