Current date: 2026-10-01

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Created/updated limit: 2026-09-24 (7 days ago)

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OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-10-01&until=2026-10-01&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 1080

Keyword score statistics

score 10 -- 1 abstracts

score 8 -- 1 abstracts

score 6 -- 3 abstracts

score 5 -- 2 abstracts

score 4 -- 4 abstracts

score 3 -- 7 abstracts

score 2 -- 17 abstracts

in total -- 35 abstracts

Articles that appeared on 2026-10-01

[abstract 1 / 35] Wow! (score: 10)
arXiv:2605.17397 [pdf, ps, other]

Title: Exploring the Transitional Parameter Space of Blazars using Gamma-ray and X-ray Population Diagnostics

Authors: Zahoor Malik, Sikandar Akbar, Zahir Shah, B. van Soelen,

Comments: 20 pages, 12 figures, Accepted in JHEAP

Subjects: astro-ph.HE

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We investigate the $γ$-ray and X-ray population properties of changing-look BLAZARs (CLBs) using sources from the Fourth \textit{FERMI} LAT Source Catalog Data Release 4 (4FGL-DR4) together with X-ray information from the Living \textit{SWIFT} XRT Point Source (LSXPS) catalog. The CLB sample is compared with large populations of confirmed BL Lac objects (BLLs) and flat-spectrum radio QUASARs (FSRQs) using spectral, variability, and broadband properties. In the $γ$-ray parameter space, CLBs mainly occupy intermediate and overlap regions between the BLL and FSRQ populations. However, the centroid locations in different parameter planes, along with the PCA and UMAP projections, show that the CLB population lies closer to the FSRQ region. The X-ray analysis also shows a similar behavior, where the overall distribution of CLBs in the X-ray parameter space is found to be nearer to FSRQs than to BLLs. In addition, the X-ray/$γ$-ray coupling relations and random-forest classification probabilities are consistent with this trend. Overall, the results suggest that CLBs form a transitional population between the two main BLAZAR subclasses while retaining characteristics closer to the FSRQ population.

[abstract 2 / 35] Wow! (score: 8)
arXiv:2609.38590 [pdf, ps, other]

Title: Chandra X-ray Spectral Evidence of the Dual AGN Nature of the Gravitational lens MG B2016+112 at z=3.273 with 175 pc separation

Authors: Daniel A. Schwartz, Julia M. Sisk-Reynes, Anna Barnacka,

Comments: 8 pages, 4 figures

Subjects: astro-ph.HE

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

We use a new 175 ks Chandra X-ray observation of the z=3.273 radio-loud gravitational lens system MG B2016+112 to present definitive X-ray spectral evidence that it contains a dual ACTIVE GALACTIC NUCLEus (AGN). With a projected separation of 175 parsecs, this is the tightest separation confirmed AGN pair at high redshift. Prior multi-epoch very long baseline interferometry (VLBI) and archival Chandra data had revealed two distinct emitters, but could not rule out a single AGN with a complex, highly magnified JET. Our new Chandra observations allow a separate spectral analysis of each source. We find strong intrinsic absorption (N_H > 4 x 10^22 cm^-2, 3 sigma confidence) at the source redshift for the highly magnified source inside the caustic. This identifies it as an obscured AGN. In addition to the previously known type II AGN outside the caustic, this confirms a compact dual AGN system in MG B2016+112. On-going and future surveys using facilities such as Euclid, SKA, and the Rubin and Roman observatories will uncover more such systems, probing SMBH evolution and gravitational wave precursors.

[abstract 3 / 35] Yes (score: 6)
arXiv:2601.07918 [pdf, ps, other]

Title: Relativistic JETs from millisecond proto-MAGNETars

Authors: Dhruv K. Desai, Luciano Combi, Daniel M. Siegel, Brian D. Metzger,

Comments: 16 pages, 6 figures. v2: accepted version, published in ApJL

Subjects: astro-ph.HE gr-qc

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Rapidly rotating, strongly MAGNETized neutron stars (``millisecond proto-MAGNETars'') formed in stellar core-collapse, neutron star mergers, and white dwarf accretion-induced collapse have long been proposed as central engines of GAMMA-RAY BURSTs (GRB) and accompanying SUPERNOVAe/kilonovae. However, during the first few seconds after birth, neutrino heating drives baryon-rich winds from the neutron star surface, potentially limiting the MAGNETization and achievable Lorentz factors of the outflow and casting doubt on whether proto-MAGNETars can launch ultra-RELATIVISTIC JETs at early times, as needed to power short-duration GRB. We present 3D general-RELATIVISTIC MAGNETohydrodynamic simulations of neutrino-heated proto-MAGNETar winds that incorporate M0 neutrino transport. While the global wind properties broadly agree with previous analytic estimates calibrated to one-dimensional models, our simulations reveal essential multidimensional effects. For rapidly rotating models with spin periods P = 1 ms, centrifugal forces strongly enhance mass loss near the rotational equator, producing a dense, sub-RELATIVISTIC outflow ( ~0.1c). This equatorial wind naturally confines and collimates less baryon-loaded outflows emerging from higher latitudes, leading to the formation of a structured bipolar JET with a peak MAGNETization up to ~ 30-100 along the pole, sufficient to reach bulk Lorentz factors ~ 100 on larger scales. The resulting angular stratification of the outflow energy into ultra-RELATIVISTIC polar and sub-RELATIVISTIC equatorial components is broadly consistent with the observed partition between beaming-corrected GRB energies and SUPERNOVA/kilonova ejecta. Our results demonstrate that millisecond proto-MAGNETars can launch RELATIVISTIC JETs within seconds of formation and highlight their potential role in powering the diverse electroMAGNETic counterparts of compact-object explosions.

[abstract 4 / 35] Yes (score: 6)
arXiv:2609.38553 [pdf, ps, other]

Title: Nonthermal hotspot orbiting the supermassive BLACK HOLE Sgr A*

Authors: Alejandro Cruz-Osorio, David Barrero-González, Juan J. Zaldívar, Yosuke Mizuno,

Comments: Published in MNRAS

Subjects: astro-ph.HE

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

Recent millimeter wavelength observations at 230 GHz by the Event Horizon Telescope have resolved the innermost structure of the Galactic Center, Sgr A*, revealing a ring-like structure consistent with SYNCHROTRON emission from a MAGNETized torus surrounding a supermassive BLACK HOLE. These observations reveal two key features: three prominent hotspots near the photon ring and low light-curve variability, with a modulation index of $\barσ/\barμ \lesssim 0.1$. State-of-the-art general RELATIVISTIC MAGNETohydrodynamic and radiative transfer simulations cannot simultaneously reproduce the three hotspots and low light-curve variability observed in Sgr A*. We propose that an orbiting hot blob, formed in the accretion disk, could account for hotspots. We systematically explore its physical properties, including size, emission amplitude, orbital radius, eccentricity, velocity, and orbital plane orientation. The results -- applying two observational constraints--show that the preferred model corresponds to a BLACK HOLE with dimensionless spin $a_{\star}=0.5$, a MAGNETically arrested disk configuration for the MAGNETic field, and the presence of a hotspot with size $σ_{\rm hs}=2\,M$ and intensity amplitude $A=10$, orbiting circularly at $r_{\rm orb}=6 M$ with Keplerian velocity in the BLACK HOLEs equatorial plane, and an inclination view angle of $i^\circ=20$.

