Gamma Ray Bursts Spectral–Energy correlations: recent results

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.

Download Full-text

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937057 ◽

2020 ◽

Vol 640 ◽

pp. A91 ◽

Cited By ~ 1

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.

Download Full-text

Gamma-ray bursts spectral correlations and their cosmological use

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2006.1976 ◽

2007 ◽

Vol 365 (1854) ◽

pp. 1385-1394 ◽

Cited By ~ 6

Author(s):

Giancarlo Ghirlanda

Keyword(s):

Gamma Ray ◽

Gamma Ray Bursts ◽

Spectral Energy ◽

Selection Effects ◽

Emission Energy ◽

X Ray ◽

New Class ◽

The Universe ◽

Prompt Emission ◽

Open Issues

The correlations involving the long-gamma-ray bursts (GRBs) prompt emission energy represent a new key to understand the GRB physics. These correlations have been proved to be the tool that makes long-GRBs a new class of standard candles. Gamma Ray Bursts, being very powerful cosmological sources detected in the hard X-ray band, represent a new tool to investigate the Universe in a redshift range, which is complementary to that covered by other cosmological probes (SNIa and CMB). A review of the , , and correlations is presented. Open issues related to these correlations (e.g. presence of outliers and selection effects) and to their use for cosmographic purposes (e.g. dependence on model assumptions) are discussed. Finally, the relevance of thermal components in GRB spectra is discussed in the light of some of the models recently proposed for the interpretation of the spectral-energy correlations.

Download Full-text

GRB Polarization: A Unique Probe of GRB Physics

Galaxies ◽

10.3390/galaxies9040082 ◽

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.

Download Full-text

Prevalence of Extra Power-Law Spectral Components in Short Gamma-Ray Bursts

The Astrophysical Journal ◽

10.3847/1538-4357/ac26ba ◽

2021 ◽

Vol 922 (2) ◽

pp. 255

Author(s):

Qing-Wen Tang ◽

Kai Wang ◽

Liang Li ◽

Ruo-Yu Liu

Keyword(s):

Power Law ◽

Gamma Ray ◽

Spectral Energy Distribution ◽

Spectral Feature ◽

Gamma Ray Bursts ◽

Spectral Energy ◽

Spectral Components ◽

Short Grbs ◽

Prompt Emission ◽

Emission Phase

Abstract A prompt extra power-law (PL) spectral component that usually dominates the spectral energy distribution below tens of keV or above ∼10 MeV has been discovered in some bright gamma-ray bursts (GRBs). However, its origin is still unclear. In this paper, we present a systematic analysis of 13 Fermi short GRBs, as of 2020 August, with contemporaneous keV–MeV and GeV detections during the prompt emission phase. We find that the extra PL component is a ubiquitous spectral feature for short GRBs, showing up in all 13 analyzed GRBs. The PL indices are mostly harder than −2.0, which may be well reproduced by considering the electromagnetic cascade induced by ultrarelativistic protons or electrons accelerated in the prompt emission phase. The average flux of these extra PL components positively correlates with that of the main spectral components, which implies they may share the same physical origin.

Download Full-text

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

International Journal of Modern Physics D ◽

10.1142/s0218271811020056 ◽

2011 ◽

Vol 20 (10) ◽

pp. 1983-1987 ◽

Cited By ~ 5

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.

Download Full-text

Limits on quantum gravity effects from Swift short gamma-ray bursts

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731332 ◽

2017 ◽

Vol 607 ◽

pp. A121 ◽

Cited By ~ 5

Author(s):

M. G. Bernardini ◽

G. Ghirlanda ◽

S. Campana ◽

P. D’Avanzo ◽

J.-L. Atteia ◽

...

Keyword(s):

Quantum Gravity ◽

Gamma Ray ◽

Lorentz Invariance ◽

Spectral Energy Distribution ◽

Gamma Ray Bursts ◽

Low Energy ◽

Energy Separation ◽

Spectral Energy ◽

Spectral Evolution ◽

Short Grbs

The delay in arrival times between high and low energy photons from cosmic sources can be used to test the violation of the Lorentz invariance (LIV), predicted by some quantum gravity theories, and to constrain its characteristic energy scale EQG that is of the order of the Planck energy. Gamma-ray bursts (GRBs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on EQG are proportional to the photon energy separation and the distance of the source. However, the LIV tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long GRBs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). Short GRBs have null intrinsic spectral lags and are therefore an ideal tool to measure any LIV effect. We considered a sample of 15 short GRBs with known redshift observed by Swift and we estimate a limit on EQG ≳ 1.5 × 1016 GeV. Our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long GRBs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense.

Download Full-text

The properties of prompt emission in short gamma-ray bursts with extended emission observed by Fermi/GBM

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa044 ◽

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.

Download Full-text

Time-resolved GRB polarization with POLAR and GBM

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935056 ◽

2019 ◽

Vol 627 ◽

pp. A105 ◽

Cited By ~ 9

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.

Download Full-text

Evidence of two spectral breaks in the prompt emission of gamma-ray bursts

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834987 ◽

2019 ◽

Vol 625 ◽

pp. A60 ◽

Cited By ~ 11

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.

Download Full-text

Physics of Gamma-Ray Bursts Prompt Emission

Advances in Astronomy ◽

10.1155/2015/907321 ◽

2015 ◽

Vol 2015 ◽

pp. 1-37 ◽

Cited By ~ 36

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.

Download Full-text