MAXI/GSC detection of rapid rebrightening of 4U 1730-22

ATel #14757; W. Iwakiri (Chuo U.), H. Negoro, M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.), T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, K. Komachi, A. Yoshida (AGU), Y. Tsuboi, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka, T. Omama, M. Kurihara (JAXA), Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team:
on 6 Jul 2021; 14:57 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)

Tweet

We report a rapid X-ray rebrightening of 4U 1730-22 observed by MAXI on July 5, 2021.
4U1730-22 was detected by MAXI on June 7, 2021, as MAXI J1733-222 with an X-ray flux of ~60 mCrab in the 4-10 keV band (ATel#14683). It was identified by Swift follow-up observations as 4U1730-22, which was also confirmed to be fainter than the MAXI detection (ATel#14686, ATel#14688). MAXI observations showed that the X-ray luminosity increased to ~20 mCrab from June 21 and remained at a constant luminosity. However, a rapid increase was observed from July 5, and the X-ray intensity reached ~100 mCrab on July 6. The average X-ray spectrum of MAXI on July 5 to 6 is well represented by the absorbed powerlaw model with a photon index of 2.45 +/- 0.16. The hydrogen column density was fixed at 0.73 x 10²² cm^-2 according to the Swift observation result (ATel#14686). The estimated X-ray flux in the 2 - 20 keV and 0.3 - 10 keV band are 2.75 +0.26, -0.23 x 10^-9 ergs cm^-2 s^-1 and 2.99 +0.18, -0.31 x 10^-9 ergs cm^-2 s^-1, respectively.
We encourage multi-wavelength observations of 4U 1730-22.

MAXI/GSC data for 4U 1730-22