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Both observational and theoretical studies of black-hole activity or active galactic nucleus (AGN) feedback have been ongoing since the first indication of supermassive black holes powering quasar activity in the 1960s. Although several crucial astrophysical questions have been answered in the following decades, a number of open problems remain, in particular how AGN feedback operates over nearly eight orders of magnitude - from scales of $\sim 10^{-3}\,{\rm pc}$ to the galaxy-cluster scales of a few hundred kiloparsecs. At the beginning of June 2022, about 50 junior as well as senior researchers met in Brno for the post-lockdown edition of the Cologne-Prague-Brno meeting to try to connect the dots., Comment: in print in Nature Astronomy as a meeting report; 5 pages, 1 figure

We use 118 H$\beta$ quasar (QSO) observations in the redshift range $0.0023 \leq z \leq 0.89$ to simultaneously constrain cosmological model parameters and QSO 2-parameter radius-luminosity ($R-L$) relation parameters in six different cosmological models. We find that the $R-L$ relation parameters for these QSOs are independent of the assumed cosmology so these QSOs seem to be standardizable through the $R-L$ relation (although there is a complication that might render this untrue). Cosmological constraints obtained using these QSOs are weak, more favor currently decelerated cosmological expansion, and typically are in $\sim 2\sigma$ tension with those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements. Extending the $R-L$ relation to a 3-parameter one to try to correct for the accretion rate effect does not result in a reduction of the cosmological constraints discrepancy nor does it result in the hoped-for significant reduction of the intrinsic scatter of the $R-L$ relation., Comment: 20 pages, 7 figures, H$\beta$ QSO data are given

To date, the proposed observation of Young Stellar Objects (YSOs) in the Galactic center (GC) still raises the question where and how these objects could have formed due to the violent vicinity of Sgr~A*. Here, we report the multi-wavelength detection of a highly dynamic YSO close to Sgr~A* that might be a member of the IRS13 cluster. We observe the beforehand known coreless bow-shock source X3 in the near- and mid-infrared (NIR/MIR) with SINFONI (VLT), NACO (VLT), ISAAC (VLT), VISIR (VLT), SHARP (NTT), and NIRCAM2 (KECK). In the radio domain, we use CO continuum and H30$\alpha$ ALMA observations to identify system components at different temperatures and locations concerning the central stellar source. It is suggested that these radio/submm observations in combination with the NIR Br$\gamma$ line can be associated with a protoplanetary disk of the YSO which is consistent with manifold VISIR observations that reveal complex molecules and elements such as PAH, SIV, NeII and ArIII in a dense and compact region. Based on the photometric multi-wavelength analysis, we infer the mass of $15^{+10}_{-5} M_{\odot}$ for the YSO with a related age of a few $10^4$ yr. Due to this age estimate and the required relaxation time scales for high-mass stars, this finding is an indication for ongoing star formation in the inner parsec. The proper motion and 3d distance imply a relation of X3 and IRS13. We argue that IRS13 may serve as a birthplace for young stars that are ejected due to the evaporation of the cluster., Comment: 36 pages, 28 figures, accepted by ApJ

We use 78 reverberation-measured Mg II time-lag quasars (QSOs) in the redshift range $0.0033 \leq z \leq 1.89$ to constrain cosmological parameters in six different cosmological models. The basis of our method is the use of the radius-luminosity or $R-L$ relation to standardize these 78 Mg II QSOs. In each cosmological model we simultaneously determine $R-L$ relation and cosmological model parameters, thus avoiding the circularity problem. We find that the $R-L$ relation parameter values are independent of the cosmological model used in the analysis thus establishing that current Mg II QSOs are standardizable candles. Cosmological constraints obtained using these QSOs are significantly weaker than, but consistent with, those obtained from a joint analysis of baryon acoustic oscillation (BAO) observations and Hubble parameter [$H(z)$] measurements. So, we also analyse these QSOs in conjunction with the BAO + $H(z)$ data and find cosmological constraints consistent with the standard spatially-flat $\Lambda$CDM model as well as with mild dark energy dynamics and a little spatial curvature. A larger sample of higher-quality reverberation-measured QSOs should have a smaller intrinsic dispersion and so should provide tighter constraints on cosmological parameters., Comment: 16 pages, 11 figure, Mg II QSO data are given, MNRAS accepted version. arXiv admin note: text overlap with arXiv:2105.12692

Binary black hole systems in close orbits are thought to be the precursors of gravitational wave events and their identification has fundamental implications for our understanding of black hole growth and evolution. However, a gravitationally bound companion orbiting closer than about a milli-parsec to an accreting supermassive black hole (SMBH, mass ≥106 solar masses) in an external galaxy cannot be spatially resolved with present-day instruments. Instead, its detection requires a combination of indirect observational methods and advanced modelling. Here we report the detection of quasi-periodic variability in X-ray spectral features after an outburst from a previously low-luminosity Active Galactic Nucleus (AGN) in a galaxy at redshift z=0.056. We interpret this variability as due to Quasi-Periodic Outflows (QPOuts) from the SMBH. The puzzling phenomenon repeats roughly once every 8.5 days and photo-ionization modeling of the energy spectra implies that the outflowing material moves with a high velocity of about a third of the speed of light. The mass of the central black hole, roughly 30 million solar masses, as derived from the optical broad line--SMBH mass scaling relation, implies that the outflows are launched from a few tens of gravitational radii from the SMBH event horizon. By performing 2D and 3D general relativistic magnetohydrodynamic (GRMHD) simulations and by comparing their results over a broad range of the system parameters we show that these QPOuts can be explained with an orbiting intermediate-mass black hole (IMBH) secondary (mass range of 100--10,000 solar masses) at a distance of about 100 gravitational radii (less than a milli-parsec) from the primary SMBH. Outflows are naturally enhanced when the secondary object punches through the SMBH's inner accretion disc during each orbital period and this is revealed as regular increases in X-ray absorption along our line of sight. The overall optical, UV and X-ray outburst properties indicate that a major accretion episode -- perhaps from a stellar tidal disruption by the SMBH -- could have provided the gas to illuminate the presence of the pre-existing IMBH secondary. Our work highlights the new astrophysical phenomenon of QPOuts and the importance of high cadence X-ray monitoring observations to potentially uncover electromagnetic signatures of such tight binary black hole systems.

