Physical processes behind the periodic radio and gamma-ray emission from the X-ray binary LS I +61°303

X-ray binaries are binary stars composed of a normal star and a compact object which, via Roche-lobe overflow or wind accretion, accretes matter from the companion. X-ray emission from these objects can be either thermal emission from an accretion disk formed around the compact object, or the result of inverse Compton scattering. Emission in the radio regime is synchrotron emission from relativistic electrons gyrating in the magnetic fields of a jet. Some X-ray binaries are also emitters of -ray emission, the physical processes behind the nonthermal emission of these objects are still poorly understood. Subject of this thesis is the investigation on physical processes behind the emission from one particular -ray-loud X-ray binary, LS I +61°303. This source is composed of a Be type star and a compact object of still unknown nature, i.e., either a neutron star or a black hole. Accretion onto the compact object along the eccentric orbit of this source is predicted to peak twice per orbit, giving rise to emission all over the electromagnetic spectrum modulated by the orbital period P1 ≈ 26:5 days. Analysis of the astrometry of VLBI images of the source resulted in a precession period of a jet of 27–28 days, expected to give rise to periodic variable Doppler boosting. Timing analysis of archived radio data revealed that a compatible period of P2 ≈ 26:9 days modulates the radio lightcurve in addition to P1, giving rise to a beating with a long-term period of ∼ 4:5 years, in agreement with previous findings. The methods employed for this thesis are timing analysis of radio and GeV lightcurves, and the modelling of physical processes which can lead to radio and GeV emission from LS I +61°303. The first result of this thesis is how the knowledge about the beating between the periodic ejection of particles and the jet precession can be used for a straightforward prediction of the radio outbursts observable by radio telescopes. The GeV light curve has previously been reported to peak around periastron only. The second result presented here is the discovery of a periodic apastron GeV peak, also explaining a previously reported disappearance of the orbital period from the power spectrum of the GeV light curve during some epochs. We further find that, while the apastron GeV peak is modulated by P1 and P2, the periastron GeV peak is only modulated by P1. This timing characteristic is explained by a physical model of a self-absorbed, adiabatically expanding jet, refilled with a population of relativistic electrons twice along the orbit, the bulk velocity of the jet being slower at periastron than at apastron, giving rise to smaller variable Doppler boosting at periastron, and consequently, P2 is not present in the power spectrum during these orbital phases. In addition, the absence of a periastron radio peak is explained by catastrophic inverse Compton losses of the electrons at periastron, leading to a jet too short for radio emission. We further report on the detection of radio emission of the first proven case of a binary star composed of a Be type star and a black hole, MWC 656, a source which has also been detected in the GeV regime and therefore bears resemblance to LS I +61°303. The source LS I +61°303 does not only feature variability in the order of months to years, but there is also evidence for short-term variability over time scales of days and shorter. We observed LS I +61°303 with the 100-m telescope in Effelsberg, quasi-simultanously at three radio frequencies with unprecedented sampling rate for a multiwavelength observation of this source. We present our results on possible periodic behavior on time-scales of hours, which can possibily contribute to future investigations on transient phenomena related to the jet. In conlcusion, we show that an accretion scenario for LS I +61°303, including a precessing relativistic jet, can explain the periodic emission from this X-ray binary and may help to understand the physical processes in related sources.Röntgendoppelsterne bestehen aus aus einem normalen Stern und einem kompakten Objekt, das, durch Überschreitung der Roche-Grenzen oder durch Akkretion des Sternenwindes, Masse vom Begleitstern akkretiert. Röntgenstrahlung ensteht in diesen Objekten entweder als thermische Strahlung von der Akkretionsscheibe oder als Folge des inversen Compton-Effekts. Strahlung im Radiobereich ist Synchrotronstrahlung, emittiert