Gamma-ray bursts are the most luminous explosions in the Universe, and their origin and mechanism are the focus of intense research and debate. More than three decades after their discovery, and after pioneering breakthroughs from space and ground experiments, their study is entering a new phase with the recently launched Swift satellite. The interplay between these observations and theoretical models of the prompt gamma-ray burst and its afterglow is reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/69/8/R01/pdf

Gamma-ray bursts

The physics of gamma-ray bursts & relativistic jets

We provide a comprehensive review of major developments in our understanding of gamma-ray bursts, with particular focus on the discoveries made within the last fifteen years when their true nature was uncovered. We describe the observational properties of photons from the radio to multi-GeV bands, both in the prompt emission and the afterglow phases. Mechanisms for the generation of these photons in GRBs are discussed and confronted with observations to shed light on the physical properties of these explosions, their progenitor stars and the surrounding medium. After presenting observational evidence that a powerful, collimated, jet moving at close to the speed of light is produced in these explosions, we describe our current understanding regarding the generation, acceleration, and dissipation of the jet and compare these properties with jets associated with AGNs and pulsars. We discuss mounting observational evidence that long duration GRBs are produced when massive stars die, and that at least some short duration bursts are associated with old, roughly solar mass, compact stars. The question of whether a black-hole or a strongly magnetized, rapidly rotating neutron star is produced in these explosions is also discussed. We provide a brief summary of what we have learned about relativistic collisionless shocks and particle acceleration from GRB afterglow studies, and discuss the current understanding of radiation mechanism during the prompt emission phase. We discuss theoretical predictions of possible high-energy neutrino emission from GRBs and the current observational constraints. Finally, we discuss how these explosions may be used to study cosmology, e.g. star formation, metal enrichment, reionization history, as well as the formation of first stars and galaxies in the universe.

/pdf/the-physics-of-gamma-ray-bursts-and-relativistic-jets-571z4a98ye.pdf

The Physics of Gamma-Ray Bursts and Relativistic Jets

Since the successful launch of NASA's dedicated gamma-ray burst (GRB) mission, Swift, the study of cosmological GRBs has entered a new era. Here I review the rapid observational and theoretical progress in this dynamical research field during the first two-year of the Swift mission, focusing on how observational breakthroughs have revolutionized our understanding of the physical origins of GRBs. Besides summarizing how Swift helps to solve some pre-Swift mysteries, I also list some outstanding problems raised by the Swift observations. An outlook of GRB science in the future, especially in the GLAST era, is briefly discussed.

http://www.physics.unlv.edu/~bzhang/zhang07-ChJAA.pdf

Gamma-Ray Bursts in the Swift Era

The correlation between the cosmological rest-frame vF v spectrum peak energy, E p,i , and the isotropic-equivalent radiated energy, E iso , discovered by Amati et al. in 2002 and confirmed/extended by subsequent osbervations, is one of the most intriguing and debated observational evidences in gamma-ray burst (GRB) astrophysics. In this paper, I provide an update and a re-analysis of the E p,i -E iso correlation basing on an updated sample consisting of 41 long GRBs/X-ray flashes (XRFs) with firm estimates of z and observed peak energy, E p,obs , 12 GRB s with uncertain values of z and/or E p,obs , two short GRBs with firm estimates of z and E p,obs and the peculiar subenergetic events GRB 980425/SN1998bw and GRB 031203/SN20031w. In addition to standard correlation analysis and power-law fitting, the data analysis here reported includes modelling that accounts for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift events with published spectral parameters and fluences, have E p,i and E iso values, or upper/lower limits, consistent with the correlation, which shows a chance probability as low as ∼7 x 10 -15 , a slope of ∼0.57 (∼0.5 when fitting by accounting for sample variance) and an extra-Poissonian logarithmic dispersion of ∼0.15, it extends over ∼5 orders of magnitude in E iso and ∼3 orders of magnitude in E p,i and holds from the closer to the higher z GRBs. Subenergetic GRBs (980425 and possibly 031203) and short GRBs are found to be inconsistent with the E p,i -E iso correlation, showing that it can be a powerful tool for discriminating different classes of GRBs and understanding their nature and differences. I also discuss the main implications of the updated E p,i -E iso correlation for the models of the physics and geometry of GRB emission, its use as a pseudo-redshift estimator and the tests of possible selection effects with GRBs of unknown redshift.

The Ep,i–Eiso correlation in gamma-ray bursts: updated observational status, re-analysis and main implications

An E-gamma,E-jet proportional to E-p'(1.5) relationship with a small scatter for current gamma-ray burst (GRB) data was recently reported, where E-gamma,E-jet is the beaming-corrected gamma-ray energy and E'(p) is the nuF(nu) peak energy in the local observer frame. By considering this relationship for a sample of 12 GRBs with known redshift, peak energy, and break time of afterglow light curves, we constrain the mass density of the universe and the nature of dark energy. We find that the mass density Omega(M) = 0.35(-0.15)(+0.15) (at the 1 sigma confidence level) for a flat universe with a cosmological constant, and the w parameter of an assumed static dark energy equation of state w = -0.84(-0.83)(+0.57) ( 1 sigma). Our results are consistent with those from Type Ia supernovae. A larger sample established by the upcoming Swift satellite is expected to provide further constraints.

https://iopscience.iop.org/article/10.1086/424694/pdf

Constraining ΩM and Dark Energy with Gamma-Ray Bursts

By considering synchrotron radiative process in the internal shock model and assuming that all internal shocks are nearly equally energetic, we analyze the gamma-ray burst (GRB) emission at different radii corresponding to different observed times. We apply this model to GRB 050904 and find that our analytical results can provide a natural explanation for the multiband observations of GRB 050904. This suggests that the X-ray flare emission and the optical emission of this burst could have originated from internal shocks due to collisions among nearly equally energetic shells ejected from the central engine. Thus, GRB 050904 appears to be a burst with superlong central engine activity.

D. Xu

Papers

Constraining ΩM and Dark Energy with Gamma-Ray Bursts

Is GRB 050904 a Superlong Burst