3,521 research outputs found
Quantum Estimation of Parameters of Classical Spacetimes
We describe a quantum limit to measurement of classical spacetimes.
Specifically, we formulate a quantum Cramer-Rao lower bound for estimating the
single parameter in any one-parameter family of spacetime metrics. We employ
the locally covariant formulation of quantum field theory in curved spacetime,
which allows for a manifestly background-independent derivation. The result is
an uncertainty relation that applies to all globally hyperbolic spacetimes.
Among other examples, we apply our method to detection of gravitational waves
using the electromagnetic field as a probe, as in laser-interferometric
gravitational-wave detectors. Other applications are discussed, from
terrestrial gravimetry to cosmology.Comment: 23 pages. This article supersedes arXiv:1108.522
Quantum Connectivity of Space-Time and Gravitationally Induced Decorrelation of Entanglement
We discuss an alternative formulation of the problem of quantum optical
fields in a curved space-time using localized operators. We contrast the new
formulation with the standard approach and find observable differences for
entangled states. We propose an experiment in which an entangled pair of
optical pulses are propagated through non-uniform gravitational fields and find
that the new formulation predicts de-correlation of the optical entanglement
under experimentally realistic conditions
Time-Resolved Ultraviolet Observations of the Globular Cluster X-ray Source in NGC 6624: The Shortest Known Period Binary System
Using the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope,
we have obtained the first time-resolved spectra of the King et al.
ultraviolet-bright counterpart to the 11-minute binary X-ray source in the core
of the globular cluster NGC 6624. This object cannot be readily observed in the
visible, even from HST, due to a much brighter star superposed <0.1'' distant.
Our FOS data show a highly statistically significant UV flux modulation with a
period of 11.46+-0.04 min, very similar to the 685 sec period of the known
X-ray modulation, definitively confirming the association between the King et
al. UV counterpart and the intense X-ray source. The UV amplitude is very large
compared with the observed X-ray oscillations: X-ray variations are generally
reported as 2-3% peak-to-peak, whereas our data show an amplitude of about 16%
in the 126-251 nm range. A model for the system by Arons & King predicts
periodic UV fluctuations in this shortest-known period binary system, due to
the cyclically changing aspect of the X-ray heated face of the secondary star
(perhaps a very low mass helium degenerate). However, prior to our
observations, this predicted modulation has not been detected. Employing the
Arons & King formalism, which invokes a number of different physical
assumptions, we infer a system orbital inclination 35deg<i<50 deg. Amongst the
three best-studied UV/optical counterparts to the intense globular cluster
X-ray sources, two are now thought to consist of exotic double-degenerate
ultrashort period binary systems.Comment: 10 pages including 2 figures in Latex (AASTeX 4.0). Accepted for
publication in vol. 482 (1997 June 10 issue) of The Astrophysical Journal
(Letters
Infrared and radio observations of W51: Another Orion-KL at a distance of 7kpc
The bright infrared sources W51-IRS2 has at least three components with different physical and evolutionary properties. The spatial distribution and the near infrared spectra of the components in IRS2 are remarkably similar to, but more luminous than those found in Orion, where an H2 region of comparable linear size is also located close to a cluster of compact infrared sources. The characteristics of the nearby W51-NORTH H2O maser source, and the detection of 2 micro m H2 quadrupole emission in IRS2 indicate that the mass loss phenomena found in Orion-KL also exist in W51
The faint counterparts of MAMBO mm sources near the NTT Deep Field
We discuss identifications for 18 sources from our MAMBO 1.2mm survey of the
region surrounding the NTT Deep Field. We have obtained accurate positions from
Very Large Array 1.4GHz interferometry and in a few cases IRAM mm
interferometry, and have also made deep BVRIzJK imaging at ESO. We find
thirteen 1.2mm sources associated with optical/near-infrared objects in the
magnitude range K=19.0 to 22.5, while five are blank fields at K>22. The median
redshift of the radio-identified mm sources is ~2.6 from the radio/mm
estimator, and the median optical/near-infrared photometric redshifts for the
objects with counterparts ~2.1. This suggests that those radio-identified mm
sources without optical/near-infrared counterparts tend to lie at higher
redshifts than those with optical/near-infrared counterparts. Compared to
published identifications of objects from 850micron surveys of similar depth,
the median K and I magnitudes of our counterparts are roughly two magnitudes
fainter and the dispersion of I-K colors is less. Real differences in the
median redshifts, residual mis-identifications with bright objects, cosmic
variance, and small number statistics are likely to contribute to this
significant difference, which also affects redshift measurement strategies. We
discuss basic properties of the near-infrared/(sub)mm/radio spectral energy
distributions of our galaxies and of interferometrically identified submm
sources from the literature. From a comparison with submm objects with
CO-confirmed spectroscopic redshifts we argue that roughly two thirds of the
(sub)mm galaxies are at z>~2.5. This fraction is probably larger when including
sources without radio counterparts. (abridged)Comment: 45 pages, 9 figures. Accepted by ApJ. The resolution of figures 2 and
3 has been degraded. A higher quality pdf version of this paper is available
at http://www.mpe.mpg.de/~dannerb
The distance to the SNR CTB109 deduced from its environment
We conducted a study of the environment around the supernova remnant CTB109.
