MAXI and NICER observations of a giant X-ray flare from the RS CVn stellar binary system, IM Peg
ATel #16152; W. Iwakiri (Chiba U.), K. Hamaguchi (NASA/GSFC & UMBC), K. Gendreau, Z. Arzoumanian (NASA/GSFC), N. Nemoto, E. Goto, S. Urabe, S. Nawa, Y. Tsuboi (Chuo U.), M. Serino (AGU), H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), 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)
on 26 Jul 2023; 03:47 UT
Credential Certification: Wataru Iwakiri (iwakiri@chiba-u.jp)
Subjects: X-ray, Star, Transient
We report the MAXI/GSC detection of a giant X-ray flare from the RS CVn-type star IM Peg and the results of the follow-up observations of NICER which started at about 4.6 hours after the MAXI automated alert email notification.
The MAXI/GSC nova alert system triggered an X-ray flare from IM Peg at 2023-07-23 10:41 UT. The X-ray flux at this time was about 60 mCrab in the 2 - 10 keV band. MAXI detected no significant flux from the star during the 09:08 transit (about 1.5 hours before the trigger) at an upper limit flux of 20 mCrab. On the next MAXI scan transit around 12:14, the X-ray flux increased to 90 mCrab, and an automated alert email notification was sent to the MAXI team.
The NICER follow-up observations began at 2023-07-23 16:52 UT, monitoring approximately every 90 minutes for about a day. The X-ray spectrum obtained from the first NICER observation (16:52 - 17:13 UT) showed clear He-like and H-like Fe emission lines. The spectrum in the 3-10 keV band is well reproduced by the single thin thermal plasma model with a temperature of 8 keV and metal abundance of 0.5 solar. The NICER 2-10 keV lightcurve from 2023-07-23 16:52 to 07-24 13:21 is well reproduced by a constant + an exponential decay with a time constant of 0.3 days. The estimated total flare energy is about 5x1037 erg. NICER will continue to observe IM Peg.
The flare was also detected in a Halpha observation using the Spectroscopic Chuo university Astronomical Telescope (SCAT) located on the Korakuen campus of Chuo University in Tokyo, Japan (Kawai et al. 2022). The SCAT data analysis is ongoing.
(Reference: Kawai et al., 2022, PASJ, 74, 477)
