MAXI/GSC detection of an X-ray brightening from the Be/X-ray binary pulsar XTE J1859+083
ATel #17730; M. Nakajima, H. Negoro (Nihon U.), T. Mihara (RIKEN), K. Takagi, H. Nishio (Nihon U.), T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, D. Iijima, 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, 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 28 Mar 2026; 06:33 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 17770
On 2026 March 24 (MJD 61123), the MAXI/GSC nova alert system triggered on a faint X-ray enhancement at a position consistent with the Be/X-ray binary pulsar XTE J1859+083. The X-ray flux averaged over the scans on March 24 was 34 ± 5 mCrab (4.0-10.0 keV, 1σ error). The previous X-ray activity from this source was recorded in 2015 (ATel #7034, #7037, #7045, #7067, #7425).
Prior to this detection, the region containing XTE J1859+083 had been within the field of view of degraded GSC cameras (camera IDs: 3 and 6) since 2026 March 11 (MJD 61110), making it difficult to monitor faint X-ray activity (see: https://maxi.riken.jp/pubdata/v7.6l/skyimg/skyimg_mjd61110.html). However, due to an attitude change of the ISS on March 24 (MJD 61123), the source was observed by the nominal GSC cameras for one day (https://maxi.riken.jp/pubdata/v7.6l/skyimg/skyimg_mjd61123.html).
Following the return of the ISS to its nominal attitude on March 25 (MJD 61124; https://maxi.riken.jp/pubdata/v7.6l/skyimg/skyimg_mjd61124.html), XTE J1859+083 again became unobservable by the operational cameras. Monitoring with the nominal GSC cameras is expected to resume at the end of March. Multi-wavelength follow-up observations are encouraged to confirm the development of the current outburst.
