Enhanced Doppler Beaming for Dust-Enshrouded Objects and Pulsars in the Galactic Center

Stars within the innermost part of the Nuclear Star Cluster can reach orbital velocities up to a few percent of the light speed. As analyzed by Rafikov (2020), Doppler boosting of stellar light may be of relevance at the pericenter of stellar orbits, especially with the upcoming high-precision photometry in the near- and mid-infrared bands. Here we analyze the previously neglected effect of infrared spectral index of monitored objects on the Doppler-boosted continuum emission in a narrow band. In contrast to main-sequences stars, the detected compact infrared-excess dust-enshrouded objects have an enhanced Doppler-boosting effect by as much as an order of magnitude, with the variability amplitude of the order of ten percent for the most eccentric orbits. In a similar way, pulsars dominated by non-thermal synchrotron emission are also expected to exhibit a stronger Doppler-boosted signal by a factor of at least four in comparison with canonical S stars. In case the stellar orbit is robustly determined, the relative flux variation can thus provide hints about the nature of the objects. For extended dust-enshrouded objects, such as G1, that are variable due to tidal, ellipsoidal, bow-shock, and irradiation effects, the subtraction of the expected Doppler-boosting variations will help to better comprehend their internal physics. In addition, the relative flux variability due to higher-order relativistic effects is also modified for different negative spectral indices in a way that it can obtain both positive and negative values with the relative variability of the order of one percent.Comment: 9 pages, 5 figures, 1 table; accepted by the Astrophysical Journal; in commemoration of Christian Doppler's presentation in front of the Royal Bohemian Society of the Sciences in Prague on May 25th, 184

MAD UFOs: Magnetically Arrested Discs with persistent Ultra-Fast Outflows

General-relativistic magneto-hydrodynamical (GRMHD) simulations of accreting black holes suggest that the accretion flows form toroidal structures embedded in a large scale component of magnetic field, which becomes organized on length-scales exceeding the gravitational radius of the central black hole. Magnetic field grows gradually until a Magnetically Arrested Disc (MAD) develops that diminishes or inhibits further accretion. We study an outflow that develops in the MAD state in 3D GRMHD simulations. We show that the outflow can be accelerated to relativistic velocities and persist over the course of our simulation. We compare the properties of the outflow from MAD discs with those launched by orbiting secondary at close orbit. The main difference is that the orbiting body launches a more coherent, quasiperiodic ultrafast outflow at lower velocities ($v<0.5c$) while the outflow launched in the MAD state (without the body) has a stochastic behaviour and has an approximately flat velocity distribution between lower and higher outflow velocities, $0.2c0.5c$.Comment: 11 pages, 4 figures, accepted to Proceedings of RAGtime 23-2

Velké pozdní bombardování v různých místech sluneční soustavy

Tato práce se zabývá velkým pozdním bombardováním ve sluneční soustavě, které se odehrálo před 4,1 až 3,8 miliardami let. Jedná se o období intenzivních kolizií, jejichž stopy jsou pozorovány na Měsíci a jiných tělesech, především v podobě kráterů nebo impaktních tavenin. První část práce je rešerší o velkém pozdním bombardování se zaměřením na observační důkazy a nedávné dynamické modely. V druhé části testujeme konkrétní dynamický a kolizní model bombardování, a to pomocí míry kráterovaní na různých tělesech sluneční soustavy, což nebylo učiněno dříve v takovém rozsahu. K tomuto účelu jsme použili symplektický integrátor SyMBA, kolizní kód Boulder a různé škálovací zákony projektil/kráter. Diskutujeme zdroje nejistot pozorování i nejistot modelů. Naše výsledky navíc využíváme k omezení rozdělení velikostí primordiální populace komet.In this work, we study the Late Heavy Bombardment (LHB) in the Solar System which took place from 4.1 to 3.8 billion years ago, and represents a period of intense collisions whose traces are observed on the Moon and other bodies mainly in the form of craters or impact melts. The first part of the thesis is a review on the LHB with the focus on observational evidence and recent dynamical models. In the second part, we test a particular dynamical model of the LHB using the observed cratering records on various Solar-System bodies, which was not done previously to such an extent. For this purpose, we use the symplectic integrator SyMBA, the collisional code Boulder, and various projectile-crater scaling laws. We discuss the sources of uncertainties of the observations as well as that of the models. Furthermore, we use our results to constrain the size-frequency distribution of the primordial cometary population.Astronomical Institute of Charles UniversityAstronomický ústav UKFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

