Origin Of Gamma-ray Bursts Research Articles

Gamma-ray bursts as standard candles to constrain the cosmological parameters

Gamma-ray bursts (GRBs) are among the most powerful sources in the Universe: they emit up to 1054 erg in the hard x-ray band in a few tens of seconds. The cosmological origin of GRBs has been confirmed by several spectroscopic measurements of their redshifts, distributed in the range z∊(0.1,6.3). These two properties make GRBs very appealing for investigating the far Universe. Indeed, they can be used to constrain the geometry of the present-day Universe and the nature and evolution of dark energy by testing the cosmological models in a redshift range hardly achievable by other cosmological probes. Moreover, the use of GRBs as cosmological tools could unveil the ionization history of the Universe, the inter-galactic medium (IGM) properties and the formation of massive stars in the early Universe. The energetics implied by the observed fluences and redshifts span at least four orders of magnitudes. Therefore, at first sight, GRBs are all but standard candles. But there are correlations among some observed quantities which allow us to know the total energy or the peak luminosity emitted by a specific burst with a great accuracy. Through these correlations, GRBs become ‘known’ candles, and then a new tool to constrain the cosmological parameters. One of these correlation is between the rest frame peak spectral energy Epeak and the total energy emitted in γ-rays Eγ, properly corrected for the collimation factor. Another correlation, discovered very recently, relates the total GRB luminosity Liso, its peak spectral energy Epeak and a characteristic timescale T0.45, related to the variability of the prompt emission. This last correlation is based only on prompt emission properties, it is completely phenomenological, model independent and assumption-free. These correlations have been already used to constrain ΩM and ΩΛ, which are found to be consistent with the concordance model. The present limited sample of bursts and the lack of low redshift events, necessary to calibrate the correlations used to standardize GRBs energetics, make the cosmological constraints obtained with GRBs still large compared to those obtained with other cosmological probes (e.g. SNIa or CMB). However, the newly born field of GRB-cosmology is very promising for the future.

Relativistic magnetohydrodynamics in dynamical spacetimes: Numerical methods and tests

Many problems at the forefront of theoretical astrophysics require the treatment of magnetized fluids in dynamical, strongly curved spacetimes. Such problems include the origin of gamma-ray bursts, magnetic braking of differential rotation in nascent neutron stars arising from stellar core collapse or binary neutron star merger, the formation of jets and magnetized disks around newborn black holes, etc. To model these phenomena, all of which involve both general relativity (GR) and magnetohydrodynamics (MHD), we have developed a GRMHD code capable of evolving MHD fluids in dynamical spacetimes. Our code solves the Einstein-Maxwell-MHD system of coupled equations in axisymmetry and in full $3+1$ dimensions. We evolve the metric by integrating the Baumgarte-Shapiro-Shibata-Nakamura equations, and use a conservative, shock-capturing scheme to evolve the MHD equations. Our code gives accurate results in standard MHD code-test problems, including magnetized shocks and magnetized Bondi flow. To test our code's ability to evolve the MHD equations in a dynamical spacetime, we study the perturbations of a homogeneous, magnetized fluid excited by a gravitational plane wave, and we find good agreement between the analytic and numerical solutions.

The effect of neutrinos on the initial fireballs in gamma-ray bursts

We investigate the fate of very compact, sudden energy depositions that may lie at the origin of gamma-ray bursts. Following on from the work of Cavallo and Rees (1978), we take account of the much higher energies now believed to be involved. The main effect of this is that thermal neutrinos are present and energetically important. We show that these may provide sufficient cooling to tap most of the explosion energy. However, at the extreme energies usually invoked for gamma-ray bursts, the neutrino opacity suffices to prevent dramatic losses, provided that the heating process is sufficiently fast. In a generic case, a few tens of percent of the initial fireball energy will escape as an isotropic millisecond burst of thermal neutrinos with a temperature of about 60 MeV, which is detectable for nearby gamma-ray bursts and hypernovae. For parameters we find most likely for gamma-ray burst fireballs, the dominant processes are purely leptonic, and thus the baryon loading of the fireball does not affect our conclusions.

