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MAXI/GSC detection of an onset of X-ray outburst from Be/X-ray binary pulsar 4U 0115+63

ATel #8179; M. Nakajima, T. Masumitsu, H. Negoro (Nihon U.), N. Kawai (Tokyo Tech), T. Mihara, M. Sugizaki (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), 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 (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 17 Oct 2015; 06:15 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 8231, 9149, 9172, 10608, 15967

On 2015 October 15 (MJD 57310), the MAXI/GSC nova alert system detected an X-ray flux enhancement at a position consistent with that a transient Be/X-ray binary pulsar of 4U 0115+63. The data of 6 hour bin showed that the source flux in 4-10 keV band started to increase since October 15.12 (MJD 57310.12), and reached 0.128 +- 0.043 photons/s/cm2 (103 +- 35 mCrab) on October 15.87 (MJD 57310.87). The Swift/BAT transient monitor and the Fermi/GBM also detected the current X-ray brightening, and found a possible activity in October 12. The latest 15-50 keV flux reached 0.0115 +- 0.0014 counts/s/cm2 (52 +- 6 mCrab) on October 15 (MJD 57310). The orbital phase of the onset of the current outburst is ~0.24 (Porb=24.3174 d, T0=53243.038(MJD); Raichur et al. 2010). No outburst was reported whose onset was later than ~0.24 orbital phase since 1996 when the RXTE/ASM started operation. For example, in the case of the last giant outburst in 2011 June (Atel#3430,#3434), the onset of that was corresponding to the orbital phase of ~0.03. Therefore, the formation of the warped Be-disc would be expected around the Be star and there is a possibility that the current activity of this source might develop into the new giant outburst (Okazaki et al. 2013). The latest source flux can be checked at the following pages;
MAXI(http://maxi.riken.jp/top/index.php?cid=1&jname=J0118+637),
Swift/BAT(http://swift.gsfc.nasa.gov/results/transients/weak/4U0115p634/),
Fermi/GBM(http://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/4u0115.html),
and the BeXRB monitor page (http://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php).