以毫角秒精度定位银河系中心的VHE源
Locating the VHE source in the Galactic Centre with milli-arcsecond accuracy
摘要：
从银河系中心方向探测到的极高能伽马射线（VHE; E>100 GeV）能量高达E>10 TeV。到目前为止，由于观测仪器的位置精度有限，这种发射的起源尚不清楚。其中一个对应的候选者是超大质量黑洞（SMBH）Sgr A*。如果VHE辐射产生于SMBH的~10^{15} cm ~1000 r_G（r_G=G M/c^2为史瓦西半径）范围内，那么当早期型或巨星在~毫角秒（mas）内接近视线时，VHE光子通量在100--300 GeV能量范围内会减少。通量的变暗是由于在恒星的软光子场中VHE光子的成对产生的吸收，我们称之为成对产生食（PPE）。根据目前已知的银河系内角秒恒星的轨道，我们发现PPE导致100- 300 GeV波段的系统性变暗，其水平为百分之几，并持续数周。由于PPE只影响一个狭窄的能带，并且与恒星的通过有很好的相关性，它可以清楚地与其他系统性甚至源固有效应区分开来。虽然这种效应太小，无法用当前一代的VHE探测器观察到，但即将到来的高计数率实验，如切伦科夫望远镜阵列（CTA）将足够灵敏。测量PPE的时间特征有可能定位VHE发射区域在内部1000 r_G内的位置和大小，或者在未检测到的情况下，完全排除SMBH的直接环境作为伽马射线产生的场所。
英文摘要：
Very high-energy gamma-rays (VHE; E>100 GeV) have been detected from the direction of the Galactic Centre up to energies E>10 TeV. Up to now, the origin of this emission is unknown due to the limited positional accuracy of the observing instruments. One of the counterpart candidates is the super-massive black hole (SMBH) Sgr A*. If the VHE emission is produced within ~10^{15} cm ~1000 r_G (r_G=G M/c^2 is the Schwarzschild radius) of the SMBH, a decrease of the VHE photon flux in the energy range 100--300 GeV is expected whenever an early type or giant star approaches the line of sight within ~ milli-arcseconds (mas). The dimming of the flux is due to absorption by pair-production of the VHE photons in the soft photon field of the star, an effect we refer to as pair-production eclipse (PPE). Based upon the currently known orbits of stars in the inner arcsecond of the Galaxy we find that PPEs lead to a systematic dimming in the 100--300 GeV band at the level of a few per cent and lasts for several weeks. Since the PPE affects only a narrow energy band and is well correlated with the passage of the star, it can be clearly discriminated against other systematic or even source-intrinsic effects. While the effect is too small to be observable with the current generation of VHE detectors, upcoming high count-rate experiments like the Cherenkov telescope array (CTA) will be sufficiently sensitive. Measuring the temporal signature of the PPE bears the potential to locate the position and size of the VHE emitting region within the inner 1000 r_G or in the case of a non-detection exclude the immediate environment of the SMBH as the site of gamma-ray production altogether.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
