Comparing Rees-Sciama and Integrated Sachs Wolfe effects
AIP Conference Proceedings, 2006
Both the Rees-Sciama (RS) and the Integrated Sachs-Wolfe (ISW) effects are produced by the peculi... more Both the Rees-Sciama (RS) and the Integrated Sachs-Wolfe (ISW) effects are produced by the peculiar gravitational potential of cosmological inhomogeneities. This potential fully defines a scalar perturbation of the Robertson-Walker metric in the longitudinal gauge. The RS (ISW) effect is produced by nonlinear (linear) structures which grow as a result of gravitational instability. The anisotropies corresponding to these two effects
The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intens... more The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in compact binary systems, which provide variable conditions along eccentric orbits. Despite this, the nature of some of these systems, and of the accelerated particles producing the VHE emission, is unclear. To answer some of these open questions, we conducted a multiwavelength campaign of the VHE gamma-ray emitting X-ray binary LS I +61 303 including the MAGIC telescope, XMM-Newton, and Swift during 60% of an orbit in 2007 September. We detect
Publications of the Astronomical Society of Japan, 2009
Suzaku observations of the blazar OJ 287 were performed in 2007 April 10-13 and November 7-9. The... more Suzaku observations of the blazar OJ 287 were performed in 2007 April 10-13 and November 7-9. They correspond to a quiescent and a flaring state, respectively. The X-ray spectra of the source can be well-described with single power-law models in both exposures. The derived X-ray photon index and the flux density at 1 keV were found to be Γ = 1.65˙0.02 and S 1keV = 215˙5 nJy in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum (Γ = 1.50˙0.01) with a nearly doubled X-ray flux density of S 1keV = 404 +6 5 nJy. Moreover, significant hard X-ray signals were detected up to 27 keV. In cooperation with Suzaku, simultaneous radio, optical, and very-high-energy-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04˙0.46 Jy and 8.93˙0.05 mJy at 86.75 Hz and in the V-band, respectively) were found to be higher by a factor of 2-3 than those in the quiescent state (1.73˙0.26 Jy and 3.03˙0.01 mJy at 86.75 Hz and in the V-band, respectively). No notable-ray events were detected in either observation. The spectral energy distribution of OJ 287 indicated that the X-ray spectrum was dominated by inverse Compton radiation in both observations, while synchrotron radiation exhibited a spectral cutoff at around the optical frequency. Furthermore, no significant difference in the synchrotron cutoff frequency was found between the quiescent and flaring states. According to a simple synchrotron self-Compton model, the change of the spectral energy distribution is due to an increase in the energy density of electrons with small changes of both the magnetic field strength and the maximum Lorentz factor of electrons.
Monthly Notices of the Royal Astronomical Society, 2006
Small maps of the Rees-Sciama (RS) effect are simulated by using an appropriate N-body code and a... more Small maps of the Rees-Sciama (RS) effect are simulated by using an appropriate N-body code and a certain ray-tracing procedure. A method designed for the statistical analysis of cosmic microwave background (CMB) maps is applied to study the resulting simulations. These techniques, recently proposed-by our team-to consider lens deformations of the CMB, are adapted to deal with the RS effect. This effect and the deviations from Gaussianity associated to it seem to be too small to be detected in the near future. This conclusion follows from our estimation of both the RS angular power spectrum and the RS reduced n-direction correlation functions for n 6.
From emission to inertial coordinates: a numerical approach
Journal of Physics: Conference Series, 2011
We numerically implement the coordinate transformation between emission and inertial coordinates ... more We numerically implement the coordinate transformation between emission and inertial coordinates recently derived -in Minkowski space-time- by Coll et al. [1]. In order to carry out this transformation, we must know both proper times from four satellites and the inertial coordinates of these satellites when they emitted. It allows us to determine the position and the time coordinate of the receiver. Since we need to know the satellite positions at any time, we have simulated satellite constellations similar to those of GPS and Galileo global positioning system. All the satellite positions are calculated, at any time, with respect to an inertial frame with the origin at the Earth center. The orientation criterion described by the same authors [2] has been also implemented. The code has been appropiately tested and, then it has been applied to perform a preliminary study about the structure of the emission coordinate region and the grid region. The errors due to uncertainties in satellite positions have been also estimated.
