Current date: 2026-08-20
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Created/updated limit: 2026-08-13 (7 days ago)
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Scoring abstracts
Number of records retrieved: 654
Keyword score statistics
score 9 -- 1 abstracts
score 8 -- 1 abstracts
score 7 -- 1 abstracts
score 6 -- 1 abstracts
score 4 -- 4 abstracts
score 3 -- 7 abstracts
score 2 -- 11 abstracts
in total -- 26 abstracts
Articles that appeared on 2026-08-20
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[abstract 1 / 26] Wow! (score: 9)
- Title: The Total and Polarized Radio Emission from the Innermost Jets of a High-Redshift Quasar and a Candidate at Parsec-Scale ResolutionAuthors: Bence Husvéth, Krisztina É. Gabányi, Tao An, Sándor Frey, Jun Yang, Iván Agudo, Yingkang Zhang,Comments: 17 pages, 3 figures, accepted for publication in MDPI UniverseSubjects: astro-ph.GACreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
High-frequency very long baseline interferometry (VLBI) polarimetry probes SYNCHROTRON-emitting plasma closer to the central engines of radio-loud ACTIVE GALACTIC NUCLEi (AGNs), but observations above 43 GHz are technically demanding. We present 22-GHz European VLBI Network observations of the $z=4.31$ QUASAR J1510+5702 and J1606+3124, whose published spectroscopic redshift, $z=4.56$, is uncertain; a photometric estimate gives $z_{\rm phot}=0.9\pm0.1$. For the published $z>4$ redshifts, 22 GHz corresponds to rest-frame frequencies above 118 GHz. Polarized emission is detected in J1510+5702, and a low-level polarized signal is recovered from the brightest feature of J1606+3124. Adopting $z=4.56$, that feature has a brightness temperature of $T_{\mathrm{b,VLBI}}=(7.4\pm0.8)\cdot10^{10}$ K, allowing a mildly Doppler-boosted interpretation, while the young compact-source scenario also remains viable. The core of J1510+5702 has $T_{\mathrm{b,VLBI}}=(1.08\pm0.15) \cdot10^{12}$ K, implying a Doppler factor of ${\sim}22$ under the equipartition assumption. This component has a ${\sim}3.5$ % fractional POLARIZATION. These observations show that cm-wavelength VLBI can access rest-frame millimeter-band POLARIZATION in bright $z>4$ JETs.
[abstract 2 / 26] Wow! (score: 8) - Title: Multi-zone Modeling of Blazar Jets: Constraints from GeV-Optical Correlation and Short-Timescale VariabilityAuthors: Arit Bala, Kaustav Mitra, Ritaban Chatterjee,Comments: 13 pages, 10 figures, Accepted for publication in MNRASSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
We have developed a multi-zone model of BLAZAR JET emission, in which the emission region contains many cells with individual MAGNETic fields and electron energy distributions. Nonthermal emission from radio to $γ$-rays is generated by electrons accelerated by shocks passing through the region via SYNCHROTRON and inverse-Compton (IC) processes. The optical and GeV variability at days-to-months time-scale simulated from our model are strongly correlated with no significant time lag, as observed in most BLAZARs and indicated by the standard shock-in-JET model. However, the mechanism of the shorter time-scale variability has been less explored, although such fluctuations at X-rays, $γ$-rays and optical bands have been observed regularly in recent years. In our model, the hr time-scale variability of the SYNCHROTRON radiation is due to the spatial fluctuation of the MAGNETic field in the emission region. We found that to reproduce the short-timescale variability of the observed SYNCHROTRON emission in BLAZARs, the required fluctuations of the MAGNETic field are in the range $1-2\%$ to $25-30\%$. Similar variability of the IC emission, which does not depend on the MAGNETic field, may be reproduced in our model by implementing equipartition of energy between the MAGNETic field and particles. We found that orphan flares in the optical or GeV band, or optical-GeV correlation with a significant time delay, as observed occasionally, may be reproduced in certain special conditions related to the orientation of the MAGNETic field in the cells.
[abstract 3 / 26] Wow! (score: 7) - Title: Constraining Cosmic-Ray Acceleration and Escape in Middle-Aged Supernova Remnants with GeV-TeV Gamma-Ray ObservationsAuthors: Siyu Chen, Bing Theodore Zhang, Yi Xing, Siming Liu,Comments: 11 pages, 11 figuresSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
In this work, we perform a systematic, time-dependent study of the gamma-ray emission from four representative middle-aged SNRs (W51C, IC~443, W44, W28), incorporating both CRs within the remnant shells and escaped CRs interacting with surrounding molecular clouds. We compare our results with GeV--TeV gamma-ray observations from FERMI-LAT, H.E.S.S., MAGIC, and LHAASO, including a dedicated analysis of the FERMI-LAT data for regions A and B associated with W28. We find that the observed spectra favor steeper CR injection spectra with indices of \(α\sim4.2\)--\(4.3\), maximum proton energies of $\sim$ \(100\)--\(300\) TeV, diffusion coefficients below the Galactic average, and CR acceleration efficiencies from a few to tens of percent. In particular, the VHE emission detected by LHAASO from W51C is more naturally explained by escaped CRs interacting with a nearby molecular cloud. We also investigate the contribution of escaped CRs to the VHE emission from IC~443, W44, and W28. We further demonstrate that escaped CRs can substantially enhance the TeV neutrino flux from middle-aged SNRs, improving their prospects as potential neutrino sources. These results provide new constraints on CR acceleration and escape in middle-aged SNRs and highlight the important role of escaped CRs in shaping their high-energy gamma-ray and neutrino emission.
