MAXI/GSC detection of the outburst onset from the Be/X-ray binary pulsar 2S 1417-624

ATel #11479; M. Nakajima, H. Negoro (Nihon U.), M. Serino (AGU), T. Mihara (RIKEN), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), M. Sugizaki, S. Nakahira, W. Iwakiri, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), T. Kawase, A. Sakamaki, Y. Maruyama (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda, T. Morita, S. Yamada (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Yamauchi, C. Hanyu, K. Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.)
on 27 Mar 2018; 09:11 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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The MAXI/GSC nova-alert system (Negoro et al. 2016) detected the X-ray brightening from the Be/X-ray binary pulsar 2S 1417-624 on 24 March 2018 (MJD 58201). The day-averaged 4-10 keV flux indicates that the current X-ray outburst started from 18 March 2018 (MJD 58195), which corresponds to the binary orbital phase of 0.31 (P_orb=42.12d, T_peri=51485.059(MJD); Raichur et al. 2010). The moderate flux increase still continues, and the 4-10 keV flux has reached 0.0267 +- 0.0087 ph/s/cm² (27 +- 8 mCrab) on 25 March 2018 (MJD 58202). Swift/BAT also observes the on-going outburst. The 15-50 keV flux shows the steady increase, and reached 0.0083 +/- 0.0019 counts/s/cm2 (38 +/- 9 mCrab) on 26 March 2018 (MJD 58203). Before this brightening, Fermi/GBM (Beklen et al. 2009, ATel#2275), Swift/BAT (Krimm et al. 2009, ATel#2276), and MAXI/GSC observed the giant X-ray outburst from this source in 2009. The onset of the previous giant event coincides with the orbital phase of ~0.3. Since there are similarities in the outburst onset phase and the increasing trend, the current outburst might be a giant one since 2009. We encourage multi-wavelength observations to monitor the current event.

The latest source flux can be checked at the following pages;
MAXI(http://maxi.riken.jp/pubdata/v3/J1421-626/index.html),
Swift/BAT(https://swift.gsfc.nasa.gov/results/transients/weak/H1417-624/),
Fermi/GBM(https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/2s1417.html),and
the BeXRB monitor page(http://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php).