MAXI/GSC observation of brightest outburst of the Be/X-ray binary pulsar 4U 0115+63 in 27 years

ATel #15975; M. Nakajima, H. Negoro (Nihon U.), W. Iwakiri (Chiba U.), K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, J. Kohara, S. Urabe, S. Nawa, N. Nemoto (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba, Y. Nakatani (Kyoto U.), M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 3 Apr 2023; 14:28 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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We report on the latest observation of the ongoing giant outburst source, the Be/X-ray binary pulsar 4U 0115+63 (ATel#15967). The day-averaged 5-12 keV flux has been increasing, and reached 0.673 ± 0.040 photons/s/cm² (715 ± 43 mCrab) on 2023 April 3 (MJD 60037). This is the brightest state observed by RXTE/ASM and MAXI/GSC in 27 years. In addition, the average flux increase rate between March 31 and April 3 records 130 mCrab/day which is the highest value observed in the 5-12 keV band so far. Further brightening might be expected from the latest scans observed by MAXI/GSC. We strongly encourage multi-wavelength observations to monitor this source.

The latest X-ray light-curve can be checked at the following pages;
MAXI ( http://maxi.riken.jp/pubdata/v7lrkn/J0118+637/index.html ),
Swift/BAT ( https://swift.gsfc.nasa.gov/results/transients/weak/4U0115p634/ ),
Fermi/GBM ( https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/4u0115.html ), and
the BeXRB monitor page ( http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_4U0115+63.html ).