[abstract 4 / 26] Yes (score: 6) - Title: An invariant energy release hierarchy in a repeating fast radio burstAuthors: X. Yang, S. B. Zhang, Y. Li, D. Xiao, W. L. Zhang, J. -J. Wei, J. -J. Geng, J. -S. Wang, Y. P. Yang, F. Y. Wang, X. F. Wu, Z. G. Dai,Comments: 38 pages, 9 figuresSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
Fast radio bursts (FRBs) are luminous millisecond radio transients whose physical origin remains unsettled. A key diagnostic is whether their burst-energy distributions retain characteristic physical scales that are intrinsic and temporally stable within an individual engine. Here we report a 3.2-year monitoring campaign of the hyperactive repeater FRB~20220529 with FAST and Parkes, yielding more than 1,300 bursts spanning nearly five orders of magnitude in spectral energy density. The cumulative burst-rate distribution is described by an exponential-plus-power-law (EXP+PL) form, linking a low-energy exponential component with characteristic scale (E_0) to a scale-free bright-end tail. This scale remains invariant despite the burst rate declining by more than an order of magnitude, revealing a stable dissipation scale decoupled from the source's macroscopic trigger activity. Within a MAGNETar interpretation, this phenomenology is consistent with localized sub-critical RECONNECTion episodes coexisting with plasmoid-mediated MAGNETic avalanches in a twisted MAGNETosphere. The invariant (E_0) constrains the dissipation region to the inner-to-middle MAGNETosphere and reveals a robust energy-release hierarchy beneath the variable activity of repeating FRBs, providing an observational benchmark for RELATIVISTIC RECONNECTion in an ultra-MAGNETized neutron-star environment.
[abstract 5 / 26] Yes (score: 4) - Title: Particle Acceleration, Coronal Neutrino Production, and the Diffuse Extragalactic Neutrino Background from Supermassive Black HolesAuthors: Rostom Mbarek,Comments: Accepted to PRDSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
We present a generalized neutrino luminosity function for protons accelerated in the X-ray coronae of supermassive BLACK HOLEs in Seyfert-like galaxies. A major uncertainty in assessing the diffuse neutrino contribution of these systems is the underlying particle acceleration physics. We address this using a theoretical acceleration framework informed by plasma kinetic simulations, enabling a more self-consistent connection between coronal conditions, nonthermal proton populations, and neutrino production. In this picture, the neutrino luminosity depends primarily on the coronal X-ray luminosity and MAGNETization, and only weakly on BLACK HOLE mass. We find that the cosmologically integrated emission from these systems can account for the sub-PeV diffuse extragalactic neutrino flux observed by IceCube. We further argue that, although diffusive confinement is relatively well understood, the MAGNETic field topology near BLACK HOLEs naturally allows for COSMIC RAY-driven outflows near the X-ray corona. Such outflows may accompany additional efficient neutrino production at the PeV-level and influence the dynamics of the innermost galactic environment.
[abstract 6 / 26] Yes (score: 4) - Title: Spectral energy-loss bump and $γ$-ray pulsar halosAuthors: Kun Fang,Comments: 8 pages, 6 figures, 2 tablesSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
The parent electron spectrum of $γ$-ray pulsar halos is determined by continuous injection and radiative energy losses, with the nonlinear nature of the latter expected to produce an age-dependent energy-loss bump in the halo spectrum. We demonstrate that the broadband $γ$-ray spectrum of the Geminga halo measured by FERMI-LAT and HAWC is consistent with this expectation. Its energy-loss bump appears in the GeV region and is primarily produced by electrons injected at the earliest stage. Therefore, fitting the data allows us to constrain parameters governing early electron injection, such as the pulsar braking index $n$ and initial spin period $P_0$. In addition, we show that another crucial condition for explaining the Geminga halo spectrum is a power-law index of the injection spectrum close to $1$, consistent with the X-ray observations of the Geminga pulsar wind nebula. Currently, no significant energy-loss bump has been detected in the spectrum of the Monogem halo; based on this, we also place preliminary constraints on $n$ and $P_0$ of Monogem. This work demonstrates that pulsar halo spectra can be used not only to constrain electron injection parameters, but also to provide independent estimates of certain intrinsic pulsar properties.
[abstract 7 / 26] Yes (score: 4) - Title: Continuum Variability in AGN: Evidence for Systematically Suppressed Fluctuations in the BAL PopulationAuthors: A. Aliaga, P. Arévalo, M. L. Martínez-Aldama, W. Zuo, B. Muñoz-Bravo,Comments: Accepted for publication in A&ASubjects: astro-ph.GACreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
We aim to compare the flux variability of Broad Absorption Line QUASARs (BAL) to non-BAL QUASARs, controlling for BLACK HOLE parameters to inform models concerning the generation of the BAL phenomenon. Using SDSS DR16 and ZTF $g$- and $r$-band light curves, we select QUASARs with $1.57 \leq z \leq 2.00$ and $18.5 \leq rmag \leq 19.8$. This redshift range ensures that the $g$-band covers the C IV emission line (and trough in BALs) while the $r$-band probes continuum variability, and allows BLACK HOLE mass (MBH) estimates via Mg II. We quantify variability using excess variance and damped random walk (DRW) parameters ($σ_{\mathrm{DRW}}$, $τ_{\mathrm{DRW}}$). We also compared the DRW metrics in bins of MBH and Eddington ratio (REdd) to isolate the influence of the BAL phenomenon in objects with the same physical properties. Excess variance and $σ_{\mathrm{DRW}}$ are consistently smaller for BALs, confirming lower long-term variability, while the $g$-band exhibits higher variability than the $r$-band across both populations. These differences persist in fixed bins of MBH and REdd, indicating that the suppressed variability in BALs is not simply driven by differences in these properties between BAL and non-BAL samples. These results show that BAL QUASARs are systematically less variable than non-BAL QUASARs in both bands, confirming that this suppression is an intrinsic feature of the continuum rather than an effect of emission or absorption line contamination. The samples could be made to agree if BAL MBH values were systematically overestimated by a factor $\gtrsim 4$, implying a significantly higher REdd. Alternatively, the lower variability in BALs can be related to their lower X-ray luminosities, or to significant nuclear obscuration, if the inner part of the accretion disc were more obscured in BALs and more variable than the rest of the disc.
