MAXI/GSC observation of a series of X-ray outbursts with a ∼60 day interval from the Be/X-ray binary pulsar LS V +44 17 (RX J0440.9+4431)

ATel #18071; M. Nakajima, H. Negoro (Nihon 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.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS)
on 22 Sep 2026; 13:10 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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We report on anomalous X-ray activity from the Be/X-ray binary pulsar LS V +44 17 (RX J0440.9+4431). This binary system, hosting a ∼205 sec X-ray pulsar, had previously been suggested to have an orbital period of ∼150 days, estimated from the recurrence intervals of a series of X-ray outbursts observed in 2010-2011 (Reig 2011; Tsygankov et al. 2012; Ferrigno et al. 2013). In 2022, the source again exhibited a normal outburst, with its onset phase consistent with the anticipated ∼150-day period (e.g., Li et al. 2026). However, the source has not repeated this ∼150 day periodicity recently. Since 2026 March 3, four consecutive X-ray outbursts have been detected: in 2026 March (SVOM/ECLAIR, ATel #17712), 2026 May (MAXI/GSC, ATel #17816), 2026 July (MAXI/GSC, ATel #17931), and 2026 September (EP/WXT, ATel #18063; Fermi/GBM, ATel #18067; MAXI/GSC). These outbursts occurred at recurring intervals of ∼60 days, significantly deviating from the previously claimed ~150 day period. These short outburst intervals may be related to major structural changes in the circumstellar disk around the Be star, or they could suggest a different, shorter orbital period. Multi-wavelength observations are strongly encouraged to elucidate the origin of this anomalous periodicity.

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 ).

the MAXI alert information