Relation between winds and jets in radio-loud AGN

We investigate the relation between the two modes of outflow (wind and jet) in radio-loud active galactic nuclei (AGN). For this study we have carried out a systematic and homogeneous analysis of XMM-Newton spectra of a sample of 16 suitable radio-loud Seyfert-1 AGN. The ionised winds in these AGN are parameterised through high-resolution X-ray spectroscopy and photoionisation modelling. We discover a significant inverse correlation between the column density NH of the ionised wind and the radio-loudness parameter R of the jet. We explore different possible explanations for this NH-R relation and find that ionisation, inclination, and luminosity effects are unlikely to be responsible for the observed relation. We argue that the NH-R relation is rather a manifestation of the magnetic driving mechanism of the wind from the accretion disk. Change in the magnetic field configuration from toroidal to poloidal, powering either the wind or the jet mode of the outflow, is the most feasible explanation for the observed decline in the wind NH as the radio jet becomes stronger. Our findings provide evidence for a wind-jet bimodality in radio-loud AGN and shine new light on the link between these two modes of outflow. This has far-reaching consequences for the accretion disk structure and the wind ejection mechanism.Comment: Accepted for publication in Astronomy & Astrophysics (A&A), 10 pages, 4 figure

Timing the warm absorber in NGC 4051

We investigated, using spectral-timing analysis, the characterization of highly ionized outflows in Seyfert galaxies, the so-called warm absorbers. Here, we present our results on the extensive ~ 600 ks of XMM-Newton archival observations of the bright and highly variable Seyfert 1 galaxy NGC 4051, whose spectrum has revealed a complex multicomponent wind. Making use of both RGS and EPIC-pn data, we performed a detailed analysis through a time-dependent photoionization code in combination with spectral and Fourier spectral-timing techniques. The source light curves and the warm absorber parameters obtained from the data were used to simulate the response of the gas due to variations in the ionizing flux of the central source. The resulting time variable spectra were employed to predict the effects of the warm absorber on the time lags and coherence of the energy dependent light curves. We have found that, in the absence of any other lag mechanisms, a warm absorber with the characteristics of the one observed in NGC 4051, is able to produce soft lags, up to 100 s, on timescales of ~ hours. The time delay is associated with the response of the gas to changes in the ionizing source, either by photoionization or radiative recombination, which is dependent on its density. The range of radial distances that, under our assumptions, yield longer time delays are comparable to the existing estimates of the location of the warm absorber in NGC 4051. For this reason, we suggest that it is likely that the observed X-ray time lags may carry a signature of the warm absorber response time, to changes in the ionizing continuum. These results highlight the importance of understanding the contribution of the warm absorber to the AGN X-ray time lags, since it is also vital information for interpreting the lags associated with propagation and reverberation effects in the inner emitting regions.Comment: 13 pages, 12 figures, Accepted for publication by A&

Scattering and Absorption of X-rays by Interstellar Dust

In dieser Arbeit habe ich die Eigenschaften der interstellaren Staubpartikel untersucht, wie sie sich aus deren Wechselwirkung mit Roentgen strahlung ergeben. Tatsaechlich werden Photonen, die von einer entfernten Punktquelle stammen, von den Staubteilchen nicht nur absorbiert sondern auch in Vorwaertsrichtung gestreut. Ich habe mehrere Quellen untersucht, die mit unterschiedlichen Instrumenten an Bord der Roentgen satelliten Chandra und XMM beobachtet wurden. Dabei lag der Schwerpunkt sowohl auf den Absorptionsmerkmalen, die das interstellare Medium den Spektren eingepraegt hat, als auch auf der spektralen und raeumlichen Untersuchung der gestreuten Strahlung, die einen Halo aus schwacher diffuser Emission um die Punktquelle erzeugt. Als vorlaeufigen Schritt habe ich die instrumentelle Punktbildfunktion der EPIC-pn-Kamera und der ACIS-Kamera (an Bord von XMM beziehungsweise Chandra) bestimmt unter Benutzung von Daten aus der Flugphase, und diese mit Vorhersagen aus Bodenkalibrationen verglichen. Eine genaue Kenntnis der Punktbildfunktion ist unerlaeßlich fuer eine korrekte Bestimmung der Flaechenhelligkeitsverteilung der ausgedehnten gestreuten Emission. Aus der Analyse von sieben Chandra-Quellen (beobachtet mit ACIS-S und ACIS-I) ergibt sich, daß fuer einige Quellen (namentlich Cen X-3 und der Große Annihilator die Form der Flaechenhelligkeitsverteilung eine einfache gleichförmige Verteilung der Staubkörner entlang der Sichtlinie ausschließt und stattdessen ein Modell mit einem geklumpten Medium bevorzugt wird. Dies ist in uebereinstimmung mit der Geometrie der Galaxis selbst: ein Sehstrahl kann einen oder mehrere Spiralarme durchdringen oder auch mehrere Wolken. Ich habe einige Bedingungen fuer die Lage dieser Staubklumpen aufstellen können. Die Untersuchung der ausgewaehlten Quellen, zusammen mit Daten von frueheren Missionen, hat es mir erlaubt, die innere Struktur der Staubkörner einzugrenzen, und die Grenzen der Streutheorie zu analysieren, wenn diese auf astrophysikalische Objekte angewandt wird. Ich habe mit einer weiteren Auswahl von Chandra-Quellen, die mit dem HETG-Spektrometer beobachtet worden waren, ein besonderes Absorptionsmerkmal (die sogenannten XAFS) untersucht, das von den festen Teilchen im interstellaren Medium verursacht wird. Die am meisten absorbierten Quellen erscheinen als die besten Kandidaten fuer eine erflgreiche Erkennung der XAFS. Da der Absorptionsquerschnitt fuer Staub den fuer Gas oberhalb von 1.3 keV uebersteigt, sind die Elemente mit erwarteten XAFS Magnesium und Silizium. Mittels Beobachtungen von XMM habe ich anhand von Daten des RGS-Spektrometers und der EPIC-pn-Kamera zwei Roentgen-Doppelstenssysteme (LMXB) untersucht ({em Cyg X-2, GX,339-4}). Cyg X-2 ist eine "schwache Haloquelle", was bedeutet, daß die Staubsaeulendichte relativ gering ist. Wegen dieser bei weichen Roentgen energien nur moderaten Absorption konnte der Bereich unterhalb 1 keV sowohl durch Streuung (mittels des Halospektrums) als auch durch Absorption (durch das hochaufgelöste RGS-Spektrum der absorbierten Quelle). Von diesem gestreuten Spektrum konnte -- erstmals -- the Streueigenschaften der Elemente im Staub bestimmen. Die Daten konnten gut an eine Mischung aus Graphit und Silikaten angepaßt werden. Bei der Untersuchung des RGS-Spektrums lag der Schwerpunkt auf der komplexen Struktur der Sauerstoff-Kante und der Eisen-L-Kante, wo viele Absorptionsmerkmale gefunden wurden, und ich habe die beobachteten resonanten Uebergaenge im Lichte neuer Labormessungen identifiziert