[abstract 8 / 26] Yes (score: 4) - Title: Simulation of advective accretion flows around BLACK HOLEs under various outer boundary conditionsAuthors: Rajiv Kumar, Seong-Jae Lee,Comments: 17 pages, 6 figuresSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
We simulated various accretion disc structures with viscous hydrodynamic (HD) flow around a BLACK HOLE (BH). We found that the structure of the accretion disc is significantly influenced by changes in the physical parameters of the initial inflowing gases. These physical parameters can be called outer boundary conditions (OBCs) at the outer-accretion boundary and represented on an OBC plane, which is primarily divided into hot-mode and cold-mode inflowing gases. We found smooth and shocked flows in the simulation, which follow the semi-analytical solutions with their OBCs. Interestingly, we observed that certain types of OBCs can produce shocks with JET-like features in the accretion flow. However, other OBCs can produce smooth or shock-free accretion flow, which may or may not have outflows. The smooth flows can display both the lowest and highest angular momentum distributions among the advective flows, depending on the OBCs. Additionally, the nature of the accretion flows can be either steady or quasi-steady, also influenced by the OBCs. We also observed that solutions corresponding to hot-mode gases have a greater tendency to generate outflows compared to those with the cold-mode. Therefore, this qualitative study of OBCs is crucial for understanding accretion physics, which can aid in modeling accretion discs, similar to the quantitative studies (which involve only changing mass accretion rates) of the inflowing gases. Thus, we assert that an accretion model should be based on both the qualitative and quantitative aspects of the initial inflowing gases.
[abstract 9 / 26] (score: 3) - Title: Magnetohydrodynamic Simulations of Transonic Accretion FlowsAuthors: Raj Kishor Joshi, Antonios Tsokaros, Sanjit Debnath, Indranil Chattopadhyay, Ramiz Aktar,Comments: Published in Universe SI: Mechanisms Behind Black Holes and Relativistic JetsSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
Theoretical studies of transonic accretion onto BLACK HOLEs reveal a wide range of possible solutions, broadly classified into smooth flows and flows featuring shocks. Accretion solutions that involve the formation of shocks are particularly intriguing, as they are expected to naturally produce observable variability features. However, despite their theoretical significance, time-dependent studies exploring the stability and evolution of such shocked solutions remain relatively scarce. To address this gap, we perform simulations of transonic accretion flows around a BLACK HOLE in an ideal MAGNETohydrodynamic framework. Our simulations are initialized using boundary conditions derived from semi-analytical hydrodynamical models, allowing us to explore the stability of these flows under varying MAGNETic field strengths. Our results indicate that mildly MAGNETized flows in a uniform vertical MAGNETic field alter the accretion dynamics through MAGNETic pressure, with the resulting force imbalance driving oscillations in the shock front. Variations in the emitted luminosity arising from shock oscillations appear as quasi-periodic oscillations (QPOs), a characteristic feature commonly observed in accreting BLACK HOLEs. We find that the QPO frequency is determined by the radial position of the shock front: oscillations occurring closer to the BLACK HOLE produce frequencies of tens of hertz, whereas shocks located farther out yield sub-hertz frequencies.
[abstract 10 / 26] (score: 3) - Title: Compact Stars as Portals to Extra-Dimensional Dark MatterAuthors: Raghuveer Garani, Chris Kouvaris, Michel H. G. Tytgat, Jérôme Vandecasteele,Comments: 25 pages, 7 figures; matches journal versionSubjects: hep-ph astro-ph.HE hep-exCreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
We investigate hydrostatic configurations of asymmetric DARK MATTER (DM) spheres in scenarios where fermionic DM can propagate into extra spatial dimensions, while Standard Model fields remain confined to ordinary three dimensions. As the number of extra dimensions increases, the effective equation of state for non-RELATIVISTIC matter softens, making even modest DM accumulation inside neutron stars susceptible to gravitational collapse into extra-dimensional BLACK HOLEs. These BLACK HOLEs are longer lived than their $3$ dimensional counterparts and can accrete enough material to consume an entire neutron star, ultimately producing solar-mass BLACK HOLEs. For geometric cross sections, DM with masses above $\mathcal{O}(10\,{\rm TeV})$ may already be excluded for more than two extra dimensions of size ${\mathcal{O}(\rm fm})$ -- sharply contrasting with the standard $3$ dimensional case, where comparable limits only appear for masses $\gtrsim 10^{5}$ TeV at typical halo densities of $0.3\, \rm{GeV/cm^3}$.
