MAXI/GSC detection of an X-ray brightening from the Be/X-ray binary pulsar XTE J1946+274
ATel #17847; M. Nakajima, H. Negoro (Nihon U.), W. Iwakiri (Chiba U.), T. Mihara (RIKEN), K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, 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.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS)
on 17 Jun 2026; 08:37 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The MAXI/GSC nova alert system triggered on a weak X-ray brightening from the position consistent with the Be/X-ray binary pulsar XTE J1946+274 on 2026 June 16 (MJD 61207). The last X-ray outburst from this source was observed in 2024 by MAXI/GSC (ATel #16717), SVOM/ECLAIRs (ATel #16719), EP-WXT (ATel #16723), and NICER (ATel #16744). In addition, the optical follow-up observations of this outburst were performed by KAIT (ATel #16720) and SVOM/C-GFT (ATel #16722) and no obvious brightness changes were reported.
Our preliminary analysis revealed that the 4-10 keV flux averaged over four scans between 05:23 UT and 13:07 UT on 2026 June 16 was 0.0568 ± 0.0140 photons s-1 cm-2 (45 ± 11 mCrab). Using the orbital ephemeris (Porb = 172.7 ± 0.6 d, Tperi = 55514.8+0.8-1.1 MJD ; Marcu-Cheatham et al. 2015), we confirmed that the trigger date corresponds to an orbital phase of ∼0.96. Since the 12-50 keV pulsed flux observed by Fermi/GBM has been significantly detected since 2026 June 10 (MJD 61201), the precise onset phase of this outburst is estimated to be ∼0.93. Compared with the previous outburst in 2024, the current outburst has already reached 1.3 times of the previous peak flux.
Follow-up observations are encouraged to investigate whether the source will again exhibits a series of outbursts similar to those observed in 2010 (e.g. Marcu-Cheatham et al. 2015).
The latest X-ray light-curve can be checked at the following pages;
MAXI ( https://maxi.riken.jp/pubdata/v7.7l/J1945+273/index.html ) and
Fermi/GBM ( https://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/xtej1946.html ).
the MAXI alert information
