1,293 research outputs found
Simultaneous multiwavelength observations of the Low/Hard State of the X-ray transient source SWIFT J1753.5-0127
We report the results of simultaneous multiwavelength observations of the
X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT,
REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst
since 2005 May 30, was observed during the INTEGRAL Target of Opportunity
program dedicated to new X-ray novae located in the Galactic Halo. Broad-band
spectra and fast timing variability properties of SWIFT J1753.5-0127 are
analyzed together with the optical, near infra-red and radio data. We show that
the source was significantly detected up to 600 keV with Comptonization
parameters and timing properties typical of the so-called Low/Hard State of
black hole candidates. We build a spectral energy distribution and we show that
SWIFT J1753.5-0127 does not follow the usual radio/X-ray correlation of X-ray
binaries in the Low/Hard State. We give estimates of distance and mass. We
conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class and that it is
likely a black hole candidate transient source of the Galactic Halo which
remained in the Low/Hard State during its main outburst. We discuss our results
within the context of Comptonization and jet models.Comment: Accepted for publication in ApJ, 25 pages, 4 tables, 11 figures (3 in
color
Does backreaction enforce the averaged null energy condition in semiclassical gravity?
The expected stress-energy tensor of quantum fields generically
violates the local positive energy conditions of general relativity. However,
may satisfy some nonlocal conditions such as the averaged null energy
condition (ANEC), which would rule out traversable wormholes. Although ANEC
holds in Minkowski spacetime, it can be violated in curved spacetimes if one is
allowed to choose the spacetime and quantum state arbitrarily, without
imposition of the semiclassical Einstein equation G_{ab} = 8 \pi . In
this paper we investigate whether ANEC holds for solutions to this equation, by
studying a free, massless scalar field with arbitrary curvature coupling in
perturbation theory to second order about the flat spacetime/vacuum solution.
We "reduce the order" of the perturbation equations to eliminate spurious
solutions, and consider the limit in which the lengthscales determined by the
incoming state are much larger than the Planck length. We also need to assume
that incoming classical gravitational radiation does not dominate the first
order metric perturbation. We find that although the ANEC integral can be
negative, if we average the ANEC integral transverse to the geodesic with a
suitable Planck scale smearing function, then a strictly positive result is
obtained in all cases except for the flat spacetime/vacuum solution. This
result suggests --- in agreement with conclusions drawn by Ford and Roman from
entirely independent arguments --- that if traversable wormholes do exist as
solutions to the semiclassical equations, they cannot be macroscopic but must
be ``Planck scale''. A large portion of our paper is devoted to the analysis of
general issues concerning the nature of the semiclassical Einstein equation and
of prescriptions for extracting physically relevant solutions.Comment: 54 pages, 3 figures, uses revtex macros and epsf.tex, to appear in
Phys Rev D. A new appendix has been added showing consistency of our results
with recent results of Visser [gr-qc/9604008]. Some corrections were made to
Appendix A, and several other minor changes to the body of the paper also
were mad
Discovery of a broad iron line in the black-hole candidate Swift J1753.5-0127, and the disk emission in the low/hard state revisited
We analyzed simultaneous archival XMM-Newton and RXTE observations of the
X-ray binary and black hole candidate Swift J1753.5-0127. In a previous
analysis of the same data a soft thermal component was found in the X-ray
spectrum, and the presence of an accretion disk extending close to the
innermost stable circular orbit was proposed. This is in contrast with the
standard picture in which the accretion disk is truncated at large radii in the
low/hard state. We tested a number of spectral models and we found that several
of them fit the observed spectra without the need of a soft disk-like
component. This result implies that the classical paradigm of a truncated
accretion disk in the low/hard state can not be ruled out by these data. We
further discovered a broad iron emission line between 6 and 7 keV in these
data. From fits to the line profile we found an inner disk radius that ranges
between ~6-16 gravitational radii, which can be in fact much larger, up to ~250
gravitational radii, depending on the model used to fit the continuum and the
line. We discuss the implications of these results in the context of a fully or
partially truncated accretion disk.Comment: 10 pages, 3 figures, 1 table, accepted for publication on MNRAS,
using mn2e.cls style fil
Multiwavelength spectral and high time resolution observations of SWIFT J1753.5-0127: new activity?
