On the multiwavelength emission from gamma ray burst afterglows

Abstract

Aims. Drawing an analogy with active galactic nuclei, we investigate the one-zone synchrotron self-compton (SSC) model of gamma ray bursts (GRB) afterglows in the presence of electron injection and cooling both by synchrotron and SSC losses. Methods. We solve the spatially averaged kinetic equations which describe the simultaneous evolution of particles and photons, obtaining the multi-wavelength spectrum as a function of time. We back up our numerical calculations with analytical solutions of the equations using various profiles of the magnetic field evolution under certain simplifying assumptions. Results. We apply the model to the afterglow evolution of GRBs in a uniform density environment and examine the impact various parameters have on the multiwavelength spectra. We find that in cases where the electron injection and/or the ambient density is high, the losses are dominated by SSC and the solutions depart significantly from the ones derived in the synchrotron standard cases.

Temporal Evolution of the Gamma-ray Burst Afterglow Spectrum for an Observer: GeV–TeV Synchrotron Self-Compton Light Curve

“…The numerical results show curved spectra rather than the broken-power-law. Those curved features are similar to the time-dependent calculations in Petropoulou & Mastichiadis (2009, see also Pennanen et al (2014; Uhm & Zhang (2014)). The analytic broken-power-law formula roughly reproduces the overall spectral shape.…”

“…Our numerical code is based on the one-zone approximation, but the time-dependent treatment is completely applied for the bulk motion of the shell and the electron and photon energy distributions. Our method is similar to that in the previous studies (Petropoulou & Mastichiadis 2009;Pennanen et al 2014;Uhm & Zhang 2014), but the light curves were not calculated in their studies. Our code consistently transforms the energy and arrival time of photons that escaped from the shocked shell into those for an observer.…”

Blazar flares powered by plasmoids in relativistic reconnection

“…The operators L denote particle energy losses and/or sinks of particles, while the operators Q denote terms of energy and/or particle injection. The physical processes which are included in the aforementioned equations are: (i) electron synchrotron radiation ("syn") and synchrotron self-absorption ("ssa"); (ii) inverse Compton scattering ("ics"); (iii) photon-photon pair production ("γγ") and (iv) adiabatic losses ("ad"), which become relevant only in Phase II; in the first phase the plasmoid size increases due to the accumulation of fresh particles rather than the work done by the particles themselves (for more details, see Petropoulou & Mastichiadis (2009)). The particle injection rate in Phase I is benchmarked with PIC simulations and is modelled as Q (inj) e,I ∝ w 2 .…”

Effects of the upper cutoff of the electron distribution on the light curves of GRB afterglows

“…[12] for a review) where electrons are being accelerated and radiate their energy in the Relativistic Blast Wave (RBW) formed by the initial explosion. By solving numerically the kinetic equations of electrons and photons which form a system of two coupled partial differential equations we can calculate self consistently the time evolution of the electron distribution and photon spectra taking into account both synchrotron and SSC losses [7,13]. In cases where electrons are injected with a power-law distribution between two cutoffs, γ min and γ max , with the upper cutoff being not much greater than the lower one, the obtained X-ray light curves show in general (i) an early-time fast decaying power law segment which is then followed by (ii) a 'plateau'-like and then by (iii) a late-time decaying power law segment.…”

“…Figure 2: Different light curve morphologies obtained using the numerical code described in [13] for different values of γ max and ε e . Light curves from each panel can be tentatively compared to the corresponding ones of Fig.…”