MAXI/GSC observation of an X-ray outburst from the Be/X-ray binary pulsar GS 0834-430
ATel #18031; M. Nakajima, H. Negoro (Nihon U.), M. Serino, S. Sugita (AGU), K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS)
on 6 Sep 2026; 08:02 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The MAXI/GSC nova alert system triggered an X-ray transient source at (R.A., Dec) = (128 deg, -43 deg) on August 29, 2026 (MJD 61281). Since the source was observed during high-background orbits in late August, its position could not be precisely determined from those scans. After the high-background conditions subsided, we attempted to determine the source position using 9 scan transits between 16:47 UT on September 2 (MJD 61285) and 06:22 UT on September 3 (MJD 61286), and obtained the following position:
(R.A., Dec) = (129.216 deg, -43.165 deg) = (08 36 51, -43 09 55) (J2000)
with a 90% C.L. statistical error of 0.31 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). This position is consistent with that of the Be/X-ray binary pulsar GS 0834-430. This marks the third firm detection of this source by MAXI since the start of the mission in 2009. The previous outbursts from this source in the 21st century were recorded in 2012 (ATel #4218, #4235; 4-10 keV peak flux of ∼100 mCrab) and 2015 (ATel #8175; ∼30 mCrab). Based on the orbital ephemeris of Porb = 105.8 ± 0.4 d and Tperi = 48809.6+1.6-1.4 (MJD), determined by Wilson et al. (1997), the orbital phases of the onset of these outbursts correspond to ∼0.90 (2012), ∼0.24 (2015), and ∼0.80 (2026), respectively. While none of these outbursts began precisely at periastron, the onset phase of the current event is close to that of the bright outburst in 2012, suggesting the possibility that this activity could develop into a major outburst. The latest 1-day averaged 4-10 keV flux reached 0.064 ± 0.011 photons cm-2 s-1 (52 ± 9 mCrab) on September 4 (MJD 61287), exceeding the peak flux of the previous outburst in 2015. Multi-wavelength follow-up observations are encouraged.
the MAXI alert information