[abstract 11 / 26] (score: 3) - Title: Synthetic Spectral Library of Optically Thick Atmospheres for Little Red DotsAuthors: Hanpu Liu, Yan-Fei Jiang, Eliot Quataert, Jenny E. Greene, Yilun Ma, Xiaojing Lin,Comments: 28 pages, 16 figures, accepted for publication in ApJ. Comments welcome!Subjects: astro-ph.GA astro-ph.CO astro-ph.HE astro-ph.SRCreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
Little Red Dots (LRDs) challenge conventional models of ACTIVE GALACTIC NUCLEi. At rest-optical-to-near-infrared (IR) wavelengths, these compact extragalactic objects show blackbody-like continuum emission and spectral features reminiscent of stars, motivating models with an optically thick atmosphere at $T_{\rm\!\,eff}\sim4000-5000{\rm~K}$. We develop (and publicly release) a synthetic spectral library of optically thick atmospheres with gas conditions tailored for LRDs, parameterized by effective temperature $T_{\rm\!\,eff}$ and surface gravity $g$. Given the uncertain dynamical structure of LRDs, we interpret $g$ mainly as a proxy for the photospheric density $ρ_{\rm\!\,ph}$. We show that blackbodies are only crude approximations to the emission from LRD-like atmospheres. Spectral features are abundant, many of which are sensitive diagnostics of photospheric density, including the overall curvature of the continuum, the rest-$1.6{\rm~μm}$ ``kink'' from $\rm H^-$ opacity, and the Ca~II triplet (CaT) absorption at rest-$8500~\mathring{A}$. When compared against a local LRD, the Egg, all three features are consistent with a low photospheric density $ρ_{\rm ph}\sim10^{-11}{\rm~g~cm^{-3}}$ ($g\sim10^{-3}{\rm~cm~s^{-2}}$ in our library), although CaT alone admits another higher-density solution. This low $ρ_{\rm ph}$ directly results from our radiative transfer modeling; with the additional assumption that the CaT line width traces turbulent support at the continuum photosphere in a spherical geometry, we infer a mass within the photosphere (BLACK HOLE plus gas) of $\sim10^4~M_\odot$, with an Eddington ratio $λ_{\rm Edd}\gtrsim20$. For higher-redshift LRDs, we advocate for rest-near-IR spectroscopic surveys and high-resolution spectra of potential absorption lines as a test of the optically thick atmosphere scenario and as a unique probe of the central engine mass.
[abstract 12 / 26] (score: 3) - Title: A NUSTAR Reflection-Spectroscopy Survey of Cygnus X-1Authors: Kshitij Duraphe, Kartik Mandar, Chooda Khanal, Gopal Bhatta,Comments: Under review at ApJ. v2: Fixed author orderSubjects: astro-ph.HECreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
Relativistic-reflection measurements of Cygnus X-1 disagree on the extent of disk truncation and commonly infer supersolar iron abundances. We analyze a selected sample of 26 archival NUSTAR observations obtained between 2012 and 2024 using two configurations from one reflection-model family, with posterior modes sampled by preconditioned sequential Monte Carlo. In the baseline recovered modes, disk-surface ionization increases with photon index (Pearson r = +0.59), with state medians rising from log xi approximately 3.3 in the hard state to approximately 3.9 in the soft state. The corresponding free-emissivity fits give median inner radii of 6.6, 4.4, and 4.0 R_ISCO in the hard, intermediate, and soft states. Fixing q = 3 moves three of eight soft-state observations to the ISCO and one to 2.4 R_ISCO; four fixed-q fits have lower chi^2 than the sampled free-q solutions, showing that those runs missed higher-likelihood regions. The inferred radii are therefore model- and mode-dependent, and the spectra neither require nor exclude an ISCO disk or R_in greater than or approximately 20 R_ISCO. Baseline fitted abundances span A_Fe = 1.6-8.6, with a median of 4.9. Two observations separated by 7.2 hr yield A_Fe = 1.9 +/- 0.2 and 4.5 +/- 1.0, indicating that fitted abundance is not a direct composition measurement. Fixing A_Fe = 1.6 drives some densities toward the grid boundary and worsens the fits relative to A_Fe = 4.5. The wind parameters remain sensitive to the continuum, abundance, and orbital-phase sampling.
[abstract 13 / 26] (score: 3) - Title: A deep learning algorithm for BLACK HOLE spin estimation using hot-spot secondary imagesAuthors: Aristomenis I. Yfantis, Rami Al-Belmpeisi,Comments:Subjects: astro-ph.HE astro-ph.IMCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
Sagittarius A* exhibits frequent flaring activity across the electroMAGNETic spectrum that is often associated with a localized region of strong emission known as a hot spot. We aim to train a deep learning model to provide a link between key parameters of this phenomenon - hot-spot emission radius, and BLACK HOLE inclination and spin - to the observed angle difference between the primary and secondary image ($ΔPA$) that present and future interferometric arrays could resolve. Using the general RELATIVISTIC radiative transfer code IPOLE, we generated a library of $\sim100.000$ models with varying system parameters and computed the position angle difference on the image plane between the primary and secondary images of the hot spot. We explore equatorial and non-equatorial circular orbits and evaluate our models against approximate observational constraints, including partial-orbit visibility and observational errors. Our algorithm STIHOS shows remarkable accuracy in calculating spin and inclination from the majority of the observational tests we perform ($σ_{a_*}=0.04,\,σ_i=2^{\circ}$), even in extreme conditions where only half of the orbit is visible. The off-equatorial estimation provides softer constraints in the absence of prior information. Our results demonstrate the importance of hot-spot observations for spacetime estimations. Given the increasing efforts to detect the photon-ring, our framework could prove valuable in interpreting the first observations of lensed emission.
