Untersuchung der Langzeitvariabilität von Doppelsternsystemen mit schwarzen Löchern

This work considers the variability of X-ray binaries with black holes as the compact objects, i.e., binaries, where the originally more massive star has reached the final stage of its evolution. Matter can be accreted onto the black hole either through stellar winds of because of the increasing volume of the companion in the late stages of stellar evolution, and lead to high energy emission. The deep gravitational well of the black hole and the high temperatures of the accreted plasma results in a complex interplay of quantum mechanical and general relativistic effects that are further complicated by the presence of magnetic fields and, until today, hardly understood. Typical combinations of observed spectral and timing characteristics of such objects are called states (mainly soft, hard and intermediate states) and likely correspond to different configurations of accretion and ejection flows, i.e., accretion disk, corona, accretion disk winds and jets. In the presented work we choose an empirical approach to classify the long term changes of different parameters that describe spectral and timing features of the source and to create a basis for comparison with theoretical models. The emphasis is on the differences between the states and on the description of state transitions. After presenting the state of knowledge and especially the multitude of open questions of black hole binary research, we give and overview over the instrumentation we used (telescopes on board the satellites RXTE, INTEGRAL, Swift and Fermi and on the International Space Station ISS, as well as the Ryle/AMI radio telescope) and an introduction to the analysis techniques, especially the Fourier-bases timing analysis. We follow with an analysis of individual observations of the black hole binaries Cygnus X-1 and H1743-322 that serves as an example for how states and state transitions are classified based on spectral and timing features. The first step in the investigation of the long term variability is the spectral analysis of Cygnus X-1 over the whole 16 years (1996-2011) of the RXTE lifetime. Known correlations between the parameters of simple models for the spectral shape are confirmed with a much better coverage of different source states than previously. The black hole and the X-ray radiation created in its immediate surroundings serve as a probe for the investigation of the stellar wind of the normal companion of the black hole, the O-type super giant HDE 226868. We show qualitatively that the observed orbital modulation of the wind is consistent with models of a clumpy stellar wind focused towards the black hole. We continue with a statistical analysis of Cygnus X-1 observations with X-ray all sky monitors that span a total of 17 years, in which the source has shown numerous state transitions and periods of different activity. For this purpose, we develop a classification scheme for low spectral resolution but high cadence observations with all sky monitors that is based of higher resolved but much more infrequent observations with RXTE-PCA and RXTE-HEXTE. This scheme allows us to analyze states and state transition with a time resolution below a day over the whole 17 years and shows that the transitional state ismuch less stable than the hard and soft states. The detailed display of the development of this state classification offers a stepping stone for similar approaches for other sources and source types. We highlight applications of this classifications as additional resources in high resolution observations in soft X-rays and as a basis for state-resolved polarization analysis in the gamma-rays. Attributing XMM observations to the intermediate state is, for example, crucial for the interpretations of spectroscopic peculiarities of these observations. The 2 ms high time resolution of RXTE-PCA allows us to take the next step and conduct a timing analysis of over 1900 individual, on average thirty minutes long, observations of Cygnus X-1 that span a total of over 13 years. We can show the presence of clear relationships between the spectral shape of the source and Fourier-based quantities (power spectra, time lags and coherence function), a dependency of the shape of the power spectra on the considered energy band and correlations between structures in the power spectra and in the frequency-dependent time lags and coherence function. These results imply that the dominant short term variability in the different states originates in different parts of the accretion and ejection flows and that none of today’s models, which partly strongly differ in their basic assumptions, e.g., in the source of the X-ray emission in corona or in the jets, can explain all parameters and their interplay. This work shows the importance of long-term analyses that can answer questions that single observations, even if they are of high quality, fail to answer if the context of the observations is not taken into account. The methods developed in this thesis can be easily transferred to other source, while the presented results for the case of Cyg X-1 put strong constraints on physical models of accretion and ejection flows and emphasize the significance of model-independent approaches, which guard from an overinterpretation of individual observations outside of their long-term context.Diese Arbeit beschäftigt sich mit der Variabilität von Röntgendoppelsternen mit einem schwarzen Loch als kompaktem Begleiter, also Doppelsternen, in welchen der ursprünglich massereichere Stern auf der letzten Stufe seiner Entwicklung angelangt ist. Durch Sternwinde oder aufgrund der Vergrößerung des Volumens des Begleitestern in späten Phasen der