XRISM/Xtend Transient Search (XTS) detected an X-ray flare from EQ CVn
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Maeda, Y., T. Yoshida, K. Fukushima, et al. “XRISM/Xtend Transient Search (XTS) Detected an X-Ray Flare from EQ CVn.” The Astronomer’s Telegram, November 12, 2025. https://www.astronomerstelegram.org/?read=16905.
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Abstract
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 × D₄₀₀ₚ꜀ × 10³¹ erg s⁻¹ by assuming the distance to XRISM J1226+3347 of D₄₀₀ₚ꜀.
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.