[abstract 14 / 26] (score: 3) - Title: Accretion of AGN Stars under Influence of Disk Geometry II: The Adiabatic Regime and Runaway Collapse Induced by Self-gravityAuthors: Yi-Xian Chen, Yan-Fei Jiang, Jeremy Goodman,Comments: Accepted to ApJSubjects: astro-ph.GA astro-ph.EP astro-ph.HE astro-ph.SRCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
Accretion onto massive stars embedded in Active Galactic Nuclei (AGN) disks around supermassive BLACK HOLEs (SMBHs) is regulated to the stellar Eddington rate in the fast-diffusion or radiatively-efficient limit, $c/τ> c_s$, where $τ$ is the optical depth of the accretion flow and $c_s$ the sound speed. However, when the ambient density is sufficiently high, the opposite slow-diffusion limit applies. In this regime, accretion proceeds quasi-adiabatically and forms a hydrostatic circumstellar envelope (CSE) that stalls further mass inflow in the absence of self-gravity. We perform 3D hydrodynamic simulations in the adiabatic limit to investigate the structure and evolution of such envelopes. For low thermal mass ratios, $q_{\rm th} \equiv M_\star/M_{\rm th}$ where $M_{\rm th}=c_s^3/(GΩ)$ is the thermal mass, the CSE boundary smoothly matches the ambient disk entropy and density without forming a shock. In contrast, when $q_{\rm th} \gg 1$, a strong shock develops at the envelope boundary, substantially increasing the entropy of the envelope and thereby regulating its structure and mass, $M_{\rm env}$. In marginally self-gravitating disks with Toomre parameter $Q \sim 1$, we find that at sufficiently large $q_{\rm th}$ the envelope mass satisfies $M_{\rm env}/M_\star \gtrsim 1$. This condition is equivalent to stating that the post-shock material entering the envelope possesses lower radiation entropy than the characteristic stellar value, which triggers dynamical runaway growth on a dynamical timescale once envelope self-gravity is included in our simulations. In realistic AGN disk environments with SMBH mass $\sim 10^8M_\odot$, runaway may occur close to the minimum self-gravitating radii and produce supermassive stars of $\sim 10^5M_\odot$.
[abstract 15 / 26] (score: 3) - Title: Numerical investigations of low-latitude ground MAGNETic fields due to cavity mode oscillationsAuthors: Khilav Majmudar, Robert L. Lysak, Kazue Takahashi,Comments: 22 pages, 10 figuresSubjects: physics.plasm-ph physics.space-phCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
Pi2 oscillations have been known to be associated with cavity mode oscillations (CMOs) in the inner MAGNETosphere at low latitudes. CMOs can also be excited by interplanetary shocks on the dayside. We present results from a global linear MHD wave model in spherical coordinates that allows us to analyse these waves at equatorial latitudes. We see that the model reproduces some of the principal CMO harmonics. The standing wave cavity modes are set up due to a dense plasmasphere. The CMOs associated with interplanetary shocks are compared with ground observations from the EMMA array at mid-latitudes. In accordance with observations of Pi2 pulsations, we also see a small phase difference between compressional mode Alfvén waves at midnight at low altitudes and on the noon ground, both at equatorial latitudes. This supports the finding that upon being excited in the nightside inner MAGNETosphere, these waves travel quickly around to the dayside. We compare our results to observations of the night-to-day time delay of ground Pi2 pulsations.
[abstract 16 / 26] (score: 2) - Title: Latent thermal instabilityAuthors: Prakriti Pal Choudhury, Archie F. A. Bott,Comments: 10 pages, 4 figures, 1 table. Accepted in ApJ LettersSubjects: astro-ph.GA physics.plasm-phCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
Multiscale temperature fluctuations are abundant in the intracluster medium (ICM) outside of galaxy cluster cores ($\sim 100~{\rm kpc}$). Their origin is often attributed to turbulent stirring by subhalos or accreting baryons crossing the virial radius. However, their apparent resistance to mixing and thermal conduction in a collisional medium has not been explained. We propose a new mechanism by which steady-state temperature fluctuations can form and persist outside the cluster core. Local thermal instability, or Field instability, is used to explain filamentary condensates in cluster cores but is usually dismissed outside them because thermal conduction should suppress instability. In weakly collisional or collisionless plasmas, however, thermal conduction can be anomalously suppressed by heat-flux-driven plasma instabilities triggered in presence of a local MAGNETic field, leading to two effects: (i) condensates form in a new parameter regime that overlaps with conditions outside the core, and (ii) condensates reach a steady state as in the hydrodynamic limit. This extends the regime of instability-driven fluctuations to over $\gtrsim50\%$ (depending on hot plasma temperature) of the cluster. We use one-dimensional hydrodynamic simulations of condensates to test our analytical ideas.
[abstract 17 / 26] (score: 2) - Title: The impact of recombination during tidal disruption eventsAuthors: Simona Pacuraru, Clément Bonnerot, Martin E. Pessah,Comments: Submitted to MNRAS. Comments are welcome!Subjects: astro-ph.HE astro-ph.GACreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
During a tidal disruption event, the resulting debris stream cools down adiabatically due to the tidal stretching. As the temperature drops, the gas is expected to undergo chemical processes, which can release thermal energy into the stream, potentially affecting the subsequent gas evolution. For the first time, we investigate in detail this effect and its dynamical impact on the early-time evolution of the stream by making use of three dimensional hydrodynamic simulations coupled with a realistic equation of state. We find that a few days after disruption, the energy injected by hydrogen recombination and molecular hydrogen formation causes the stream thickness to grow much more rapidly. In the bound debris, this effect stops the stream's confinement by self-gravity before the gas reaches apocentre. As a result, the maximum stream thickness increases by a factor that ranges from a few, for the most bound gas, to a few tens for the near-parabolic gas, reaching $\approx 30 \, R_{\star} $ around the peak of the mass fallback rate. We discuss how this accelerated stream expansion may affect the subsequent evolution of the gas, estimate the luminosity powered by recombination in the unbound debris, and evaluate the potential influence of non-ideal MAGNETo-hydrodynamic effects. By characterizing the thermodynamic and hydrodynamic properties of the stream before its return near pericentre, our results provide physically motivated initial conditions to self-consistently model the later stages of tidal disruption events, offering a promising pathway to unveiling the physical origins of their observed emission.
