arXiv subjects

Johannes Buchner

Publications and source records attributed to Johannes Buchner.

At least 37 records · Page 2Linked to original sources

arXiv2025

Genuine Retrieval of the AGN Host Stellar Population (GRAHSP)

The assembly and co-evolution of supermassive black holes (SMBH) and their host galaxy stellar population is a key open questions in galaxy evolution. Stellar mass ($M_\star$) and star formation rate (SFR), are inferred by modeling the spectral energy distribution (SED). For galaxies triggering SMBH activity, the active galactic nucleus (AGN) contaminates the light at all wavelengths, hampering the inference of galaxy parameters. Incomplete AGN templates can lead to systematic overestimates of the stellar mass, biasing our understanding of AGN-galaxy co-evolution. This challenge has gained further impetus with the advent of sensitive wide-area surveys with millions of luminous AGN, including by eROSITA, Euclid and LSST. We aim to estimate the accuracy and bias of AGN host galaxy parameters and improve upon existing techniques. This work makes two contributions: 1) a new SED fitting code, GRAHSP, with a flexible, empirically motivated AGN model including a power law continuum emission lines, a FeII forest and a flexible infrared torus. We verify that our model reproduces published X-ray to infrared SEDs of AGN to better than 20\% accuracy. A fully Bayesian fit with nested sampling includes uncertainties in the model and the data, making the inference highly robust. 2) we created a benchmark photometric dataset where pure quasars are merged with non-AGN pure galaxies into a hybrid (Chimera) object but with known galaxy and AGN properties. Comparing the true and retrieved $M_\star$, SFR and AGN luminosities shows that previous codes systematically over-estimate $M_\star$ and SFR by 0.5 dex with a wide scatter of 0.7 dex, at AGN luminosities above 10^44 erg/s. In contrast, GRAHSP shows no bias on $M_\star$ and SFR. GRAHSP also estimates more realistic uncertainties. GRAHSP enables characterization of the environmental conditions conducive to black hole growth. (abridged)

astro-ph.GA↗

arXiv2025

High-impact Scientific Software in Astronomy and its creators

In the last decades, scientific software has graduated from a hidden side-product to a first-class member of the astrophysics literature. We aim to quantify the activity and impact of software development for astronomy, using a systematic survey. Starting from the Astrophysics Source Code Library and the Journal of Open Source Software, we analyse 3432 public git-based scientific software packages. Paper abstract text analysis suggests seven dominant themes: cosmology, data reduction pipelines, exoplanets, hydrodynamic simulations, radiative transfer spectra simulation, statistical inference and galaxies. We present key individual software contributors, their affiliated institutes and countries of high-impact software in astronomy & astrophysics. We consider the number of citations to papers using the software and the number of person-days from their git repositories, as proxies for impact and complexity, respectively. We find that half of the mapped development is through US-affiliated institutes, and a large number of high-impact projects are led by a single person. Our results indicate that there are currently over 200 people active on any given day to improve software in astronomy.

astro-ph.IM↗

arXiv2025

Revisiting the X-ray-to-UV relation of Quasars in the era of all-sky surveys

The X-ray--to--UV relation of active galactic nuclei (AGNs), commonly parametrized via the monochromatic luminosities at $2500\,\mathring{A}$ and $2\,keV$, reflects the energetic interplay between the accretion disc and the X-ray-emitting corona, and is key for understanding accretion physics. Previous studies suggest that disc-dominated emission becomes more prominent with increasing optical luminosity. However, the redshift evolution of this relation remains debated, and a dependence on Eddington ratio, predicted by accretion flow models, is still observationally unconstrained. We revisit this relation using a large, nearly all-sky sample by combining the SDSS DR16Q QSO catalogue with X-ray data from XMM-Newton and the SRG/eROSITA All-Sky Survey DR1, yielding 136,745 QSOs at redshifts $0.5 \leq z < 3.0$. We introduce a hierarchical Bayesian framework that treats X-ray detections and upper limits uniformly, enabling robust inference from both parametric and non-parametric models. We confirm a tight, sublinear $\log L_X({\rm 2\,keV})$-$\log L_ν({\rm 2500\,\mathring{A}})$ correlation, but with a normalization at the lower end of previous estimates. Contrary to most literature results, we detect a mild but systematic redshift evolution: the relation flattens and its intrinsic scatter decreases at higher redshift. This trend is consistent with disc emission increasingly dominated by scattering and enhanced energy transfer to the X-ray corona, potentially indicating redshift evolution in the X-ray bolometric correction. We find no significant dependence on Eddington ratio, in tension with recent accretion flow models.

