Current date: 2026-10-20

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Scoring abstracts

Number of records retrieved: 299

Keyword score statistics

score 7 -- 1 abstracts

score 6 -- 1 abstracts

score 4 -- 2 abstracts

score 3 -- 2 abstracts

score 2 -- 11 abstracts

in total -- 17 abstracts

Articles that appeared on 2026-10-20

[abstract 1 / 17] Wow! (score: 7)
arXiv:2610.24097 [pdf, ps, other]

Title: The evolution of 3C 306 in the galaxy cluster RXCJ1454.4+1622: linking spectral ageing, ICM conditions, and JET dynamics through MHD simulations

Authors: A. S. R. Antas, A. Caproni, L. Loinard, G. S. Souza, T. F. Laganá,

Comments: 22 pages. Published in Monthly Notices of the Royal Astronomical Society

Subjects: astro-ph.HE astro-ph.GA

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

We present a methodology for analysing radio sources in galaxy clusters by combining multi-frequency radio observations, X-ray analysis of the intracluster medium (ICM), and three-dimensional MAGNETohydrodynamic (MHD) simulations, and apply it to the galaxy cluster RXCJ1454.4+1622 and its associated FR II RADIO GALAXy 3C 306 (IC 4516). The radio emission exhibits a curved structure connecting the lobes, likely indicating a complex dynamical evolution influenced by environmental effects. Spectral index and break-frequency maps reveal a relatively homogeneous radiative ageing distribution, with characteristic spectral ages of $\sim220$ Myr and a smooth spatial gradient. From equipartition arguments, we estimate an equivalent JET MAGNETic field of $2.1 \pm 0.3\,μ$G, consistent with values observed in FR II RADIO GALAXies. These observational constraints are used to initialise non-RELATIVISTIC MHD simulations exploring three scenarios: JET precession, bulk motion of the source through the ICM, and a combined model including both effects. Neither pure precession nor pure source motion alone fully reproduces the observed morphology, whereas the combined model provides a more consistent representation of the JET curvature and lobe asymmetries. Nevertheless, the simulations indicate that source motion is the dominant mechanism shaping the large-scale radio morphology, with JET precession playing a secondary role. The inferred source velocity ($\sim280$ km s$^{-1}$) and precession timescale ($\sim250$ Myr) are compatible with the spectral ageing constraints. These results suggest that the morphology of 3C 306 is influenced by the interplay between JET precession and dynamical interaction with the ICM, highlighting the role of environmental effects in radio-galaxy evolution in clusters.

[abstract 2 / 17] Yes (score: 6)
arXiv:2610.24195 [pdf, ps, other]

Title: Modeling Multi-band Active Galactic Nuclei Lightcurves Using an Self-supervised Attentive Neural Process Network

Authors: Tzuken Shen, Chengcheng Xin, Joshua Fagin, Ashley Villar, Matthew J. Graham, K. E. Saavik Ford,

Comments:

Subjects: astro-ph.HE astro-ph.GA

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

With the the Legacy Survey of Space and Time (LSST), observations of tens of millions of QUASARs are expected. We present a machine-learning framework based on an attentive neural process (ANP) that models stochastic QUASAR variability and jointly performs two tasks: (i) probabilistic reconstruction of QUASAR light curves in all six LSST bands, and (ii) inference of physical parameters of the AGN system --- BLACK HOLE mass, Eddington ratio, and intrinsic variability timescale --- with joint, full-covariance posteriors. The model processes all six bands within a single masked attention mechanism, so that observations in any band constrain the shared driving process, and natively handles irregularly and asynchronously sampled light curves with realistic heteroscedastic noise. We train and evaluate on full ten-year light curves simulated with a RELATIVISTIC accretion-disk reprocessing model, observed through the fielded Rubin baseline cadence with per-visit photometric noise. The light-curve model is trained with self-supervised, learning from the sparse noisy observations alone and never accessing the underlying noiseless light curves. On a held-out test set, we show that our ANP model reach comparable performances to that of the near-optimal baseline Gaussian process model, while exceeding it in power spectrum reconstruction and damped-random walk timescale estimation. The compact learned latent representation supports future downstream applications, and the fully observation-driven training objective enables direct fine-tuning on real LSST light curves.

