Mass Accretion Research Articles

Evolution of massive black holes in galactic nuclei

Abstract We propose a scenario for mass evolution of massive black holes (MBHs) in galactic nuclei, to explain both the mass correlation of supermassive black holes (SMBHs) with bulges and the downsizing behavior of active galactic nuclei. Primordial gas structures that produce galactic bulges are supposed to be formed at $z \sim 10$ and the core region, called the nuclear region (NR) here, is considered to be a place for an MBH to grow to an SMBH. The downsizing behavior requires the MBH to significantly increase its mass in a time $\sim$1 Gyr. The rapid mass increase is discussed as being realized only when the MBH stays in a very high-density region such as the core of a molecular cloud throughout the period $\sim$1 Gyr. According to these arguments, MBHs formed from population III stars born in mini-halos at $z \sim 20$–30 are excluded from the candidates for the seed black hole for an SMBH and only MBHs from population II stars born in the core of the central molecular cloud (CMC) in the NR are left as candidates. The MBHs in the dense core of the CMC started increasing in mass through mass accretion and the most massive black hole (MMBH) saw the most rapid evolution, possibly restraining the relatively slow evolutions of the less massive black holes. Dynamical interactions of the MMBH with ambient MCs induced the wandering motion and the further mass increase. However, when the MMBH mass exceeds a boundary mass, dynamical friction with field stars brakes the MMBH wandering and mass accretion. This scenario can semi-quantitatively reproduce both the downsizing behavior and the SMBH mass–bulge mass correlation with reasonable parameter values.

Detection of a Highly Ionized Outflow in the Quasiperiodically Erupting Source GSN 069

Quasiperiodic eruptions (QPEs) are high-amplitude, soft X-ray bursts recurring every few hours, associated with supermassive black holes. Many interpretations for QPEs were proposed since their recent discovery in 2019, including extreme mass ratio inspirals and accretion disk instabilities. But, as of today, their nature still remains debated. We perform the first high-resolution X-ray spectral study of a QPE source using the Reflection Grating Spectrometers' gratings on board XMM-Newton, leveraging nearly 2 Ms of exposure on GSN 069, the first discovered source of this class. We resolve several absorption and emission lines including a strong line pair near the N vii rest-frame energy, resembling the P-Cygni profile. We apply photoionization spectral models and identify the absorption lines as an outflow blueshifted by 1700−2900 km s−1, with a column density of about 1022 cm−2 and an ionization parameter log(ξ /erg cm s−1) of 3.9−4.6. The emission lines are instead redshifted by up to 2900 km s−1, and likely originate from the same outflow that imprints the absorption features, and covers the full 4π sky from the point of view of GSN 069. The column density and ionization are comparable to the outflows detected in some tidal disruption events, but this outflow is significantly faster and has a strong emission component. The outflow is more highly ionized when the system is in the phase during which QPEs are present, and from the limits, we derive on its location, we conclude that the outflow is connected to the recent complex, transient activity of GSN 069, which began around 2010.

Filament Accretion and Fragmentation in the Perseus Molecular Cloud

Observations suggest that filaments in molecular clouds can grow by mass accretion while forming cores via fragmentation. Here, we present one of the first large-sample studies of filament accretion using velocity gradient measurements of star-forming filaments on the ∼0.05 pc scale with NH3 observations of the Perseus Molecular Cloud, primarily obtained as a part of the Green Bank Ammonia Survey. In this study, we find significant correlations between the velocity gradient, velocity dispersion, mass per unit length, and number of cores per unit length of the Perseus filaments. Our results suggest a scenario in which filaments not only grow through mass accretion, but also form new cores continuously in the process, well into the thermally supercritical regime. Such behavior is contrary to that expected from isolated filament models but consistent with how filaments form within a more realistic cloud environment, suggesting that the cloud environment plays a crucial role in shaping core formation and evolution in filaments. Furthermore, even though velocity gradients within filaments are not oriented randomly, we find no correlation between velocity gradient orientation and the filament properties we analyzed. This result suggests that gravity is unlikely to be the dominant mechanism imposing order on the ∼0.05 pc scale for dense star-forming gas.