astro-ph.GA↗

arXiv2025

Characterising the X-ray variability of QSOs to the highest Eddington ratios and black hole masses with eROSITA light curves

An important diagnostic of the inner structure of accretion flows onto supermassive black holes are the stochastic flux variations at X-ray wavelengths. Despite its significance, a systematic characterisation of the statistical properties of the X-ray variability to the highest Eddington ratios and most massive black holes is still lacking. In this paper we address this issue using SRG/eROSITA 5-epoch light curves to characterise the mean X-ray variability of optically selected SDSS QSOs extending to black holes masses of $10^{10}$ solar and accretion rates close to the Eddington limit. The adopted variability statistic is the ensemble normalised excess variance, which is measured using a novel hierarchical Bayesian model (eBExVar) tailored to the Poisson nature of the X-ray light curves. We find a clear anti-correlation of the ensemble variability with black hole mass, extending previous results to time scales of months. This can be interpreted as evidence for an X-ray corona size and/or physical conditions that scale with black holes mass. We also find an unexpected increase of the ensemble normalised excess variance close to the Eddington limit, which is contrary to the predictions of empirical variability models. This result suggests an additional variability component for fast growing black holes that may be related to systematic variations of the hot corona size with Eddington ratio or shielding of the hot corona by an inner puffed-up disk and/or outflows.

astro-ph.HE↗

arXiv2025

The $M_{\rm BH}-M_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots

JWST has identified a large population of faint, broad-line active galactic nuclei (AGN) in the early universe that are powered by black holes (BHs) that often appear overmassive relative to their host galaxies. In this study, we examine the relationship between BH mass and galaxy stellar mass at $3 3σ$ above the relationship measured for local broad-line AGN. We derive an intrinsic scatter in this relationship of $0.9$ dex, which does not vary over the redshift range of our sample. We also find that the $M_{\rm BH}/M_{\star}$ ratio increases by $2.3$ dex from $z = 3.5$ and $z = 6.5$ with a confidence level of $ > 3σ$. We attribute this trend with the increasing fraction of LRDs in our sample at $z>4$ as their host masses are $\sim1$ dex lower than the non-LRD AGN in our sample. These results support a picture in which the BHs powering JWST's broad-line AGN are genuinely overmassive and become increasingly so with redshift. We discuss the implications of our findings on early BH growth relative to that of their host galaxies and the constraints it places on BH seeding models.

astro-ph.GA↗

arXiv2025

Characterizing the roles of transitory obscured phases and inner torus in shaping the fractions of obscured AGN at cosmic noon

The origin of obscuration in Active Galactic Nuclei (AGN) is still a matter of contention. It is unclear whether obscured AGN are primarily due to line-of-sight effects, a transitory, dust-enshrouded phase in galaxy evolution, or a combination of both. The role of an inner torus around the central SMBH also remains unclear in pure Evolution models. We use cosmological semi-analytic models and semi-empirical prescriptions to explore obscuration effects in AGN at 1<z<3. We consider a realistic object-by-object modelling of AGN evolution including different light curves (LCs) composed of phases of varying levels of obscuration, mimicking the possible clearing effects of strong AGN feedback. Evolution models characterized by AGN LCs with relatively short pre-peak obscured phases followed by more extended optical/UV visible post-peak phases, struggle to reproduce the high fraction of obscured AGN at z~2-3 inferred from X-ray surveys. Evolution models characterised by LCs with sharp post-peak declines or persistent or multiple obscuration phases are more successful, although they still face challenges in reproducing the steady drop in the fractions of obscured AGN with increasing luminosity measured by some groups. Invoking a fine-tuning in the input LCs, with more luminous AGN defined by longer optical/UV visible windows, can improve the match to the decreasing fractions of obscured AGN with luminosity. Alternatively, a long-lived central torus-like component, with thickness decreasing with increasing AGN power, naturally boosts the luminosity-dependent fractions of obscured AGN, suggesting that small-scale orientation effects may still represent a key component even in Evolution models. We also find that in our models major mergers and starbursts, when considered in isolation, fall short in accounting for the large fractions of highly obscured faint AGN detected at cosmic noon.

