Observations show that at least some gamma-ray bursts (GRBs) happen simultaneously with core-collapse supernovae (SNe), thus linking by a common thread nature's two grandest explosions. We review here the growing evidence for and theoretical implications of this association, and conclude that most long-duration soft-spectrum GRBs are accompanied by massive stellar explosions (GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe appear to be greater than those of ordinary SNe, but evidence exists, even in a limited sample, for considerable diversity. The existing sample also suggests that most of the energy in the explosion is contained in nonrelativistic ejecta (producing the supernova) rather than in the relativistic jets responsible for making the burst and its afterglow. Neither all SNe, nor even all SNe of Type Ibc produce GRBs. The degree of differential rotation in the collapsing iron core of massive stars when they die may be what makes the difference.

The Supernova Gamma-Ray Burst Connection

The cosmological gamma-ray burst (GRB) phenomenon is reviewed. The broad observational facts and empirical phenomenological relations of the GRB prompt emission and afterglow are outlined. A well-tested, successful fireball shock model is introduced in a pedagogical manner. Several important uncertainties in the current understanding of the phenomenon are reviewed, and prospects of how future experiments and extensive observational and theoretical efforts may address these problems are discussed.

Gamma-Ray Bursts: Progress, Problems & Prospects

With its rapid-response capability and multiwavelength complement of instruments, the Swift satellite has transformed our physical understanding of γ-ray bursts (GRBs). Providing high-quality observations of hundreds of bursts, and facilitating a wide range of follow-up observations within seconds of each event, Swift has revealed an unforeseen richness in observed burst properties, shed light on the nature of short-duration bursts, and helped realize the promise of GRBs as probes of the processes and environments of star formation out to the earliest cosmic epochs. These advances have opened new perspectives on the nature and properties of burst central engines, interactions with the burst environment from microparsec to gigaparsec scales, and the possibilities for nonphotonic signatures. Our understanding of these extreme cosmic sources has thus advanced substantially; yet, more than 40 years after their discovery, GRBs continue to present major challenges on both observational and theoretical fronts.

/pdf/gamma-ray-bursts-in-the-swift-era-47w6h8pz18.pdf

Gamma-Ray Bursts in the Swift Era

We present a complete sample of 29 gamma-ray bursts (GRBs) for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically corrected gamma-ray energies about 133 x 10(exp 51) ergs; the burst-to-burst variance about this value is 035 dex, a factor of 22 Despite this rather small scatter, we demonstrate in a series of GRB Hubble diagrams that the current sample cannot place meaningful constraints upon the fundamental parameters of the universe Indeed, for GRBs to ever be useful in cosmographic measurements, we argue the necessity of two directions First, GRB Hubble diagrams should be based upon fundamental physical quantities such as energy, rather than empirically derived and physically ill-understood distance indicators (such as those based upon prompt burst time-profiles and spectra) Second, a more homogeneous set should be constructed by culling subclasses from the larger sample These subclasses, although now first recognizable by deviant energies, ultimately must be identifiable by properties other than those directly related to energy We identify a new subclass of GRBs (" f-GRBs ") that appear both underluminous by factors of at least 10 and exhibit a rapid fading (f(sub nu is proportional to t(sup -2) at early times (t < or = 05 day) About 10%-20% of observed long-duration bursts appear to be f-GRBs

Gamma-Ray Burst Energetics and the Gamma-Ray Burst Hubble Diagram: Promises and Limitations

The gamma-ray burst (GRB) 050904 at z =6 .3 provides the first opportunity to probe the intergalactic medium (IGM) by GRBs at the epoch of reionization. Here, we present a spectral modeling analysis of the optical afterglow spectrum taken by the Subaru Telescope, aiming to constrain the reionization history. The spectrum shows a clear damping wing at wavelengths redward of the Lyman break, and the wing shape can be fitted either by a damped Lyα system with a column density of log[NHI(cm −2 )] ∼ 21.6 at a redshift close to the detected metal absorption lines (zmetal =6 .295), or by almost neutral IGM extending to a slightly higher redshift of zIGM,u ∼ 6.36. In the latter case, the difference between the two redshifts may be explained by the acceleration of metal absorbing shells in the activities of the GRB or its progenitor. However, we exclude this possibility by using the light transmission feature around the Lyβ resonance, leading to a firm upper limit of zIGM,u ≤ 6.314. We then show evidence that the IGM was already largely ionized at z =6 .3 with the best-fit neutral fraction of IGM, xHI (≡ nHI/nH )=0 .00, and upper limits of xHI 6. Various systematic uncertainties are examined, but none of them appears large enough to change our conclusion. To get further information on the reionization, it is important to increase the sample size of z 6 GRBs, in order to find GRBs with low column densities (log NHI 20) within their host galaxies and to make statistical studies of Lyα line emission from host galaxies.

