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 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 Time-resolved spectral analysis of prompt emission from long gamma-ray bursts with GeV emission

2013 ◽  
Vol 14 (1) ◽  
pp. 35-46 ◽  
Author(s):  
Arikkala Raghurama Rao ◽  
Rupal Basak ◽  
Jishnu Bhattacharya ◽  
Sarthak Chandra ◽  
Nikunj Maheshwari ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Time Resolved ◽  
Prompt Emission

scholarly journals Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario

2019 ◽  
Vol 485 (1) ◽  
pp. 474-497 ◽  
Author(s):  
Björn Ahlgren ◽  
Josefin Larsson ◽  
Erik Ahlberg ◽  
Christoffer Lundman ◽  
Felix Ryde ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Full Range ◽  
Lorentz Factor ◽  
Gamma Ray Bursts ◽  
Time Resolved ◽  
Cent Efficiency ◽  
Table Model ◽  
Photospheric Model ◽  
Prompt Emission ◽  
Specific Scenario

ABSTRACT It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.

Constraints on Association of Single‐Pulse Gamma‐Ray Bursts and Supernovae

1999 ◽  
Vol 518 (2) ◽  
pp. 901-908 ◽  
Author(s):  
J. P. Norris ◽  
J. T. Bonnell ◽  
K. Watanabe
Keyword(s):  
Gamma Ray ◽  
Single Pulse ◽  
Gamma Ray Bursts

scholarly journals Interpreting the X-ray afterglows of gamma-ray bursts with radiative losses and millisecond magnetars

2020 ◽  
Vol 499 (4) ◽  
pp. 5986-5992
Author(s):  
Nikhil Sarin ◽  
Paul D Lasky ◽  
Gregory Ashton
Keyword(s):  
Gravitational Wave ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Dipole Radiation ◽  
X Ray ◽  
Radiative Efficiency ◽  
Central Engine ◽  
Radiative Losses ◽  
Wave Emission ◽  
Prompt Emission

ABSTRACT The spin-down energy of millisecond magnetars has been invoked to explain X-ray afterglow observations of a significant fraction of short and long gamma-ray bursts. Here, we extend models previously introduced in the literature, incorporating radiative losses with the spin-down of a magnetar central engine through an arbitrary braking index. Combining this with a model for the tail of the prompt emission, we show that our model can better explain the data than millisecond-magnetar models without radiative losses or those that invoke spin-down solely through vacuum dipole radiation. We find that our model predicts a subset of X-ray flares seen in some gamma-ray bursts. We can further explain the diversity of X-ray plateaus by altering the radiative efficiency and measure the braking index of newly born millisecond magnetars. We measure the braking index of GRB061121 as $n=4.85^{+0.11}_{-0.15}$ suggesting the millisecond-magnetar born in this gamma-ray burst spins down predominantly through gravitational-wave emission.

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.

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 Gamma-Ray Bursts Polarization

2016 ◽  
Vol 12 (S324) ◽  
pp. 54-61
Author(s):  
Diego Götz ◽  
Stefano Covino
Keyword(s):  
Black Hole ◽  
Kinetic Energy ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Central Source ◽  
Poynting Flux ◽  
Relativistic Jet ◽  
Theoretical Status ◽  
Prompt Emission ◽  
Open Point

AbstractWe review the current observational and theoretical status of the polarization measurements of Gamma-ray Bursts at all wavelengths. Gamma-Ray Bursts are thought to be produced by an ultra-relativistic jet, possibly powered by a black hole. One of the most important open point is the composition of the jet: the energy may be carried out from the central source either as kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting flux). The polarization properties are expected to help disentangling main energy carrier. The prompt emission and afterglow polarization are also a powerful diagnostic of the jet geometry.

Prompt emission from gamma-ray bursts

2013 ◽  
pp. 121-150 ◽  
Author(s):  
Tsvi Piran ◽  
Re'em Sari ◽  
Robert Mochkovitch
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Prompt Emission

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.

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