The average GeV-band emission from gamma-ray bursts

Lange, J.; Pohl, M.

doi:10.1051/0004-6361/201220652

Cited by 6 publications

(6 citation statements)

References 22 publications

(28 reference statements)

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“…Our detection of ubiquitous long-lived emission, albeit below the LAT detection threshold, is consistent with similar work performed by Lange & Pohl (2013). In their work, the authors examined a sample of 99 GBM localized GRBs that were not detected by LAT and found evidence for long-lived subthreshold emission that lasted for as much as 10 times the bursts' T 90 duration in the keV-MeV energy range.…”

Section: Discussionsupporting

confidence: 90%

“…In their work, the authors examined a sample of 99 GBM localized GRBs that were not detected by LAT and found evidence for long-lived subthreshold emission that lasted for as much as 10 times the bursts' T 90 duration in the keV-MeV energy range. Unlike the conclusions drawn by Lange & Pohl (2013), though, we find that the photon index of the subthreshold population derived from our joint likelihood analysis is largely consistent with that observed in the LAT-detected bursts. The different results may be due to the different techniques employed, with the hardest bursts in our sample contributing most significantly to the joint likelihood results, and hence possibly providing a harder average photon index than that measured by Lange & Pohl (2013).…”

Section: Discussionsupporting

confidence: 71%

“…Unlike the conclusions drawn by Lange & Pohl (2013), though, we find that the photon index of the subthreshold population derived from our joint likelihood analysis is largely consistent with that observed in the LAT-detected bursts. The different results may be due to the different techniques employed, with the hardest bursts in our sample contributing most significantly to the joint likelihood results, and hence possibly providing a harder average photon index than that measured by Lange & Pohl (2013).…”

Section: Discussionsupporting

confidence: 71%

“…We find a significant excess above the combined background during time intervals including and exceeding the durations characterizing the prompt emission observed at keV energies using both methods. This analysis follows a similar study by Lange & Pohl (2013), who performed a counting analysis of GBM-detected bursts with no detectable emission in the LAT above 100 MeV. In their study, the authors found similar evidence for extended subthreshold emission.…”

Section: Introductionsupporting

confidence: 79%

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Fermi LAT Stacking Analysis of Swift Localized Gamma-ray Bursts

2016

Preprint

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We perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of gamma-ray bursts (GRB) localized by the Swift spacecraft, which were not detected by the LAT but which fell within the instrument's field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst's

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Section: Discussionsupporting

confidence: 90%

Section: Discussionsupporting

confidence: 71%

Section: Discussionsupporting

confidence: 71%

Section: Introductionsupporting

confidence: 79%

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Fermi LAT Stacking Analysis of Swift Localized Gamma-ray Bursts

2016

Preprint

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“…Several observations are related to the temporal variations of spectra. This way, the spectral lags were found between different low energy bands [5] and the very-high-energy radiation was discovered to be extended relative to the x-ray emission [6,7,1]. In this paper we go further and compare the temporal extension of GRB gamma-ray radiation in the two energy bands 100 MeV < E < 1 GeV and E > 1 GeV (hereafter, low and high-energy bands) using the data from the Large Area Telescope (LAT) of the Fermi satellite [8,9].…”

Section: Introductionmentioning

confidence: 95%

TIME STRETCHING OF THE GeV EMISSION OF GRBs: FERMI-LAT DATA VERSUS GEOMETRICAL MODEL

Piskunov

Рубцов

2016

ApJ

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It is known that the high energy (> 100 MeV) emission of gamma-ray bursts is delayed with respect to the low energy emission. However, the dependence of light curves on energy has not been studied for the high energy bands. In this paper we consider the bursts observed by Fermi LAT from 2008 August 4 to 2011 August 1, for which at least 10 photons were observed with the energy greater than 1 GeV. These include 4 bursts: GRB 080916C, GRB 090510, GRB 090902B, and GRB 090926A. We use the Kolmogorov-Smirnov test to compare the light curves in the two bands, 100 MeV < E < 1 GeV and E > 1 GeV. For GRB 080916C and GRB 090510 the light curves in the two bands are statistically compatible. However, for GRB 090926A, the higher-energy light curve is stretched compared to the lower-energy one with a statistical significance of 3.3σ and, for GRB 090902B, on the contrary, the lower-energy curve is stretched with 2.3σ significance. We argue that the observed diversity of stretching factors may be explained in a simple geometrical model. The model assumes that the jet opening angle depends on the emission energy in a way that the most energetic photons are radiated near the axis of the jet. All the bursts are considered equivalent in their rest frames and the observed light curves differ only due to different redshifts and view directions. The model conforms to the total burst energy constraint and matches the Fermi-LAT observations of the fraction of GRBs visible in 100 MeV < E < 1 GeV band, which may be observed at higher energies. The model predicts the distribution of observable stretching factors, which may be tested in the future data. Finally, we propose a method to estimate observer's off-axis angle based on the stretching factor and the fraction of the high-energy photons. The code for modeling is open source and is publicly available on GitHub (https:

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Uhecr Escape Mechanisms for Protons and Neutrons From Gamma-Ray Bursts, and the Cosmic-Ray-Neutrino Connection

Baerwald

Bustamante

Winter

2013

ApJ

118

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The paradigm that gamma-ray burst (GRB) fireballs are the sources of the ultra-high energy cosmic rays (UHECRs) is being probed by neutrino observations. Very stringent bounds can be obtained from the cosmic ray (proton)-neutrino connection, assuming that the UHECRs escape as neutrons. In this study, we identify three different regimes as a function of the fireball parameters: the standard "one neutrino per cosmic ray" case, the optically thick (to neutron escape) case, and the case where leakage of protons from the boundaries of the shells (direct escape) dominates. In the optically thick regime, photomeson production is very efficient, and more neutrinos will be emitted per cosmic ray than in the standard case, whereas in the direct escape-dominated regime, more cosmic rays than neutrinos will be emitted. We demonstrate that, for efficient proton acceleration, which is required to describe the observed UHECR spectrum, the standard case only applies to a very narrow region of the fireball parameter space. We illustrate with several observed examples that conclusions on the cosmic rayneutrino connection will depend on the actual burst parameters. We show that the definition of the pion production efficiency currently used by the IceCube collaboration underestimates the neutrino production in the optically thick case. Finally, we point out that the direct escape component leads to a spectral break in the cosmic ray spectrum emitted from a single source. The resulting "twocomponent model" can be used to even more strongly pronounce the spectral features of the observed UHECR spectrum than the dip model.

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The average GeV-band emission from gamma-ray bursts

Cited by 6 publications

References 22 publications

Fermi LAT Stacking Analysis of Swift Localized Gamma-ray Bursts

Fermi LAT Stacking Analysis of Swift Localized Gamma-ray Bursts

TIME STRETCHING OF THE GeV EMISSION OF GRBs: FERMI-LAT DATA VERSUS GEOMETRICAL MODEL

Uhecr Escape Mechanisms for Protons and Neutrons From Gamma-Ray Bursts, and the Cosmic-Ray-Neutrino Connection

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