astro-ph.GA↗

arXiv2025

Accretion onto supermassive and intermediate mass black holes in cosmological simulations

Accretion is the dominant contribution to the cosmic massive black hole density in the Universe today. Yet, modelling it in cosmological simulations is challenging due to the dynamic range involved, as well as the theoretical uncertainties of the underlying mechanisms driving accretion from galactic to black hole horizon scales. We present a simple, flexible parametrization for gas inflows onto massive black holes in order to manage this uncertainty in large-volume cosmological simulations. This is done as part of the "Learning the Universe'' collaboration, which aims to jointly infer the initial conditions and physical processes governing the evolution of the Universe using a Bayesian forward-modelling approach. To allow such a forward-modelling, we update the prescription for accretion with a two-parameter free-fall based inflow estimate that allows for a radius-dependent inflow rate and add a simple model for unresolved accretion disks. We use uniform resolution cosmological hydrodynamical simulations and the IllustrisTNG framework to study the massive black hole population and its dependence on the introduced model parameters. Once the parameters of the accretion formula are chosen to result in a roughly similar redshift zero black hole mass density, the differences caused by the details in the accretion formula are moderate in the supermassive black hole regime, indicating that it is difficult to distinguish between accretion mechanisms based on luminous active galactic nuclei powered by supermassive black holes. Applying the same models to intermediate mass black holes at high redshift, however, reveals significantly different accretion rates in high redshift, moderate luminosity active galactic nuclei and different frequencies and mass distributions of intermediate mass black hole mergers for the same black hole formation model.

astro-ph.GA↗

arXiv2025

Optical Emission-Line Properties of eROSITA-selected SDSS-V Galaxies

We present and discuss optical emission line properties obtained from the analysis of Sloan Digital Sky Survey (SDSS) spectra for an X-ray selected sample of 3684 galaxies (0.002 < z < 0.55), drawn from the eRASS1 catalog. We modeled SDSS-V DR19 spectra using the NBursts full spectrum fitting technique with E-MILES simple stellar populations (SSP) models and emission line templates to decompose broad and narrow emission line components for correlation with X-ray properties. We place the galaxies on the Baldwin-Phillips-Terlevich (BPT) diagram to diagnose their dominant excitation mechanism. We show that the consistent use of the narrow component fluxes shifts most galaxies systematically and significantly upward to the active galactic nuclei (AGN) region on the BPT diagram. On this basis, we confirm the dependence between a galaxys position on the BPT diagram and its (0.2-2.3 keV) X-ray/H$α$ flux ratio. We also verified the correlation between X-ray luminosity and emission line luminosities of the narrow [O\iii]$λ5007$ and broad H$α$ component; as well as the relations between the Supermassive Black Hole (SMBH) mass, the X-ray luminosity, and the velocity dispersion of the stellar component ($σ_{*}$) on the base on the unique sample of optical spectroscopic follow-up of X-ray sources detected by eROSITA. These results highlight the importance of emission line decomposition in AGN classification and refine the connection between X-ray emission and optical emission line properties in galaxies.