[abstract 5 / 35] Yes (score: 6)
arXiv:2609.39977 [pdf, ps, other]

Title: A New Sample of Closely Separated Dual and Binary AGN Candidates Revealed with the Radio Fundamental Catalog

Authors: Emma Schwartzman, Ryan Pfeifle, Tracy Clarke, Nathan Secrest, Henrique Schmitt, Barry Rothberg,

Comments: 39 pages, 22 figures, submitted to ApJ, comments welcome

Subjects: astro-ph.GA

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The Big Multi-AGN Catalog (BigMAC) provides the first literature-complete compilation of confirmed and candidate dual, binary, and recoiling ACTIVE GALACTIC NUCLEi (AGN). The BigMAC provides a basis for the first population-wide radio study of multiple AGN (multi-AGN). The Radio Fundamental Catalog (RFC) is composed of four decades of Very Long Baseline Interferometry (VLBI) observations capable of resolving parsec-scale structure. All BigMAC candidate and confirmed multi-AGN were cross-matched to the RFC, highlighting a total of 241 BigMAC sources with available RFC imaging. We present the first detailed analysis of the ten systems exhibiting multiple compact components, most likely to be radio multi-AGN. Using multi-frequency radio and supporting multiwavelength information, we assess whether each system is more consistent with dual/binary AGN or intrinsic JET structure. The dual/binary nature of six systems is further supported by our radio analysis, while the four remaining systems are more plausibly explained by compact JET activity. Several candidate multi-AGN systems exhibit projected separations of only a few to tens of parsecs. In many cases, the parsec-scale radio separations are orders of magnitude smaller than the separations inferred from the observations that originally motivated their selection, emphasizing the importance of VLBI follow-up. Because all ten sources are members of the International Celestial Reference Frame (ICRF) and display significant intrinsic radio structure, they also represent potential sources of astrometric error. This work establishes the RFC as an archival resource for characterizing the closest SMBH pairs while improving future ICRF realizations.

[abstract 6 / 35] Yes (score: 5)
arXiv:2609.38330 [pdf, ps, other]

Title: Cosmic-neighbor-associated distances to VHE and candidate VHE BL Lacs via SDSS photometric redshifts

Authors: Karri I. I. Koljonen, Elina Lindfors,

Comments: 11 pages, 10 figures, 5 tables. This article has been accepted for publication in MNRAS published by Oxford University Press on behalf of the Royal Astronomical Society

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

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

BL Lac objects have distances that are difficult to estimate because their optical spectra rarely show identifiable emission or absorption lines. We present a method to constrain BL Lac distances by associating them with their cosmic neighborhoods (local overdensities in the cosmic web) identified in optical fields. Distances to galaxies in these neighborhoods are estimated using the Sloan Digital Sky Survey (SDSS) photometric redshifts. Using cosmic-neighborhood associations previously established from multi-object spectroscopy and BL Lacs with spectroscopically measured redshifts as control samples, we find that the redshifts of the associated neighborhoods can be recovered with an accuracy of $Δz \sim 0.02-0.04$. When multiple candidate neighborhoods are present in the field, we rank the candidate associations using a central-location criterion. In 50% of cases, the BL Lac is associated with the correct neighborhood. We provide distance estimates for BL Lac objects without secure redshift measurements, focusing on sources detected at very high energies (VHE; $E>100$,GeV) and on candidate VHE emitters. Combining intervening absorption systems, host-galaxy imaging, $γ$-ray constraints, and our SDSS group-association method, we propose likely redshifts for TXS 0141$+$268 ($z\sim0.93-0.95$), PKS 0735$+$178 ($z=0.64$), 3FHL J0905.5$+$1357 ($z=0.644$), B2 0912$+$29 ($z = 0.53$), 3FHL J1120.8$+$4212 ($z=0.363$), BZB J1243$+$3627 ($z=0.485$), 3FHL J1253.1$+$5300 ($z=0.664$), and RX J2156.0$+$1818 ($z=0.635$). Finally, we discuss how forthcoming narrow-band photometric-redshift surveys can improve BLAZAR distance estimates via group-association techniques.

[abstract 7 / 35] Yes (score: 5)
arXiv:2609.39224 [pdf, ps, other]

Title: ElectroMAGNETic Counterparts of Stellar-mass Binary Black Hole Mergers in AGN Accretion Disks: Theoretical Models and Observational Status

Authors: Lei He, Liang-Gui Zhu, Ken Chen, Zi-Gao Dai, Ye-Fei Yuan, Jian-Min Wang, Wen Zhao,

Comments: 42 pages, 14 figures, invited review

Subjects: astro-ph.HE astro-ph.CO

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The discovery of the binary neutron star merger GW170817 and its electroMAGNETic counterparts marked the beginning of the era of multimessenger gravitational-wave astronomy. In contrast, binary BLACK HOLE (BBH) mergers, which constitute the majority of gravitational-wave sources detected to date, are generally expected to be electroMAGNETically dark. However, if BBH mergers occur within the dense gaseous environments of ACTIVE GALACTIC NUCLEus (AGN) accretion disks, interactions between the merging BLACK HOLEs and surrounding gas may produce electroMAGNETic emission across multiple wavelengths. AGN disks may therefore provide a natural multimessenger laboratory for studying BBH mergers and their astrophysical environments. A key question is whether such a scenario is supported by current observations and whether the associated electroMAGNETic signatures are sufficiently distinctive and detectable. In this review, we summarize the current theoretical and observational status of BBH mergers in AGN accretion disks, focusing on the evidence for their occurrence, the physical mechanisms and expected signatures of electroMAGNETic emission, and searches for candidate counterparts. We also discuss the major challenges in identifying and confirming these associations and the prospects for future multimessenger observations with current and forthcoming multiwavelength facilities.