[abstract 3 / 17] Yes (score: 4)
arXiv:2610.24049 [pdf, ps, other]

Title: Multiline Spectropolarimetric Evidence for Photospheric Reconnection in Ellerman Bombs from DKIST

Authors: Rahul Yadav, Maria D. Kazachenko, Viggo Hansteen,

Comments: accepted for publication in The Astrophysical Journal Letters

Subjects: astro-ph.SR

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

Ellerman bombs (EBs) are compact, transient brightenings observed in the wings of Balmer lines and are believed to result from MAGNETic RECONNECTion in the lower solar atmosphere. However, their signatures have rarely been observed simultaneously in multiple spectral lines sensitive to the lower atmosphere. We present novel high-resolution multiline spectropolarimetric observations of EBs obtained with the Visible Spectro-Polarimeter (ViSP) on the Daniel K. Inouye Solar Telescope (DKIST). Simultaneous observations reveal remarkable H$β$ wing enhancements extending up to $\sim$4~Å from the line core and intensity enhancements in the \ion{Na}{1}~D1 and \ion{Fe}{1}~6302 lines. Using multiline non-LTE inversion of the \ion{Na}{1} and \ion{Fe}{1} lines, we infer localized photospheric heating of up to $ΔT\sim$800~K, accompanied by weak upflows and downflows at EB locations. Comparing with synthetic observables from Bifrost radiative-MHD simulations, we find that synthetic spectra reproduce the observed H$β$ and \ion{Na}{1}~D wing enhancements and yield atmospheric stratification broadly consistent with those inferred from the non-LTE inversion. This study provides strong evidence that EBs are driven by photospheric MAGNETic RECONNECTion below the temperature-minimum region, and places new constraints on the realistic EB models and small-scale energy release in the lower solar atmosphere.

[abstract 4 / 17] Yes (score: 4)
arXiv:2610.24103 [pdf, ps, other]

Title: Effect of induced frame dragging on energy extraction from axially symmetric MAGNETized Reissner-Nordström BH and observational benchmarks

Authors: Ikhtiyor Eshtursunov, Chen Zhou, Sanjar Shaymatov, Pankaj Sheoran, Chengxun Yuan,

Comments: 17 pages, 10 captioned figures

Subjects: gr-qc

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

In this paper, we probe the effect of induced frame dragging on the energy extraction process via MAGNETic RECONNECTion in axially symmetric MAGNETized Reissner-Nordström BLACK HOLE (MRNBH) spacetime and show the influence of BH charge $Q$ and the MAGNETic field $B$ parameters, respectively. We start by analyzing the metric and present the distinction between the geometrical and induced ergospheres. We argue that the induced ergosphere, unlike the geometric ergosphere, is not a property of the spacetime metric but rather a particle-dependent negative energy region that changes as the charge on the particle varies. We find the region where MAGNETic RECONNECTion can extract energy from the axially symmetric MRNBH and determine the conditions required for this process. We further examine the energies of the accelerated and decelerated plasma outflows and the corresponding MAGNETic RECONNECTion efficiency. We show that within the parameter ranges considered, the extraction efficiency increases with the MRNBH charge $Q$ and the MAGNETic field parameter $B$. For sufficiently large $B$, it reaches the efficiency comparable to that of an extremal Kerr BH case. Our results therefore show that electroMAGNETically induced frame dragging can support energy extraction efficiencies similar to those associated with rotation parameter. To connect with observations, we evaluate the RECONNECTion power directly from the decelerated-plasma energy at infinity and compare it with the observed power scales of M87* and Sgr~A*. For $Q=M$, RECONNECTion extraction appears in our scan only for $|B|M\gtrsim0.2$ ($B\sim10^{9}\,\mathrm{G}$ for M87*, $\sim10^{12}\,\mathrm{G}$ for Sgr~A*), where $P_{\mathrm{ext}}\sim10^{53}$--$10^{57}\,\mathrm{erg\,s^{-1}}$ exceeds the observed power scales by many orders of magnitude.

