The peak energy of dissipative gamma-ray burst photospheres

Giannios, Dimitrios

doi:10.1111/j.1365-2966.2012.20825.x

Cited by 107 publications

(124 citation statements)

References 49 publications

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“…If it is a consequence of the dominant radiation mechanism at work in GRBs, as we expect, theoretical studies may help understanding the nature and the true location of this boundary (see for instance Eichler & Levinson 2004;Yamazaki et al 2004;Rees & Mészáros 2005;Thompson et al 2007;Giannios 2012;Mochkovitch et al 2012;Beniamini & Piran 2013;Shahmoradi 2013, for explanations within the framework of different theoretical or phenomelogical models). The observation of an E pi -E iso relation in time-resolved spectra (e.g.…”

Section: Discussionmentioning

confidence: 96%

TheE_peak–E_isorelation revisited withFermiGRBs

Heussaff

Atteia

Zolnierowski

2013

A&A

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Aims. We used a sample of gamma-ray bursts (GRBs) detected by Fermi and Swift to reanalyze the correlation discovered by Amati et al. (2002, A&A, 390, 81) between E pi , the peak energy of the prompt GRB emission, and E iso , the energy released by the GRB assuming isotropic emission. This correlation has been disputed by various authors, and our aim is to assess whether it is an intrinsic GRB property or the consequence of selection effects. Methods. We constructed a sample of Fermi GRBs with homogeneous selection criteria, and we studied their distribution in the E pi -E iso plane. Our sample is made of 43 GRBs with a redshift and 243 GRBs without a redshift. We show that GRBs with a redshift follow a broad E pi -E iso relation, while GRBs without a redshift show several outliers. We use these samples to discuss the impact of selection effects associated with GRB detection and with redshift measurement. Results. We find that the E pi -E iso relation is partly due to intrinsic GRB properties and partly due to selection effects. The lower right boundary of the E pi -E iso relation stems from a true lack of luminous GRBs with low E pi . In contrast, the upper left boundary is attributed to selection effects acting against the detection GRBs with low E iso and large E pi that appear to have a lower signal-to-noise ratio. In addition, we demonstrate that GRBs with and without a redshift follow different distributions in the E pi -E iso plane. GRBs with a redshift are concentrated near the lower right boundary of the E pi -E iso relation. This suggests that it is easier to measure the redshift of GRBs close to the lower E pi -E iso boundary and that GRBs with a redshift follow the Amati relation better than the general population. In this context, we attribute the controversy about the reality of the Amati relation to the complex nature of this relation resulting from the combination of a true physical boundary and biases favoring the detection and the measurement of the redshift of GRBs located close to this boundary.

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Section: Discussionmentioning

confidence: 96%

TheE_peak–E_isorelation revisited withFermiGRBs

Heussaff

Atteia

Zolnierowski

2013

A&A

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“…In these models, the prompt emission is produced above the photosphere as suggested by the nonthermal spectrum. However, it has been shown that nonthermal emission can also be produced at the photosphere if a subphotospheric dissipation mechanism is at work Pe'er et al 2005;Ryde et al 2011;Giannios 2012;Beloborodov 2013). After the prompt phase, the afterglow is produced at larger distances and is due to the interaction of the jet with the ambient medium, which creates a strong external shock.…”

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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“…Generally, several types of dissipation processes have been proposed: i) the so-called internal shock (IS) model (Rees & Meszaros 1994;Narayan et al 1992), in which the kinetic energy of a baryon load is dissipated into gamma rays through shocks that take place far away from the Thomson photosphere, at 10 14 -10 16 cm; ii) the photospheric models, in which the dissipation occurs near the photosphere, and where a Planckian spectrum is modified by some heating and Compton scattering (Rees & Mészáros 2005;Pe'er et al 2006; Thompson et al 2007;Derishev et al 1999;Rossi et al 2006;Beloborodov 2010;Titarchuk et al 2012;Giannios 2008;Mészáros & Rees 2011;Giannios 2012); iii) magnetised ejecta Full Tables 1−4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A98 (σ = B 2 /4πΓρc 2 > 1) dissipate their energy at distances similar to those of IS (Lyutikov & Blandford 2003;Zhang & Yan 2011;Beniamini & Granot 2015).…”

Section: Introductionmentioning

confidence: 99%

Individual power density spectra ofSwiftgamma-ray bursts

Guidorzi

Dichiara

Amati

2016

A&A

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Context. Timing analysis can be a powerful tool with which to shed light on the still obscure emission physics and geometry of the prompt emission of gamma-ray bursts (GRBs). Fourier power density spectra (PDS) characterise time series as stochastic processes and can be used to search for coherent pulsations and, more in general, to investigate the dominant variability timescales in astrophysical sources. Because of the limited duration and of the statistical properties involved, modelling the PDS of individual GRBs is challenging, and only average PDS of large samples have been discussed in the literature thus far. Aims. We aim at characterising the individual PDS of GRBs to describe their variability in terms of a stochastic process, to explore their variety, and to carry out for the first time a systematic search for periodic signals and for a link between PDS properties and other GRB observables.Methods. We present a Bayesian procedure that uses a Markov chain Monte Carlo technique and apply it to study the individual PDS of 215 bright long GRBs detected with the Swift Burst Alert Telescope in the 15−150 keV band from January 2005 to May 2015. The PDS are modelled with a power-law either with or without a break. Results. Two classes of GRBs emerge: with or without a unique dominant timescale. A comparison with active galactic nuclei (AGNs) reveals similar distributions of PDS slopes. Unexpectedly, GRBs with subsecond-dominant timescales and duration longer than a few tens of seconds in the source frame appear to be either very rare or altogether absent. Three GRBs are found with possible evidence for a periodic signal at 3.0-3.2σ (Gaussian) significance, corresponding to a multi-trial chance probability of ∼1%. Thus, we found no compelling evidence for periodic signal in GRBs. Conclusions. The analogy between the PDS of GRBs and of AGNs could tentatively indicate similar stochastic processes that rule BH accretion across different BH mass scales and objects. In addition, we find evidence that short dominant timescales and duration are not completely independent of each other, in contrast with commonly accepted paradigms.

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The peak energy of dissipative gamma-ray burst photospheres

Cited by 107 publications

References 49 publications

TheE_peak–E_isorelation revisited withFermiGRBs

TheE_peak–E_isorelation revisited withFermiGRBs

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

Individual power density spectra ofSwiftgamma-ray bursts

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The peak energy of dissipative gamma-ray burst photospheres

Cited by 107 publications

References 49 publications

TheEpeak–Eisorelation revisited withFermiGRBs

TheEpeak–Eisorelation revisited withFermiGRBs

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

Individual power density spectra ofSwiftgamma-ray bursts

Contact Info

Product

Resources

About

TheE_peak–E_isorelation revisited withFermiGRBs

TheE_peak–E_isorelation revisited withFermiGRBs