MAXI/GSC detection of an X-ray brightening from V 0332+53

ATel #7685; M. Nakajima (Nihon U.), T. Mihara (RIKEN), H. Negoro (Nihon U.), N. Kawai (Tokyo Tech), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), M. Arimoto, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech),A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R. Imatani (Osaka U.), K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM)
on 22 Jun 2015; 07:01 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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On 2015 June 20, the MAXI/GSC nova alert system detected an X-ray flux increase from the position consistent with a Be/X-ray binary pulsar, V 0332+53. The source flux in 4-10 keV band reached 0.102 +- 0.024 ph/s/cm² (82 +- 19 mCrab) on 2015 June 19. Because the source region was out of the MAXI FOV until June 18, the onset of the current brightening was not covered by the MAXI/GSC. Meanwhile, the Swift/BAT continuously monitored the source and detected its onset on June 18. The source intensity in the 15-50 keV band showed rapid increase; 0.0087 +- 0.0019 ct/cm²/sec (40 +- 8.7 mCrab) on June 18, 0.0237 +- 0.0024 ct/cm²/sec (108 +- 11 mCrab) on June 19. On June 20, the 15-50 keV band reached 0.0340 +- 0.0016 ct/cm²/sec (154 +- 7 mCrab) which exceeded the peak fluxes of the normal outbursts observed in 2009-2010 (Atel#2319, #2369, #2381, #2427). The derived flux increasing rate in the 15-50 keV band, ~0.016 ct/cm²/sec/day, is higher than the previous ones (an average of the normal outbursts, ~0.003 ct/cm²/sec/day). According to the orbital parameters (T₀=53330.584 (MJD) and P_orb=36.50 d ; Raichur et al. 2010), the onset orbital phase of this outburst is 0.76. These results suggest that the current brightening is probably a giant outburst. The optical enhancement (Camero-Arranz et al. Atel#7682) that is greater than those of the previous normal outbursts also supports that idea.

The latest source flux can be checked at the following page;
http://maxi.riken.jp/top/index.php?cid=1&jname=J0334+531