Global navigation satellite systems use appropriate satellite constellations to get the coordinat... more Global navigation satellite systems use appropriate satellite constellations to get the coordinates of an user-close to Earth-in an almost inertial reference system. We have simulated both GPS and GALILEO constellations. Uncertainties in the satellite world lines lead to dominant positioning errors. In this paper, a detailed analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called relativistic positioning systems. Our study is based on the Jacobian (J) of the transformation giving the emission coordinates in terms of the inertial ones. Around points of vanishing J, positioning errors are too large. We show that, for any 4-tuple of satellites, the points with J = 0 are located at distances, D, from the Earth centre greater than about 2R/3, where R is the radius of the satellite orbits which are assumed to be circumferences. Our results strongly suggest that, for Ddistances greater than 2R/3 and smaller than 10 5 km, a rather good positioning may be achieved by using appropriate satellite 4-tuples without J = 0 points located in the user vicinity. The way to find these 4-tuples is discussed for arbitrary users with D < 10 5 km and, then, preliminary considerations about satellite navigation at D < 10 5 km are presented. Future work on the subject of space navigation-based on appropriate simulations-is in progress.
Global navigation satellite systems use appropriate satellite constellations to get the coordinat... more Global navigation satellite systems use appropriate satellite constellations to get the coordinates of an user-close to Earth-in an almost inertial reference system. We have simulated both GPS and GALILEO constellations. Uncertainties in the satellite world lines lead to dominant positioning errors. In this paper, a detailed analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called relativistic positioning systems. Our study is based on the Jacobian (J) of the transformation giving the emission coordinates in terms of the inertial ones. Around points of vanishing J, positioning errors are too large. We show that, for any 4-tuple of satellites, the points with J = 0 are located at distances, D, from the Earth centre greater than about 2R/3, where R is the radius of the satellite orbits which are assumed to be circumferences. Our results strongly suggest that, for Ddistances greater than 2R/3 and smaller than 10 5 km, a rather good positioning may be achieved by using appropriate satellite 4-tuples without J = 0 points located in the user vicinity. The way to find these 4-tuples is discussed for arbitrary users with D < 10 5 km and, then, preliminary considerations about satellite navigation at D < 10 5 km are presented. Future work on the subject of space navigation-based on appropriate simulations-is in progress.
We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU)... more We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the Schwarzschild space-time produced by an idealized spherically symmetric non rotating Earth. The trajectories are then circumferences centered at the same point as Earth. Photon motions are described in Minkowski space-time, where there is a well known relation, Coll, Ferrando & Morales-Lladosa (2010), between the emission and inertial coordinates of any event. Here, this relation is implemented in a numerical code, which is tested and applied. The first application is a detailed numerical four-dimensional analysis of the so-called emission coordinate region and co-region. In a second application, a GPS (Galileo) satellite is considered as the receiver and its emission coordinates are given by four Galileo (GPS) satellites. The bifurcation problem (double localization) in the positioning of the receiver satellite is then pointed out and discussed in detail.
In the context of relativistic positioning, the coordinates of a given user may be calculated by ... more In the context of relativistic positioning, the coordinates of a given user may be calculated by using suitable information broadcast by a 4-tuple of satellites. Our 4-tuples belong to the Galileo constellation. Recently, we estimated the positioning errors due to uncertainties in the satellite world lines (U-errors). A distribution of U-errors was obtained, at various times, in a set of points covering a large region surrounding Earth. Here, the positioning errors associated to the simplifying assumption that photons move in Minkowski space-time (S-errors) are estimated and compared with the U-errors. Both errors have been calculated for the same points and times to make comparisons possible. For a certain realistic modeling of the world line uncertainties, the estimated S-errors have proved to be smaller than the U-errors, which shows that the approach based on the assumption that the Earth's gravitational field produces negligible effects on photons may be used in a large reg...
