Conveners
Emission mechanisms in gamma-ray bursts: Monday block 1
- Damien Begue (Bar Ilan University)
- Gregory Vereshchagin (ICRANet)
Emission mechanisms in gamma-ray bursts: Monday block 2
- Gregory Vereshchagin (ICRANet)
- Damien Begue (Bar Ilan University)
Description
We will discuss basic radiation mechanisms producing observed spectra and light curves of gamma-ray bursts and their respective roles. Special attention will be given to theoretical and observational results aiming at discrimination between these mechanisms, in particular synchrotron and photospheric emission. In addition radiation mechanisms of high energy emission observed recently by the ground based Cherenkov detectors such as MAGIC and HESS as well as Air Shower Observatories such as LHAASO will be discussed.
We explore the properties of photospheric emission in gamma-ray bursts (GRBs) based on relativistic hydrodynamical simulations and Monte Carlo radiation transfer calculations. Our simulations confirm that photospheric emission gives rise to correlations between the spectral peak energy and luminosity that agree with the observed Yonetoku, Amati, and Golenetskii correlations. It is also shown...
We investigate the photon analogue of Fermi acceleration where a photon scatters within the shearing layers of a relativistic plasma and produces power-law-shaped spectra at high energies. It is an alternative to existing explanations of power law spectra such as synchrotron process or inverse Comptonization. Among several potential applications of this phenomenon, I will describe its...
GRB spectra seem to be well fitted by models based on marginally fast-cooled synchrotron radiation. This observation challenges the synchrotron process as a viable mechanism as it leads to (too) large emission radii and (too) large bulk Lorentz factors. To overcome this difficulty, it was proposed that proton could be the particles radiating synchrotron emission. I will show that if protons...
In this talk, I will present two recent models for explaining the observed GRB spectra.
As a GRB jet drills its way through the collapsing star, it traps a baryonic "cork" ahead of it. If the jet does not cross this cork, but rather photons that are emitted deep in the flow (e.g., by pair annihilation) are scattered by the cork, an observer close to the jet axis will see these photons due to...
Large-scale cosmic emissions of explosive energy that occur during the explosions of certain supernovae or the merger of compact objects are called gamma-ray bursts. We study the radiation of the ultrarelativistic shell in the diffusion approximation, which takes place at the initial stage of a gamma-ray burst. We get the effective temperature, instantaneous and time-integrated spectra for the...
One of the main arguments in favour of magnetically dominated outflows is the absence of photospheric component in their broad-band time-resolved spectra, with such notable example as GRB 080916C. Detection of subdominant thermal component in this GRB is actually consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. Therefore, the magnetic...
Gamma-ray bursts (GRBs) are the brightest sources in the Universe.
They appear as gamma-ray flashes, with a spectrum that peaks around a few hundred keV . The prompt spectra of GRBs were historically characterised through the phenomenological Band function, composed of two power laws smoothly connected around the peak. Because of the broad spectral shape, GRB spectra seem consistent with...
Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. How efficiently the jet converts its energy to radiation is a long-standing problem and it is poorly constrained. The standard model invokes a relativistic fireball with a bright photosphere emission component. A definitive diagnosis of GRB radiation components and measurement of GRB radiative efficiency require prompt...
In this talk, I will present and discuss evidence for cocoon emission in the early afterglow emission phases of the nearby GRB-SN 171205A. Special attention will be given to the multi-wavelength analysis, and to modeling of the cocoon component.
GRB afterglows are powered by emission from relativistic collisionless shocks.
The converter acceleration mechanism, which is specific just for
relativistic shocks, makes them efficient emitters and at the same time
modifies the shock structure. As a result, the shock balances itself within
a region in the parameter space that can be estimated analytically or
evaluated numerically with...
The origin of the prompt emission in gamma-ray bursts (GRBs) remains debated. Our understanding is primarily derived from wide-field telescopes that operate within the 10 keV-10 MeV range. However, capturing early emissions at higher energies (above 100 GeV) is challenging because of the time required for slewing of the telescopes. I will discuss multi-messenger observational strategies aimed...