Sternentwicklung kann es dabei zu Akkretion von Materie auf das schwarze Loch kommen, in deren Folge hochenergetische Strahlung freigesetzt wird. Das tiefe Gravitationspotential des schwarzen Lochs und die hohen Temperaturen des Plasmas, das akkretiert wird, resultieren in einem komplexen Zusammenspiel quantenmechanischer und relativistischer Effekte, das durch die Anwesenheit von Magnetfeldern zusätzlich verkompliziert wird und bis heute nur in Ansätzen verstanden ist. Typische Kombinationen beobachteter spektraler und Zeitreiheneigenschaften solcher Objekte werden als Zustände (vor allem weicher, harter und Zwischenzustand) bezeichnet und entsprechen wahrscheinlich verschiedenen Anordnungen von Akkretions- und Auswurfströmen, also von Akkretionsscheibe, Korona, Akkretionsscheibenwinden und Jets. In der vorliegenden Arbeit wird ein empirischer Ansatz gewählt, um die Langzeitänderungen verschiedener Parameter zu klassifizieren, die die spektralen und Zeitreiheneigenschaften der Quellen beschreiben, und um so eine Grundlage für den Vergleich mit theoretischen Modellen zu schaffen. Der Schwerpunkt liegt dabei auf den Unterschieden zwischen den Zuständen und auf der Beschreibung der Zustandsübergänge. Nach einer Darstellung des heutigen Wissensstandes und besonders der Vielzahl der offenen Fragen, werden ein Überblick über die verwendeten Instrumente (verschiedene Teleskope auf den Satelliten RXTE, INTEGRAL, Swift und Fermi und auf der international Weltraumstation ISS, sowie das Ryle/AMI Radio Teleskop) sowie eine Einleitung in die verwendeten Analyseverfahren, vor allem Verfahren der Zeitreihenanalyse im Fourierraum, gegeben. Es folgt die Analyse einzelner Beobachtungen der Röntgendoppelsterne Cygnus X-1 und H1743-322, die als Beispiel dafür dient, wie Zustände und Zustandsübergänge anhand von spektralen und Zeitreiheneigenschaften klassifiziert werden. Der erste Schritt in der Untersuchung der Langzeitvariabilität ist die spektrale Analyse von Cygnus X-1 über die gesamten 16 Jahre (1996–2011) der Lebenszeit des RXTESatelliten. Bekannten Korrelationen zwischen Bestandteilen einfacher Modelle für die Spektralform werden mit weit besserer Abdeckung verschiedener Quellenzustände als zuvor bestätigt. Bei der Untersuchung des Sternwindes des normalen Begleiters des schwarten Lochs, also des blauen O-Riesen HDE 226868, fungieren das schwarze Loch und die in seiner unmittelbarer Nähe erzeugte Röntgenstrahlung als Sonde für den Wind. Es wird qualitativ gezeigt, dass die beobachtete orbitale Modulation des Windes mit Modellen eines stark geklumpten Windes, das zum schwarzen Loch hin fokussiert ist, in Übereinstimmung ist. Hierauf schließt sich die statistische Analyse von Beobachtung von Cygnus X-1 mit Himmelsmonitoren im Röntgenbereich, die insgesamt einen Zeitraum von 17 Jahren umfassen, in welchen die Quelle zahlreiche Zustandsübergänge sowie Phasen verschiedener Aktivität gezeigt hat. Dafür wird auf der Grundlage einzelnen höher aufgelöster Beobachtungen mit den RXTE-PCA und RXTE-HEXTE Instrumenten ein Zustandsklassifizierungsschema für niedrig aufgelöste aber sehr häufige Beobachtungen mit Himmelsmonitoren entwickelt. Dieses Schema erlaubt die Analyse von Zuständen und Zustandsübergängen mit einer Zeitauflösung von unter einem Tag über den gesamten 17-jährigen Zeitraum und zeigt, dass der Zwischenzustand viel weniger stabil ist als harte und weiche Zustände. Die detaillierte Darstellung der Entwicklungsschritte der Zustandsklassifikation bietet zudem eine Vorlage für ähnliche Vorgehensweise für andere Quellen und Quellenarten. Weiter werden Anwendungen dieser Zustandsklassifikation als Hilfsmittel für höchstaufgelösten Beobachtungen im weichen Röntgenbereich und als Grundlage für zustandsaufgelöste Polarisationsanalyse von Gammastrahlung beleuchtet. So ist zum Beispiel die Zuordnung von XMM Beobachtungen dem Zwischenzustand entscheidend für die Interpretation der spektroskopischen Besonderheiten der Beobachtungen. Die hohe Zeitauflösung der RXTE-PCA Beobachtungen von 2 ms ermöglicht im nächsten Schritt eine Zeitreihenanalyse von über 1900 einzelnen im Schnitt dreissigminütigen Beobachtungen von Cygnus X-1, die insgesamt einen Zeitraum von über 13 Jahren umspannen. Dabei werden klare Zusammenhänge zwischen der spektralen Form der Quelle und den Fouriergrößen (den Periodogrammen sowie den Zeitverzögerungen und der Kohärenzfunktion), eine Abhängigkeit der Form der Periodogramme von dem betrachteten Energieband, sowie Korrelationen zwischen den Strukturen in den Periodogrammen und in den frequenzabhängigen Zeitverzögerungen und der Kohärenzfunktion gezeigt. Die Ergebnisse sind ein klarer Hinweis, dass die maßgebliche Kurzzeitvariabilität in verschiedenen Zuständen ihren Ursprung in verschiedenen Bestandteilen der Akkretions- und Ausstroßströme hat, und dass keines der heutigen theoretischen Modelle, die sich zum Teil stark in der Grundannahmen, z.B. dem Ursprung der Röntgenstrahlung in der Korona oder in Jets, unterscheiden, alle Parameter und ihre Wechselwirkung erklären kann. Insgesamt zeigt diese Arbeit dieWichtigkeit von systematischen Langzeitanalysen auf, die viele Fragen beantworten können, an denen die Untersuchung einzelner Beobachtungen, auch hoher Qualität, scheitern, wenn der Kontext der Beobachtung nicht berücksichtigt wird. Die hier entwickelten Methoden und Darstellungsformen können leicht auf anderen Quellen übertragen werden, während die vorgestellten Ergebnisse für den Fall von Cygnus X-1 starke Bedingungen an physikalische Modelle für die Akkretions- und Ausstoßströme stellen und die Wichtigkeit einer möglichst modellunabhängigen Herangehensweise betonen, die vor einer Überinterpretation einzelner Beobachtungen außerhalb des Langzeitzusammenhangs schützt

