GB3 - Cosmology from GRBs |
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Speaker |
Frontera, Filippo |
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Coauthors |
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| Talk Title |
Possible Physical Explanation of the Ep,i - "Intensity" Correlation Commonly Used to "Standardize" GRBs |
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Abstract |
In several papers, the so called “Amati relation”, i.e., the found correlation between the photon energy at which the νFν spectrum peaks and the GRB radiated energy, has been successfully used to estimate the cosmological density parameter ΩM. The reliability of this correlation is still discussed, given that, according to some authors, it could be the influenced or be the result of selection effects. However, it is found that the Ep – “intensity” correlation also holds within each single GRB, and for GRB with known redshift, normalization and slope of the Ep,i vs. Luminosity correlation is consistent with that obtained with time-averaged spectra. This means that very likely the correlation is intrinsic to GRBs and that its physical origin has to be found. Several authors have debated the possible physical mechanisms that give rise to the Amati relation. I will will report on its interpretation in the light of a GRB prompt emission model, GRBCOMP, proposed by us (Titarchuk et al. 2012). 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: subrelativistic outflow up to photospheric radius, convolution of the Comptonized photons in the first phase with a Green function, 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 keV to 2 MeV (Frontera et al. (2013). |
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