[abstract 5 / 17] (score: 3)
arXiv:2509.02254 [pdf, ps, other]

Title: A High Incidence of Mid-infrared Variability in Local Ultraluminous Infrared Galaxies

Authors: Shun Hatano, Masatoshi Imanishi, Takanobu Kirihara, Takashi Yamamoto, Yuxing Zhong, Chenghao Zhu,

Comments: 14 pages, 10 figures. Published in PASJ

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

We explore mid-infrared (MIR) variability in local ultraluminous infrared galaxies (ULIRGs; infrared luminsoity $L_{\rm IR}>10^{12}\ L_\odot$) utilizing the $\sim$11 years of photometry from the NEOWISE multi-epoch catalog of {\it Wide-field Infrared Survey Explorer} ({\it WISE}). We identify 30 variable ULIRGs with statistically significant MIR variability. The variability is observed on timescales of a few years, implying that the MIR-emitting regions are compact ($\lesssim 1$ pc). The difference between maximum and minimum $W2$ (4.6 ${\rm μ}$m) band luminosity ($ΔL_{\rm W2}$) of the 30 variable ULIRGs range from $ΔL_{W2}$ = $7\times10^{42}$ to $5\times 10^{44}$ erg s$^{-1}$. The $ΔL_{W2}$ of 25 variable ULIRGs out of 30 are greater than $ΔL_{W2}$ = $1\times10^{43}$ erg s$^{-1}$, surpassing the MIR luminosity {range} observed in known SUPERNOVAe (SNe; $L_{\rm 3.6\ {\rm μm}}$ and $L_{\rm 4.5\ {\rm μm}}$ < 10$^{42.3}$ erg s$^{-1}$). Therefore, the MIR variabilities in these 25 ULIRGs are most likely driven by tidal disruption events (TDEs) or intrinsic changes in their ACTIVE GALACTIC NUCLEi (AGN) torus emission. Our sample includes hard X-ray detected AGNs (e.g., UGC 05101) and previously reported TDE candidates (IRAS F01004-2237, IRAS 05189-2524). All 25 also exhibit at least one AGN signature(s) besides the MIR variability, suggesting that even if the MIR variability originates from TDEs, the BLACK HOLEs responsible are likely AGNs. Our results suggest that MIR variability is an effective tool for detecting buried AGNs and highlights the intense nuclear activity in ULIRGs.

[abstract 6 / 17] (score: 3)
arXiv:2610.24394 [pdf, ps, other]

Title: Critical MAGNETic Reynolds number of the weakly-collisional turbulent dynamo in supersonic plasmas

