Search results for "Spectral Density"
showing 10 items of 223 documents
Discovery of periodic dips in the light curve of GX 13+1: the X-ray orbital ephemeris of the source
2014
The bright low-mass X-ray binary (LMXB) GX 13+1 is one of the most peculiar Galactic binary systems. A periodicity of 24.27 d with a formal statistical error of 0.03 d was observed in its power spectrum density obtained with RXTE All Sky Monitor (ASM) data spanning 14 years. Starting from a recent study, indicating GX 13+1 as a possible dipping source candidate, we systematically searched for periodic dips in the X-ray light curves of GX 13+1 from 1996 up to 2013 using RXTE/ASM, and MAXI data to determine for the first time the X-ray orbital ephemeris of GX 13+1. We searched for a periodic signal in the ASM and MAXI light curves, finding a common periodicity of 24.53 d. We folded the 1.3-5 …
Numerical study of broadband spectra caused by internal shocks in magnetized relativistic jets of blazars
2013
The internal-shocks scenario in relativistic jets has been used to explain the variability of blazars' outflow emission. Recent simulations have shown that the magnetic field alters the dynamics of these shocks producing a whole zoo of spectral energy density patterns. However, the role played by magnetization in such high-energy emission is still not entirely understood. With the aid of \emph{Fermi}'s second LAT AGN catalog, a comparison with observations in the $\gamma$-ray band was performed, in order to identify the effects of the magnetic field.
Threshold expansion of Feynman diagrams within a configuration space technique
2000
The near threshold expansion of generalized sunset-type (water melon) diagrams with arbitrary masses is constructed by using a configuration space technique. We present analytical expressions for the expansion of the spectral density near threshold and compare it with the exact expression obtained earlier using the method of the Hankel transform. We formulate a generalized threshold expansion with partial resummation of the small mass corrections for the strongly asymmetric case where one particle in the intermediate state is much lighter than the others.
Revisiting a vector-tensor theory of gravitation
2011
A certain vector-tensor theory of gravitation has been recently studied. In this theory, the zero-order energy density of the vector field could play the role of dark energy. In such a case, the question is: could the theory explain current cosmological observations as well as the so-called concordance model? Previous papers on the subject only consider a reduced number of current observations. We consider a wider set of observations including supernovae of type Ia, cosmic microwave background anisotropies, and the power spectrum of the energy density fluctuations. Results imply that, for negligible scalar perturbations of the vector field, the theory does not work.
Corrigendum: Fabrication and heating rate study of microscopic surface electrode ion traps
2012
We report heating rate measurements in a microfabricated goldon-sapphire surface electrode ion trap with a trapping height of approximately 240 μm. Using the Doppler recooling method, we characterize the trap heating rates over an extended region of the trap. The noise spectral density of the trap falls in the range of noise spectra reported in ion traps at room temperature. We find that during the first months of operation, the heating rates increase by approximately one order of magnitude. The increase in heating rates is largest in the ion-loading region of the trap, providing a strong hint that surface contamination plays a major role for excessive heating rates. We discuss data found i…
Primordial Black Holes and Slow-Roll Violation
2017
For primordial black holes (PBH) to be the dark matter in single-field inflation, the slow-roll approximation must be violated by at least ${\cal O}(1)$ in order to enhance the curvature power spectrum within the required number of efolds between CMB scales and PBH mass scales. Power spectrum predictions which rely on the inflaton remaining on the slow-roll attractor can fail dramatically leading to qualitatively incorrect conclusions in models like an inflection potential and misestimate the mass scale in a running mass model. We show that an optimized temporal evaluation of the Hubble slow-roll parameters to second order remains a good description for a wide range of PBH formation models …
Linking Jet Emission, X‐Ray States, and Hard X‐Ray Tails in the Neutron Star X‐Ray Binary GX 17 \documentclass{aastex} \usepackage{amsbsy} \usepackag…
2007
We present the results from simultaneous radio (Very Large Array) and X-ray (Rossi-X-ray Timing Explorer) observations of the Z-type neutron star X-ray binary GX~17+2. The aim is to assess the coupling between X-ray and radio properties throughout its three rapidly variable X-ray states and during the time-resolved transitions. These observations allow us, for the first time, to investigate quantitatively the possible relations between the radio emission and the presence of the hard X-ray tails and the X-ray state of the source. The observations show: 1) a coupling between the radio jet emission and the X-ray state of the source, i.e. the position in the X-ray hardness-intensity diagram (HI…
O(αs)corrections to the correlator of finite mass baryon currents
2000
We present analytical next-to-leading order results for the correlator of baryonic currents at the three-loop level with one finite mass quark. We obtain the massless and the HQET limit of the correlator from the general formula as particular cases. We also give explicit expressions for the moments of the spectral density.
Digital simulation of wind field velocity
1998
Abstract In this paper some computational aspects on the generation procedure of n -variate wind velocity vectors are discussed in detail. Decompositions of the power spectral density matrix are also discussed showing the physical significance of eigenquantities of this matrix.
Line Features in Psds of X-Ray Binaries
1994
There is a great deal of evidence that the X-ray emission from High Mass X-Ray Binaries (HMXRB) is often associated with the accretion of matter from a “normal” companion to a degenerate (neutron) star. Provided the magnetic field in these systems is very high (B ~ 1012 — 1013 G), the accretion should occur via the formation of discrete “blobs” which should emit through bremsstrahlung process due to the sudden stop near the surface of the neutron star[2, 3, 5]. There are a number of detections of non-Poissonian aperiodic variations in the intensity of emitted radiation (often referred to as “flickering”) with a characteristic Power Spectrum Density (PSD) broad band feature (red noise)[4, 1]…