[abstract 18 / 26] (score: 2) - Title: Recurrent Multi-year Mg II BAL Variability in SDSS J1333+0012Authors: M. Vivek, P. Aromal, R. Srianand, K. A. Anjali, S. C. Gallagher, Rachana,Comments: 5 Figures, 1 Table, Accepted for publication in ApJSubjects: astro-ph.GACreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
We present a long-term spectroscopic study of Broad Absorption Line (BAL) variability in the QUASAR J1333+0012 (\zem = 0.9197) using an extensive multi-epoch dataset spanning nearly two decades. The dataset comprises multi-epoch observations from multiple observatories, delivering nearly uniform temporal coverage of the Mg II BAL profile, with close to one spectroscopic observation per year spanning the period from 2008 to 2025. We identify recurrent multi-year variability in the BAL absorption strength, characterized by a rest-frame timescale of $\sim$4 yr. Because the well-sampled baseline covers only a small number of candidate cycles, we present J1333+0012 as a candidate quasi-periodic BAL system. In contrast, contemporaneous optical photometric light curves from CRTS, Pan-STARRS, ZTF, and PTF show no statistically significant correlated variability on comparable timescales. However, ionization-driven variability cannot be ruled out, as the observed optical continuum does not directly trace the unobserved extreme-UV ionizing continuum. The coherence of the variability across distinct velocity components, coupled with the absence of large-scale profile reshaping, is consistent with a geometric origin. We interpret the observed behavior as modulation of the line-of-sight absorption by the rotation of an inhomogeneous shielding-gas structure.
[abstract 19 / 26] (score: 2) - Title: Quasar Impostors: Two Extremely UV-Bright ($M_{\rm UV}\approx-23.5$) Reionisation-Epoch Galaxies Powered by Very Massive StarsAuthors: Daming Yang, Joseph F. Hennawi, Sarah E. I. Bosman, Frederick B. Davies, Rychard Bouwens, Timo Kist, Eduardo Bañados, Jiamu Huang, Alice E. Shapley, Marianne Vestergaard, Hiddo S. B. Algera, Silvia Belladitta, Anna-Christina Eilers, Xiaohui Fan, Francesco Guarneri, Xiangyu Jin, Romain A. Meyer, Elia Pizzati, Huub Röttgering, Jan-Torge Schindler, Mauro Stefanon, Feige Wang, Jinyi Yang,Comments: 18 figures, 4 tables. SubmittedSubjects: astro-ph.GA astro-ph.SRCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
The extreme bright end of the galaxy UV luminosity function during reionisation remains poorly constrained, particularly where the galaxy and QUASAR luminosity functions overlap and source classification becomes ambiguous. We present JWST/NIRSpec and ALMA Band-6 observations of J1450-0144 ($z=6.627$) and J1429-0104 ($z=6.796$), two $M_{\rm UV}\simeq-23.5$ sources originally classified as faint QUASARs by SHELLQs. NIRSpec reveals blue UV continua, strong P Cygni profiles in N V, Si IV, and C IV, broad He II $\lambda1640$ emission with rest-frame equivalent widths of $8.8\pm1.2$ and $3.7\pm1.1$ Å, respectively, and narrow nebular lines, reclassifying both as extremely UV-luminous galaxies. Standard population-synthesis models cannot simultaneously reproduce the strong He II and wind features, whereas models incorporating very massive stars (VMS; $M\gtrsim100\,M_\odot$) with dedicated wind prescriptions can. These models favor a star-formation duration of 2-4 Myr for J1450-0144, with a broader allowed range for J1429-0104, stellar masses of $\log(M_\star/M_\odot)\approx9.2$-$9.9$, and star-formation rates of $\simeq300$-$540\,M_\odot\,{\rm yr}^{-1}$. Under the same VMS wind models, equivalent-width diagnostics imply $M_{\rm up}\gtrsim225\,M_\odot$ for J1429-0104, while J1450-0144 lies beyond even the $M_{\rm up}=475\,M_\odot$ grid. ALMA detects luminous [C II] 158 $μ$m emission in both systems, with $L_{\rm [CII]}\approx0.8$ and $4.1\times10^{9}\,L_\odot$, respectively. J1429-0104 additionally shows bright dust continuum, with both [C II] and dust offset by $\sim5.4$ kpc from its UV emission. These sources demonstrate that VMS can power some of the most UV-luminous galaxies at cosmic dawn and show that source classifications, and hence the inferred demographics of both galaxies and QUASARs in the crossover regime, need revisiting.
[abstract 20 / 26] (score: 2) - Title: Modeling the Gravitational Wave Signal from the X-ray Pulsar Her X-1Authors: I. D. Markozov, G. K. Pimenov, A. A. Mushtukov,Comments: accepted for publication in Astronomy Letters, 12 pages, 2 figuresSubjects: astro-ph.HECreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
The paper is devoted to modeling the gravitational waves from the X-ray pulsar Her X-1. The neutron star is considered as a freely precessing ellipsoid. The gravitational wave signal is calculated in the quadrupole approximation. The $h_{\times}$ and $h_{+}$ POLARIZATION profiles are constructed for the precession parameters of the neutron star in Her X-1 measured in up-to-date works. The possibility of signal detection with the DECIGO telescope is assessed. The formulas for the semi-analytical modeling of the gravitational wave signal from precessing neutron stars by the method of perturbations in the small neutron star ellipticity parameter are deduced.