We have conducted an extensive observational campaign of SWIFT J1753.5-0127
during June 2007 after its bright outburst episode in 2005. We have performed
multi-band optical photometry, optical spectroscopy, X-ray spectroscopy and
timing and ULTRACAM optical photometry simultaneously in three bands. Both the
optical spectrum and the X-ray spectrum, along with enhanced brightness in
broad-band photometry point to recent increased activity. We analyze the
different spectral regions, finding a smooth optical continuum with a
remarkable lack of lines and a very blue component modulated with a period of
3.2hr and a hard power-law X-ray spectrum. Both the X-ray and optical power
spectra are flat at low frequencies up to the 0.1 Hz (10 s) range, then
decreasing roughly as a power law consistent with flickering. Furthermore, the
optical data show quasi-periodic oscillations (QPOs) near 0.08 Hz (13 s).
Together with a dynamical and auto-correlation analysis of the light curves we
attempt to construct a complete physical picture of this intriguing system.Comment: 20 pages. Accepted for publication in MNRA
BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
During the last ~50 years, the population of black hole candidates in X-ray
binaries has increased considerably with 59 Galactic objects detected in
transient low-mass X-ray binaries, plus a few in persistent systems (including
~5 extragalactic binaries). We collect near-infrared, optical and X-ray
information spread over hundreds of references in order to study the population
of black holes in X-ray transients as a whole. We present the most updated
catalogue of black hole transients, which contains X-ray, optical and
near-infrared observations together with their astrometric and dynamical
properties. It provides new useful information in both statistical and
observational parameters providing a thorough and complete overview of the
black hole population in the Milky Way. Analysing the distances and spatial
distribution of the observed systems, we estimate a total population of ~1300
Galactic black hole transients. This means that we have already discovered less
than ~5% of the total Galactic distribution. The complete version of this
catalogue will be continuously updated online and in the Virtual Observatory,
including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in
Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table
Phloem sap intricacy and interplay with aphid feeding
Aphididae feed upon the plant sieve elements (SE), where they ingest sugars, nitrogen compounds and other nutrients. For ingestion, aphid stylets penetrate SE, and because of the high hydrostatic pressure in SE, phloem sap exudes out into the stylets. Severing stylets to sample phloem exudates (i.e. stylectomy) has been used extensively for the study of phloem contents. Alternative sampling techniques are spontaneous exudation upon wounding that only works in a few plant species, and the popular EDTA-facilitated exudation technique. These approaches have allowed fundamental advances on the understanding of phloem sap composition and sieve tube physiology, which are surveyed in this review. A more complete picture of metabolites, ions, proteins and RNAs present in phloem sap is now available, which has provided large evidence for the phloem role as a signalling network in addition to its primary role in partitioning of photo-assimilates. Thus, phloem sap sampling methods can have remarkable applications to analyse plant nutrition, physiology and defence responses. Since aphid behaviour is suspected to be affected by phloem sap quality, attempts to manipulate phloem sap content were recently undertaken based on deregulation in mutant plants of genes controlling amino acid or sugar content of phloem sap. This opens up new strategies to control aphid settlement on a plant host
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
Measurement of the mass and lifetime of the baryon
A proton-proton collision data sample, corresponding to an integrated
luminosity of 3 fb collected by LHCb at and 8 TeV, is used
to reconstruct , decays. Using the , decay mode for calibration, the lifetime ratio and absolute
lifetime of the baryon are measured to be \begin{align*}
\frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\
\tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the
uncertainties are statistical, systematic and from the calibration mode (for
only). A measurement is also made of the mass difference,
, and the corresponding mass, which
yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm
MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2.
\end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm
Study of and decays and determination of the CKM angle
We report a study of the suppressed and favored
decays, where the neutral meson is detected
through its decays to the and CP-even and
final states. The measurement is carried out using a proton-proton
collision data sample collected by the LHCb experiment, corresponding to an
integrated luminosity of 3.0~fb. We observe the first significant
signals in the CP-even final states of the meson for both the suppressed
and favored modes, as well as
in the doubly Cabibbo-suppressed final state of the decay. Evidence for the ADS suppressed decay , with , is also presented. From the observed
yields in the , and their
charge conjugate decay modes, we measure the value of the weak phase to be
. This is one of the most precise
single-measurement determinations of to date.Comment: 22 pages, 9 figures; All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-020.htm
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