1,820 research outputs found
Coating thermal noise for arbitrary shaped beams
Advanced LIGO's sensitivity will be limited by coating noise. Though this
noise depends on beam shape, and though nongaussian beams are being seriously
considered for advanced LIGO, no published analysis exists to compare the
quantitative thermal noise improvement alternate beams offer. In this paper, we
derive and discuss a simple integral which completely characterizes the
dependence of coating thermal noise on shape. The derivation used applies
equally well, with minor modifications, to all other forms of thermal noise in
the low-frequency limit.Comment: 3 pages. Originally performed in August 2004. Submitted to CQG. (v2)
: Corrections from referee and other
Bounds on Expected Black Hole Spins in Inspiraling Binaries
As a first step towards understanding the angular momentum evolution history
of black holes in merging black-hole/neutron-star binaries, we perform
population synthesis calculations to track the distribution of accretion
histories of compact objects in such binaries. We find that there are three
distinct processes which can possibly contribute to the black-hole spin
magnitude: a birth spin for the black hole, imparted at either (i) the collapse
of a massive progenitor star to a black hole or (ii) the accretion-induced
collapse of a neutron star to a black hole; and (iii) an accretion spin-up when
the already formed black hole [via (i) or (ii)] goes through an accretion
episode (through an accretion disk or a common-envelope phase). Our results
show that, with regard to accretion-induced spinup in merging BH-NS binaries
[method (iii) above], only
{\em accretion episodes associated with common-envelope phases and
hypercritical accretion rates} occur in the formation history of merging black
hole/neutron star binaries. Lacking unambiguous experimental information about
BH birth spins [i.e., regarding the results of processes (i) and (ii)], we
choose two fiducial values for the BH birth angular momentum parameter a=J/M^2,
consistent with observations of (i) NS birth spins (a roughly 0) and (ii) X-ray
binaries (a=0.5). Using these two fiducial values and a conservative upper
bound on the specific angular momentum of accreted matter, we discuss the
expected range of black hole spins in the binaries of interest. We conclude
with comments on the significance of these results for ground-based
gravitational-wave searches of inspiral signals from black hole binaries.Comment: Submitted to ApJ. (v1) Uses emulateapj.cls. 5 figures. (v2):
corrected reference list and uses smaller figures (v3): Includes changes in
response to referee comments, including new discussion of XRBs. Figures
merged, so only 3 figures (v4) Minor typo correction, plus updated abstract
posted onlin
Precession during merger 1: Strong polarization changes are observationally accessible features of strong-field gravity during binary black hole merger
The short gravitational wave signal from the merger of compact binaries
encodes a surprising amount of information about the strong-field dynamics of
merger into frequencies accessible to ground-based interferometers. In this
paper we describe a previously-unknown "precession" of the peak emission
direction with time, both before and after the merger, about the total angular
momentum direction. We demonstrate the gravitational wave polarization encodes
the orientation of this direction to the line of sight. We argue the effects of
polarization can be estimated nonparametrically, directly from the
gravitational wave signal as seen along one line of sight, as a slowly-varying
feature on top of a rapidly-varying carrier. After merger, our results can be
interpreted as a coherent excitation of quasinormal modes of different angular
orders, a superposition which naturally "precesses" and modulates the
line-of-sight amplitude. Recent analytic calculations have arrived at a similar
geometric interpretation. We suspect the line-of-sight polarization content
will be a convenient observable with which to define new high-precision tests
of general relativity using gravitational waves. Additionally, as the nonlinear
merger process seeds the initial coherent perturbation, we speculate the
amplitude of this effect provides a new probe of the strong-field dynamics
during merger. To demonstrate the ubiquity of the effects we describe, we
summarize the post-merger evolution of 104 generic precessing binary mergers.
