scholarly journals Study of emission mechanism of GRBs probed by the gamma-ray polarization with IKAROS-GAP

2011 ◽  
Vol 7 (S279) ◽  
pp. 425-426
Author(s):  
Daisuke Yonetoku ◽  
Toshio Murakami ◽  
Tomonori Sakashita ◽  
Yoshiyuki Morihara ◽  
Shuichi Gunji ◽  
...  
Keyword(s):  
Confidence Level ◽  
Gamma Ray ◽  
Polarization Measurement ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Average Polarization ◽  
Angular Scale ◽  
Relativistic Jet ◽  
Two Parameters ◽  
Prompt Emission

AbstractWe report a polarization measurement in prompt γ-ray emission of GRB 100826A with the Gamma-Ray Burst Polarimeter (GAP) aboard the small solar power sail demonstrator IKAROS. We detected a firm change of polarization angle (PA) during the prompt emission with 99.9% (3.5 σ) confidence level, and an average polarization degree (Π) of 27 ± 11% with 99.4% (2.9 σ) confidence level. Here the quoted errors are given at 1 σ confidence level for two parameters of interest. Non-axisymmetric (e.g., patchy) structures of the magnetic fields and/or brightness inside the relativistic jet are therefore required within the observable angular scale of ~ Γ−1. Our observation strongly indicates that the polarization measurement is a powerful tool to constrain the GRB production mechanism, and more theoretical works are needed to discuss the data in more details.

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 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.

scholarly journals The synchrotron polarization in decaying magnetic field in gamma-ray bursts

2020 ◽  
Vol 498 (3) ◽  
pp. 3492-3502
Author(s):  
K F Cheng ◽  
X H Zhao ◽  
J M Bai
Keyword(s):  
Magnetic Field ◽  
Energy Band ◽  
Large Scale ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Polarization Degree ◽  
Band Spectrum ◽  
Polarization Angle ◽  
Radiation Mechanism

ABSTRACT Polarization can serve as a probe of the radiation mechanism and magnetic field (MF) configuration in gamma-ray bursts (GRBs). In the case of constant MF, the synchrotron polarization in the prompt phase of GRBs has been widely studied. In this paper, we consider the case of the decaying MF. We calculate the time-averaged and instantaneous synchrotron polarizations in a pulse for different viewing angles and for the large-scale decaying MF model, which can explain the so-called Band spectrum. We find that the on-axis time-averaged polarization degree (PD) in the energy band of 50–500 keV for the decaying large-scale MF model (∼0.6 for typical parameters) is higher than that in the constant MF model (∼0.5). An interesting result is the instantaneous PD in the off-axis case will experience a turnover, i.e. the PD will evolve from a positive value to a negative one. This suggests the polarization angle (PA) change by an angle of 90°. Such a result is roughly consistent with the discovery of the PA evolution within a pulse in some bursts, such as GRB 170114A and GRB 160821A. Our result implies at least a part of bursts (off-axis bursts) should have the PA evolution in a pulse.

scholarly journals Multiwavelength analysis of brightness variations of 3C 279: probing the relativistic jet structure and its evolution

2019 ◽  
Vol 626 ◽  
pp. A78 ◽  
Author(s):  
Pedro P. B. Beaklini ◽  
Tânia P. Dominici ◽  
Zulema Abraham ◽  
Juliana C. Motter
Keyword(s):  
High Energy ◽  
Light Curves ◽  
Radio Continuum ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Time Lags ◽  
Strong Activity ◽  
Relativistic Jet ◽  
Line Region ◽  
Jet Structure

Aims. We studied the correlation between brightness and polarization variations in 3C 279 at different wavelengths, over time intervals long enough to cover the time lags due to opacity effects. We used these correlations together with VLBI images to constrain the radio and high energy source position. Methods. We made 7 mm radio continuum and R-band polarimetric observations of 3C 279 between 2009 and 2014. The radio observations were performed at the Itapetinga Radio Observatory, while the polarimetric data were obtained at Pico dos Dias Observatory, both in Brazil. We compared our observations with the γ-ray Fermi/LAT and R-band SMARTS light curves. Results. We found a good correlation between 7 mm and R-band light curves, with a delay of 170 ± 30 days in radio, but no correlation with the γ rays. However, a group of several γ-ray flares in April 2011 could be associated with the start of the 7 mm strong activity observed at the end of 2011. We also detected an increase in R-band polarization degree and rotation of the polarization angle simultaneous with these flares. Contemporaneous VLBI images at the same radio frequency show two new strong components close to the core, ejected in directions very different from that of the jet. Conclusions. The good correlation between radio and R-band variability suggests that their origin is synchrotron radiation. The lack of correlation with γ-rays produced by the Inverse Compton process on some occasions could be due to the lack of low energy photons in the jet direction or to absorption of the high energy photons by the broad line region clouds. The variability of the polarization parameters during flares can be easily explained by the combination of the jet polarization parameters and those of newly formed jet components.

