The Fermi LAT collaboration has built up a detailed Monte Carlo simulation to characterize the instrument response and tune its performance. The simulation code is built around the widely used GEANT4 toolkit and was carefully validated against beam test and flight data. This poster shows how the full LAT simulation is used to develop the event selection for the Cosmic-Ray Electron (\emph{CRE}) analysis so as to optimize the instrument performance. In particular, we will show in detail the determination of the geometry factor and the residual hadron contamination. The very accurate MC simulation proved to be fundamental to control the systematic uncertainties on the CRE spectrum measured by the Fermi LAT.
The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration
费米大面积望远镜(Fermi Large Area Telescope,Fermi-LAT,以下简称LAT)是费米伽马射线太空望远镜(Fermi Gamma-ray Space Telescope,Fermi)任务的主要仪器,是一个成像,宽视场,高能γ射线望远镜,覆盖能量范围从20 MeV到300 GeV以上。在飞行任务的头几年,LAT团队对仪器的飞行性能有了相当深入的了解。因此,我们更新了用于减少LAT数据的分析以供公开发布,以及仪器响应函数(IRF),即为数据分析提供的仪器性能描述。在本文中,我们描述了这些更新的动机的影响。此外,我们还讨论了我们最初是如何从蒙特卡罗模拟中推导出IRF的,以及后来如何根据飞行数据和模拟数据之间的差异对这些IRF进行校正的。我们还给出了使用飞行数据进行验证的细节,并量化了IRFs中的剩余不确定性。最后,我们描述的技术LAT团队已经开发出传播这些不确定性的系统误差的估计,如通量和光谱的天体物理源的共同测量。
费米伽马射线太空望远镜(英语:Fermi Gamma-ray Space Telescope)的大面积望远镜(英语:Large Area Telescope)是一个对转换望远镜,对超过40个能量十年的伽马射线敏感,介于20 MeV和300 GeV之间。LAT与伽马射线暴监测器(GBM)-任务上的另一种仪器-协同作用,在研究伽马射线暴(GRB)方面,在光谱覆盖范围、有效面积和仪器死时间方面具有前所未有的灵敏度。我们将回顾GRB的Fermi-LAT观测的主要结果,介绍GeV能区GRB的主要性质。
We investigate the physical mechanisms of high-energy gamma-ray emission from the TeV-emitting misaligned active galactic nucleus IC 310. Eight years of data from the Fermi Large Area Telescope (Fermi-LAT) between 100 MeV and 500 GeV are reduced and analysed to study the temporal and spectral characteristics of IC 310. Point spread function-partitioned instrument response functions are used to improve the resolvability of IC 310 from nearby NGC 1275. Systematic effects due to this choice of instrument response functions and the proximity of NGC 1275 are investigated. We find strong spectral va…
Cosmic Rays (CRs) propagating through dense molecular clouds (MCs) produce gamma rays which carry direct information about the CR distribution throughout the Galaxy. Observations of gamma rays in different energy bands allow exploration of the average CR density in the Galactic Disk, the so-called level of the "CR Sea". Fermi-LAT observations have demonstrated the method's feasibility based on two dozen MCs in our Galaxy. However, the potential of Fermi-LAT is limited by the most massive and relatively nearby MCs; thus, the current observations cover only a tiny fraction of the Milky Way. In t…
The Fermi Gamma-ray Space Telescope, a key mission in multiwavelength and multimessenger studies, has been surveying the gamma-ray sky from its low-Earth orbit since 2008. Its two scientific instruments, the Gamma-ray Burst Monitor (GBM) and the Large Area Telescope (LAT), cover 8 orders of magnitude in photon energy. The GBM consists of 12 Sodium Iodide detectors and 2 Bismuth Germinate detectors, covering the 10 keV - 40 MeV energy range, arrayed on two sides of the spacecraft so as to view the entire sky that is not occulted by the Earth. The LAT is a pair production telescope based on sili…
A Comprehensive Analysis of Fermi Gamma-ray Burst Data: III. Energy-Dependent T90 Distributions of GBM GRBs and Instrumental Selection Effect on Duration Classification
The analysis and combination of data from different gamma-ray instruments involves the use of collaboration proprietary software and case-by-case methods. The effort of defining a common data format for high-level data, namely event lists and instrument response functions (IRFs), has recently started for very-high-energy gamma-ray instruments, driven by the upcoming Cherenkov Telescope Array (CTA). In this work we implemented this prototypical data format for a small set of MAGIC, VERITAS, FACT, and H.E.S.S. Crab nebula observations, and we analyzed them with the open-source gammapy software p…
A Multi-Mission Detection Framework for High-Energy Transients: Application to a 13-year Fermi/GBM and Swift/BAT Sample
