MAXI/GSC detection of the onset of an X-ray outburst from the Be/X-ray binary pulsar 4U 0115+63
ATel #17858; M. Uenishi (Ehime U.), M. Serino (AGU), M. Nakajima, H. Negoro, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, 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 29 Jun 2026; 10:03 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 an X-ray brightening from the Be/X-ray binary pulsar 4U 0115+63 on 2026 June 29 (MJD 61220). The previous X-ray outburst from this source was observed on April 2024 (ATel #16573). The latest X-ray flux in 4-10 keV band, averaged over 4 scan transits between 20:48 UT on June 28 (MJD 61219) and 01:27 UT on June 29 (MJD 61220), was 47 ± 9 mCrab. The trigger date corresponds to an orbital phase of ∼0.06, calculated using the orbital ephemeris of Porb=24.3174 d and T0=53243.038(MJD) (Raichur & Paul 2010). At this stage, it is unclear whether this outburst will develop into a giant one. Multi-wavelength follow-up observations are encouraged to monitor the evolution of this outburst.
The latest X-ray light curves can be monitored at the following pages;
MAXI ( https://maxi.riken.jp/v7l3h/J0118+637/index.html ), and
Fermi/GBM ( https://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/4u0115.html ).
the MAXI alert information
