scholarly journals Gamma-Ray Burst Spectral Breaks and Source Beaming

1994 ◽  
Vol 142 ◽  
pp. 899-903
Author(s):  
Matthew G. Baring
Keyword(s):  
Lower Bound ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Additional Constraint ◽  
Gamma Ray Bursts ◽  
Radiation Mechanisms ◽  
Two Photon ◽  
Source Spectra ◽  
The Relationship

AbstractThe principal discovery of the ComptonGamma-Ray Observatory(GRO) concerning gamma-ray bursts is that these sources are isotropic but with a comparative deficiency of fainter sources, suggesting that they are probably cosmological in origin. If they are at such large distances from Earth then they are extremely luminous and compact. A consequence of this is that two-photon pair production attenuation of the gamma-ray continuum cannot be avoided unless the source radiation is substantially beamed. Most sources do not display gamma-ray turnovers although a few GRB detected byGROexhibit distinct spectral breaks in the MeV range. A derivation of the relationship defining of the degree of beaming in burst sources with spectral breaks due toγ-γattenuation, as a function of source spectral index and break energy, is presented. It is found that sources at distances of ~1 Gpc must typically be beamed with bulk Lorentz factors of around 103-104, indicating powerful bulk acceleration in bursts, although these Lorentz factors are reduced markedly for steep source spectra. Since the source spectra are not strongly Comptonized, such beaming will blueshift the γ-γ attenuation breaks to energies much higher than 1 MeV; an absolute lower bound to the source bulk Lorentz factor is determined from this additional constraint. This blueshifting suggests that those sources with MeV breaks may not be cosmological, or that their breaks are produced by a mechanism that dominates γ-γ attenuation at these energies.Subject headings:gamma-rays: bursts — radiation mechanisms: nonthermal

scholarly journals Acceleration Processes for Gamma-Ray Bursts

1994 ◽  
Vol 142 ◽  
pp. 869-876 ◽  
Author(s):  
Igor G. Mitrofanov
Keyword(s):  
Particle Acceleration ◽  
Electric Field ◽  
Neutron Stars ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Initial Energy ◽  
Gamma Ray Bursts ◽  
Acceleration Of Particles ◽  
Radiation Mechanisms ◽  
Radiative Pressure

AbstractIs it shown that for those astronomical models of cosmic gamma-ray bursts (GRBs) which are associated with galactic neutron stars (NSs), the initial energy of the outburst could be converted to gamma-rays through processes of particle acceleration. The main emission mechanisms are considered for two basic alternatives, when particles are accelerated either by radiative pressure or by an electric field.Subject headings: acceleration of particles — gamma rays: bursts — radiation mechanisms: nonthermal

scholarly journals Optical Afterglows as Probes for the Central Engine and Fireball of Gamma-Ray Bursts

2012 ◽  
Vol 8 (S290) ◽  
pp. 263-264
Author(s):  
Liang Li ◽  
En-Wei Liang ◽  
He Gao ◽  
Bing Zhang
Keyword(s):  
Statistical Analysis ◽  
Gamma Rays ◽  
Density Profile ◽  
Gamma Ray ◽  
Ambient Medium ◽  
Gamma Ray Bursts ◽  
Prompt Gamma ◽  
Medium Density ◽  
Central Engine ◽  
Prompt Emission

AbstractWell-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are compiled from literature. We identify possible emission components based on our empirical fits and present statistical analysis for these components. We find that the flares are related to prompt emission, suggesting that they could have the same origin in different episodes. The shallow decay segment is not correlated with prompt gamma-rays. It likely signals a long-lasting injected wind from GRB central engines. Early after onset peak is closely related with prompt emission. The ambient medium density profile is likely n ∝ r−1. No correlation between the late re-brightening bump and prompt gamma-rays or the onset bump is found. They may be from another jet component.

GAMMA-RAY BURSTS AS VHE-UHE SOURCES

2008 ◽  
Vol 17 (09) ◽  
pp. 1319-1332
Author(s):  
PETER MÉSZÁROS
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Lower Energy ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Model Parameters ◽  
Fundamental Interaction ◽  
Acceleration Mechanism ◽  
Inverse Compton ◽  
Tev Gamma Rays

Gamma-ray bursts are capable of accelerating cosmic rays up to GZK energies Ep ~ 1020 eV, which can lead to a flux at Earth comparable to that observed by large EAS arrays such as Auger. The semi-relativistic outflows inferred in GRB-related hypernovae are also likely sources of somewhat lower energy cosmic rays. Leptonic processes, such as synchrotron and inverse Compton, as well as hadronic processes, can lead to GeV-TeV gamma-rays measurable by GLAST, AGILE, or ACTs, providing useful probes of the burst physics and model parameters. Photo-meson interactions also produce neutrinos at energies ranging from sub-TeV to EeV, which will be probed with forthcoming experiments such as IceCube, ANITA and KM3NeT. This would provide information about the fundamental interaction physics, the acceleration mechanism, the nature of the sources and their environment.