Authors: Radhika Achikanath Chirakkara, Christoph Federrath,

Comments: 10 pages, 5 figures, submitted to MNRAS

Subjects: astro-ph.CO physics.plasm-ph

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

Weakly-collisional plasmas are found in several turbulent astrophysical environments, such as the Intra-galaxy-cluster medium (ICM) and the solar wind, where MAGNETic fields can be amplified by the turbulent dynamo. The onset of dynamo action is determined by the critical MAGNETic Reynolds number, ${\rm Rm}_{\rm crit}$, above which turbulent motions amplify MAGNETic energy. Although ${\rm Rm}_{\rm crit}$ has been studied extensively in collisional MAGNETohydrodynamic (MHD) turbulence, its value in supersonic weakly-collisional plasmas remains unknown. Here we determine ${\rm Rm}_{\rm crit}$ using three-dimensional hybrid particle-in-cell (HPIC) simulations of solenoidally driven turbulence with a sonic Mach number $\approx 2$. We vary the MAGNETic Reynolds number over ${\rm Rm}\approx31$-$1000$ and consider two initial plasma MAGNETisations, characterised by initial Larmor ratios $r_{\rm Larmor, 0}/L_{\rm box}=1$ and $100$. We find that the MAGNETic energy grows exponentially at sufficiently large ${\rm Rm}$ and decays when MAGNETic diffusion dominates at low ${\rm Rm}$. By fitting the MAGNETic-energy growth rate as a function of ${\rm Rm}$, we measure ${\rm Rm}_{\rm crit}=190^{+21}_{-17}$ and $198^{+16}_{-18}$ for the initially MAGNETised and unMAGNETised plasma, respectively. These values are the same within their uncertainties, indicating that the initial plasma MAGNETisation does not significantly affect ${\rm Rm}_{\rm crit}$ in the supersonic regime. The measured values are higher than those previously obtained for the subsonic weakly-collisional dynamo, showing that increasing compressibility makes weakly-collisional turbulent dynamo action more difficult to excite. The measured values are also approximately 1.5 times higher than the ${\rm Rm}_{\rm crit}$ value reported for supersonic MHD turbulence.

[abstract 7 / 17] (score: 2)
arXiv:2605.03239 [pdf, ps, other]

Title: Squid funnels time their elastic recoil to amplify pulsed JETs

Authors: Daehyun Choi, Paras Singh, Ian Bergerson, Minho Kim, Jieun Park, Halley J. Wallace, Kenny Zhang, Sandy Y. Hsieh, Aqua T. Asberry, Theodore A. Uyeno, William F. Gilly, Hyungmin Park, Daeshik Kang, Chandan Bose, Saad Bhamla,

Comments: 49 pages (11 pages main text, 38 pages Supplementary Materials), 3 main figures, 28 supplementary figures, 1 table. Revised version

Subjects: physics.flu-dyn

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

Pulsed JETs propel squid across nearly four orders of magnitude in body size. Each pulse leaves through the funnel, a soft nozzle, but whether its compliance acts within a pulse is not known. We tracked chromatophores on two squid species and found that the funnel dilates and recoils, with a repeatable phase lag, while the mantle is still contracting, and that the lag persists after denervation. For inertia-dominated JETs, silicone nozzles, 3D fluid-structure simulations and a reduced-order model agree that the impulse reaches about 4$\times$ the rigid value when the nozzle response time is 0.2 to 0.4 of the JET-acceleration time, a range that overlaps the in vivo timing. The wall stores strain energy during acceleration and returns it during expulsion (akin to an elastic capacitor), which we term "superpropulsion". Synthetic nozzles tuned for superpropulsion launch JETs farther in air, disperse dye faster, and drive a boat faster at a lower cost of transport.

[abstract 8 / 17] (score: 2)
arXiv:2607.15362 [pdf, ps, other]

Title: Lattice Boltzmann Methods for Navier-Stokes Equations in General Orthogonal Coordinates for Efficient Flow Simulations using Nonuniform Clustered Grids