TheSwiftGamma‐Ray Burst Mission

The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr � 1 and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to (1) determine the origin of GRBs, (2) classify GRBs and search for new types, (3) study the interaction of the ultrarelativistic outflows of GRBs with their surrounding medium, and (4) use GRBs to study the early universe out to z >10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a newgeneration wide-field gamma-ray (15‐150 keV) detector that will detect bursts, calculate 1 0 ‐4 0 positions, and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5 00 positions and perform spectroscopy in the 0.2‐10 keV band; and a narrow-field UV/optical telescope that will operate in the 170‐ 600 nm band and provide 0B3 positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of � 1m crab (� 2;10 � 11 ergs cm � 2 s � 1 in the 15‐150 keV band), more than an order of magnitude better than HEAO 1 A-4. A flexible data and operations system will allow rapid follow-up observations of all types of

Testing Lorentz Invariance with GRB 021206

Since the discovery of the cosmological origin of gamma-ray bursts (GRBs), there has been growing interest in using these transient events to probe the quantum gravity energy scale in the range 1016-1019 GeV, up to the Planck mass scale. This energy scale can manifest itself through a measurable modification in the electromagnetic radiation dispersion relation for high-energy photons originating from cosmological distances. We have used data from the GRB of 2002 December 6 (GRB 021206) to place an upper bound on the energy dispersion of the speed of light. The limit on the first-order quantum gravity effects derived from this single GRB indicates that the energy scale is in excess of 1.8 × 1017 GeV. We discuss a program to further constrain the energy scale by systematically studying such GRBs.

Galactic and extragalactic Fast X-ray Transient sources

Abstract Fast X-ray Transients (FXTs) have long been an enigma in x-ray astronomy. These non-recurrent and bright x-ray sources, lasting up to a day and without quiescent x-ray emission, have been studied with the Wide Field Cameras (WFCs) during the 6 years of operational life of BeppoSAX. They were among the prime motivations for building the instrument. The WFC observations allow for the determination of duration, lightcurves and spectra, while the positional information is sufficiently good to search for counterparts. The results show the heterogeneous nature of FXTs. If we exclude the x-ray counterparts of Gamma Ray Bursts, at least two types can be distinguished, both seen at high galactic latitude with a spatial distribution consistent with isotropy. A galactic population of FXTs has a typical duration of an hour and is associated with stellar sources exhibiting coronal activity. An extragalactic population of FXTs, called X-ray Flashes, has a duration of order minutes. They are explosive events whose origin has most likely a connection with the origin of Gamma Ray Bursts. Recently the first spectroscopic distance determination from the optical afterglow of an X-ray Flash has been found at z=0.25. These results, together with recent developments in GRBs, indicate a two component cosmic explosion in which the prompt ultra-relativistic γ-ray energy can be minor, whereas the total energy release of the explosion is similar in XRFs and GRBs.

Monitoring and detecting X-ray transients with the Swift Observatory

Abstract Swift is a multi-wavelength observatory specifically designed to detect transient sources in the γ-ray energy band 15-200 keV. The primary goals of the mission involve gamma ray burst (GRB) astronomy, namely to determine the origin of GRBs and their afterglows, and use bursts to probe the early Universe. However, Swift will also discover new X-ray transient sources, and it will be possible to bring Swift's considerable multi-wavelength capabilities to bear on these sources, and those discovered by other means. The Burst Alert Telescope (BAT) is a coded mask instrument sensitive to 15-200 keV γ-rays, and has a field of view which covers approximately 1/8th of the sky in a single pointing. Over a typical observing day, almost the entire sky will be observed and monitored for new transient sources. Sources will be detected within several hours of observation. The two narrow field instruments, the X-ray Telescope and Ultra-Violet Optical Telescope, can provide sensitive simultaneous imaging and spectroscopy observations in the optical through soft X-ray bands.

Astronomy. Long gamma-ray bursts.

Gamma-ray bursts (GRBs) are the most luminous events in our universe. In his Perspective, MacFadyen discusses the likely origin of long-duration GRBs. Recent observations show that they are associated with the death of massive stars, as suggested by earlier observations and theoretical arguments. Supernova 2003dh coincided with GRB030329, confirming this picture. In a related Perspective, Rosswog discusses short-duration GRBs, which may be caused by a different mechanism involving the merger of two neutron stars or of a neutron star and a low-mass black hole.

X-ray spectroscopy of Gamma-Ray Bursts

In this review we briefly summarize the recent developments in the research on Gamma-Ray Bursts (GRB), and discuss in more detail the recent results derived from X-ray spectroscopy, in particular the detection of X-ray narrow features and their implication on our understanding on the origin of GRB. Finally, we outline the importance of high-resolution spectroscopy in X-rays, which can provide new clues on the nature of progenitors, and a powerful probe of the early universe and primordial galaxy formation.

