Short-Timescale Variability in the External Shock Model of Gamma-Ray Bursts

Quilligan

et al. 2001

A&A

Abstract.A temporal analysis has been performed on a sample of 100 bright gamma-ray bursts (GRBs) with T90 < 2 s from the BATSE Current Catalog. The GRBs were denoised using a median filter and subjected to an automated pulse selection algorithm as an objective way of identifing the effects of neighbouring pulses. The rise times, fall times, F W HM, pulse amplitudes and areas were measured and the frequency distributions are presented here. All are consistent with lognormal distributions. The distribution of time intervals between pulses is not random but consistent with a lognormal distribution. The time intervals between pulses and pulse amplitudes are highly correlated with each other. These results are in excellent agreement with a similar analysis that revealed lognormal distributions for pulse properties and correlated time intervals between pulses in bright GRBs with T90 > 2 s. The two sub-classes of GRBs appear to have the same emission mechanism which is probably caused by internal shocks. They may not have the same progenitors because of the generic nature of the fireball model.

Section: Discussionsupporting

confidence: 86%

Temporal properties of the short gamma-ray bursts

Quilligan

et al. 2001

A&A

“…Radiative efficiency higher than 50% is unexpected for external shocks. Dermer & Mitman (1999), for example, find that 10% ( = E E 9 k ph ) efficiency is more consistent with this scenario. In this case, the measured fluence and the peak energy yields a Lorentz factor and external density of (4×10 −5 cm −3 , 3300).…”

Section: Efficiency Of External Shocksmentioning

confidence: 71%

“…External shocks were initially proposed (Rees & Meszaros 1992) as a model for GRB prompt emission, but had problems interpreting the strong variability of lightcurves (Kobayashi et al 1997; see however Dermer & Mitman 1999). On the other hand, it is a very successful model for interpreting the multiwavelength afterglow (Mészáros & Rees 1997;Chiang & Dermer 1999).…”

Section: External Shocksmentioning

confidence: 99%

Gravitational-Wave Observations May Constrain Gamma-Ray Burst Models: The Case of Gw150914–gbm

Vereš

Preece

Goldstein

et al. 2016

ApJL

The possible short gamma-ray burst (GRB) observed by Fermi/GBM in coincidence with the first gravitationalwave (GW) detection offers new ways to test GRB prompt emission models. GW observations provide previously inaccessible physical parameters for the black hole central engine such as its horizon radius and rotation parameter. Using a minimum jet launching radius from the Advanced LIGO measurement of GW150914, we calculate photospheric and internal shock models and find that they are marginally inconsistent with the GBM data, but cannot be definitely ruled out. Dissipative photosphere models, however, have no problem explaining the observations. Based on the peak energy and the observed flux, we find that the external shock model gives a natural explanation, suggesting a low interstellar density (∼10 −3 cm −3 ) and a high Lorentz factor (∼2000). We only speculate on the exact nature of the system producing the gamma-rays, and study the parameter space of a generic Blandford-Znajek model. If future joint observations confirm the GW-short-GRB association we can provide similar but more detailed tests for prompt emission models.

The Astrophysical Journal

“…The large-area detectors of BATSE provided excellent light curves of GRBs. Time variability in light curves expected in different models of GRBs differs significantly from one model to another (e.g., Sari & Piran 1997;Dermer & Mitman 1999;Fenimore et al 1999;Piran 1999; this Letter) and may be a clue to the nature of the GRB sources. Some properties of the light curves expected for GRBs in a magnetized rotator model are considered and compared with available data in § 3.…”

Section: Introductionmentioning

confidence: 93%

Precursors of Gamma-Ray Bursts: A Clue to the Burster’s Nature

Lyutikov¹,

Усов²

2000

In relativistic strongly magnetized winds outflowing from the fast-rotating compact progenitors of gamma-ray bursts (GRBs), there are three regions where powerful high-frequency emission may be generated: (1) the thermal photosphere, (2) the region of the internal wind instability, and (3) the region of the wind interaction with an ambient gas. This results in a multicomponent structure of GRBs. The emission from the thermal photosphere may be observed as a weak precursor to the main burst. The precursor should have a blackbody-like spectrum with the mean energy of photons of ∼1 MeV, and its intensity should be tens to hundreds of times smaller than that of the main GRB emission. Observations of such precursors with future g-ray missions like the GammaRay Large-Area Space Telescope can clarify the nature of bursters.