scholarly journals GRB Polarization: A Unique Probe of GRB Physics

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 82
Author(s):  
Ramandeep Gill ◽  
Merlin Kole ◽  
Jonathan Granot
Keyword(s):  
Gamma Ray ◽  
High Sensitivity ◽  
Theoretical Models ◽  
Current Status ◽  
Radiation Mechanisms ◽  
Reverse Shock ◽  
Radiation Mechanism ◽  
Time Resolved ◽  
Polarization Measurements ◽  
Prompt Emission

Over half a century from the discovery of gamma-ray bursts (GRBs), the dominant radiation mechanism responsible for their bright and highly variable prompt emission remains poorly understood. Spectral information alone has proven insufficient for understanding the composition and main energy dissipation mechanism in GRB jets. High-sensitivity polarimetric observations from upcoming instruments in this decade may help answer such key questions in GRB physics. This article reviews the current status of prompt GRB polarization measurements and provides comprehensive predictions from theoretical models. A concise overview of the fundamental questions in prompt GRB physics is provided. Important developments in gamma-ray polarimetry including a critical overview of different past instruments are presented. Theoretical predictions for different radiation mechanisms and jet structures are confronted with time-integrated and time-resolved measurements. The current status and capabilities of upcoming instruments regarding the prompt emission are presented. The very complimentary information that can be obtained from polarimetry of X-ray flares as well as reverse-shock and early to late forward-shock (afterglow) emissions are highlighted. Finally, promising directions for overcoming the inherent difficulties in obtaining statistically significant prompt-GRB polarization measurements are discussed, along with prospects for improvements in the theoretical modeling, which may lead to significant advances in the field.

scholarly journals Gamma Ray Bursts Spectral–Energy correlations: recent results

2010 ◽  
Vol 6 (S275) ◽  
pp. 344-348
Author(s):  
Giancarlo Ghirlanda
Keyword(s):  
Gamma Ray ◽  
Direct Proof ◽  
Spectral Energy ◽  
Selection Effects ◽  
Radiation Mechanism ◽  
Isotropic Energy ◽  
Time Resolved ◽  
Open Issue ◽  
Short Grbs ◽  
Prompt Emission

AbstractThe correlations between the rest frame peak of the νFν spectrum of GRBs (Epeak) and their isotropic energy (Eiso) or luminosity (Liso) could have several implications for the understanding of the GRB prompt emission. These correlations are presently founded on the time–averaged spectral properties of a sample of 95 bursts, with measured redshifts, collected by different instruments in the last 13 years (pre–Fermi). One still open issue is wether these correlations have a physical origin or are due to instrumental selection effects. By studying 10 long and 14 short GRBs detected by Fermi we find that a strong time–resolved correlation between Epeak and the luminosity Liso is present within individual GRBs and that it is consistent with the time–integrated correlation. This result is a direct proof of the existence in both short and long GRBs of a similar physical link between the hardness and the luminosity which is not due to instrumental selection effects. The origin of the Epeak – Liso correlation should be searched in the radiation mechanism of the prompt emission.

scholarly journals Time-resolved GRB polarization with POLAR and GBM

2019 ◽  
Vol 627 ◽  
pp. A105 ◽  
Author(s):  
J. M. Burgess ◽  
M. Kole ◽  
F. Berlato ◽  
J. Greiner ◽  
G. Vianello ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Single Pulse ◽  
Current Data ◽  
Gamma Ray Bursts ◽  
Polarization Angle ◽  
Analysis Pipeline ◽  
Time Resolved ◽  
Polarization Models ◽  
Probabilistic Context ◽  
Prompt Emission