The Wind Dynamics of Super-Eddington Sources in FRADO

We perform non-hydrodynamical 2.5D simulations to study the dynamics of material above accretion disk based on the disk radiation pressure acting on dust. We assume a super-accreting underlying disk with the accretion rate of 10 times the Eddington rate with central black hole mass ranging from $10^7$ up to $10^9 M_{\odot}$. Such high accretion rates are characteristic for extreme sources. We show that for high accretors radiatively dust-driving mechanism based on FRADO model always leads to a massive outflow from the disk surface, and the failed wind develops only at larger radii. The outflow rate strongly depends on the black hole mass, and in optically-thick energy-driven solution can exceed the accretion rate for masses larger than $10^ 8 M_{\odot}$ but momentum-driven outflow does not exceed the accretion rate even for super-Eddington accretion, therefore not violating the adopted stationarity of the disk. However, even in this case the outflow from the disk implies a strong mechanical feedback.Comment: 13 pages, 3 figures, Accepted for publication in the journal of Dynamics (MDPI

Distribution of Radio Spectral Slopes of Galaxies in Optical Diagnostic Diagrams

For about 500 intermediate-redshift sources ($0.04<z<0.4$), whose radio flux densities at $1.4\,{\rm GHz}$ are larger than 10 mJy, we performed additional observations at 4.85 GHz and 10.45 GHz using 100-m Effelsberg telescope. Our radio-optical galaxies are located preferentially in the composite and AGN spectral classes in the narrow line optical diagnostic diagrams (ODD). In the analysis, we focused on the distribution of radio spectral indices of radio synchrotron power-law profiles, $S_{\nu}\propto \nu^{+\alpha}$, in the ODDs. Using different analysis techniques, both observationally motivated and machine-learning based, we found three distinct groups--clusters in the radio loudness, [OIII]/H$\beta$ ratio, and spectral index volume: (1) sources with steep radio spectral index, large radio loudness and large [OIII]/H$\beta$ ratio; (2) sources with flat radio spectral index, intermediate radio loudness and lower [OIII]/H$\beta$ ratio; (3) sources with inverted radio spectral index, low radio loudness and low [OIII]/H$\beta$. The groups (1), (2), and (3) are located along the Seyfert-LINER spectral classes towards lower ionization ratios in the ODDs and hence can represent different activity cycles/accretion modes of AGNs, which could be in some cases associated with different merger stages.Comment: 7 pages, 3 figures, 2 tables; accepted for publication by the Polish Astronomical Society Proceedings (volume 123

Spectral Energy Distribution profiles from AGN accretion disc in multi-gap setup

Spectral Energy Distribution (SED) of the broad-band continuum emission from black-hole accretion discs can serve as a tool to measure parameters of the central body and constrain the geometry of the inner accretion flow. We focus on the case of an active galactic nucleus (AGN), with an accretion disc dominating the UV/optical bands. We parameterize the changes in the thermal and power-law components, which can reveal the diminution of the emissivity. To this end we explore the effects of gaps in the accretion disc and the emerging SED that can be caused by the presence of either (i) the inner, optically thin, radiatively inefficient hot flow; (ii) a secondary black hole embedded within the accretion disc; or (iii) a combination of both components. We suggest that the resulting changes in the SED of the underlying continuum can help us to understand some departures from the standard-disc scenario. We estimate that the data required for such a project must be sampled in detail over the far-UV to soft X-ray bands during the interval of about a month corresponding to the characteristic variability timescale of an AGN. Detecting a gap at intermediate radii of a few 100 gravitational radii would require quality photometry with uncertainties up to $\sim$ 1%. The presence of the central cavity in the standard disc can be recovered in UV photometric data with an accuracy of 5% and better. We show the effect of the intrinsic reddening of the source and demonstrate when it can be disentangled.Comment: 17 pages, 10 figures and 5 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Societ