Recently, wavelets and R/S analysis have been used as statistical tools to characterize the optical flickering of cataclysmic variables. Here we present the first comprehensive study of the statistical properties of X-ray flickering of cataclysmic va
riables in order to link them with physical parameters. We analyzed a sample of 97 X-ray light curves of 75 objects of all classes observed with the XMM-Newton space telescope. By using the wavelets analysis, each light curve has been characterized by two parameters, alpha and Sigma, that describe the energy distribution of flickering on different timescales and the strength at a given timescale, respectively. We also used the R/S analysis to determine the Hurst exponent of each light curve and define their degree of stochastic memory in time. The X-ray flickering is typically composed of long time scale events (1.5 < alpha < 3), with very similar strengths in all the subtypes of cataclysmic variables (-3 < Sigma < -1.5). The X-ray data are distributed in a much smaller area of the alpha-Sigma parameter space with respect to those obtained with optical light curves. The tendency of the optical flickering in magnetic systems to show higher Sigma values than the non-magnetic systems is not encountered in the X-rays. The Hurst exponents estimated for all light curves of the sample are larger than those found in the visible, with a peak at 0.82. In particular, we do not obtain values lower than 0.5. The X-ray flickering presents a persistent memory in time, which seems to be stronger in objects containing magnetic white dwarf primaries. The similarity of the X-ray flickering in objects of different classes together with the predominance of a persistent stochastic behavior can be explained it terms of magnetically-driven accretion processes acting in a considerable fraction of the analyzed objects.
We study the optical properties of a two-axis galvanometric optical scanner constituted by a pair of rotating planar mirrors, focusing our attention on the transformation induced on the polarization state of the input beam. We obtain the matrix that
defines the transformation of the propagation direction of the beam and the Jones matrix that defines the transformation of the polarization state. Both matrices are expressed in terms of the rotation angles of two mirrors. Finally, we calculate the parameters of the general rotation in the Poincare sphere that describes the change of polarization state for each mutual orientation of the mirrors.
A significant number of cataclysmic variables were detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type. We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS
J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class. Timing and spectral analysis of IGR J00234+6141 are based on a XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725 we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data. We determine a spin period of 561.64 +/- 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to about 2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 +/- 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of about 50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of about 100 eV. This latter adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars. (abridged)
We study the properties of the Fraunhofer diffraction patterns produced by Gaussian beams crossing spiral phase plates. We show, both analytically and numerically, that off-axis displacements of the input beam produce asymmetric diffraction patterns.
The intensity profile along the direction of maximum asymmetry shows two different peaks. We find that the intensity ratio between these two peaks decreases exponentially with the off-axis displacement of the incident beam, the decay being steeper for higher strengths of the optical singularity of the spiral phase plate. We analyze how this intensity ratio can be used to measure small misalignments of the input beam with a very high precision.
We analyze the first X-ray observations with XMM-Newton of RXS J070407.9+262501 and 1RXS 180340.0+401214, in order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as Intermediate P
olars. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS 180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2-10.0 keV range to characterize the emission properties of both sources. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3-5 keV, by strong pulsations at the white dwarf rotational periods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS 180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beat variability at 1697 s which, together with our new optical spectroscopy, favours an orbital period of 4.4 hr that is longer than previously estimated. Both systems show complex spectra with a hard (up to 40 keV) optically thin and a soft (85-100 eV) optically thick components heavily absorbed by material partially covering the X-ray sources. Our observations confirm the two systems as Intermediate Polars and also add them as new members of the growing group of soft systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation.