[abstract 8 / 35] Yes (score: 4)
arXiv:2608.01750 [pdf, ps, other]

Title: AGNI: A differentiable MHD stability solver & optimizer for MAGNETic confinement fusion devices

Authors: Rahul Gaur, Sanket Patil, Prateek Gupta, Djin Patch, Tony Qian,

Comments: 28 pages, 8 figures, added AI use declaration, link to source code, improved readability

Subjects: physics.plasm-ph

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The existence of an ideal MagnetoHydroDynamic (MHD) equilibrium does not guarantee its stability. Finite toroidal mode number (n) instabilities degrade performance in both tokamaks and stellarators and differentiable stability optimization tools to date have operated only in the infinite-n limit. We present AGNI (Analysis of Global Normal modes in Ideal MHD), a GPU-accelerated, automatically differentiable finite-n ideal MHD stability solver and optimizer. AGNI discretizes the ideal MHD energy principle pseudospectrally in real space using differentiation matrices and geometric coefficients from a DESC equilibrium, giving a variational eigenvalue problem for the plasma displacement, and efficiently finds the most unstable modes. Built on jax, AGNI yields reverse-mode gradients of the growth rate with respect to boundary-shape and profile parameters without re-solving the equilibrium. We benchmark AGNI against the initial-value code NIMSTELL for a modified Landreman-Bulle-Drevlak quasi-helically symmetric stellarator and a DSHAPE tokamak,recovering the dominant mode with agreement in terms of growth rate and eigenfunction structure, and verify the automatic differentiation gradients against central finite differences. We quantify CPU and GPU cost for eigenvalue and gradient evaluation, establish the finite-precision limit on resolving near-marginal eigenvalues, and present a numerical scheme to impose incompressibility, compatible with gradient-based optimization. AGNI will allow us to optimize tokamaks, stellarators, and mirrors against ideal MHD instabilities.

[abstract 9 / 35] Yes (score: 4)
arXiv:2609.38341 [pdf, ps, other]

Title: HESS J1507-622: A Plausible Young Galactic Kilonova Remnant

Authors: Prantik Sarmah, Xilu Wang, Myles Carley, Shu-Xu Yi, Ming-Yu Ge, Rebecca Surman,

Comments: 11 pages, 3 captioned figures. Prepared for submission to ApjL. Queries and comments are most Welcome

Subjects: astro-ph.HE astro-ph.SR hep-ph

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

HESS J1507$-$622 is an unusual TeV gamma-ray source in the H.E.S.S. Galactic Plane Survey, distinguished by its off-plane location ($b \simeq -3.5^{\circ}$) and compact angular extent ($\sim 0.3^{\circ}$). Its location and morphology challenge conventional pulsar wind nebula and SUPERNOVA remnant interpretations, and the absence of a detected shell or associated pulsar leaves its origin unresolved. Here, we propose that HESS J1507$-$622 is a young Galactic kilonova remnant with gamma-ray emission of leptonic origin. In this scenario, the source's off-plane location is naturally explained by the natal kick imparted to the progenitor binary neutron star system. We demonstrate that a leptonic kilonova remnant model can successfully reproduce the observed GeV-TeV flux via inverse-Compton scattering from shock-accelerated electrons, while the corresponding SYNCHROTRON emission remains below current X-ray and radio upper limits. Based on the source's energetics and angular size, we infer a distance of 3.8-14.3 kpc and an age of 0.2-3.0 kyr. Importantly, our analysis favors a kilonova remnant younger than 1 kyr. The lack of a historical naked-eye record can be explained by the transient's rapid fading, far-southern declination, and potential line-of-sight extinction. We further assess the detectability of unique multi-wavelength signatures that could confirm this hypothesis. We find promising prospects for detecting the unique MeV gamma rays from the decay of $r$-process radioisotopes using future observatories, alongside complementary low-energy signatures from thermal dust emission and a possible optical light echo. These distinct signals offer definitive tests of the kilonova remnant interpretation and motivate targeted observations with current and future facilities.

[abstract 10 / 35] Yes (score: 4)
arXiv:2609.38350 [pdf, ps, other]

Title: A New Hope for AGN SED Fitting: X-Ray Spectral Analysis of 12MGS AGN with the C2PO-Torus Model

Authors: Carys J. E. Gilbert, Lucia Marchetti, Luigi Barchiesi, Mattia Vaccari, Cristian Vignali, Stefano Marchesi, Francesca Pozzi, Francesco Salvestrini, Anna Feltre, Malebo Moloko, Carlotta Gruppioni,

Comments: Accepted for publication by MNRAS. 27 pages, 12 figures, 5 tables

Subjects: astro-ph.GA

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

In this paper, we present the results of comprehensive, broadband X-ray spectral analysis of a subsample of 43 mid-Infrared (IR) selected star-forming ACTIVE GALACTIC NUCLEi (AGN). We analysed archival NUSTAR, Chandra, and XMM-Newton data, and present the first pointed X-ray observation of IRASF03450+0055. We introduce a new physically-based X-ray spectral model, C2PO-Torus, based on a two-phase clumpy torus geometry. It is designed to provide constraints on physical parameters of the torus that can be directly linked to the parameters of the AGN model SKIRTOR. This model will allow us to exploit the synergies between the X-ray and IR regimes, place stronger constraints on the torus properties, and improve spectral energy distribution (SED) fitting by providing priors for the SKIRTOR parameters. We compare the results from the C2PO-Torus fitting to those obtained from traditional models, finding that it is an extremely effective tool for fitting a wide variety of X-ray spectra. We observe that our sample closely follows the established L_[OIII] - L_X AGN relation, while presenting an IR and Radio excess with respect to the L_X - L_12micron and L_X - L_1.4GHz AGN relations at low luminosities. We believe that this excess is due to contamination from STAR FORMATION related emission. We anticipate that the C2PO-Torus model will aid substantially in completing full-spectrum SED fitting of this sample, allowing us to properly disentangle the different emission components of these objects, which are local analogues of AGN at Cosmic Noon.

