ON THE ORIGIN OF &gt; 10 GeV PHOTONS IN GAMMA-RAY BURST AFTERGLOWS

Wang, Xiangyu; Liu, Ruo-Yu; Lemoine, Martin

doi:10.1088/2041-8205/771/2/l33

Cited by 55 publications

(55 citation statements)

References 35 publications

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“…While only a small fraction of Fermi detected GRBs have also been detected by LAT, some of these cases (about 10 events) are particularly interesting, since they show characteristics suggestive of an external shock origin for the GeV radiation: first, the onset of these emission is delayed relative to the onset of the prompt sub-MeV emission (Abdo et al 2009a); second the LAT component extends long after the prompt sub-MeV emission stops and third the flux of this long lasting component decays as a power-law in time. Indeed, these observations are compatible with expectations from forward shock radiation (Kumar & Barniol Duran 2009Ghisellini et al 2010;Wang et al 2013;Nava et al 2014).…”

Section: Introductionsupporting

confidence: 88%

Energies of GRB blast waves and prompt efficiencies as implied by modelling of X-ray and GeV afterglows

Beniamini

Nava

Duran

et al. 2015

Mon. Not. R. Astron. Soc.

147

150

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We consider a sample of ten GRBs with long lasting ( 10 2 sec) emission detected by Fermi/LAT and for which X-ray data around 1 day are also available. We assume that both the X-rays and the GeV emission are produced by electrons accelerated at the external forward shock, and show that the X-ray and the GeV fluxes lead to very different estimates of the initial kinetic energy of the blast wave. The energy estimated from GeV is on average ∼ 50 times larger than the one estimated from X-rays. We model the data (accounting also for optical detections around 1 day, if available) to unveil the reason for this discrepancy and find that good modelling within the forward shock model is always possible and leads to two possibilities: either the X-ray emitting electrons (unlike the GeV emitting electrons) are in the slow cooling regime or ii) the X-ray synchrotron flux is strongly suppressed by Compton cooling, whereas, due to the Klein-Nishina suppression, this effect is much smaller at GeV energies. In both cases the X-ray flux is no longer a robust proxy for the blast wave kinetic energy. On average, both cases require weak magnetic fields (10 −6 B 10 −3 ) and relatively large isotropic kinetic blast wave energies 10 53 erg < E 0,kin < 10 55 erg corresponding to large lower limits on the collimated energies, in the range 10 52 erg < E θ,kin < 5 × 10 52 erg for an ISM environment with n ∼ 1cm −3 and 10 52 erg < E θ,kin < 10 53 erg for a wind environment with A * ∼ 1. These energies are larger than those estimated from the Xray flux alone, and imply smaller inferred values of the prompt efficiency mechanism, reducing the efficiency requirements on the still uncertain mechanism responsible for prompt emission.

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Section: Introductionsupporting

confidence: 88%

Energies of GRB blast waves and prompt efficiencies as implied by modelling of X-ray and GeV afterglows

Beniamini

Nava

Duran

et al. 2015

Mon. Not. R. Astron. Soc.

147

150

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“…Wang et al 2013;Beniamini et al 2015). It is worth noting that bursts with subTeV photons at dozens of seconds from the trigger might be interpreted as SSC radiation from FS and be detected by TeV γ-ray observatories as the High Altitude Water Cherenkov observatory (HAWC) (Abeysekara & et al 2012(Abeysekara & et al , 2014.…”

Section: Application: Grb 090510mentioning

confidence: 99%

Modeling the Early Afterglow in the Short and Hard GRB 090510

Fraija

Lee

Vereš

et al. 2016

ApJ

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The bright, short and hard GRB 090510 was detected by all instruments aboard Fermi and Swift satellites. The multiwavelength observations of this burst presented similar features with the Fermi-LAT-detected gammaray bursts. In the framework of the external shock model of early afterglow, a leptonic scenario that evolves in a homogeneous medium is proposed to revisit GRB 090510 and explain the multiwavelength light curve observations presented in this burst. These observations are consistent with the evolution of a jet before and after the jet break. The long-lasting LAT, X-ray and optical fluxes are explained in the synchrotron emission from the adiabatic forward shock. Synchrotron self-Compton emission from the reverse shock is consistent with the bright LAT peak provided that progenitor environment is entrained with strong magnetic fields. It could provide compelling evidence of magnetic field amplification in the neutron star merger.

