XRISM/Xtend Transient Search (XTS) detected an X-ray flare from High Proper Motion Star UCAC4 661-042690

Abstract

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J0604+4209 on 2025-02-23 TT. The source position is determined to be (R.A., Dec.) = (90.974, 42.144), with a systematic error of ∼ 40 arcsec. A plausible counterpart is M2 dwarf high proper motion star UCAC4 661-042690 which corresponds to the X-ray source 4XMM J060352.2+420833. UCAC4 661-042690 is located ∼ 17 arcsec apart from the position of XRISM J0604+4209.

The flare started at 2025-02-23 at ∼ 01:00 with the flux of 7 × 10⁻¹⁴ erg s⁻¹ cm⁻² and reached its peak on 2025-02-23 at ∼ 01:35 with the flux of 4 × 10⁻¹³ erg s⁻¹ cm⁻². The flare exponentially decayed in 3 × 10³ sec. The above fluxes are in the 0.4 – 2.0 keV. The corresponding peak luminosity is 4 × 10²⁹ erg s⁻¹ cm⁻² when we assume the distance to XRISM J0604+4209 of D₉₆ ₚ꜀. 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.