Authors: Eman Yahia, Kannan Premnath, William Schupbach,

Comments: 92 pages, 24 figures

Subjects: physics.flu-dyn physics.comp-ph

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

Resolving multiscale fluid flows or boundary layers effectively requires the use of nonuniform meshes with local grid clustering. The standard lattice Boltzmann method (LBM), a kinetic theory-based approach for computational fluid dynamics, however, is restricted to the use of uniform Cartesian grids. We present new and improved formulations of the LBM that accommodate continuously varying spatial grids via coordinate transformations to simulate the Navier-Stokes equations (NSE) in the general orthogonal coordinates (GOC). They are constructed using a Chapman-Enskog analysis to specify the equilibrium moments of the distribution functions and the geometric force terms used in the collision step to be dependent on the local metric factors and their spatial derivatives, along with the density, momentum and their fluxes, and some correction terms related to the normal velocity gradients so as to accurately represent the NSE in the GOC. The resulting GOC-LBM importantly maintains the simplicity of the collide-and-stream approach and is Galilean invariant that is free of the cubic velocity artifacts. Our GOC-LBM is general and modular in that it can be used with any collision model with appropriate modifications to the equilibria and forcing terms. We present its implementation details for a variety of collision models while the central moments-based model using multiple relaxation times was found to be the most robust in practical implementations. We validate the GOC-LBM through numerical simulations for various benchmark flow problems. Moreover, we demonstrate significant computational advantages of our approach for a case study on simulating boundary layer flows efficiently that involves coupling the GOC-LBM for the NSE with a new GOC-LB scheme for solving the MAGNETic induction equation for MAGNETohydrodynamics (MHD), and for another case study involving orthogonal curvilinear grids.

[abstract 9 / 17] (score: 2)
arXiv:2608.27744 [pdf, ps, other]

Title: The Impact of Errors in the Shape Function of Rotating Neutron Stars in the Oblate Schwarzschild Approximation

Authors: John Ming Ngo, Charlee Amason, Sharon M. Morsink,

Comments: Accepted by Physical Review D. This revision matches the accepted version

Subjects: astro-ph.HE

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

Measurements of thermal X-ray flux emitted by neutron stars can constrain their radii and the equation of state of cold dense matter. Accurate flux modeling of rapidly rotating neutron stars requires an approximation for their oblate surface shape, usually given by a shape function. We examine the accuracy of five shape functions by comparing them against numerical RELATIVISTIC stellar surfaces for seven representative equations of state over a broad range of compactness and spin. We characterize their errors in the surface radius and their derivative with respect to colatitude, test the extent of quasi-universality, and propagate these errors into the differential solid angle dΩ, a geometric factor underlying the observed flux, under the oblate Schwarzschild approximation. We find that the shape functions produce distinct error patterns associated with their forms and parameter ranges. These errors remain structured in compactness, spin, and colatitude. Simple polynomial corrections substantially reduce the radius errors of several shape functions, with most corrected errors within approximately 0.5%. We show that errors in dΩ may be understood as coming from an area contribution, which scales with twice the relative radius error, and a projection contribution controlled primarily by the error in the surface derivative. The projection contribution grows towards the limb, where small surface errors can produce much larger local errors in dΩ. We provide a set of guidelines for the construction of improved quasi-universal shape functions that can be used in future radius estimation efforts. Our recommendations include that both the shape and its derivative be modeled accurately, that more accurate predictions of the polar radius be developed, and that the shape function be calibrated over the same compactness-spin range that is to be tested.

[abstract 10 / 17] (score: 2)
arXiv:2609.05906 [pdf, ps, other]

Title: Observational properties of MAGNETized quantum Oppenheimer-Snyder BLACK HOLEs

Authors: Anuar Idrissov, Hernando Quevedo,

Comments: 17 pages, 14 figures, 2 tables

Subjects: gr-qc

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

We consider a thin accretion disk around the quantum Oppenheimer-Snyder BLACK HOLE immersed in an asymptotically uniform MAGNETic field, together with the gravitational capture of test particles by the BLACK HOLE. The field is described as a Wald test field and acts only on the weakly charged matter of the disk. We find that the quantum correction affects the disk only slightly, while the MAGNETic coupling strongly increases its radiative efficiency and luminosity and suppresses the Doppler blue peak of the iron K$α$ line, which becomes a single peak below the rest frame energy. On the other hand, the quantum correction reduces all capture cross sections, while the MAGNETic field does not affect the capture of photons and confines charged particles to a finite region. Therefore, in principle, the two effects may be distinguished by combining spectral and shadow observations.

