MAXI/GSC detection of an X-ray flare from HR1099 on 2025-08-11 UT
ATel #17328; H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, Y. Niida, C. Kang, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), report on behalf of the MAXI team:
on 12 Aug 2025; 02:16 UT
Credential Certification: Yohko Tsuboi (tsuboi@phys.chuo-u.ac.jp)
Subjects: X-ray, Binary, Star, Transient, Variables
At 10:38 on 2025-08-11 UT, the MAXI/GSC nova alert system triggered on a source at a position consistent with that of the RS CVn star HR1099.
The position of the X-ray enhancement is determined to be (R.A., Dec) = (54.233 deg, 0.370 deg) = (03 36 55, +00 22 11) (J2000) with a statistical 90% C.L. elliptical error region
with long and short radii of 0.41 deg and 0.32 deg, respectively, for the data at the scan transit from 10:34 on 2025-08-11 UT to 10:39 on 2025-08-11 UT. The roll angle of long axis from the north direction is 76.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). This position is consistent with that of HR1099.
The flux at the transit is 2 × 10-9 erg s-1 cm-2 (2-10 keV). Corresponding luminosity is 2 × 1032 erg s-1 for an assumed distance of 30 pc.
