X-ray and H-alpha detection of a flare from II Peg with MAXI/GSC and SCAT
ATel #15606; S. Urabe, N. Nemoto, W. Iwakiri, Y. Tsuboi, J. Kohara, S. Nawa, K. Naoki (Chuo U.), H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, M. Serino, H. Hiramatsu, A. Yoshida (AGU), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba (Kyoto U.), M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 10 Sep 2022; 09:39 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)
Subjects: Optical, X-ray, Star, Transient
The MAXI/GSC detected a bright X-ray flare from RS CVn type binary II Peg at 6:04 on 2022 September 3. We estimated X-ray peak flux in the 2 – 10 keV band of this flare to be 1.5 (1.1 – 2.1) × 10-9 erg/cm2/s assuming the thermal bremsstrahlung model with a temperature of 4.8 keV. Considering a distance of 42 pc, the peak luminosity is 2.9 (2.1 – 4.0) × 1032 erg/s. If we assume that the flare flux decayed exponentially with time, the estimated e-folding time and the total energy in the 2 – 10 keV band of this flare are 7.5 (4.7 – 9.8) ksec and 2.2 (1.1 – 3.2) × 1036 erg, respectively.
We also carried out a follow-up observation using the Spectroscopic Chuo university Astronomical Telescope (SCAT) located in the Korakuen campus of Chuo University in Tokyo, Japan. It consists of a 355 mm diameter Kasai Trading GS-350 RC/TR telescope and an ATIK 460EX CCD camera with a Shelyak Alpy 600 spectrometer whose spectral resolution is 600. The SCAT observation was made on 11:44 – 12:24 UT 2022 September 3 (approximately 5.5 hours after MAXI’s trigger) with a net exposure of 2400 sec. The obtained spectrum showed a Hα emission line with an equivalent width of 7Å. The average equivalent width of Hα emission lines obtained from SCAT observations of II Peg between October 2021 and February 2022 was about 1Å. Comparing these results, we conclude that we have detected a Hα flare associated with the X-ray flare observed by MAXI.
