On the generation of high-energy photons detected by the Fermi Satellite from gamma-ray bursts

Kumar, Pawan; Duran, R. Barniol

doi:10.1111/j.1745-3933.2009.00766.x

Cited by 242 publications

(274 citation statements)

References 51 publications

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“…Ghisellini et al 2010;Kumar & Barniol Duran 2009b) or a hadronic model (Razzaque et al 2009). Razzaque et al (2009) demonstrate that synchrotron radiation from cosmic-ray protons accelerated in a GRB, delayed by the proton synchrotron cooling timescale in a jet of magnetically-dominated shocked plasma moving at highly relativistic speeds, explains the delayed GeV emission as observed in many Fermi/LAT bursts.…”

Section: Bumps In the Afterglow Light Curvesmentioning

confidence: 99%

Optical and near-infrared follow-up observations of fourFermi/LAT GRBs: redshifts, afterglows, energetics, and host galaxies

McBreen

Krühler

Rau

et al. 2010

A&A

114

100

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Aims. Fermi can measure the spectral properties of gamma-ray bursts over a very large energy range and is opening a new window on the prompt emission of these energetic events. Localizations by the instruments on Fermi in combination with follow-up by Swift provide accurate positions for observations at longer wavelengths leading to the determination of redshifts, the true energy budget, host galaxy properties and facilitate comparison with pre-Fermi bursts. Methods. Multi-wavelength follow-up observations were performed on the afterglows of four bursts with high energy emission detected by Fermi/LAT: GRB 090323, GRB 090328, GRB 090510 and GRB 090902B. They were obtained in the optical/near-infrared bands with GROND mounted at the MPG/ESO 2.2 m telescope and additionally of GRB 090323 in the optical with the 2 m telescope in Tautenburg, Germany. Three of the events are classified as long bursts while GRB 090510 is a well localized short GRB with GeV emission. In addition, host galaxies were detected for three of the four bursts. Spectroscopic follow-up was initiated with the VLT for GRB 090328 and GRB 090510. Results. The afterglow observations in 7 bands are presented for all bursts and their host galaxies are investigated. Knowledge of the distance and the local dust extinction enables comparison of the afterglows of LAT-detected GRBs with the general sample. The spectroscopic redshifts of GRB 090328 and GRB 090510 were determined to be z = 0.7354 ± 0.0003 and z = 0.903 ± 0.001 and dust corrected star-formation rates of 4.8 M yr −1 and 0.60 M yr −1 were derived for their host galaxies, respectively. Conclusions. The afterglows of long bursts exhibit power-law decay indices (α) from less than 1 to ∼2.3 and spectral indices (β opt ) values from 0.65 to ∼1.2 which are fairly standard for GRB afterglows. Constraints are placed on the jet half opening angles of < ∼ 2.1 • to > ∼ 6.4 • , which allows limits to be placed on the beaming corrected energies. These range from < ∼ 5 × 10 50 erg to the one of the highest values ever recorded, > ∼ 2.2 × 10 52 erg for GRB 090902B, and are not consistent with a standard candle. The extremely energetic long Fermi bursts have optical afterglows which lie in the top half of the brightness distribution of all optical afterglows detected in the Swift era or even in the top 5% if incompleteness is considered. The properties of the host galaxies of these LAT detected bursts in terms of extinction, star formation rates and masses do not appear to differ from previous samples.