astro-ph.GA↗

arXiv2025

Sloan Digital Sky Survey-V: Pioneering Panoptic Spectroscopy

The Sloan Digital Sky Survey-V (SDSS-V) is pioneering panoptic spectroscopy: it is the first all-sky, multi-epoch, optical-to-infrared spectroscopic survey. SDSS-V is mapping the sky with multi-object spectroscopy (MOS) at telescopes in both hemispheres (the 2.5-m Sloan Foundation Telescope at Apache Point Observatory and the 100-inch du Pont Telescope at Las Campanas Observatory), where 500 zonal robotic fiber positioners feed light from a wide-field focal plane to an optical (R$\sim 2000$, 500 fibers) and a near-infrared (R$\sim 22,000$, 300 fibers) spectrograph. In addition to these MOS capabilities, the survey is pioneering ultra wide-field ($\sim$ 4000~deg$^2$) integral field spectroscopy enabled by a new dedicated facility (LVM-I) at Las Campanas Observatory, where an integral field spectrograph (IFS) with 1801 lenslet-coupled fibers arranged in a 0.5 degree diameter hexagon feeds multiple R$\sim$4000 optical spectrographs that cover 3600-9800 angstroms. SDSS-V's hardware and multi-year survey strategy are designed to decode the chemo-dynamical history of the Milky Way Galaxy and tackle fundamental open issues in stellar physics in its Milky Way Mapper program, trace the growth physics of supermassive black holes in its Black Hole Mapper program, and understand the self-regulation mechanisms and the chemical enrichment of galactic ecosystems at the energy-injection scale in its Local Volume Mapper program. The survey is well-timed to multiply the scientific output from major all-sky space missions. The SDSS-V MOS programs began robotic operations in 2021; IFS observations began in 2023 with the completion of the LVM-I facility. SDSS-V builds upon decades of heritage of SDSS's pioneering advances in data analysis, collaboration spirit, infrastructure, and product deliverables in astronomy.

astro-ph.IM↗

arXiv2025

The Average Soft X-ray Spectra of eROSITA Active Galactic Nuclei

Context. AGNs are strong X-ray emitters shaped by disk-corona interactions. The soft excess (0.5-2.0 keV) reveals key information about the "warm corona" bridging the disk and hot corona. Yet, how this feature evolves with accretion properties remains poorly constrained, especially in large samples using spectral stacking. Aims. The eROSITA All-Sky Survey (eRASS:5) provides an unprecedented sample. We investigate how the average AGN X-ray spectra evolve with accretion parameters, and explore disk-corona connection by further combining stacked UV data. Methods. We developed Xstack, a novel tool that stacks rest-frame X-ray spectra and responses while preserving spectral shape through optimized weighting. We stack 17929 AGNs ("spec-z" sample, 23 Ms) with similar X-ray loudness alpha_ox, UV luminosity L_UV, and 4159 AGNs ("BH-mass" sample, 3 Ms) with similar Eddington ratio lambda_Edd and black hole mass M_BH. The resulting stacked X-ray spectra are analyzed with a phenomenological model. We further fit the stacked optical-UV-Xray SED with AGNSED model. Results. Soft excess strengthens strongly with alpha_ox and lambda_Edd (~5), while the hard X-ray spectral shape remains largely unchanged, supporting that soft excess is dominated by warm corona rather than reflection. AGNSED modeling reveals that warm corona radius (R_g units) generally increases with lambda_Edd and decreases with M_BH, or equivalently the disk-to-warm-corona transition consistently occurs near 1e4 K. The hot corona contracts with lambda_Edd and is unaffected by M_BH, aligning with disk evaporation predictions. Conclusions. The soft excess likely originates from a warm corona, with the disk to warm corona transition tied to hydrogen ionization near 1e4 K - supporting earlier eFEDS-HSC stacking results (Hagen et al. 2024). This study shows the strength of spectral stacking in probing AGN disk-corona physics.

astro-ph.HE↗

arXiv2025

An Analysis of Pseudo-Goodwin Cycles in a Wage-Led Minsky Model

The goal of these notes is to make the concept of "pseudo goodwin cycles" mathematically more precise. At first the title seems like a contradiction to have a wage-led model and still find goodwin cycles in it, but the point we try to make in the paper is that those are only `pseudo-goodwin' cycles, and not real goodwin cycles.

