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

Shunke Ai; Bing Zhang

doi:10.3847/2041-8213/ac097d

paper

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

arXiv:2105.14592 · doi:10.3847/2041-8213/ac097d

Abstract

XRT 201423 is an X-ray transient with a nearly flat plateau lasting 4.1 ks followed by a steep decay. This feature indicates that it might come from a magnetar formed through a binary neutron star merger, similar to CDF-S XT2 and as predicted as a type of electromagnetic counterpart of binary neutron star mergers. We test the compliance of the data with this model and use the observed duration and flux of the X-ray signal as well as upper limits of optical emission to pose constraints on the parameters of the underlying putative magnetar. Both the free-zone and trapped-zone geometric configurations are considered. We find that the data are generally consistent with such a model. The surface dipolar magnetic field and the ellipticity of the magnetar should satisfy $B_{p} < 7 \times 1 0^{14} G$ ( $B_{p} < 4.9 \times 1 0^{14} G$ ) and $ε < 1.5 \times 1 0^{- 3}$ ( $ε < 1.1 \times 1 0^{- 3}$ ) under free zone (trapped zone) configurations, respectively. An upper limit on the distance (e.g. $z < 0.55$ with $η_{x} = 1 0^{- 4}$ or $z < 3.5$ with $η_{x} = 1 0^{- 2}$ ) can be derived from the X-ray data which depends on the X-ray dissipation efficiency $η_{x}$ of the spin-down luminosity. The non-detection of an optical counterpart places a conservative lower limit on the distance of the source, i.e. $z > 0.045$ regardless of the geometric configuration.

arXiv comment8 pages, 1 figure, accepted for publication in ApJ Letters

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

Abstract

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