LS 5039轨道谱的Fermi-LAT诊断
A diagnostic on the orbital spectrum of LS 5039 with Fermi-LAT
摘要：
LS 5039是一个著名的$γ$射线双星系统，它由一个未知的致密天体和一颗大质量伴星O组成。它显示出多年来在高能量下相当稳定的发射，因此可以作为一个理想的实验室来研究这种发射突出$γ$射线的特殊系统的发射机制。为此，我们采取的轨道相位分辨的能量谱观测\fermi超过10年。我们将轨道分为四个轨道相位，每个相位的轨道相位范围为0.25，分别以0.00，0.25，0.50和0.75为中心，其中相位0.0是近星点，相位0.5是近星点。0.25和0.75附近的相位是对称的，因此应该具有相同的局部加速度环境。光谱分析表明，\fermi光谱与这两个对称轨道相位有很大不同：轨道相位0.25的发射明显强于0.75的发射。如果LS 5039具有与PSR B 1259 -63相似的激波构形，则该结果不符合$γ$射线是来自弓形激波尾部的多普勒增强发射的假设，并表明激波加速等离子体与恒星粒子环境之间的逆康普顿散射是一个重要过程。我们还发现，以前关于在3- 20 GeV处轨道调制消失的报道是由于不同轨道相位的光谱翻转能相似所致。的光谱特性的近星点和apastron区域的背景下，在相位区域约0.25和0.75的测量。
英文摘要：
LS 5039 is a well-known $γ$-ray binary system which consists of an unknown compact object and a massive companion O star. It shows rather stable emissions at high energies over years and hence serves as an ideal laboratory to investigate the emission mechanism for such peculiar systems which emit prominent $γ$-rays. To this end, we take the orbital phase resolved energy spectrum as observed by \fermi over 10 years. We divide the orbit into four orbital phases, each with an orbital phase range of 0.25, centered at 0.00, 0.25, 0.50 and 0.75 respectively, where the phase 0.0 is the periastron and phase 0.5 is the apastron. The phases around 0.25 and 0.75 are symmetric and hence are supposed to have identical local acceleration environment. The spectral analysis shows that, the \fermi spectra are largely different from these two symmetric orbital phases: the emission from orbital phase 0.25 turns out to be significantly stronger than that from 0.75. This result does not fit a scenario that $γ$-rays are Doppler boosted emission from bow shock tails if LS 5039 has a shock configuration similar to PSR B1259-63, and indicates that the inverse Compton scatterings between the shock accelerated plasma and the stellar particle environment is the underline procedure. We also find that the previous report for a disappearance of the orbital modulation at 3--20 GeV is due to the similar spectral turn-over energies of the different orbital phases. The spectral properties of periastron and apastron regions are addressed in the context of the measurements in phase regions around 0.25 and 0.75.
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