论文标题
减小宇宙X射线的亮度和软伽玛射线背景朝向星系簇
Decrease in the Brightness of the Cosmic X-ray and Soft Gamma-ray Background toward Clusters of Galaxies
论文作者
论文摘要
我们表明，星系簇中热层次气体的电子散射应导致宇宙背景X射线和软γ射线辐射的特殊扭曲 - E <60-100 KeV的亮度和较高能量时的亮度增加。扭曲允许测量最重要的群集参数。已经使用蒙特卡洛计算研究了扭曲的频谱及其对气体温度，光学深度和表面密度分布定律的依赖性，并通过分析估计进行了证实。在群集框架中，由于后坐力效应而导致的背景最大减小发生在〜500-600 KEV。 H-和HE样铁和镍离子的光电离会导致背景光谱中的其他变形 - 在〜9 keV处的阈值具有强吸收线（并且在〜2 keV处的吸收量为〜2 keV，用于冷簇）。这些离子从簇气中吸收固有的热辐射也导致了这种线。在附近（z <1）中，〜2 keV处的线在其周围（〜3 mpc）区域的较冷（〜10^6 K）血浆中的吸收明显增强。此外，〜1.3 KeV的吸收线从中分离出来。远处簇的红移将背景光谱（在〜2，〜9和〜500 keV）中移动到降低能量。因此，与微波背景散射效果相反，该效果取决于簇红移Z，但以非常特殊的方式。当观察z> 1的簇时，效果使人们可以确定X射线背景的演变方式以及如何用z“收集”。为了检测效果，测量的准确性应达到约0.1％。我们考虑了观察效果的最有希望的簇，并讨论了阻碍检测背景扭曲的热气体辐射的影响的技术。
We show that Compton scattering by electrons of the hot intergalactic gas in galaxy clusters should lead to peculiar distortions of the cosmic background X-ray and soft gamma-ray radiation - an increase in its brightness at E<60-100 keV and a drop at higher energies. The distortions allow the most important cluster parameters to be measured. The spectral shape of the distortions and its dependence on the gas temperature, optical depth, and surface density distribution law have been studied using Monte Carlo computations and confirmed by analytical estimations. In the cluster frame the maximum of the background decrease due to the recoil effect occurs at ~500-600 keV. The photoionization of H- and He-like iron and nickel ions leads to additional distortions in the background spectrum - a strong absorption line with the threshold at ~9 keV (and also to an absorption jump at ~2 keV for cold clusters). The absorption of intrinsic thermal radiation from the cluster gas by these ions also leads to such lines. In nearby (z<1) clusters the line at ~2 keV is noticeably enhanced by absorption in the colder (~10^6 K) plasma of their peripheral (~3 Mpc) regions; moreover, the absorption line at ~1.3 keV splits off from it. The redshift of distant clusters shifts the absorption lines in the background spectrum (at ~2, ~9, and ~500 keV) to lower energies. Thus, in contrast to the microwave background scattering effect, this effect depends on the cluster redshift z, but in a very peculiar way. When observing clusters at z>1, the effect allows one to determine how the X-ray background evolved and how it was "gathered" with z. To detect the effect, the accuracy of measurements should reach ~0.1%. We consider the most promising clusters for observing the effect and discuss the techniques whereby the influence of the thermal gas radiation hindering the detection of background distortions should be minimal.
