scholarly journals Is spectral width a reliable measure of GRB emission physics?

2019 ◽  
Vol 629 ◽  
pp. A69 ◽  
Author(s):  
J. M. Burgess
Keyword(s):  
Power Law ◽  
Gamma Ray ◽  
Spectral Width ◽  
Empirical Models ◽  
Physical Parameters ◽  
Synchrotron Emission ◽  
Reliable Measure ◽  
Spectral Fitting ◽  
Peak Flux ◽  
Rule Out

The spectral width and sharpness of unfolded, observed gamma-ray burst (GRB) spectra have been presented as a new tool to infer physical properties about GRB emission via spectral fitting of empirical models. Following the tradition of the “line-of-death”, the spectral width has been used to rule out synchrotron emission in a majority of GRBs. This claim is investigated via reexamination of previously reported width measures. Then, a sample of peak-flux GRB spectra are fit with an idealized, physical synchrotron model. It is found that many spectra can be adequately fit by this model even when the width measures would reject it. Thus, the results advocate for fitting a physical model to be the sole tool for testing that model. Finally, a smoothly-broken power law is fit to these spectra allowing for the spectral curvature to vary during the fitting process in order to understand why the previous width measures poorly predict the spectra. It is found that the failing of previous width measures is due to a combination of inferring physical parameters from unfolded spectra as well as the presence of multiple widths in the data beyond what the Band function can model.

scholarly journals Resolving the excess of long GRB’s at low redshift in the Swift era

2020 ◽  
Vol 493 (1) ◽  
pp. 1479-1491 ◽  
Author(s):  
Truong Le ◽  
Cecilia Ratke ◽  
Vedant Mehta
Keyword(s):  
Physical Parameter ◽  
Power Law ◽  
Gamma Ray ◽  
Hubble Constant ◽  
High Energy ◽  
Star Formation History ◽  
Physical Parameters ◽  
Data Set ◽  
Energy Indices ◽  
Parameter Values

ABSTRACT Utilizing more than 100 long gamma-ray bursts (LGRBs) in the Swift-Ryan-2012 sample that includes the observed redshifts and jet angles, Le & Mehta performed a timely study of the rate density of LGRBs with an assumed broken power-law GRB spectrum and obtained a GRB-burst-rate functional form that gives acceptable fits to the pre-Swift and Swift redshift, and jet angle distributions. The results indicated an excess of LGRBs at redshift below z ∼ 2 in the Swift sample. In this work, we are investigating if the excess is caused by the cosmological Hubble constant H0, the gamma-ray energy released ${\cal E}_{*\gamma }$, the low- and high-energy indices (α, β) of the Band function, the minimum and maximum jet angles θj, min and θj, max, or that the excess is due to a bias in the Swift-Ryan-2012 sample. Our analyses indicate that none of the above physical parameters resolved the excess problem, but suggesting that the Swift-Ryan-2012 sample is biased with possible afterglow selection effect. The following model physical parameter values provide the best fit to the Swift-Ryan-2012 and pre-Swift samples: the Hubble constant $H_0 = 72 \, {\rm km s^{-1} Mpc^{-1}}$, the energy released ${\cal E}_{*\gamma }\sim 4.47 \times 10^{51}$ erg, the energy indices α ∼ 0.9 and β ∼ −2.13, the jet angles of θj, max ∼ 0.8 rad, and θj, min ∼ 0.065 and ∼0.04 rad for pre-Swift and Swift, respectively, s ∼ −1.55 the jet angle power-law index, and a GRB formation rate that is similar to the Hopkins & Beacom observed star formation history and as extended by Li. Using the Swift Gamma-Ray Burst Host Galaxy Legacy Survey (SHOALS) Swift-Perley LGRB sample and applying the same physical parameter values as above, however, our model provides consistent results with this data set and indicating no excess of LGRBs at any redshift.

scholarly journals A Bayesian Fermi-GBM short GRB spectral catalogue

2019 ◽  
Vol 490 (1) ◽  
pp. 927-946 ◽  
Author(s):  
J Michael Burgess ◽  
Jochen Greiner ◽  
Damien Bégué ◽  
Franceso Berlato
Keyword(s):  
Light Curve ◽  
Gravitational Wave ◽  
Power Law ◽  
Gamma Ray ◽  
Posterior Distributions ◽  
Time Resolved ◽  
Gamma Ray Burst ◽  
Posterior Predictive Checks ◽  
Peak Flux ◽  
Reduced Data

