MAXI/GSC detection of X-ray brightening from the X-ray pulsar XTE J1829-098

ATel #14554; M. Nakajima, H. Negoro (Nihon U.), T. Kawamuro (UDP/NAOJ), T. Mihara (RIKEN), M. Aoki, K. Kobayashi, R. Takagi, K. Asakura, K. Seino (Nihon U.), T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, K. Komachi, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, R. Adachi, M. Niwano, R. Hosokawa (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA), Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, K. Kurogi, K. Miike (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 16 Apr 2021; 01:11 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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Following the report of the outburst onset observed by SRG/ART-XC (Shtykovsky et al. 2021, ATel #14521), the MAXI/GSC nova alert system triggered on an X-ray activity from the 7.8 second transient X-ray pulsar XTE J1829-098 on 2021-04-12 (MJD 59316). The average daily flux in the 5-12 keV band rose to 0.055 +- 0.014 photons/s/cm² (55 +- 13 mCrab), and exhibited a moderate decrease trend. Prior to this brightening, we found that there are two X-ray outbursts in the MAXI/GSC archive data. The previous outbursts took place in December 2019 and August 2020, both events were not posted to the MAXI mailing list. Thus, including the first our report about this source (ATel#11927), MAXI detected four X-ray outbursts from this pulsar in the 11 years observation so far. The time intervals between each outburst can be explained with the proposed outburst periodicity of ∼246 d (Markwardt et al. 2009). In order to obtain the precise orbital (outburst) periodicity, we used a period search techniques. A new ephemeris derived from the MAXI/GSC data spanning the past 11 years predicts the X-ray outbursts as:
T_outburst = MJD 58341.73 + n * (243.66 +- 3.07)
where n is the number of orbit since the outburst in August 2018. The derived outburst periodicity is consistent with the former result (Markwardt et al. 2009). Using a new ephemeris, it is turned out that the date of the triggered event by the MAXI/GSC nova-search system is 0.998 in the orbital phase. It nicely matches with the outburst expected phase.