MAXI/GSC detection of an X-ray outburst from GK Per
ATel #17958; T. Mihara (RIKEN), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (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), S. Ogawa (TUS)
on 11 Aug 2026; 23:46 UT
Credential Certification: Tatehiro Mihara (mihara@crab.riken.jp)
Subjects: X-ray, Binary, Cataclysmic Variable, Nova, Transient
The MAXI/GSC nova alert system triggered on an X-ray brightening from a position consistent with the white dwarf binary GK Per (intermediate polar and dwarf nova)
on 2026 August 9 (MJD 61261) 08:23 UT. The one-day-averaged flux was 40 ± 10 mCrab in 4-10 keV of 8 good scans between August 8 10:43 - August 9 8:23 UT.
Prior to this trigger, the source kept no detection by the MAXI/GSC since 2026 August 2 (MJD 61254).
Before that, it was
no detection in 2026 May 21 (MJD 61181) - July 4 (MJD 61225), and
lack of observation in July 5 (MJD 61226) - August 1 (MJD 61253).
Note that the AAVSO V-band data started to brighten on 2026 July 7 (61228 MJD), and reached 2.5 magnitude brighter state on August 11 (MJD 61263) than the quiescent.
Multi-wavelength follow-up observations are encouraged.
The latest X-ray light-curve can be checked at
MAXI HP ( https://maxi.riken.jp/pubdata/v7.7l/J0331+439/index.html ).