X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity

We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4 in the hard state comprising 77 million counts collected over 196 ks. The source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we re-calibrate the data to a precision of 0.1\%, an order of magnitude improvement over all earlier work. Using our advanced reflection model {\tt relxill}, we target the strong features in the component of emission reflected from the disk, namely, the relativistically-broadened Fe K emission line, the Fe K edge and the Compton hump. We report results for two joint fits to the six spectra: For the first fit, we fix the spin parameter to its maximal value ($a_*=0.998$) and allow the inner disk radius $R_{\rm in}$ to vary. Results include (i) precise measurements of $R_{\rm in}$, with evidence that the disk becomes slightly truncated at a few percent of Eddington; and (ii) an order-of-magnitude swing with luminosity in the high energy cutoff, which reaches $>890$ keV at our lowest luminosity. For the second fit, we make the standard assumption in estimating spin that the inner edge of the accretion disk is located at the innermost stable circular orbit ($R_\mathrm{in} = R_\mathrm{ISCO}$) and find $a_* = 0.95^{+0.03}_{-0.05}$ (90\% confidence, statistical). For both fits, and at the same level of statistical confidence, we estimate that the disk inclination is $i = 48\pm 1$ deg and that the Fe abundance is super-solar, $A_\mathrm{Fe} = 5\pm1$.Comment: Accepted for publication in ApJ, 20 pages, 13 figure

Simultaneous multiwavelength observations of V404 Cygni during its 2015 June outburst decay strengthen the case for an extremely energetic jet-base

We present results of multiband optical photometry of the black hole X-ray binary system V404 Cygni obtained using Wheaton College Observatory's 0.3m telescope, along with strictly simultaneous INTEGRAL and Swift observations during 2015 June 25.15--26.33 UT, and 2015 June 27.10--27.34 UT. These observations were made during the 2015 June outburst of the source when it was going through an epoch of violent activity in all wavelengths ranging from radio to $\gamma$-rays. The multiwavelength variability timescale favors a compact emission region, most likely originating in a jet outflow, for both observing epochs presented in this work. The simultaneous INTEGRAL/Imager on Board the Integral Satellite (IBIS) 20--40 keV light curve obtained during the June 27 observing run correlates very strongly with the optical light curve, with no detectable delay between the optical bands as well as between the optical and hard X-rays. The average slope of the dereddened spectral energy distribution was roughly flat between the $I_C$- and $V$-bands during the June 27 run, even though the optical and X-ray flux varied by $>$25$\times$ during the run, ruling out an irradiation origin for the optical and suggesting that the optically thick to optically thin jet synchrotron break during the observations was at a frequency larger than that of $V$-band, which is quite extreme for X-ray binaries. These observations suggest that the optical emission originated very close to the base of the jet. A strong H$\alpha$ emission line, probably originating in a quasi-spherical nebula around the source, also contributes significantly in the $R_C$-band. Our data, in conjunction with contemporaneous data at other wavelengths presented by other groups, strongly suggest that the jet-base was extremely compact and energetic during this phase of the outburst.Comment: 15 pages, 2 tables, 5 figures. Accepted for publication in Ap

