Martin J. Rees's research while affiliated with University of Cambridge and other places

Publications (227)

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In light of the latest IceCube data, we discuss the implications of the cosmic ray energy input from hypernovae and supernovae into the Universe, and their propagation in the hosting galaxy and galaxy clusters or groups. The magnetic confinement in these environments may lead to efficient $pp$ collisions, resulting in a diffuse neutrino spectrum ex...
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Gamma-ray bursts are the most luminous explosions in the Universe. They appear connected to supernova remnants from massive stars or the merger of their remnants, and their brightness makes them temporarily detectable out to the larges distances yet explored in the Universe. After pioneering breakthroughs from space and ground experiments, their st...
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Magnetic fields may play a dominant role in gamma-ray bursts, and recent observations by the Fermi satellite indicate that GeV radiation, when detected, arrives delayed by seconds from the onset of the MeV component. Motivated by this, we discuss a magnetically dominated jet model where both magnetic dissipation and nuclear collisions are important...
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We discuss a model of Poynting-dominated gamma-ray bursts from the collapse of very massive first generation (pop. III) stars. From redshifts of order 20, the resulting relativistic jets would radiate in the hard X-ray range around 50 keV and above, followed after roughly a day by an external shock component peaking around a few keV. On the same ti...
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This White Paper to the National Academy of Sciences Astro2010 Decadal Review Committee outlines some of the outstanding questions regarding the assembly history of Massive Black Holes in the nuclei of galaxies and the revolutionary contributions anticipated in this field from low-frequency gravitational wave astronomy.
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We explore the qualitative changes that would occur if the amplitude Q ~ 10-5 of cosmological density fluctuations were different. If Q 10-6, the cosmological objects that form would have such low virial temperatures that they may be unable to cool and form stars, and they would be so loosely bound that even if they could produce a supernova explos...
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We consider fireball models where the ejecta have a range of bulk Lorentz factors, so that the inner (lower Γ) parts may carry most of the mass, or even most of the energy. The outer shock and contact discontinuity decelerate as the fireball sweeps up external matter. This deceleration allows slower ejecta to catch up, replenishing and reenergizing...
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In this talk I shall try to highlight some themes that seem to promise specially interesting progress in the coming decades. I can't claim to be much of a prophet myself, but I'd like to recall someone who was: Arthur C. Clarke. He lived in Sri Lanka, and died in 2007, aged 90. I'd like to discuss three issues that he would have found interesting:...
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The early stage in the formation of a galaxy inevitably involves a spatially extended distribution of infalling, cold gas. If a central luminous quasar turned on during this phase, it would result in significant extended Lyα emission, possibly accompanied by other lines. For halos condensing at redshifts 3 z 8 and having virial temperatures 2 × 105...
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Motivated by the recent detection by WMAP of a large optical depth to Thomson scattering -- implying a very early reionization epoch -- we assess a scenario where the universe was reionized by `miniquasars' powered by intermediate-mass black holes (IMBHs), the remnants of the first generation of massive stars. Pregalactic IMBHs form within minihalo...
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Subphotospheric internal shocks and transverse differences of the bulk Lorentz factor in relativistic fireball models of gamma-ray bursts (GRBs) lead to neutron diffusion relative to protons, resulting in inelastic nuclear collisions. This results in significant fluxes of νμ(μ) of ~3 GeV and νe(e) of ~2 GeV, scaling with the flow Lorentz factor η <...
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The role of a photospheric component and of pair breakdown is examined in the internal shock model of gamma-ray bursts. We discuss some of the mechanisms by which they would produce anomalously steep low-energy slopes, X-ray excesses and preferred energy breaks. Subrelativistic Comptonization should dominate in high comoving luminosity bursts with...
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We investigate the relationship between the quasi-thermal baryon-related photosphere in relativistic outflows and the internal shocks arising outside them, which out to a limiting radius may be able to create enough pairs to extend the optically thick region. Variable gamma-ray light curves are likely to arise outside this limiting pair-forming sho...
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We calculate evolution, collapse, explosion, and nucleosynthesis of Population III very massive stars with 500Msolar and 1000Msolar. It was found that both 500Msolar and 1000Msolar models enter the region of pair-instability but continue to undergo core collapse to black holes. For moderately aspherical explosions, the patterns of nucleosynthesis m...
