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。
英文摘要：
The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope observatory is a pair conversion telescope sensitive to gamma-rays over more than four energy decades, between 20 MeV and more than 300 GeV. Acting in synergy with the Gamma-ray Burst Monitor (GBM) - the other instrument onboard the mission - the LAT features unprecedented sensitivity for the study of gamma-ray bursts (GRBs) in terms of spectral coverage, effective area, and instrumental dead time. We will review the main results from Fermi-LAT observation of GRB, presenting the main properties of GRBs at GeV energies.
We performed a systematic search for X-ray bursts of the SGR J1935+2154 using the Fermi Gamma-ray Burst Monitor continuous data dated from Jan 2013 to October 2021. Eight bursting phases, which consist of a total of 353 individual bursts, are identified. We further analyze the periodic properties of our sample using the Lomb-Scargle periodogram. The result suggests that those bursts exhibit a period of ~ 238 days with a ~ 63.2% duty cycle. Based on our analysis, we further predict two upcoming active windows of the X-ray bursts. Since July 2021, the beginning date of our first prediction has b…
We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with Fermi/GBM from October 4th 2019 through May 20th 2020, excluding a ~130 s segment with a very high burst density on April 27th 2020. The 148 bursts presented here, are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of inc…
Although it is generally assumed that there are two dominant classes of gamma-ray bursts (GRB) with different typical durations, it has been difficult to unambiguously classify GRBs as short or long from summary properties such as duration, spectral hardness, and spectral lag. Recent work used t-distributed stochastic neighborhood embedding (t-SNE), a machine learning algorithm for dimensionality reduction, to classify all Swift gamma-ray bursts as short or long. Here, the method is expanded, using two algorithms, t-SNE and UMAP, to produce embeddings that are used to provide a classification …
We report the results of the rapid follow-up observations of gamma-ray bursts (GRBs) detected by the Fermi satellite to search for associated fast radio bursts. The observations were conducted with the Australian Square Kilometre Array Pathfinder at frequencies from 1.2-1.4 GHz. A set of 20 bursts, of which four were short GRBs, were followed up with a typical latency of about one minute, for a duration of up to 11 hours after the burst. The data was searched using 4096 dispersion measure trials up to a maximum dispersion measure of 3763 pc cm$^{-3}$, and for pulse widths $w$ over a range of d…
Many different physical processes have been suggested to explain the prompt gamma-ray emission in gamma-ray bursts (GRBs). Although there are examples of both bursts with photospheric and synchrotron emission origins, these distinct spectral appearances have not been generalized to large samples of GRBs. Here, we search for signatures of the different emission mechanisms in the full Fermi Gamma-ray Space Telescope GBM catalogue. We use Gaussian Mixture Models to cluster bursts according to their parameters from the Band function ($α$, $β$, and $E_{pk}$) as well as their fluence and $T_{90}$. W…
We present an analysis of more than 11 years of Fermi-GBM data in which 217 Gamma-Ray Bursts (GRBs) are found for which their main burst is preceded by a precursor flash. We find that short GRBs ($<$2 s) are ~10 times less likely to produce a precursor than long GRBs. The quiescent time profile is well described by a double Gaussian distribution, indicating that the observed precursors have two distinct physical progenitors. The light curves of the identified precursor GRBs are publicly available in an online catalog (https://icecube.wisc.edu/~grbweb_public/Precursors.html).