Suzaku and XMM-Newton Observations of the North Polar Spur: Charge Exchange or ISM Absorption?

By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O VII and Ne IX forbidden-to-resonance ratios, and a high O VIII Ly$\beta$ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase CIE component with temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of $0.4-0.8$ solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O VIII Ly$\alpha$ line. The ionized absorber is characterized by a balance temperature of $0.17-0.20$ keV and a column density of $3-5 \times 10^{19}$ cm$^{-2}$. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by Galactic ISM in the line of sight.Comment: Accepted for publication in Astronomy and Astrophysic

Modelling the disk atmosphere of the low mass X-ray binary EXO 0748-676

Low mass X-ray binaries exhibit ionized emission from an extended disk atmosphere that surrounds the accretion disk. However, its nature and geometry is still unclear. In this work we present a spectral analysis of the extended atmosphere of EXO 0748-676 using high-resolution spectra from archival XMM-Newton observations. We model the RGS spectrum that is obtained during the eclipses. This enables us to model the emission lines that come only from the extended atmosphere of the source, and study its physical structure and properties. The RGS spectrum reveals a series of emission lines consistent with transitions of O VIII, O VII, Ne IX and N VII. We perform both Gaussian line fitting and photoionization modelling. Our results suggest that there are two photoionization gas components, out of pressure equilibrium with respect to each other. One with ionization parameter of 2.5 and a large opening angle, and one with 1.3. The second component is possibly covering a smaller fraction of the source. From the density diagnostics of the O vii triplet using photoionization modelling, we detect a rather high density plasma of > 10^13 cm^-3 for the lower ionization component. This latter component also displays an inflow velocity. We propose a scenario where the high ionization component constitutes an extended upper atmosphere of the accretion disk. The lower ionization component may instead be a clumpy gas created from the impact of the accretion stream with the disk.Comment: A&A accepted, 10 pages, 9 figure

The cooling, mass and radius of the neutron star in EXO 0748-676 in quiescence with XMM-Newton

We analyse four XMM-Newton observations of the neutron-star low-mass X-ray binary EXO 0748$-$676 in quiescence. We fit the spectra with an absorbed neutron-star atmosphere model, without the need for a high-energy (power-law) component; with a 95 per cent confidence the power-law contributes less than 1 per cent to the total flux of the source in $0.5-10.0$ keV. The fits show significant residuals at around 0.5 keV which can be explained by either a hot gas component around the neutron star or a moderately broad emission line from a residual accretion disc. The temperature of the neutron-star has decreased significantly compared to the previous observation, from 124 eV to 105 eV, with the cooling curve being consistent with either an exponential decay plus a constant or a (broken) power law. The best-fitting neutron-star mass and radius can be better constrained if we extend the fits down to the lowest possible energy available. For an assumed distance of 7.1 kpc, the best-fitting neutron-star mass and radius are $2.00_{-0.24}^{+0.07}~M_\odot$ and $11.3_{-1.0}^{+1.3}$ km if we fit the spectrum over the $0.3-10$ keV range, but $1.50_{-1.0}^{+0.4}~M_\odot$ and $12.2_{-3.6}^{+0.8}$ km if we restrict the fits to the $0.5-10$ keV range. We finally discuss the effect of the assumed distance to the source upon the best-fitting neutron-star mass and radius. As systematic uncertainties in the deduced mass and radius depending on the distance are much larger than the statistical errors, it would be disingenuous to take these results at face value.Comment: 12 pages, 6 figure

The effect of X-ray dust-scattering on a bright burst from the magnetar 1E 1547.0-5408

A bright burst, followed by an X-ray tail lasting ~10 ks, was detected during an XMM-Newton observation of the magnetar 1E 1547.0-5408 carried out on 2009 February 3. The burst, also observed by SWIFT/BAT, had a spectrum well fit by the sum of two blackbodies with temperatures of ~4 keV and 10 keV and a fluence in the 0.3-150 keV energy range of ~1e-5 erg/cm2. The X-ray tail had a fluence of ~4e-8 erg/cm2. Thanks to the knowledge of the distances and relative optical depths of three dust clouds between us and 1E 1547.0-5408, we show that most of the X-rays in the tail can be explained by dust scattering of the burst emission, except for the first ~20-30 s. We point out that other X-ray tails observed after strong magnetar bursts may contain a non-negligible contribution due to dust scattering.Comment: 8 pages, 2 tables and 10 figures; accepted to publication in MNRA