[abstract 11 / 35] Yes (score: 4)
arXiv:2609.39923 [pdf, ps, other]

Title: Raising the Optical Depth to Reionization with Dark Matter Decay

Authors: Yu-Ning Wang, Paulo Montero-Camacho, Ziwei Wang, Yin Li, Yue-Lin Sming Tsai,

Comments:

Subjects: astro-ph.CO

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

DESI DR2 baryon acoustic oscillation measurements have sharpened a discrepancy with cosmic microwave background (CMB) inferences that can be recast as a preference for a reionization optical depth of $τ_{\rm reio}\simeq 0.09$, well above the $\simeq 0.06$ inferred from large-scale CMB POLARIZATION measurements. Here we test whether electroMAGNETic energy injection from DARK MATTER (DM) decaying through $χ\rightarrow e^{+}e^{-}$ can provide this additional optical depth. Adopting a Gompertzian model for astrophysical reionization, which provides an asymmetric, simulation-calibrated description of cosmic reionization, we derive $τ_{\rm reio}$ self-consistently from the evolution of the free-electron fraction, including the contribution from DM decay. We jointly constrain cosmological and reionization parameters and the DM decay rate using ACT+Planck CMB temperature and POLARIZATION anisotropies, CMB lensing, BAO measurements, and QUASAR damping-wing observations. For $m_χ=1\,{\rm GeV}$, DM decay raises the marginalized optical depth from $τ_{\rm reio}=0.064$ to $0.072$, but does not significantly improve the fit. The additional optical depth arises primarily from a broad ionization tail extending through the cosmic dark ages, rather than from an earlier onset of astrophysical reionization. Across $m_χ=2\,{\rm MeV}$--$7\,{\rm GeV}$, the central $68\%$ credible intervals remain below the $τ_{\rm reio}\simeq 0.08$ level previously found sufficient to bring both the neutrino-mass tension and the exclusion of $Λ$CDM below the $2σ$ level. The corresponding DM lifetime constraints are complementary to cosmic-ray and gas-heating bounds and competitive with previous CMB limits. Decaying DM therefore shifts the inferred optical depth in the direction required to ease the CMB--BAO discrepancy, but the allowed increase remains insufficient to alleviate it substantially.

[abstract 12 / 35] (score: 3)
arXiv:2606.20787 [pdf, ps, other]

Title: Gas-induced gravitational-wave dephasing and accretion periodicities of live post-Newtonian massive BLACK HOLE binaries: warm disk

Authors: Mudit Garg, Alessia Franchini, Alessandro Lupi,

Comments: 15 pages, 9 figures. under review at ApJ. Comments welcome

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

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We perform 3D hydrodynamical simulations of an equal-mass quasi-circular live $10^6~{\rm M}_\odot$ massive BLACK HOLE binary (MBHB) embedded in a prograde, locally isothermal circumbinary disk (CBD) with $0.1$ aspect ratio. The binary evolves under the effect of gaseous torques and $2.5$ post-Newtonian dynamics. This approach allows us to track the influence of the CBD on a gravitational-wave (GW) driven MBHB inspiral all the way down to merger from $53$ Schwarzschild radii ($r_s$) over $1.5$ years. Comparing the GW inspiral rate with the viscous inflow, we find the binary to decouple from the CBD just $\approx2$ days before merger. We measure gas torques (gravitational and accretion) with and without concurrent GW emission, finding that their sums agree to within $\lesssim5\%$ down to $25~r_s$. We then measure a gas-induced phase-shift in the GW signal of $\approx9.0\times10^{-4}$ rad that accumulates over a year until $40~r_s$ and saturates afterward, which should be LISA-detectable at redshift $z{\lesssim0.2}$. We further characterize the mass accretion rate modulations. We recover the periodicity associated with the ``lump" at the inner cavity edge. The periodicities at the binary orbital period and at half of it are shifted to lower frequencies. We measure the former, due to RELATIVISTIC apsidal precession, in an inspiraling binary for the first time, and newly identify the latter as due to the precession of the eccentric cavity. Our results have implications for multi-messenger astronomy, since observation of accretion rate modulation by LSST/Roman surveys and phase-shift by LISA will provide crucial information on the complex environment surrounding MBHBs.

[abstract 13 / 35] (score: 3)
arXiv:2609.26380 [pdf, ps, other]

Title: Inelastic scattering effects on POLARIZATION predictions for cold and warm atmospheres in the X-rays

Authors: J. Podgorný, L. Marra, M. Dovčiak, R. Taverna, R. W. Goosmann, M. Gupta, F. Marin, G. Matt, J. Poutanen, A. Różańska, A. Veledina,

Comments: 7 pages, 3 figures, resubmitted

Subjects: astro-ph.HE

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

X-ray POLARIZATION models of accreting compact objects often assume the so-called Chandrasekhar-Sobolev POLARIZATION prescription for elastic Thomson scattering in electron-scattering semi-infinite atmospheres. In this letter, we examine the effects of inelastic Compton scattering. We assume homogeneous slabs of cold and warm (up to 1 keV) electrons. We use a Monte Carlo approach. We discuss the POLARIZATION difference arising in the X-rays between the elastic and inelastic scattering assumptions for plane-parallel transmission and reflection, and the role it can play in the interpretation of X-ray polarimetric observations of accreting compact objects.

[abstract 14 / 35] (score: 3)
arXiv:2609.38322 [pdf, ps, other]

Title: Revealing the accretion disc structure in Changing State AGN: NGC1566

Authors: Huimei Wang, Chris Done, Riccardo Middei, Xue-Bing Wu,

Comments:

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

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

NGC1566 is a low mass ($\sim 6\times 10^6M_\odot$) Active Galactic Nuclei (AGN) with unusual large amplitude variabilty in its accretion flow. In the optical it cycles between recurring short bright episodes with strong blue/UV continuum and clear broad line emission, and a much weaker persistent level without strong broad lines, making it a repeating changing-state (CS) AGN. We re-analyse the intensive optical/UV and X-ray monitoring during the 2018 bright flare, showing for the first time the corresponding evolution of the (host galaxy subtracted) optical/UV AGN spectrum as well as the X-ray emission. As seen in other CS-AGN, the strongest spectral evolution is in a UV/soft X-ray component which likely disappears below $0.01L_{\rm Edd}$ while the hot corona and a redder optical/UV component show weaker variability. We show that the red optical emission is likely a composite of the intrinsic and reprocessed emission from the outer disc, together with diffuse continuum from the BLR, and discuss the different signatures predicted by this for continuum reverberation across the changing-state event. The historical lightcurves show repeated changing-state events tied to unusually large amplitude discrete flares in the lightcurve. While these do not appear to be periodic, the behaviour does support previous suggestions that the accretion flow is repeatedly perturbed, perhaps by an intermediate mass BLACK HOLE companion.

