MAXI/GSC observation of flaring activity from Be/X-ray binary pulsar GRO J1008-57
ATel #13544; M. Nakajima (Nihon U.), T. Mihara (RIKEN), H. Negoro, W. Maruyama, M. Aoki, K. Kobayashi, R. Takagi (Nihon U.), C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, 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), M. Sugizaki (NAOC)
on 6 Mar 2020; 10:02 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
GRO J1008-57 is the 93.7 sec X-ray pulsar in the highly eccentric (e=0.68) binary orbit (e.g. Sugizaki et al. 2017). This system shows regular X-ray outbursts synchronized with the binary orbital period of Porb=249.48 d (and Tperi=54424.71(MJD); Kühnel et al. 2013). On 2020-02-08 (MJD 58887), the source started the regular X-ray brightening (Atel#13480), and the day-averaged flux in 4-10 keV band reached the peak (0.064 +- 0.005 photons/s/cm2 ; 56 +- 4 mCrab) on 2020-02-16 (MJD 58895). In comparison with the normal outbursts observed from this pulsar, the peak time came about 10 days earlier than that of the regular ones. After the peak, the source flux exhibited a moderate decrease for a few days and stayed in the constant level of ∼35 mCrab. On 2020-02-28 (MJD 58907), the flare-up event was detected and lasted for ∼1 day. The 4-10 keV flux binned at 0.25 days reached the maximum flux of 0.132 +- 0.025 photons/s/cm2 (115 +- 22 mCrab). The pulsar is still in the same flux of ∼50 mCrab after the flare event. The current situation resembles the X-ray brightening event prior to the first observed giant outburst from this source in 2012 (Atel#4319, #4355, #4561, #4573, #4577, and http://maxi.riken.jp/figure/groj1008/groj1008_maxi_lc_gob_comp.png ). Therefore, the present event could develop into a giant ones in the next months. In addition, MAXI light curve shows that the intervals of the giant outbursts distributes within 2-2.5 years ( http://maxi.riken.jp/figure/groj1008/groj1008_maxi_lc_10yr.png ).
We encourage the optical follow-up observations to reveal the state of the circumstellar disc.
The latest X-ray light-curve can be checked at the following pages;
MAXI ( http://maxi.riken.jp/star_data/J1009-582/J1009-582.html ),
Swift/BAT ( http://swift.gsfc.nasa.gov/results/transients/GROJ1008-57/ ),
Fermi/GBM ( https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/groj1008.html ), and
the BeXRB monitor page ( http://integral.esac.esa.int/bexrbmonitor/Plots/sim_plot_GROJ1008-57.html ).