标题： 不同状态方程的奇异星引力波回声 显示英文标题

标题： Gravitational wave echoes from strange stars for various equations of state

摘要： 在约$72\,Hz$的频率处，最近在 GW170817 事件中以$4.2\sigma$显著性水平声称发现了暂定的引力波回声（GWE）。 GWE 可以作为研究超致密恒星物体特性的工具。 考虑到最终的超致密并合后天体为奇异星，可以计算 GWE 频率。 然而，仅观察到那些致密性介于 0.33 和 0.44 之间的致密恒星结构的 GWE。 另外，对于具有光子球且致密性不越过 Buchdahl 极限半径$R_{B}=9/4M$的致密恒星，可以获得 GWE。 光子球是一个位于$R=3M$的表面，$R$是半径，$M$是超致密天体的总质量。 最近，使用最简单的 MIT 袋模型状态方程（EoS），据报道奇异星可以产生频率为几十千赫兹的 GWE。 鉴于此，为了进行比较研究，我们考虑了三种奇异星 EoS 模型，即 MIT 袋模型、线性和多级 EoSs\cite{JB}，计算了与奇异星相关的回声频率。 我们发现，如果多级 EoS 不太刚硬，则不能发射 GWE，而 MIT 袋模型和线性 EoS 可以在大约几十千赫兹的频率范围内发射 GWE。 此外，GWE频率随着袋常数$B$值的增加而增加，并随着线性常数$b$值的增加而减少。 因此，观察到GWE频率具有模型依赖性。 显示英文摘要

摘要： The tentative Gravitational Wave Echo (GWE) at a frequency of about $72\,Hz$ has been recently claimed at $4.2\sigma$ significance level in the GW170817 event. GWEs can be used as a tool to study the characteristics of ultra-compact stellar objects. Considering the final ultra-compact, post-merger object as a strange star, the GWE frequency can be calculated. However, GWEs are observed for only those compact stellar structures whose compactness lies in between 0.33 and 0.44. Alternatively, GWE can be obtained for those compact stars which feature a photon sphere and compactness not crossing the Buchdahl's limit radius $R_{B}=9/4M$. A photon sphere is a surface located at $R=3M$, $R$ being the radius and $M$ is the total mass of the ultra-compact object. Recently using the simplest MIT Bag model Equation of State (EoS) it has been reported that strange stars can produce GWEs with frequencies of tens of kilohertz. In view of this, for a comparative study, we have calculated the respective echo frequencies associated with strange stars by considering three models of strange star EoSs, viz., MIT bag model, linear and polytropic EoSs \cite{JB}. We found that, not being too stiff the polytropic EoS can not emit GWE, whereas the MIT Bag model and the linear EoSs can emit GWEs at a frequency range of about tens of kilohertz. Also, GWE frequency increases with the increase in values of bag constant $B$ and decreases with the increasing values of linear constant $b$. So a model-dependent nature of GWE frequencies is observed.