scholarly journals Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

2019 ◽  
Vol 625 ◽  
pp. A60 ◽  
Author(s):  
M. E. Ravasio ◽  
G. Ghirlanda ◽  
L. Nava ◽  
G. Ghisellini
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Emission Region ◽  
Peak Energy ◽  
Standard Scenario ◽  
Low Magnetic Field ◽  
Short Grbs ◽  
Prompt Emission ◽  
Good Agreement

The long-lasting tension between the observed spectra of gamma-ray bursts (GRBs) and the predicted synchrotron emission spectrum might be solved if electrons do not completely cool. Evidence of incomplete cooling was recently found in Swift GRBs with prompt observations down to 0.1 keV, and in one bright Fermi burst, GRB 160625B. Here we systematically search for evidence of incomplete cooling in the spectra of the ten brightest short and long GRBs observed by Fermi. We find that in eight out of ten long GRBs there is compelling evidence of a low-energy break (below the peak energy) and good agreement with the photon indices of the synchrotron spectrum (respectively −2/3 and −3/2 below the break and between the break and the peak energy). Interestingly, none of the ten short GRBs analysed shows a break, but the low-energy spectral slope is consistent with −2/3. In a standard scenario, these results imply a very low magnetic field in the emission region (B′∼10 G in the comoving frame), at odd with expectations.

scholarly journals The properties of prompt emission in short gamma-ray bursts with extended emission observed by Fermi/GBM

2020 ◽  
Vol 492 (3) ◽  
pp. 3622-3630
Author(s):  
Lin Lan ◽  
Rui-Jingi Lu ◽  
Hou-Jun Lü ◽  
Jun Shen ◽  
Jared Rice ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Large Scatter ◽  
Intrinsic Properties ◽  
Temporal Properties ◽  
Peak Energy ◽  
Peak Flux ◽  
Short Grbs ◽  
Prompt Emission ◽  
Extended Emission

ABSTRACT Short gamma-ray bursts (GRB) with extended emission (EE) that are composed of an initial short hard spike followed by a long-lasting EE are thought to comprise a sucategory of short GRBs. The narrow energy band available during the Swift era, combined with a lack of spectral information, prevented the discovery of the intrinsic properties of these events. In this paper, we perform a systematic search of short GRBs with EE using all available Fermi/GBM data. The search identified 26 GBM-detected short GRBs with EE that are similar to GRB 060614 observed by Swift/BAT. We focus on investigating the spectral and temporal properties of both the hard spike and the EE component of all 26 GRBs, and explore differences and possible correlations between them. We find that while the peak energy (Ep) of the hard spikes is slightly harder than that of the EE, their fluences are comparable. The harder Ep seems to correspond to a larger fluence and peak flux, with a large scatter for both the hard spike and the EE component. Moreover, the Ep of both the hard spike and the EE are compared with other short GRBs. Finally, we also compare the properties of GRB 170817A with those of short GRBs with EE and find no significant statistical differences between them. We find that GRB 170817A has the lowest Ep, probably because it is off-axis.

scholarly journals Limits on quantum gravity effects from Swift short gamma-ray bursts

2017 ◽  
Vol 607 ◽  
pp. A121 ◽  
Author(s):  
M. G. Bernardini ◽  
G. Ghirlanda ◽  
S. Campana ◽  
P. D’Avanzo ◽  
J.-L. Atteia ◽  
...  
Keyword(s):  
Quantum Gravity ◽  
Gamma Ray ◽  
Lorentz Invariance ◽  
Spectral Energy Distribution ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Energy Separation ◽  
Spectral Energy ◽  
Spectral Evolution ◽  
Short Grbs

The delay in arrival times between high and low energy photons from cosmic sources can be used to test the violation of the Lorentz invariance (LIV), predicted by some quantum gravity theories, and to constrain its characteristic energy scale EQG that is of the order of the Planck energy. Gamma-ray bursts (GRBs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on EQG are proportional to the photon energy separation and the distance of the source. However, the LIV tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long GRBs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). Short GRBs have null intrinsic spectral lags and are therefore an ideal tool to measure any LIV effect. We considered a sample of 15 short GRBs with known redshift observed by Swift and we estimate a limit on EQG ≳ 1.5 × 1016 GeV. Our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long GRBs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense.