[abstract 11 / 17] (score: 2)
arXiv:2610.23976 [pdf, ps, other]

Title: Onset of Chaos and Orbital Instabilities around Rotating Weyl Black Holes

Authors: Shubham Kala, M. Yousaf, Pradeep Singh, Faisal Javed, Hemwati Nandan, G. Mustafa,

Comments: 22 pages, 10 figures, comments are welcome

Subjects: gr-qc

Created: 2026-10-13; Updated: 2026-10-20; Datestamp: 2026-10-20

We investigate nonlinear photon motion in the vicinity of a rotating BLACK HOLE (BH) within Weyl conformal gravity (WCG) by employing Poincare sections, Lyapunov exponents, Fast Lyapunov Indicators (FLI), Kolmogorov-Sinai (KS) entropy, and Discrete Indicator of Chaos (DIG) maps. The joint influence of BH spin and higher order curvature corrections, governed by the parameters $ξ$ and $γ$, induces a transition from nearly integrable trajectories to markedly chaotic dynamics in the strong field domain. As $ξ$ and $γ$ increase, the invariant tori are increasingly deformed and eventually break up. Resonance islands and stochastic layers then form, producing large chaotic regions in phase space, especially near the extremal spin regime. Increasing Lyapunov exponents, faster FLI growth, and higher KS entropy provide quantitative measures of the enhanced dynamical instability, the increased sensitivity to initial conditions, and the corresponding rate of information production. DIG maps show shrinking regular regions and expanding chaotic domains around the photon sphere, indicating that conformal gravity corrections destabilize null circular orbits. Taken together, these findings clarify how RELATIVISTIC frame dragging and higher order curvature terms jointly control photon chaos and point to nonlinear photon dynamics as a potential probe of departures from General Relativity in the strong-gravity regime.

[abstract 12 / 17] (score: 2)
arXiv:2610.23993 [pdf, ps, other]

Title: Astrophysical Signatures of Charged Anisotropic Compact Star in f(R,T) Gravity via Minimal Geometric Deformation

Authors: Hira Shadab, M. Sharif, Tayyab Naseer,

Comments: 38 pages, 9 figures

Subjects: gr-qc

Created: 2026-10-15; Updated: 2026-10-20; Datestamp: 2026-10-20

This work employs minimal geometric deformation to develop two new anisotropic solutions under the effects of an electroMAGNETic field in the context of $f(R,T)$ theory. Our investigation begins with a static spherical system with an anisotropic fluid as a seed source. After that, a new source is inserted to the existing fluid distribution and both the fluid distributions are assumed to be gravitationally coupled with each other. After computing the Einstein-Maxwell field equations, a radial transformation is applied which results in two different sets of equations. These systems are solved individually under different constraints, generating new solutions. To obtain the constants in our interior solutions, we match the internal geometry with the external Reissner-Nordström spacetime at the surface. We further validate our models by using the known mass and radius of a star LMC X-4. Our investigation confirms that both RELATIVISTIC stellar models satisfy all the physical requirements for the specified decoupling parametric values.

[abstract 13 / 17] (score: 2)
arXiv:2610.24057 [pdf, ps, other]

Title: A Two-Population von Mises--Fisher Distribution of the Magnetic Field Direction in the Young Solar Wind

Authors: Gang Li, N. H. Bian, S. Y. Huang, A. Chian, R. Santos-Lima, E. L. Rempel, R. A. Miranda, B. Raphaldini, Yasmmin Tamburus,

