Macrolensing of gamma-ray bursts (GRBs) is expected to manifest as a GRB recurring with the same light curve and spectrum as a previous one, but with a different flux and a slightly offset position. Identifying such lensed GRBs may give important information about the lenses, cosmology, as well as the GRBs themselves. Here we present a search for lensed GRBs among $\sim 2700$ GRBs observed by the Fermi Gamma-ray Burst Monitor (GBM) during 11 years of operations. To identify lensed GRBs, we perform initial cuts on position, time-averaged spectral properties and relative duration. We then use the cross-correlation function to assess the similarity of light curves, and finally analyze the time-resolved spectra of the most promising candidates. We find no convincing lens candidates. The most similar pairs are single-pulsed GRBs with relatively few time bins for the spectral analysis. This is best explained by similarities within the GRB population rather than lensing. However, the null result does not rule out the presence of macrolensed GRBs in the sample. In particular, we find that observational uncertainties and Poisson fluctuations can lead to significant differences within a pair of lensed GRBs.
Gravitational lensing of gamma-ray bursts (GRBs) can provide an opportunity to probe the massive compact objects in the universe at different redshifts. We have discovered two consecutive pulses in the light curve of GRB 090717034, with the same temporal profile and different count rate, separated by a time interval, which is identified as gravitationally lensed candidate in Fermi/GBM GRB catalogue \citep{Kalantari}. Here, we use the $χ^2$ method to investigate the similarity of the temporal profile variability of the two pulses as a gravitationally lensed candidate GRB. We find the magnificat…
Observing gravitationally lensed objects in the time domain is difficult, and well-observed time-varying sources are rare. Lensed gamma-ray bursts (GRBs) offer improved timing precision to this class of objects complementing observations of quasars and supernovae. The rate of lensed GRBs is highly uncertain, approximately 1 in 1000. The Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-ray Space Telescope has observed more than 3000 GRBs making it an ideal instrument to uncover lensed bursts. Here we present observations of GRB 210812A showing two emission episodes, separated by 33.3 s, an…
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 ($<$2 s) are ~10 times less likely to produce a precursor than long GRBs. The quiescent time profile is well described by a double Gaussian distribution, indicating that the observed precursors have two distinct physical progenitors. The light curves of the identified precursor GRBs are publicly available in an online catalog (https://icecube.wisc.edu/~grbweb_public/Precursors.html).
We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with Fermi/GBM from October 4th 2019 through May 20th 2020, excluding a ~130 s segment with a very high burst density on April 27th 2020. The 148 bursts presented here, are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of inc…
Many different physical processes have been suggested to explain the prompt gamma-ray emission in gamma-ray bursts (GRBs). Although there are examples of both bursts with photospheric and synchrotron emission origins, these distinct spectral appearances have not been generalized to large samples of GRBs. Here, we search for signatures of the different emission mechanisms in the full Fermi Gamma-ray Space Telescope GBM catalogue. We use Gaussian Mixture Models to cluster bursts according to their parameters from the Band function ($α$, $β$, and $E_{pk}$) as well as their fluence and $T_{90}$. W…
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…
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…
A Coherent Search for New Galactic Magnetars using Fermi/GBM and follow-up Swift/BAT: 7 Candidates and a Large Burst Catalog
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（印度基本研究学院国际理论科学中心）
The Fermi Gamma-ray Burst Monitor (GBM) is currently the most prolific detector of Gamma-Ray Bursts (GRBs). Recently the detection rate of short GRBs (SGRBs) has been dramatically increased through the use of ground-based searches that analyze GBM continuous time tagged event (CTTE) data. Here we examine the efficiency of a method developed to search CTTE data for sub-threshold transient events in temporal coincidence with LIGO/Virgo compact binary coalescence triggers. This targeted search operates by coherently combining data from all 14 GBM detectors by taking into account the complex spati…
We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-Ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the ten year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events of which we identifyied 2356 as cosmic GRBs. Additional trigger events were due to solar are events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to th…
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…
Context. Fast Radio Bursts (FRBs) are millisecond-long bursts uniquely detected at radio frequencies. FRB 131104 is the only case for which a $γ$-ray transient positionally and temporally consistent was claimed. This high-energy transient had a duration of $\sim400$~s and a 15-150~keV fluence $S_γ\sim4\times10^{-6}$ erg $\mathrm{cm}^{-2}$. However, the association with the FRB is still debated. Aims. We aim at testing the systematic presence of an associated transient high-energy counterpart throughout a sample of the FRB population. Methods. We used an approach like that used in machine learn…
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 …
We review more than 10 years of continuous monitoring of accreting X-ray pulsars with the all-sky Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope. Our work includes data from the start of GBM operations in August 2008, through to November 2019. Pulsations from 39 accreting pulsars are observed over an energy range of $10-50\,$keV by GBM. The GBM Accreting Pulsars Program (GAPP) performs data reduction and analysis for each accreting pulsar and makes histories of the pulse frequency and pulsed flux publicly available. We examine in detail the spin histories, outbursts a…
We present the systematic spectral analyses of gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor (GBM) during its first ten years of operation. This catalog contains two types of spectra; time-integrated spectral fits and spectral fits at the brightest time bin, from 2297 GRBs, resulting in a compendium of over 18000 spectra. The four different spectral models used for fitting the spectra were selected based on their empirical importance to the shape of many GRBs. We describe in detail our procedure and criteria for the analyses, and present the bulk results in the form of …
The localizations of gamma-ray bursts (GRBs) detected with the Gamma-ray Burst Monitor (GBM) onboard the Fermi satellite are known to be affected by significant systematic errors of 3-15 degrees. This is primarily due to mismatch of the employed Band function templates and the actual GRB spectrum. This problem can be avoided by simultaneously fitting for the location and the spectrum of a GRB, as demonstrated with an advanced localization code, BALROG (arXiv:1610.07385). Here, we analyze in a systematic way a sample of 105 bright GBM-detected GRBs for which accurate reference localizations are…
Millilensing of Gamma-Ray Bursts (GRBs) is expected to manifest as multiple emission episodes in a single triggered GRB with similar light-curve patterns and similar spectrum properties. Identifying such lensed GRBs could help improve constraints on the abundance of compact dark matter. Here we present a systemic search for millilensing among 3000 GRBs observed by the \textit{Fermi} GBM up to 2021 April. Eventually we find 4 interesting candidates by performing auto-correlation test, hardness test, and time-integrated/resolved spectrum test to the whole sample. GRB 081126A and GRB 090717A are …
The Fermi GBM catalog provides a large database with many measured variables that can be used to explore and verify gamma-ray burst classification results. We have used Principal Component Analysis and statistical clustering techniques to look for clustering in a sample of 801 gamma-ray bursts described by sixteen classification variables. The analysis recovers what appears to be the Short class and two long-duration classes that differ from one another via peak flux, with negligible variations in fluence, duration and spectral hardness. Neither class has properties entirely consistent with th…
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）
In light of the joint multimessenger detection of a binary neutron star merger as the gamma-ray burst GRB 170817A and in gravitational waves as GW170817, we reanalyze the Fermi Gamma-ray Burst Monitor data of one of the closest short gamma-ray bursts: GRB 150101B. We find this burst is composed of a short hard spike followed by a comparatively long soft tail. This apparent two-component nature is phenomenologically similar to that of GRB 170817A. While GRB 170817A was distinct from the previously known population of short gamma-ray bursts in terms of its prompt intrinsic energetics, GRB 150101…