von relativistischen Elektronen, die in den Magnetfeldern des Jets auf Kreisbahnen gelenkt werden. Einige Röntgendoppelsterne sind darüber hinaus Quellen von Gammastrahlung, wobei die physikalischen Prozesse, die für die Strahlung von diesen Objekten verantwortlich sind, noch immer nicht gut verstanden sind. Gegenstand dieser Doktorarbeit ist die Erforschung der physikalischen Prozessen, die die elektromagnetischen Emission eines bestimmten gamma-emittierenden Röntgendoppelsterns, LS I +61°303, erklären können. Diese Quelle besteht aus einem Be-Stern und einem kompakten Objekt, von dem noch unbekannt ist, ob es sich um einen Neutronenstern oder ein schwarzes Loch handelt. Aufgrund der hohen Exzentrizität des Orbits wird vorhergesagt, dass Akkretion von Materie auf das kompakte Objekt zwei Maxima per Orbit ausbildet, und es, als Konsequenz davon, zu einer Modulation mit der orbitalen Periode P1 ≈ 26:5 Tage der resultierenden Strahlung über den gesamten Bereich des elektromagnetischen Spektrums kommt. Eine Analyse der Astrometrie von VLBI-Bildern der Quelle hatte eine Präzessionsperiode des Jets von 27–28 Tagen zum Ergebnis, was erwartungsgemäß zu variablem Doppler-Boosting führen sollte. Durch Zeitreihenanalyse von archivierten Radiodaten stellte sich heraus, dass eine mit diesem Ergebnis zu vereinbarende Periode von P2 ≈ 26:9 Tagen die Radiolichtkurze zusätzlich zu P1 moduliert, was eine Schwebung mit einer Periode von ca. 4.5 Jahren zur Folge hat, und was in Übereinstimmung mit vorhergehenden Beobachtungen ist. Die in dieser Arbeit zum Einsatz kommenden Methoden beinhalten Zeitreihenanalyse von Radiound GeV-Lichtkurven sowie die Modellierung von physikalischen Prozessen, die zur Emission im Radio- und GeV-Bereich im Doppelsternsystem LS I +61°303 führen können. Als erstes Ergebnis dieser Arbeit wird gezeigt, wie das Wissen über die Schwebung zwischen der periodischen Beschleunigung von Teilchen und der Präzession des Jets für eine unkomplizierte Vorhersage der Radiostrahlungsmaxima für die Beobachtung mit Radioteleskopen genutzt werden kann. Bisher wurde berichtet, dass die GeV-Lichtkurve Strahlungsmaxima ausschließlich bei Periastron aufweist. Das zweite hier vorgestellte Ergebnis ist die Entdeckung eines periodischen GeV-Strahlungsmaximum während des Apastron, ein Ergebnis, das auch ein zeitweises Verschwinden der orbitalen Periode aus dem Periodenspektrum der GeV-Lichtkurve erklärt. Gleichzeitig finden wir heraus, dass, während das Apastron-GeVMaximum von P1 und P2 moduliert wird, das Periastron-Maximum nur einer Modulation mit P1 unterliegt. Dieses Verhalten wird, als ein weiteres Ergebnis dieser Arbeit, erklärt durch ein physikalisches Modell eines selbstabsorbierenden, adiabatisch expandierenden Jet, der periodisch, zweimal pro Orbit mit einer Population von relativistischen Elektronen befüllt wird, wobei die Geschwindigkeit entlang des Jets bei Periastron langsamer ist als bei Apastron, was bei Periastron geringeres Doppler-Boosting als bei Apastron zur Folge hat, und infolgedessen P2 im Periodenspektrum bei Periastron nicht auftaucht. Darüber hinaus wird die Abwesenheit eines Periastron-Radiomaximums erklärt durch katastrophale Energieverluste der Elektronen durch den inversen Compton-Effekt beim Periastron, was in einem Jet, der zu kurz für Radioemission ist, resultiert. Ein weiteres Ergebnis dieser Arbeit ist die Detektion von Radiostrahlung vom ersten nachgewiesenen Fall eines Doppelsterns bestehend aus einem Be-Stern und einem schwarzen Loch, MWC 656, eine Quelle, die auch im GeV-Bereich detektiert wurde und daher starke Ähnlichkeit mit LS I +61°303 aufweist. LS I +61°303 ist nicht nur variabel auf Zeitskalen von Monaten oder Jahren, sondern es gibt auch Hinweise auf Kurzzeitvariabilität auf Zeitskalen von Tagen oder kürzer.Wir haben LS I +61°303 mit dem 100-m- Teleskop in Effelsberg beobachtet, quasisimultan auf drei Frequenzen mit der bisher höchsten Abtastrate, die bei einer gleichzeitigen Beobachtung dieser Quelle mit mehrerenWellenlängen erreicht wurde. Hier werden Ergebnisse bezüglich möglichen Periodizitäten auf Zeitskalen von Stunden vorgestellt, was möglicherweise als Grundlage für die Erforschung von kurzzeitigen Phänomen im Jet dienen kann. Zusammenfassend wird gezeigt, dass ein Akkretionsszenario für LS I +61°303 in Zusammenhang mit einem präzedierenden Jet die periodische Emission dieses Röntgendoppelsterns erklären kann und zum Verständnis der physikalischen Prozesse in verwandten Objekten beitragen kann