As Setti & Woltjer noted back in 1973, quasars could be used to construct the Hubble diagram but the actualapplication was not that straightforward. It took years to implement the idea successfully. Most of the ways to use quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal bias, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit close to the black hole, discussed 50 years ago, which later led to the development of the slim disk scenario, but was recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) disk models. We also discuss the hot/warm corona issue, which is still under discussion and complicates the analysis of the X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a mostly failed wind powered by radiation pressure acting on dust (FRADO - Failed Radiatively Driven Dusty Outflow model). Next, we discuss the cosmological constraints that are currently achievable with quasars, mostly concentrating on light echo methods (continuum time delays and spectral line time delays with respect to the continuum) which are (or should be) incorporating the progress mentioned above. Finally, we briefly mention future prospects in this direction.

As Setti & Woltjer noted back in 1973, quasars could be used to construct the Hubble diagram but the actual application was not that straightforward. It took years to implement the idea successfully. Most of the ways to use quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal bias, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit close to the black hole, discussed 50 years ago, which later led to the development of the slim disk scenario, but was recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) disk models. We also discuss the hot/warm corona issue, which is still under discussion and complicates the analysis of the X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a mostly failed wind powered by radiation pressure acting on dust (FRADO - Failed Radiatively Driven Dusty Outflow model). Next, we discuss the cosmological constraints that are currently achievable with quasars, mostly concentrating on light echo methods (continuum time delays and spectral line time delays with respect to the continuum) which are (or should be) incorporating the progress mentioned above. Finally, we briefly mention future prospects in this direction., Astrophysics and Space Science (in press)

The ongoing monitoring of the Galactic center and Sgr A*, the central supermassive black hole, produces surprising and unexpected findings. This goes hand in hand with the technical evolution of ground- and space-based telescopes and instruments, but also with the progression of image filter techniques such as the Lucy Richardson algorithm. As we continue to trace the members of the S cluster close to Sgr A* on their expected trajectory around the supermassive black hole, we present the finding of a new stellar source, which we call S4716. The newly found star orbits SgrA* in about 4.0 yr and can be detected with NIRC2 (Keck), OSIRIS (Keck), SINFONI (VLT), NACO (VLT), and GRAVITY (VLTI). With a periapse distance of about 100 au, S4716 shows an equivalent distance toward Sgr A* as S4711. These fast-moving stars undergo a similar dynamical evolution, since S4711-S4716 share comparable orbital properties. We will furthermore draw a connection between the recent finding of a new faint star called S300 and the data presented here. Additionally, we observed a blend-star event with S4716 and another newly identified S star S148 in 2017., 33 pages, 23 figures, published at ApJ

Context. In the hierarchical model of evolution of the Universe, galaxy mergers play an important role, especially at high redshifts. Interactions among galaxies appear to be associated with incidences of radio-loudness in quasars and it is of interest to study the galaxies that are in the process of interacting with each other, where there is at least one nucleus that is active in the radio regime. Aims. In order to understand the various processes taking place within colliding galaxies, it is important to study the radio and optical properties of these sources, as well as any possible correlations that might exist. Methods. To this end, we present optical long-slit spectroscopy data for ten pairs of interacting galaxies selected from SDSS-FIRST at redshifts of ∼0.05, observed using the multi-object double spectrographs at the Large Binocular Telescope. Results. We used line fluxes extracted from the spectra of the nuclear regions of galaxies to plot optical diagnostic diagrams and estimate the masses of the central supermassive black holes, as well as their Eddington ratios. Additionally, we used previously published Effelsberg radio telescope data at 4.85 GHz and FIRST survey data at 1.4 GHz to estimate radio spectral slopes and the radio-loudness parameters for all of the radio-detected sources. We also used WISE data to plot a mid-infrared colour-colour diagram. Conclusions. We see that while the sample of galaxies covers all of the classes on the optical diagnostic diagrams, the sources that are radio-detected fall in the composite or transition region of the diagram. Additionally, we notice a trend of the highest radio-loudness parameter in a pair of interacting galaxies being associated with the galaxy that hosts the more massive central supermassive black hole. We do not see any obvious trends with respect to the radio spectral slope, radio-loudness parameter, and Eddington ratio. With respect to the mid-infrared data of the galaxies detected by WISE, we see that most of them have some type of contribution from star formation, however, two of them seem to have a significant contribution from an AGN as well.

We use 38 C IV quasar (QSO) reverberation-mapped (RM) observations, which span eight orders of magnitude in luminosity and the redshift range $0.001064 \leq z \leq 3.368$, to simultaneously constrain cosmological-model and QSO radius-luminosity ($R-L$) relation parameters in six cosmological models, using an improved technique that more correctly accounts for the asymmetric errors bars of the time-lag measurements. We find that $R-L$ relation parameters are independent of the cosmological models used in the analysis and so the $R-L$ relation can be used to standardize the C IV QSOs. The C IV QSO cosmological constraints are consistent with those from Mg II QSOs, allowing us to derive joint C IV + Mg II QSO cosmological constraints which are consistent with currently accelerated cosmological expansion, as well as consistent with cosmological constraints derived using better-established baryon acoustic oscillation (BAO) and Hubble parameter [$H(z)$] measurements. When jointly analyzed with $H(z)$ + BAO data, current C IV + Mg II QSO data mildly tighten current $H(z)$ + BAO data cosmological constraints., 19 pages, 11 figures, MNRAS accepted version

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., Mid-infrared (MIR) images of the Galactic center show extended gas and dust features along with bright infrared sources (IRS). Some of these dust features are a part of ionized clumpy streamers orbiting Sgr A*, known as the mini-spiral. We present their proper motions over a 12 yr time period and report their flux densities in N-band filters and derive their spectral indices. The observations were carried out by VISIR at the ESO's Very Large Telescope. High-pass filtering led to the detection of several resolved filaments and clumps along the mini-spiral. Each source was fit by a 2D Gaussian profile to determine the offsets and aperture sizes. We perform aperture photometry to extract fluxes in two different bands. We present the proper motions of the largest consistent set of resolved and reliably determined sources. In addition to stellar orbital motions, we identify a stream-like motion of extended clumps along the mini-spiral. We also detect MIR counterparts of the radio tail components of the IRS 7 source. They show a clear kinematical deviation with respect to the star. They likely represent Kelvin–Helmholtz instabilities formed downstream in the shocked stellar wind. We also analyze the shape and orientation of the extended late-type IRS 3 star that is consistent with the Atacama Large Millimeter/submillimeter Array submillimeter detection of the source. Its puffed-up envelope with a radius of ∼2 × 106 R⊙ could be the result of the red-giant collision with a nuclear jet, which was followed by tidal prolongation along the orbit. © 2022. The Author(s). Published by the American Astronomical Society., This work was supported in part by SFB 956, "Conditions and Impact of Star Formation." H.B. and E.H. are members of the International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne. We thank the Collaborative Research Centre 956, subproject A02, funded by the Deutsche Forschungsgemeinschaft (DFG), project ID 184018867. N.B.S. acknowledges financial support from the Austrian National Science Foundation through a FWF standalone grant No. P31154-N27. M.Z. acknowledges financial support by the GAČR EXPRO grant No. 21-13491X, "Exploring the Hot Universe and Understanding Cosmic Feedback." R.S. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (grant No. SEV-2017-0709) and financial support from national project PGC2018-095049-B-C21 (MCIU/AEI/FEDER, UE).

