河外TeV能段γ射线背景下限的估算

An Estimation of the Lower Bound on the Extragalactic TeV γ-ray Background

Fermi卫星对GeV能段的河外伽马射线背景(Extragalactic Gamma-ray Back-ground,EGB)进行了较为精确的测量,极大提高了对高能伽马射线背景的认识,但是在TeV能段,使用空间探测器进行观测非常困难,只能依赖地面伽马射线探测器,如成像大气切伦科夫望远镜.目前,对于TeV能段的河外伽马射线背景的认识还不完善.使用有低活跃状态能谱的61个TeV源(包含2个星暴星系、6个射电星系以及53个耀变体)的累计流量给出河外TeV伽马射线背景的下限.结果显示,低能段(0.5–4.5 TeV)流量由两个临近的耀变体Mrk 421和Mrk 501主导,贡献了大约58%的累计背景流量;而大于4.5 TeV的能段,由3个已观测到10 TeV以上能段流量的极端耀变体H 1426+428、1ES 1959+650以及1ES 0229+200主导.最后分别探究了星暴星系、射电星系以及耀变体对河外TeV伽马射线背景的贡献,不同耀变体子类对河外TeV伽马射线背景的贡献以及不同红移区间TeV源对河外伽马射线背景的贡献.

Fermi satellite released fairly accurate measurement of extragalactic gamma-ray background(EGB)from 100 MeV to 820 GeV,which dramatically improve our understanding of the high energy gamma-ray background.But for TeV band,space detector is too small to help,and we must rely on ground based gamma-ray telescopes such as imaging atmospheric Cherenkov telescopes(IACTs).Until now,the extra-galactic TeV gamma-ray background has not been well investigated.In this paper,we calculate the lower bound of extragalactic TeV gamma-ray background radiation by using the energy spectrum of low state of 61 TeV sources,including 53 blazars,6 radio galaxies,and 2 starburst galaxies,respectively.Our results show that blazars is the main contributor of the extragalactic TeV gamma-ray background,especially for Mrk 501 and Mrk 421,whose contribution at 0.5–4.5 TeV is about 58%.And the contri-bution above 4.5 TeV are mainly from the sources H 1426+428,1ES 1959+650 and 1ES 0229+200,and their energy spectrum distribution has been extended to more than 10 TeV.Finally,we calculate the contribution of blazars,radio galaxies,and starburst galaxies,respectively.Similar calculation is used to subclass of blazars and sources with different redshifts.