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 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 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 The Low-Energy Spectral Index of Gamma-Ray Burst Prompt Emission from Internal Shocks

Galaxies ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 68
Author(s):  
Kai Wang ◽  
Zi-Gao Dai
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Gamma Ray ◽  
Emission Spectra ◽  
Injection Rate ◽  
Low Energy ◽  
Energy Photon ◽  
Internal Shock ◽  
Photon Index ◽  
Prompt Emission

The prompt emission of most gamma-ray bursts (GRBs) typically exhibits a non-thermal Band component. The synchrotron radiation in the popular internal shock model is generally put forward to explain such a non-thermal component. However, the low-energy photon index α∼−1.5 predicted by the synchrotron radiation is inconsistent with the observed value α∼−1. Here, we investigate the evolution of a magnetic field during propagation of internal shocks within an ultrarelativistic outflow, and revisit the fast cooling of shock-accelerated electrons via synchrotron radiation for this evolutional magnetic field. We find that the magnetic field is first nearly constant and then decays as B′∝t−1, which leads to a reasonable range of the low-energy photon index, −3/2<α<−2/3. In addition, if a rising electron injection rate during a GRB is introduced, we find that α reaches −2/3 more easily. We thus fit the prompt emission spectra of GRB 080916c and GRB 080825c.

A NEW SPECTRAL ENERGY DISTRIBUTION OF PHOTONS IN THE FIRESHELL MODEL OF GRBS

2011 ◽  
Vol 20 (10) ◽  
pp. 1983-1987 ◽  
Author(s):  
B. PATRICELLI ◽  
M. G. BERNARDINI ◽  
C. L. BIANCO ◽  
L. CAITO ◽  
L. IZZO ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Observational Data ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Emission Spectra ◽  
Spectral Energy ◽  
Isotropic Energy ◽  
Thermal Spectrum ◽  
Power Law Index ◽  
Prompt Emission

The analysis of various Gamma-Ray Bursts (GRBs) having a low energetics (an isotropic energy E iso ≲ 1053 ergs) within the fireshell model has shown how the N(E) spectrum of their prompt emission can be reproduced in a satisfactory way by a convolution of thermal spectra. Nevertheless, from the study of very energetic bursts (E iso ≳ 1054 ergs) such as, for example, GRB 080319B, some discrepancies between the numerical simulations and the observational data have been observed. We investigate a different spectrum of photons in the comoving frame of the fireshell in order to better reproduce the spectral properties of GRB prompt emission within the fireshell model. We introduce a phenomenologically modified thermal spectrum: a thermal spectrum characterized by a different asymptotic power-law index in the low energy region. Such an index depends on a free parameter α, so that the pure thermal spectrum corresponds to the case α = 0. We test this spectrum by comparing the numerical simulations with the observed prompt emission spectra of various GRBs. From this analysis it has emerged that the observational data can be correctly reproduced by assuming a modified thermal spectrum with α = -1.8.

scholarly journals GRB 110731A within the IGC paradigm

2018 ◽  
Vol 168 ◽  
pp. 04008
Author(s):  
Daria Primorac ◽  
Remo Ruffini ◽  
Giovanni Battista Pisani ◽  
Yerlan Aimuratov ◽  
Carlo Luciano Biancol ◽  
...  
Keyword(s):  
Light Curve ◽  
Gamma Ray ◽  
Emission Spectra ◽  
Lorentz Factor ◽  
High Energy ◽  
Integrated Analysis ◽  
Isotropic Energy ◽  
Time Resolved ◽  
Star Binary

Bright gamma-ray burst (GRB) 110731A was simultaneously observed by Fermi and Swift observatories, with a follow up optical observation which inferred the redshift of z = 2.83. Thus, available data are spanning from optical to high energy (GeV) emission. We analyze these data within the induced gravitational collapse (IGC) paradigm, recently introduced to explain temporal coincidence of some long GRBs with type Ic supernovae. The case of binary-driven hypcrnova (BdHN) assumes a close system, which starts as an evolved core - neutron star binary. After the core-collapse event, the new NS - black hole system is formed, emitting the GRB in the process. We performed the time-resolved and time-integrated analysis of the Fermi data. Preliminary results gave isotropic energy Eiso = 6.05 × 1053 erg and the total P-GRB energy of Ep–GRB = 3.7 × 1052 erg. At transparency point we found a Lorentz factor Γ ~ 2.17 × 103 laboratory radius of 8.33 x 1013 cm, P-GRB observed temperature of 168 keV and a baryon load B = 4.35 × 10-4. Simulated light-curve and prompt emission spectra showed the average circum burst medium density to be n ~ 0.03 particles per cm3. We reproduced the X-ray light-curve within the rest-frame of the source, finding the common late power-law behavior, with α = –1.22. Considering these results, we interpret GRB 110731A as a member of a BdHNe group.

scholarly journals Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 220
Author(s):  
Emil Khalikov
Keyword(s):  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Cascade Model ◽  
Point Sources ◽  
Spectral Energy ◽  
Observation Data ◽  
Cherenkov Telescopes ◽  
The Universe

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

scholarly journals On the High‐Energy Spectral Component and Fine Time Structure of Terrestrial Gamma Ray Flashes

2019 ◽  
Vol 124 (14) ◽  
pp. 7484-7497 ◽  
Author(s):  
M. Marisaldi ◽  
M. Galli ◽  
C. Labanti ◽  
N. Østgaard ◽  
D. Sarria ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Spectral Component ◽  
High Energy ◽  
Time Structure ◽  
Fine Time

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 Detection of a flaring blazar coincident with an IceCube high-energy neutrino

2019 ◽  
Vol 207 ◽  
pp. 02001
Author(s):  
Anna Franckowiak
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Neutrino Flux ◽  
High Energy ◽  
Spectral Energy ◽  
Large Area ◽  
High Energy Neutrino ◽  
Energy Neutrino ◽  
Radio Wavelength ◽  
First Time

In September 22, 2017, IceCube released a public alert announcing the detection of a 290 TeV neutrino track event with an angular uncertainty of one square degree (90% containment). A multi-messenger follow-up campaign was initiated resulting in the detection of a GeV gamma-ray flare by the Fermi Large Area Telescope positionally consistent with the location of the known Bl Lac object, TXS 0506+056 , located only 0.1 degrees from the best-fit neutrino position. The probability of finding a GeV gamma-ray flare in coincidence with a high-energy neutrino event assuming a correlation of the neutrino flux with the gamma-ray energy flux in the energy band between 1 and 100 GeV was calculated to be 3σ (after trials correction). Following the detection of the flaring blazar the imaging air Cherenkov telescope MAGIC detected the source for the first time in the > 100 GeV gamma-ray band. The activity of the source was confirmed in X-ray, optical and radio wavelength. Several groups have developed lepto-hadronic models which succeed to explain the multi-messenger spectral energy distribution.

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