math.DS↗

arXiv2025

Reinforcement Learning and Life Cycle Assessment for a Circular Economy -- Towards Progressive Computer Science

The aim of this paper is to discuss the potential of using methods from Reinforcement Learning for Life Cycle Assessment in a circular economy, and to present some new ideas in this direction. To give some context, we explain how Reinforcement Learning was successfully applied in computer chess (and beyond). As computer chess was historically called the "drosophila of AI", we start by describing a method for the board representation called 'rotated bitboards' that can potentially also be applied in the context of sustainability. In the first part of this paper, the concepts of the bitboard-representation and the advantages of (rotated) bitboards in move generation are explained. In order to illustrate those ideas practice, the concrete implementation of the move-generator in FUSc# (a chess engine developed at FU Berlin in C# some years ago) is described. In addition, rotated binary neural networks are discussed briefly. The second part deals with reinforcement learning in computer chess (and beyond). We exemplify the progress that has been made in this field in the last 15-20 years by comparing the "state of the art" from 2002-2008, when FUSc# was developed, with the ground-breaking innovations connected to "AlphaZero". We review some application of the ideas developed in AlphaZero in other domains, e.g. the "other Alphas" like AlphaFold, AlphaTensor, AlphaGeometry and AlphaProof. In the final part of the paper, we discuss the computer-science related challenges that changing the economic paradigm towards (absolute) sustainability poses and in how far what we call 'progressive computer science' needs to contribute. Concrete challenges include the closing of material loops in a circular economy with Life Cycle Assessment in order to optimize for (absolute) sustainability, and we present some new ideas in this direction.

cs.AI↗

arXiv2025

The eROSITA Final Equatorial Depth Survey (eFEDS): SDSS spectroscopic observations of X-ray sources

We present one of the largest uniform optical spectroscopic surveys of X-ray selected sources to date that were observed as a pilot study for the Black Hole Mapper (BHM) survey. The BHM program of the Sloan Digital Sky Survey (SDSS)-V is designed to provide optical spectra for hundreds of thousands of X-ray selected sources from the SRG/eROSITA all-sky survey. This significantly improves our ability to classify and characterise the physical properties of large statistical populations of X-ray emitting objects. Our sample consists of 13079 sources in the eROSITA eFEDS performance verification field, 12011 of which provide reliable redshifts from 0 6.5x10^-15 erg/s/cm^2) and were observed for about 20 years with fibre-fed SDSS spectrographs. After including all available redshift information for the eFEDS sources from the dedicated SDSS-V plate programme and archival data, we visually inspected the SDSS optical spectra to verify the reliability of these redshift measurements and the performance of the SDSS pipeline. The visual inspection allowed us to recover reliable redshifts (for 99% of the spectra with a signal-to-noise ratio of >2) and to assign classes to the sources, and we confirm that the vast majority of our sample consists of active galactic nuclei (AGNs). Only ~3% of the eFEDS/SDSS sources are Galactic objects. We also show the diversity of the optical spectra of the X-ray selected AGNs and provide spectral stacks with a high signal-to-noise ratio in various sub-samples with different redshift and optical broad-band colours. Our AGN sample contains optical spectra of (broad-line) quasars, narrow-line galaxies, and optically passive galaxies. It is considerably diverse in its colours and in its levels of nuclear obscuration.

astro-ph.HE↗

arXiv2025

An obscured quasar census with the 4MOST IR AGN survey: design, predicted properties, and scientific goals

