MAXI/GSC detection of the X-ray outbursts from Be/X-ray binary pulsars, A 0535+26 and GRO J10087-57
ATel #12092; M. Nakajima, H. Negoro (Nihon U.), K. Morita (Tokyo Tech), A. Sakamaki, W. Maruyama (Nihon U.), T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, T. Midooka (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, S. Ogawa (Kyoto U.), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.) report on behalf of the MAXI team:
on 10 Oct 2018; 09:15 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 14171
We report on the observations of the X-ray outbursts from two Be/X-ray binary pulsars triggered by the MAXI/GSC nova-alert system (Negoro et al. 2016, PASJ, 68, S1).
The X-ray brightening of A 0535+26 was triggered on 2018-09-22 (MJD 58383). According to the 4-10 keV data extracted from the MAXI/GSC On-demand system with the modified background region, the present outburst started from 2018-09-20 (MJD 58381), and the flux reached 0.0473 +- 0.0170 ph/s/cm2 (41 +- 15 mCrab) on 2018-09-24 (MJD 58385). The onset date of the current outburst corresponds to the orbital phase of ~0.06, which is derived from following orbital parameters, T0=44943.5(MJD), Porb=111.0 d (Giovannelli et al. 2013, A&A, 560, 1). The moderate flux increase rate in 4-10 keV energy band is comparable to that of the normal outburst in 2014 (Nakajima et al. Atel#6569). Therefore, we consider that the source again exhibited the normal outburst since the last weak X-ray outburst observed in October 2016 (Iwakiri et al. Atel#8977). Because the source region was in the out of the field of view from 2018-09-24 (MJD 58385), the outburst peak was not observed by the MAXI/GSC. Neil Gehrels Swift observatory and Fermi/GBM also detected this X-ray brightening. The 15-50 keV flux peaked at 2018-09-26 (MJD 58387), and faded on 2018-09-29 (MJD 58390). The day-averaged maximum flux was 0.0201 +/- 0.0025 counts/s/cm2 (91 +/- 11 mCrab).
The source light curves can be checked at the following pages;
MAXI(http://maxi.riken.jp/pubdata/v3.rkn/J0538+263/index.html),
Swift/BAT(https://swift.gsfc.nasa.gov/results/transients/1A0535p262/),
Fermi/GBM(https://gammaray.nsstc.nasa.gov/gbm/science/pulsars/lightcurves/a0535.html), and
the BeXRB monitor page(http://integral.esac.esa.int/bexrbmonitor/webpage_oneplot.php).
A weak X-ray emission from GRO J1008-57 was triggered on 2018-09-30 (MJD 58391). After the trigger, the source flux in 4-10 keV band started to increase from 2018-10-04 (MJD 58395) and reached 0.1036 +- 0.0146 photons/s/cm2 (89 +- 13 mCrab) on 2018-10-09 (MJD 58400). The trigger date corresponds to the orbital phase of ~0.9 (T0=54416.65 (MJD) and Porb=249.48 d (Kühnel et al. 2013). The average flux increase rate in recent days is ~0.015 photons/s/cm2/day which is twice the nominal value of the normal outburst of this source. The 15-50 keV band data observed by Swift/BAT also exhibits the high flux increase rate of ~0.008 count/s/day (average rate of ~0.002 count/s/day). Multi-wavelength observations are encouraged to monitor this source
activities.
The latest X-ray light-curve can be followed at the following pages:
MAXI (http://maxi.riken.jp/top/index.php?cid=1&jname=J1009-582),
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).