626 research outputs found
Gravitational-wave confusion background from cosmological compact binaries: Implications for future terrestrial detectors
Increasing the sensitivity of a gravitational-wave (GW) detector improves our
ability to measure the characteristics of detected sources. It also increases
the number of weak signals that contribute to the data. Because GW detectors
have nearly all-sky sensitivity, they can be subject to a confusion limit: Many
sources which cannot be distinguished may be measured simultaneously, defining
a stochastic noise floor to the sensitivity. For GW detectors operating at
present and for their planned upgrades, the projected event rate is
sufficiently low that we are far from the confusion-limited regime. However,
some detectors currently under discussion may have large enough reach to binary
inspiral that they enter the confusion-limited regime. In this paper, we
examine the binary inspiral confusion limit for terrestrial detectors. We
consider a broad range of inspiral rates in the literature, several planned
advanced gravitational-wave detectors, and the highly advanced "Einstein
Telescope" design. Though most advanced detectors will not be impacted by this
limit, the Einstein Telescope with a very low frequency "seismic wall" may be
subject to confusion noise. At a minimum, careful data analysis will be require
to separate signals which will appear confused. This result should be borne in
mind when designing highly advanced future instruments.Comment: 19 pages, 6 figures and 3 tables; accepted for publication in Phys.
Rev.
KUV 01584-0939: A Helium-transferring Cataclysmic Variable with an Orbital Period of 10 Minutes
High speed photometry of KUV 01584-0939 (alias Cet3) shows that is has a
period of 620.26 s. Combined with its hydrogen-deficient spectrum, this implies
that it is an AM CVn star. The optical modulation is probably a superhump, in
which case the orbital period will be slightly shorter than what we have
observed.Comment: Published by PASP. See also the latest Early-Release Research Paper
website of the PAS
Cosmological Gamma-Ray Bursts and Evolution of Galaxies
Evolution of the rate density of cosmological gamma-ray bursts (GRBs) is
calculated and compared to the BATSE brightness distribution in the context of
binary neutron-star mergers as the source of GRBs, taking account of the
realistic star formation history in the universe and evolution of compact
binary systems. We tried two models of the evolution of cosmic star formation
rate (SFR): one is based on recent observations of SFRs at high redshifts,
while the other is based on a galaxy evolution model of stellar population
synthesis that reproduces the present-day colors of galaxies. It is shown that
the binary merger scenario of GRBs naturally results in the comoving
rate-density evolution of \propto (1+z)^{2-2.5} up to z ~ 1, that has been
suggested independently from the compatibility between the number-brightness
distribution and duration-brightness correlation. If the cosmic SFR has its
peak at z ~ 1--2 as suggested by recent observations, the effective power-index
of GRB photon spectrum, \alpha >~ 1.5$ is favored, that is softer than the
recent observational determination of \alpha = 1.1 \pm 0.3. However, high
redshift starbursts (z >~ 5) in elliptical galaxies, that have not yet been
detected, can alleviate this discrepancy. The redshift of GRB970508 is likely
about 2, just below the upper limit that is recently determined, and the
absorption system at z = 0.835 seems not to be the site of the GRB.Comment: ApJ Lett. in press, very minor change just making clear that the
predicted rate-density evolution is in a comoving sense. (Received 1997 May
15; Accepted 1997 July 2
The evolution of relative frequencies of ONe and CO SNe Ia
In this population synthesis work we study a variety of possible origin
channels of supernovae type Ia (SNe Ia) Among them mergers of carbon-oxygen
(CO) and oxygen-neon (ONe) white dwarfs (WDs) under the influence of
gravitational waves are considered as the primary channel of SNe Ia formation.
We estimated frequencies of mergers of WDs with different chemical compositions
and distributions of masses of merging WDs. We computed the dependence of the
ratio of merger frequencies of ONe and CO WDs as primaries in corresponding
binaries on time. The scatter of masses of considered sources (up to the factor
) of SNe Ia is important and should be carefully studied with other
sophisticated methods from theoretical point of view. Our ``game of
parameters'' potentially explains the increased dimming of SNe Ia in the
redshift range by the changes in the ratio of ONe and CO WDs,
i.e., to describe the observed accelerated expansion of the Universe in terms
of the evolution of properties of SNe Ia instead of cosmological explanations.
This example shows the extreme importance of theoretical studies of problems
concerning SNe Ia, because evolutionary scenario and parameter games in nature
potentially lead to confusions in their empirical standardization and,
therefore, they can influence on cosmological conclusions.Comment: MNRAS, accepted, 12 pages, 4 figures, 1 tabl
The Progenitors of Subluminous Type Ia Supernovae
We find that spectroscopically peculiar subluminous SNe Ia come from an old
population. Of the sixteen subluminous SNe Ia known, ten are found in E/S0
galaxies, and the remainder are found in early-type spirals. The probability
that this is a chance occurrence is only 0.2%. The finding that subluminous SNe
Ia are associated with an older stellar population indicates that for a
sufficiently large lookback time (already accessible in current high redshift
searches) they will not be found. Due to a scarcity in old populations,
hydrogen and helium main sequence stars and He red giant stars that undergo
Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia.
Earlier findings that overluminous SNe Ia (dM15(B) < 0.95) come from a young
progenitor population are confirmed. The fact that subluminous SNe Ia and
overluminous SNe Ia come from different progenitor populations and also have
different properties is a prediction of the CO white dwarf merger progenitor
scenario.Comment: 7 pages, 1 figure, Accepted to ApJ Letter
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