2,507 research outputs found

    The Environments of Short-Duration Gamma-Ray Bursts and Implications for their Progenitors

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    [Abridged] The study of short-duration gamma-ray bursts (GRBs) experienced a complete revolution in recent years thanks to the discovery of the first afterglows and host galaxies in May 2005. These observations demonstrated that short GRBs are cosmological in origin, reside in both star forming and elliptical galaxies, are not associated with supernovae, and span a wide isotropic-equivalent energy range of ~10^48-10^52 erg. However, a fundamental question remains unanswered: What are the progenitors of short GRBs? The most popular theoretical model invokes the coalescence of compact object binaries with neutron star and/or black hole constituents. However, additional possibilities exist, including magnetars formed through prompt channels (massive star core-collapse) and delayed channels (binary white dwarf mergers, white dwarf accretion-induced collapse), or accretion-induced collapse of neutron stars. In this review I summarize our current knowledge of the galactic and sub-galactic environments of short GRBs, and use these observations to draw inferences about the progenitor population. The most crucial results are: (i) some short GRBs explode in dead elliptical galaxies; (ii) the majority of short GRBs occur in star forming galaxies; (iii) the star forming hosts of short GRBs are distinct from those of long GRBs (lower star formation rates, and higher luminosities and metallicities), and instead appear to be drawn from the general field galaxy population; (iv) the physical offsets of short GRBs relative to their host galaxy centers are significantly larger than for long GRBs; (v) the observed offset distribution is in good agreement with predictions for NS-NS binary mergers; and (vi) short GRBs trace under-luminous locations within their hosts, but appear to be more closely correlated with the rest-frame optical light (old stars) than the UV light (young massive stars).Comment: Solicited review in New Astronomy Reviews; accepted version; 24 pages, 23 figures; version with full resolution figures available from https://www.cfa.harvard.edu/~eberger/eberger_shb_nar.pd

    Population III X-Ray Binaries

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    Understanding of the role of X-rays for driving the thermal evolution of the intergalactic medium (IGM) at high redshifts is one of important questions in astrophysics. High-mass X-ray binaries (HMXBs) in early stellar populations are prime X-ray source; however, their formation efficiency is not well understood. Using NN-body simulations, we estimate the HMXB formation rate via mutual gravitational interactions of nascent, small groups of the Population~III stars. We find that HMXBs form at a rate of one per ≳104M⊙\gtrsim 10^{4}M_{\odot} in newly born stars, and that they emit with a power of ∼1041erg s−1\sim 10^{41} {\rm erg}~{\rm s}^{-1} in the 2−102-10 keV band per star formation rate (SFR). This value is a factor ∼102\sim 10^{2} larger than what is observed in star forming galaxies at lower redshifts; the X-ray production from early HMXBs would have been even more copious, if they also formed \textit{in situ} or via migration in protostellar disks. Combining our results with earlier studies suggests that early HMXBs were highly effective at heating the IGM and leaving a strong 21 cm signature. We discuss broader implications of our results, such as the rate of long gamma-ray bursts from Population~III stars and the direct collapse channel for massive black hole formation.Comment: 19 pages, 8 figures, conference title : Frontier Research in Astrophysics - II (https://pos.sissa.it/269/