We found that the SNR is part of a large complex of HII regions extending over
an area of 400 pc along the Galactic plane at a distance of about 3 kpc at the
closer edge of the Perseus spiral arm. At this distance CTB109 has a diameter
of about 24 pc. We demonstrated that including spiral shocks in the distance
estimation is an ultimate requirement to determine reliable distances to
objects located in the Perseus arm. The most likely explanation for the high
concentration of HII regions and SNRs is that the star formation in this part
of the Perseus arm is triggered by the spiral shock.Comment: 6 pages, 6 figures. accepted for publication in the Astrophysical
Journa
The Chandra Deep Field-North Survey. XIV. X-ray detected Obscured AGNs and Starburst Galaxies in the Bright Submm Source Population
We provide X-ray constraints and perform the first X-ray spectral analyses
for bright (f_850>=5mJy; S/N>=4) SCUBA sources in an 8.4'x8.4' area of the 2 Ms
Chandra Deep Field-North survey containing the Hubble Deep Field-North. X-ray
emission is detected from 7 of the 10 bright submm sources in this region,
corresponding to an X-ray detected submm source density of ~360 deg^-2 (>~36%
of the bright submm source population). Two of the X-ray detected sources have
nearby (within 3") X-ray companions, suggesting merging/interacting sources or
gravitational lensing effects, and 3 lie within the approximate extent of a
proto-cluster candidate. Five of the X-ray detected sources have flat X-ray
spectral slopes, suggesting obscured AGN activity. X-ray spectral analyses
suggest that one of these AGNs may be a Compton-thick source; of the other 4
AGNs, 3 appear to be Compton-thin sources and one has poor constraints. The
rest-frame unabsorbed X-ray luminosities of these AGNs are more consistent with
those of Seyfert galaxies than QSOs. Thus, the low X-ray detection rate of
bright submm sources by moderately deep X-ray surveys appears to be due to the
relatively low luminosities of the AGNs rather than Compton-thick absorption. A
comparison of these sources to the well-studied heavily obscured AGN NGC6240
shows that the average AGN contribution is negligible at submm wavelengths. The
X-ray properties of the other 2 X-ray detected sources are consistent with
those expected from luminous star formation; however, we cannot rule out the
possibility that low-luminosity AGNs are present. The 3 X-ray undetected
sources appear to lie at high redshift (z>4) and could be either AGNs or
starbust galaxies.Comment: AJ in press (February 2003), 16 pages, includes emulateapj5.st
MHD Models of Axisymmetric Protostellar Jets
We present the results of a series of axisymmetric time-dependent
magnetohydrodynamic (MHD) simulations of the propagation of cooling, overdense
jets, motivated by the properties of outflows associated with young stellar
objects. A variety of initial field strengths and configurations are explored
for both steady and time-variable (pulsed) jets. Even apparently weak magnetic
fields with strengths B < 60 micro-G in the pre-shocked jet beam can have a
significant effect on the dynamics, for example by altering the density, width,
and fragmentation of thin shells formed by cooling gas. A linear analysis
predicts that axisymmetric pinch modes of the MHD Kelvin-Helmholtz instability
should grow only slowly for the highly supermagnetosonic jets studied here; we
find no evidence for them in our simulations. Some of our models appear
unstable to current-driven pinch modes, however the resulting pressure and
density variations induced in the jet beam are not large, making this mechanism
an unlikely source of emission knots in the jet beam. In the case of pulsed
jets, radial hoop stresses confine shocked jet material in the pulses to the
axis, resulting in a higher density in the pulses in comparison to purely
hydrodynamic models.Comment: 28 pages, 16 figures, accepted by Ap.
Galaxy Cluster Scaling Relations between Bolocam Sunyaev-Zel'dovich Effect and Chandra X-ray Measurements
We present scaling relations between the integrated Sunyaev-Zel'dovich Effect
(SZE) signal, , its X-ray analogue, , and total mass, , for the 45 galaxy clusters in
the Bolocam X-ray-SZ (BOXSZ) sample. All parameters are integrated within
. values are measured using SZE data collected with
Bolocam, operating at 140 GHz at the Caltech Submillimeter Observatory (CSO).
The temperature, , and mass, , of the intracluster
medium are determined using X-ray data collected with Chandra, and is derived from assuming a constant gas mass fraction. Our
analysis accounts for several potential sources of bias, including: selection
effects, contamination from radio point sources, and the loss of SZE signal due
to noise filtering and beam-smoothing effects. We measure the
-- scaling to have a power-law index of , and
a fractional intrinsic scatter in of at fixed , both of which are consistent with previous analyses. We also measure the
scaling between and , finding a power-law index of
and a fractional intrinsic scatter in at fixed mass of
. While recent SZE scaling relations using X-ray mass proxies have
found power-law indices consistent with the self-similar prediction of 5/3, our
measurement stands apart by differing from the self-similar prediction by
approximately 5. Given the good agreement between the measured
-- scalings, much of this discrepancy appears to be caused
by differences in the calibration of the X-ray mass proxies adopted for each
particular analysis.Comment: 31 pages, 15 figures, accepted by ApJ 04/11/2015. This version is
appreciably different from the original submission: it includes an entirely
new appendix, extended discussion, and much of the material has been
reorganize
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