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The recent report of X-ray Fe features in the afterglow of the gamma-ray burst GRB 991216 may provide important clues for identifying the nature of its progenitor and constraining the burst mechanism. We argue that the strong line emission can be attributed to the interaction of a continuing (but decaying) post-burst relativistic outflow from the c...
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We discuss the implications of rapid (few-minute) variability in the TeV flux of blazars, which has been observed recently with the HESS and MAGIC telescopes. The variability time-scales seen in PKS 2155−304 and Mrk 501 are much shorter than inferred light-crossing times at the black hole horizon, suggesting that the variability involves enhanced e...
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Gamma-ray bursts (GRBs) are immensely powerful explosions, originating at cosmological distances, whose outbursts persist for durations ranging from milliseconds to tens of seconds or more. In these brief moments, the explosions radiate more energy than the Sun will release in its entire 10 Gyr lifetime. Current theories attribute these phenomena t...
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A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy...
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In recent years increasing evidence has emerged for a thermal component in the gamma- and X-ray spectrum of the prompt emission phase in gamma-ray bursts. The temperature and flux of the thermal component show a characteristic break in the temporal behavior after a few seconds. We show here, that measurements of the temperature and flux of the ther...
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Supermassive black holes are nowadays believed to reside in most local galaxies. Observations have revealed us vast information on the population of local and distant black holes, but the detailed physical properties of these dark massive objects are still to be proven. Accretion of gas and black hole mergers play a fundamental role in determining...
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Quasars are interpreted as massive black holes in galactic nuclei which are fuelled by capturing gas or stars from their surroundings. This paper discusses the supply of gas, the nature of the inflow (disclike or quasispherical) and the radiation processes.
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The interpretation of strong double radio sources in terms of the "beam" model is reviewed. Implications of this model for source evolution and the nature of radio trails are briefly discussed. A final section is concerned with deductions about the properties of compact and variable components in quasars and galactic nuclei.
Chapter
A substantial magnetic field could conceivably have been generated in the ultra-early Universe. However, the relevant physics at those eras is very uncertain and no very plausible mechanism has been proposed. It seems more likely that the first significant cosmic fields, and the seed field for galactic dynamos, had to await the formation of the fir...
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Three basic questions about the physics of the early universe are briefly discussed: the origin of the entropy, the amplitude of initial fluctuations, and the overall homogeneity of the universe.
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Do the ‘special’ values of the constants of physics and cosmology need an explanation? In his book Galaxies, Nuclei and Quasars [1], Fred Hoyle wrote that ‘one must at least have a modicum of curiosity about the strange dimensionless numbers that appear in physics’. Hoyle was among the first to conjecture that the so-called ‘constants of nature’ mi...
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We have systematically investigated Galactic models for classical gammaray bursts (GRBs) in which gamma-ray bursters are ejected from the Galactic disk. It is relatively easy to construct models in which the predicted GRB sky distribution is isotropic and consistent with the present BATSE data if the outer halo is not spherically symmetric. The bur...
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We have heard a wide-ranging set of talks on cosmology and high energy astrophysics at this conference. All I can really do in this short talk is to present my subjective impression of an arbitrary selection of highlights.
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The nature of gamma-ray bursts, an enigma for more than 25 years, is now coming into focus. They involve extraordinary power outputs, and highly relativistic dynamics. The "trigger" is probably a binary merger or collapse involving stellar-mass compact objects. The most plausible progenitors, ranging from NS-NS mergers to various hypernova-like sce...
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We present an interpretation of the phenomenological relations between the spectral peak, isotropic luminosity and duration of long gamma ray bursts that have been discovered by Amati et al., Ghirlanda et al., Firmani et al., and Liang & Zhang. In our proposed model, a jet undergoes internal dissipation which prevents its bulk Lorentz factor from e...
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The Sloan Digital Sky survey detected luminous quasars at very high redshift, z>6. Follow-up observations indicated that at least some of these quasars are powered by supermassive black holes (SMBHs) with masses in excess of billion solar masses. SMBHs, therefore, seem to have already existed when the Universe was less than 1 Gyr old, and the bulk...
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We calculate evolution, collapse, explosion, and nucleosynthesis of Population III very massive stars with 500 M⊙ and 1000 M⊙. It was found that both 500 M⊙ and 1000 M⊙ models enter the region of pair-instability but continue to undergo core collapse to black holes. For moderately aspherical explosions, the patterns of nucleosynthesis match the obs...
