Possible physical explanation of the intrinsic Ep,i-“intensity” correlation commonly used to “standardize” GRBs

2016 ◽  
Vol 25 (05) ◽  
pp. 1630014 ◽  
Author(s):  
Filippo Frontera ◽  
Lorenzo Amati ◽  
Ruben Farinelli ◽  
Simone Dichiara ◽  
Cristiano Guidorzi ◽  
...  
Keyword(s):  
Thermal Bath ◽  
Time Resolved ◽  
Peak Energy ◽  
Inverse Compton ◽  
Energy Formula ◽  
Two Phases ◽  
Photospheric Model ◽  
Photospheric Radius ◽  
Prompt Emission ◽  
Broad Energy

It is recognized that very likely the correlation between peak energy [Formula: see text] and bolometric intensity is intrinsic to GRBs. However, its physical origin is still debated. In this paper, we will discuss a possible interpretation of the correlation in the light of a GRB prompt emission spectral model, grbcomp, proposed in [L. Titarchuk, R. Farinelli, F. Frontera and L. Amati, Astrophys. J. 752 (2012) 116]. grbcomp is essentially a photospheric model for the prompt emission of GRBs. Its main ingredients are a thermal bath of soft seed photons and a subrelativistically expanding outflow plasma, consequence of the star explosion. The emerging spectrum is the result of two phases: first, up to the photospheric radius, Comptonization of a subrelativistic electron outflow with thermal bath of soft photons, then, convolution of the Comptonized photons in the first phase with a Green function. The result of this convolution is consistent with different physical processes, in particular Inverse Compton. grbcomp has been successfully tested using a significant sample of GRB time resolved spectra in the broad energy band from 2[Formula: see text]keV to 2[Formula: see text]MeV [F. Frontera, L. Amati, R. Farinelli, S. Dichiara, C. Guidorzi, R. Landi and L. Titarchuk, Astrophys. J. 779 (2013) 175].

scholarly journals OBSERVATIONAL PROPERTIES OF TEV DETECTED GRB 180720B, GRB 190114C AND GRB 190829A

2021 ◽  
Vol 53 ◽  
pp. 113-123
Author(s):  
R. Gupta ◽  
S. B. Pandey ◽  
A. J. Castro-Tirado ◽  
A. Kumar ◽  
A. Aryan ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Late Time ◽  
Energy Evolution ◽  
Radiation Mechanisms ◽  
Radiation Mechanism ◽  
Peak Energy ◽  
Inverse Compton ◽  
Γ Ray ◽  
Prompt Emission

TeV emissions from γ-ray bursts are very important to study their origin and the radiation mechanisms in detail. Recent observations of TeV photons in some of the GRBs are challenging to be explained by the traditional Synchrotron radiation mechanism. In this work, we present the results of a detailed investigation of the prompt and afterglow emissions of recently discovered TeV GRBs (GRB 180720B, GRB 190114C, and GRB 190829A) based on the publicly available prompt and afterglow data including 10.4m GTC and 1.3m DFOT telescopes observations of the first HESS and MAGIC bursts, respectively. Timeresolved spectroscopy of prompt emission of GRB 180720B and GRB 190114C shows an intensity tracking nature of peak energy. In the case of GRB 190829A, peak energy evolution shows a hard to soft tracking trend followed by a very soft and chaotic trend. GRB 190829A is a peculiar intermediate luminous two episodic burst with first emission episode outlier to Amati correlation. We analyzed the late time Fermi-LAT emission that encapsulates the H.E.S.S. and MAGIC observations. Some of the LAT photons are likely to be associated with these GRBs and they could have an Inverse Compton radiation mechanism.

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.

scholarly journals Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films

2000 ◽  
Vol 5 (S1) ◽  
pp. 796-802 ◽  
Author(s):  
Yong-Hoon Cho ◽  
G. H. Gainer ◽  
J. B. Lam ◽  
J. J. Song ◽  
W Yang ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Stokes Shift ◽  
Energy Shift ◽  
Peak Position ◽  
Time Resolved ◽  
Temperature Range ◽  
Al Content ◽  
Peak Energy ◽  
Emission Behavior ◽  
Pl Intensity

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.

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 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 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.

