Outflow and feedback in active galactic nuclei: high-resolution X-ray spectroscopy and variability

Active Galactic Nuclei (AGN) are accreting supermassive black holes at the centers of galaxies. They can have a profound impact on the evolution of their host galaxies and surroundings by means of their outflows of ionized gas. However we still lack a solid understanding of how strong their outflows are and where they originate. Without this, we can not quantify the effect of feedback in a proper way. This thesis focusses on investigating the properties of the outflows by using high-resolution X-ray spectroscopy and variability studies. These outflows show their presence by blue-shifted absorption lines. A single, good quality observation can be used to characterize the properties of the outflow, such as outflow velocity, ionization structure and column densities of the different ions detected in the outflow. However, multiple observations of the same source are needed to constrain its location. By constraining the timescale on which changes in the ionization structure of the outflow occur, the distance to the outflow can be constrained. This has been done for two sources in this thesis, NGC 5548 and Mrk 509, leading to distance limits of several lightyears in both cases. AGN not only have outflows, but also show emission lines in their spectra. Whether these lines are produced by the same gas as that responsible for the absorption (i.e. the outflow) is unclear at the moment. The emission lines in NGC 5548 changed in flux between two observations and this has allowed us to for the first time constrain the geometry and location of the emitting region, showing that the emission lines could indeed be produced by the outflowing gas. A further systematic study including other sources did not show any evidence for variable emission lines however, mostly due to the limited signal to noise ratio of most observations

Tides in asynchronous binary systems

Context. Stellar oscillations are excited in non-synchronously rotating stars in binary systems due to the tidal forces. Tangential components of the tides can drive a shear flow which behaves as a differentially forced rotating structure in a stratified outer medium. Aims. The aims of this paper are to show that our single-layer approximation for the calculation of the forced oscillations yields results that are consistent with the predictions for the synchronization timescales in circular orbits, τsync ∼ a6, thus providing a simplified means of computing the energy dissipation rates, ˙E . Furthermore, by calibrating our model results to fit the relationship between synchronization timescales and orbital separation, we are able to constrain the value of the kinematical viscosity parameter, ν. Methods. We compute the values of ˙E for a set of 5 M + 4 M model binary systems with different orbital separations, a, and use these to estimate the synchronization timescales. Results. The resulting τsynch vs. a relation is comparable to that of Zahn (1977, A&A, 57, 383) for convective envelopes, providing a calibration method for the values of ν. For the 4 + 5 M binary modeled in this paper, ν is in the range 0.0015–0.0043 R2 /day for orbital periods in the range 2.5–25 d. In addition, ˙E is found to decrease by ∼2 orders of magnitude as synchronization is approached, implying that binary systems may approach synchronization relatively quickly but that it takes a much longer timescale to actually attain this condition. Conclusions. The relevance of these results is threefold: 1) our model allows an estimate for the numerical value of ν under arbitrary conditions in the binary system; 2) it can be used to calculate the energy dissipation rates throughout the orbital cycle for any value of eccentricity and stellar rotational velocity; and 3) it provides values of the tangential component of the velocity perturbation at any time throughout the orbit and predicts the location on the stellar surface where the largest shear instabilities may be occurring. We suggest that one of the possible implication of the asymmetric distribution of ˙E over the stellar surface is the generation of localized regions of enhanced surface activity

Tides in asynchronous binary systems

Context. Stellar oscillations are excited in non-synchronously rotating stars in binary systems due to the tidal forces. Tangential components of the tides can drive a shear flow which behaves as a differentially forced rotating structure in a stratified outer medium. Aims. The aims of this paper are to show that our single-layer approximation for the calculation of the forced oscillations yields results that are consistent with the predictions for the synchronization timescales in circular orbits, τsync ∼ a6, thus providing a simplified means of computing the energy dissipation rates, ˙E . Furthermore, by calibrating our model results to fit the relationship between synchronization timescales and orbital separation, we are able to constrain the value of the kinematical viscosity parameter, ν. Methods. We compute the values of ˙E for a set of 5 M + 4 M model binary systems with different orbital separations, a, and use these to estimate the synchronization timescales. Results. The resulting τsynch vs. a relation is comparable to that of Zahn (1977, A&A, 57, 383) for convective envelopes, providing a calibration method for the values of ν. For the 4 + 5 M binary modeled in this paper, ν is in the range 0.0015–0.0043 R2 /day for orbital periods in the range 2.5–25 d. In addition, ˙E is found to decrease by ∼2 orders of magnitude as synchronization is approached, implying that binary systems may approach synchronization relatively quickly but that it takes a much longer timescale to actually attain this condition. Conclusions. The relevance of these results is threefold: 1) our model allows an estimate for the numerical value of ν under arbitrary conditions in the binary system; 2) it can be used to calculate the energy dissipation rates throughout the orbital cycle for any value of eccentricity and stellar rotational velocity; and 3) it provides values of the tangential component of the velocity perturbation at any time throughout the orbit and predicts the location on the stellar surface where the largest shear instabilities may be occurring. We suggest that one of the possible implication of the asymmetric distribution of ˙E over the stellar surface is the generation of localized regions of enhanced surface activity

