The INTEGRAL high energy cut-off distribution of type 1 AGN

In this letter we present the primary continuum parameters, the photon index Gamma and the high energy cut-off Ec, of 41 type-1 Seyfert galaxies extracted from the INTEGRAL complete sample of AGN. We performed a broad band (0.3-100 keV) spectral analysis by fitting simultaneously the soft and hard X-ray spectra obtained by XMM and INTEGRAL/IBIS-Swift/BAT respectively in order to investigate the general properties of these parameters in particular their distribution and mean values. We find a mean photon index for the whole sample of 1.73 with a standard deviation of 0.17 and a mean high energy cut-off of 128 keV with a standard deviation of 46 keV. This is the first time that the cut-off energy is constrained in a such large number of AGN. We have 26 measurements of the cut-off, which corresponds to 63% of the entire sample, distributed between 50 and 200 keV. There are a further 11 lower limits mostly below 300 keV. Using the main parameters of the primary continuum, we have been able to obtain the actual physical parameters of the Comptonizing region i.e. the plasma temperature kT_e from 20 to 100 keV and the optical depth tau <4. Finally, with the high S/N spectra starting to come from NuSTAR it will soon be possible to better constrain the cut-off values in many AGN, allowing the determination of more physical models and so to better understand the continuum emission and geometry of the region surrounding black holes.Comment: 21 pages, 4 figures, 1 table. Accepted for publication on ApJ Letter

Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

International audienceMexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere

Distinct wind convergence patterns due to thermal and momentum forcing of the low level jet into the Mexico City basin

International audienceMexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A low level jet entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the jet. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The low level jet is found to occur on most days of the campaign and is primarily due to thermal forcing which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the jet and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to stronger jets and a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere

Stationary Localized States Due to a Nonlinear Dimeric Impurity Embedded in a Perfect 1-D Chain

The formation of Stationary Localized states due to a nonlinear dimeric impurity embedded in a perfect 1-d chain is studied here using the appropriate Discrete Nonlinear Schr$\ddot{o}$dinger Equation. Furthermore, the nonlinearity has the form, $\chi |C|^\sigma$ where $C$ is the complex amplitude. A proper ansatz for the Localized state is introduced in the appropriate Hamiltonian of the system to obtain the reduced effective Hamiltonian. The Hamiltonian contains a parameter, $\beta = \phi_1/\phi_0$ which is the ratio of stationary amplitudes at impurity sites. Relevant equations for Localized states are obtained from the fixed point of the reduced dynamical system. $|\beta|$ = 1 is always a permissible solution. We also find solutions for which $|\beta| \ne 1$. Complete phase diagram in the $(\chi, \sigma)$ plane comprising of both cases is discussed. Several critical lines separating various regions are found. Maximum number of Localized states is found to be six. Furthermore, the phase diagram continuously extrapolates from one region to the other. The importance of our results in relation to solitonic solutions in a fully nonlinear system is discussed.Comment: Seven figures are available on reques

1/f noise in the Two-Body Random Ensemble

We show that the spectral fluctuations of the Two-Body Random Ensemble (TBRE) exhibit 1/f noise. This result supports a recent conjecture stating that chaotic quantum systems are characterized by 1/f noise in their energy level fluctuations. After suitable individual averaging, we also study the distribution of the exponent \alpha in the 1/f^{\alpha} noise for the individual members of the ensemble. Almost all the exponents lie inside a narrow interval around \alpha=1 suggesting that also individual members exhibit 1/f noise, provided they are individually unfoldedComment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.

Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry

International audienceContinuous ambient measurements with aerosol time-of-flight mass spectrometry (ATOFMS) were carried out in an industrial/residential section in the northern part of Mexico City as part of the Mexico City Metropolitan Area ? 2006 campaign (MCMA-2006) between 7?27 March, 2006. Biomass and organic carbon (OC) particle types were found to dominate the accumulation mode both day and night. The concentrations of both organic carbon and biomass particles were roughly equal early in the morning, but biomass became the largest contributor to the accumulation mode mass from the late morning until early evening. The diurnal pattern can be attributed to aging and/or a change in meteorology. Fresh elemental carbon (EC) particles were observed during rush hour. The majority of the EC particles were mixed with nitrate, sulfate, organic carbon and potassium. Submicron particles from industrial sources in the northeast were composed of an internal mixture of Pb, Zn, EC and Cl and peaked early in the morning. A unique nitrogen-containing organic (NOC) particle type was observed, and is hypothesized to be from industrial emissions based on the temporal profile and back trajectory analysis. This study provides unique insights into the real-time changes in single particle mixing state as a function of size and time for aerosols in Mexico City. These new findings indicate that biomass burning and industrial operations make significant contributions to particles in Mexico City. These sources have received relatively little attention in previous intensive field campaigns

Effect of nonlinearity on the dynamics of a particle in dc field-induced systems

Dynamics of a particle in a perfect chain with one nonlinear impurity and in a perfect nonlinear chain under the action of dc field is studied numerically. The nonlinearity appears due to the coupling of the electronic motion to optical oscillators which are treated in adiabatic approximation. We study for both the low and high values of field strength. Three different range of nonlinearity is obtained where the dynamics is different. In low and intermediate range of nonlinearity, it reduces the localization. In fact in the intermediate range subdiffusive behavior in the perfect nonlinear chain is obtained for a long time. In all the cases a critical value of nonlinear strength exists where self-trapping transition takes place. This critical value depends on the system and the field strength. Beyond the self-trapping transition nonlinearity enhances the localization.Comment: 9 pages, Revtex, 6 ps figures include