The motion of satellite constellations similar to GPS and Galileo is numerically simulated and, t... more The motion of satellite constellations similar to GPS and Galileo is numerically simulated and, then, the region where bifurcation (double positioning) occurs is appropriately represented. In the cases of double positioning, the true location may be found using additional information (angles or times). The zone where the Jacobian, J, of the transformation from inertial to emission coordinates vanishes is also represented and interpreted. It is shown that the uncertainties in the satellite world lines produce positioning errors, which depend on the value of |J|. The smaller this quantity the greater the expected positioning errors. Among all the available 4tuples of satellites, the most appropriate one-for a given location-should minimize positioning errors (large enough |J| values) avoiding bifurcation. Our study is particularly important to locate objects which are far away from Earth, e.g., satellites.
The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intens... more The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in compact binary systems, which provide variable conditions along eccentric orbits. Despite this, the nature of some of these systems, and of the accelerated particles producing the VHE emission, is unclear. To answer some of these open questions, we conducted a multiwavelength campaign of the VHE gamma-ray emitting X-ray binary LS I +61 303 including the MAGIC telescope, XMM-Newton, and Swift during 60% of an orbit in 2007 September. We detect
Proceedings of CMB and Physics of the Early Universe — PoS(CMB2006)
The fully nonlinear evolution of galaxy clusters and substructures-given by N-body simulationsis ... more The fully nonlinear evolution of galaxy clusters and substructures-given by N-body simulationsis used to simulate maps of the Rees-Sciama (RS) effect. The universe is covered by simulation boxes and photons move across them. A recent technique for ray-tracing through N-body simulations is described in detail and implemented. It is based on the existence of preferred directions (to move photons through the boxes), and also on the use of an appropriate cutoff. By the moment, only small RS maps (around 2 • × 2 •) have been obtained with this technique. We justify that our ray-tracing procedure is also appropriate in the case of large simulation cubes (∼ 1000 M pc per edge), where high enough resolutions can be obtained with appropriate N-body codes and modern computers.
In the context of relativistic positioning, the coordinates of a given user may be calculated by ... more In the context of relativistic positioning, the coordinates of a given user may be calculated by using suitable information broadcast by a 4-tuple of satellites. Our 4-tuples belong to the Galileo constellation. Recently, we estimated the positioning errors due to uncertainties in the satellite world lines (U-errors). A distribution of U-errors was obtained, at various times, in a set of points covering a large region surrounding Earth. Here, the positioning errors associated to the simplifying assumption that photons move in Minkowski space-time (S-errors) are estimated and compared with the U-errors. Both errors have been calculated for the same points and times to make comparisons possible. For a certain realistic modeling of the world line uncertainties, the estimated S-errors have proved to be smaller than the U-errors, which shows that the approach based on the assumption that the Earth's gravitational field produces negligible effects on photons may be used in a large region surrounding Earth. The applicability of this approach-which simplifies numerical calculations-to positioning problems, and the usefulness of our S-error maps, are pointed out. A better approach, based on the assumption that photons move in the Schwarzschild space-time governed by an idealized Earth, is also analyzed. More accurate descriptions of photon propagation involving non symmetric space-time structures are not necessary for ordinary positioning and spacecraft navigation around Earth.
The motion of satellite constellations similar to GPS and Galileo is numerically simulated and, t... more The motion of satellite constellations similar to GPS and Galileo is numerically simulated and, then, the region where bifurcation (double positioning) occurs is appropriately represented. In the cases of double positioning, the true location may be found using additional information (angles or times). The zone where the Jacobian, J, of the transformation from inertial to emission coordinates vanishes is also represented and interpreted. It is shown that the uncertainties in the satellite world lines produce positioning errors, which depend on the value of |J|. The smaller this quantity the greater the expected positioning errors. Among all the available 4-tuples of satellites, the most appropriate one -for a given location- should minimize positioning errors (large enough |J| values) avoiding bifurcation. Our study is particularly important to locate objects which are far away from Earth, e.g., satellites.
Numerical simulations of the gravitational wave background produced by binaries
The incoherent gravitational waves produced by the elements of some toy distributions of binaries... more The incoherent gravitational waves produced by the elements of some toy distributions of binaries are numerically superimposed and, then, the effect of the resulting signal on a detector formed by three particles (which move along geodesics in the solar system space-time) is calculated. The numerical code created in this preliminary work must be improved with the essential aim of performing appropriate simulations to be used -for data analysis- in LISA mission for the detection of gravitational waves (NASA/ESA).
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Papers by Neus Puchades