We use measurements of 59/58 quasars (QSOs), over a redshift range $0.0041\leq z \leq 1.686$, to do a comparative study of the radius--luminosity ($R-L$) and X-ray$-$UV luminosity ($L_X-L_{UV}$) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining $R-L$ or $L_X-L_{UV}$ relation parameters and cosmological parameters in six different cosmological models, we find that both $R-L$ and $L_X-L_{UV}$ relations are standardizable but provide only weak cosmological parameter constraints, with $L_X-L_{UV}$ relation data favoring larger current non-relativistic matter density parameter $\Omega_{m0}$ values than $R-L$ relation data and most other available data. We derive $L_X-L_{UV}$ and $R-L$ luminosity distances for each of the sources in the six cosmological models and find that $L_X-L_{UV}$ relation luminosity distances are shorter than $R-L$ relation luminosity distances as well as standard flat $\Lambda$CDM model luminosity distances. This explains why $L_X-L_{UV}$ relation QSO data favor larger $\Omega_{m0}$ values than do $R-L$ relation QSO data or most other cosmological measurements. While our sample size is small and only spans a small $z$ range, these results indicate that more work is needed to determine whether the $L_X-L_{UV}$ relation can be used as a cosmological probe., Comment: 20 pages, 10 figures, MNRAS in press

We present the results of the reverberation monitoring aimed at MgII broad line and FeII pseudocontinuum for the luminous quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope covering the years 2012-2021. We aimed at disentangling the MgII and UV FeII variability and the first measurement of UV FeII time delay for a distant quasar. We used several methods for time-delay measurements and determined both FeII and MgII time delays as well as performed a wavelength-resolved time delay study for a combination of MgII and FeII in the 2700 - 2900 \AA restframe wavelength range. We obtain the time delay for MgII of $275.5^{+12.4}_{-19.5}$ days in the rest frame, while for FeII we have two possible solutions of $270.0^{+13.8}_{-25.3}$ days and $180.3^{+26.6}_{-30.0}$ in the rest frame. Combining this result with the old measurement of FeII UV time delay for NGC 5548 we discuss for the first time the radius-luminosity relation for UV FeII with the slope consistent with $0.5$ within uncertainties. Since FeII time delay has a shorter time-delay component but lines are narrower than MgII, we propose that the line delay measurement is biased towards the BLR part facing the observer, with the bulk of the Fe II emission may arise from the more distant BLR region, one that is shielded from the observer., Comment: 22 pages, 19 Figures, 6 Tables, Submitted to Astronomy and Astrophysics, Comments are welcome

We present a near-UV space telescope on a ~70kg micro-satellite with a moderately fast repointing capability and a near real-time alert communication system that has been proposed in response to a call for an ambitious Czech national mission. The mission, which has recently been approved for Phase 0, A, and B1 study shall measure the brightness evolution of kilonovae, resulting from mergers of neutron stars in the near-UV band and thus it shall distinguish between different explosion scenarios. Between the observations of transient sources, the satellite shall perform observations of other targets of interest, a large part of which will be chosen in open competition., Comment: SPIE Astronomical Telescopes and Instrumentation

Since many years we know that dust in the form of the dusty-molecular torus is responsible for the obscuration in active galactic nuclei (AGN) at large viewing angles and thus for the classification of AGN. Recently, we gained some observational and theoretical insight into geometry of the region and the role of the dust in the dynamics of the outflow and failed winds. We will briefly touch on all these aspects, including our dust-based model (FRADO - Failed Radiatively Accelerated Dusty Outflow) of the formation of the Balmer lines in AGN., Comment: Partially based on talk at 31st Symposium on the Physics of Ionized Gases in Belgrade, accepted for European Physical Journal D Topical Issue: "Physics of Ionized Gases and Spectroscopy of Isolated Complex Systems: Fundamentals and Applications"

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., 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, 1842

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 Journal

Observations of the near-infrared excess object G2/DSO increased attention toward the Galactic center and its vicinity. The predicted flaring event in 2014 and the outcome of the intense monitoring of the supermassive black hole in the center of our Galaxy did not fulfill all predictions about a significantly enhanced accretion event. Subsequent observations addressed the question concerning the nature of the object because of its compact shape, especially during its periapse in 2014. Theoretical approaches have attempted to answer the contradictory behavior of the object, resisting the expected dissolution of a gaseous cloud due to tidal forces in combination with evaporation and hydrodynamical instabilities. However, assuming that the object is instead a dust-enshrouded young stellar object seems to be in line with the predictions of several groups and observations presented in numerous publications. Here we present a detailed overview and analysis of the observations of the object that have been performed with SINFONI (VLT) and we provide a comprehensive approach to clarify the nature of G2/DSO. We show that the tail emission consists of two isolated and compact sources with different orbital elements for each source rather than an extended and stretched component as it appeared in previous representations of the same data. Considering our recent publications, we propose that the monitored dust-enshrouded objects are remnants of a dissolved young stellar cluster whose formation was initiated in the circumnuclear disk. This indicates a shared history, which agrees with our analysis of the D- and X-sources. © 2021. The American Astronomical Society. All rights reserved., This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG) via the Cologne Bonn Graduate School (BCGS), the Max Planck Society through the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics as well as special funds through the University of Cologne. Conditions and Impact of Star Formation is carried out within the Collaborative Research Centre 956, subproject [A02], funded by the Deutsche Forschungsgemeinschaft (DFG)—project ID 184018867. B.Sh. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). M.Z. acknowledges the financial support by the National Science Center, Poland, grant No. 2017/26/A/ST9/00756 (Maestro 9) and the NAWA financial support under the agreement PPN/WYM/2019/1/00064 to perform a three-month exchange stay at the Charles University in Prague and the Astronomical Institute of the Czech Academy of Sciences. M.Z. also acknowledges the GAČR EXPRO grant 21-13491X ("Exploring the Hot Universe and Understanding Cosmic Feedback") for financial support. Part of this work was supported by fruitful discussions with members of the European Union funded COST Action MP0905: Black Holes in a Violent Universe and the Czech Science Foundation—DFG collaboration (V.K., No. 19-01137J). A.P., J.C., S.E., and G.B. contributed useful points to the discussion. We also would like to thank the members of the SINFONI/NACO/VISIR and ESO's Paranal/Chile team for their support and collaboration.