Mass evolution of broad-line regions to explain the luminosity variability of broad Hα in the tidal disruption event ASASSN-14li

We propose an oversimplified model to explain the different variability trends in the observed broad Hα emission line luminosity, LHα(t), and the tidal disruption event (TDE) model-determined bolometric luminosity, Lbol(t), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, MBLRs(t), can be determined as the maximum mass, MBLRs, 0, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, MBLRs(t), can be applied to describe the observed LHα(t). Although our proposed model is oversimplified – with only one free model parameter, MBLRs, 0 – with MBLRs, 0 ∼ 0.02 M⊙, it describes the observed LHα(t) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed LHα(t) in the TDE ASASSN-14ae. The reasonable descriptions of the observed LHα(t) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of MBLRs related to central accreted debris in TDEs.

Nutritional Supplementation to Preserve Healthy Lean Mass and Function During Periods of Pharmacological and Nonpharmacological-Induced Weight Loss: Protocol for a Systematic Review and Meta-Analysis.

Weight loss without adequate anabolic stimuli can lead to reductions in lean, as well as adipose, tissue. Health benefits typically associated with weight loss are therefore attenuated,as body composition potentially shifts from an obese to sarcopenic/frail phenotype. In contrast to the traditional connotation of frailty, this might occur in younger adults and is characterized by reduced performance in functional tasks of daily living. Nutritional supplements as an adjunct to weight loss intervention could support the maintenance of lean mass, particularly if structured exercise is contraindicated. This systematic review aims to quantify the effect of nutritional supplements, without concurrent exercise, on lean mass in individuals undergoing pharmacological and nonpharmacological-induced weight loss. This protocol describes a prospective systematic review and meta-analysis of randomized controlled trials investigating the effect of nutritional supplements on lean mass during weight loss. Comparison arms will not use nutritional supplements. Literature searches will be conducted using the following online databases: Embase, MEDLINE, Web of Science, Google Scholar, and OpenGrey. Outcome measures related to body composition, lean mass, skeletal muscle mass/size, or physical function will be extracted. Risk of bias will be assessed using the United States National Heart Lung and Blood Institute quality assessment tool for controlled intervention studies. A meta-analysis will be conducted to synthesize comparable outcomes. The results of this review will be reported in adherence to PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols) standards, and published in a peer-reviewed journal. This study will be the first to systematically review nutritional interventions for the preservation or accretion of lean mass during weight loss. This review will identify gaps in the literature and inform the development of optimized weight loss strategies, for use in research and practice. International Prospective Register of Systematic Reviews: PROSPERO CRD42024521540.

H2–H2O demixing in Uranus and Neptune: Adiabatic structure models

Context. Demixing properties of major planetary constituents influence the interior structure and evolution of planets. Comparing experimental and computational data on the miscibility of hydrogen and water to adiabatic profiles suggests that phase separation between these two components occurs in the ice giants Uranus and Neptune. Aims. We aim to predict the atmospheric water abundance and transition pressure between the water-poor outer envelope and the water-rich deep interior in Uranus and Neptune. Methods. We constructed seven H2–H2O phase diagrams from the available experimental and computational data. We computed interior adiabatic structure models and compared these to the phase diagrams to infer whether demixing occurred. Results. We obtain a strong water depletion in the top layer due to the rain-out of water and find upper limits on the atmospheric water-mass fraction Zatm of 0.21 for Uranus and 0.16 for Neptune. The transition from the water-poor to the water-rich layer is sharp and occurs at pressures PZ between 4 and 11 GPa. Using these constraints on Zatm and PZ, we find that the observed gravitational harmonics J2 and J4 can be reproduced if PZ ≳ 10 GPa in Uranus and ≳5 GPa in Neptune, and if the deep interior has a high primordial water-mass fraction of 0.8, unless rocks are also present. The agreement with J4 is improved if rocks are confined deeper than PZ, for instance, below a rock cloud level at 2000 K (20–30 GPa). Conclusions. These findings confirm classical few-layer models and suggest that a layered structure may result from a combination of primordial mass accretion and subsequent phase separation. Reduced observational uncertainty in J4 and its dynamic contribution, atmospheric water abundance measurements from the Uranus Orbiter and Probe (UOP) or a Neptune mission, and better understanding of the mixing behaviour of constituents are needed to constrain the interiors of ice giants.

