2,507 research outputs found
The Environments of Short-Duration Gamma-Ray Bursts and Implications for their Progenitors
[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
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 -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
in newly born stars, and that they emit with a power of in the keV band per star formation rate (SFR). This
value is a factor 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
Following the faint gamma-ray burst, GRB 170817A, coincident with a
gravitational wave-detected binary neutron star merger at Mpc, we
consider the constraints on a local population of faint short duration GRBs
(defined here broadly as s). We review proposed low-redshift
short-GRBs and consider statistical limits on a 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 y at Mpc, corresponding to % of
SGRBs. Cross-correlation of selected CGRO/BATSE and Fermi/GBM GRBs with
Mpc galaxy positions returns a weaker constraint of . A separate search for correlations due to SGR giant flares in nearby
( Mpc) galaxies finds an upper limit of . 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 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
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
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
NSM). The merger releases ergs, mostly as
neutrinos and gravitational radiation. A small fraction of this energy suffices
to power -ray bursts (GRBs) at cosmological distances. Cosmological
GRBs must pass, however, an optically thick fireball phase and the observed
-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 NSMs 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
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
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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