【作者】 王凯；

【导师】 戴子高；

【作者基本信息】 南京大学 ， 天体物理， 2017， 博士

【摘要】 近年来,Fermi/LAT对伽玛暴的观测,明确地指出其中是存在的GeV高能辐射成分的。这些高能辐射存在于伽玛暴的瞬时辐射阶段,也存在于余辉阶段。高能辐射的观测为我们理解伽玛暴的物理起源和辐射机制提供了新的契机。另外,极高能宇宙射线的起源问题一直是高能天体物理领域的一个热点。极高能宇宙射线在星系空间中传播,与背景光子的作用,会生成相应的高能中微子,电子和光子。次级的电子和光子的级联过程不仅会影响邻近宇宙中高能电子和光子的探测也会对整体的弥散GeV高能光子的观测具有指导意义。再者,伽玛暴被认为有可能是极高能宇宙射线的候选体。伽玛暴如果是极高能宇宙射线的加速区,不可避免会产生与伽玛暴辐射成协的中微子辐射。基于IceCube对伽玛暴中微子的探测,会对伽玛暴加速区的一些加速机制,包括喷流的重子负载率,强子过程的反应效率都有限制。本文我们重要研究了伽玛暴中的高能辐射的起源以及极高能宇宙射线传播中生成的次级粒子的级联效应。第一章,对伽玛暴的基本观测性质,包括能谱、光变、以及伽玛暴的火球已经内外正反激波模型做了介绍。另外讨论了伽玛暴瞬时辐射和X射线耀发期间的GeV高能辐射。再者,介绍了极高能宇宙射线的可能的源,以及伽玛暴作为极高能宇宙射线源的一些优势和挑战。最后我们对包括伽玛暴在内的一些高能天体物理现象中的一些基本的辐射过程做了一个总结讨论。第二章,对于Fermi/LAT观测到的伽玛暴瞬时辐射中的额外GeV成分的强子起源我们进行了详细研究。这些额外的成分可以起源于包括光介子过程和Bethe-Heitler过程的强子过程中次级粒子的级联过程。然而,很多文章指出,Bohm近似情况下给出的质子的加速最大能量在极端相对论性激波中不能到达。所以在质子有限加速的情况下,我们对于质子支配的伽玛暴外流体中的电磁级联过程进行了重新分析。这样的模型可以对三种分类的额外GeV成分给出解释。除此之外,根据强子模型,通过额外的GeV成分我们可以校准伽玛暴参数,并给出期待的中微子流量。基于校准之后的参数,对于所有LAT伽玛暴,将来强子模型可以被Icecube观测的中微子上限用来进行限制。在第三章,我们对伽玛暴100728A的X射线耀发期间的高能GeV辐射做了研究。基于滞后内激波模型,我们研究了两个均匀壳层的碰撞的动力学和辐射性质。双壳层碰撞形成的正反激波会加速把电子加速到相对论性,这些电子和X射线耀发的光子之间的逆康普顿散射可以贡献观测的GeV辐射。除了通常同步自康普顿过程,我们还考虑了正反激波之间的交叉逆康普顿散射。通过解析和数值的计算,对GRB 100728A的观测能谱性质进行了很好的解释。在第四章,我们对极高能宇宙射线在宇宙背景光子场中传播生成的极高能光子的传播过程进行了研究。考虑各种可能的作用过程,我们发现极高能光子的有效穿透距离在较低的星系际磁场和射电背景环境下,可以比它的自由程大10倍。这原则上可以根据对邻近宇宙中观测的极高能光子数据,对传播环境的参数给出一些限制。再者,这些极高能的光子((?)1018eV)的光子和低能的宇宙背景光子之间的作用,会生成正负μ子对。尽管这个过程相比于正负电子对过程较弱,不过在极端Klein-Nishina机制下,由于电子对生成过程和逆康普顿散射过程的极端leading效应,使得级联过程中的高能粒子的能量能够有效的保存,从而使得μ子对生成过程得到加强。我们对星际空间中不同红移不同环境下的几种情况做了分别地讨论,发现这种额外的中微子贡献,在较低的星系际磁场和射电背景环境下,可以对通常的Cosmogenic中微子贡献10%。精确的贡献比例可能依赖于传播环境和宇宙射线能谱和成分,这些在这章中也进行了讨论。第五章,我们对伽玛暴的瞬时辐射能谱的低能谱指数进行了研究。内激波中加速电子的同步辐射对于解释伽玛暴瞬时辐射的能谱被认为是普遍流行的模型。然而同步辐射预言的低能光子指数为α～-1.5,这与实际观测的伽玛暴的低能谱指数集中在α～-1附近不相符。我们对伽玛暴的极端相对论性外流体中的磁场的演化进行了研究,发现在衰减的磁场下,激波加速的电子谱型会不同于我们通常假定的谱型。而这样的电子分布,通过同步辐射,使得我们观测到的低能谱指数会处于-3/2<α<-2/3。这就变得与观测一致。除此之外,对可能的上升的电子注入率也做了讨论。第六章我们对伽玛暴中高能辐射的问题与极高能宇宙射线的问题做了总结和展望。并且我们期望未来仪器的探测,能进一步指明一些问题,包括伽玛暴的加速机制,重子负载率,以及伽玛暴能否作为极高能宇宙射线的源,极高能宇宙射线的各向异性程度以及成分组成。更多还原

