MeV Gamma-ray imaging spectroscopic observation for Galactic Centre and Cosmic Background MeV gammas by SMILE-2+ Balloon Experiment
MeV Gamma-ray imaging spectroscopic observation for Galactic Centre and Cosmic Background MeV gammas by SMILE-2+ Balloon Experiment
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Mev伽马射线成像光谱观察银河中心和宇宙背景Mev Gammas by Smile-2气球实验
DOI：
10.1088/1742-6596/1468/1/012046
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
T.Tanimori
中科院分区：
文献类型：
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作者：
T.Ikeda;T.Tanimori et al.;T.Tanimori
近年来，出现了大量关于MeV和亚GeV尺度下暗物质(DM)的可能性的论文。到目前为止，只有INTEGAL和COMPTEL提供了银心511keV的实验数据，而银河系扩散MeV伽马(GDMG)和COMPTEL的两个光谱为间接探测光DM提供了宽天的宇宙背景MeV伽马(CBMG)。然而，尽管进行了10年的观测，但除了511keV外，漫射伽马的这些谱包含了很大的统计和系统误差，因为这两台仪器在太空中都遭受了严重的本底辐射。2018年4月，我们(京都大学漫画组的SMILE项目)在澳大利亚使用JAXA气球的电子跟踪康普顿相机(ETCC)在一天的时间里观测到了整个南方天空的MeV伽马射线。(SMILE2+项目)通过测量每个伽马中的康普顿散射的所有参数，ETCC首次实现了与光学望远镜一样获得MeV伽马的完整方向，并清晰地区分了空间中的信号伽马和巨大的背景伽马。在这次观测中，ETCC用3SR的大视场观测了包括银心、半盘、螃蟹和大部CBMG在内的所有天空的3/5 MeV伽马。通过重建康普顿过程，我们成功地将背景降低了2个数量级，获得了纯漫画伽马，这清楚地证明了在银心穿过视场时，探测到的伽马通量明显增加了30%，这与CBMG和GDMG的比例一致。目前在银河系中心附近已初步探测到511keV伽马GDMG，分别为5σ和10 keV。此外，我们还获得了近105个CBMG事件，背景相当低，仅占CBMG事件总数的10%。因此，即使是一天的观测，我们也获得了很好的数据，既有很高的统计量，也有很低的系统性。
Recently, there appears lots of papers on the possibility of light Dark Matter (DM) in MeV and sub-GeV scale. Until now, only INTEGRAL and COMPTEL provided experimental data of 511keV of galactic center, and two spectra of Galactic Diffuse MeV gammas (GDMG) and COMPTEL provided the Cosmic Background MeV gammas (CBMG) for wide sky for indirect detection of light DMs. However except 511keV, those spectra for diffuse gammas included large statistical and systematic errors in spite of 10 years observation, since both two instruments suffered from severe background radiation in space. In 2018 April, we (SMILE-project in Comic-ray Group of Kyoto University) have observed MeV gamma rays for whole southern sky by Electron Tracking Compton Camera (ETCC) using JAXA balloon at Australia during one-day.(SMILE2+ Project) By measuring all parameters of Compton scattering in every gamma, ETCC has achieved for the first time to obtain the complete direction of MeV gammas as same as optical telescopes, and also to distinguish signal gammas from huge background gammas in space clearly. In this observation, ETCC with a large Field of View of 3sr observed MeV gammas from 3/5 of all sky including galactic centre, a half disk, crab, and most of CBMG By reconstructing the Compton process, we successfully obtained pure comic gammas by reducing background by more 2 orders, which is clearly certificated by the clear enhancement of detected gamma flux with 30% during galactic center passing through the Field of View, which is consistent with the ratio of CBMG and GDMG. Now 511keV gammas GDMG are preliminarily detected with 5 and> 10σ respectively around Galactic Centre. Also we have obtained near 10 5 events of CBMG in with quite low background of only a few 10% in total CBMG events. Thus we obtained good data for both with high statistics and very low systematics even one day observation.