发表机构
Radboud University; University of Warwick; Institute of Space Sciences (ICE), CSIC; Institut d’Estudis Espacials de Catalunya (IEEC)（拉德堡德大学; 华威大学; 空间科学研究所（ICE），西班牙高等科学研究委员会; 加泰罗尼亚空间研究学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文研究暗快速X射线暂现源（FXTs），发现软X射线吸收使其偏向高红移，并通过EP-WXT观测和模拟证实其与暗GRBs选择函数不同。
AI 中文摘要
许多快速X射线暂现源（FXTs）和γ射线暴（GRBs）的前身星密切相关。鉴于“暗”GRBs通常被发现是宿主星系中遭受增强消光的事件，我们研究了“暗”FXTs的性质。然而，与γ射线不同，软X射线受吸收影响强烈，这意味着爱因斯坦探针宽视场X射线望远镜（EP-WXT）发现的暗FXTs必须在静止系能量$>$2--3 keV处发射，因此红移$z\trsim2$。为说明这一点，我们展示了EP-WXT发现的两个暗FXTs：EP241103a和EP260409a。对于EP241103a，高消光阻碍了光学对应体的探测，而对于可能的源红移$\trsim2.5$，静止系X射线光子未受到严重影响。对于EP260409a，光学波段未探测到对应体，但我们确实探测到了近红外对应体。EP260409a的一个合理场景是它位于红移$z \trsim 4$。此外，我们进行了EP-WXT观测到的FXTs模拟，表明对于吸收事件（$N_{\mathrm{H}}\trsim10^{22}$~cm$^{-2}$），在低红移处探测到的计数强烈减少，阻碍了它们的探测。这些结果支持了理论预测，即暗FXTs具有中等到高红移，并且与暗GRBs具有不同的选择函数。
英文摘要
The progenitors of many Fast X-ray Transients (FXTs) and those of $γ$-ray bursts (GRBs) are strongly linked. Given that "dark" GRBs are typically found to be events suffering from enhanced extinction in the host galaxy, we investigate the nature of "dark" FXTs. However, unlike $γ$-rays, soft X-rays are strongly affected by absorption, implying that dark FXTs discovered by Einstein Probe's Wide-field X-ray Telescope (EP-WXT) have to be emitted at energies $>$2--3 keV restframe hence at a redshift $z\gtrsim2$. To illustrate this we present two dark FXTs, EP241103a and EP260409a, discovered by EP-WXT. For EP241103a, the high extinction precluded the detection of the optical counterpart, while for a probable source redshift of $\sim2.5$, the rest-frame X-ray photons are not severely affected. For EP260409a no counterpart is detected in the optical, but we do detect a near-infrared counterpart. A plausible scenario for EP260409a is that it lies at a redshift $z \gtrsim 4$. Additionally, we conduct simulations of FXTs observed with EP-WXT, showing that the detected counts for absorbed events ($N_{\mathrm{H}}\gtrsim10^{22}$~cm$^{-2}$) strongly decrease at low redshifts, hindering their detection. These results support the theoretical prediction that dark FXTs have an intermediate to high redshift and a different selection function from those of dark GRBs.
CommentsAccepted for publication in MNRAS
