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

ATel #12841; M. Nakajima, H. Negoro (Nihon U.), K. Shiraishi (Tokyo Tech), Y. Sugawara (JAXA), S. Sugita (AGU), W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), S. Nakahira, T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Sugizaki, M. Oeda (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, N. Isobe, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
on 5 Jun 2019; 11:28 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 weak X-ray activity from the Be/X-ray binary pulsar 2S 1417-624. The system informed us of the activity several times in recent 10 days, but the source flux did not develop into normal outburst or giant one yet. The MAXI/GSC monitor data revealed that this faint activity started approximately from January 2019. With the flux increase rate of ~7E-5 ph/s/cm²/day (~0.06 mCrab/day), the 10-days averaged 5-12 keV flux reached 0.0186 +/- 0.0036 ph/s/cm² (20 +/- 4 mCrab) on 2019-05-29 (MJD 58632). A clear orbital modulation in the 2-20 keV X-ray flux was not confirmed. In this low acitive period, the 5-12keV/3-5keV hardness ratio increased to ~2.5 which is corresponding to the observed value of the previous giant outburst peak (Krimm et al., Atel #11569). The Neil Gehrels Swift observatory also monitor the current low-level activity. In the 15-50 keV band, the 10-days averaged flux reached 0.011 +/- 0.004 counts/s/cm2 (50 +/- 18 mCrab) on 2019-05-26 (MJD 58629). Among the Be/X-ray binaries except for X Persei, such a gradual flux increase in the time span of half year is not observed so far. We encourage multi-wavelength observations to investigate this peculiar event.

The latest source flux can be checked at the following pages;
MAXI(http://maxi.riken.jp/pubdata/v6l.rkn/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).