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We describe a mechanism by which supermassive black holes (SMBHs) can form directly in the nuclei of protogalaxies, without the need for ‘seed’ black holes left over from early star formation. Self-gravitating gas in dark matter haloes can lose angular momentum rapidly via runaway, global dynamical instabilities, the so-called ‘bars within bars’ me...
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We calculate evolution, collapse, explosion, and nucleosynthesis of Population III very massive stars with 500 and 1000 Msolar. Presupernova evolution is calculated in spherical symmetry. Collapse and explosion are calculated by a two-dimensional code, based on the bipolar jet models. We compare the results of nucleosynthesis with the abundance pat...
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The first significant cosmic fields, and the seed field for galactic dynamos probably developed after the formation of the first non-linear structures. The history of star formation and the intergalactic medium is controlled, at least in part, by how and when galaxies and their precursors acquired their fields. The amplification of fields behind sh...
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A thermal radiative component is likely to accompany the first stages of the prompt emission of Gamma‐ray bursts (GRB’s) and X‐ray flashes (XRF’s). We study the properties of plasmas containing a low energy thermal photon component at comoving temperature θ ≡ kT ′ / mec 2 ∼ 10−5 – 10−2 interacting with an energetic electron component. We show that,...
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Observations of early afterglow emission from gamma-ray bursts (GRB's) with the Swift satellite show steep decay of the X-ray light curve, F_\nu(t) ~ t^{-\alpha} with \alpha ~ 2.5 - 4 at ~300-500 s after the burst trigger. The spectrum in this time interval is consistent with a spectrum F_\nu ~ \nu^{-\beta} with \beta ~1. Here, we show that these r...
Chapter
Physical models for g\gamma -ray emission from a relativistic fireball and the ensuing synchrotron emission from the decelerating shock have generally neglected the feedback of the intense g\gamma -ray flux on the dynamics of the fireball, or on the prompt and delayed emission. There are, however, several reasons to believe that this interaction...
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We identify 31 dimensionless physical constants required by particle physics and cosmology, and emphasize that both microphysical constraints and selection effects might help elucidate their origin. Axion cosmology provides an instructive example, in which these two kinds of arguments must both be taken into account, and work well together. If a Pe...
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Relativistic neutron-loaded outflows in gamma-ray bursts are studied at their early stages, before deceleration by a surrounding medium. The outflow has four components: radiation, electrons, protons and neutrons. The components interact with each other and exchange energy as the outflow expands. The presence of neutrons significantly changes the o...
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Attempts of Magain et al. to detect the host galaxy of the bright quasi-stellar object (QSO) HE0450–2958 have not been successful. We suggest that the supermassive black hole (SMBH) powering the QSO was ejected from the observed ultraluminous infrared galaxy (ULIRG) at the same redshift and at 1.5 arcsec distance. Ejection could have been caused ei...
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We calculate evolution, explosion and nucleosynthesis of 1000M&sun; stars. Even such massive stars may explode at the end of their lives if they rotate. We use a dimensional hydrodynamical code to take aspherisity by the effect of rotation into account. Our results show that (1) abundance pattern of ejected matter by explosion is consistent with ob...
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It is an obvious fact that we live at a time in the universe when conditions are right for life to exist. Less obvious and much more controversial is the notion that this fact may provide useful bounds on cosmological theories. In their Perspective, Livio and Rees argue that this kind of "anthropic reasoning" not only has a role in valid speculativ...
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We discuss a model for the early assembly of supermassive black holes (SMBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo `merger tree'. Motivated by the observations of luminous quasars around redshift z=6 with SMBH masses of billion solar masses, we assess the possibility of an early phase of stable su...
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We study the properties of plasmas containing a low energy thermal photon component at comoving temperature \theta \equiv kT'/m_e c^2 \sim 10^{-5} - 10^{-2} interacting with an energetic electron component, characteristic of, e.g., the dissipation phase of relativistic outflows in gamma-ray bursts (GRB's), X-ray flashes, and blazars. We show that,...
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Two authors, P. T. Boyd and M. Still, were inadvertently left off the author list in our original paper. We apologize for the omission.
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We consider the production of electron cyclotron maser emission by low-density, highly magnetized plasmas in relativistic jets. The population inversion required to drive cyclotron maser instability could occur in localized, transient sites where hydromagnetic instabilities, shocks, and/or turbulence lead to magnetic mirroring along current-carryin...