[abstract 15 / 35] (score: 3)
arXiv:2609.38573 [pdf, ps, other]

Title: Angular structure of finite-field vacuum birefringence in MAGNETars

Authors: Shahram Abbassi, S. R. Valluri,

Comments: v1: 8 pages, 5 figures. Comments are welcome

Subjects: astro-ph.HE

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

Vacuum birefringence in a strong MAGNETic field is often modelled by combining the finite-field splitting for perpendicular propagation with the familiar $\sin^2θ$ angular factor. That separation is exact only at leading response order. Continuing our previous study of the field-strength dependence of the birefringence, we examine the angular dependence of the full one-loop refractive indices in the local Heisenberg--Euler theory. We show analytically that, on the positive-birefringence branch, the usual factorized form systematically overestimates the exact splitting away from perpendicular propagation. The relative correction is largest close to the MAGNETic-field direction, where the absolute birefringence itself vanishes. Compact analytic expansions expose the sign, scaling, and angular location of the correction throughout the MAGNETar-relevant range $B/B_{\rm cr}\le100$, while an independent proper-time calculation verifies the underlying one-loop coefficients. In centred-dipole applications the correction is sub-percent for moderate MAGNETar fields but reaches several percent for the strongest sources; surface averaging and radial phase accumulation reduce its physical weight as the field decreases away from the stellar surface. The result separates finite-field amplitude and angular corrections and provides controlled analytic benchmarks for precision POLARIZATION transport in strongly MAGNETized environments.

[abstract 16 / 35] (score: 3)
arXiv:2609.38694 [pdf, ps, other]

Title: HLX-1 as a Repeating Partial Tidal Disruption Event around an Intermediate-Mass Black Hole

Authors: Fangyuan Yu, Andrew Mummery, Muryel Guolo,

Comments: 19 pages, 9 figures; revised and resubmitted to ApJ

Subjects: astro-ph.HE

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

ESO 243$-$49 HLX--1 is one of the first known compelling intermediate-mass BLACK HOLE (IMBH) candidates, but the origin of its recurrent X-ray outbursts remains unsettled. In this work we fit the HLX--1 outbursts simultaneously with a RELATIVISTIC thin-disk time-dependent model. The black-hole and disk-geometry parameters are tied across epochs, while the injected mass and timing parameters are fitted separately for each outburst. We also include a contemporaneous \textit{HST} UV/optical/IR spectral energy distribution obtained near the peak of one outburst, which constrains the global temperature and radius scales of the disk. The soft-state data are consistent with a common global solution, with BLACK HOLE mass $\log_{10}(M_{\bullet}/M_\odot)=4.5\pm0.2$ and disk formation radius $\log_{10}(r_0/r_g)=3.8\pm0.3$. The differences between outbursts are mainly described by modest changes in disk mass and viscous timescales. The inferred injected masses are typically $\sim 10^{-3}\,M_\odot$ per outburst, requiring a total fuel supply of at least a few $\times 10^{-3}\,M_\odot$ across the observed sequence. This mass scale, and the disk size, are consistent with repeated partial stripping of a low-mass donor. A simple Keplerian mapping of the flare gaps and fitted disk radius implies a highly eccentric orbit with a pericenter just outside the donor's tidal radius. These results support a repeating partial tidal disruption interpretation for the origin of HLX--1.

[abstract 17 / 35] (score: 3)
arXiv:2609.38937 [pdf, ps, other]

Title: The impact of the turbulent Mach number on STAR FORMATION and the initial mass function

Authors: Sajay Sunny Mathew, Christoph Federrath, Amit Seta,

Comments: 11 pages, 8 Figures, 3 Tables, MNRAS accepted

Subjects: astro-ph.GA

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Turbulence regulates STAR FORMATION by influencing the density structure and fragmentation of molecular clouds, and therefore it is expected to play a key role in setting the initial mass function (IMF). We study how the strength of the turbulent shocks affects STAR FORMATION and the IMF by comparing a series of MAGNETohydrodynamical (MHD) simulations of star cluster formation in clouds with three different rms Mach number values, $M=2.5, 5$, and $10$, but otherwise the same Alfvén Mach number ($M_\mathrm{A}\sim3$) and virial parameter ($α_\mathrm{vir}\sim0.5$). All three simulations include stellar feedback in the form of protostellar JETs/outflows and accretion heating. We find that the STAR FORMATION rate per freefall time ($\mathrm{SFR_{ff}}$) for the $M=10$ model is higher by a factor of $\sim3$ compared to the $M=2.5$ and $5$ cases, which have similar $\mathrm{SFR_{ff}}$. In terms of the IMF, the $M=5$ and $10$ models produce almost similar distributions, resembling typical observed IMFs. The $M=2.5$ model, on the other hand, produces a bimodal IMF with a primary peak at supersolar masses ($\sim 2\, \mathrm{M_\odot}$) and a secondary peak in the substellar regime ($< 0.1\, \mathrm{M_\odot}$). The $M=2.5$ and $5$ simulations producing significantly different IMFs while having similar $\mathrm{SFR_{ff}}$, suggest that a distinct set of physical processes governs the SFR and IMF. Through a resolution study for the $M=2.5$ case, we find our base models have reached near numerical convergence, potentially only slightly underestimating close-binary formation. We also see signatures of bimodality in the $M=2.5$ model for the multiplicity fraction and stellar angular momentum distribution.

[abstract 18 / 35] (score: 3)
arXiv:2609.40166 [pdf, ps, other]

Title: Axion corrections to photon superradiant scattering by Kerr BLACK HOLEs

Authors: Zhi-Qing Zhu, Jun Zhang,

Comments: 13 pages, 6 figures

Subjects: gr-qc

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We study photon superradiant scattering by a Kerr BLACK HOLE in the presence of an axion-photon coupling and investigate how this coupling modifies the electroMAGNETic amplification factor. We solve the coupled axion and electroMAGNETic equations in a fully RELATIVISTIC framework. We distinguish two regimes according to the relation between the sourced axion frequency and the axion mass. In the radiative regime, the axion can propagate to spatial infinity and carry away energy, thereby suppressing photon amplification. In the subthreshold regime, the axion is confined by the mass barrier and exchanges energy with the black-hole horizon through quasibound-state excitations. In this regime, photon amplification can be either enhanced or suppressed, depending on whether the relevant axion modes satisfy the superradiance condition.