Effects of ultrafast outflows on X-ray time lags in active galactic nuclei

Context. The time lag between soft (e.g., 0.3–1 keV) and hard (e.g., 1–4 keV) X-ray photons has been observed in many active galactic nuclei (AGNs) and can reveal the accretion process and geometry around supermassive black holes. High-frequency Fe K and soft lags are considered to originate from the light-travel distances between the corona and the accretion disk, while the propagation of the inward mass accretion fluctuation usually explains the low-frequency hard lags. Ultrafast outflows (UFOs) with a velocity range of ∼0.03 to 0.3c have also been discovered in numerous AGNs and are believed to be launched from the inner accretion disk. However, it remains unclear whether UFOs can affect the X-ray time lags. Aims. As a pilot work, we aim to investigate the potential influence of UFOs on X-ray time lags of AGNs in a small sample. Methods. By performing the UFO-resolved Fourier spectral timing analysis of archival XMM-Newton observations of three AGNs with transient UFOs – PG 1448+273, IRAS 13224-3809, and PG 1211+143 – we compare the X-ray timing products, such as lag-frequency and lag-energy spectra, of observations with and without UFO obscuration. Results. Our results find that in each AGN, low-frequency hard lags become weak or even disappear when they are accompanied by UFOs. This change is confirmed by Monte Carlo simulations at a confidence level of at least 2.7σ. In the high-frequency domain, soft lags remain unchanged, while the Fe K reverberation lags tentatively disappear. The comparison between timing products of low- and high-flux observations on another three AGNs without UFOs (Ark 564, NGC 7469, and Mrk 335) suggests that the disappearance of low-frequency hard lags is likely related to the emergence of UFOs, not necessarily related to the source flux. Conclusions. The presence of UFOs can affect X-ray time lags of AGNs by suppressing the low-frequency hard lags, which can be explained by an additional time delay introduced by UFOs or disk accretion energy, which should transferred to heat the corona, carried away by UFOs.

Multizone Modeling of Black Hole Accretion and Feedback in 3D GRMHD: Bridging Vast Spatial and Temporal Scales

Simulating accretion and feedback from the horizon scale of supermassive black holes (SMBHs) out to galactic scales is challenging because of the vast range of scales involved. Elaborating on H. Cho et al., we describe and test a “multizone” technique, which is designed to tackle this difficult problem in three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations. While short-timescale variability should be interpreted with caution, the method is demonstrated to be well-suited for finding dynamical steady states over a wide dynamic range. We simulate accretion on a nonspinning SMBH (a * = 0) using initial conditions and the external galactic potential from a large-scale galaxy simulation and achieve a steady state over eight decades in radius. As found in H. Cho et al., the density scales with radius as ρ ∝ r −1 inside the Bondi radius R B , which is located at R B = 2 × 105 r g (≈60 pc for M87), where r g is the gravitational radius of the SMBH; the plasma-β is ∼ unity, indicating an extended magnetically arrested state; the mass accretion rate Ṁ is ≈1% of the analytical Bondi accretion rate ṀB; and there is continuous energy feedback out to ≈100R B (or beyond > kpc) at a rate ≈0.02Ṁc2 . Surprisingly, no ordered rotation in the external medium survives as the magnetized gas flows to smaller radii, and the final steady solution is very similar to when the exterior has no rotation. Using the multizone method, we simulate GRMHD accretion over a wide range of Bondi radii, R B ∼ 102−107 r g, and find that Ṁ/ṀB≈(RB/6rg)−0.5 .