Weizmann Institute of Science(魏茨曼科学研究所);University of California at Santa Barbara(加州大学圣塔芭芭拉分校);International Centre for Theoretical Sciences, Tata Institute of Fundamental Research(塔塔基础研究院国际理论科学中心)
The Fermi Large Area Telescope (LAT) has amassed a large data set of primary cosmic-ray protons throughout its mission. The LAT's wide field of view and full-sky survey capabilities make it an excellent instrument for studying cosmic-ray anisotropy. As a space-based survey instrument, the LAT is sensitive to anisotropy in both right ascension and declination, while ground-based observations only measure the anisotropy in right ascension. We present the results of the first ever proton anisotropy search using Fermi LAT. The data set uses eight years of data and consists of approximately 179 mil…
No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields
我们分析了Ap. J. Lett.中报道的堆积活动星系核周围的伽马射线晕,2010,722,L39。首先,我们表明,周围的堆叠活动星系核的γ射线的角分布是一致的蟹状星云脉冲星,这是费米/LAT的点源周围的γ射线的角分布。这使得它不太可能晕是由电磁级联TeV光子在星系际空间。然后,我们比较周围的堆叠活动星系核的γ射线的角分布与费米/LAT的点扩散函数(PSF),并确认存在一个多余的PSF以上。然而,我们证明,这种效果的幅度和角度大小是不同的费米/LAT仪器的前部和后部转换的光子,因此是一种仪器效应。
The search for Dark Matter (DM) has great potential to reveal physics beyond the Standard Model. As such, searches for evidence of DM particles are being carried out using a wide range of techniques, such as direct searches for DM particles, searches for DM produced with colliders, and indirect searches for the Standard Model annihilation products of DM. Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect Dark Matter searches due to their relatively high DM content and negligible expected astrophysical background. A collaboration was formed to maximise the sensitivity of DM se…
A handedness in the arrival directions of high-energy photons from outside our Galaxy can be related to the helicity of an intergalactic magnetic field. Previous estimates by arXiv:1310.4826 and arXiv:1412.3171 showed a hint of a signal present in the photons observed by the Fermi Large Area Telescope (LAT). An update on the measurement of handedness in Fermi-LAT data is presented using more than 10 years of observations. Simulations are performed to study the uncertainty of the measurements, taking into account the structure of the exposure caused by the energy-dependent instrument response a…
We revisit the well-studied outburst of the low mass X-ray binary (LMXB) system V404 Cygni, and claims of gamma-ray excesses observed with the Fermi-LAT instrument. Upon analysing an 11.5 year dataset with the 8-year LAT point source catalogue and 8-year background models, we find no evidence to suggest that there is high energy gamma-ray emission during the outburst period (or at any other time) from V404 Cygni. This is due to the proximity of V404 Cygni to the gamma-ray emitting blazar B2023+336, a luminous source approximately 0.3 degrees away, which causes source confusion at the position …
The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is carrying out a detailed survey of the northern sky at TeV energies. 2HWC J2006+341 is a newly discovered source reported by the point source search in the 2HWC HAWC Observatory Gamma Ray Catalog. Using $\sim$1038 days of HAWC data we carried out a detailed analysis of the region revealing extended emission. No emission has been detected by other TeV instruments at the location of 2HWC J2006+341. We also analyzed publicly available data from the \textit{Fermi}-LAT that show for the first time the existence of an extended GeV sour…
Tentative observation of a gamma-ray line at the Fermi LAT
使用费米大天区望远镜43个月的公共伽马射线数据,我们发现在接近银河系中心的区域,能量为130 GeV,超过4.6 sigma,这与暗物质湮灭的伽马射线线并不矛盾。当考虑到别处效应时,观察到的签名的显著性为3.2西格玛。如果按照暗物质粒子湮灭为光子对的观点来解释,观测结果表明部分湮灭截面约为10^-27 cm ^3 s ^-1,暗物质质量约为130 GeV。我们回顾了统计分析的各个方面,并对可能的工具适应症进行了评论。
Fermi LAT detection of two high Galactic latitude gamma-ray sources, Fermi J1049.7+0435 and J1103.2+1145
第二个费米LAT源目录(Nolan et al. 2012)包括多达1,873个源,但最初尝试识别其他波长的对应物导致575个源仍然未被识别。2FGL目录是基于自2008年推出以来的前24个月LAT观测,但LAT现在已经积累了超过5年的高能伽马射线数据,几乎没有任何变化,这表明有可能找到新的来源,这些来源太微弱而无法在前两年的数据中检测到,或者在目录创建后显示出耀斑活动。在本文中,我们报告两个新的伽玛射线源偶然发现的星座狮子座和讨论可能的对应物的基础上无线电观测。