XRISM/Xtend Transient Search (XTS) detected an X-ray flare from EQ CVn

ATel #16905; Y. Maeda, T. Yoshida, K. Fukushima, K. Hayashi, Y. Kanemaru, S. Ogawa (JAXA), M. Audard (U. de Geneve), E. Behar (Technion), S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), T. Kohmura (TUS), Y. Maeda (JAXA), M. Mizumoto (UTEF), M. Nobukawa (NUE), K. Pottschmidt (UMBC, NASA GSFC, CRESST), M. Shidatsu (Ehime U.), Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.), H. Uchida (Kyoto U.), T. Yanagi (Chuo U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Osaka U.)
on 12 Nov 2024; 15:22 UT
Credential Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)

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XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J1226+3347 on 2024-11-10 TT. The source position is determined to be (R.A., Dec.) = (186.488, 33.781), with a systematic error of ∼ 40 arcsec. A Plausible counterpart is an eclipsing G0V type star EQ CVn which corresponds to an X-ray source RX J1225.9+3346. EQ CVn is located ∼ 10 arcsec apart from the position of XRISM J1226+3347. All statistical uncertainties in this report will be provided as a 90% confidence level unless stated otherwise.

The flare started at 2024-11-10 at ∼ 16:30 TT. The flare reached its peak on 2024-11-10 at ∼ 17:40. The flare exponentially decayed in 10⁴ sec. In order to estimate the source flux, we fit the spectrum in the flare peak phase with an absorbed APEC model with a temperature of kT = 0.9 keV and hydrogen column density NH = 4 × 10²¹ cm^-2. Then, the model flux is calculated as 2 × 10^-12 erg s^-1 cm^-2 (0.4 – 10.0 keV). A systematic error of roughly 20% should be added to the statistical error. Corresponding luminosity is 4 × D_400pc × 10³¹ erg s^-1 by assuming the distance to XRISM J1226+3347 of D_400pc.

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 with the corresponding counterparts in the same field of view.