ABSTRACT Inspired by the confirmed detection of a short gamma-ray burst (GRB) in association with a gravitational wave signal, we present the first Bayesian Fermi-Gamma-ray Burst Monitor (GBM) short GRB spectral catalogue. Both peak flux and time-resolved spectral results are presented. Data are analysed with the proper Poisson likelihood allowing us to provide statistically reliable results even for spectra with few counts. All fits are validated with posterior predictive checks. We find that nearly all spectra can be modelled with a cut-off power law. Additionally, we release the full posterior distributions and reduced data from our sample. Following our previous study, we introduce three variability classes based on the observed light-curve structure.

scholarly journals The synchrotron mechanism and the high energy flare from PKS 1510-089

2021 ◽  
pp. 417-424
Author(s):  
Z. N. Osmanov
Keyword(s):  
Gamma Ray ◽  
Reaction Force ◽  
High Energy ◽  
Physical Parameters ◽  
Synchrotron Emission ◽  
Linear Diffusion ◽  
Wide Range ◽  
Energy Domain ◽  
Field Lines ◽  
Major Factors

In order to understand the role of the synchrotron emission in the high energy gamma-ray flares from PKS 1510-089, we study generation of the synchrotron emission by means of the feedback of cyclotron waves on the particle distribution via the diffusion process. The cyclotron resonance causes the diffusion of particles along and across the magnetic field lines. This process is described by the quasi-linear diffusion (QLD) that leads to the increase of pitch angles and generation of the synchrotron emission. We study the kinetic equation which defines the distribution of emitting particles. The redistribution is conditioned by two major factors, QLD and the dissipation process, that is caused by synchrotron reaction force. The QLD increases pitch angles, whereas the synchrotron force resists this process. The balance between these two forces guarantees the maintenance of the pitch angles and the corresponding synchrotron emission process. The model is analyzed for a wide range of physical parameters and it is shown that the mechanism of QLD provides the generation of high energy (HE) emission in the GeV energy domain. According to the model the lower energy, associated with the cyclotron modes, provokes the synchrotron radiation in the higher energy band.

scholarly journals Long and Short Fast Radio Bursts Are Different from Repeating and Nonrepeating Transients

2021 ◽  
Vol 923 (2) ◽  
pp. 230
Author(s):  
X. J. Li ◽  
X. F. Dong ◽  
Z. B. Zhang ◽  
D. Li
Keyword(s):  
Flux Density ◽  
Power Law ◽  
Pulse Width ◽  
Gamma Ray ◽  
Bimodal Distribution ◽  
Gamma Ray Bursts ◽  
Radio Bursts ◽  
Central Frequency ◽  
Peak Flux ◽  
Near Future

Abstract We collect 133 fast radio bursts (FRBs), including 110 nonrepeating and 23 repeating ones, and systematically investigate their observational properties. To check the frequency dependence of FRB classifications, we define our samples with a central frequency below/above 1 GHz as subsample I/II. First, we find that there is a clear bimodal distribution of pulse width for subsample I. If we classify FRBs into short FRBs (sFRBs; <100 ms) and long FRBs (lFRBs; >100 ms) as done for short and long gamma-ray bursts (GRBs), the sFRBs at higher central frequency are commonly shorter than those at lower central frequency not only for nonrepeating but also repeating sFRBs. Second, we find that fluence and peak flux density are correlated with a power-law relation of F ∝ S p , obs γ for both sFRBs and lFRBs whose distributions are obviously different. Third, the lFRBs with isotropic energies ranging from 1042 to 1044 erg are more energetic than the sFRBs in the F–DM EX plane, indicating that they are two representative types. Finally, it is interesting to note that the peak flux density behaves independently on the redshift when the distance of the FRBs becomes far enough, which is similar to the scenario of the peak flux evolving with redshift in the field of GRBs. We predict that fainter FRBs at a higher redshift of z > 2 can be successfully detected by FAST and the Square Kilometre Array in the near future.

scholarly journals Modelling synchrotron self-Compton and Klein–Nishina effects in gamma-ray burst afterglows