【Abstract】 In the past years,based on the observations of Fermi/LAT,indeed,the GeV emission component exists during Gamma-ray Bursts(GRBs),not only in the prompt emission phase,but also in the afterglow phase.The observations of the GeV emissions give a new chance for us to understand the physical origin and the radiation mechanism of GRBs.Besides,the origin of Ultra-high En-ergy Cosmic Rays(UHECRs)has always been a great contention of high energy astrophysics.During the propagation of UHECRs,they would interact with the background photons through the photopion process and the subsequent high energy neutrinos,electrons and photons would be produced.The cascades of the secondary electrons and photons would effect the detections of them from nearby universe,as well as the diffused GeV photons background.GRBs have proposed as a possible candidate of the source of UHECRs,and if so,it is unavoidable to gen-erate the neutrinos during the interactions between the UHECRs and the keV-MeV emission of GRBs.According to the non/detections of neutrinos corresponding to GRBs by IceCube,some constrains on the baryon loading and the interaction efficiencies of hadronic processes in the outflows of GRBs can be given.In this thesis,the origin of the high energy emission of GRBs and the cascades of secondaries produced during the propagations of the UHECRs would be studied.In the first Chapter,the basic properties of the observations of GRBs,including the spectra,lightcurves,the fireball model and the internal-external forward-reverse shocks model have been introduced.Besides,the GeV emission during the prompt phases and X-ray flares of GRBs is discussed as well.The possible sources of UHECRs and the advantages and challenges of GRBs as the sources of UHECRs are introduced.In last,a summary of some basic radiation processes in the GRBs or other astrophysical phenomena is given.In the second Chapter,The extra GeV component observed by Fermi/LAT during the prompt phases of gamma-ray bursts(GRBs)could arise from the cascades emission of the secondaries generated by the hadronic processes,including the photomeson and Bethe-Heitler processes.However,suggested by many papers,the highest energy of proton given by the Bohm approximation could not be reached in ultra-relativistic shock waves.So in the limited accelera-tion of protons,we reinvestigate the cascades emission inside of the proton-dominated outflows of GRBs,which could be responsible to the extra GeV component in three classifications,i.e.,090926A-type,090902B-type and 080916C-type.Besides,according to the hadronic model,the expected neutrinos flux is given as well by calibrating the GRB parameters through fitting the extra GeV spectra.Based on the calibrated parameters,for all LAT GRBs,the hadronic model could be tested by the upper limit given by IceCube observations in the future.In the third Chapter,the GeV emission during the X-ray flares of GRB 100728A is stud-ied.Based on the late internal shock,we investigate the dynamics of the shell-shell collision and corresponding radiation.The electrons would be accelerated to the very high energy by the forward-reverse shocks formed during shell-shell collision,and the keV-MeV photons would be upscattered by these electrons through the inverse Compton scattering.In addition to the syn-chrotron self-Compton,the cross inverse Compton scattering between the electrons and photons inside of the forward and reverse shocks is also considered.By the analytical and numerical calculations,the spectrum of the GeV emission of GRB 100728A is well explained.In the fourth Chapter,the propagation of ultra-high energy(UHE)photons generated dur-ing the interactions between the UHECRs and cosmic background radiation is studied.Taking all possible interaction processes,we found the effective penetration distance of UHE photons can be one order larger than the mean free length of UHE photons in the absence of strong intergalactic magnetic field and radio background.In principle,according to the upper limit of UHE photons given in nearby universe,the constrains of the propagation environment can be given.Moreover,muon pairs can be produced in the annihilation of ultrahigh energy(UHE,E(?)1018 eV)photons with low energy cosmic background radiation in the intergalactic space,giving birth to neutrinos.Although the branching ratio of muon pair production is low,prod-ucts of other channels,which are mainly electron/positron pairs,will probably transfer most of their energies into the new generated UHE photon in the subsequent interaction with the cosmic background radiation via Compton scattering in deep Klein-Nishina regime.The regeneration of these new UHE photons then provides a second chance to produce the muon pairs,enhanc-ing the neutrino flux.Through taking several environments into account,we find that an extra component of UHE neutrinos will arise from the propagation of UHE cosmic rays due to the generated UHE photons and electron/positrons.This component is with a flux of at most 10%of that of the conventional cosmogenic neutrino at a few EeV,in the absence of a strong inter-galactic magnetic field and a strong cosmic radio background.The precise contribution of extra component depends on several factors,e.g.,cosmic radio background,intergalactic magnetic field,and the spectrum of proton,which are discussed in this chapter.In the fifth Chapter,the low energy photon index of prompt phase of GRBs is studied.The prompt emission of most of gamma-ray bursts(GRBs)typically exhibits a non-thermal Band component.The synchrotron radiation in the popular internal shock model is generally put forward to explain such a non-thermal component.However,the low-energy photon indexα～-1.5 predicted by the synchrotron radiation is inconsistent with the observed value α～-1.Here we investigate the evolution of a magnetic field during propagation of internal shocks within an ultrarelativistic outflow,and revisit the fast cooling of shock-accelerated electrons via synchrotron and synchrotron self-Compton emission for this evolutional magnetic field.We find that the magnetic field is first nearly constant and then decays as B’∝t-1,which leads to a reasonable range of the low-energy photon index,-3/2<α<-2/3.In addition,if a rising electron injection rate during a GRB is introduced,we find that α reaches-2/3 more easily.We thus fit the prompt emission spectra of GRBs 080916c and 080825c.Finally,since there is only the Band component without a high-energy excess for most of GRBs,we obtain a general constraint on the ratio of the two energy equipartition factors behind the shocks.∈C/∈B(?)few.In the last Chapter,a summary and prospect of the high energy emission of GRBs and UHECRs is given.We hope,in future,more observations can make some questions clear,in-cluding the acceleration mechanism and the baryon loading of GRBs,GRBs-UHECRs scenario,the anisotropy and the chemical component of UHECRs.更多还原