[abstract 21 / 26] (score: 2) - Title: Plasma dynamics near the MAGNETic X-point of the two-wire model: Theory and SimulationAuthors: Bin Ahn,Comments: 98 pages, 26 figures. Based on the author's PhD thesis (KAIST, 2026). Parts of this work are published in B. Ahn et al., J. Plasma Phys. 90, 975900204 (2024), doi:10.1017/S0022377824000321, and parts are under review in a peer-reviewed journalSubjects: physics.plasm-phCreated: 2026-08-18; Updated: 2026-08-20; Datestamp: 2026-08-20
The two-wire model (TWM) is a MAGNETic configuration generated by two parallel current-carrying wires, and it contains an X-point at its center and a separatrix. Since the TWM MAGNETic field is described by a closed-form analytic expression and contains no guide field, it offers a tractable setting for studying how a true MAGNETic null shapes plasma dynamics. This work investigates two complementary regimes: collisionless charged particle dynamics and collisional low temperature plasma transport. In the collisionless regime, a Lagrangian analysis identifies two particle motion invariants: the total kinetic energy and the base field line value, which is derived from the conserved axial canonical momentum. Collisionless test particle simulations show that the MAGNETic moment undergoes shifts when the particle traverses the large gradient region near the null. These shifts enable particles to migrate, the phenomenon in which a particle gyrating about one branch of a base field line jumps to the corresponding branch on the other side of the X-point. A threshold energy for migration is derived, and an empirical expression for the migration confinement time is formulated. In the collisional regime, reduced drift-diffusion models for low temperature plasmas are developed in a conformal field-aligned coordinate system, and they predict density plateau formation near the separatrix in the strongly MAGNETized regime. Self-consistent particle-in-cell simulations are performed to verify the predicted density plateau. The two complementary studies establish a fundamental understanding of plasma dynamics near a true MAGNETic null for both the collisionless and collisional regimes.
[abstract 22 / 26] (score: 2) - Title: A model for the enhanced production rate of early-type hypervelocity stars in the Galactic haloAuthors: Chunyang Cao, F. K. Liu, Xian Chen, Shuo Li,Comments: 11 Pages, 5 figures, accepted for publication in ApJLSubjects: astro-ph.GA astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
About twenty late B-type hypervelocity stars (HVSs) traveling faster than the Galactic escape velocity have been discovered in the Galactic halo, many of which were ejected from the Galactic center (GC). Recently, we have advocated that these HVSs most likely formed in the nuclear star cluster (NSC) $150$--$500\, \rm{Myr}$ ago and were predominantly ejected via the gravitational slingshot of a past intermediate-mass BLACK HOLE (IMBH) orbiting the supermassive BLACK HOLE (SMBH) Sgr~A$^{*}$. Here we explore the constraints of the production rate of young HVSs on the STAR FORMATION region of the NSC. We propose that the young HVS progenitors are born in a lopsided eccentric disk that is comparable in radius to the NSC. By numerically tracking the orbital evolution of disk stars, we find that they undergo rapid angular momentum relaxation at formation due to eccentric disk instability, and that their slingshot interactions with the SMBH-IMBH binary at distances $\simeq 100\, \rm{au}$ produce HVSs at a rate of $10^{-5}$--$10^{-4}\, \rm{yr}^{-1}$. The rate is expected to trace the disk formation history, increasing with the accumulation of disk stars and dropping rapidly after the STAR FORMATION stopped at $150\, \rm{Myr}$ ago. The rate is consistent with the observation and orders of magnitude higher than that expected for an old relaxed population in the literature, enhanced due to the gravitational torque from the non-spherical GC potential and radial velocity anisotropies of the disk stars. Our results imply that young HVSs should have a distinct radial and angular distribution from old ones.
[abstract 23 / 26] (score: 2) - Title: Hybrid disc geometry for shocked accretion flows: Unveiling QPOs in BLACK HOLE X-ray binariesAuthors: Monu Singh, Sudip Kumar Garain, Santabrata Das,Comments: Accepted for publication in MNRASSubjects: astro-ph.HECreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
We investigate the efficacy of semi-analytical global accretion solutions in capturing the flow properties observed in two-dimensional numerical simulations of shocked accretion onto BLACK HOLEs. A comparative analysis reveals that no single disc geometry adequately matches the simulation profiles across the entire radial domain. The pre-shock region exhibits closer agreement with the conical disc geometry, while the post-shock region is better described by the vertical equilibrium disc, where enhanced thermal pressure leads to substantial vertical expansion. Motivated by these complementary behaviours, we introduce a hybrid disc geometry in which the pre-shock flow follows the conical solution and the post-shock flow attains vertical equilibrium. This hybrid model satisfactorily reproduces both dynamical and thermodynamical properties of shocked accretion flows with the predicted Mach number and temperature profiles closely matching the simulations and the inferred shock location differing by $\sim10\%$. Within this framework, we delineate the shock parameter space spanned by the energy ($\mathcal{E}$) and angular momentum ($λ$) of the flow for weakly and rapidly rotating BLACK HOLEs and investigate the possible origin of Quasi-periodic Oscillations (QPOs) in BLACK HOLE X-ray binaries (BH-XRBs). We constrain flow parameters that reproduce observed QPO centroid frequencies ($ν_{\rm QPO}$) demonstrating that oscillations of the shock front provide a self-consistent mechanism for both low and high frequency QPOs. Extending the analysis to ten Galactic BH-XRBs, we demonstrate that the observed $ν_{\rm QPO}$ are reproduced within physically plausible parameter ranges, which establishes shocked global accretion solutions as a potentially compelling framework for interpreting accretion driven temporal variability.