Using the six years of the spectroscopic monitoring of the luminous quasar HE 0435-4312 ($z=1.2231$) with the Southern African Large Telescope (SALT), in combination with the photometric data (CATALINA, OGLE, SALTICAM, and BMT), we determined the rest-frame time-delay of $296^{+13}_{-14}$ days between the MgII broad-line emission and the ionizing continuum using seven different time-delay inference methods. Artefact time-delay peaks and aliases were mitigated using the bootstrap method, prior weighting probability function as well as by analyzing unevenly sampled mock light curves. The MgII emission is considerably variable with the fractional variability of $\sim 5.4\%$, which is comparable to the continuum variability ($\sim 4.8\%$). Because of its high luminosity ($L_{3000}=10^{46.4}\,{\rm erg\,s^{-1}}$), the source is beneficial for a further reduction of the scatter along the MgII-based radius-luminosity relation and its extended versions, especially when the high-accreting subsample that has an RMS scatter of $\sim 0.2$ dex is considered. This opens up a possibility to use the high-accretor MgII-based radius-luminosity relation for constraining cosmological parameters. With the current sample of 27 reverberation-mapped sources, the best-fit cosmological parameters $(\Omega_{\rm m}, \Omega_{\Lambda})=(0.19; 0.62)$ are consistent with the standard cosmological model within 1$\sigma$ confidence level., Comment: 34 pages, 23 figures, 6 tables; accepted by the Astrophysical Journal; Main body as well as the Appendix extended; added references

Recent measurements of the parameters of the Concordance Cosmology Model ($\Lambda$CDM) done in the low-redshift Universe with Supernovae Ia/Cepheids, and in the distant Universe done with Cosmic Microwave Background (CMB) imply different values for the Hubble constant (67.4 $\pm$ 0.5 km s$^{-1}$ Mpc$^{-1}$ from Planck vs 74.03 $\pm$ 1.42 km s$^{-1}$ Mpc$^{-1}$, Riess et al. 2019). This Hubble constant tension implies that either the systematic errors are underestimated, or the $\Lambda$CDM does not represent well the observed expansion of the Universe. Since quasars - active galactic nuclei - can be observed in the nearby Universe up to redshift z $\sim$ 7.5, they are suitable to estimate the cosmological properties in a large redshift range. Our group develops two methods based on the observations of quasars in the late Universe up to redshift z$\sim $4.5, with the objective to determine the expansion rate of the Universe. These methods do not yet provide an independent measurement of the Hubble constant since they do not have firm absolute calibration but they allow to test the $\Lambda$CDM model, and so far no departures from this model were found., Comment: 6 pages, 2 figures, contribution to the Proceedings of the 100 years of the Polish Physical Society Congress, 16-18 October 2020, Warsaw, Poland. http://info.ifpan.edu.pl/APP/

We analyze the gas and dust emission in the immediate vicinity of the supermassive black hole Sgr~A* at the Galactic center (GC) with the ESO VLT (Paranal/Chile) instruments SINFONI and VISIR. The SINFONI H+K data cubes show several emission lines with related line map counterparts. From these lines, the Br$\gamma$ emission is the most prominent one and appears to be shaped as a bar extending along the North-South direction. With VISIR, we find a dusty counterpart to this filamentary emission. In this work, we present evidence that this feature can be most likely connected to the mini-spiral and potentially influenced by the winds of the massive stars in the central cluster or an accretion wind from Sgr~A*. To this end, we co-add the SINFONI data between 2005 and 2015. The spectroscopic analysis reveals a range of Doppler-shifted emission lines. We also detect substructures in the shape of clumps that can be investigated in the channel maps of the Br$\gamma$-bar. In addition, we compare the detection of the near-infrared (NIR) Br$\gamma$ feature to PAH1 mid-infrared (MIR) observations and published 226 GHz radio data. These clumps show a proper motion of about $320$km/s that are consistent with other infrared continuum detected filaments in the Galactic center. Deriving a mass of $2.5\,\times\,10^{-5}\,M_{\odot}$ for the investigated Br$\gamma$-feature shows an agreement with former derived masses for similar objects. Besides the North-South Br$\gamma$-bar, we find a comparable additional East-West feature. Also, we identify several gas reservoirs that are located west of Sgr~A* that may harbor dusty objects., Comment: 19 pages,6 figures, 8 tables, submitted to and accepted by ApJ

The density profile of the ambient medium around a supermassive black hole plays an important role in understanding the inflow-outflow mechanisms in the Galactic Centre. We constrain the spherical density profile using the stellar bow shock of the star S2 which orbits the supermassive black hole at the Galactic Centre with the pericentre distance of 14.4 mas ($\sim$ 1500 R$_\text{s}$). Assuming an elliptical orbit, we apply celestial mechanics and the theory of bow shocks that are at ram pressure equilibrium. We analyse the measured infrared flux density and magnitudes of S2 in the L'-band (3.8 micron) obtained over seven epochs in the years between 2004-2018. We detect no significant change in S2 flux density until the recent periapse in May 2018. The intrinsic flux variability of S2 is at the level of 2 - 3%. Based on the dust-extinction model, the upper limit on the number density at the S2 periapse is $\sim$1.87$\times$10$^9$ cm$^{-3}$, which yields a density slope of at most 3.20. Using the synchrotron bow-shock emission, we obtain an ambient density of $\leq$ 1.01$\times$10$^5$ cm$^{-3}$ and a slope of $\leq$ 1.47. These values are consistent with a wide variety of media from hot accretion flows to potentially colder and denser media comparable in properties to broad-line region clouds. A standard thin disc can be, however, excluded at the distance of the S2 pericentre. Based on our sensitivity of 0.01 mag, we can distinguish between hot accretion flows and thin, cold discs, where the latter can be excluded at the scale of the S2 periapse. Future observations of stars with smaller pericentre distances in the S cluster using instruments such as METIS@ELT with a photometric sensitivity of as much as 10$^{-3}$ mag will allow to probe the Galactic Centre medium at intermediate scales at densities as low as $\sim$ 700 cm$^{-3}$ in case of non-thermal bow-shock emission., Comment: 17 pages, 12 figures, accepted for publication by A&A journal