The role of magnetospheric current sheets in pair enrichment and ultra-high energy proton acceleration in M87*

Recent advances in numerical simulations of magnetically arrested accretion onto supermassive black holes have shed light on the formation and dynamics of magnetospheric current sheets near the black hole horizon. By considering the pair magnetization σ e in the upstream region and the mass accretion rate ṁ (in units of the Eddington mass accretion rate) as free parameters we estimate the strength of the magnetic field and develop analytical models, motivated by recent three-dimensional particle-in-cell simulations, to describe the populations of relativistic electrons and positrons (pairs) in the reconnection region.Applying our model to M87*, we numerically compute the non-thermal photon spectra for various values of σ e . We show that pairs that are accelerated up to the synchrotron radiation-limited energy while meandering across both sides of the current sheet, can produce MeV flares with luminosity of ∼ 1041 erg s-1 — independent of σ e — for a black hole accreting at ṁ=10-5. Pairs that are trapped in the transient current sheet can produce X-ray counterparts to the MeV flares, lasting about a day for current sheets with length of a few gravitational radii. We also show that the upstream plasma can be enriched due to photon-photon pair creation, and derive a new equilibrium magnetization of σ e ∼ 103-104 for ṁ = 10-6 - 10-5. Additionally, we explore the potential of magnetospheric current sheets to accelerate protons to ultra-high energies, finding that while acceleration to such energies is limited by various loss mechanisms, such as synchrotron and photopion losses from the non-thermal emission from pairs, maximal proton energies in the range of a few EeV are attainable in magnetospheric sheets forming around supermassive sub-Eddington accreting black holes.

The emergence of the MD − Ṁ* correlation in the magnetohydrodynamic wind scenario

Context. There is still much uncertainty around the mechanism that rules the accretion of proto-planetary disks. In recent years, magnetohydrondynamic (MHD) wind-driven accretion has been proposed as a valid alternative to the more conventional viscous accretion. In particular, winds have been shown to reproduce the observed correlation between the mass of the disk MD and the mass accretion rate onto the central star Ṁ*, but this has been done only for specific conditions. It is not clear whether this implies fine tuning or if it is a general result. Aims. We investigated under which conditions the observed correlation between the mass of the disk MD and the mass accretion rate onto the central star Ṁ*, can be obtained. Methods. We present mainly analytical calculations, supported by Monte Carlo simulations. We also perform a comparison with the observed data to test our predictions. Results. In the absence of a correlation between the initial mass M0 and the initial accretion timescale tacc,0 , we find that the slope of the MD − Ṁ* correlation depends on the value of the spread of the initial conditions of masses and lifetimes of disks. Then we clarify the conditions under which a disk population can be fitted with a single power law. Moreover, we derive an analytical expression for the spread of log(MD/Ṁ*) valid when the spread of tacc is taken to be constant. In the presence of a correlation between M0 and tacc,0, we derive an analytical expression for the slope of the MD−Ṁ* correlation in the initial conditions of disks and at late times. In this new scenario, we clarify under which conditions the disk population can be fitted by a single power law, and we provide empirical constraints on the parameters ruling the evolution of disks in our models. Conclusions. We conclude that MHD winds can predict the observed values of the slope and the spread of the MD−Ṁ* correlation under a broad range of initial conditions. This is a fundamental expansion of previous works on the MHD paradigm, exploring the establishment of this fundamental correlation beyond specific initial conditions.

The interacting double white dwarf population with LISA: Stochastic foreground and resolved sources