Simultaneous long-term monitoring of LS I +61°303 by OVRO and Fermi-LAT

Previous long-term monitorings of the γ-ray-loud X-ray binary LS I +61°303 have revealed the presence of a long-term modulation of ∼4.5 yr. After 9 yr of simultaneous monitoring of LS I +61°303 by the Owens Valley Radio Observatory and the Fermi-LAT, two cycles of the long-term period are now available. Here we perform timing analysis on the radio and the γ-ray light curves. We confirm the presence of previously detected periodicities at both radio and GeV γ-ray wavelengths. Moreover, we discover an offset of the long-term modulation between radio and γ-ray data which could imply different locations of the radio (15 GHz) and GeV emission along the precessing jet

Simultaneous long-term monitoring of LS I +61°303 by OVRO and Fermi-LAT

Previous long-term monitorings of the γ-ray-loud X-ray binary LS I +61°303 have revealed the presence of a long-term modulation of ∼4.5 yr. After 9 yr of simultaneous monitoring of LS I +61°303 by the Owens Valley Radio Observatory and the Fermi-LAT, two cycles of the long-term period are now available. Here we perform timing analysis on the radio and the γ-ray light curves. We confirm the presence of previously detected periodicities at both radio and GeV γ-ray wavelengths. Moreover, we discover an offset of the long-term modulation between radio and γ-ray data which could imply different locations of the radio (15 GHz) and GeV emission along the precessing jet

Precession-induced Variability in AGN Jets and OJ 287

The combined study of the flaring of Active Galactic Nuclei (AGN) at radio wavelengths and pc-scale jet kinematics with Very Long Baseline Interferometry (VLBI) has led to the view that i) the observed flares are associated with ejections of synchrotron blobs from the core, and ii) most of the flaring would follow a one-to-one correlation with the component ejection. Recent results have provided mounting evidence that the quasi-regular component injections into the relativistic jet may not be the only cause of the flux variability. We propose that AGN flux variability and jet morphology changes can both be of deterministic nature, i.e. having a geometric/kinetic origin linked to the time-variable Doppler beaming of the jet emission as its direction changes due to precession (and nutation). The physics of the underlying jet leads to shocks, instabilities, or to ejections of plasmoids. The appearance (morphology, flux, etc.) of the jet can, however, be strongly affected and modulated by precession. We demonstrate this modulating power of precession for OJ 287. For the first time, we show that the spectral state of the Spectral Energy Distribution (SED) can be directly related to the jet's precession phase. We model the SED evolution and reproduce the precession parameters. Further, we apply our precession model to eleven prominent AGN. We show that for OJ 287 precession seems to dominate the long-term variability ($\gtrsim 1\,{\rm yr}$) of the AGN flux, SED spectral state, and jet morphology, while stochastic processes affect the variability on short timescales ($\lesssim 0.2\,{\rm yr}$).Comment: 48 pages, 26 figures, 14 tables; published in the Astrophysical Journa

