Observational evidence of dissipative photospheres in gamma-ray bursts

Ryde, F.; Pe’er, Asaf; Nymark, Tanja; Axelsson, M.; Moretti, E.; Lundman, Christoffer; Battelino, Milan; Bissaldi, E.; Chiang, J.; Jackson, M. S.; Larsson, Stefan; Longo, F.; McGlynn, S.; Omodei, N.

doi:10.1111/j.1365-2966.2011.18985.x

Cited by 118 publications

(131 citation statements)

References 79 publications

Supporting

Mentioning

128

Contrasting

Order By: Relevance

“…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

View full text Add to dashboard Cite

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.

show abstract

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

View full text Add to dashboard Cite

show abstract

“…Mészáros & Rees 2000). However, thermal emission need not take the form of a standard Planckian model but may take a more complex form depending on several factors including the relative leptonic and hadronic populations, viewing angles and source region (e.g., Ryde et al 2011). Non-thermal emission can take the form of synchrotron emission from the extreme magnetic fields needed to create a GRB (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…The prompt emission of GRBs has been detected over a wide spectral range from keV to GeV energies and is generally well modelled by one or a combination of the following: a smoothly broken power-law (e.g. Band et al 1993;Abdo et al 2009b), a quasi-thermal component (e.g., Preece 2000; Guiriec et al 2011;Ryde et al 2011;Axelsson et al 2012), an extra nonthermal power-law component extending to high energies (e.g. González et al 2003;Kaneko et al 2008;Abdo et al 2009a) or a cut-off in the MeV regime (e.g., Ackermann et al 2012b).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

Tierney

McBreen

Preece

et al. 2013

A&A

View full text Add to dashboard Cite

Context. A Band function has become the standard spectral function used to describe the prompt emission spectra of gamma-ray bursts (GRBs). However, deviations from this function have previously been observed in GRBs detected by BATSE and in individual GRBs from the Fermi era. Aims. We present a systematic and rigorous search for spectral deviations from a Band function at low energies in a sample of the first two years of high fluence, long bursts detected by the Fermi Gamma-ray Burst Monitor (GBM). The sample contains 45 bursts with a fluence greater than 2 × 10 −5 erg/cm 2 (10−1000 keV).Methods. An extrapolated fit method is used to search for low-energy spectral anomalies, whereby a Band function is fit above a variable low-energy threshold and then the best fit function is extrapolated to lower energy data. Deviations are quantified by examining residuals derived from the extrapolated function and the data and their significance is determined via comprehensive simulations which account for the instrument response. This method was employed for both time-integrated burst spectra and time-resolved bins defined by a signal-to-noise ratio of 25σ and 50σ. Results. Significant deviations are evident in 3 bursts (GRB 081215A, GRB 090424 and GRB 090902B) in the time-integrated sample (∼7%) and 5 bursts (GRB 090323, GRB 090424, GRB 090820, GRB 090902B and GRB 090926A) in the time-resolved sample (∼11%). Conclusions. The advantage of the systematic, blind search analysis is that it can demonstrate the requirement for an additional spectral component without any prior knowledge of the nature of that extra component. Deviations are found in a large fraction of high fluence GRBs; fainter GRBs may not have sufficient statistics for deviations to be found using this method.

show abstract

“…However, the detailed spectral indices can not be read directly from the thermal radiation to fit observations. By including the reasonable ingredients like the bulk motion of the jet, the location of the dissipation and the viewing angles, the photosphere emission can also lead to a variety of non-thermal spectral shapes (Ryde et al 2011). The more popular idea about prompt emission of GRB is the relativistic fireball model (Rees & Mészáros 1992;Mészáros 2002Mészáros , 2006).…”

Section: Introductionmentioning

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.

View full text Add to dashboard Cite

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. ‡

show abstract

Observational evidence of dissipative photospheres in gamma-ray bursts

Cited by 118 publications

References 79 publications

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

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

Anomalies in low-energy gamma-ray burst spectra with theFermiGamma-ray Burst Monitor

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

Contact Info

Product

Resources

About