XMM-Newton X-ray and Ultraviolet Observations of the Fast Nova V2491 Cyg during the Supersoft Source Phase

Two XMM-Newton observations of the fast classical nova V2491 Cyg were carried out in short succession on days 39.93 and 49.62 after discovery, during the supersoft source (SSS) phase, yielding simultaneous X-ray and UV light curves and high-resolution X-ray spectra. The first X-ray light curve is highly variable, showing oscillations with a period of 37.2 minutes after an extended factor of three decline lasting ∼3 hr, while the second X-ray light curve is less variable. The cause of the dip is currently unexplained and has most likely the same origin as similar events in the early SSS light curves of the novae V4743 Sgr and RS Oph, as it occurred on the same timescale. The oscillations are not present during the dip minimum and also not in the second observation. The UV light curves are variable but contain no dips and no period. High-resolution X-ray spectra are presented for four intervals of differing intensity. All spectra are atmospheric continua with deep absorption lines and absorption edges. Two interstellar lines of Oi and Ni are clearly seen at their rest wavelengths, while a large number of high-ionization absorption lines are found at blueshifts indicating an expansion velocity of 3000–3400 km s−1, which does not change significantly during the epochs of observation. Comparisons with the slower nova V4743 Sgr and the symbiotic recurrent nova RS Oph are presented. The SSS spectrum of V4743 Sgr is much softer with broader and more complex photospheric absorption lines. The ejecta are extended, allowing us to view a larger range of the radial velocity profile. Meanwhile, the absorption lines in RS Oph are as narrow as in V2491 Cyg, but they are less blueshifted. A remarkable similarity in the continua of V2491 Cyg and RS Oph is found. The only differences are smaller line shifts and additional emission lines in RS Oph that are related to the presence of a dense stellar wind from the evolved companion. Three unidentified absorption lines are present in the X-ray spectra of all three novae, with projected rest wavelengths 26.05 Å, 29.45 Å, and 30.0Å. No entirely satisfactory spectral model is currently available for the soft X-ray spectra of novae in outburst, and careful discussion of assumptions is required

Biomass burning fuel consumption rates: a field measurement database

Landscape fires show large variability in the amount of biomass or fuel consumed per unit area burned. Fuel consumption (FC) depends on the biomass available to burn and the fraction of the biomass that is actually combusted, and can be combined with estimates of area burned to assess emissions. While burned area can be detected from space and estimates are becoming more reliable due to improved algorithms and sensors, FC is usually modeled or taken selectively from the literature. We compiled the peer-reviewed literature on FC for various biomes and fuel categories to understand FC and its variability better, and to provide a database that can be used to constrain biogeochemical models with fire modules. We compiled in total 77 studies covering 11 biomes including savanna (15 studies, average FC of 4.6 t DM (dry matter) hag-1 with a standard deviation of 2.2), tropical forest (n Combining double low line 19, FC Combining double low line 126 ± 77), temperate forest (n Combining double low line 12, FC Combining double low line 58 ± 72), boreal forest (n Combining double low line 16, FC Combining double low line 35 ± 24), pasture (n Combining double low line 4, FC Combining double low line 28 ± 9.3), shifting cultivation (n Combining double low line 2, FC Combining double low line 23, with a range of 4.0-43), crop residue (n Combining double low line 4, FC Combining double low line 6.5 ± 9.0), chaparral (n Combining double low line 3, FC Combining double low line 27 ± 19), tropical peatland (n Combining double low line 4, FC Combining double low line 314 ± 196), boreal peatland (n Combining double low line 2, FC Combining double low line 42 [42-43]), and tundra (n Combining double low line 1, FC Combining double low line 40). Within biomes the regional variability in the number of measurements was sometimes large, with e.g. only three measurement locations in boreal Russia and 35 sites in North America. Substantial regional differences in FC were found within the defined biomes: for example, FC of temperate pine forests in the USA was 37% lower than Australian forests dominated by eucalypt trees. Besides showing the differences between biomes, FC estimates were also grouped into different fuel classes. Our results highlight the large variability in FC, not only between biomes but also within biomes and fuel classes. This implies that substantial uncertainties are associated with using biome-averaged values to represent FC for whole biomes. Comparing the compiled FC values with co-located Global Fire Emissions Database version 3 (GFED3) FC indicates that modeling studies that aim to represent variability in FC also within biomes, still require improvements as they have difficulty in representing the dynamics governing FC

