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Although the observed spectra for gamma-ray burst (GRB) prompt emission is well constrained, the underlying radiation mechanism is still not very well understood. We explore photospheric emission in GRB jets by modelling the Comptonization…

High Energy Astrophysical Phenomena · Physics 2021-10-29 Mukul Bhattacharya , Pawan Kumar

Gonz\'alez et al. (2003) have reported the discovery of an anomalous radiation component from ~ 1 -- 200 MeV in GRB 941017. This component varies independently of and contains >~ 3 times the energy found in the prompt ~ 50 keV -- 1 MeV…

Astrophysics · Physics 2009-11-10 C. D. Dermer , A. Atoyan

The initial Lorentz factor ($\Gamma_{\text{0}}$) plays a crucial role in uncovering the physical characteristics of gamma-ray bursts (GRBs). Previous studies have indicated that the ambient medium density index $k$ for GRBs falls in the…

High Energy Astrophysical Phenomena · Physics 2025-04-17 Sheng-Jin Sun , Shuang-Xi Yi , Yuan-Chuan Zou , Yu-Peng Yang , Ying Qin , Qing-Wen Tang , Fa-Yin Wang

The radiative process responsible for gamma-Ray Burst (GRB) prompt emission has not been identified yet. If dominated by fast-cooling synchrotron radiation, the part of the spectrum immediately below the $\nu F_\nu$ peak energy should…

High Energy Astrophysical Phenomena · Physics 2017-09-20 Gor Oganesyan , Lara Nava , Giancarlo Ghirlanda , Annalisa Celotti

The emission mechanism during the prompt phase in gamma-ray bursts (GRBs) can be investigated through correlations between spectral properties. Here, we revisit the correlation relating the instantaneous flux, $F$, and the photon index…

High Energy Astrophysical Phenomena · Physics 2019-01-16 Felix Ryde , Hoi-Fung Yu , Hüsne Dereli-Bégué , Christoffer Lundman , Asaf Pe'er , Liang Li

Discerning the radiative dissipation mechanism for prompt emission in Gamma-Ray Bursts (GRBs) requires detailed spectroscopic modeling that straddles the $\nu F_{\nu}$ peak in the 100 keV - 1 MeV range. Historically, empirical fits such as…

The temporal and spatial coincidence between FRB 20200428 and hard peaks of the X-ray burst from SGR 1935+2154 suggests their potential association. We attributed them to the plasma synchrotron maser emission and synchrotron radiation of…

High Energy Astrophysical Phenomena · Physics 2025-08-28 Xiao Li , En-Wei Liang

The emission region of $\rm \gamma$-ray bursts (GRBs) is poorly constrained. The uncertainty on the size of the dissipation site spans over 4 orders of magnitude ($\rm 10^{12}-10^{17}$ cm) depending on the unknown energy composition of the…

We test the models of synchrotron emission presented in Part I of this series (Lloyd & Petrosian, these proceedings) against the distributions and evolution of GRB spectral parameters (particularly the low energy index, $\alpha$). With…

Astrophysics · Physics 2018-11-06 Nicole M. Lloyd-Ronning , Vahe' Petrosian , Robert D. Preece

There is no consensus on the emission mechanism of $\gamma$-ray bursts (GRBs). A synchrotron model can produce $\gamma$-ray spectra with the empirical Band function form, from a piece-wise two-power-law electron energy distribution (2EPLS).…

High Energy Astrophysical Phenomena · Physics 2019-09-06 Bruce Grossan , Pawan Kumar , George F. Smoot

We analyze the >100MeV data for 3 GRBs detected by Fermi (GRBs 080916C, 090510, 090902B) and find that these photons were generated via synchrotron emission in the external forward shock. We arrive at this conclusion by four different…

High Energy Astrophysical Phenomena · Physics 2010-12-13 Pawan Kumar , Rodolfo Barniol Duran

We aim to obtain a measure of the curvature of time-resolved spectra that can be compared directly to theory. This tests the ability of models such as synchrotron emission to explain the peaks or breaks of GBM prompt emission spectra. We…

GRB 160625B is an extremely-bright outburst with well-monitored afterglow emission. The geometry-corrected energy is high up to $\sim 5.2\times10^{52}$ erg or even $\sim 8\times 10^{52}$ erg, rendering it the most energetic GRB prompt…

High Energy Astrophysical Phenomena · Physics 2017-02-15 Yuan-Zhu Wang , Hao Wang , Shuai Zhang , Yun-Feng Liang , Zhi-Ping Jin , Hao-Ning He , Neng-Hui Liao , Yi-Zhong Fan , Da-Ming Wei

For over two decades, gamma-ray burst (GRB) prompt emission spectra were modelled with smoothly-broken power laws (Band function), and a positive and tight correlation between the spectral rest-frame peak energy $E_p$ and the total…

High Energy Astrophysical Phenomena · Physics 2024-09-16 Alessio Mei , Gor Oganesyan , Samanta Macera

When an emitting spherical shell with a constant Lorentz factor turns off emission abruptly at some radius, its high-latitude emission would obey the relation of $\hat{\alpha}$ (the temporal index) = $2 + \hat{\beta}$ (the spectral index).…

High Energy Astrophysical Phenomena · Physics 2018-01-16 Jin-Jun Geng , Yong-Feng Huang , Zi-Gao Dai

Despite more than fifty years of gamma-ray burst (GRB) observations, several questions regarding the origin of the prompt emission, particularly at high energies, remain unresolved. We present a comprehensive analysis of 35 GRBs observed by…

High Energy Astrophysical Phenomena · Physics 2025-01-22 Samanta Macera , Biswajit Banerjee , Alessio Mei , Pawan Tiwari , Gor Oganesyan , Marica Branchesi

Synchrotron emission of relativistic particles in magnetic fields is a process of paramount importance in astrophysics. Although known for over thirty years, there are still aspects of this radiative process that have received little…

Astrophysics · Physics 2009-11-07 Roberto Aloisio , Pasquale Blasi

An equation is derived to calculate the dynamics of relativistic magnetized plasma which decelerates by sweeping up matter from the ISM. Reduction to the non-radiative and radiative regimes is demonstrated. The evolving electron momentum…

Astrophysics · Physics 2016-08-30 Charles D. Dermer , James Chiang

The prompt emission mechanism of gamma-ray bursts (GRBs) is still unclear, and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes. We performed a detailed time-resolved spectral…

High Energy Astrophysical Phenomena · Physics 2024-01-29 Wan-Kai Wang , Wei Xie , Zhi-Fu Gao , Shuo Xiao , Ai-Jun Dong , Bin Zhang , Qi-Jun Zhi

We present an analysis of the Internal Shock Model of GRBs, where gamma-rays are produced by internal shocks within a relativistic wind. We show that observed GRB characteristics impose stringent constraints on wind and source parameters.…

Astrophysics · Physics 2009-10-31 D. Guetta , M. Spada , E. Waxman