Finally, we provide estimates for the detectable impacts of precession on the
waveforms from high-mass sources. These expressions may identify new precessing
binary parameters whose waveforms are dissimilar from the existing sample.Comment: 11 figures; v2 includes response to referee suggestion
Blindly detecting orbital modulations of jets from merging supermassive black holes
In the last few years before merger, supermassive black hole binaries will
rapidly inspiral and precess in a magnetic field imposed by a surrounding
circumbinary disk. Multiple simulations suggest this relative motion will
convert some of the local energy to a Poynting-dominated outflow, with a
luminosity 10^{43} erg/s * (B/10^4 G)^2(M/10^8 Msun)^2 (v/0.4 c)^2, some of
which may emerge as synchrotron emission at frequencies near 1 GHz where
current and planned wide-field radio surveys will operate. On top of a secular
increase in power on the gravitational wave inspiral timescale, orbital motion
will produce significant, detectable modulations, both on orbital periods and
(if black hole spins are not aligned with the binary's total angular momenta)
spin-orbit precession timescales. Because the gravitational wave merger time
increases rapidly with separation, we find vast numbers of these transients are
ubiquitously predicted, unless explicitly ruled out (by low efficiency
) or obscured (by accretion geometry f_{geo}). If the fraction of
Poynting flux converted to radio emission times the fraction of lines of sight
accessible is sufficiently large (f_{geo} \epsilon > 2\times 10^{-4}
for a 1 year orbital period), at least one event is accessible to future blind
surveys at a nominal 10^4 {deg}^2 with 0.5 mJy sensitivity. Our procedure
generalizes to other flux-limited surveys designed to investigate EM signatures
associated with many modulations produced by merging SMBH binaries.Comment: Submitted to ApJ. v1 original submission; v2 minor changes in
response to refere
The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers
In second-generation, ground-based interferometric gravitational-wave
detectors such as Advanced LIGO, the dominant noise at frequencies
Hz to Hz is expected to be due to thermal fluctuations in the
mirrors' substrates and coatings which induce random fluctuations in the shape
of the mirror face. The laser-light beam averages over these fluctuations; the
larger the beam and the flatter its light-power distribution, the better the
averaging and the lower the resulting thermal noise. In semi-infinite mirrors,
scaling laws for the influence of beam shape on the four dominant types of
thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and
substrate thermoelastic) have been suggested by various researchers and derived
with varying degrees of rigour. Because these scaling laws are important tools
for current research on optimizing the beam shape, it is important to firm up
our understanding of them. This paper (1) gives a summary of the prior work and
of gaps in the prior analyses, (2) gives a unified and rigorous derivation of
all four scaling laws, and (3) explores, relying on work by J. Agresti,
deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra
Binary compact object coalescence rates: The role of elliptical galaxies
We estimate binary compact object merger detection rates for LIGO, including
the binaries formed in ellipticals long ago. Specifically, we convolve hundreds
of model realizations of elliptical- and spiral-galaxy population syntheses
with a model for elliptical- and spiral-galaxy star formation history as a
function of redshift. Our results favor local merger rate densities of 4\times
10^{-3} {Mpc}^{-3}{Myr}^{-1} for binary black holes (BH), 3\times 10^{-2}
{Mpc}^{-3}{Myr}^{-1} for binary neutron stars (NS), and 10^{-2}
{Mpc}^{-3}{Myr}^{-1} for BH-NS binaries. Mergers in elliptical galaxies are a
significant fraction of our total estimate for BH-BH and BH-NS detection rates;
NS-NS detection rates are dominated by the contribution from spiral galaxies.
Using only models that reproduce current observations of Galactic NS-NS
binaries, we find slightly higher rates for NS-NS and largely similar ranges
for BH-NS and BH-BH binaries. Assuming a detection signal-to-noise ratio
threshold of 8 for a single detector (as part of a network), corresponding to
radii \Cv of the effective volume inside of which a single LIGO detector could
observe the inspiral of two 1.4 M_\sun neutron stars of 14 Mpc and 197 Mpc, for
initial and advanced LIGO, we find event rates of any merger type of 2.9*
10^{-2} -- 0.46 and 25-400 per year (at 90% confidence level), respectively. We
also find that the probability P_{detect} of detecting one or more mergers with
this single detector can be approximated by (i) P_{detect}\simeq 0.4+0.5\log
(T/0.01{yr}), assuming \Cv=197 {Mpc} and it operates for T years, for T between
2 days and 0.1 {yr}); or by (ii) P_{detect}\simeq 0.5 + 1.5 \log \Cv/32{Mpc},
for one year of operation and for \Cv between 20 and 70 Mpc. [ABRIDGED]Comment: 22 pages, 11 figures. Accepted by ApJ. v2 adds several figures, an
electronic-only table of all intermediate binary evolution simulations
(tab1.txt here), and new subsections outlining broader significance (e.g.,
5.4; 4.6; 6.1
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