Very high energy gamma-ray emission beyond 10 TeV from GRB 221009A
Z. CaoF AharonianQi AnA. AxikeguY. X. BaiYiwang BaoD. BastieriXiao-Jun BiY.J. BiJ. T. CaiQing CaoW.Y CaoZhe CaoJ. ChangJ. F. ChangAikang ChenE. S. ChenLiang ChenChen LinLong ChenM.J ChenM.L ChenQin ChenShaw H. ChenS. Z. ChenT. L. ChenY ChenNing ChengY.D ChengMing-Yang CuiS. W. CuiX.H CuiYongde CuiB. Z. DaiH. L. DaiZ. G. DaiDanzengluobu DanzengluobuD. della VolpeX.Q DongK. K. DuanJunhui FanYi-Zhong FanJun FangKai FangC.F FengL. FengF. ShiX.T FengYulong FengS. GabiciB. GaoChuyue GaoL. Q. GaoQ. GaoWei GaoWei GaoM.M GeLi-Sheng GengGwenael GiacintiGuanghua GongQ. B. GouM. H. GuFulai GuoXu GuoYing GuoYong GuoY.A HanH.H HeHongbin HeJiangbiao HeXiao-Rong HeYong HeMatthieu HellerY. K. HorBowen HouChao HouXingsong HouH.B HuQi HuS. C. HuD.H HuangT.Q HuangWeidong HuangX. T. HuangX.Y HuangYong-Feng HuangZhongjie HuangX. L. JiH.Y JiaKe JiaK. JiangXiaojun JiangZ.J JiangMingzhou JinM. M. KangT. KeD. KuleshovK. KurinovBing LiCheng LiCong LiDi LiLi FeiHaibo LiH.C LiHuaijiang LiJ. LiJian LiJie LiK. LiW.L LiW.L LiX.R LiXin LiYang LiZhe LiZhuo LiE.W LiangLiang YuS. J. LinBing LiuC. LiuDong LiuH. LiuH.D LiuJ LiuJ.L LiuJinxiang LiuMingyi LiuRui LiuS.M LiuWenzhao LiuYangjié LiuYu‐Rong LiuR. LuQi LuoH.K LvB. Q.L. L.Xinhua MaJ. R. MaoM. ZhaW. MitthumsiriHaowei MuY. C. NanA. NeronovZ. W. OuB. Y. PangP. PattarakijwanichZ. Y. PeiMing QiY. Q. QiBing-Qiang QiaoJ. J. QinD. RuffoloA. SáizD. SemikozCaoyang ShaoL. ShaoO. ShchegolevX. D. ShengFengchun ShuH. C. SongYu.V StenkinV. I. StepanovYang SuQ. N. SunX.N SunZhifeng SunP. H. T. TamQ.W TangZ.B TangW. W. TianChunling WangC.B WangG.W WangHui WangH.H WangJ. WangKaiying WangL.P WangL.Y WangPing WangRuoju WangWei WangX.G WangXuefeng WangYang WangY.D WangY.J WangZ.H WangZ.X WangZhen WangZ. WangD. M. WeiJinjia WeiY. WeiTian WenChuan‐Yu WuH. R. WuShengbiao WuX.F WuYong WuShichuan XiJianxin XiaJunji XiaG. M. XiangDong XiaoGang XiaoG. G. XinY. XinXing YangXiong ZhangD.L XuR.F XuRui XuW. L. XuW. XuD.H YanJing‐Zhi YanT YanChul Woo YangFan YangF.F YangH. W. YangJunyou YangLili YangMo YangRuizhi YangS. B. YangY. YaoZ. G. YaoY. M. YeLina YinN. YinX. H. YouZ. Y. YouY.H. YuQuan YuanHui YueHoudun ZengT. X. ZengWeihe ZengM. ZhaBin‐Bin ZhangFan ZhangH.M ZhangHengyun ZhangJ.L ZhangL.X ZhangLi ZhangPeng ZhangP.P ZhangR. ZhangShengbai ZhangS.R ZhangS.S ZhangXin ZhangX.P ZhangY.F ZhangYi ZhangYong ZhangBei ZhaoJunqian ZhaoLinlin ZhaoLei ZhaoShujie ZhaoF. ZhengBo ZhouH. ZhouJingzhi ZhouMeng ZhouPing ZhouRongpu ZhouX. X. ZhouC. G. ZhuF. R. ZhuH. ZhuK. J. ZhuX. Zuo
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Abstract:
The highest energy gamma-rays from gamma-ray bursts (GRBs) have important implications for their radiation mechanism. Here we report for the first time the detection of gamma-rays up to 13 TeV from the brightest GRB 221009A by the Large High Altitude Air-shower Observatory (LHAASO). The LHAASO-KM2A detector registered more than 140 gamma-rays with energies above 3 TeV during 230$-$900s after the trigger. The intrinsic energy spectrum of gamma-rays can be described by a power-law after correcting for extragalactic background light (EBL) absorption. Such a hard spectrum challenges the synchrotron self-Compton (SSC) scenario of relativistic electrons for the afterglow emission above several TeV. Observations of gamma-rays up to 13 TeV from a source with a measured redshift of z=0.151 hints more transparency in intergalactic space than previously expected. Alternatively, one may invoke new physics such as Lorentz Invariance Violation (LIV) or an axion origin of very high energy (VHE) signals.Keywords:
Air shower
Extragalactic background light
Blazars are effective emitters of γ-rays with spectra extending to GeV and TeV energies. In the case of distant TeV blazars, γ-rays undergo severe absorption due to interactions with diffuse intergalactic radiation fields resulting in significant deformations of the initial (source) spectra. Even for the lowest possible level of the Extragalactic Background Light (EBL), the absorption-corrected γ-ray spectra from some TeV blazars appear unusually hard, which cannot be explained within the standard particle acceleration models of blazars. The simplest and most natural solution of this problem seems to us the realization of internal absorption of γ-rays in narrow (e.g. Planckian type) radiation fields in the immediate vicinity of the γ-ray production region.
