Beaming, Baryon Loading, and the Synchrotron Self‐Compton Component in Gamma‐Ray Bursts

Abstract

We present detailed calculations of nonthermal synchrotron and synchrotron self-Compton (SSC) spectra radiated by blast waves that are energized by interactions with a uniform surrounding medium. Radio, optical, X-ray and gamma-ray light curves and spectral indices are calculated for a standard parameter set that yields hard GRB spectra during the prompt emission phase. Because no lateral spreading of the blast-wave is assumed, the calculated temporal breaks represent the sharpest breaks possible from collimated outflows in a uniform surrounding medium. Absence of SSC hardenings in observed GRB X-ray afterglows indicates magnetic field generation toward equipartition as the blast wave evolves. EGRET detections of 100 MeV-GeV photons observed promptly and 90 minutes after GRB 940217 are attributed to nonthermal synchrotron radiation and SSC emission from a decelerating blast wave, respectively. The SSC process will produce prompt TeV emission that could be observed from GRBs with redshifts z < ∼ 0.1, provided γ-γ opacity in the source is small. Measurements of the time dependence of the 100 MeV-GeV spectral indices with the planned GLAST mission will chart the evolution of the SSC component and test the external shock scenario. Transient optical and X-ray emissions from misaligned GRBs are generally much weaker than on-axis emissions produced by dirty and clean fireballs that would themselves not trigger a GRB detector; thus detection of long wavelength transients not associated with GRBs will not unambiguously demonstrate GRB beaming.

Neutrino, Neutron, and Cosmic‐Ray Production in the External Shock Model of Gamma‐Ray Bursts

“…The major difference between the fits derived to GRB spectra during the prompt and afterglow phases is thus the stronger value of field at later times. Other arguments that the magnetic field evolves to its equipartition value following the prompt phase are given by Dermer et al (2000b). As can be seen from Figure 1, the relative timescales for photomeson production in the external shock model usually dominate the other processes and approach or exceed unity for the highest energy protons during the afterglow phase.…”

“…Other than E 0 and p, Figure 1a employs the parameter set in Figure 1 of Dermer, Chiang, & Mitman (2000b), which was shown to give good fits to burst spectra during the gamma-ray luminous phase of GRBs (Chiang & Dermer 1999; there we used E 0 ¼ 10 54 ergs and p ¼ 2:5). The remaining parameters used in Figure 1a are À 0 ¼ 300, n 0 ¼ 100 cm À3 , e B ¼ 10 À4 , and e e ¼ 0:5.…”

JITTER SELF-COMPTON PROCESS: GeV EMISSION OF GRB 100728A

“…In general, the photons produced by synchrotron radiation can be scattered by the relativistic electrons. Therefore, an inverse Compton process or synchrotron self-Compton (SSC) process is proposed naturally to explain the GRB emission above the GeV band (Mészáros et al 1993;Dermer et al 2000;Wang et al 2001;Zhang & Mészáros 2001;Granot & Guetta 2003;Fan et al 2008;Zou et al 2009;Corsi et al 2010). In particular, the possibility was suggested that the photons from X-ray flares can be scattered to the GeV band by those relativistic electrons (Wang et al 2006;Galli & Guetta 2008).…”

Muon enhancements at sea level in association with Swift-BAT and MILAGRO triggers

“…The Tupi experiment is in the process of expansion, and within the next six months we are able to increase the number of telescopes to fourteen, increasing in 85% the field of view of the Tupi experiment. Our objective is to take advantage of our location inside the anomaly to detect gamma ray burst in the range of GeV to TeV, because there are theoretical models that predict GRBs in this energy region [15][16][17], with strong astrophysical implications. Naturally, we will continue to study solar transient phenomena, and monitoring the precipitation of particles.…”