XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a YSO candidate

Abstract

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source XRISM J1718-3711 on 2025-03-06 TT. The source position is determined to be (R.A., Dec.) = (259.375, -37.183), with a systematic error of ∼ 40 arcsec. A Plausible counterpart is an X-ray source 2CXO J171728.2-371120, which corresponds to YSO candidates Gaia DR3 5973684576802979712 or Gaia DR3 5973684572499673216. Gaia DR3 5973684576802979712 and Gaia DR3 5973684572499673216 are located ∼ 30 arcsec apart from the position of XRISM J1718-3711. All statistical uncertainties in this report will be provided as a 90% confidence level unless stated otherwise.

The flare started on 2025-03-06 at 08:31 TT. The flare rapidly peaked on 2025-03-06 at 08:40 TT. The flare exponentially decayed in 1.5 (+0.4/-0.3) × 10⁴ sec, which is derived by fitting the 0.4 – 2.0 keV light curve with a constant + burst model in the QDP software package.

In order to estimate the source flux, we fit the spectrum in the flare phase with an absorbed APEC model with a temperature of kT = 1.8 (+0.7/-0.3) keV and a hydrogen column density N<sub>H<sub> < 7 × 10²⁰ cm⁻². Then, the model flux is calculated as (1.6 +/- 0.2) × 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 (3.3 +/- 0.4) D²₁₃₃ ₚ꜀ × 10³⁰ erg s⁻¹.

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. <sub> : subscript