标题： 最重中子星的质量和半径：状态方程及微扰QCD的探针 显示英文标题

标题： Mass and radius of the most massive neutron star: The probe of the equation of state and perturbative QCD

摘要： 近期，有研究声称引力波事件GW190425与快速射电暴FRB 20190425A存在关联，并推测其残骸为高度磁化的中子星（NS）。 鉴于FRB 20190425A的出现延迟时间（$\sim 2.5$-h），均匀旋转的超质量磁星更受青睐，因为差速自转会在磁制动作用下迅速终止。 非旋转NS的最大引力质量（$M_{\rm TOV}$）为$\approx 2.77M_\odot$，这与当前包含微扰量子色动力学（pQCD）信息的状态方程（EOS）约束所获得的相对较低的$M_{\rm TOV}\approx 2.25M_\odot$存在强烈矛盾。 然而，目前中子星的质量-半径和质量-潮汐变形率测量数据本身并不能充分排除高$M_{\rm TOV}$的可能性。 通过进行状态方程约束的模拟测量，我们发现，如果能精确确定类似PSR J0740+6620的中子星半径（$2\%$），则有可能区分低和高$M_{\rm TOV}$场景。 我们进一步探讨了利用未来的大质量中子星观测或确定$M_{\rm TOV}$和/或$R_{\rm TOV}$来解决施加 pQCD 约束的适当密度问题的前景。结果表明，测量类似于 PSR J0740+6620 的中子星半径不足以探测接近 5 倍核饱和密度的 EOS，此时 pQCD 提供的信息变得相关。无论如何，额外精确的$M_{\rm TOV}$测量可以为该密度下的 EOS 提供见解。事实上，假设 GRB 170817A 的中心引擎是通过超质量中子星坍缩形成的黑洞，则由此产生的$M_{\rm TOV}\approx 2.2M_\odot$大大软化了最重中子星中心的 EOS，这有利于在超出当前中子星所能达到的密度下施加 pQCD 约束。 显示英文摘要

摘要： Recently, an association of GW190425 and FRB 20190425A had been claimed and a highly magnetized neutron star (NS) remnant was speculated. Given the $\sim 2.5$-h delay of the occurrence of FRB 20190425A, a uniformly rotating supramassive magnetar is favored since the differential rotation would have been promptly terminated by the magnetic braking. The required maximum gravitational mass ($M_{\rm TOV}$) of the nonrotating NS is $\approx 2.77M_\odot$, which is strongly in tension with the relatively low $M_{\rm TOV}\approx 2.25M_\odot$ obtained in current equation of state (EOS) constraints incorporating perturbative quantum chromodynamics (pQCD) information. However, the current mass-radius and mass-tidal deformability measurements of NSs alone do not convincingly exclude the high $M_{\rm TOV}$ possibility. By performing EOS constraints with mock measurements, we find that with a $2\%$ determination for the radius of PSR J0740+6620-like NS it is possible to distinguish between the low and high $M_{\rm TOV}$ scenarios. We further explore the prospect to resolve the issue of the appropriate density to impose the pQCD constraints with future massive NS observations or determinations of $M_{\rm TOV}$ and/or $R_{\rm TOV}$. It turns out that measuring the radius of a PSR J0740+6620-like NS is insufficient to probe the EOSs around 5 nuclear saturation density, where the information from pQCD becomes relevant. The additional precise $M_{\rm TOV}$ measurements anyhow could provide insights into the EOS at such a density. Indeed, supposing the central engine of GRB 170817A is a black hole formed via the collapse of a supramassive NS, the resulting $M_{\rm TOV}\approx 2.2M_\odot$ considerably softens the EOS at the center of the most massive NS, which is in favor of imposing the pQCD constraint at density beyond the one achievable in the NSs.