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We consider dissipative effects occurring in the optically thick inner parts of the relativistic outflows producing gamma-ray bursts and X-ray flashes, emphasizing specially the Comptonization of the thermal radiation flux that is advected from the base of the outflow. Such dissipative effects --e.g. from magnetic reconnection, neutron decay or sho...
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We study the expected distribution of massive black hole (MBH) spins and its evolution with cosmic time in the context of hierarchical galaxy formation theories. Our model uses Monte Carlo realizations of the merger hierarchy in a LCDM cosmology, coupled to semi-analytical recipes, to follow the merger history of dark matter halos, the dynamics of...
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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...
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Full-text available
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...
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In a recent paper Pelló et al. have reported a candidate z= 10 galaxy, A1835–1916, which was found in a near-infrared survey of the central regions of the gravitational lensing cluster A1835. If this detection is confirmed and the detection rate turns out to be typical, then the volume-averaged ultraviolet emissivity must be rising rapidly with inc...
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The existence of black holes remains open to doubt until other conceivable options are excluded. With this motivation, we consider a model of a compact star in which most of the mass consists of dark particles of some kind, and a small fraction of the mass is in the form of ordinary nucleonic gas. The gas does not interact with the dark matter othe...
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Fireballs with high energy per baryon rest mass (> 400) contain a relatively slow neutron component. We show here that in this situation the thermal history of fireballs is very different from the standard adiabatic cooling. Comment: 5 pages, 2 figures; to appear in the Santa Fe GRB Conference Proceedings, 2003
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It is embarrassing that 95% of the Universe is unaccounted for. Galaxies and larger-scale cosmic structures are composed mainly of "dark matter", whose nature is still unknown. Favoured candidates are weakly interacting particles that have survived from the very early Universe, but more exotic options cannot be excluded. (There are strong arguments...
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The cosmic ultraviolet (UV) ionizing background impacts the formation of dwarf galaxies in the low-redshift universe (z=3) by suppressing gas infall into galactic halos with circular velocities up to v(circ)=75 km/s. Using a one-dimensional, spherically symmetric hydrodynamics code (Thoul & Weinberg 1995), we examine the effect of an ionizing backg...
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The recent claim by Coburn & Boggs to have detected a very high degree of linear polarization in the prompt emission of GRB 021206 has stimulated interest in how much polarization could arise in gamma-ray bursts (GRBs) from synchrotron emission. Alternatively, as Shaviv & Dar have shown, GRB polarization could be produced by inverse Compton scatter...
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Fred Hoyle famously drew attention to the significance of apparent coincidences in the energy levels of the carbon and oxygen nucleus. This paper addresses the possible implications of other coincidences in cosmology.
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1 Department of Astronomy and Astrophysics, Department of Physics, Pennsylvania State University, University Park, PA 16803 2 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
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We give an overview of an interdisciplinary meeting held last year in Windsor to discuss the evidence for fine-tuning in living systems. Many of the papers presented there appear in this volume, so this serves as an introduction to them. We also briefly review a meeting held the previous year in Cambridge to assess the evidence for fine-tuning in p...
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We present models for reprocessing of an intense flux of X-rays and gamma rays expected in the vicinity of gamma ray burst sources. We consider the transfer and reprocessing of the energetic photons into observable features in the X-ray band, notably the K lines of iron. Our models are based on the assumption that the gas is sufficiently dense to a...
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The capture rates of stars and dark particles onto supermassive black holes depend strongly on the spatial and kinematical distribution of the stellar and dark matter at the centre of bulges and elliptical galaxies. We here explore the possibility that all ellipticals/bulges have initially isothermal cusps (ρ∝r−2). If the orbits can be adequately r...
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Gamma-ray bursts are often modelled as jet-like outflows directed towards the observer; the cone angle of the jet is then commonly inferred from the time at which there is a steepening in the power-law decay of the afterglow. We consider an alternative model in which the jet has a beam pattern where the luminosity per unit solid angle (and perhaps...
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The emission features observed in the X-ray afterglow of Gamma Ray Bursts are extremely powerful. Since they last at least for several hours, they imply energies of the order of 1e49 ergs. This in turn implies that the energy contained in the illuminating continuum thought to be responsible of the line production must exceed 1e51 ergs. This is a st...
