MAXI/GSC observations of the new X-ray transient Swift J1727.8-1613 (GRB 230824A)
ATel #16206; M. Nakajima, H. Negoro (Nihon U.), M. Serino (AGU), T. Mihara (RKEN), K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto (Chuo U.), M. Shidatsu (Ehime U.), I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA), Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani (Kyoto U.), M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), W. Iwakiri (Chiba U.)
on 25 Aug 2023; 13:16 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)
Subjects: X-ray, Binary, Black Hole, Transient
Referred to by ATel #: 16207, 16208, 16210, 16211, 16216, 16219, 16225, 16230, 16231, 16232, 16235, 16237, 16242, 16243, 16245, 16247, 16273, 16276, 16279, 16287, 16295, 16490, 16541
We report MAXI observations of the new X-ray transient Swift J1727.8-1613 discovered by Swift/BAT (GCN #34537). This source was initially recognized as GRB 230824A. However, the subsequent observation revealed that the source exhibited a rapid flux increase and is identified as a new galactic X-ray transient (GCN #34540 ; ATel#16205). Since before the discovery, MAXI/GSC has monitored the source every 90 min. The latest X-ray flux in 2-20 keV reached 11.0 ± 0.5 photons/s/cm2 (2.8 ± 0.1 Crab) on MJD 60181.33. MAXI/GSC also detected the short-term variability in a time scale of a few seconds. The 2-20 keV spectra obtained by the MAXI/GSC observations can be represented by a power-law model. The photon indices might flatten from 2.2 ± 0.5 in MJD 60180.25 - 60180.5 to 1.7 ± 0.1 in MJD 60181.0 - 60181.25 as the source flux increased from 150 mCrab to 3 Crab. These observational results are consistent with the properties of black holes in a hard state. We strongly encourage the multi-wavelength observations to reveal the unknown source nature.
The latest X-ray light-curve can be checked on the following page,
http://maxi.riken.jp/star_data/J1727-162/J1727-162.html .