Lipopolysaccharide enhances FcγR-dependent functions in vivo through CD11b/CD18 up-regulation

Fc receptors for immunoglobulin G (IgG) (FcγR) mediate several defence mechanisms in the course of inflammatory and infectious diseases. In Gram-negative infections, cellular wall lipopolysaccharides (LPS) modulate different immune responses. We have recently demonstrated that murine LPS in vivo treatment significantly increases FcγR-dependent clearance of immune complexes (IC). In addition, we and others have reported the induction of adhesion molecules on macrophages and neutrophils by LPS in vivo and by tumour necrosis factor-α (TNF-α) in vitro. The aim of this paper was to investigate CD11b/CD18 participation in LPS enhancing effects on Fcγ-dependent functionality of tissue macrophages. Our results have demonstrated that LPS can enhance antibody-dependent cellular cytotoxicity (ADCC) and IC-triggered cytotoxicity (IC-Ctx), two reactions which involve the Fcγ-receptor but different lytic mechanisms. In vitro incubation of splenocytes from LPS-treated mice with anti-CD11b/CD18 abrogated ADCC and IC-Ctx enhancement, without affecting FcγR expression. Similar results were obtained with physiological concentrations of fibrinogen. In this way cytotoxic values of LPS-splenocytes decreased to the basal levels of control mice. Time and temperature requirements for such inhibition strongly suggested that anti-CD11b/CD18 could modulate intracellular signals leading to downregulation of FcγR functionality. Data presented herein support the hypothesis that functional and/or physical associations between integrins and FcγR could be critical for the modulation of effector functions during an inflammatory response

Global satellite observations of column-averaged carbon dioxide and methane: The GHG-CCI XCO2 and XCH4 CRDP3 data set

International audienceCarbon dioxide (CO2) and methane (CH4) are the two most important greenhouse gases emitted by mankind. Better knowledge of the surface sources and sinks of these Essential Climate Variables (ECVs) and related carbon uptake and release processes is needed for important climate change related applications such as improved climate modelling and prediction. Some satellites provide near-surface-sensitive atmospheric CO2 and CH4 observations that can be used to obtain information on CO2 and CH4 surface fluxes. The goal of the GHG-CCI project of the European Space Agency's (ESA) Climate Change Initiative (CCI) is to use satellite data to generate atmospheric CO2 and CH4 data products meeting demanding GCOS (Global Climate Observing System) greenhouse gas (GHG) ECV requirements. To achieve this, retrieval algorithms are regularly being improved followed by annual data reprocessing and analysis cycles to generate better products in terms of extended time series and continuously improved data quality. Here we present an overview about the latest GHG-CCI data set called Climate Research Data Package No. 3 (CRDP3) focusing on the GHG-CCI core data products, which are column-averaged dry-air mole fractions of CO2 and CH4, i.e., XCO2 and XCH4, as retrieved from SCIAMACHY/ENVISAT and TANSO/GOSAT satellite radiances covering the time period end of 2002 to end of 2014. We present global maps and time series including initial validation results obtained by comparisons with Total Carbon Column Observing Network (TCCON) ground-based observations. We show that the GCOS requirements for systematic error (< 1 ppm for XCO2, < 10 ppb for XCH4) and long-term stability (< 0.2 ppm/year for XCO2, < 2 ppb/year for XCH4) are met for nearly all products (an exception is SCIAMACHY methane especially since 2010). For XCO2 we present comparisons with global models using the output of two CO2 assimilation systems (MACC version 14r2 and CarbonTracker version CT2013B). We show that overall there is reasonable consistency and agreement between all data sets (within ~ 1–2 ppm) but we also found significant differences depending on region and time period