Accretion Disc Evolution in GRO J1655-40 and LMC X-3 with Relativistic and Non-Relativistic Disc Models

Black hole X-ray binaries are ideal environments to study the accretion phenomena in strong gravitational potentials. These systems undergo dramatic accretion state transitions and analysis of the X-ray spectra is used to probe the properties of the accretion disc and its evolution. In this work, we present a systematic investigation of $\sim$1800 spectra obtained by RXTE PCA observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion disc via non-relativistic and relativistic disc models describing the thermal emission in black-hole X-ray binaries. We demonstrate that the non-relativistic modelling throughout an outburst with the phenomenological multi-colour disc model DISKBB yields significantly lower and often unphysical inner disc radii and correspondingly higher ($\sim$50-60\%) disc temperatures compared to its relativistic counterparts KYNBB and KERRBB. We obtained the dimensionless spin parameters of $a_{*}=0.774 \pm 0.069$ and $a_{*}=0.752 \pm 0.061$ for GRO J1655-40 with KERRBB and KYNBB, respectively. We report a spin value of $a_{*}=0.098 \pm 0.063$ for LMC X-3 using the updated black hole mass of 6.98 ${M_{\odot}}$. Both measurements are consistent with the previous studies. Using our results, we highlight the importance of self-consistent modelling of the thermal emission, especially when estimating the spin with the continuum-fitting method which assumes the disc terminates at the innermost stable circular orbit at all times.Comment: Accepted for publication in MNRAS, 23 pages 17 figure

Spectral and Timing Properties of IGR J17091-3624 in the Rising Hard State During its 2016 Outburst

We present a spectral and timing study of the NuSTAR and Swift observations of the black hole candidate IGR J17091-3624 in the hard state during its outburst in 2016. Disk reflection is detected in each of the NuSTAR spectra taken in three epochs. Fitting with relativistic reflection models reveals that the accretion disk is truncated during all epochs with $R_{\rm in}>10~r_{\rm g}$, with the data favoring a low disk inclination of $\sim 30^{\circ}-40^{\circ}$. The steepening of the continuum spectra between epochs is accompanied by a decrease in the high energy cut-off: the electron temperature $kT_{\rm e}$ drops from $\sim 64$ keV to $\sim 26$ keV, changing systematically with the source flux. We detect type-C QPOs in the power spectra with frequency varying between 0.131 Hz and 0.327 Hz. In addition, a secondary peak is found in the power spectra centered at about 2.3 times the QPO frequency during all three epochs. The nature of this secondary frequency is uncertain, however a non-harmonic origin is favored. We investigate the evolution of the timing and spectral properties during the rising phase of the outburst and discuss their physical implications.Comment: 11 pages, 9 figures, accepted by Ap

Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system III. Dipping in the low/hard state

We present an analysis of three Chandra High Energy Transmission Gratings observations of the black hole binary Cyg X-1/HDE 226868 at different orbital phases. The stellar wind that is powering the accretion in this system is characterized by temperature and density inhomogeneities including structures, or "clumps", of colder, more dense material embedded in the photoionized gas. As these clumps pass our line of sight, absorption dips appear in the light curve. We characterize the properties of the clumps through spectral changes during various dip stages. Comparing the silicon and sulfur absorption line regions (1.6-2.7 keV $\equiv$ 7.7-4.6 {\AA}) in four levels of varying column depth reveals the presence of lower ionization stages, i.e., colder or denser material, in the deeper dip phases. The Doppler velocities of the lines are roughly consistent within each observation, varying with the respective orbital phase. This is consistent with the picture of a structure that consists of differently ionized material, in which shells of material facing the black hole shield the inner and back shells from the ionizing radiation. The variation of the Doppler velocities compared to a toy model of the stellar wind, however, does not allow us to pin down an exact location of the clump region in the system. This result, as well as the asymmetric shape of the observed lines, point at a picture of a complex wind structure.Comment: 19 pages, 15 figures, accepted for publication in A&