MAXI/GSC detection of the outburst onset from Be/X-ray binary pulsar V 0332+53 (X0331+53)

ATel #9988; M. Nakajima, T. Kawase (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki (Tokyo Tech), T. Masumitsu, K. Tanaka, H. Negoro (Nihon U.), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), Y. Ueda, T. Kawamuro, T. Hori, S. Oda, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 23 Jan 2017; 15:42 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 an X-ray brightening from the Be/X-ray binary pulsar V 0332+53 (X0331+53) on 2017 January 21 (MJD 57774). The 4-10 keV flux of 6 hour binned data reached 0.045 +- 0.017 ph/s/cm² (36 +- 14 mCrab) on 2017 January 21.12 (MJD 57774.12). The trigger date corresponds to the orbital phase of ~0.21 which is derived from the following orbital parameters, P_orb=33.850 d, T₀=57157.88(MJD) (Doroshenko et al. 2016). Swift/BAT also detected the current X-ray outburst. The 15-50 keV flux reached 0.0112 +- 0.0017 ct/cm²/sec (51 +- 8 mCrab) on January 22 (MJD 57775). Although the MAXI/GSC data did not observe the outburst onset due to the source was in the out of FOV, the Swift/BAT data clearly exhibited that the current outburst started from the orbital phase of ~0.1. Comparing with the onset phase of the previous normal outbursts (~0.9 orbital phase; Atel#9447,#9596), it is turned out that the current outburst started later than the previous ones. The 15-50 keV flux increase rate is ~0.001 ct/cm²/sec/day, which is 1/3 times smaller than that of the previous normal outbursts. Above observational results somewhat differ from the characteristics of the normal outbursts observed from this source. We encourage multi wave-length observations to monitor the current event.

The latest source flux can be checked at the following pages;
MAXI(http://maxi.riken.jp/top/index.php?cid=1&jname=J0334+531),
Swift/BAT(http://swift.gsfc.nasa.gov/results/transients/V0332p53/),
Fermi/GBM(http://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/v0332.html), and
the BeXRB monitor page(http://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php).