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“…A possible interpretation of these results -for example, delayed onset of the GeV emission and power-law temporal decay of the long-lived GeV emission -considers the synchrotron emission from electrons accelerated at the external shock to explain the entire signal detected by the LAT (Razzaque 2010;Kumar & Barniol Duran 2010;Ghisellini et al 2010;De Pasquale et al 2010;Ackermann et al 2013b; Lemoine et al 2013;Wang et al 2013). There is however a theoretical argument against this interpretation, as emphasized by Beloborodov et al (2014); the LAT flux usually starts to decrease well before the end of the prompt emission in the GBM, which is too early to correspond to the self-similar stage of the afterglow evolution, expected on theoretical grounds at somewhat later times.…”

Section: Introductionmentioning

confidence: 99%

Time evolution of the spectral break in the high-energy extra component of GRB 090926A

Yassine

Piron

Mochkovitch

et al. 2017

A&A

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Aims. The prompt light curve of the long GRB 090926A reveals a short pulse ∼10 s after the beginning of the burst emission, which has been observed by the Fermi observatory from the keV to the GeV energy domain. During this bright spike, the high-energy emission from GRB 090926A underwent a sudden hardening above 10 MeV in the form of an additional power-law component exhibiting a spectral attenuation at a few hundreds of MeV. This high-energy break has been previously interpreted in terms of gamma-ray opacity to pair creation and has been used to estimate the bulk Lorentz factor of the outflow. In this article, we report on a new time-resolved analysis of the GRB 090926A broadband spectrum during its prompt phase and on its interpretation in the framework of prompt emission models. Methods. We characterized the emission from GRB 090926A at the highest energies with Pass 8 data from the Fermi Large Area Telescope (LAT), which offer a greater sensitivity than any data set used in previous studies of this burst, particularly in the 30−100 MeV energy band. Then, we combined the LAT data with the Fermi Gamma-ray Burst Monitor (GBM) in joint spectral fits to characterize the time evolution of the broadband spectrum from keV to GeV energies. We paid careful attention to the systematic effects that arise from the uncertainties on the LAT response. Finally, we performed a temporal analysis of the light curves and we computed the variability timescales from keV to GeV energies during and after the bright spike. Results. Our analysis confirms and better constrains the spectral break, which has been previously reported during the bright spike. Furthermore, it reveals that the spectral attenuation persists at later times with an increase of the break characteristic energy up to the GeV domain until the end of the prompt phase. We discuss these results in terms of keV−MeV synchroton radiation of electrons accelerated during the dissipation of the jet energy and inverse Compton emission at higher energies. We interpret the high-energy spectral break as caused by photon opacity to pair creation. Requiring that all emissions are produced above the photosphere of GRB 090926A, we compute the bulk Lorentz factor of the outflow, Γ. The latter decreases from 230 during the spike to 100 at the end of the prompt emission. Assuming, instead, that the spectral break reflects the natural curvature of the inverse Compton spectrum, lower limits corresponding to larger values of Γ are also derived. Combined with the extreme temporal variability of GRB 090926A, these Lorentz factors lead to emission radii R ∼ 10 14 cm, which are consistent with an internal origin of both the keV−MeV and GeV prompt emissions.

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ON THE ORIGIN OF > 10 GeV PHOTONS IN GAMMA-RAY BURST AFTERGLOWS

Cited by 55 publications

References 35 publications

Energies of GRB blast waves and prompt efficiencies as implied by modelling of X-ray and GeV afterglows

Energies of GRB blast waves and prompt efficiencies as implied by modelling of X-ray and GeV afterglows

Modeling the Early Afterglow in the Short and Hard GRB 090510

Time evolution of the spectral break in the high-energy extra component of GRB 090926A

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