IceCube has reported the detection of a diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars （FSRQs） have been proposed to be the candidate sources. Here we assume that the neutrino flux from...IceCube has reported the detection of a diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars （FSRQs） have been proposed to be the candidate sources. Here we assume that the neutrino flux from FSRQs is proportional to their gamma-ray ones, and obtain the gamma-ray/neutrino flux ratio by the diffuse gamma-ray flux from Fermi-LAT measurement of FSRQs and the diffuse neutrino flux detected by IceCube. We apply this ratio to individual FSRQs and hence predict their neutrino flux. We find that a large fraction of candidate FSRQs from the northern sky in the IceCube point source search has predicted neutrino flux above the IceCube upper limit; and for the sample of stacking search for neutrinos by IceCube, the predicted stacked flux is even larger than the upper limit of stacked flux by orders of magnitude. Therefore the IceCube limit from stacking searches, combined with the Fermi-LAT observations, already rejects FSRQs as the main sources of IceCube-detected diffuse neutrinos： FSRQs can only account for 〈 10% 〈 4%） of the IceCube-detected diffuse neutrino flux, according to the stacking searches from the whole （northern） sky. The derived small neutrino/gamma-ray flux ratio also implies that the gamma-ray emission from FSRQs cannot be produced by the secondary le^tons and photons from the Non nroduction nrocesses. The caveat in the assumntions is discussed.展开更多
文摘目的:设计一种小型伽马射线检测系统,为环境中的伽马射线检测提供技术手段。方法:该系统采用传统的闪烁晶体计数法来对伽马射线的能量进行响应,主要由一块NaI(Tl)晶体、一块对应的光电倍增管(photo-multiplier tube,PMT)阵列、位置总和电路以及上位机组成。其中定制NaI(Tl)晶体为扁平状,厚度6 mm;PMT采用多阳极位置灵敏PMT。基于LabWindows平台设计相应的系统控制及显示界面,并通过传输控制协议(transmission control protocol,TCP)实现上位机与下位机之间的通信。结果:该系统可以检测到自然环境和特殊环境下的伽马射线,而且测量的准确性也达到了要求。结论:该系统可有效、实时地检测伽马射线的存在,为后续研制成熟的小动物活体核素成像伽马相机提供了技术支持和实践基础。
基金supported by the National Natural Science Foundation of China(Grant No.11273005)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120001110064)the National Program on Key Basic Research Project(Grant No.2014CB845800)
文摘IceCube has reported the detection of a diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars （FSRQs） have been proposed to be the candidate sources. Here we assume that the neutrino flux from FSRQs is proportional to their gamma-ray ones, and obtain the gamma-ray/neutrino flux ratio by the diffuse gamma-ray flux from Fermi-LAT measurement of FSRQs and the diffuse neutrino flux detected by IceCube. We apply this ratio to individual FSRQs and hence predict their neutrino flux. We find that a large fraction of candidate FSRQs from the northern sky in the IceCube point source search has predicted neutrino flux above the IceCube upper limit; and for the sample of stacking search for neutrinos by IceCube, the predicted stacked flux is even larger than the upper limit of stacked flux by orders of magnitude. Therefore the IceCube limit from stacking searches, combined with the Fermi-LAT observations, already rejects FSRQs as the main sources of IceCube-detected diffuse neutrinos： FSRQs can only account for 〈 10% 〈 4%） of the IceCube-detected diffuse neutrino flux, according to the stacking searches from the whole （northern） sky. The derived small neutrino/gamma-ray flux ratio also implies that the gamma-ray emission from FSRQs cannot be produced by the secondary le^tons and photons from the Non nroduction nrocesses. The caveat in the assumntions is discussed.