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The extragalactic background light (EBL) from the infrared to the ultraviolet is difficult to measure directly, but can be constrained with a variety of methods. EBL photons absorb gamma-rays from distant blazars, allowing one to use blazar spectra from atmospheric Cherenkov telescopes (ACTs) to put upper limits on the EBL by assuming a blazar source spectrum. Here we apply a simple technique, similar to the one developed by Schroedter (2005), to the most recent very-high energy (VHE) gamma-ray observations of blazars to put upper limits on the EBL energy density. This technique is independent of the EBL model and has well-defined errors on the constraints. Our results are consistent with EBL measurements and constraints but marginally inconsistent with several EBL models.
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Abstract Recent gamma-ray observations of the blazar 1ES 1101−232 (redshift z= 0.186) reveal that the unabsorbed TeV spectrum is hard, with spectral index α≲ 0.5 [F(ν) ∝ν−α]. We show that simple one-zone synchrotron self-Compton model can explain such hard spectra if we assume a power law energy distribution of the emitting electrons with a relatively high minimum energy. In this case the intrinsic TeV spectrum can be as hard as F(ν) ∝ν1/3, while the predicted X-ray spectrum can still be much softer. The observations of 1ES 1101−232 can therefore be reconciled with relatively high intensities of the infrared background, even if some extreme background levels can indeed be excluded. We show that the other TeV sources (Mrk 421, Mrk 501 and PKS 2155−304) can be interpreted in the same framework, with a somewhat larger minimum energy.
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Aims. Our goal is to research the upper limits to the extragalactic background light (EBL). Methods. The upper limits to the extragalactic background light (EBL) are presented, using the Fermi and very high energy (VHE) spectra recently observed in TeV blazars. We use an assumption that the VHE intrinsic photon index cannot be harder than the Fermi index measured by the Fermi-LAT. Results. These upper limits are compatible with ones given by most EBL models; however, the models of high EBL density are contradicted by TeV blazars.
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Recently, a new method to constrain the distance of blazars with unknown redshift using combined observations in the GeV and TeV regimes has been developed, with the underlying assumption that the Very High Energy (VHE) spectrum corrected for the absorption of TeV photons by the Extragalactic Background Light (EBL) via photon-photon interaction should still be softer than the gamma-ray spectrum observed by Fermi/LAT. The constraints found are related to the real redshifts by a simple linear relation, that has been used to infer the unknown distance of blazars. The sample will be revised with the up-to-date spectra in both TeV and GeV bands, the method tested with the more recent EBL models and finally applied to the unknown distance blazars detected at VHE.
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The intergalactic magnetic field (IGMF) in cosmic voids can be indirectly probed through its effect on electromagnetic cascades initiated by a source of TeV gamma rays, such as blazars, a subclass of active galactic nuclei. Blazars that are sufficiently luminous at TeV energies, "extreme TeV blazars", can produce detectable levels of secondary radiation from inverse Compton scattering of the electrons in the cascade, provided that the IGMF is not too large. We reveiw recent work in the literature which utilizes this idea to derive constraints on the IGMF for three TeV-detected blazars-1ES 0229+200, 1ES 1218+304, and RGB J0710+591, and we also investigate four other hard-spectrum TeV blazars in the same framework. Through a recently developed detailed 3D particle tracking Monte Carlo simulation code, incorporating all major effects of QED and cosmological expansion, we research effects of major uncertainties such as the spectral properties of the source, uncertainty in the intensity of the UV - far IR extragalactic background light (EBL), under-sampled Very High Energy (VHE; energy > 100 GeV) coverage, past history of gamma-ray emission, source vs. observer geometry, and jet AGN Doppler factor. The implications of these effects on the recently reported lower limits of the IGMF are thoroughly examined to conclude that presently available data are compatible with a zero IGMF hypothesis.
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The direct measurement of the extragalactic background light (EBL) is difficult at optical to infrared wavelengths because of the strong foreground radiation originating in the Solar System. Very high energy (VHE, E$>$100 GeV) gamma rays interact with EBL photons of these wavelengths through pair production. In this work, the available VHE spectra from six blazars are used to place upper limits on the EBL. These blazars have been detected over a range of redshifts and a steepening of the spectral index is observed with increasing source distance. This can be interpreted as absorption by the EBL. In general, knowledge of the intrinsic source spectrum is necessary to determine the density of the intervening EBL. Motivated by the observed spectral steepening with redshift, upper limits on the EBL are derived by assuming that the intrinsic spectra of the six blazars are $\propto E^{-1.8}$. Upper limits are then placed on the EBL flux at discrete energies without assuming a specific spectral shape for the EBL. This is an advantage over other methods since the EBL spectrum is uncertain.
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Given a knowledge of the density spectra intergalactic low energy photons as a function of redshift, one can derive the intrinsic gamma-ray spectra and luminosities of blazars over a range of redshifts and look for possible trends in blazar evolution. Stecker, Baring & Summerlin have found some evidence hinting that TeV blazars with harder spectra have higher intrinsic TeV gamma-ray luminosities and indicating that there may be a correlation of spectral hardness and luminosity with redshift. Further work along these lines, treating recent observations of the blazers lES02291+200 and 3C279 in the TeV and sub-TeV energy ranges, has recently been explored by Stecker & Scully. GLAST will observe and investigate many blazars in the GeV energy range and will be sensitive to blazers at higher redshifts. I examine the implications high redshift gamma-ray absorption for both theoretical and observational blazer studies.
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