scholarly journals e±-rich GRB Fireball and Infrared Flashes

2003 ◽  
Vol 214 ◽  
pp. 331-332
Author(s):  
Zhuo Li ◽  
Z. G. Dai ◽  
T. Lu
Keyword(s):  
Gamma Ray ◽  
Lorentz Factor ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Rapid Response ◽  
Model Parameters ◽  
Wide Range ◽  
Very High Energy ◽  
Very High

Gamma-ray bursts (GRBs) are believed to originate from ultra-relativistic fireballs, with initial Lorentz factor η ∼ 102 − 103. However very high energy photons may still suffer from γγ interaction. We show here that in a wide range of model parameters, the resulting pairs may dominate electrons associated with the fireball baryons. This may provide an explanation for the rarity of prompt optical detections. A rapid response to the GRB trigger at the IR band would detect such a strong flash.

scholarly journals INTERNAL ENERGY DISSIPATION OF GAMMA-RAY BURSTS OBSERVED WITHSWIFT: PRECURSORS, PROMPT GAMMA-RAYS, EXTENDED EMISSION, AND LATE X-RAY FLARES

2014 ◽  
Vol 789 (2) ◽  
pp. 145 ◽  
Author(s):  
You-Dong Hu ◽  
En-Wei Liang ◽  
Shao-Qiang Xi ◽  
Fang-Kun Peng ◽  
Rui-Jing Lu ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Internal Energy ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Prompt Gamma ◽  
X Ray ◽  
Extended Emission

scholarly journals Gamma-Ray Burst Observations with BATSE

1998 ◽  
Vol 188 ◽  
pp. 159-162
Author(s):  
Gerald J. Fishman
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Gamma Ray Burst ◽  
New Era ◽  
X Ray ◽  
Time Profiles ◽  
Random Direction ◽  
Wide Range ◽  
New Phenomena

Gamma-ray bursts (GRBs) will be recorded as one of the outstanding new phenomena discovered in astronomy this century. About once per day, a burst of gamma rays appears from a random direction on the sky. Often, the burst outshines all other sources of gamma-rays in the sky, combined. This paper reviews some of the key observed phenomenon of bursts in the hard x-ray/gamma-ray region, as observed with the BATSE experiment on the Compton Gamma Ray Observatory. The observed time profiles, spectral properties and durations of gamma-ray bursts cover a wide range. Recent breakthroughs in the observation of gamma-ray burst counterparts and afterglows in other wavelength regions have marked the beginning of a new era in gamma-ray burst research. Those observations are described in following papers in these proceedings.

THE INTERPLAY OF PROMPT AND AFTERGLOW EMISSION IN GRB 060418

2008 ◽  
Vol 17 (09) ◽  
pp. 1343-1349 ◽  
Author(s):  
S. D. VERGANI ◽  
D. MALESANI ◽  
E. MOLINARI
Keyword(s):  
Gamma Rays ◽  
Spectral Properties ◽  
Gamma Ray ◽  
Early Time ◽  
Lorentz Factor ◽  
X Ray ◽  
Central Engine ◽  
Low Energies ◽  
Prompt Emission

We present observations of the early afterglow emission of GRB 060418. Thanks to the simultaneous coverage at optical, X-ray and gamma-ray wavelengths, we can detect and separate the external shock emission (visible in the optical and late X-ray data) and the central engine activity (early X and gamma rays). The two components are clearly distinguished based on temporal and spectral properties. The detection of the afterglow onset (in the optical) allows the determination of the fundamental fireball properties, namely its bulk Lorentz factor and total energy. The early time X-ray flare closely resembles the prompt emission gamma-ray pulses in its temporal profile, being wider at low energies and showing lags between the hard and soft bands. This provides a strong suggestion that X-ray flares are a continuation of the prompt emission.

scholarly journals Gamma-Ray Burst Theory: Back to the Drawing Board

1994 ◽  
Vol 142 ◽  
pp. 863-868
Author(s):  
Alice K. Harding
Keyword(s):  
Particle Acceleration ◽  
Neutron Stars ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Acceleration Of Particles ◽  
Gamma Ray Burst ◽  
History Of ◽  
Drawing Board ◽  
The Impact

AbstractGamma-ray bursts have always been intriguing sources to study in terms of particle acceleration, but not since their discovery two decades ago has the theory of these objects been in such turmoil. Prior to the launch of Compton Gamma-Ray Observatory and observations by BATSE, there was strong evidence pointing to magnetized Galactic neutron stars as the sources of gamma-ray bursts. However, since BATSE the observational picture has changed dramatically, requiring much more distant and possibly cosmological sources. I review the history of gamma-ray burst theory from the era of growing consensus for nearby neutron stars to the recent explosion of halo and cosmological models and the impact of the present confusion on the particle acceleration problem.Subject headings: acceleration of particles — gamma rays: bursts

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