Neutron stars and the distance to gamma-ray bursters

Abstract

Assuming that gamma-ray bursts originate from galactic neutron stars, we outline an analytic method for studying their statistical properties. If a significant fraction of all neutron stars are born with space velocities ^ 100 km s _1 , as suggested by studies of pulsar statistics, then the sampling distance to gamma-ray burst sources should be less than ~ several hundred pc. These results have important implications on theories of radio pulsar evolution and magnetic-field decay.

Nonthermal Synchrotron Radiation from Gamma‐Ray Burst External Shocks and the X‐Ray Flares Observed withSwift

“…Simulations of GRB Light Curves Fig. 11 shows Monte Carlo simulations, described in more detail in Dermer & Mitman (2004), of GRB light curves under the assumption that the cold blast wave shell remains thin and the interaction forms a strong forward shock. The parameters of the simulation are shown in Table 2, and here we use fixed cloud sizes with radius r 1 that are "uniformly randomly" distributed in the volume between R 1 and R 2 .…”

“…argued that highly variable light curves cannot be constructed from blast-wave interactions with surrounding density inhomogeneities by superposing pulses made near the outer region of the Doppler cone to show how they overlap due to the large angular timescales; hence the sources of GRBs must require an active central engine to make discrete pulses. Dermer & Mitman (2004) showed that this argument, made also more recently by Piran (2005) and Ioka et al (2005), mistakenly uses the angular time scale near the outer edge of the Doppler cone, and misses a number of important points: One is that the beaming factors, not considered in these papers, heavily weight the total fluence for near on-axis clouds, and even more so the pulse peak flux because of the smaller kinematic variability timescale for nearly on-axis clouds; another is the different (observer) times for the clouds nearly on-axis as compared with those off-axis, so that flux ratios from different parts of the shell are time-dependent; a third is the assumption that clouds are distributed with azimuthal symmetry within the Doppler cone; a fourth is that the beaming factor of the relativistic jet that forms γ-ray pulses in the prompt phase may be smaller than ∼ Γ −1 0 and the typical angles inferred from optical afterglow breaks, which will reduce the importance of offaxis events. The crucial role of the narrow cold blastwave fluid shell (not the shocked fluid shell considered by Nakar & Granot (2007)) to ensure a strong forward shock has also been overlooked in past studies.…”

“…As shown in the simulations, STV in the external shock model with moderate (∼ 10%) efficiency is possible if the blast wave interacts with clouds with thick columns and sizes ∆ cl ≪ x/Γ 0 , because then the condition of "local spherical symmetry" (Fenimore et al 1996) is broken. The shortest pulses carrying a significant fraction of the total fluence are made by interactions of the blast wave with small clouds at angles θ ≪ 1/Γ 0 to the observer line-of-sight (Dermer & Mitman 2004). Efficiency concerns are reduced if the fraction of energy dissipated as X-rays and γ rays is a small fraction of the total (Dermer 2007).…”

The obscured universe

“…[15,16] discusses various scenarios for accelerating UHECRs with significant ion content in GRB environments, including capturing supernova shell material by a jetted relativistic wind, external shock capture of circumburst material, and hypernovae [40]. We favor the hypothesis [41] that an external shock is important during the prompt and early afterglow phases of a GRB. GRBs formed by core collapse of C or O Wolf-Rayet stellar progenitors would be surrounded by a wind enriched in these light elements that could be captured and accelerated to ultra-high energies.…”