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According to the collapsar model, gamma-ray bursts are thought to be produced in shocks that occur after the relativistic jet has broken free from the stellar envelope. If the mass density of the collimated outflow is less than that of the stellar envelope, the jet will then be surrounded by a cocoon of relativistic plasma. This material would itse...
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In models for gamma ray burst afterglows, it is normally assumed that the external shock strongly amplifies the magnetic field and that this field maintains a steady value throughout the shocked region. We discuss the effects of modifying this (probably simplistic) assumption by allowing for a short decay time. The observations are incompatible wit...
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We compute the luminosity of K_alpha emission lines produced by astrophysically abundant elements in the soft X-ray spectra of the early afterglow of gamma-ray bursts. We find that the detection of these lines can be a diagnostic for the geometrical set-up of the reprocessing material. In particular we can distinguish between a ``geometry dominated...
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The prompt (t≲0.16 d) light curve and initial 9th-magnitude optical flash from GRB 990123 can be attributed to a reverse external shock, or possibly to internal shocks. We discuss the time decay laws and spectral slopes expected under various dynamical regimes, and the constraints imposed on the model by the observations, arguing that they provide...
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How and when did the first stars form in our universe? Recent computational studies are beginning to provide an answer to this question. In his Perspective, [Rees][1] highlights the report by [ Abel et al .][2], who report three-dimensional calculations of star formation in the core of a collapsing primordial cloud. The first stars began to form ju...
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Absorption or emission against the cosmic microwave background radiation (CMB) may be observed in the redshifted 21cm line if the spin temperature of the neutral intergalactic medium prior to reionization differs from the CMB temperature. This so-called 21cm tomography should reveal important information on the physical state of the intergalactic m...
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In the collapsar scenario, gamma-ray bursts are caused by relativistic jets expelled along the rotation axis of a collapsing stellar core. We discuss how the structure and time dependence of such jets depend on the stellar envelope and central engine properties, assuming a steady jet injection. It takes a few seconds for the jet to bore its way thr...
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Recent numerical simulations of the fragmentation of primordial molecular clouds in hierarchical cosmogonies have suggested that the very first stars (the so-called Population III) may have been rather massive. Here we point out that a numerous population of massive black holes (MBHs) -- with masses intermediate between those of stellar and superma...
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In this month's essay, the last in the Pathways of Discovery series, Martin J. Rees celebrates the way astronomers and cosmologists have systematically uncovered the biography of the universe. Rife with neutron stars, black holes, and multiple universes that emerge from quantum fluctuation, it's a story as grand as it is strange.
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Gamma-ray bursts, an enigma for more than 25 years, are now coming into focus. They involve extraordinary power outputs, and highly relativistic dynamics. The most plausible progenitors, ranging from NS-NS mergers to collapsars (sometimes called "hypernovae") eventually lead to the formation of a black hole with a debris torus around it, the extrac...
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Within the framework of the internal-external shocks model for γ-ray bursts, we study the various mechanisms that can give rise to quiescent times in the observed γ-ray light curves. In particular, we look for the signatures that can provide us with evidence as to whether or not the central engine goes dormant for a period of time comparable to the...
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We assess supernova (SN)-driven pregalactic outflows as a mechanism for distributing the product of stellar nucleosynthesis over large cosmological volumes prior to the reionization epoch. SN ejecta will escape the grasp of halos with virial temperatures T_vir>10^{4.3} K (corresponding to masses M>10^8 h^{-1} M_sun at redshift z=9 when they collaps...
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We calculate the spectrum resulting from the interaction of a fireball with ambient soft photons. These photons are assumed to be produced by the walls of a funnel in a massive star. By parametrizing the radial dependence of the funnel temperature we calculate the deceleration of the fireball self-consistently, taking into account the absorption of...
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The universe would have been completely dark between the epoch of recombination and the development of the first non-linear structure. But at redshifts beyond 5 – perhaps even beyond 20 – stars formed within ‘subgalaxies’ and created the first heavy elements; these same systems (together perhaps with ‘miniquasars’) generated the UV radiation that i...
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The hardness of the ionizing continuum from the first sources of UV radiation plays a crucial role in the reionization of the intergalactic medium (IGM). While usual stellar populations have soft spectra, mini-quasars or metal-free stars with high effective temperatures may emit hard photons, capable of doubly ionizing helium and increasing the IGM...