Comments: submitted to ApJL

Subjects: astro-ph.SR

Created: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20

The one-point distribution of the MAGNETic field direction in the young solar wind is found to be a superposition of two populations rather than a single exponential. Using Parker Solar Probe (PSP) Encounter 1 MAGNETometer data, we show that the distribution of the pitch-angle cosine mu(t) = bhat(t) . bhat_0 is well described by a two-component von Mises-Fisher (vMF) mixture: a broad, weakly confined component of concentration kappa_1 ~ 3.6 that accounts for the large-amplitude rotations and switchback tail, and a field-aligned component that reduces, in the small-angle limit, to a Gaussian in the polar angle theta of width sigma ~ 15 degrees (concentration kappa_2 ~ 14). The concentration of the field-aligned component is not a free parameter: it is set by the level of the transverse Alfvenic fluctuation through kappa_2 = 2<|B|^2>/ = 2/<1-mu^2> ~ 16.2, in agreement with the fitted value to within ~12%. The transverse fluctuations are weakly anisotropic (/ ~ 1.1), so the core is a weakly anisotropic Bingham distribution rather than a pure vMF. The broad component is exponential in mu, not in theta, confirming that switchbacks saturate toward mu = -1 rather than decaying away, consistent with the drift-diffusion framework of Bian et al. (2024, ApJ, 960, L15). This physics-based two-population framework connects macroscopic fluid parameters directly to those describing the directional statistics, offering a powerful diagnostic for probing the structural evolution of MHD turbulence and switchbacks in the inner heliosphere.

[abstract 14 / 17] (score: 2)
arXiv:2610.24360 [pdf, ps, other]

Title: Spiraling into the `snail' cluster MCXC J0157.4-0550

Authors: Chao Geng, Chong Ge, Ming Sun, Li Ji, Guilin Liu, Zhicheng He, Haiguang Xu, John ZuHone, Paul Nulsen, Craig Sarazin, Nobuhiro Okabe,

Comments: 13 pages, 5 figures, submitted to ApJ

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

We present a deep Chandra (130 ks) study of a striking, tidally induced cold front in a subcluster merging with the galaxy cluster MCXC J0157.4-0550. The subcluster, nicknamed the `snail' (J0157), displays an extensive spiral structure that extends to $\sim 260$ kpc --- one of the largest spiral cold fronts identified to date. Surface brightness and spectral analysis across four sectors reveal a consistent density jump of a factor of $\sim 3$ across the front, together with significant temperature discontinuities, and thermodynamic mapping further delineates the coherent, low-entropy structure of the stripped gas. Unlike classical sloshing cold fronts, the spiral in J0157 arises not from oscillation of a displaced cool core, but from subcluster gas that has been ram pressure stripped and tidally wound into a spiral by orbital rotation. Applying Gaussian Gradient Magnitude filtering and azimuthal surface-brightness analysis, we identify quasi-periodic corrugations along the front consistent with candidate Kelvin-Helmholtz (KH) instabilities, with a characteristic scale of $\sim 90$ kpc. The presence of these KH rolls constrains the effective ICM viscosity to $\lesssim 0.59$ times the Spitzer value and the MAGNETic field strength at the interface to $\lesssim 5.9\ μ$G. These results establish J0157 as a useful laboratory for probing macro-scale merger-induced gas dynamics and micro-scale plasma transport processes in the intracluster medium.

[abstract 15 / 17] (score: 2)
arXiv:2610.24396 [pdf, ps, other]

Title: Prospects for submillimeter VLBI of BLACK HOLE photon rings with a stratospheric balloon-borne telescope

Authors: Mayukh Bagchi, Dominic W. Pesce, Felix M. Thiel, Laura M. Fissel, Lindy Blackburn,

