Thermalization in Relativistic Outflows and the Correlation between Spectral Hardness and Apparent Luminosity in Gamma‐Ray Bursts

Abstract

We present an interpretation of the phenomenological relations between the spectral peak, isotropic luminosity, and duration of long gamma-ray bursts that have been discovered by Amati and coworkers, Ghirlanda and coworkers, Firmani and coworkers, and Liang & Zhang. In our proposed model, a jet undergoes internal dissipation which prevents its bulk Lorentz factor from exceeding 1/ ( being the jet opening angle) until it escapes from the core of its progenitor star, at a radius of order 10 10 cm; dissipation may continue at larger radii. The dissipated radiation will be partially thermalized, and we identify its thermal peak ( Doppler boosted by the outflow) with E pk . The radiation comes, in effect, from within the jet photosphere. The nonthermal, high-energy part of the GRB emission arises from Comptonization of this radiation by relativistic electrons and positrons outside the effective photosphere. This model can account naturally not only for the surprisingly small scatter in the various claimed correlations, but also for the normalization, as well as the slopes. It then has further implications for the jet energy, the limiting jet Lorentz factor, and the relation of the energy, opening angle and burst duration to the mass and radius of the stellar stellar progenitor. The observed relation between pulse width and photon frequency can be reproduced by inverse Compton emission at $10 14 cm from the engine, but there are significant constraints on the energy distribution and isotropy of the radiating particles.

TheEpeak–Eisorelation revisited withFermiGRBs

“…If it is a consequence of the dominant radiation mechanism at work in GRBs, as we expect, theoretical studies may help understanding the nature and the true location of this boundary (see for instance Eichler & Levinson 2004;Yamazaki et al 2004;Rees & Mészáros 2005;Thompson et al 2007;Giannios 2012;Mochkovitch et al 2012;Beniamini & Piran 2013;Shahmoradi 2013, for explanations within the framework of different theoretical or phenomelogical models). The observation of an E pi -E iso relation in time-resolved spectra (e.g.…”

Individual power density spectra ofSwiftgamma-ray bursts

“…Generally, several types of dissipation processes have been proposed: i) the so-called internal shock (IS) model (Rees & Meszaros 1994;Narayan et al 1992), in which the kinetic energy of a baryon load is dissipated into gamma rays through shocks that take place far away from the Thomson photosphere, at 10 14 -10 16 cm; ii) the photospheric models, in which the dissipation occurs near the photosphere, and where a Planckian spectrum is modified by some heating and Compton scattering (Rees & Mészáros 2005;Pe'er et al 2006; Thompson et al 2007;Derishev et al 1999;Rossi et al 2006;Beloborodov 2010;Titarchuk et al 2012;Giannios 2008;Mészáros & Rees 2011;Giannios 2012); iii) magnetised ejecta Full Tables 1−4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A98 (σ = B 2 /4πΓρc 2 > 1) dissipate their energy at distances similar to those of IS (Lyutikov & Blandford 2003;Zhang & Yan 2011;Beniamini & Granot 2015).…”

Correlation between peak energy and Fourier power density spectrum slope in gamma-ray bursts

“…In the ICMART model (Zhang & Yan 2011) magnetic reconnection is a consequence of the distortion of the magnetic field lines entrained in the ejecta and triggered by IS (see Kagan et al 2015 for a recent review on relativistic magnetic reconnection). For models ii), energy dissipation takes place at or below the photosphere, either for baryonicdominated outflows (Rees & Mészáros 2005;Pe'er et al 2006; Thompson et al 2007;Derishev et al 1999;Rossi et al 2006;Beloborodov 2010;Titarchuk et al 2012), or for magnetically dominated outflows (Giannios 2008;Mészáros & Rees 2011;Giannios 2012). See Zhang (2014), Pe'er (2015) and Granot et al (2015) for recent reviews of the different models of prompt emission.…”