Observations in the near-infrared domain showed the presence of the flat core of bright late-type stars inside $\sim 0.5\,{\rm pc}$ from the Galactic center supermassive black hole (Sgr A*), while young massive OB/Wolf-Rayet stars form a cusp. Several dynamical processes were proposed to explain this apparent paradox of the distribution of the Galactic center stellar populations. Given the mounting evidence about a significantly increased activity of Sgr A* during the past million years, we propose a scenario based on the interaction between the late-type giants and a nuclear jet, whose past existence and energetics can be inferred from the presence of $\gamma$-ray Fermi bubbles and bipolar radio bubbles. Extended, loose envelopes of red giant stars can be ablated by the jet with kinetic luminosity in the range of $L_{\rm j}\approx 10^{41}$-$10^{44}\,{\rm erg\,s^{-1}}$ within the inner $\sim 0.04\,{\rm pc}$ of Sgr A* (S cluster region), which would lead to their infrared luminosity decrease after several thousand jet-star interactions. The ablation of the atmospheres of red giants is complemented by the process of tidal stripping that operates at distances of $\lesssim 1\,{\rm mpc}$, and by the direct mechanical interaction of stars with a clumpy disc at $\gtrsim 0.04\,{\rm pc}$, which can explain the flat density profile of bright late-type stars inside the inner half parsec from Sgr A*., Comment: 24 pages, 10 figures, 3 tables; accepted for publication by the Astrophysical Journal

We present the monitoring of the AGN continuum and MgII broad line emission for the quasar HE 0413-4031 ($z=1.38$) based on the six-year monitoring by the South African Large Telescope (SALT). We managed to estimate a time-delay of $302.6^{+28.7}_{-33.1}$ days in the rest frame of the source using seven different methods: interpolated cross-correlation function (ICCF), discrete correlation function (DCF), $z$-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and $\chi^2$ method. This time-delay is below the value expected from the standard radius-luminosity relation. However, based on the monochromatic luminosity of the source and the SED modelling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of $\sim 0.4$. The MgII line luminosity of HE 0413-4031 responds to the continuum variability as $L_{\rm line}\propto L_{\rm cont}^{0.43\pm 0.10}$, which is consistent with the light-travel distance of the location of MgII emission at $R_{\rm out} \sim 10^{18}\,{\rm cm}$. Using the data of 10 other quasars, we confirm the radius-luminosity relation for broad MgII line, which was previously determined for broad H$\beta$ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to H$\beta$ sample. After the accretion-rate correction of the light-travel distance, the MgII-based radius-luminosity relation has a small scatter of only $0.10$ dex., Comment: 39 pages (23 pages - Main text, 16 pages - Appendix), 21 figures, 14 tables; accepted for publication in the Astrophysical Journal

We present a detailed analysis of the kinematics of 112 stars that mostly comprise the high velocity S-cluster and orbit the super massive black hole SgrA* at the center of the Milky Way. For 39 of them orbital elements are known, for the remainder we know proper motions. The distribution of inclinations, and proper motion flight directions deviate significantly from a uniform distribution which one expects if the orientation of the orbits are random. Across the central arcseconds the S-cluster stars are arranged in two almost edge on disks that are located at a position angle approximately +-45 o with respect to the Galactic plane. The angular momentum vectors for stars in each disk point in both directions, i.e. the stars in a given disk rotate in opposite ways. The poles of this structure are located only about 25 o from the line of sight. This structure may be the result of a resonance process that started with the formation of the young B-dwarf stars in the cluster about 6 Myr ago. Alternatively, it indicated the presence of a disturber at a distance from the center comparable to the distance of the compact stellar association IRS13., Comment: published in Astrophysical Journal 23 pages, 6 tabels, 16 figures, ENHANCED GRAPHICS in ApJ in fullorbits.gif circularized.gif normalized.gif

The Galactic centre Nuclear Star Cluster is one of the densest stellar clusters in the Galaxy. The stars in its inner portions orbit the supermassive black hole associated with compact radio source Sgr~A* at the orbital speeds of several thousand km/s. The B-type star S2 is currently the best case to test the general relativity as well as other theories of gravity based on its stellar orbit. Yet its orbital period of $\sim 16\,{\rm yr}$ and the eccentricity of $\sim 0.88$ yields the relativistic pericentre shift of $\sim 11'$, which is observationally still difficult to reliably measure due to possible Newtonian perturbations as well as reference-frame uncertainties. A naive way to solve this problem is to find stars with smaller pericentre distances, $r_{\rm p}\lesssim 1529$ Schwarzschild radii ($120\,{\rm AU}$), and thus more prominent relativistic effects. In this contribution, we show that to detect stars on relativistic orbits is progressively less likely given the volume shrinkage and the expected stellar density distributions. Finally, one arrives to a sparse region, where the total number of bright stars is expected to fall below one. One can, however, still potentially detect stars crossing this region. In this contribution, we provide a simple formula for the detection probability of a star crossing a sparse region. We also examine an approximate time-scale on which the star reappears in the sparse region, i.e. a "waiting" time-scale for observers., 7 pages, 6 figures, 2 tables, accepted by the Astronomical Notes as a contribution to the proceedings of the IBWS 2018 workshop (Carlsbad, https://www.ibws.cz/), added references