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Section: Bumps In the Afterglow Light Curvesmentioning

confidence: 99%

Optical and near-infrared follow-up observations of fourFermi/LAT GRBs: redshifts, afterglows, energetics, and host galaxies

McBreen

Krühler

Rau

et al. 2010

A&A

114

100

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“…As an example, the ES luminosity and peak energy are usually determined in the literature by introducing two additional parameters ò B and ò e , which parametrize the microphysics (magnetic content and internal energy in random motion of electrons) of the shocked plasma. Precise values of these parameters are unknown, and limits are often obtained such that the emission of the forward shock is not detectable in the MeV band (Kumar & Barniol Duran 2009), which usually translates to low density n 0 and low ò B . However, we note that the limits on the Lorentz factor do not change substantially with the introduction of ò B and ò e , which justifies our simplified treatment.…”

Section: Discussionmentioning

confidence: 99%

“…Sari (1997) considered the early onset of the afterglow (due to an external shock), which leads to mixed emission from an unspecified mechanism during the prompt phase of the GRB and the external shock. More recently, this idea was also put forth by Kumar & Barniol Duran (2009), who tried to explain the late onset of the GeV emission with synchrotron emission of electrons accelerated at the external shock.…”

Section: Introductionmentioning

confidence: 99%

The Anatomy of a Long Gamma-Ray Burst: A Simple Classification Scheme for the Emission Mechanism(s)

Bégué

Burgess

2016

ApJ

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Ultra-relativistic motion and efficient conversion of kinetic energy to radiation are required by gamma-ray burst (GRB) observations, yet they are difficult to simultaneously achieve. Three leading mechanisms have been proposed to explain the observed emission emanating from GRB outflows: radiation from either relativistic internal or external shocks, or thermal emission from a photosphere. Previous works were dedicated to independently treating these three mechanisms and arguing for a sole, unique origin of the prompt emission of GRBs. In contrast, herein, we first explain why all three models are valid mechanisms and that a contribution from each of them is expected in the prompt phase. Additionally, we show that a single parameter, the dimensionless entropy of the GRB outflow, determines which mechanism contributes the most to the emission. More specifically, internal shocks dominate for low values of the dimensionless entropy, external shocks for intermediate values, and finally, photospheric emission for large values. We present a unified framework for the emission mechanisms of GRBs with easily testable predictions for each process.

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“…The Compton scattering processes are in the deep KN regime. In the circum-stellar medium (CSM), B ′ is at the order of µ-Gauss (Kumar 2009). The shocked magnetic field can be amplified to hundred times larger.…”

Section: The α ∼ −1 Problemmentioning

confidence: 99%

Time-resolved GRB spectra in the complex radiation of synchrotron and Compton processes

Jiang¹,

Hu²,

Chen³

et al. 2016

Mon. Not. R. Astron. Soc.

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Under the steady state condition, the spectrum of electrons is investigated by solving the continuity equation under the complex radiation of both the synchrotron and Compton processes. The resulted GRB spectrum is a broken power law in both the fast and slow cooling phases. On the basis of this electron spectrum, the spectral indices of the Band function in four different phases are presented. In the complex radiation frame, the detail investigation on physical parameters reveals that both the reverse shock photosphere model and the forward shock with strong coupling model can answer the α ∼ −1 problem. A possible marginal to fast cooling phase transition in GRB 080916C is discussed. The time resolved spectra in different pulses of GRB 100724B, GRB 100826A and GRB 130606B are investigated. We found that the flux is proportional to the peak energy in almost all pulses. The phases for different pulses are determined according to the spectral index revolution. We found the strong correlations between spectral indices and the peak energy in GRB 100826A, which can be explained by the Compton effect in the fast cooling phase. However, the complex scenario predicts a steeper index for the injected electrons, which challenges the acceleration mechanism in GRBs. ‡

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On the generation of high-energy photons detected by the Fermi Satellite from gamma-ray bursts

Cited by 242 publications

References 51 publications

Optical and near-infrared follow-up observations of fourFermi/LAT GRBs: redshifts, afterglows, energetics, and host galaxies

Optical and near-infrared follow-up observations of fourFermi/LAT GRBs: redshifts, afterglows, energetics, and host galaxies

The Anatomy of a Long Gamma-Ray Burst: A Simple Classification Scheme for the Emission Mechanism(s)

Time-resolved GRB spectra in the complex radiation of synchrotron and Compton processes

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