2021 ◽  
Vol 504 (1) ◽  
pp. 528-542 ◽  
Author(s):  
Taylor E Jacovich ◽  
Paz Beniamini ◽  
Alexander J van der Horst
Keyword(s):  
Gamma Ray ◽  
Broad Band ◽  
Spectral Shape ◽  
Physical Parameters ◽  
Synchrotron Emission ◽  
Gamma Ray Burst ◽  
Profound Impact ◽  
X Ray ◽  
Self Consistent ◽  
Parameter Distributions

ABSTRACT We present an implementation of a self-consistent way of modelling synchrotron self-Compton (SSC) effects in gamma-ray burst afterglows, with and without approximated Klein–Nishina suppressed scattering for the afterglow modelling code boxfit, which is currently based on pure synchrotron emission. We discuss the changes in spectral shape and evolution due to SSC effects, and comment on how these changes affect physical parameters derived from broad-band modelling. We show that SSC effects can have a profound impact on the shape of the X-ray light curve using simulations including these effects. This leads to data that cannot be simultaneously fit well in both the X-ray and radio bands when considering synchrotron-only fits, and an inability to recover the correct physical parameters, with some fitted parameters deviating orders of magnitude from the simulated input parameters. This may have a significant impact on the physical parameter distributions based on previous broad-band modelling efforts.

scholarly journals Synchrotron Emission from Particles Having A Truncated Power-law Energy Spectrum

1974 ◽  
Vol 168 (2) ◽  
pp. 379-397 ◽  
Author(s):  
L. J. Gleeson ◽  
M. P. C. Legg ◽  
K. C. Westfold
Keyword(s):  
Energy Spectrum ◽  
Power Law ◽  
Synchrotron Emission

scholarly journals Physical parameters and emission mechanism in gamma-ray bursts

2001 ◽  
Vol 372 (3) ◽  
pp. 1071-1077 ◽  
Author(s):  
E. V. Derishev ◽  
V. V. Kocharovsky ◽  
Vl. V. Kocharovsky
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Physical Parameters ◽  
Emission Mechanism

scholarly journals Detection of the Geminga pulsar with MAGIC hints at a power-law tail emission beyond 15 GeV

2020 ◽  
Vol 643 ◽  
pp. L14
Author(s):  
◽  
V. A. Acciari ◽  
S. Ansoldi ◽  
L. A. Antonelli ◽  
A. Arbet Engels ◽  
...  
Keyword(s):  
Energy Range ◽  
Power Law ◽  
Gamma Ray ◽  
Low Energy ◽  
Significance Level ◽  
Inverse Compton Scattering ◽  
Curvature Radiation ◽  
Sensitivity Range ◽  
Inverse Compton ◽  
First Time

We report the detection of pulsed gamma-ray emission from the Geminga pulsar (PSR J0633+1746) between 15 GeV and 75 GeV. This is the first time a middle-aged pulsar has been detected up to these energies. Observations were carried out with the MAGIC telescopes between 2017 and 2019 using the low-energy threshold Sum-Trigger-II system. After quality selection cuts, ∼80 h of observational data were used for this analysis. To compare with the emission at lower energies below the sensitivity range of MAGIC, 11 years of Fermi-LAT data above 100 MeV were also analysed. From the two pulses per rotation seen by Fermi-LAT, only the second one, P2, is detected in the MAGIC energy range, with a significance of 6.3σ. The spectrum measured by MAGIC is well-represented by a simple power law of spectral index Γ = 5.62 ± 0.54, which smoothly extends the Fermi-LAT spectrum. A joint fit to MAGIC and Fermi-LAT data rules out the existence of a sub-exponential cut-off in the combined energy range at the 3.6σ significance level. The power-law tail emission detected by MAGIC is interpreted as the transition from curvature radiation to Inverse Compton Scattering of particles accelerated in the northern outer gap.

The correlation between gamma-ray burst duration and peak flux

1996 ◽  
Author(s):  
R. E. Rutledge ◽  
W. H. G. Lewin ◽  
G. Pendleton ◽  
J. P. Lestrade ◽  
C. Kouveliotou ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Burst Duration ◽  
Gamma Ray Burst ◽  
Peak Flux
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