3C 84 (NGC 1275, Perseus A) is a bright radio source at the center of an ongoing merger, where HST observations show two colliding spiral galaxies. 3C 84 holds promise to improve our understanding about how of the activity of active galactic nuclei, the formation of supermassive binary black holes, feedback processes, and galaxy collisions are interrelated. 3C,84 is one of only six radio galaxies, which reveal TeV emission. The origin of this TeV emission is still a matter of debate. Our present study is based on high resolution radio interferometric observations (15 GHz) of the pc-scale jet in this complex radio galaxy. We have re-modeled and re-analyzed 42 VLBA observations of 3C 84, performed between 1999.99 and 2017.65. In order to enable a proper alignment of the VLBA observations, we developed a method of a &ldquo, differential&rdquo, alignment whereby we select one reference point and minimize the deviations from this reference point in the remaining epochs. As a result, we find strong indication for a precession of the 3C 84 jet&mdash, not only for its central regions, but also for the outer lobe at 10 mas distance. These findings are further supported by our kinematic precession modeling of the radio flux-density monitoring data provided by the University of Michigan Radio Observatory and the Owens Valley Radio Observatory, which yields a precession time scale of about 40 yr. This time scale is further supported by literature maps obtained about 40 yr ago (1973 and 1974.1) which reveal a similar central radio structure. We suggest that the TeV flare detected by MAGIC may correlate with the precession of 3C 84, as we disentangle a projected reversal point of the precessing motion that correlates with the flaring time. This may physically be explained by a precessing jet sweeping over a new region of so far undisturbed X-ray gas which would then lead to shock-produced TeV-emission. In addition, we perform a correlation analysis between the radio data and GeV data obtained by the Fermi Gamma-ray Space Telescope and find that the &gamma, ray data are lagging the radio data by 300&ndash, 400 days. A possible explanation could be that the radio and the GeV data stem from different emission regions. We discuss our findings and propose that the detected jet precession can also account for the observed cavities in the X-ray emission on kpc-scales.

We report the detection of the far-infrared (FIR) fine-structure line of singly ionised nitrogen, \Nplusa, within the peak epoch of galaxy assembly, from a strongly lensed galaxy, hereafter ``The Red Radio Ring''; the RRR, at z = 2.55. We combine new observations of the ground-state and mid-J transitions of CO (J$_{\rm up} =$ 1,5,8), and the FIR spectral energy distribution (SED), to explore the multi-phase interstellar medium (ISM) properties of the RRR. All line profiles suggest that the HII regions, traced by \Nplusa, and the (diffuse and dense) molecular gas, traced by the CO, are co-spatial when averaged over kpc-sized regions. Using its mid-IR-to-millimetre (mm) SED, we derive a non-negligible dust attenuation of the \Nplusa line emission. Assuming a uniform dust screen approximation results a mean molecular gas column density $> 10^{24}$\, cm$^{-2}$, with a molecular gas-to-dust mass ratio of 100. It is clear that dust attenuation corrections should be accounted for when studying FIR fine-structure lines in such systems. The attenuation corrected ratio of $L_{\rm NII205} / L_{\rm IR(8-1000��m)} = 2.7 \times 10^{-4}$ is consistent with the dispersion of local and $z >$ 4 SFGs. We find that the lower-limit, \Nplusa -based star-formation rate (SFR) is less than the IR-derived SFR by a factor of four. Finally, the dust SED, CO line SED and $L_{\rm NII205}$ line-to-IR luminosity ratio of the RRR is consistent with a starburst-powered ISM., 13 pages, 6 figures, accepted to MNRAS

A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study radio-optical properties of a large sample of extragalactic sources. In particular, we aim at studying the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. To this goal, we combine flux densities from the radio FIRST survey at $1.4\,{\rm GHz}$ (with the flux density range $10\,{\rm mJy} \leq F_{1.4} \leq 1000\,{\rm mJy}$) for 209 SDSS sources at intermediate redshift $(0.04\leq z \leq 0.4)$ with the Effelsberg radiotelescope measurements at $4.85\,{\rm GHz}$ and $10.45\,{\rm GHz}$. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star-formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with steep radio index, high ionization ratio and high radio loudness, (ii) sources with flat radio index, lower ionization ratio and intermediate radio loudness, (iii) sources with inverted radio index, low ionization ratio and low radio loudness. The classes (i), (ii), (iii) cluster mainly along the transition from Seyfert to LINER sources in the BPT diagram. We interpret these groups as a result of the recurrent nuclear-jet activity., 20 pages, 15 figures, 2 tables; in print in Astronomy & Astrophysics journal; minor typos corrected and a few references added

Quasars have been proposed as a new class of standard candles analogous to Supernovae, as their large redshift range and high luminosities make them excellent candidates. Reverberation mapping (RM) method enables to estimate the distance to the source from the time delay measurement of the emission lines with respect to the continuum, since the time delay depends on the absolute luminosity of the source. This radius-luminosity (RL) relation exhibits a low scatter and it was thus proposed for cosmological purposes. However, in recent years the increase in the studied sample, and in particular the inclusion of highly accreting QSO has increased the dispersion in the RL relation, with many objects showing time delays shorter than the expected. Using H$\beta$ RM measurements for 117 sources with $0.002, Comment: 26 pages, 9 Figures, 4 tables; accepted for publication in ApJ

We provide an up-to-date summary of the current observational and theoretical studies of stellar bow-shock sources close to the Galactic centre. The symmetry axis of a bow shock provides the information on the relative motion of the star with respect to the ambient medium, while the photometry and spectroscopy in NIR domain give information about the 3D motion of the star. Hence, it is possible from this data to obtain an estimate on the motion of the ambient medium. In combination with the estimate of the bow-shock size, it is possible to infer the valuable information on the density of the hot accretion flow close to the Galactic centre. In particular, we outline a statistical method to determine the ambient density slope based on either multiple bow-shock detections for one star along its orbit or multiple bow-shock detections for several sources at different distances from Sgr A*., Comment: 12 pages, 2 figures; to be published in Proceedings of Science; presented at Accretion Processes in Cosmic Sources II (APCS2018), 3-8 September 2018, Saint Petersburg, Russian Federation

Context. The neutrino event IceCube−170922A appears to originate from the BL Lac object TXS 0506+056. To understand the neutrino creation process and to localize the emission site, we studied the radio images of the jet at 15 GHz.Aims. Other BL Lac objects show properties similar to those of TXS 0506+056, such as multiwavelength variability or a curved jet. However, to date only TXS 0506+056 has been identified as neutrino emitter. The aim of this paper is to determine what makes the parsec-scale jet of TXS 0506+056 specific in this respect.Methods. We reanalyzed and remodeled 16 VLBA 15 GHz observations between 2009 and 2018. We thoroughly examined the jet kinematics and flux-density evolution of individual jet components during the time of enhanced neutrino activity between September 2014 and March 2015, and in particular before and after the neutrino event.Results. Our results suggest that the jet is very strongly curved and most likely observable under a special viewing angle of close to zero. We may observe the interaction between jet features that cross each other’s paths. We find subsequent flux-density flaring of six components passing the likely collision site. In addition, we find a strong indication for precession of the inner jet, and model a precession period of about 10 yr via the Lense-Thirring effect. We discuss an alternative scenario, which is the interpretation of observing the signature of two jets within TXS 0506+056, again hinting toward a collision of jetted material. We essentially suggest that the neutrino emission may result from the interaction of jetted material in combination with a special viewing angle and jet precession.Conclusions. We propose that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings seem capable of explaining the neutrino generation at the time of a low gamma-ray flux and also indicate that TXS 0506+056 might be an atypical blazar. It seems to be the first time that a potential collision of two jets on parsec scales has been reported and that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.

