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

ATel #17816; M. Nakajima (Nihon U.), T. Mihara (RIKEN), H. Negoro, 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, 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, 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 27 May 2026; 02:00 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

Tweet

The MAXI/GSC nova alert system triggered on a weak X-ray brightening from the Be/X-ray binary pulsar LS V +44 17 (RX J0440.9+4431) on 2026 May 22 (MJD 61182). This source had been below the detection limit of MAXI/GSC for three years since its last major outburst in 2023 (ATel #15835, #15848, #15868, #15874, #15880, #15892, #15907, #15913). The day-averaged flux in the 4-10 keV band, derived from the MAXI/GSC public data (https://maxi.riken.jp/v7l3h/J0440+445/index.html), was 0.025±0.006 photons cm^-2 s^-1 (21±5 mCrab) on May 22 (MJD 61182). Because the region with the LS V +44 17 was outside the FOV of MAXI/GSC until May 18 (MJD 61178), the exact onset time of this brightening is unclear. The source flux remained at a nearly constant level of ∼0.019 photons cm^-2 s^-1 (∼16 mCrab) for a week since May 19 (MJD 61179). However, on May 26 (MJD 61186), the source flux exhibited a further brightening. The flux doubled to 0.044±0008 photons cm^-2 s^-1 (36±6 mCrab). Multi-wavelength follow-up observations are encouraged.

The latest X-ray light-curve can be checked at the following pages;
MAXI ( https://maxi.riken.jp/v7l3h/J0440+445/index.html ),
Swift/BAT ( https://swift.gsfc.nasa.gov/results/transients/weak/LSVp4417/ ),
Fermi/GBM ( https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/rxj0440.html ).