A Dynamical Unification Scheme from General Conservation Laws

The aim of this work is to present an unification scheme of fundamental interactions based on a well defined dynamics, the non-introduction of ad hoc hypotheses and the consideration of the minimal necessary number of free parameters and dimensions. A dynamical unification scheme of fundamental interactions can be achieved assuming a 5D space where conservation laws are always and absolutely valid, i.e. never violated. This approach gives rise to an induced-matter theory in the usual 4D space-time through a process of embedding and dimensional reduction by which masses, spins and charges of particles naturally spring out, and also the the hierarchy problem can be successfully faced thanks to the mass spectrum. The emergence of asymptotic freedom also for gravitational interaction, the existence of two time arrows together with the possibility of closed time-like paths are intrinsic results of such a theory, leading to a recovering of the causality principle and to a formal, dynamical explanation of several paradoxes and questioning problems of modern physics e.g. entanglement of EPR-type quantum states, quantum teleportation, gamma ray bursts origin, black hole singularities and cosmic primary antimatter absence.

Supernova hosts for gamma-ray burst jets: dynamical constraints

I constrain a possible supernova origin for gamma-ray bursts (GRBs) by modelling the dynamical interaction between a relativistic jet and a stellar envelope surrounding it. The delay in observer time introduced by the jet traversing the envelope should not be long compared with the duration of gamma-ray emission; also, the jet should not be swallowed by the spherical explosion it powers. The only stellar progenitors that comfortably satisfy these constraints, if one assumes that jets move ballistically within their host stars, are compact carbon–oxygen or helium post-Wolf–Rayet stars (type Ic or Ib supernovae); type II supernovae are ruled out. Notably, very massive stars do not appear to be capable of producing the observed bursts at any redshift unless the stellar envelope is stripped prior to collapse. The presence of a dense stellar wind places an upper limit on the Lorentz factor of the jet in the internal shock model; however, this constraint may be evaded if the wind is swept forward by a photon precursor. Shock breakout and cocoon blowout are considered individually; neither presents a likely source of precursors for cosmological GRBs. These envelope constraints could conceivably be circumvented if jets are laterally pressure-confined while traversing the outer stellar envelope. If so, jets responsible for observed GRBs must have been launched from a region several hundred kilometres wide, have been crossed by strong shocks, or have mixed with envelope material as they travel. A phase of pressure confinement and mixing would imprint correlations among jets that may explain observed GRB variability–luminosity and lag–luminosity correlations.

Observing scattered X-ray radiation from gamma-ray bursts: A way to measure their collimation angles

There are observational facts and theoretical arguments for an origin of gamma-ray bursts (GRBs) in molecular clouds in distant galaxies. If this is true, one could detect a significant flux of GRB prompt and early afterglow X-ray radiation scattered into our line of sight by the molecular and atomic matter located within tens of parsecs of the GRB site long after the afterglow has faded away. The scattered flux directly measures the typical density of the GRB ambient medium. Furthemore, if the primary emission is beamed, the scattered X-ray flux will be slowly decreasing for several months to years before falling off rapidly. Therefore, it should be possible to estimate the collimation angle of a burst from the light curve of its X-ray echo and a measured value of the line-of-sight absorption column depth. It is shown that detection of such an echo is for the brightest GRBs just within the reach of the Chandra and XMM-Newton observatories.

Gamma-ray bursts: the most powerful cosmic explosions

With the detection of gamma-ray burst (GRB) afterglows, the cosmological origin of GRBs has been firmly established. Recent observations suggest that (long-duration) GRBs are due to the collapse of a massive star forming a black hole. Besides theoretical arguments, observational evidence supporting this hypothesis comes from the coincidence of several GRBs with a supernova. Also, all accurately located GRBs are contained in the optical (restframe UV) extent of distant, blue galaxies. Some of these host galaxies show relatively high star-formation rates, which is expected when massive stars and GRBs are physically linked. Alternatively, GRBs can be produced by the merging of a binary neutron star system, such as the Hulse-Taylor binary pulsar. Very likely GRBs trace the massive-star populations in distant galaxies. With their enormous brightness, GRBs are powerful probes of the early universe, providing information on the properties of their host galaxies, the cosmic star-formation history, and potentially the first generations of massive stars.