In the framework of understanding the gas and stellar kinematics and their relations to AGNs and galaxy evolution scenarios, we present spatially resolved distributions and kinematics of the stars and gas in the central ∼800 pc radius of the nearby Seyfert galaxy NGC 1365. We obtained H + K- and K-band near-infrared (NIR) integral-field observations from VLT/SINFONI. Our results reveal strong broad and narrow emission-line components of ionized gas (hydrogen recombination lines Paα and Brγ) in the nuclear region, as well as hot dust with a temperature of ∼1300 K, both typical for type-1 AGNs. From MBH − σ* and the broad components of hydrogen recombination lines, we find a black-hole mass of (5 − 10)×106 M⊙. In the central ∼800 pc, we find a hot molecular gas mass of ∼615 M⊙, which corresponds to a cold molecular gas reservoir of (2 − 8)×108 M⊙. However, there is a molecular gas deficiency in the nuclear region. The gas and stellar-velocity maps both show rotation patterns consistent with the large-scale rotation of the galaxy. However, the gaseous and stellar kinematics show deviations from pure disk rotation, which suggest streaming motions in the central < 200 pc and a velocity twist at the location of the ring which indicates deviations in disk and ring rotation velocities in accordance with published CO kinematics. We detect a blueshifted emission line split in Paα, associated with the nuclear region only. We investigate the star-formation properties of the hot spots in the circumnuclear ring which have starburst ages of ≲10 Myr and find indications for an age gradient on the western side of the ring. In addition, our high-resolution data reveal further substructure within this ring which also shows enhanced star forming activity close to the nucleus.

In the near future, new surveys promise a significant increase in the number of quasars (QSO) at large redshifts. This will help to constrain the dark energy models using quasars. The Large Synoptic Survey Telescope (LSST) will cover over 10 million QSO in six photometric bands during its 10-year run. QSO will be monitored and subsequently analyzed using the photometric reverberation mapping (RM) technique. In low-redshift quasars, the combination of reverberation-mapped and spectroscopic results have provided important progress. However, there are still some facts which have to be taken into account for future results. It has been found that super-Eddington sources show time delays shorter than the expected from the well-known Radius-Luminosity ($R\mathrm{_{H\beta}}-L_{5100}$) relation. Using a sample of 117 H$\beta$ reverberation-mapped AGN with $0.02, Comment: 12 pages, 5 figures. Proceedings of the Frascati Workshop 2019: Multifrequency Behaviour of High Energy Cosmic Sources XIII, 3 - 8 June 2019, Palermo. Italy. To be published in the proceedings of in electronic form by the Proceedings of Science (PoS-SISSA)

By applying different statistically robust methods, we analyze the time-lag between the continuum and ionized line-emission (Mg II line) light curves for the distant bright quasar CTS C$30.10$ (redshift $z \sim 0.9$). The data were obtained by the 10-meter SALT telescope in South Africa. In detail, we demonstrate the application of several methods using interpolated cross-correlation function (ICCF), discrete correlation function (DCF), z-transformed discrete correlation function (zDCF), von Neumann estimator, and the JAVELIN code package. In particular, we discuss the uncertainties of these methods. In conclusion, we find that the quasar lies on the broad-line region (BLR) size -- monochromatic luminosity power-law scaling, $R_{\rm BLR}\propto L_{5100}^{1/2}$, which was already confirmed for low-redshift sources. In case the BLR size-luminosity relation holds for other distant sources, quasars could be used for probing cosmological models as ``standard candles'' complementary to supernovae Ia., Comment: 9 pages, 5 figures, 2 tables; to appear in Astronomical Notes as a contribution presented at the IBWS 2019 conference (Karlovy Vary, Czechia, 20 - 24 May 2019)

Recently, near-infrared GRAVITY@ESO observations at $2.2\,\mu{\rm m}$ have announced the detection of three bright "flares" in the vicinity of the Galactic center supermassive black hole (SMBH) that exhibited orbital motion at a distance of about $6 - 11$ gravitational radii from an $\sim 4\times 10^6\, M_{\odot}$ black hole. There are indications of the presence of a large-scale, organized component of the magnetic field at the Galactic center. Electromagnetic effects on the flare dynamics were previously not taken into account despite the relativistic motion of a plasma in magnetic field leading to the charge separation and nonnegligible net charge density in the plasma. Applying various approaches, we find the net charge number density of the flare components of the order of $10^{-3} - 10^{-4}$ cm$^{-3}$, while the particles' total number density is of the order of $10^{6} - 10^{8}$ cm$^{-3}$. However, even such a tiny excess of charged particles in the quasi-neutral plasma can significantly affect the dynamics of flare components, which can then lead to the degeneracy in the measurements of spin of the SMBH. Analyzing the dynamics of recent flares in the case of the rapidly rotating black hole, we also constrain the inclination angle between the magnetic field and spin axis to $\alpha < 50^{\circ}$, as for larger angles, the motion of the hot spot is strongly chaotic., Comment: 28 pages, 7 figures; to appear in the Astrophysical Journal; accepted version

