MAXI/GSC detection of a recurrent X-ray outburst from the Be/X-ray binary pulsar LS V +44 17 (RX J0440.9+4431)

ATel #17931; T. Usuki (Ehime. Univ.), 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, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, 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 30 Jul 2026; 10:00 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 a position consistent with the Be/X-ray binary pulsar LS V +44 17 (RX J0440.9+4431) on 2026 July 30 (MJD 61251). Prior to this trigger, the source region had been outside the MAXI/GSC FOV since July 1 (MJD 61222), thus the exact onset of the current outburst remains uncertain. Preliminary analysis reveals that the latest 4-10 keV flux, averaged over 4 scans between 23:06 UT on July 29 (MJD 61250) and 03:45 UT on July 30 (MJD 61251), reached 119 ± 17 mCrab. Compared to the peak flux of the previous activity in 2026 May (∼50 mCrab; ATel #17816), the flux has already doubled. Multi-wavelength follow-up observations are encouraged to monitor whether this event develops into a major outburst.

The latest X-ray light-curve can be checked at the following pages;
MAXI ( https://maxi.riken.jp/v7l3h/J0440+445/index.html ) and
Fermi/GBM ( https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/rxj0440.html ).

the MAXI alert information