A ring accelerator? Unusual jet dynamics in the IceCube candidate PKS 1502+106

On 2019/07/30.86853 UT, IceCube detected a high-energy astrophysical neutrino candidate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 percent uncertainty region of the event. Our analysis of 15 GHz Very Long Baseline Array (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after the IceCube event, reveals evidence for a radio ring structure which develops with time. Several arc-structures evolve perpendicular to the jet ridge line. We find evidence for precession of a curved jet based on kinematic modelling and a periodicity analysis. An outflowing broad line region (BLR) based on the C IV line emission (Sloan Digital Sky Survey, SDSS) is found. We attribute the atypical ring to an interaction of the precessing jet with the outflowing material. We discuss our findings in the context of a spine-sheath scenario where the ring reveals the sheath and its interaction with the surroundings (narrow line region, NLR, clouds). We find that the radio emission is correlated with the $\gamma$-ray emission, with radio lagging the $\gamma$-rays. Based on the $\gamma$-ray variability timescale, we constrain the $\gamma$-ray emission zone to the BLR (30-200 $r_{\rm g}$) and within the jet launching region. We discuss that the outflowing BLR provides the external radiation field for $\gamma$-ray production via external Compton scattering. The neutrino is most likely produced by proton-proton interaction in the blazar zone (beyond the BLR), enabled by episodic encounters of the jet with dense clouds, i.e. some molecular cloud in the NLR.Comment: 35 pages, 33 figures, 3 tables; accepted by the MNRAS Main Journa

Sustainable computational science: the ReScience initiative

Computer science o ers a large set of tools for prototyping, writing, running, testing, validating, sharing and reproducing results, however computational science lags behind. In the best case, authors may provide their source code as a compressed archive and they may feel con dent their research is reproducible. But this is not exactly true. Jonathan Buckheit and David Donoho proposed more than two decades ago that an article about computational results is advertising, not scholarship. e actual scholarship is the full so ware environment, code, and data that produced the result. is implies new work ows, in particular in peer-reviews. Existing journals have been slow to adapt: source codes are rarely requested, hardly ever actually executed to check that they produce the results advertised in the article. ReScience is a peer-reviewed journal that targets computational research and encourages the explicit replication of already published research, promoting new and open-source implementations in order to ensure that the original research can be replicated from its description. To achieve this goal, the whole publishing chain is radically di erent from other traditional scienti c journals. ReScience resides on GitHub where each new implementation of a computational study is made available together with comments, explanations, and so ware tests

Rhinitis associated with asthma is distinct from rhinitis alone: TARIA‐MeDALL hypothesis

Asthma, rhinitis, and atopic dermatitis (AD) are interrelated clinical phenotypes that partly overlap in the human interactome. The concept of “one-airway-one-disease,” coined over 20 years ago, is a simplistic approach of the links between upper- and lower-airway allergic diseases. With new data, it is time to reassess the concept. This article reviews (i) the clinical observations that led to Allergic Rhinitis and its Impact on Asthma (ARIA), (ii) new insights into polysensitization and multimorbidity, (iii) advances in mHealth for novel phenotype definitions, (iv) confirmation in canonical epidemiologic studies, (v) genomic findings, (vi) treatment approaches, and (vii) novel concepts on the onset of rhinitis and multimorbidity. One recent concept, bringing together upper- and lower-airway allergic diseases with skin, gut, and neuropsychiatric multimorbidities, is the “Epithelial Barrier Hypothesis.” This review determined that the “one-airway-one-disease” concept does not always hold true and that several phenotypes of disease can be defined. These phenotypes include an extreme “allergic” (asthma) phenotype combining asthma, rhinitis, and conjunctivitis.info:eu-repo/semantics/publishedVersio

A Precessing Jet Scenario for the Multi-Wavelength Long-Term Modulation of LS I +61°303

The high-mass X-ray binary LS I +61°303 is detected across the electromagnetic spectrum from radio until the very high energy γ-ray regime. The emission is not only highly variable on many time scales, but is also periodic at all observed wavelengths. Periodic modulation was observed on different time-scales, ranging from hours, over months to several years. The subject of this article is a super-orbital, long-term modulation of ∼4.6 years. We review the observation of this periodic modulation at multiple wavelengths and investigate systematic relationships between them. IN particular, radio observations reveal that the long-term modulation is a very stable feature of the source. Observations at other wavelengths result in a phase-shift of the modulationpattern that is a systematic function of energy. The stability of this period favors a scenario in which the long-term modulation is the result of a precessing jet giving rise to periodic changes in the Doppler factor, beating with the orbital modulation of the accretion rate. We explain the phase-shifts across energy bands in a scenario with shorter wavelengths originating closer to the base of the presessing jet. A significant deviation of the TeV emission from this trend possibly requires a different explanation related to magnetic reconnection events