[abstract 19 / 35] (score: 2)
arXiv:2606.18081 [pdf, ps, other]

Title: The Chirp-Mass Ladder: A New Rung Emerges

Authors: Vaibhav Tiwari,

Comments:

Subjects: astro-ph.HE

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

We study the binary BLACK HOLE (BBH) population observed through gravitational waves (GWs) using 256 events from the latest release of GWTC-5.0. The inferred chirp-mass distribution shows prominent peaks at approximately $7.5M_{\odot}$, $14M_{\odot}$, and $27M_{\odot}$, with subsequent peaks spaced by approximately a factor of two. A parsimonious explanation for this structured distribution is a hierarchical merger scenario, in which the first peak arises from mergers of BLACK HOLEs of stellar origin, and higher-mass peaks arise from repeated mergers. Notably, with the addition of new observations, an intermediate peak near $19M_{\odot}$ emerges. This feature was anticipated in earlier work as a consequence of intergenerational mergers involving second- and third-generation (G) BLACK HOLEs, highlighting the predictive expectations of the hierarchical-merger interpretation. Furthermore, two groups of $1G+2G$ mergers recently reported in separate studies can be understood as distinct rungs---$1G+2G$ and $3G+4G$---within this hierarchical chirp-mass ladder, a unification that describes both spin transitions with a single mechanism. Although we observe expected correlations between mass ratios and spins in multiple events across the mass range, the lack of clear signatures across all rungs invites investigation into the role of hierarchical mergers in shaping the BBH population.

[abstract 20 / 35] (score: 2)
arXiv:2606.21087 [pdf, ps, other]

Title: Wave-Energy Partition Governs Weak Collisional Damping in Cold Plasmas

Authors: Yanzeng Zhang, Xingming Zeng, Xianzhu Tang, Ge Zhuang,

Comments:

Subjects: physics.plasm-ph

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Weak dissipation can control wave propagation, mode competition, and instability thresholds in plasmas, yet the physical origin of large branch-to-branch differences in collisional damping is often obscured by dielectric-tensor calculations. We show that weak collisional damping in cold plasmas is governed by wave-energy partition. In the one-rate cold-plasma model, the damping rate of a collisionless eigenmode is exactly the collision frequency multiplied by the fraction of the total wave energy stored in plasma motion. This result recasts the standard perturbative damping formula into a compact and physically transparent law, immediately explaining why field-dominated branches such as whistlers can be much less damped than the collision frequency, whereas quasi-electrostatic modes can exhibit damping of comparable magnitude. Analytic examples for Langmuir, transverse electroMAGNETic, whistler, and extraordinary waves show that the energy-partition form classifies weak collisional damping across distinct branches and provides a simple diagnostic for mode competition in multibranch plasma-wave systems.

[abstract 21 / 35] (score: 2)
arXiv:2607.05508 [pdf, ps, other]

Title: Radiation-hydrodynamics of star-disc collisions: From system parameters to outflows and lightcurves

Authors: Taj Jankovič, Sergey Karpov, Michal Zajaček, Vladimír Karas, Marzena Śniegowska,

Comments: Accepted in A&A

Subjects: astro-ph.HE astro-ph.SR

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Quasi-periodic eruptions (QPEs) are nuclear transients producing bright, repeating soft X-ray flares superimposed on quiescent emission. A promising interpretation is that they are powered by star-disc collisions, in which a star crosses an accretion disc around a supermassive BLACK HOLE, drives shocks, and launches dense outflows from which radiation emerges. We present a systematic study of star-disc collisions, linking the physical parameters of the collision to the resulting outflows and emerging bolometric luminosities. We perform three-dimensional local radiation-hydrodynamics simulations, varying the disc surface density and vertical density profiles, stellar velocity and radius, and local collision angle. We focus on the regime where the star remains unperturbed by the collision. We find that variations in stellar velocity and accretion disc surface density leave the bow shock and outflow morphology largely unchanged. Faster stars produce brighter flares, while denser discs mainly increase the flare duration. Increasing the stellar radius increases the momentum of the forward outflow and produces brighter and longer flares. More centrally concentrated discs yield brighter and shorter flares because radiation escapes more efficiently through outer low-density layers. More oblique crossings reduce the momentum and luminosity asymmetry of two outflows, and lengthen the flares. We provide empirical scalings of the peak luminosity and flare duration with the individual system parameters and apply them to GSN 069. The best candidate solutions favour a star with a radius $\sim R_\odot$ on a retrograde orbit, colliding with a dense post-TDE disc with a vertically concentrated density profile. Our findings suggest that specific combinations of system parameters can reproduce characteristic flare amplitudes, durations, duty cycles, and strong-weak flare patterns observed in QPE sources.

[abstract 22 / 35] (score: 2)
arXiv:2608.30455 [pdf, ps, other]

Title: Magnetizing nonlinear plasma wakefields for positron acceleration

Authors: Yung-Kun Liu, Pisin Chen, Ching-En Lin, Spencer Gessner, Bernhard Hidding,

Comments: 6 pages, 4 figures; companion paper: arXiv:2609.33175

Subjects: physics.acc-ph physics.plasm-ph

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

It is known that only a narrow plasma wakefield sliver in the electron-beam-driven blowout regime suits positron acceleration. Using 3D simulations, we show that matching the cyclotron frequency $ω_{c}$ with the plasma frequency $ω_{p}$ forms a stable electron column on axis, expanding the suitable phase space for positron acceleration sizably. For a plasma density $n_p = 10^{16}\text{ cm}^{-3}$ in a 35 T field, the interval expands 4.3 times, and a witness positron beam gains 100--150 MeV over 6 cm ($1.6$--$2.5$~GeV/m) with a 92\% capture rate.

[abstract 23 / 35] (score: 2)
arXiv:2609.09767 [pdf, ps, other]

Title: Connecting Dynamo Theory with DNS Data: A Computational Analysis of $α$ and $β$ effects

Authors: Kiwan Park,

Comments: 26p, IDL analysis code in Appendix

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

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We investigate the influence of current helicity on the turbulent MAGNETic diffusivity $β$ using three complementary derivations of the $α$ and $β$ coefficients, based on the large-scale MAGNETic field $\overline{\mathbf{B}}$, the turbulent velocity $\mathbf{u}$, and the turbulent MAGNETic field $\mathbf{b}$. Applying these coefficients to raw DNS data, we reconstruct $\overline{\mathbf{B}}$ and compare the results with the original simulations. In the kinematic regime all models agree well with the DNS data. In the nonlinear regime, however, $β_{\mathrm{vv-vw}}$ alone produces unbounded growth of $\overline{\mathbf{B}}$. Including the contribution from turbulent MAGNETic fields ($β_{\mathrm{bb+jb}}$) suppresses this unphysical growth and restores agreement with the DNS results. We find that kinetic helicity drives $β$ more negative, while current helicity shifts it back toward zero. Weighted combinations of the coefficients further show that the $β$ effect dominates the evolution of $\overline{\mathbf{B}}$ throughout, whereas the $α$ effect becomes important mainly for sustaining the field in the nonlinear regime. The corresponding IDL analysis scripts are provided to facilitate practical implementation of the theoretical models.