Aims. We investigate the impact of tidal torques and mass transfer on the population of double white dwarfs that will be observed with LISA. Methods. Our Galactic distribution of double white dwarfs is based on the combination of a cosmological simulation and a binary population synthesis model. We used a semi-analytical model to evolve double white dwarf binaries considering ten different hypotheses for the efficiency of tidal coupling and three hypotheses for the birth spins of white dwarfs. We then estimated the stochastic foreground and the population of resolvable binaries for LISA for these different combinations. Results. Our predicted double white dwarf binary distribution can differ substantially from the distribution expected if only gravitational waves (GWs) are considered. If white dwarfs spin slowly, then we predict an excess of systems around a few due to binaries that outspiral after the onset of mass transfer. This excess of systems leads to differences in the confusion noise, which are most pronounced for strong tidal coupling. In that case, we find a significantly higher number of resolvable binaries than in the GW-only scenario. If instead white dwarfs spin rapidly and tidal coupling is weak, then we find no excess around a few mHz, and the confusion noise due to double white dwarfs is very low. In that scenario, we also predict a subpopulation of outspiralling binaries below 0.1 mHz. Using the Fisher matrix approximation, we estimate the uncertainty on the GW-frequency derivative of resolvable systems. We find that, even for non-accreting systems, the mismodelling error due to neglecting effects other than GWs is larger than the statistical uncertainty, and thus this neglect would lead to biased estimates for mass and distance. Conclusions. Our results suggest that the population of double white dwarfs is likely to be different from what is expected in the standard picture, which highlights the need for flexible tools in LISA data analysis. Because our semi-analytical model hinges upon a simplistic approach to determining the stability of mass accretion, it will be important to deepen our comprehension of stability in mass-transferring double white dwarf binaries.

The role of thermal instability in accretion outbursts in high-mass stars

High-mass young stellar objects (HMYSOs) can exhibit episodic bursts of accretion, accompanied by intense outflows and luminosity variations. Understanding the underlying mechanisms driving these phenomena is crucial for elucidating the early evolution of massive stars and their feedback on star formation processes. Thermal instability (TI) due to hydrogen ionisation is among the most promising mechanisms of episodic accretion in low-mass ($M_* protostars. Its role in HMYSOs has not yet been determined. Here we investigate the properties of TI outbursts in young massive ($M_* 5$ msun ) stars, and compare them to those that have been observed to date. We employed a 1D numerical model to simulate TI outbursts in HMYSO accretion discs. We varied the key model parameters, such as stellar mass, mass accretion rate onto the disc, and disc viscosity, to assess the TI outburst properties. Our simulations show that modelled TI bursts can replicate the durations and peak accretion rates of long outbursts (a few years to decades) observed in HMYSOs with similar mass characteristics. However, they struggle with short-duration bursts (less than a year) with short rise times (a few weeks or months), suggesting the need for alternative mechanisms. Moreover, while our models match the durations of longer bursts, they fail to reproduce the multiple outbursts seen in some HMYSOs, regardless of model parameters. We also emphasise the significance of not just evaluating model accretion rates and durations, but also performing photometric analysis to thoroughly evaluate the consistency between model predictions and observational data. Our findings suggest that some other plausible mechanisms, such as gravitational instabilities and disc fragmentation, can be responsible for generating the observed outburst phenomena in HMYSOs, and we underscore the need for further investigation into alternative mechanisms driving short outbursts. However, the physics of TI is crucial in sculpting the inner disc physics in the early bright epoch of massive star formation, and comprehensive parameter space exploration; the use of 2D modelling is essential to obtaining a more detailed understanding of the underlying physical processes. By bridging theoretical predictions with observational constraints, this study contributes to advancing our knowledge of HMYSO accretion physics and the early evolution of massive stars.

Using the Ca ii Lines in T Tauri Stars to Infer the Abundance of Refractory Elements in the Innermost Disk Region

We present a study of the abundance of calcium in the innermost disk of 70 T Tauri stars in the star-forming regions of Chamaeleon I, Lupus, and Orion OB1b. We use calcium as a proxy for the refractory material that reaches the inner disk. We used magnetospheric accretion models to analyze the Ca ii emission lines and estimate abundances in the accretion flows of the stars, which feed from the inner disks. We find Ca depletion in disks of all three star-forming regions, with 57% of the sample having [Ca/H] < –0.30 relative to the solar abundance. All disks with cavities and/or substructures show depletion, consistent with trapping of refractories in pressure bumps. Significant Ca depletion ([Ca/H] < –0.30) is also measured in 60% of full disks, although some of those disks may have hidden substructures or cavities. We find no correlation between Ca abundance and stellar or disk parameters except for the mass accretion rate onto the star. This could suggest that the inner and outer disks are decoupled, and that the mass accretion rate is related to a mass reservoir in the inner disk, while refractory depletion reflects phenomena in the outer disk related to the presence of structure and forming planets. Our results of refractory depletion and timescales for depletion are qualitatively consistent with expectations of dust growth and radial drift, including partitioning of elements, and constitute direct evidence that radial drift of solids locked in pebbles takes place in disks.

