A characterization of the NGC 4051 soft X-ray spectrum as observed by XMM-Newton

Soft X-rays high resolution spectroscopy of obscured AGNs shows the existence of a complex soft $X$-ray spectrum dominated by emission lines of He and H-like transitions of elements from Carbon to Neon, as well as L-shell transitions due to iron ions. In this paper we characterize the XMM-Newton RGS spectrum of the Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the physical properties of the emitting and absorbing gas in the soft X-ray regime. X-ray high-resolution spectroscopy offers a powerful diagnostic tool since the observed spectral features strongly depend on the physical properties of matter (ionization parameter U, electron density n_e, hydrogen column density N_H), which in turn are tightly related to the location and size of the X-ray emitting clouds. We carried out a phenomenological study to identify the atomic transitions detected in the spectra. This study suggests that the spectrum is dominated by emission from a photoionised plasma. Then, we used the photoionization code Cloudy to produce synthetic models for the emission line component and the warm absorber observed during phases of high intrinsic luminosity. The low state spectrum cannot be described by a single photoionization component. A multi-ionization phase gas with ionization parameter in the range log U = 0.63-1.90 and column density log N_H = 22.10-22.72 cm^-2 is required, while the electron density n_e remains unconstrained. A warm absorber medium is required by the fit with parameters log U = 0.85, log N_H = 23.40 and log n_e \ut< 5. The model is consistent with an X-ray emitting regions at a distance > 5 x 10^-2 pc from the central engine.Comment: Accepted for publication on section 4 "Extragalactic astronomy" of Astronomy and Astrophysics, 2010, 12 pages, 8 Figures, 4 Tables, in printer format. A few typos corrected

A USB3.0 FPGA Event-based Filtering and Tracking Framework for Dynamic Vision Sensors

Dynamic vision sensors (DVS) are frame-free sensors with an asynchronous variable-rate output that is ideal for hard real-time dynamic vision applications under power and latency constraints. Post-processing of the digital sensor output can reduce sensor noise, extract low level features, and track objects using simple algorithms that have previously been implemented in software. In this paper we present an FPGA-based framework for event-based processing that allows uncorrelated-event noise removal and real-time tracking of multiple objects, with dynamic capabilities to adapt itself to fast or slow and large or small objects. This framework uses a new hardware platform based on a Lattice FPGA which filters the sensor output and which then transmits the results through a super-speed Cypress FX3 USB microcontroller interface to a host computer. The packets of events and timestamps are transmitted to the host computer at rates of 10 Mega events per second. Experimental results are presented that demonstrate a low latency of 10us for tracking and computing the center of mass of a detected object.Ministerio de Economía y Competitividad TEC2012-37868-C04-0

On the driver of relativistic effects strength in Seyfert galaxies

Spectroscopy of X-ray emission lines emitted in accretion discs around supermassive black holes is one of the most powerful probes of the accretion flow physics and geometry, while also providing in principle observational constraints on the black hole spin.[...] We aim at determining the ultimate physical driver of the strength of this relativistic reprocessing feature. We first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties depends on the AGN optical classification, as expected from the Seyfert unification scenarios. There is also no correlation between the accretion disc inclination, as derived from formal fits of the line profiles, and the optical type or host galaxy aspect angle, suggesting that the innermost regions of the accretion disc and the host galaxy plane are not aligned. [...]. Data are not sensitive enough to the detailed ionisation state of the line-emitting disc. However, the lack of dependency of the line EW on either the luminosity or the rest-frame centroid energy rules out that disc ionisation plays an important role on the EW dynamical range in Seyferts. The dynamical range of the relativistically broadened K-alpha iron line EW in nearby Seyferts appears to be mainly determined by the properties of the innermost accretion flow. We discuss several mechanisms (disc ionisation, disc truncation, aberration due to a mildly relativistic outflowing corona) which can explain this. [...] Observational data are still not in contradiction with scenarios invoking different mechanisms for the spectral complexity around the iron line, most notably the "partial covering" absorption scenario. (abridged).Comment: Accepted for publication on Astronomy & Astrophysics. 14 pages, 9 figure

Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385

This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy H0557-385 obtained in 2006, which show the source at an historical low flux state, more than a factor of 10 lower than a previous XMM-Newton look in 2002. The low flux spectrum presents a strong Fe Kalpha line associated to a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially covering the primary emission, which still contributes for a few percent of the soft X-ray emission. Absorption by ionised material on the line of sight is required to fit the deep trough below 1 keV. The comparison of the two spectral states shows that the flux transition is to be ascribed entirely to intervening line-of-sight clouds with high column density.Comment: 5 pages, accepted for publication on MNRAS Letter

The rise of an ionized wind in the Narrow Line Seyfert 1 Galaxy Mrk 335 observed by XMM-Newton and HST

We present the discovery of an outflowing ionized wind in the Seyfert 1 Galaxy Mrk 335. Despite having been extensively observed by most of the largest X-ray observatories in the last decade, this bright source was not known to host warm absorber gas until recent XMM-Newton observations in combination with a long-term Swift monitoring program have shown extreme flux and spectral variability. High resolution spectra obtained by the XMM-Newton RGS detector reveal that the wind consists of three distinct ionization components, all outflowing at a velocity of 5000 km/s. This wind is clearly revealed when the source is observed at an intermediate flux state (2-5e-12 ergs cm^-2 s^-1). The analysis of multi-epoch RGS spectra allowed us to compare the absorber properties at three very different flux states of the source. No correlation between the warm absorber variability and the X-ray flux has been determined. The two higher ionization components of the gas may be consistent with photoionization equilibrium, but we can exclude this for the only ionization component that is consistently present in all flux states (log(xi)~1.8). We have included archival, non-simultaneous UV data from HST (FOS, STIS, COS) with the aim of searching for any signature of absorption in this source that so far was known for being absorption-free in the UV band. In the COS spectra obtained a few months after the X-ray observations we found broad absorption in CIV lines intrinsic to the AGN and blueshifted by a velocity roughly comparable to the X-ray outflow. The global behavior of the gas in both bands can be explained by variation of the covering factor and/or column density, possibly due to transverse motion of absorbing clouds moving out of the line of sight at Broad Line Region scale.Comment: 24 pages, 12 figures, ApJ accepte

Electrical conductances of Tetrabutylammonium and Decamethylferrocenium Hexafluorophosphate in organic solvents

The electrical conductances of tetrabutylammonium hexafluorophosphate in acetone and of decamethylferrocenium hexafluorophosphate in acetone, acetonitrile 1,2-dichloroethane, and dichloromethane have been measured at 25°C. The Walden product of the Bu4N+ cation and the PF-6 anion in acetone and other solvents is discussed in relation to the dielectric friction. The electric conductance at infinite dilution and the association constant of decamethylferrocenium hexafluorophosphate were determined in the four solvents investigated. The association constant of this electrolyte increases with decreasing reduced temperature, as expected in the framework of the association theory, within the primitive model of electrolytes.Fil: Goldfarb, Darío L.. Comisión Nacional de Energía Atómica; ArgentinaFil: Longinotti, María Paula. Comisión Nacional de Energía Atómica; ArgentinaFil: Corti, Horacio Roberto. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Relativistic inflow in the Seyfert 1 Mrk 335 revealed through X-ray absorption

The analysis of hard X-ray features in XMM-Newton data of the bright Sy 1 galaxy Mrk 335 is reported here. The presence of a broad, ionised iron K alpha emission line in the spectrum, first found by Gondoin et al.(2002), is confirmed. The broad line can be modeled successfully by relativistic accretion disc reflection models. Regardless of the underlying continuum we report, for the first time in this source, the detection of a narrow absorption feature at the rest frame energy of ~5.9 keV. If the feature is identified with a resonance absorption line of iron in a highly ionised medium, the redshift of the line corresponds to an inflow velocity of ~0.11-0.15 c. Preliminary results from a longer (100ks) exposure are also presented