用GTC对不寻常中子星Calvera的深光学观测
Deep optical observations of unusual neutron star Calvera with the GTC
摘要：
卡尔韦拉是一颗不寻常的孤立中子星，具有典型的超新星遗迹中心致密天体的纯热X射线光谱。另一方面，它的旋转周期和自旋下降率是普通旋转动力行星的典型特征。它是在X射线中发现和研究的，尚未在其他光谱域中检测到。我们提出了深光学成像的Calvera领域获得的大加那利望远镜在$g'$和$i'$波段。在卡尔韦拉附近的$\approx 1^{\prime\prime}$，我们发现了两个在以前的浅层观测中看不到的点状物体。然而，精确的天体测量表明，它们中没有一个可以与脉冲星相鉴别。我们对$g' > 27.87$和$i' > 26.84$的光学亮度提出了新的上限。我们还重新分析了所有可用的Calvera档案X射线数据。将Calvera的热发射参数和光学和非热X射线发射上限与旋转动力双星的相应数据进行比较，表明Calvera可能属于普通的中年双星，如果我们假设它的距离在$1.5-5$ kpc的范围内。
英文摘要：
Calvera is an unusual isolated neutron star with pure thermal X-ray spectrum typical for central compact objects in supernova remnants. On the other hand, its rotation period and spin-down rate are typical for ordinary rotation-powered pulsars. It was discovered and studied in X-rays and not yet detected in other spectral domains. We present deep optical imaging of the Calvera field obtained with the Gran Telescopio Canarias in $g'$ and $i'$ bands. Within $\approx 1^{\prime\prime}$ vicinity of Calvera, we detected two point-like objects invisible at previous shallow observations. However, accurate astrometry showed that none of them can be identified with the pulsar. We put new upper limits on its optical brightness of $g' > 27.87$ and $i' > 26.84$. We also reanalyzed all available archival X-ray data on Calvera. Comparison of the Calvera thermal emission parameters and upper limits on optical and non-thermal X-ray emission with respective data on rotation-powered pulsars shows that Calvera might belong to the class of ordinary middle-aged pulsars, if we assume that its distance is in the range of $1.5-5$ kpc.
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