Gamma-ray bursts prompt emission spectrum: an analysis of a photosphere model

2007 ◽  
Vol 365 (1854) ◽  
pp. 1171-1175 ◽  
Author(s):  
Asaf Pe'er ◽  
Peter Mészáros ◽  
Martin J Rees
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Dissipation Process ◽  
Internal Shock ◽  
Peak Energy ◽  
Wide Range ◽  
Low Energies ◽  
Steep Slopes ◽  
The Magnetic Field ◽  
Prompt Emission

A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy densities in the thermal and leptonic components, the dominant emission mechanism is Compton scattering. This leads to a nearly flat energy spectrum ( νF ν ∝ ν 0 ) above the thermal peak at approximately 10–100 keV and below 10–100 MeV, for a wide range of optical depths 0.03≲ τ ≲100, regardless of the details of the dissipation mechanism or the strength of the magnetic field. For higher values of the optical depth, a Wien peak is formed at 100 keV to 1 MeV. In particular, these results are applicable to the internal shock model of GRBs, as well as to slow dissipation models, e.g. as might be expected from reconnection, if the dissipation occurs at a sub-photospheric radii. We conclude that dissipation near the thermal photosphere can naturally explain (i) clustering of the peak energy at sub-MeV energies at early times, (ii) steep slopes observed at low energies, and (iii) a flat spectrum above 10 keV at late times. Our model thus provides an alternative scenario to the optically thin synchrotron–synchrotron self-Compton model.

scholarly journals HIGH ENERGETIC GAMMA RAY BURSTS AND THEIR SPECTRAL PROPERTIES WITHIN THE FIRESHELL MODEL

2012 ◽  
Vol 12 ◽  
pp. 385-389
Author(s):  
B. PATRICELLI ◽  
M.G. BERNARDINI ◽  
C.L. BIANCO ◽  
L. CAITO ◽  
G. DE BARROS ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Observational Data ◽  
Spectral Properties ◽  
Gamma Ray ◽  
Emission Spectra ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Isotropic Energy ◽  
Thermal Spectrum ◽  
Prompt Emission

The analysis of various Gamma Ray Bursts (GRBs) characterized by an isotropic energy Eiso ≲ 1053 ergs within the fireshell model has shown how that the observed N(E) spectrum of their prompt emission can be reproduced in a satisfactory way by assuming a thermal spectrum in the comoving frame of the fireshell. Nevertheless, from the study of higher energetic bursts (Eiso ≳ 1054 ergs ) such as, for example, GRB 080319B, some discrepancies between the numerical simulations and the observational data have been observed. We investigate a different spectrum of photons in the comoving frame of the fireshell in order to better reproduce the spectral properties of GRB prompt emission within the fireshell model. We introduce a phenomenologically modified comoving thermal spectrum: a spectrum characterized by a different asymptotic low energy slope with respect to the thermal one. We test this spectrum by comparing the numerical simulations with the observed prompt emission spectra of various GRBs; we present, as an exaple, the case of GRB 080319B.

STOCHASTIC WAKEFIELD PLASMA ACCELERATION IN GAMMA-RAY BURSTS

2007 ◽  
Vol 21 (03n04) ◽  
pp. 627-632
Author(s):  
G. BARBIELLINI ◽  
F. LONGO ◽  
N. OMODEI ◽  
D. GIULIETTI ◽  
A. CELOTTI ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Plasma Acceleration ◽  
Gamma Ray Burst ◽  
Initial Burst ◽  
X Ray ◽  
Wake Field ◽  
Prompt Emission

Gamma-Ray Burst (GRB) prompt emission can, for specific conditions, be so powerful and short-pulsed to strongly influence any surrounding plasma. In this paper, we briefly discuss the possibility that a very intense initial burst of radiation produced by GRBs satisfy the intensity and temporal conditions to cause stochastic wake-field particle acceleration in a surrounding plasma of moderate density. We consider a simple but realistic GRB model for which particle wake-field acceleration can first be excited by a very strong low-energy precursor, and then be effective in producing the observed prompt X-ray and gamma-ray GRB emission.

scholarly journals On the Reclassification of Short GRBs

2012 ◽  
Vol 8 (S290) ◽  
pp. 361-363
Author(s):  
Zhibin Zhang ◽  
Yongfeng Huang ◽  
Hongchao Liu
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Radiation Mechanism ◽  
Duration Time ◽  
Central Engine ◽  
Peak Energy ◽  
Thermal Origin ◽  
Γ Ray ◽  
Short Grbs ◽  
Extended Emission

AbstractBy collecting 17 short gamma-ray bursts with necessary data, we find a correlation of Lp ∝ Ep,i1.7, which is very consistent with that derived from a greatly expanded sample of 148 Swift long gamma-ray bursts. It is argued that the radiation mechanism of both long and short gamma-ray bursts should be similar, i.e., of quasi-thermal origin caused by the photosphere and the dissipation occurring very near the central engine. In addition, we suggest that the Ep,i-Lp relation can be used to identified a burst among normal short bursts, short bursts with extended emission and long bursts with short-hard properties. We also find the ratio of peak energy to fluence in the prompt γ-ray band is a prospective discriminator, similar to the traditional duration time.

