On the Binary Neutron Star Post-merger Magnetar Origin of XRT 210423

XRT 201423 is an X-ray transient with a nearly flat plateau lasting 4.1 ks followed by steep decay. This feature indicates that it might come from magnetar formed through binary neutron star merger, similar to CDF-S XT2 and as predicted type of electromagnetic counterpart mergers. We test the compliance data this model use observed duration flux signal well upper limits optical emission pose constraints on parameters underlying putative magnetar. Both free-zone trapped-zone geometric configurations are considered. find generally consistent such model. The surface dipolar magnetic field ellipticity should satisfy $B_p < 7\times 10^{14}{\rm G}$ ($B_p 4.9 \times G}$) $\epsilon 1.5 10^{-3}$ ($\epsilon 1.1 10^{-3}$) under free zone (trapped zone) configurations, respectively. An limit distance (e.g. $z 0.55$ $\eta_x = 10^{-4}$ or 3.5$ 10^{-2}$) can be derived which depends dissipation efficiency $\eta_x$ spin-down luminosity. non-detection places conservative lower source, i.e. > 0.045$ regardless configuration.