We present the 4MOST IR AGN survey, the first large-scale optical spectroscopic survey characterizing mid-infrared (MIR) selected obscured active galactic nuclei (AGN). The survey targets $\approx 212,000$ obscured infrared (IR) AGN candidates over $\approx 10,000 \rm \: deg^2$ down to a magnitude limit of $r_{\rm AB}=22.8 \, \rm mag$ and will be $\approx 100 \times$ larger than any existing obscured IR AGN spectroscopic sample. We select the targets using a MIR colour criterion applied to the unWISE catalogue from the WISE all-sky survey, and then apply a $r-W2\geq 5.9 \rm \: mag$ cut; we demonstrate that this selection will mostly identify sources obscured by $N_{\rm H}>10^{22} \rm \: cm^{-2}$. The survey complements the 4MOST X-ray survey, which will follow up $\sim 1\rm M$ eROSITA-selected (typically unobscured) AGN. We perform simulations to predict the quality of the spectra that we will obtain and validate our MIR-optical colour-selection method using X-ray spectral constraints and UV-to-far IR spectral energy distribution (SED) modelling in four well-observed deep-sky fields. We find that: (1) $\approx 80-87\%$ of the WISE-selected targets are AGN down to $r_{\rm AB}=22.1-22.8 \: \rm mag$ of which $\approx 70\%$ are obscured by $N_{\rm H}>10^{22} \: \rm cm^{-2}$, and (2) $\approx 80\%$ of the 4MOST IR AGN sample will remain undetected by the deepest eROSITA observations due to extreme absorption. Our SED fitting results show that the 4MOST IR AGN survey will primarily identify obscured AGN and quasars ($\approx 55\%$ of the sample is expected to have $L_{\rm AGN,IR}>10^{45} \rm \: erg \: s^{-1}$) residing in massive galaxies ($M_{\star}\approx 10^{10}-10^{12} \rm \: M_{\odot}$) at $z\approx 0.5-3.5$ with $ \approx 33\%$ expected to be hosted by starburst galaxies.

astro-ph.GA↗

arXiv2025

The population of tidal disruption events discovered with eROSITA

This paper presents a systematic study of X-ray-selected canonical tidal disruption events (TDEs) discovered in the western Galactic hemisphere of the first two eROSITA all-sky surveys (eRASS1 and eRASS2) performed between Dec 2019 and Dec 2020. We compiled a TDE sample from the catalog of eROSITA's extragalactic transients and variables eRO-ExTra, which includes X-ray sources with a variability significance and fractional amplitude over four between eRASS1 and eRASS2, not associated with known AGNs. Each X-ray source is associated with an optical counterpart from the Legacy Survey DR10. Canonical TDEs were selected based on their X-ray light-curve properties (single flare or decline), soft X-ray spectra ($Γ>3$), and the absence of archival X-ray variability and AGN signatures in their host photometry and spectroscopy. The sample includes 31 X-ray-selected TDE candidates with redshifts of $0.02< z<0.34$ and luminosities of $5.7 \times 10^{41}<L_X<5.3 \times 10^{44}$ erg/s in the 0.2-6.0 keV rest frame, of which 30 are canonical TDEs and one is an off-nuclear TDE candidate. The derived X-ray luminosity function is best fit by a double power law with a luminosity break at $10^{44}$ erg/s, corresponding to the Eddington-limiting prediction. This corresponds to a TDE volumetric rate of $ (2.3^{+1.2}_{-0.9})\times10^{-7}\,Mpc^{-3} yr^{-1}$ ($\approx1.2\times 10^{-5}$ events per galaxy per year). TDE host galaxies show a green-valley overdensity. In addition, 20%, 30%, and 15% of the sample exhibit flares in the optical, mid-infrared (mid-IR), or radio bands, respectively. We discuss the differences between X-ray, optical, and mid-IR TDE populations and the origins of multiwavelength flares in the context of the obscuring envelope and stream-stream collision models. Finally, we highlight TDE subpopulations that are not included in the canonical sample and should be explored in the future.