Implications for Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z = 6.3

We present spectra of the optical transient of GRB 021004 obtained with the Hobby-Eberly Telescope starting 15.48 hr, 20.31 hr, and 4.84 days after the ?-ray burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hr after the ?-ray burst. GRB 021004 is the first burst afterglow for which the spectrum is dominated by absorption lines from high-ionization species with multiple velocity components separated by up to 3000 km s-1. We argue that these absorption lines are likely to come from shells around a massive progenitor star. The high velocities and high ionizations arise from a combination of acceleration and flash ionization by the burst photons and the wind velocity and steady ionization by the progenitor. We also analyze the broadband spectrum and the light curve so as to distinguish the structure of gas within 0.3 pc of the burster. We delineate six components in the medium surrounding the ?-ray burst along the line of sight: (1) The z 2.293 absorption lines arise from the innermost region closest to the burst, where the ionization will be highest and the 3000 km s-1 velocity comes from the intrinsic velocity of a massive star wind boosted by acceleration from the burst flux. For a mass-loss rate of ~ 6 ? 10-5 M? yr-1, this component also provides the external medium with which the jet collides over radial distances 0.004-0.3 pc to create the afterglow light. (2) A second cloud or shell produces absorption lines with a relative velocity of 560 km s-1. This component could be associated with the shell created by the fast massive star wind blowing a bubble in the preceding slow wind at a radial distance on the order of 10 pc or by a clump at ~0.5 pc accelerated by the burst. (3) More distant clouds within the host galaxy that lie between 30 and 2500 pc and have been ionized by the burst will create the z 2.33 absorption lines. (4-6) If the three bumps in the afterglow light curve at 0.14, 1.1, and 4.0 days are caused by clumps or shells in the massive star wind along the line of sight, then the radii and overdensities of these are 0.022, 0.063, and 0.12 pc and 50%, 10%, and 10%, respectively. The immediate progenitor of the ?-ray burst could be either a WC-type Wolf-Rayet star with a high-velocity wind or a highly evolved massive star the original mass of which was too small for it to become a WN-type Wolf-Rayet star. In summary, the highly ionized lines with high relative velocities most likely come from shells or clumps of material close to the progenitor, and these shells were plausibly produced by a massive star soon before its collapse.

GRB 021004: A Massive Progenitor Star Surrounded by Shells

We present spectra of the optical transient of GRB021004 obtained with the Hobby-Eberly telescope starting 15.48, 20.31 hours, and 4.84 days after the burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hours after the burst. GRB021004 is the first afterglow whose spectrum is dominated by absorption lines from high ionization species with multiple velocity components separated by up to 3000 km/s. We argue that these lines are likely to come from shells around a massive progenitor star. The high velocities and high ionizations arise from a combination of acceleration and flash-ionization by the burst photons and the wind velocity and steady ionization by the progenitor. We also analyze the broad-band spectrum and the light curve. We distinguish six components along the line of sight: (1) The z~2.293 absorption lines arise from the wind of a massive star. For a mass loss rate of ~6 x 10^{-5} solar masses per year, this component also provides the external medium to create the afterglow light. (2) A second shell produces absorption lines with a relative velocity of 560 km/s, and this is associated with the shell created by the fast massive star wind blowing a bubble in the preceding slow wind at a radial distance of order 10 pc. (3) More distant clouds within the host galaxy lie between 30-2500 pc, where they have been ionized by the burst. (4-6) The massive star wind has clumps with radii and over-densities of 0.022, 0.063, and 0.12 parsecs and 50%, 10%, and 10% respectively. The immediate progenitor of the burster could either be a WC-type Wolf-Rayet star or a highly evolved star whose original mass was just too small for it to become a WN-type Wolf-Rayet star.

https://arxiv.org/pdf/astro-ph/0211189.pdf

J. Mader

Papers

GRB 021004: A Massive Progenitor Star Surrounded by Shells

GRB 021004: a Massive Progenitor Star Surrounded by Shells