Cosmic Headlights and the Origin of Gamma Ray Bursts

Cosmic Headlights and the Origin of Gamma Ray Bursts

Cosmic Headlights and the Origin of Gamma Ray Bursts

Cosmic Headlights and the Origin of Gamma Ray Bursts

GAMMA-RAY BURSTS FROM GRAVITATIONAL COLLAPSE

A possible origin of gamma-ray bursts is the gravitational collapse of compact objects. A semiclassical analysis, which employs the Born-Oppenheimer approximation in order to treat gravity as classical while matter is quantized1, was first applied to homogeneous spheres of dust2,3 and (thick) non-radiating shells 4. We later derived an effective Lagrangian for (thin) radiating shells5 which allowed us to study the evolution of a self-gravitating shell of bosonic matter coupled to a scalar radiation field. We showed that the matter can form a condensate and the matter degrees of freedom are excited, because of the non-adiabaticity of the collapse, at the expense of gravitational energy4,6. Upon decaying back to the ground state, the excited matter energy is subsequently transferred to the radiation field. In fact, the system can convert large fractions of its gravitational energy into radiation and the time evolution of the radius of the shell is then significantly slowed down with respect to the non-radiating case. This provides a new mechanism to extract energy from collapsing matter which might play a role as a source of gamma-ray bursts.

Discovery of a Black Hole Mass‐Period Correlation in Soft X‐Ray Transients and Its Implication for Gamma‐Ray Burst and Hypernova Mechanisms

We investigate the soft X-ray transients with black hole primaries, which may have been the sources of gamma-ray bursts (GRBs) and hypernovae earlier in their evolution. For systems with evolved donors, we are able to reconstruct the pre-explosion periods and find that the black hole mass increases with the orbital period of the binary. This correlation can be understood in terms of angular momentum support in the helium star progenitor of the black hole, if the systems with shorter periods had more rapidly rotating primaries prior to their explosion; centrifugal support will then prevent more of its mass from collapsing into the black hole on a dynamical time. This trend of more rapidly rotating stars in closer binaries is usual in close binaries and in the present case can be understood in terms of spin-up during spiral-in and subsequent tidal coupling. We investigate the relation quantitatively and obtain reasonable agreement with the observed mass-period correlation. An important ingredient is the fact that the rapidly rotating new black hole powers both a GRB and the hypernova explosion of the remaining envelope, so that the material initially prevented from falling into the black hole will be expelled rather than accreted. For systems in which the donor is now and will remain in main sequence, we cannot reconstruct the pre-explosion period in detail, because some of their history has been erased by angular momentum loss through magnetic braking and gravitational waves. We can, however, show that their periods at the time of black hole formation were most likely 0.4-0.7 days, somewhat greater than their present periods. Furthermore, their black holes would have been expected to accrete ~1 M? of material from the donor during their previous evolution. Comparison with predictions suggests that little mass will be lost in the explosion for the relatively high pre-explosion periods of these binaries. A natural consequence of the He star rotation is that black holes formed in the shorter period (before explosion) soft X-ray transients acquire significant Kerr parameters. This makes them good sources of power for GRBs and hypernovae, via the Blandford-Znajek mechanism, and thus supports our model for the origin of GRBs in soft X-ray transients.

The Birthplace of Gamma-Ray Bursts: Abundance Gradients and Constraints on Progenitors

The physics of gamma-ray bursts (GRBs) and their offsets from the centers of their host galaxies are used to investigate the evolutionary state of their progenitors, motivated by the popular idea that GRBs are linked with the cataclysmic collapse of massive stars. We suggest that GRB progenitors in the inner and outer regions of hosts may be intrinsically different: outer bursts appear to have systematically greater isotropic equivalent energies (or narrower jets). This may provide an interesting clue to the nature of GRBs and may reflect a relation between metallicity and the evolution of GRB progenitors. If true, this offset-isotropic luminosity correlation is a strong argument for a collapsar origin of long-duration GRBs.

Evidence for a molecular cloud origin of gamma-ray bursts: Implications for the nature of star formation in the universe

Evidence for a molecular cloud origin of gamma-ray bursts: Implications for the nature of star formation in the universe

Relative Spacetime Transformations in Gamma-Ray Bursts

GRB 991216 and its relevant data acquired from the BATSE and the Rossi X-Ray Timing Explorer and Chandra satellites are used as a prototypical case to test the theory linking the origin of gamma-ray bursts (GRBs) to the process of vacuum polarization occurring during the formation phase of a black hole endowed with electromagnetic structure. The relative spacetime transformation paradigm is presented. It relates the observed signals of GRBs to their past light cones, defining the events on the worldline of the source that is essential for the interpretation of the data. Since GRBs present regimes with unprecedentedly large Lorentz factors, and also sharply varying with time, particular attention is given to the constitutive equations relating the four time variables: the comoving time, the laboratory time, the arrival time, and the arrival time at the detector corrected by the cosmological effects. This paradigm is at the very foundation of any possible interpretation of the data of GRBs.