[abstract 24 / 35] (score: 2)
arXiv:2609.31324 [pdf, ps, other]

Title: A statistical hardness classification of ultraluminous X-ray sources using long-term SWIFT/XRT monitoring

Authors: Sinan Allak, Wei Yu, Menglei Zhou, Honghui Liu, Andrea Santangelo,

Comments: Accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.HE

Created: 2026-09-25; Updated: 2026-10-01; Datestamp: 2026-10-01

We characterize long-term hardness behavior in 29 ultraluminous X-ray sources (ULXs) using over 3500 archival SWIFT/XRT observations. We classify observations as soft-band dominated, hard-band dominated, or uncertain from the hardness ratio (HR; 1.5--10/0.3--1.5 keV count rates) and its confidence bounds. We derive $f_{\rm soft}$ and $f_{\rm hard}$ and define the Crossing Index (CI) as the fraction of consecutive confidently classified observations on opposite sides of $HR=1$. We analyze these descriptors with rule-based classification and unsupervised hierarchical clustering. The rule-based analysis identifies eight soft-band-dominated, five hard-band-dominated, and 16 mixed-band systems; clustering yields a similar three-group structure. Known or candidate accretor types tend to occupy band-dominated groups, whereas unknown accretors are more common in the mixed-band group. All four sources with reported long-term X-ray modulation discussed in an orbital or super-orbital context are classified as mixed-band. The three-cluster solution is preferred in 25 of 29 leave-one-out trials, while bootstrap tests find the band-dominated groups more stable than the mixed-band group. As the classification uses observed count rates, the groups represent SWIFT/XRT signatures rather than intrinsic spectral states. Response-folding tests show that modeled HR depends on absorption column density and photon index. Bayesian reanalysis of a representative low-count source reduces CI from 56.3\% to 38.5\% while preserving its mixed-band classification. Random downsampling produces no systematic shift in CI; halving the observations changes median CI by at most $\sim10\%$ across four sources. Larger samples with independent absorption constraints can test links among these observational classes, accretor type, long-term periodic modulation, and other X-ray properties.

[abstract 25 / 35] (score: 2)
arXiv:2609.38344 [pdf, ps, other]

Title: VLBI Astrometric Procedure and Performance with CHIME/FRB Outriggers

Authors: Shion Andrew, Mattias Lazda, Calvin Leung, Kiyoshi W. Masui, Danté M. Hewitt, Jacob Willis, Alyssa Atkinson, Kevin Bandura, Shami Chatterjee, Nina V. Gusinskaia, Adam E. Lanman, Juan Mena-Parra, Kenzie Nimmo, Aaron B. Pearlman, Ziggy Pleunis, Alexander W. Pollak, Gurman Sachdeva, Vishwangi Shah,

Comments: Submitted to ApJ

Subjects: astro-ph.HE astro-ph.IM

Created: 2026-09-29; Updated: 2026-10-01; Datestamp: 2026-10-01

Precise localizations of fast radio bursts (FRBs) to specific environments within their host galaxies with very-long-baseline interferometry (VLBI) have provided valuable insights into the nature of their progenitors. To date, such localizations have relied primarily on traditional VLBI facilities, whose observational capabilities limit them to targeted follow-up on a small subset of repeating FRBs that are observable at frequencies above $\sim$1 GHz. CHIME/FRB Outriggers is a low-frequency (400--800 MHz), wide-field VLBI network designed to overcome these limitations, aiming to localize a substantial fraction of CHIME-detected FRBs to $\sim$50 mas precision. In this work, we detail the analysis procedure used to localize FRBs with the CHIME/FRB Outriggers VLBI array. With over a thousand test localizations consisting of continuum calibrators and pulsars with known VLBI positions, we provide a comprehensive demonstration of the VLBI array's ability to robustly meet, and under some conditions exceed, the nominal astrometric specification required for the central science goals of CHIME/FRB Outriggers. By demonstrating that a wide-field survey instrument can deliver routine $\sim$50 mas astrometry on one-off FRBs, this work lays the foundation for the upcoming generation of wide-field VLBI FRB surveys and the population-scale FRB samples they will enable.

[abstract 26 / 35] (score: 2)
arXiv:2609.38682 [pdf, ps, other]

Title: New Constraints on $r$-process Nucleosynthesis in Neutron Star Mergers from GW170817 Late-Phase Spectra

Authors: Salma Rahmouni, Masaomi Tanaka, Daiji Kato, Gediminas Gaigalas, Kenta Hotokezaka,

Comments: 25 pages, 12 figures, 3 tables, accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The neutron star merger event GW170817 provided the first direct evidence of $r$-process nucleosynthesis. Observed spectra of its electroMAGNETic counterpart AT2017gfo exhibited several features that encode information on the nature and abundance of the synthesized $r$-process elements. In this study, we investigate the late nebular-phase spectral features of AT2017gfo, which provide important probes of the elemental abundance of the ejecta. We construct an analytic spectral model that computes emission features produced by the radiative decay of collisionally excited ions through allowed and forbidden transitions. By comparing our model to AT2017gfo, we identify La III and Ce III as the main contributors to the emission features at $1.4\,μ{\rm m}$ and $1.6\,μ{\rm m}$, respectively. We also confirm Te III as the dominant contributor to the $2.1\,μ{\rm m}$ feature proposed in previous works. We infer mass fractions of $X({\rm La})\approx 0.025-0.05$, $X({\rm Ce})\approx 0.05-0.1$, and $X({\rm Te})\approx 0.04-0.08$, although the La and Ce abundance estimates remain tentative due to uncertainties in the radiation field. From the non-detections of Kr and Sb lines, we derive upper limits of $X({\rm Kr})\lesssim 0.03$ and $X({\rm Sb})\lesssim 0.003$. These results suggest that nucleosynthesis in the inner ejecta of GW170817 produced a suppressed first $r$-process peak and an enhanced heavy-element abundance compared to the solar $r$-process pattern, with an estimated lanthanide fraction of $X_{\rm LN}\approx (3-6) \times 10^{-2}$. Our conclusions are consistent with the apparent universality of heavy $r$-process elements and the lanthanide fraction inferred from observations of $r$-enhanced metal-poor stars.