Investigating the Mean Temperature of Accretion Disks and Mass Transfer Rates in Cataclysmic Variable Stars through Orbital Characteristics

Cataclysmic variable (CV) stars, characterized by their dynamic binary systems composed of a white dwarf and a donor red dwarf star, exhibit intricate mass transfer processes crucial for understanding their evolutionary pathways. This study delved into the theoretical investigation of mass transfer processes occurring within non-magnetic CV stars analyzing their orbital characteristics. A selection of eleven CV systems, encompassing a diverse range of subcategories, were chosen for the analysis of this research. Well-established Fourier and Lomb-Scargle algorithms were utilized to identify the most effective algorithm in determining the periodicity of their light curves. The calculated orbital periods for the aforementioned CV sample were then leveraged to determine the mean temperature of their accretion disks. This determination was achieved through established techniques which used spectroscopic Balmer emission lines and Stromgren photometric observations. These techniques provide robust measurements of the physical properties of accretion disks within CVs. Finally, a strong correlation was established between mean temperature of the disk which determined through spectroscopic method and system’s mass transfer rate which determined via various techniques and algorithms.

Three-dimensional magnetohydrodynamic simulations of core-collapse supernovae – I. Hydrodynamic evolution and protoneutron star properties

ABSTRACT We present results from three-dimensional, magnetohydrodynamic, core-collapse simulations of 16 progenitors following until 0.5 s after bounce. We use non-rotating solar-metallicity progenitor models with zero-age main-sequence mass between 9 and 24 ${\rm M}_{\odot }$. The examined progenitors cover a wide range of the compactness parameter including a peak around $23 \, {\rm M}_{\odot }$. We find that neutrino-driven explosions occur for all models within 0.3 s after bounce. We also find that the properties of the explosions and the central remnants are well correlated with the compactness. Early shock evolution is sensitive to the mass accretion rate on to the central core, reflecting the density profile of the progenitor stars. The most powerful explosions with diagnostic explosion energy $E_{\rm dia} \sim 0.75 \times 10^{51}$ erg are obtained by 23 and 24 ${\rm M}_{\odot }$ models, which have the highest compactness among the examined models. These two models exhibit spiral standing-accretion-shock-instability motions during 150–230 ms after bounce preceding a runaway shock expansion and leave a rapidly rotating neutron star with spin periods $\sim 50$ ms. Our models predict the gravitational masses of the neutron star ranging between $1.22$ and $1.67 {\rm M}_{\odot }$ and their spin periods 0.04 – 4 s. The number distribution of these values roughly matches observation. On the other hand, our models predict small hydrodynamic kick velocity (15–260 ${\rm km \, s}^{-1}$), although they are still growing at the end of our simulations. Further systematic studies, including rotation and binary effects, as well as long-term simulations up to several seconds, will enable us to explore the origin of various core-collapse supernova explosions.

Black hole mass estimate in OJ 287 based on the bulk-motion comptonization model

ABSTRACT The multiwavelength outburst activity in the BL Lacertae source OJ 287 has sparked a lot of controversy about whether the source contains one or two black holes (BHs) and what characteristics of this BH binary would be. In this article, we present the results of analysis of the X-ray flaring activity of OJ 287 using the data of Swift/XRT observations. We discovered that the energy spectra in all spectral states can be adequately fit with the XSPEC bulk-motion Comptonization (BMC) model. As a result, we found that the X-ray photon index of the BMC model, $\Gamma$ correlates with the mass accretion rate, $\dot{M}$. We found the photon index $\Gamma$ to increase monotonically with accretion rate $\dot{M}$ from $\Gamma \sim 2$ in the intermediate state (IS) to $\Gamma \sim 2.5$ the high/soft state (HSS) with subsequent saturation at $\Gamma \sim$ 2.6 level at higher luminosities. This type of behaviour of the spectral index is remarkably similar to the pattern observed in a number of established stellar-mass BH candidates. Assuming the universality of the observed pattern of the correlation between the photon index and mass accretion rate and using the well-studied stellar-mass binaries GX 339–4 and XTE J1859–226 to calibrate the model, we estimate a BH mass $\sim 2\times 10^8$ solar masses, which likely pertains to the secondary component of the BH binary in OJ 287.

