Detection of the 511 keV Galactic Positron Annihilation Line with COSI
Detection of the 511 keV Galactic Positron Annihilation Line with COSI
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DOI：
10.3847/1538-4357/ab89a9
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
C. Kierans;Steven E. Boggs;A. Zoglauer;A. Lowell;C. Sleator;J. Beechert;T. Brandt;Pierre Jean;Hadar Lazar;J. Roberts;T. Siegert;J. Tomsick;P. Ballmoos
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作者：
C. Kierans;Steven E. Boggs;A. Zoglauer;A. Lowell;C. Sleator;J. Beechert;T. Brandt;Pierre Jean;Hadar Lazar;J. Roberts;T. Siegert;J. Tomsick;P. Ballmoos
正电子湮没的特征，即511keV的γ-射线，在20世纪70年代首次从银河系中心的方向被探测到，但银河系正电子的来源仍然是一个谜。测量的湮没通量对应于一个强烈而稳定的正电子产生源，湮灭率约为∼1043。511keV辐射是银河系持续γ射线线信号中最强的，它显示出向银河系中心区域的集中。一个额外的低表面亮度分量与银盘对准；然而，后者的形态并没有受到很好的限制。康普顿光谱仪和成像仪(COSI)是一种气球搭载的软γ-射线(0.2-5 MeV)望远镜，旨在执行广域成像和高分辨率光谱分析。它的主要目标之一是加深我们对银河系正电子的理解。2016年5月至7月，COSI在新西兰瓦纳卡进行了一次为期46天的气球飞行，这里我们报告了那些观测到的511keV辐射的探测以及光谱和空间分析。为了将银河系正电子湮没发射从仪器背景中分离出来，我们开发了一种使用COMPTEL数据空间分离天体信号的技术。用这种方法，我们得到了对511keV谱线的7.2keV探测σ。我们发现，空间分布与单点源不一致，而且似乎比以前报道的更宽。
The signature of positron annihilation, namely the 511 keV γ-ray line, was first detected coming from the direction of the Galactic center in the 1970s, but the source of Galactic positrons still remains a puzzle. The measured flux of the annihilation corresponds to an intense steady source of positron production, with an annihilation rate on the order of ∼1043 . The 511 keV emission is the strongest persistent Galactic γ-ray line signal, and it shows a concentration toward the Galactic center region. An additional low-surface brightness component is aligned with the Galactic disk; however, the morphology of the latter is not well constrained. The Compton Spectrometer and Imager (COSI) is a balloon-borne soft γ-ray (0.2–5 MeV) telescope designed to perform wide-field imaging and high-resolution spectroscopy. One of its major goals is to further our understanding of Galactic positrons. COSI had a 46-day balloon flight in 2016 May–July from Wanaka, New Zealand, and here we report on the detection and spectral and spatial analyses of the 511 keV emission from those observations. To isolate the Galactic positron annihilation emission from instrumental background, we have developed a technique to separate celestial signals using the COMPTEL Data Space. With this method, we find a 7.2σ detection of the 511 keV line. We find that the spatial distribution is not consistent with a single point source, and it appears to be broader than what has previously been reported.