Gamma-ray bursts prompt emission spectrum: an analysis of a photosphere model

2007 ◽  
Vol 365 (1854) ◽  
pp. 1171-1175 ◽  
Author(s):  
Asaf Pe'er ◽  
Peter Mészáros ◽  
Martin J Rees
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Dissipation Process ◽  
Internal Shock ◽  
Peak Energy ◽  
Wide Range ◽  
Low Energies ◽  
Steep Slopes ◽  
The Magnetic Field ◽  
Prompt Emission

A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy densities in the thermal and leptonic components, the dominant emission mechanism is Compton scattering. This leads to a nearly flat energy spectrum ( νF ν ∝ ν 0 ) above the thermal peak at approximately 10–100 keV and below 10–100 MeV, for a wide range of optical depths 0.03≲ τ ≲100, regardless of the details of the dissipation mechanism or the strength of the magnetic field. For higher values of the optical depth, a Wien peak is formed at 100 keV to 1 MeV. In particular, these results are applicable to the internal shock model of GRBs, as well as to slow dissipation models, e.g. as might be expected from reconnection, if the dissipation occurs at a sub-photospheric radii. We conclude that dissipation near the thermal photosphere can naturally explain (i) clustering of the peak energy at sub-MeV energies at early times, (ii) steep slopes observed at low energies, and (iii) a flat spectrum above 10 keV at late times. Our model thus provides an alternative scenario to the optically thin synchrotron–synchrotron self-Compton model.

Measurements Of The Hydrogen Absorption Pressurecomposition Isotherms IN Ti/Zr-Based Quasicrystals

1998 ◽  
Vol 553 ◽  
Author(s):  
J. Y. Kim ◽  
E. H. Majzoub ◽  
P. C. Gibbons ◽  
K. F. Kelton
Keyword(s):  
Energy Distribution ◽  
Hydrogen Absorption ◽  
Structural Similarity ◽  
Half Width ◽  
Weighted Averages ◽  
Site Energy ◽  
Tetrahedral Sites ◽  
Two Phases ◽  
Almost All ◽  
Broad Energy

AbstractThe first hydrogen absorption pressure-composition isotherms (p-c-T) were measured in quasicrystalline Ti45Zr38Ni17. No evidence for a pressure plateau was found, indicating a distribution of energies for the hydrogen in interstitial sites. Fits to the p-c-T data confirmed this, giving energy peaks at -0.19 eV with a full width at half maximum (half-width) of 0.06 eV, and at -0.09 eV with a half-width of 0.08 eV. This is in contrast with the broad site energy distribution that is characteristic of a metallic glass. In agreement, fits to data taken from amorphous Ti45Zr27Ni20Si8 gave a single broad energy distribution at -0.10 eV with a half-width of 0.35 eV. Based on the weighted averages of the site energies for the pure components, the energies assigned to the tetrahedral sites in the Ti44Zr40Ni16 1/1 approximant phase are in qualitative agreement with the measured data for the quasicrystal, supporting a local structural similarity between these two phases. Almost all of the absorbed hydrogen can be desorbed at 650°C in one hour by pumping, without transforming the quasicrystal phase and without powdering the rapidly-quenched samples.

scholarly journals Consistency with synchrotron emission in the bright GRB 160625B observed by Fermi

2018 ◽  
Vol 613 ◽  
pp. A16 ◽  
Author(s):  
M. E. Ravasio ◽  
G. Oganesyan ◽  
G. Ghirlanda ◽  
L. Nava ◽  
G. Ghisellini ◽  
...  
Keyword(s):  
Power Laws ◽  
Black Body ◽  
Low Energy ◽  
Synchrotron Emission ◽  
Spectral Evolution ◽  
Spectral Parameters ◽  
Time Resolved ◽  
Central Engine ◽  
Spectral Break ◽  
Peak Energy

We present time-resolved spectral analysis of prompt emission from GRB 160625B, one of the brightest bursts ever detected by Fermi in its nine years of operations. Standard empirical functions fail to provide an acceptable fit to the GBM spectral data, which instead require the addition of a low-energy break to the fitting function. We introduce a new fitting function, called 2SBPL, consisting of three smoothly connected power laws. Fitting this model to the data, the goodness of the fits significantly improves and the spectral parameters are well constrained. We also test a spectral model that combines non-thermal and thermal (black body) components, but find that the 2SBPL model is systematically favoured. The spectral evolution shows that the spectral break is located around Ebreak ~100 keV, while the usual νFν peak energy feature Epeak evolves in the 0.5–6 MeV energy range. The slopes below and above Ebreak are consistent with the values –0.67 and –1.5, respectively, expected from synchrotron emission produced by a relativistic electron population with a low-energy cut-off. If Ebreak is interpreted as the synchrotron cooling frequency, the implied magnetic field in the emitting region is ~10 Gauss, i.e. orders of magnitudes smaller than the value expected for a dissipation region located at ~1013−14 cm from the central engine. The low ratio between Epeak and Ebreak implies that the radiative cooling is incomplete, contrary to what is expected in strongly magnetized and compact emitting regions.

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.

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