Context. We find an extended source in the direct vicinity of Sgr A∗ with an approximate projected mean distance of 425 ± 26 mas. Its sky-projected elongated shape can be described by an averaged spatial extension of x = 110 ± 20 mas and y = 180 ± 20 mas. With this, the observed object points in the analyzed SINFONI data sets between 2006 and 2016 directly toward the supermassive black hole. We discuss different possible scenarios that could explain the detected blueshifted line emission source. Aims. Here we present a detailed and extensive analysis of the adaptive optics corrected SINFONI data between 2006 and 2016 with a spatial pixel scale of 0 . ″ 025 and a corresponding field of view of 0 . ″ 8 × 0 . ″ 8 per single data cube with the focus on the newly discovered source. We spectroscopically identify the source, which we name X8, in the blueshifted Brγ line maps. Additionally, an upper limit for the continuum magnitude can be derived from the close-by S-star S41. Methods. We applied the standard reduction procedure with the SINFONI/EsoRex pipeline for the analysis. We applied pre- and post-data correction in order to establish various calibration procedures. For the sharpened images, we used the Lucy-Richardson algorithm with a low iteration number. For the high-pass filtered images, we used the smooth-subtracting process in order to increase the signal-to-noise ratio. Results. We are able to detect the elongated line emission source in quantified data sets between 2006 and 2016. We find a lower limit for the infrared continuum magnitude of K s 17.0 ± 0.1. The alignment of X8 toward Sgr A∗ can be detected in data sets that fulfill a sufficient number of observations with a defined quality level. A more detailed analysis of the results shows indications of a bipolar outflow source that might be associated with either a young stellar object, or with a post-AGB star or young planetary nebula. Conclusions. The near-infrared excess source X8 close to S24, S25, and S41 can be detected between 2006 and 2016. In addition to an apparent bow-shock morphology, the source shows clear signatures of a bipolar outflow that is consistent with both a young stellar object and a post-AGB star. If confirmed, this would be the closest ever detected bipolar outflow source to the supermassive black hole. Similar to the case of the DSO/G2 source and other dusty sources, it further supports the in situ star formation in the direct vicinity of Sgr A∗. If X8 were a bow-shock source, it would be the third object of this type that can be found in projection in the mini-cavity. This scenario would support the idea that the cavity is created by a wind from Sgr A∗. © ESO 2019., We received funding from the European Union Seventh Framework Program (FP7/2013-2017) under grant agreement no 312789 - Strong gravity: Probing Strong Gravity by Black Holes Across the Range of Masses. Michal Zajacek acknowledges the support by the National Science Centre, Poland, grant No. 2017/26/A/ST9/00756 (Maestro 9). This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG) via the Cologne Bonn Graduate School (BCGS), the Max Planck Society through the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics, as well as special funds through the University of Cologne and SFB 956 - Conditions and Impact of Star Formation.

In this contribution, we summarize our results concerning the observational constraints on the electric charge associated with the Galactic centre black hole - Sgr A*. According to the no-hair theorem, every astrophysical black hole, including supermassive black holes, is characterized by at most three classical, externally observable parameters - mass, spin, and the electric charge. While the mass and the spin have routinely been measured by several methods, the electric charge has usually been neglected, based on the arguments of efficient discharge in astrophysical plasmas. From a theoretical point of view, the black hole can attain charge due to the mass imbalance between protons and electrons in fully ionized plasmas, which yields about $\sim 10^8\,{\rm C}$ for Sgr A*. The second, induction mechanism concerns rotating Kerr black holes embedded in an external magnetic field, which leads to electric field generation due to the twisting of magnetic field lines. This electric field can be associated with the induced Wald charge, for which we calculate the upper limit of $\sim 10^{15}\,{\rm C}$ for Sgr A*. Although the maximum theoretical limit of $\sim 10^{15}\,{\rm C}$ is still 12 orders of magnitude smaller than the extremal charge of Sgr A*, we analyse a few astrophysical consequences of having a black hole with a small charge in the Galactic centre. Two most prominent ones are the effect on the X-ray bremsstrahlung profile and the effect on the position of the innermost stable circular orbit., 16 pages, 4 figures, a short review on the charge of the Galactic centre black hole (Sgr A*) presented at FISICPAC-2018 conference (University of Sharjah, UAE), submitted to the Journal of Physics: Conference Series; minor revision after the referee round; additional references added

The usage of the radius-luminosity (R-L) relation for the determination of black hole masses across the cosmic history as well as its application for cosmological studies motivates us to analyze its scatter, which has recently increased significantly both for the optical (H$\beta$) and UV (Mg II) lines. To this purpose, we determined the scatter along the R-L relation for an up-to-date reverberation-mapped Mg II sample. Studying linear combinations of the luminosity at 3000 A with independent parameters such as the Full Width at Half Maximum (FWHM), Fe II strength (R$_\mathrm{FeII}$), and the fractional variability ($F\mathrm{_{var}}$) for the whole sample, we get only a small decrease in the scatter ($\sigma{_{\rm rms}}=0.29-0.30$ dex). Linear combinations with the dimensionless accretion rate ($\dot{\mathcal{M}}$) and the Eddington ratio ($\alpha_\mathrm{Edd}$) lead to significant reductions of the scatter ($\sigma_{\rm rms}\sim 0.1$ dex), albeit both suffering from the inter-dependency on the observed time-delay. After the division into two sub-samples considering the median value of the $\dot{\mathcal{M}}$ in the full sample, we find that the scatter decreases significantly for the highly accreting sub-sample. In particular, the smallest scatter of $\sigma{_{\rm rms}}=0.17$ dex is associated with the independent parameter R$_\mathrm{FeII}$, followed by the combination with $F\mathrm{_{var}}$, with $\sigma{_{\rm rms}}=0.19$ dex. Both of these independent observationally-inferred parameters are in turn correlated with $\dot{\mathcal{M}}$ and $\alpha_\mathrm{Edd}$. These results suggest that the large scatter along the R-L relation is driven $\textit{mainly}$ by the accretion rate intensity., Comment: 20 pages, 9 figures, 2 tables. Accepted for publication in ApJ

We present high-pass filtered NACO and SINFONI images of the newly discovered stars S4711-S4715 between 2004 and 2016. Our deep H+K-band (SINFONI) and K-band (NACO) data show the S-cluster star S4711 on a highly eccentric trajectory around Sgr~A* with an orbital period of 7.6 years and a periapse distance of 144 AU to the super massive black hole (SMBH). S4711 is hereby the star with the shortest orbital period and the smallest mean distance to the SMBH during its orbit to date. The used high-pass filtered images are based on co-added data sets to improve the signal to noise. The spectroscopic SINFONI data let us determine detailed stellar properties of S4711 like the mass and the rotational velocity. The faint S-cluster star candidates, S4712-S4715, can be observed in a projected distance to Sgr~A* of at least temporarily $\leq$ 120 mas. From these stars, S4714 is the most prominent one with an orbital period of 12 years and an eccentricity of 0.985. The stars S4712-S4715 show similar properties with comparable magnitudes and stellar masses to S4711. The MCMC simulations determine confidently precise uncertainties for the orbital elements of S62 and S4711-S4715. The presence of S4711 in addition to S55, S62, and the also newly found star S4714 implies a population of faint stars that can be found at distances to Sgr~A* that are comparable to the size of our solar system. These short orbital time period stars in the dense cluster around the SMBH in the center of our Galaxy are perfect candidates to observe gravitational effects such as the periapse shift., Comment: 23 pages, accepted and published bei ApJ