Context. Simultaneousγ-ray measurements ofγ-ray burst spectra and polarization offer a unique way to determine the underlying emission mechanism(s) in these objects, as well as probing the particle acceleration mechanism(s) that lead to the observedγ-ray emission.Aims. We examine the jointly observed data from POLAR andFermi-GBM of GRB 170114A to determine its spectral and polarization properties, and seek to understand the emission processes that generate these observations. We aim to develop an extensible and statistically sound framework for these types of measurements applicable to other instruments.Methods. We leveraged the existing3MLanalysis framework to develop a new analysis pipeline for simultaneously modeling the spectral and polarization data. We derived the proper Poisson likelihood forγ-ray polarization measurements in the presence of background. The developed framework is publicly available for similar measurements with otherγ-ray polarimeters. The data are analyzed within a Bayesian probabilistic context and the spectral data from both instruments are simultaneously modeled with a physical, numerical synchrotron code.Results. The spectral modeling of the data is consistent with a synchrotron photon model as has been found in a majority of similarly analyzed single-pulse gamma-ray bursts. The polarization results reveal a slight trend of growing polarization in time reaching values of ∼30% at the temporal peak of the emission. We also observed that the polarization angle evolves with time throughout the emission. These results suggest a synchrotron origin of the emission but further observations of many GRBs are required to verify these evolutionary trends. Furthermore, we encourage the development of time-resolved polarization models for the prompt emission of gamma-ray bursts as the current models are not predictive enough to enable a full modeling of our current data.

scholarly journals Gamma-Ray Burst Prompt Correlations

2018 ◽  
Vol 2018 ◽  
pp. 1-31 ◽  
Author(s):  
M. G. Dainotti ◽  
R. Del Vecchio ◽  
M. Tarnopolski
Keyword(s):  
Gamma Ray ◽  
Theoretical Models ◽  
Gamma Ray Bursts ◽  
Gamma Ray Burst ◽  
The Past ◽  
Two Parameter ◽  
Prompt Emission

The mechanism responsible for the prompt emission of gamma-ray bursts (GRBs) is still a debated issue. The prompt phase-related GRB correlations can allow discriminating among the most plausible theoretical models explaining this emission. We present an overview of the observational two-parameter correlations, their physical interpretations, and their use as redshift estimators and possibly as cosmological tools. The nowadays challenge is to make GRBs, the farthest stellar-scaled objects observed (up to redshift z=9.4), standard candles through well established and robust correlations. However, GRBs spanning several orders of magnitude in their energetics are far from being standard candles. We describe the advances in the prompt correlation research in the past decades, with particular focus paid to the discoveries in the last 20 years.

scholarly journals Physics of Gamma-Ray Bursts Prompt Emission

2015 ◽  
Vol 2015 ◽  
pp. 1-37 ◽  
Author(s):  
Asaf Pe’er
Keyword(s):  
Gamma Ray ◽  
Magnetic Energy ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Theoretical Research ◽  
Theoretical Interpretation ◽  
Time Resolved ◽  
Physical Conditions ◽  
Major Development ◽  
Prompt Emission

In recent years, our understanding of gamma-ray bursts (GRB) prompt emission has been revolutionized, due to a combination of new instruments, new analysis methods, and novel ideas. In this review, I describe the most recent observational results and current theoretical interpretation. Observationally, a major development is the rise of time resolved spectral analysis. These led to (I) identification of a distinguished high energy component, with GeV photons often seen at a delay and (II) firm evidence for the existence of a photospheric (thermal) component in a large number of bursts. These results triggered many theoretical efforts aimed at understanding the physical conditions in the inner jet regions. I highlight some areas of active theoretical research. These include (I) understanding the role played by magnetic fields in shaping the dynamics of GRB outflow and spectra; (II) understanding the microphysics of kinetic and magnetic energy transfer, namely, accelerating particle to high energies in both shock waves and magnetic reconnection layers; (III) understanding how subphotospheric energy dissipation broadens the “Planck” spectrum; and (IV) geometrical light aberration effects. I highlight some of these efforts and point towards gaps that still exist in our knowledge as well as promising directions for the future.

scholarly journals The POLAR gamma-ray burst polarization catalog

2020 ◽  
Vol 644 ◽  
pp. A124 ◽  
Author(s):  
M. Kole ◽  
N. De Angelis ◽  
F. Berlato ◽  
J. M. Burgess ◽  
N. Gauvin ◽  
...  
Keyword(s):  
Linear Polarization ◽  
Gamma Ray ◽  
Integrated Analysis ◽  
Polarization Angle ◽  
Analysis Tool ◽  
Time Resolved ◽  
Gamma Ray Burst ◽  
Polarization Measurements ◽  
Open Questions ◽  
Polarization Studies

Context. Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%. Aims. We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux. Methods. A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (3ML), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the Fermi Gamma-ray Burst Monitor (Fermi-GBM) and the Neil Gehrels Swift Observatory to jointly model the spectral and polarimetric parameters. Results. The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when time-resolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP.