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At redshifts certainly beyond 5—and, perhaps, even beyond 20–stars formed within ‘subgalaxies’ and created the first heav elements; these same systems (together, perhaps, with ‘miniquasars’) generated the UV radiation that ionized the intergalacti medium, and maybe also the first significant magnetic fields. These uncertain processes set the backdr...
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Recent observations of high-redshift galaxies and quasars indicate that the hydrogen component of the intergalactic medium (IGM) must have been reionized at some redshift z>6. Prior to complete reionization, sources of ultraviolet radiation will be seen behind intervening gas that is still neutral, and their spectra should show the red damping wing...
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Gamma–ray bursts, an enigma for more than 25 years, are now coming into focus. They involve extraordinary power outputs, an highly relativistic dynamics. The ‘trigger’ involves stellar–mass compact objects. The most plausible progenitors, rangin from NS–NS mergers to collapsars (sometimes called ‘hypernovae’) eventually lead to the formation of a b...
Article
Gamma-ray bursts, an enigma for more than 25 years, are now coming into focus. They involve extraordinary power outputs, and highly relativistic dynamics. The ``trigger'' involves stellar-mass compact objects. The most plausible progenitors, ranging from neutron star binary mergers to collapsars (sometimes called ``hypernovae'') eventually lead to...
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This brief introduction to the NATO ASI offers comments on current controversies, on the limits and prospects of cosmology in the coming decade, and on how the `sociology' of our subject may change in the decades beyond that.
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The existence of supermassive collapsed objects in the cores of most galaxies poses still-unanswered questions. First, how did they form, and how does their mass depend on the properties of the host galaxy? Second, can observations probe the metric in the strong-field domain, testing whether it indeed agrees with the Kerr geometry predicted by gene...
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At redshifts beyond 5 - perhaps even beyond 20 - the first stars formed within `subgalaxies' and created the first heavy elements; these same systems (together perhaps with `miniquasars') generated the UV radiation that ionized the IGM, and maybe also the first significant magnetic fields. Probing these crucial cosmogonic processes is an observatio...
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Recent observations of gamma-ray bursts (GRBs) have provided growing evidence for collimated outflows and emission, and strengthened the connection between GRBs and supernovae. If massive stars are the progenitors of GRBs, the hard photon pulse will propagate in the pre-burst, dense environment. Circumstellar material will Compton scatter the promp...
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It is proposed that the gamma-ray photons that characterize the prompt emission of Gamma-Ray Bursts are produced through the Compton drag process, caused by the interaction of a relativistic fireball with a very dense soft photon bath. If gamma-ray bursts are indeed associated with Supernovae, then the exploding star can provide enough soft photons...
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Recent observations have allowed the geometry and kinematics of the M87 jet to be tightly constrained. We combine these constraints with historical Very Long Baseline Interferometry (VLBI) results and the theory of synchrotron self-absorbed radio cores in order to investigate the physical properties of the jet. Our results strongly suggest the jet...
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The growth of supermassive black holes by merging and accretion in hierarchical models of galaxy formation is studied by means of Monte Carlo simulations. A tight linear relation between masses of black holes and masses of bulges arises if the mass accreted by supermassive black holes scales linearly with the mass-forming stars and if the redshift...
Article
There is now a consensus that gamma-ray bursts involve extraordinary power outputs, and highly relativistic dynamics. The trigger is probably a binary merger or collapse involving compact objects. The most plausible progenitors, ranging from NS-NS mergers to various hypernova-like scenarios, eventually lead to the formation of a black hole with a d...
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We show how the investigation of the redshifted 21-cm radiation can give insight into the development of structures in the early universe (at redshifts z>5). In particular we investigate: the epoch of the first light; the fluctuations in the redshifted 21-cm emission induced by the density inhomogeneities in CDM dominated universes; the emission an...
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In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo-dissociating their only cooling agent, molecular H2. We self-consistently...
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The emission of 21-cm radiation from a neutral intergalactic medium (IGM) at high redshift is discussed in connection with the thermal and ionization history of the universe. The physical mechanisms that make such radiation detectable against the cosmic microwave background include Ly_alpha coupling of the hydrogen spin temperature to the kinetic t...
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The detection by BeppoSAX of afterglows from gamma-ray bursts has immensely boosted the subject. This paper outlines the class of model for the bursts that currently seems most promising, and addresses specifically the nature of the afterglow, and its importance as a probe of the burst phenomenon.
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