    The Rate of Short-Duration Gamma-Ray Bursts in the Local Universe

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    Following the faint gamma-ray burst, GRB 170817A, coincident with a gravitational wave-detected binary neutron star merger at d∼40d\sim40 Mpc, we consider the constraints on a local population of faint short duration GRBs (defined here broadly as T90<4T_{90}<4 s). We review proposed low-redshift short-GRBs and consider statistical limits on a d⪅200d\lessapprox200 Mpc population using Swift/Burst Alert Telescope (BAT), Fermi/Gamma-ray Burst Monitor (GBM), and Compton Gamma-Ray Observatory (CGRO) Burst and Transient Source Experiment (BATSE) GRBs. Swift/BAT short-GRBs give an upper limit for the all-sky rate of <4<4 y−1^{-1} at d<200d<200 Mpc, corresponding to <5<5% of SGRBs. Cross-correlation of selected CGRO/BATSE and Fermi/GBM GRBs with d<100d<100 Mpc galaxy positions returns a weaker constraint of ⪅12 y−1\lessapprox12\ {\rm y^{-1}}. A separate search for correlations due to SGR giant flares in nearby (d<11d<11 Mpc) galaxies finds an upper limit of <3 y−1<3\ {\rm y^{-1}}. Our analysis suggests that GRB 170817A-like events are likely to be rare in existing SGRB catalogues. The best candidate for an analogue remains GRB 050906, where the Swift/BAT location was consistent with the galaxy IC0327 at d≈132d\approx132 Mpc. If binary neutron star merger rates are at the high end of current estimates, then our results imply that at most a few percent will be accompanied by detectable gamma-ray flashes in the forthcoming LIGO/Virgo science runs.Comment: 16 pages, 4 figures, 1 table. Published in Galaxies as part of the Special Issue, "Observations and Theory of Short GRBs at the Dawn of the Gravitational Wave Era

    Compact Binary Coalescences in the Band of Ground-based Gravitational-Wave Detectors

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    As the ground-based gravitational-wave telescopes LIGO, Virgo, and GEO 600 approach the era of first detections, we review the current knowledge of the coalescence rates and the mass and spin distributions of merging neutron-star and black-hole binaries. We emphasize the bi-directional connection between gravitational-wave astronomy and conventional astrophysics. Astrophysical input will make possible informed decisions about optimal detector configurations and search techniques. Meanwhile, rate upper limits, detected merger rates, and the distribution of masses and spins measured by gravitational-wave searches will constrain astrophysical parameters through comparisons with astrophysical models. Future developments necessary to the success of gravitational-wave astronomy are discussed.Comment: Replaced with version accepted by CQG

    Gamma-Ray Bursts and Binary Neutron Star Mergers

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    Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1916+13, end their life in a catastrophic merge event (denoted here NS2^2M). The merger releases ≈5⋅1053\approx 5 \cdot 10^{53}ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ\gamma-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ\gamma-rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2^2Ms being only an indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational radiation signal could confirm this model.Comment: 13 pages, uuencoded ps files to apprear in IAU SYMPOSIUM 165 `COMPACT STARS IN BINARIES' 15-19 August 1994, The Hague, Netherland

    The Neutron Star Zoo

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    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission.Comment: 15 pages, 8 figure, to be published in Frontiers of Physic

    Formation Rates of Black Hole Accretion Disk Gamma-Ray Bursts

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    While many models have been proposed for GRBs, those currently favored are all based upon the formation of and/or rapid accretion into stellar mass black holes. We present population synthesis calculations of these models using a Monte Carlo approach in which the many uncertain parameters intrinsic to such calculations are varied. We estimate the event rate for each class of model as well as the propagation distance for those having significant delay between formation and burst production, i.e., double neutron star (DNS) mergers and black hole-neutron star (BH/NS) mergers. For reasonable assumptions regarding the many uncertainties in population synthesis, we calculate a daily event rate in the universe for i) merging neutron stars: ~100/day; ii) neutron-star black hole mergers: ~450/day; iii) collapsars: ~10,000/day; iv) helium star black hole mergers: ~1000/day; and v) white dwarf black hole mergers: ~20/day. The range of uncertainty in these numbers however, is very large, typically two to three orders of magnitude. These rates must additionally be multiplied by any relevant beaming factor and sampling fraction (if the entire universal set of models is not being observed). Depending upon the mass of the host galaxy, half of the DNS and BH/NS mergers will happen within 60kpc (for a Milky-Way massed galaxy) to 5Mpc (for a galaxy with negligible mass) from the galactic center. Because of the delay time, neutron star and black hole mergers will happen at a redshift 0.5 to 0.8 times that of the other classes of models. Information is still lacking regarding the hosts of short hard bursts, but we suggest that they are due to DNS and BH/NS mergers and thus will ultimately be determined to lie outside of galaxies and at a closer mean distance than long complex bursts (which we attribute to collapsars).Comment: 57 pages total, 23 figures, submitted by Ap
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