scholarly journals The optical polarization of the blazar PKS 2155–304 during an optical flare in 2010

2020 ◽  
Vol 495 (2) ◽  
pp. 2162-2169
Author(s):  
N W Peceur ◽  
A R Taylor ◽  
R C Kraan-Korteweg
Keyword(s):  
Spectral Energy Distribution ◽  
Polarization Degree ◽  
Spectral Energy ◽  
Clear Correlation ◽  
Polarization Angle ◽  
Variable Component ◽  
Optical Polarization ◽  
Relativistic Jet ◽  
Wide Range ◽  
Doppler Factor

ABSTRACT An analysis is presented of the optical polarimetric and multicolour photometric (BVRJ) behaviour of the blazar PKS 2155–304 during an outburst in 2010. This flare develops over roughly 117 d, with a flux doubling time τ ∼ 11 d, which increases from blue to red wavelengths. The polarization angle is initially aligned with the jet axis but rotates by roughly 90° as the flare grows. Two distinct states are evident at low and high fluxes. Below 18 mJy, the polarization angle takes on a wide range of values, without any clear relation to the flux. In contrast, there is a positive correlation between the polarization angle and flux above 18 mJy. The polarization degree does not display a clear correlation with the flux. We find that the photopolarimetric behaviour for the high flux state can be attributed to a variable component with a steady power-law spectral energy distribution and high optical polarization degree (13.3 per cent). These properties are interpreted within the shock-in-jet model, which shows that the observed variability can be explained by a shock that is seen nearly edge-on. Some parameters derived for the relativistic jet within the shock-in-jet model are: B = 0.06 G for the magnetic field, δ = 22.3 for the Doppler factor, and Φ = 2.6° for the viewing angle.

Polarization Study of Gamma-ray Binary Systems

2021 ◽  
Vol 922 (2) ◽  
pp. 260
Author(s):  
Hu Xingxing ◽  
Takata Jumpei
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Binary Systems ◽  
Gamma Ray ◽  
Polarization Degree ◽  
Polarization Angle ◽  
X Ray ◽  
Cone Axis ◽  
Orbital Phase ◽  
The Magnetic Field

Abstract The polarization of X-ray emission is a unique tool used to investigate the magnetic field structure around astrophysical objects. In this paper, we study the linear polarization of X-ray emissions from gamma-ray binary systems based on pulsar scenarios. We discuss synchrotron emission from pulsar wind particles accelerated by a standing shock. We explore three kinds of axisymmetric magnetic field structures: (i) toroidal magnetic fields, (ii) poloidal magnetic fields, and (iii) tangled magnetic fields. Because of the axisymmetric structure, the polarization angle of integrated emission is oriented along or perpendicular to the shock-cone axis projected on the sky and swings around 360° in one orbit. For the toroidal case, the polarization angle is always directed along the shock-cone axis and smoothly changes along the orbital phase. For the poloidal/tangled magnetic field, the direction of the polarization angle depends on the system parameters and orbital phase. In one orbit, the polarization degree for the toroidal case can reach the maximum value of the synchrotron radiation (∼70%), while the maximum polarization degree for poloidal/tangled field cases is several 10%. We apply our model to bright gamma-ray binary LS 5039 and make predictions for future observations. With the expected sensitivity of the Imaging X-ray Polarimetry Explorer, linear polarization can be detected by an observation of several days if the magnetic field is dominated by the toroidal magnetic field. If the magnetic field is dominated by the poloidal/tangled field, significant detection is expected with an observation longer than 10 days.

scholarly journals Simultaneous Radio and Optical Polarimetry of GRB 191221B Afterglow

2021 ◽  
Author(s):  
Yuji Urata ◽  
Kenji Toma ◽  
Stefano Covino ◽  
Klaas Wiersema ◽  
Kuiyun Huang ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Angle Measurement ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Zone Model ◽  
Absorption Frequency ◽  
Multi Wavelength ◽  
Radio Band ◽  
The Universe ◽  
Physical Quantities