scholarly journals Investigation of Similarity in the Spectra between Short- and Long-Duration Gamma-ray Bursts

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 106
Author(s):  
Takanori Sakamoto ◽  
Yuuki Yoshida ◽  
Motoko Serino
Keyword(s):  
Spectral Properties ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Synchrotron Emission ◽  
Energy Photon ◽  
Long Duration ◽  
Photon Index ◽  
Monitor Data ◽  
Short Grbs ◽  
Prompt Emission

We investigated the spectral properties of the prompt emission for short- and long-duration gamma-ray bursts (GRBs) using the Fermi Gamma-ray Burst Monitor data. In particular, we focused on comparing the spectral properties of short GRBs and the initial 2 s of long GRBs, motivated by the previous study of Ghirlanda et al. (2009). We confirmed the similarity in the low energy photon index α between short GRBs and the initial 2 s of long GRBs. Since about a quarter of our spectra of both short GRBs and the initial 2 s of long GRBs show α to be shallower than - 2 / 3 , it is difficult to understand in the context standard synchrotron emission.

scholarly journals Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts

2019 ◽  
Vol 628 ◽  
pp. A59 ◽  
Author(s):  
G. Oganesyan ◽  
L. Nava ◽  
G. Ghirlanda ◽  
A. Melandri ◽  
A. Celotti
Keyword(s):  
Synchrotron Radiation ◽  
Parameter Space ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Spectral Shape ◽  
Low Energy ◽  
Optical Observations ◽  
X Rays ◽  
Thermal Component ◽  
Prompt Emission

Information on the spectral shape of prompt emission in gamma-ray bursts (GRB) is mostly available only at energies ≳10 keV, where the main instruments for GRB detection are sensitive. The origin of this emission is still very uncertain because of the apparent inconsistency with synchrotron radiation, which is the most obvious candidate, and the resulting need for considering less straightforward scenarios. The inclusion of data down to soft X-rays (∼0.5 keV), which are available only in a small fraction of GRBs, has firmly established the common presence of a spectral break in the low-energy part of prompt spectra, and even more importantly, the consistency of the overall spectral shape with synchrotron radiation in the moderately fast-cooling regime, the low-energy break being identified with the cooling frequency. In this work we further extend the range of investigation down to the optical band. In particular, we test the synchrotron interpretation by directly fitting a theoretically derived synchrotron spectrum and making use of optical to gamma-ray data. Secondly, we test an alternative model that considers the presence of a black-body component at ∼keV energies, in addition to a non-thermal component that is responsible for the emission at the spectral peak (100 keV–1 MeV). We find that synchrotron radiation provides a good description of the broadband data, while models composed of a thermal and a non-thermal component require the introduction of a low-energy break in the non-thermal component in order to be consistent with optical observations. Motivated by the good quality of the synchrotron fits, we explore the physical parameter space of the emitting region. In a basic prompt emission scenario we find quite contrived solutions for the magnetic field strength (5 G < B′< 40 G) and for the location of the region where the radiation is produced (Rγ >  1016 cm). We discuss which assumptions of the basic model would need to be relaxed in order to achieve a more natural parameter space.

scholarly journals Prevalence of Extra Power-Law Spectral Components in Short Gamma-Ray Bursts

2021 ◽  
Vol 922 (2) ◽  
pp. 255
Author(s):  
Qing-Wen Tang ◽  
Kai Wang ◽  
Liang Li ◽  
Ruo-Yu Liu
Keyword(s):  
Power Law ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Spectral Feature ◽  
Gamma Ray Bursts ◽  
Spectral Energy ◽  
Spectral Components ◽  
Short Grbs ◽  
Prompt Emission ◽  
Emission Phase

Abstract A prompt extra power-law (PL) spectral component that usually dominates the spectral energy distribution below tens of keV or above ∼10 MeV has been discovered in some bright gamma-ray bursts (GRBs). However, its origin is still unclear. In this paper, we present a systematic analysis of 13 Fermi short GRBs, as of 2020 August, with contemporaneous keV–MeV and GeV detections during the prompt emission phase. We find that the extra PL component is a ubiquitous spectral feature for short GRBs, showing up in all 13 analyzed GRBs. The PL indices are mostly harder than −2.0, which may be well reproduced by considering the electromagnetic cascade induced by ultrarelativistic protons or electrons accelerated in the prompt emission phase. The average flux of these extra PL components positively correlates with that of the main spectral components, which implies they may share the same physical origin.

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