Associations of linear growth with body composition of perinatally HIV-infected African adolescents.

The prevalence of poor linear growth among African children with perinatally acquired HIV remains high. There is concern that poor linear growth may to lead to later total and central fat deposition and associated non-communicable disease risks. We investigated associations between height-for-age Z score (HAZ) and total and regional fat and lean mass measured by dual-energy X-ray absorptiometry, expressed as internal population Z scores, among 839 Zimbabwean and Zambian perinatally HIV-infected male and female adolescents aged 11-19 years. Stunting (HAZ < -2) was present in 37 % of males and 23 % of females. HAZ was strongly positively associated with total, trunk, arm and leg fat mass and lean mass Z scores, in analyses controlling for pubertal stage, socio-economic status and HIV viral load. Associations of linear growth with lean mass were stronger than those with fat outcomes; associations with total and regional fat were similar, indicating no preferential central fat deposition. There was no evidence that age of starting antiretroviral therapy was associated with HAZ or body composition. Non-suppressed HIV viral load was associated with lower lean but not fat mass. The results do not support the hypothesis that poor linear growth or stunting are risk factors for later total or central fat deposition. Rather, increased linear growth primarily benefits lean mass but also promotes fat mass, both consistent with larger body size. Nutritional and/or HIV infection control programmes need to address the high prevalence of stunting among perinatally HIV-infected children in order to mitigate constraints on the accretion of lean and fat mass.

CSIG-19. IDENTIFICATION AND TARGETING OF TUMOR DRIVER SCHWANN(NF2LOSS) CELLS IN SPORADIC AND NF2-RELATED VESTIBULAR SCHWANNOMAS

Abstract Vestibular schwannomas (VS) arise from myelinating Schwann cells of CN VIII and are associated with severe morbidity due to local tumor growth. Sporadic and neurofibromatosis type 2 (NF2) associated VS are both characterized by NF2 (merlin) loss but the mechanisms remain unexplored. Using a multiomic approach, we dissected the role of NF2 loss in VS tumor formation and proliferation. We obtained surgical samples from 15 patients undergoing surgery for VS (sporadic, n=4; NF2, n=9), and performed single-cell or single-nucleus RNA sequencing (scRNAseq, n=4; snRNAseq, n=15), transposase-accessible chromatin (snATAC-seq, n=9), whole exome (n=12), and bulk DNA methylation assays (n=15). Transcription factor binding was assayed with ChIPseq. We validated our key findings with immunoblot, ELISA, RNAscope (n=8), and multiplex immunocytochemistry (mIHC; n=8). NF2fl/fl;Periostin-Cre+mice versus their Cre- control littermates treated with novel inhibitors of TEAD auto-palmitoylation (VTs). We mapped the VS transciptome and identified canonical Schwann cells, macrophages, T-cells and endothelial cells. Using the cells that had Chr22 loss (second hit deletions at the NF2 locus), we generated a NF2loss gene signature. We then identified Schwann(NF2loss) cells in all tumors, and found these enriched for YAP1/TAZ-TEAD, NRG1, and HIF-1α signaling pathways. Schwann(NF2loss) cells showed increased TEAD1 expression and chromatin accessibility for TEAD family transcription factor motifs. TEAD1 binding was observed at promoters of genes including VEGFA, EGFR, with strong enrichment for mitogenic pathways. We also found that VEFGA expression was restricted to Schwann(NF2loss) cells, and confirmed this with RNAscope and mIHC. Schwann(NF2loss) cells were key regulators of macrophages (M2-subtype, tissue resident) through M-CSF/IL-34 signaling. NF2fl/fl;Periostin-Cre+ mice showed increased VEGFA expression, and that was reversible by TEAD inhibition in-vivo with VTs. We report that Schwann(NF2loss) cells are key tumor drivers in VS. These cells are highly proliferative (YAP/TAZ-TEAD axis), drive angiogenesis (VEGFA expression), and promote tumor mass accretion (macrophage influx via M-CSF/IL-34 pathway) that can all be targeted via TEAD inhibition.

