BAT X射线调查- I：方法和X射线识别
BAT X-ray Survey - I: Methodology and X-ray Identification
摘要：
我们将最大似然法作为图像重建算法应用于BAT X射线测量（BXS）。该方法专门设计用于保留数据中的全部统计信息，并避免具有不同指向方向的许多曝光的镶嵌，从而减少共同添加图像时的系统误差。我们在14-170 keV能量带中重建了90 x 90 deg $^2$天空区域的图像，中心位于（RA，DEC）=105 $^{\circ}$，-25 $^{\circ}$，BAT用$\sim1$ Ms的曝光时间（2005年11月）进行了调查。我们图像中的最佳灵敏度是$\sim0.85$ mCrab或$2.0\times 10^{-11}$ erg cm $^{-2}$。我们检测到49个硬X射线源以上的4.5 $σ$水平，其中，只有12个以前被称为硬X射线源（$>$ 15千电子伏）。Swift/XRT观测使我们能够确定15个对象的对应物，而2个对象具有爱因斯坦IPC对应物\citep{harris90} ;除此之外，我们通过将我们的样本与ROSAT全天巡天亮源目录\citep{voges99}相关联，发现了13个对象的可能对应物。7个物体仍不明。我们的图像的噪声特性的分析表明，$\sim75$ %的区域被调查到$\sim$ 1 mCrab的通量极限。这项研究表明，最大似然法的耦合，最敏感的，全天空的测量，硬X射线仪器，BAT，是第一次能够探测硬X射线天空的mCrab通量水平。这种方法在BAT中的成功应用表明，它也可以有利地应用于类似的仪器，如INTEGRAL-IBIS。
英文摘要：
We applied the Maximum Likelihood method, as an image reconstruction algorithm, to the BAT X-ray Survey (BXS). This method was specifically designed to preserve the full statistical information in the data and to avoid mosaicking of many exposures with different pointing directions, thus reducing systematic errors when co-adding images. We reconstructed, in the 14-170 keV energy band, the image of a 90x90 deg$^2$ sky region, centered on (RA,DEC)=105$^{\circ}$,-25$^{\circ}$, which BAT surveyed with an exposure time of $\sim1$ Ms (in Nov. 2005). The best sensitivity in our image is $\sim0.85$ mCrab or $2.0\times 10^{-11}$ erg cm$^{-2}$. We detect 49 hard X-ray sources above the 4.5 $σ$ level; of these, only 12 were previously known as hard X-ray sources ($>$15 keV). Swift/XRT observations allowed us to firmly identify the counterparts for 15 objects, while 2 objects have Einstein IPC counterparts \citep{harris90}; in addition to those, we found a likely counterpart for 13 objects by correlating our sample with the ROSAT All-Sky Survey Bright Source Catalog \citep{voges99}. 7 objects remain unidentified. Analysis of the noise properties of our image shows that $\sim75$% of the area is surveyed to a flux limit of $\sim$1 mCrab. This study shows that the coupling of the Maximum Likelihood method to the most sensitive, all-sky surveying, hard X-ray instrument, BAT, is able to probe for the first time the hard X-ray sky to the mCrab flux level. The successful application of this method to BAT demonstrates that it could also be applied with advantage to similar instruments like INTEGRAL-IBIS.
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