XRISM/Xtend Transient Search (XTS) detected an X-ray flare from 2MASS J05243337+0141527 and CVSO 228

ATel #17409; H. Kuramoto (UOsaka), H. Matsumoto (UOsaka), T. Hakamata (UOsaka), K. Fukushima, Y. Kanemaru, S. Ogawa, Y. Uchida, T. Yoneyama (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), C. Kang (Ehime U.), T. Kiyomoto (Saitama U.), T. Kohmura (TUS), J. Kurashima (U. of Miyazaki), Y. Maeda (JAXA), T. Matsushima (U. of Miyazaki), A. Miyamoto (UOsaka), M. Mizumoto (UTEF), K. Mori (U. of Miyazaki), Y. Motogami (Saitama U.), N. Nagashima (Chuo U.), T. Narita (Kyoto U.), M. Nobukawa (NUE), H. Noda (Tohoku U.), Y. Sakamoto (Tohoku U.), M. Shidatsu (Ehime U.), H. Sugai (Chuo U.), H. Takahashi (Hiroshima U.), T. Takagi (Ehime U.), S. Takatuska (UOsaka), R. Takemoto (U. of Miyazaki), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), M. Yoshimoto (Ehime U.)
on 22 Sep 2025; 02:51 UT
Credential Certification: Hironori Matsumoto (matumoto@ess.sci.osaka-u.ac.jp)

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The XRISM observatory is observing the ψ Orionis cluster (R.A., Dec.) = (81.25, 1.7), and has detected flares from two stars during this observation.

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J0525+0142 on 2025-09-20 TT. The source position is determined to be (R.A., Dec.) = (81.141, 1.698), with a systematic error of ∼ 40 arcsec. One of the plausible counterparts is a Young Stellar Object 2MASS J05243337+0141527, which is located ∼ 8 arcsec apart from the position of XRISM J0525+0142. All statistical uncertainties in this report are provided at a 90% confidence level unless stated otherwise.

The flare started at 2025-9-20 at ∼ 05:56 TT. The flare reached its peak on 2025-9-20 at ∼ 06:30. The flare exponentially decayed in (3 +/- 1) ×10³ sec. The peak flux is calculated as 3 × 10^-13 erg s^-1 cm^-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. The corresponding luminosity is 6 × 10³⁰ erg s^-1 by assuming the distance to XRISM J0525+0142 of 400pc. This distance corresponds to Gaia DR3 3222261662926508544, which is the closest source to XRISM J0525+0142.

XRISM/XTS also detected an X-ray flare from an X-ray source XRISM J0526+0146 on 2025-09-20 TT. The source position is determined to be (R.A., Dec.) = (81.526, 1.763), with a systematic error of ∼ 40 arcsec. One of the plausible counterparts is a T Tauri star CVSO 228, which is located ∼ 15 arcsec apart from the position of XRISM J0526+0146.

The flare started at 2025-9-20 at ∼ 10:46 TT. The flare reached its peak on 2025-9-20 at ∼ 11:20. The flare exponentially decayed in (5 +/- 2) ×10³ sec. The peak flux is calculated as 7 × 10^-13 erg s^-1 cm^-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. The corresponding luminosity is 1 × 10³¹ erg s^-1 by assuming the distance to XRISM J0526+0146 of 350pc. This distance corresponds to Gaia DR3 3222266713807977856, which is the closest source to XRISM J0526+0146.

We derived the above systematic error for the flux by comparing our derived values for the sources detected with XTS in several observations with those for the corresponding X-ray counterparts. We estimated the systematic error for the source position from the separations between the detected sources and the corresponding counterparts in the same field of view.