astro-ph.HE↗

arXiv2025

The X-ray statistical properties of dust-obscured galaxies detected by eROSITA

Dust-obscured galaxies (DOGs) are considered to be in a co-evolution phase, with the associated active galactic nuclei (AGN) obscured by dust and gas. Although the DOGs are thought to harbor rapidly growing SMBHs, their X-ray statistical properties, crucial for understanding the properties of obscuring gas as well as the accretion disk state and the hot electron corona around the SMBHs, remain unexplored due to the combination of the low number density of DOGs and the lack of X-ray surveys achieving both of the wide-area and uniformly high-sensitivity observations. We construct a sample of X-ray-detected DOGs in the eROSITA Final Equatorial Depth Survey (eFEDS) field and examine their X-ray statistical properties. By using Subaru/HSC SSP, VIKING, and WISE all-sky surveys, our results reveal the discovery of 5738 IR-bright DOGs in the footprint covered by both of the eFEDS and VIKING surveys (60 deg^2), with 65 objects identified as X-ray-detected DOGs (eFEDS-DOGs). Among them, 41 eFEDS-DOGs show a power-law slope in the near to mid-IR bands (power-law DOGs), indicating dust-obscured AGN. The hydrogen column density (N_H) suggests that eFEDS-DOGs cover even unobscured AGN, spanning 10^20 < N_H <= 10^23. On the other hand, the majority of IR-bright DOGs are not detected by eROSITA, suggesting that most IR-bright DOGs are heavily obscured by dust and gas with N_H > 10^23. Therefore, eFEDS-DOGs, discovered thanks to the wide-area survey by eROSITA, are newly found populations showing less obscured phases among the lifetime of DOGs. Additionally, some eFEDS-DOGs exhibit deviations, down to nearly 1.0 dex below the monochromatic luminosity at 6 micron versus absorption-corrected intrinsic X-ray luminosity between 0.5-2 keV relation, suggesting that it may signal high Eddington ratios reaching the Eddington limit.

astro-ph.GA↗

arXiv2025

Discovery of Quasi-periodic Eruptions in the Tidal Disruption Event and Extreme Coronal Line Emitter AT2022upj: implications for the QPE/TDE fraction and a connection to ECLEs

Quasi-periodic eruptions (QPEs) are recurring soft X-ray transients emerging from the vicinity of supermassive black holes (SMBHs) in nearby, low-mass galaxy nuclei; about ten QPE hosts have been identified thus far. Here we report the \textit{NICER} discovery of QPEs in the optically-selected Tidal Disruption Event (TDE) and Extreme Coronal Line Emitter (ECLE) AT2022upj, exhibiting a large spread in recurrence times from 0.5-3.5 days, durations from 0.3-1 days, peak luminosities from $10^{42.5-43.0}$ erg s$^{-1}$, and erratic flare profiles. A wealth of evidence now links at least some QPEs to the newly-formed accretion flows emerging from TDEs; AT2022upj is the third QPE reported in an optically discovered TDE. Marginalizing over the uncertain distributions of QPE peak luminosity, recurrence time, delay after TDE peak, and lifetime, we use the burgeoning sample to make a Bayesian estimate that the fraction of optical TDEs resulting in QPEs within 5 years post-disruption is $9^{+9}_{-5}$\%. Along with AT2019qiz, AT2022upj also marks the second of the three optical TDE+X-ray QPEs showing coronal line emission, suggesting ECLEs may represent a subset of TDEs particularly efficient at forming QPEs and/or that sustained QPE X-ray emission contributes to coronal line emission in some galaxy nuclei.

astro-ph.HE↗

arXiv2025

$C^{1}$-Stable-Manifolds for Periodic Heteroclinic Chains in Bianchi IX: Symbolic Computations and Statistical Properties

In this paper we study oscillatory Bianchi models of class A and are able to show that for admissible periodic heteroclinic chains in Bianchi IX there exisist $C^{1}$- stable - manifolds of orbits that follow these chains towards the big bang. A detailed study of Takens Linearization Theorem and the Non-Resonance-Conditions leads us to this new result in Bianchi class A. More precisely, we can show that there are no heteroclinic chains in Bianchi IX with constant continued fraction development that allow Takens-Linearization at all of their base points. Geometrically speaking, this excludes "symmetric" heteroclinic chains with the same number of "bounces" near all of the 3 Taub Points - the result shows that we have to require some "asymmetry" in the bounces in order to allow for Takens Linearization, e.g. by considering admissible 2-periodic continued fraction developments. We conclude by discussing the statistical properties of those solutions, including their topological and measure-theoretic genericity.

math.DS↗