scholarly journals Statistical Analyses of the Energies of X-Ray Plateaus and Flares in Gamma-Ray Bursts

2022 ◽  
Vol 924 (2) ◽  
pp. 69
Author(s):  
Shuang-Xi Yi ◽  
Mei Du ◽  
Tong Liu
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Physical Origin ◽  
Radiation Mechanisms ◽  
Gaussian Distributions ◽  
Emission Energy ◽  
X Ray ◽  
Central Engine ◽  
Positive Correlations ◽  
Prompt Emission

Abstract Distinct X-ray plateau and flare phases have been observed in the afterglows of gamma-ray bursts (GRBs), and most of them should be related to central engine activities. In this paper, we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares. There are 51 GRBs that overlap in the two selected samples. We analyze the distributions of the proportions of the plateau energy E plateau and the flare energy E flare relative to the isotropic prompt emission energy E γ,iso. The results indicate that they well meet the Gaussian distributions and the medians of the logarithmic ratios are ∼−0.96 and −1.39 in the two cases. Moreover, strong positive correlations between E plateau (or E flare ) and E γ,iso with slopes of ∼0.95 (or ∼0.80) are presented. For the overlapping sample, the slope is ∼0.80. We argue that most of X-ray plateaus and flares might have the same physical origin but appear with different features because of the different circumstances and radiation mechanisms. We also test the applicabilities of two models, i.e., black holes surrounded by fractured hyperaccretion disks and millisecond magnetars, on the origins of X-ray plateaus and flares.

scholarly journals A new fitting function for GRB MeV spectra based on the internal shock synchrotron model

2020 ◽  
Vol 640 ◽  
pp. A91 ◽  
Author(s):  
M. Yassine ◽  
F. Piron ◽  
F. Daigne ◽  
R. Mochkovitch ◽  
F. Longo ◽  
...  
Keyword(s):  
Physical Model ◽  
Gamma Ray ◽  
Spectral Component ◽  
Emission Spectra ◽  
High Energy ◽  
Spectral Energy ◽  
Parametric Function ◽  
Time Resolved ◽  
Internal Shock ◽  
Prompt Emission

Aims. The physical origin of the gamma-ray burst (GRB) prompt emission is still a subject of debate. Internal shock models have been widely explored, owing to their ability to explain most of the high-energy properties of this emission phase. While the Band function or other phenomenological functions are commonly used to fit GRB prompt emission spectra, we propose a new parametric function that is inspired by an internal shock physical model. We use this function as a proxy of the model to compare it easily to GRB observations. Methods. We built a parametric function that represents the spectral form of the synthetic bursts provided by our internal shock synchrotron model (ISSM). We simulated the response of the Fermi instruments to the synthetic bursts and fit the obtained count spectra to validate the ISSM function. Then, we applied this function to a sample of 74 bright GRBs detected by the Fermi GBM, and we computed the width of their spectral energy distributions around their peak energy. For comparison, we also fit the phenomenological functions that are commonly used in the literature. Finally, we performed a time-resolved analysis of the broadband spectrum of GRB 090926A, which was jointly detected by the Fermi GBM and LAT. This spectrum has a complex shape and exhibits a power-law component with an exponential cutoff at high energy, which is compatible with inverse Compton emission attenuated by gamma-ray internal absorption. Results. This work proposes a new parametric function for spectral fitting that is based on a physical model. The ISSM function reproduces 81% of the spectra in the GBM bright GRB sample, versus 59% for the Band function, for the same number of parameters. It gives also relatively good fits to the GRB 090926A spectra. The width of the MeV spectral component that is obtained from the fits of the ISSM function is slightly larger than the width from the Band fits, but it is smaller when observed over a wider energy range. Moreover, all of the 74 analyzed spectra are found to be significantly wider than the synthetic synchrotron spectra. We discuss possible solutions to reconcile the observations with the internal shock synchrotron model, such as an improved modeling of the shock microphysics or more accurate spectral measurements at MeV energies.

scholarly journals GAMMA-RAY BURST PROMPT EMISSION

2014 ◽  
Vol 23 (02) ◽  
pp. 1430002 ◽  
Author(s):  
BING ZHANG
Keyword(s):  
Gamma Ray ◽  
Spectral Component ◽  
Broad Band ◽  
Current Data ◽  
Radiation Mechanism ◽  
Main Band ◽  
Gamma Ray Burst ◽  
Open Questions ◽  
Dominant Band ◽  
Prompt Emission

