MAXI/GSC detection of an X-ray flare from UX Ari on 2026-06-25 UT

ATel #17866; H. Ogaki, Y. Ishihara(Chuo U.), M. Uenishi (Ehime U.), H. Negoro, M. Nakajima (Nihon U.), T. Mihara (RIKEN), 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 (Chuo U.), M. Shidatsu, C. Kang, 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), and S. Ogawa (TUS)
on 2 Jul 2026; 15:43 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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At 00:26 on 2026-06-25 UT, the MAXI/GSC nova alert system triggered on a source at a position consistent with that of the RS CVn star UX Ari. The flux started to increase at 14:20 on 2026-06-24 UT, and peaked at 15:56 on 2026-06-26 UT, and decayed with an e-folding time of 1.2 days.

The position of the X-ray enhancement is (R.A., Dec) = (51.738 deg, 28.776 deg) = (03 26 57, +28 46 33) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.30 deg and 0.1 deg, respectively. The roll angle of long axis from the north direction is 92.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The position was determined with the data obtained at fourteen scan transits from 01:09 on 2026-06-28 UT to 00:24 on 2026-06-29 UT. This position is consistent with that of UX Ari.

The peak flux was 7 × 10^-10 erg s^-1 cm^-2 (2-10 keV). Corresponding luminosity was 2 × 10³² erg s^-1 for an assumed distance of 50 pc.

MAXI data for UX Ari