[abstract 24 / 26] (score: 2) - Title: Automatically distinguishing Rubin transients from AGN using variability metricsAuthors: Dylan Magill, Matt Nicholl, Philip Wiseman, Charlotte R. Angus, Paige Ramsden, Christopher Frohmaier, Sjoert van Velzen, Vysakh Anilkumar, Jaimee Greenwood, Joshua G. Weston,Comments:Subjects: astro-ph.HE astro-ph.COCreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
Stochastic variability of ACTIVE GALACTIC NUCLEi (AGN) can produce contaminants in the search for explosive extragalactic transients (such as SUPERNOVAe and tidal disruption events). In the new era of the Rubin Observatory's Legacy Survey of Space and Time (LSST), previously uncatalogued AGN, especially those with luminosity near the survey detection limits, are expected to produce a flood of detections that have the potential to contaminate surveys targeting other transients, leading to inefficient use of spectroscopic follow-up time. For surveys aiming to statistically characterise transient demographics, it is advantageous to use easily modelled and reproducible selection criteria to distinguish AGN from other transients, rather than machine learning. We test enacting cuts based on simple data-driven photometric variability parameters to distinguish non-AGN extragalactic transients from standard AGN variability on both Zwicky Transient Facility photometry and simulated LSST photometry from the MALLORN data set. We also investigate the impact of light curve history availability, redshift range and filter selection on selection efficiency. We find that a two-dimensional cut incorporating the ratio of detection flux and pre-detection standard deviation and the ratio of detection flux to pre-detection mean flux is the most effective cut. This approach is easily scalable as these values are included in the LSST alert packets. We provide estimates of the completeness and purity of the sample produced by enacting this cut, and gauge the AGN contamination avoided. The parameters utilised in this approach could also be implemented as features for identifying AGN in a photometric classifier.
[abstract 25 / 26] (score: 2) - Title: Mach-disk formation and shock-structure transitions in underexpanded coflowing JETsAuthors: Ganesh Dhungana, Srijan Satyal, Nek Sharan,Comments:Subjects: physics.flu-dynCreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
The near-field shock structures of underexpanded sonic JETs exiting into a subsonic coflow are investigated over a range of nozzle pressure ratio (NPR) and coflow-to-nozzle-exit velocity ratio ($U_c$), representative of a propulsive nozzle in subsonic flight. Time-averaged statistics from fully-resolved axisymmetric simulations and inviscid method-of-characteristics (MOC) analysis are used to understand how coflow alters the shock-cell structures, in particular the Mach-disk formation. It is well established that increasing NPR transitions the centerline reflection from regular (characterized by oblique shocks) to Mach reflection (characterized by a near-normal Mach disk). We find that coflow has the opposite influence: a strong coflow shrinks the Mach disk until it vanishes, reverting Mach reflection to regular reflection, so the NPR for this transition increases with $U_c$. This effect has previously been attributed to a reduction in the JET-boundary inclination at the nozzle lip, which confines the lip Prandtl-Meyer fan to a smaller angle and weakens the embedded shock. We show instead that this inclination is determined by the non-uniform pressure the coflow imposes along the JET boundary, which is the primary driver of the shock-structure transitions in coflowing JETs. The non-uniform pressure weakens the boundary-reflected compression waves and orients them at shallower angles, so the embedded shock reflects regularly or fails to form. A simulation-informed MOC analysis with this non-uniform pressure boundary condition reproduces the transition behavior with increasing coflow. Coflow also lengthens the first shock cell linearly, which is accurately estimated by a simple correction to Prandtl classical shock-cell length scaling.
[abstract 26 / 26] (score: 2) - Title: High-power TCV scenario for conventional and alternative divertor studiesAuthors: K. Lee, C. Theiler, M. Carpita, M. Zurita, P. Sintre, O. Février, F. Pastore, H. Reimerdes, K. Verhaegh, M. Winkel, D. Brida, B. Y. K. Brown, M. J. H. Cornelissen, R. Ducker, G. Durr-Legoupil-Nicoud, D. Hamm, R. I. Morgan, A. Perek, O. Sauter, E. Tonello, Y. Wang, the TCV Team, the EUROfusion Tokamak Exploitation Team,Comments: 13 pages, 6 figures Submitted to Nucl. Mater. EnergySubjects: physics.plasm-phCreated: 2026-08-19; Updated: 2026-08-20; Datestamp: 2026-08-20
Alternative divertor configurations (ADCs) must be evaluated under boundary plasma conditions approaching reactor-level values to be considered a reliable, physics-based solution for tokamak power exhaust. Most ADC experiments performed to date were at relatively low exhaust power. This work presents a high-power scenario on the TCV tokamak enabling the study of a wide variety of divertor MAGNETic shapes under an expanded SOL and power exhaust parameter space. The scenario is characterized by high power levels of electron cyclotron resonance heating ($2.5\,\text{MW}$ fully absorbed in a $\sim1\,\text{m}^{3}$ plasma) at high plasma current (edge safety factor $q_{95}\approx 2.5$), and low upstream separatrix densities ($n_{e,\text{u}}\approx1\times10^{19}\,\text{m}^{-3}$, Greenwald fraction $f_{\text{G}}\approx 0.1$). Stationary parallel heat fluxes up to $100\,\text{MW m}^{-2}$ are measured at the divertor target, an order of magnitude above previous TCV power exhaust studies. The obtained SOL collisionality and Lengyel detachment scaling metric lie within range of values expected in future reactors (SPARC, ITER, ARC).
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