The origin of gamma-ray burst (GRB) prompt emission, bursts of γ-rays lasting from shorter than one second to thousands of seconds, remains not fully understood after more than 40 years of observations. The uncertainties lie in several open questions in the GRB physics, including jet composition, energy dissipation mechanism, particle acceleration mechanism and radiation mechanism. Recent broad-band observations of prompt emission with Fermi sharpen the debates in these areas, which stimulated intense theoretical investigations invoking very different ideas. I will review these debates, and argue that the current data suggest the following picture: A quasi-thermal spectral component originating from the photosphere of the relativistic ejecta has been detected in some GRBs. Even though in some cases (e.g. GRB 090902B) this component dominates the spectrum, in most GRBs, this component either forms a sub-dominant "shoulder" spectral component in the low energy spectral regime of the more dominant "Band" component, or is not detectable at all. The main "Band" spectral component likely originates from the optically thin region due to synchrotron radiation. The diverse magnetization in the GRB central engine is likely the origin of the observed diverse prompt emission properties among bursts.

Chapter 2 Galactic Gamma-ray Sources

2021 ◽  
Author(s):  
Yang Chen ◽  
Xiao Zhang
Keyword(s):  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Plane ◽  
Theoretical Models ◽  
High Energy ◽  
Maximum Energy ◽  
Radiation Mechanisms ◽  
Galactic Sources ◽  
Very High

Abstract In the gamma-ray sky, the highest fluxes come from Galactic sources: supernova remnants (SNRs), pulsars and pulsar wind nebulae, star forming regions, binaries and micro-quasars, giant molecular clouds, Galactic center, and the large extended area around the Galactic plane. The radiation mechanisms of -ray emission and the physics of the emitting particles, such as the origin, acceleration, and propagation, are of very high astrophysical significance. A variety of theoretical models have been suggested for the relevant physics and emission with energies E_1014 eV are expected to be crucial in testing them. In particular, this energy band is a direct window to test at which maximum energy a particle can be accelerated in the Galactic sources and whether the most probable source candidates such as Galactic center and SNRs are “PeVatrons”. Designed aiming at the very high energy (VHE, >100 GeV) observation, LHAASO will be a very powerful instrument in these astrophysical studies. Over the past decade, great advances have been made in the VHE -ray astronomy. More than 170 VHE -ray sources have been observed, and among them, 42 Galactic sources fall in the LHAASO field-of-view. With a sensitivity of 10 milli-Crab, LHAASO can not only provide accurate spectrum for the known -ray sources, but also search new TeV -ray sources. In the following sub-sections, the observation of all the Galactic sources with LHAASO will be discussed in details.

scholarly journals A New Era of Submillimeter GRB Afterglow Follow-Ups with the Greenland Telescope

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Yuji Urata ◽  
Kuiyun Huang ◽  
Keiichi Asada ◽  
Hiroyuki Hirashita ◽  
Makoto Inoue ◽  
...  
Keyword(s):  
First Generation ◽  
Gamma Ray ◽  
High Redshift ◽  
Greenland Ice Sheet ◽  
Theoretical Models ◽  
Reverse Shock ◽  
New Era ◽  
Forward Shock

Planned rapid submillimeter (submm) gamma-ray-bursts (GRBs) follow-up observations conducted using the Greenland Telescope (GLT) are presented. The GLT is a 12-m submm telescope to be located at the top of the Greenland ice sheet, where the high altitude and dry weather porvide excellent conditions for observations at submm wavelengths. With its combination of wavelength window and rapid responding system, the GLT will explore new insights on GRBs. Summarizing the current achievements of submm GRB follow-ups, we identify the following three scientific goals regarding GRBs: (1) systematic detection of bright submm emissions originating from reverse shock (RS) in the early afterglow phase, (2) characterization of forward shock and RS emissions by capturing their peak flux and frequencies and performing continuous monitoring, and (3) detections of GRBs at a high redshift as a result of the explosion of first generation stars through systematic rapid follow-ups. The light curves and spectra calculated by available theoretical models clearly show that the GLT could play a crucial role in these studies.

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