Comments: 15 pages, 8 figures, 4 tables. Submitted to ApJ

Subjects: astro-ph.IM

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

Submillimeter very long baseline interferometry (VLBI) achieves higher angular resolution and probes more optically thin emission near supermassive BLACK HOLEs, with less interstellar scattering toward Sgr A$^*$. Above 345 GHz, however, the atmosphere confines ground-based VLBI to a few high, dry sites. Using 2012-2022 weather, we forecast what a 2.5 m telescope floating at 35-40 km, a successor to the 22 GHz Balloon-borne VLBI Experiment (BVEX) pathfinder, would add to ground-VLBI arrays at 345-690 GHz. The balloon adds little baseline length but reaches higher frequencies, where a fixed baseline is longer in wavelengths. On an ALMA-balloon baseline, Sgr A$^*$ at 460 GHz is at the detection threshold, with ten or more 20 s detections on about half of the simulated April days. These detections lie beyond the polarimetric photon ring transition, where the $n=1$ ring dominates the polarized visibility amplitudes. M87$^*$ at 460 GHz would need frequency phase transfer from a 230 GHz reference to be detected. With phase transfer, most Sgr A$^*$ detections beyond the transition at 460 GHz are on balloon baselines, whose thermal noise meets the linear-POLARIZATION threshold within one 300 s scan. At 690 GHz such detections require phase transfer that stays coherent at three times the reference frequency. In Fisher forecasts, a 460 GHz ring-geometry constraint requires balloons but is weaker than at 345 GHz, where balloons add little improvement. High-resolution 460 GHz VLBI science would require a 32 GHz bandwidth backend, submillimeter receivers, and simultaneous 230 GHz reference recording at every station.

[abstract 16 / 17] (score: 2)
arXiv:2610.24412 [pdf, ps, other]

Title: Models of spectral bumps of primary COSMIC RAYs and multi-messenger tests

Authors: Qiang Yuan, Chuan Yue, Yi-Zhong Fan,

Comments: 7 pages, 1 table, 6 figures

Subjects: astro-ph.HE

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

The energy spectra of individual species of COSMIC RAY nuclei by recent direct detection experiments show complicated structures with spectral hardenings and softenings rather than featureless power laws, which challenge the traditional understanding of the production, acceleration, and propagation of COSMIC RAYs. Particularly, the DAMPE measurements reveal charge-dependent softenings and reject mass-dependent softenings with a high significance. Taking into account the correlated structures at similar energies in the large-scale anisotropies of COSMIC RAYs, one of the most natural interpretations of the spectral structures is the presence of a nearby COSMIC RAY source. In this case, the softening energies correspond to the acceleration upper limits of such a source, forming the so-called Peters cycle of the spectra. Alternative models such as the injection/acceleration and propagation models may also reproduce the spectral bumps, but show difficulty to explain the anisotropies. Fluxes of secondary nuclei and $γ$ rays offer additional tests of different models. Future multi-messenger observations are expected to be able to pin down the origin of COSMIC RAYs.

[abstract 17 / 17] (score: 2)
arXiv:2610.24504 [pdf, ps, other]

Title: Micrometer-thin liquid sheets from single-JET impact on a sharp edge for multi-kHz LASER-plasma experiments

Authors: Mukesh Kumar, S. Sree Harsha, Prashant Kumar Singh,

Comments: 6 Figures

Subjects: physics.plasm-ph physics.flu-dyn

Created: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20

We present a simple and robust method for generating freely suspended liquid sheets by directing a single laminar liquid JET onto the sharp edge of an inclined plate. By optimizing liquid composition, impact geometry, and flow conditions, we identify a 60:40 ethylene-glycol-deionized-water volumetric mixture for stable sheet formation. The resulting sheets span 8 mm in height and 3 mm in width, with thicknesses from 1.1 to 4.8 micrometers measured by spatial and spectral interferometry. Operated in vacuum as continuously renewed plasma mirrors, these targets demonstrate stable performance from 0.5 to 10 kHz using 175-fs Yb:KGW LASER pulses, reaching a maximum S-polarized reflectivity of 66.5% at an intensity of 4 x 10^14 W/cm^2. At higher intensities using 25-fs Ti:sapphire pulses at 1 kHz, maximum S-polarized reflectivity reaches 77% at 2 x 10^16 W/cm^2. The reflected beam exhibits high temporal stability, with angular pointing fluctuations of 18.19 +/- 0.53 microradians. Our results demonstrate a tunable, continuously renewed liquid-sheet target for multi-kHz LASER-plasma experiments.