Abstract Gamma-ray bursts (GRBs) are the most luminous gamma-ray transients in the universe, and are utilized as probes of early stars, gravitational wave counterparts, and collision less shock physics. For understanding the fundamental physical quantities of GRB jets and their environments as well as their emission mechanism, coordinated multi-wavelength (semi-)simultaneous measurements are crucial as the global communities demonstrated in the past three decades. In spite of studies on polarimetry of GRBs in individual wavelengths that characterized intriguing properties of prompt emission and afterglow, no coordinated multi-wavelength measurements has yet been performed. Here, we report the first coordinated simultaneous polarimetry in the optical and radio bands for the afterglow associated to the typical long GRB 191221B. Our observations successfully caught the radio emission, which is not affected by synchrotron self-absorption, and show that the emission is depolarized in the radio band in comparison with the optical one. This result excludes a simple one-zone model that the polarization degree is nearly constant above the synchrotron self-absorption frequency, and has important implications for plasma-scale turbulent magnetic fields and existence of cool electrons. Our simultaneous polarization angle measurement supports the latter model rather than the former one. The existence of cool electrons increases the estimate of the total jet energy by a factor of > 2 for this typical GRB. Further coordinated multi-wavelength polarimetric campaigns would improve our understanding of the total jet energies and magnetic field configurations in the emission regions of various types of GRBs, which are required to comprehend the mass scales of their progenitor systems and the physics of collisionless shocks.

scholarly journals High efficiency photospheric emission entailed by formation of a collimation shock in gamma-ray bursts

2019 ◽  
Vol 488 (1) ◽  
pp. 1416-1426 ◽  
Author(s):  
Ore Gottlieb ◽  
Amir Levinson ◽  
Ehud Nakar
Keyword(s):  
High Efficiency ◽  
Gamma Ray ◽  
Surrounding Medium ◽  
Emission Spectra ◽  
Lorentz Factor ◽  
Gamma Ray Bursts ◽  
Opening Angle ◽  
Radiative Efficiency ◽  
Relativistic Jet ◽  
Prompt Emission

ABSTRACT The primary dissipation mechanism in jets of gamma-ray bursts (GRBs), and the high efficiency of the prompt emission are long-standing issues. One possibility is strong collimation of a weakly magnetized relativistic jet by the surrounding medium, which can considerably enhance the efficiency of the photospheric emission. We derive a simple analytic criterion for the radiative efficiency of a collimated jet showing that it depends most strongly on the baryon loading. We confirm this analytic result by 3D numerical simulations, and further find that mixing of jet and cocoon material at the collimation throat leads to a substantial stratification of the outflow as well as sporadic loading, even if the injected jet is uniform and continuous. One consequence of this mixing is a strong angular dependence of the radiative efficiency. Another is large differences in the Lorentz factor of different fluid elements that lead to formation of internal shocks. Our analysis indicates that in both long and short GRBs a prominent photospheric component cannot be avoided when observed within an angle of a few degrees to the axis, unless the asymptotic Lorentz factor is limited by baryon loading at the jet base to Γ∞ < 100 (with a weak dependence on outflow power). Photon generation by newly created pairs behind the collimation shock regulates the observed temperature at $\sim 50~\theta _0^{-1}$ keV, where θ0 is the initial jet opening angle, in remarkable agreement with the observed peak energies of prompt emission spectra. Further consequences for the properties of the prompt emission are discussed at the end.

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 Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies

2018 ◽  
Vol 614 ◽  
pp. L1 ◽  
Author(s):  
A. Lähteenmäki ◽  
E. Järvelä ◽  
V. Ramakrishnan ◽  
M. Tornikoski ◽  
J. Tammi ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Spiral Galaxies ◽  
Narrow Line ◽  
Radio Jets ◽  
Relativistic Jet ◽  
Gamma Ray Emission

We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that were previously classified as radio silent and two that were classified as radio quiet. These detections reveal the presumption that NLS1 galaxies labelled radio quiet or radio silent and hosted by spiral galaxies are unable to launch jets to be incorrect. The detections are a plausible indicator of the presence of a powerful, most likely relativistic jet because this intensity of emission at 37 GHz cannot be explained by, for example, radiation from supernova remnants. Additionally, one of the detected NLS1 galaxies is a newly discovered source of gamma rays and three others are candidates for future detections.

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