A thermal component is suggested to be the physical composition of the ejecta of several bright gamma-ray bursts (GRBs). Such a thermal component is discovered in the time-integrated spectra of several short GRBs as well as long GRBs. In this work, we present a comprehensive analysis of ten very short GRBs detected by Fermi Gamma-Ray Burst Monitor to search for the thermal component. We found that both the resultant low-energy spectral index and the peak energy in each GRB imply a common hard spectral feature, which is in favor of the main classification of the short/hard versus long/soft dich…
We report on a very bright, long-duration gamma-ray burst (GRB), GRB~220426A, observed by \emph{Fermi} satellite. GRB~220426A with total duration of $T_{90}=6$~s is composed with two main pulses and some sub-peaks. The spectral analysis of this burst with Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with high $α\gtrsim 0.2$ and low $β\lesssim -3.1$. It is strong reminiscent of GRB~090902B, a special GRB with identification of the photospheric emission. Then, we perform the spectral analysis of this burst based on a non-dissipated photospheri…
Sorted by the photon fluences of short Gamma-ray Bursts (SGRBs) detected by the Fermi- Gamma Ray Burst Monitor (GBM), nine brightest bursts are selected to perform a comprehensive analysis. All GRB lightcurves are fitted well by 1 to 3 pulses that are modelled by fast-rising exponential decay profile (FRED), within which the resultant rising time is strongly positive-correlated with the full time width at half maxima (FWHM). A photon spectral model involving a cutoff power-law function and a standard blackbody function (CPL + BB) could reproduce the spectral energy distributions of these SGRBs…
The composition of a jet is still an unsolved problem in gamma-ray bursts (GRBs). Several previous studies have suggested that the prompt emission spectrum of GRBs is likely to consist of a few components that may arise from different jet compositions. Here we present a systematic analysis to search for the GRBs that seem to show the transition from a fireball to the Poynting-flux-dominated outflow between well-separated pulses within a single burst, like the GRB 160626B, using the Gamma-ray Burst Monitor data of the \emph{Fermi} satellite. We obtain 43 GRBs with clear multiple pulses and find…
We have revisited the spectral width in the EF E spectrum of gamma-ray bursts with the BEST peak flux P and time-integrated F spectral data provided by the Fermi GBM Burst Catalog. We first compute the BEST spectral widths to compare with some typical physics models. Our analysis results consist with the previous results: blackbody emission alone cannot explain the observed spectrum and most of the observed spectra cannot be interpreted by the synchrotron radiation. We then check the correlations between the spectral width and the observable model-independent burst properties of duration, flue…
Finding the Particularity of the Active Episode of SGR J1935+2154 during Which FRB 20200428 Occurred: Implication from Statistics of Fermi/GBM X-Ray Bursts
Central China Normal University（华中师范大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Key Laboratory of Quark and Lepton Physics (Central China Normal University), Ministry of Education（教育部夸克与轻子物理重点实验室（华中师范大学））；Beijing Normal University（北京师范大学）；Dezhou University（德州学院）；Qufu Normal University（曲阜师范大学）
GRB 220627A, detected by Fermi Gamma-ray Burst Monitor (GBM), shows two episodes of gamma-ray emission, which are separated by a {$\sim$700} s long quiescent phase. Due to similar temporal shapes and spectra in the two episodes, GRB 220627A is speculated to be a gravitationally lensed gamma-ray burst (GRB). We analyze the Fermi Large Area Telescope (LAT) data and find that about 49 gamma-ray photons above 100 MeV come from the GRB during the first episode, while there are no photons above 100 MeV in the second episode. Based on the broadband spectral study of the two episodes, the gravitationa…
During 2020 April and May, SGR J1935+2154 emitted hundreds of short bursts and became one of the most prolific transient magnetars. At the onset of the active bursting period, a 130 s burst "forest," which included some bursts with peculiar time profiles, were observed with the Fermi/Gamma-ray Burst Monitor (GBM). In this Letter, we present the results of time-resolved spectral analysis of this burst "forest" episode, which occurred on 2020 April 27. We identify thermal spectral components prevalent during the entire 130 s episode; high-energy maxima appear during the photon flux peaks, which …
17 Yr of Magnetar Bursts Observed with the Fermi Gamma-ray Burst Monitor
University of Alabama in Huntsville（亨茨维尔阿拉巴马大学）；Sabancı University, Faculty of Engineering and Natural Sciences（萨班哲大学工程与自然科学学院）；Beijing Normal University（北京师范大学）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Universities Space and Research Association（大学空间研究协会）；University of Galway（高威大学）；Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville（亨茨维尔阿拉巴马大学空间等离子体与高空大气研究中心）；Rice University（莱斯大学）
The Fermi Large Area Telescope (Fermi-LAT) Collaboration reported the Second Gamma-ray Burst Catalog (2FLGC), which comprises a subset of 29 bursts with photon energies above 10 GeV. Although the standard synchrotron forward-shock model has successfully explained the Gamma-ray burst (GRB) afterglow observations, energetic photons higher than 10 GeV from these transient events can hardly be described in this scenario. We present the closure relations (CRs) of synchrotron self-Compton (SSC) afterglow model in the adiabatic and radiative scenario and when the central engine injects continuous ene…