The X-ray re-brightening of GRB afterglow revisited: a possible signature from activity of the central engine

ABSTRACT Long-duration gamma-ray bursts (GRBs) are thought to be from core collapse of massive stars, and a rapidly spinning magnetar or black hole may be formed as the central engine. The extended emission in the prompt emission, flares, and plateaus in X-ray afterglow, are proposed to be as the signature of central engine re-activity. However, the direct evidence from observations of identifying the central engines remains an open question. In this paper, we systemically search for long-duration GRBs that consist of bumps in X-ray afterglow detected by Swift/XRT and find that the peak time of the X-ray bumps exhibit bimodal distribution (defined as ‘early’ and ‘late’ bumps) with division line at $t=7190$ s. Although we cannot rule out that such a bimodality arises from selection effects. We proposed that the long-duration GRBs with an early (or late) bumps may be originated from the fall-back accretion onto a new-born magnetar (or black hole). By adopting Monte Carlo Markov Chain (MCMC) method to fit the early (or late) bumps of X-ray afterglow with the fall-back accretion of magnetar (or black hole), it is found that the initial surface magnetic field and period of magnetars for most early bumps are clustered around $5.88\times 10^{13}$ G and 1.04 ms, respectively. Meanwhile, the derived accretion mass of black hole for late bumps is in the range of $[4\times 10^{-4}, 1.8\times 10^{-2}]\,{\rm M}_{\odot }$, and the typical fall-back radius is distributed range of $[1.04, 4.23]\times 10^{11}$ cm, which is consistent with the typical radius of a Wolf–Rayet star. However, we also find that the fall-back accretion magnetar model is disfavoured by the late bumps, but the fall-back accretion of black hole model cannot be ruled out to interpret the early bumps of X-ray afterglow.

Chromospheric Mg I emission lines of pre-main-sequence stars

Context. To reveal details of the internal structure, the relationship between chromospheric activity and the Rossby number has been extensively examined for main-sequence stars. For active pre-main-sequence (PMS) stars, it is suggested that the level of activity be assessed using optically thin emission lines, such as Mg I. Aims. We aim to detect Mg I chromospheric emission lines from PMS stars and to determine whether the chromosphere is activated by the dynamo process or by mass accretion from protoplanetary disks. Methods. We analyzed high-resolution optical spectra of 64 PMS stars obtained with the Very Large Telescope (VLT)/X-shooter and UVES and examined the infrared Ca II (8542 Å) and Mg I (8807 Å) emission lines. To detect the weak chromospheric emission lines, we determined the atmospheric parameters (Teff and log 𝑔) and the degree of veiling of the PMS stars by comparing the observed spectra with photospheric model spectra. Results. After subtracting the photospheric model spectrum from the PMS spectrum, we detected Ca II and Mg I as emission lines. The strengths of the Mg I emission lines in PMS stars with no veiling are comparable to those in zero-age main-sequence (ZAMS) stars if both types of stars have similar Rossby numbers. The Mg I emission lines in these PMS stars are thought to be formed by a dynamo process similar to that in ZAMS stars. In contrast, the Mg I emission lines in PMS stars with veiling are stronger than those in ZAMS stars. These objects are believed to have protoplanetary disks, where mass accretion generates shocks near the photosphere, heating the chromosphere. Conclusions. The chromosphere of PMS stars is activated not only by the dynamo process but also by mass accretion.