[abstract 27 / 35] (score: 2)
arXiv:2609.38774 [pdf, ps, other]

Title: Magnetic field diagnostics of a solar active region filament

Authors: Daiki Yamasaki, Yu Wei Huang, Yuki Hashimoto, Satoru UeNo, Kiyoshi Ichimoto,

Comments: 14 pages, 13 figures, and 5 tables. Accepted for the Publications of the Astronomical Society of Japan

Subjects: astro-ph.SR

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We performed spectropolarimetric observations of an active region filament in He I 10830 angstrom and Si I 10827 angstrom lines to investigate its MAGNETic field structure. We carried out full-Stokes inversions with the HAZEL code, which takes into account the Zeeman and Hanle effects. As a result, we yielded a mean field strength of 101 $\pm$ 33 G and a horizontal field nearly parallel to the filament axis, such that the distinction between the two classical normal- and reverse-polarity models becomes physically insignificant. In addition, we found Zeeman-like signatures in the linear POLARIZATION, characterized by double-peaked symmetric profiles, in some pixels of our observations. Since these profiles could not be well reproduced by modeling that included both the Zeeman and Hanle effects, we performed inversions assuming only the Zeeman effect. The inversion yielded a strong MAGNETic field of approximately 500 G. However, simultaneous observations of Si I 10827 angstrom indicate a photospheric MAGNETic field weaker than 100 G. Therefore, the scenario proposed by Diaz Baso et al. (2016), in which the strong field inferred from He I 10830 angstrom originates from contamination by the underlying photosphere, does not apply to our filament. The Zeeman-like profiles are preferentially found in optically thick regions ($τ$ ~ 1.4-2.5), where the simplifying assumptions adopted in HAZEL are expected to become less reliable. Our results suggest that these profiles reveal limitations of the current inversion framework in optically thick regions and motivate future radiative-transfer modeling incorporating self-consistent radiation fields, differential illumination of the multiplet components, and possibly partial frequency redistribution.

[abstract 28 / 35] (score: 2)
arXiv:2609.39036 [pdf, ps, other]

Title: The "Fork" Geometry in the DESI Main Survey DR1: Implications of Target Selection for Galaxy Evolution Studies

Authors: A. Nigoche-Netro, P. Lagos, R. J. Diaz, E. García-Manzanárez, J. A. Quezada-Pérez, R. Ibarra-Nuño,

Comments: 24 pages, 35 figures. AJ. Accepted

Subjects: astro-ph.GA

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The Dark Energy Spectroscopic Instrument (DESI) Main Survey Data Release 1 (DR1) provides an unprecedented spectroscopic view of galaxies and QUASARs across a large fraction of the observable Universe. However, the survey's tracer-dependent targeting strategy introduces complex observational selection effects that strongly influence the apparent distribution of galaxies in the redshift-luminosity plane. In this work, we investigate the origin of the characteristic "fork" geometry observed in DESI DR1 and show that the observed distribution is consistent with an interpretation in which it arises from the combined action of intrinsic galaxy bimodality and the survey's redshift-dependent selection function. We show that the observed underdensity separating the dominant galaxy populations is influenced not only by the physical Green Valley but also by survey selection effects, since it is further shaped by magnitude limits, surface-brightness selection, and structural incompleteness. Using DESI DR1 spectroscopy together with Legacy Survey photometry, we analyze the roles of the BGS, LRG, ELG, and QSO target classes in producing the observed distribution and assess their impact on luminosity-function measurements. Our results indicate that both target selection and observational biases significantly affect the observed galaxy distribution and the evolutionary trends inferred from it. We summarize practical observational considerations aimed at minimizing these effects and enabling more robust studies of galaxy evolution with DESI.

[abstract 29 / 35] (score: 2)
arXiv:2609.39208 [pdf, ps, other]

Title: Probing Helical Primordial Magnetic Fields via Chiral Gravitational Waves in the LISA-TAIJI Network

Authors: Kazuya Furusawa, Hiroyuki Tashiro,

Comments: 25 pages, 5 figures

Subjects: astro-ph.CO gr-qc

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Primordial MAGNETic fields (PMFs) are anticipated to be a cosmological candidate for generating a stochastic gravitational wave background (SGWB) through their anisotropic stress. In particular, if parity violation is present in the production of PMFs, it can induce a helical component in the PMFs, leading to circular POLARIZATION in the isotropic SGWB. In this study, we phenomenologically consider parity-violating inflationary MAGNETogenesis and compute the intensity and circular POLARIZATION of the SGWB for several assumed power spectra of helical PMFs. Using the planned sensitivity of the LISA-TAIJI network, we calculate the signal-to-noise ratio (SNR) and perform a Fisher forecast to assess the feasibility of constraining the parameters of helical PMFs. We conclude that it is possible to estimate the helical-to-non-helical power ratio~$r_H$ with $\mathrm{SNR}^{V}>2$ if the PMF strength is $\mathcal{B} \gtrsim 10~\mathrm{nG}$ ($50~\mathrm{nG}$) in the case of the delta-function-type (scale-invariant-type) PMF spectrum. Our results offer a useful criterion that indicates the future observational limit on helical PMFs at the small scale $k_\mathrm{LISA} \approx 10^{12}~\mathrm{Mpc}^{-1}$.

[abstract 30 / 35] (score: 2)
arXiv:2609.39376 [pdf, ps, other]

Title: Phase-Space Non-Integrability of Alpha Particles in Near-Omnigeneous Stellarators

Authors: A. L. Lachmann, A. R. Knyazev, E. J. Paul,

Comments:

Subjects: physics.plasm-ph

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

In a burning plasma, fusion-born alpha particles sustain the fusion reaction by heating the plasma core. Alpha-particle confinement in stellarators is sensitive to both deviations from omnigeneity and time-dependent Alfvénic perturbations. Traditional Poincaré maps rely on symmetry assumptions or dimensionality reductions that fail for stellarators with quasisymmetry (QS) error or multi-harmonic Alfvénic perturbations. To address these challenges, we investigate weighted Birkhoff averaging (WBA) as a diagnostic to detect the onset of chaos in guiding-centre trajectories subject to general MAGNETic perturbations. WBA exploits the super-convergence of time averages along quasiperiodic orbits, discriminating regular from chaotic trajectories using any smooth observable rather than an exact invariant of motion. Applying WBA to the canonical momentum $P_η$, we show that convergence tracks underlying orbit regularity even when quasisymmetry is imperfect and $P_η$ is not strictly conserved. Convergence is measured by the digit accuracy of the weighted average along guiding-centre orbits in fields with imperfect omnigeneity, with and without Alfvén eigenmodes computed using AE3D. We use this diagnostic to map phase-space chaos as a function of equilibrium invariants to identify transport barriers in unperturbed and perturbed stellarator equilibria. This work demonstrates that chaos induced by many Alfvén harmonics is often not apparent from the largest harmonic alone. We also find evidence that the onset of chaotic behaviour is sensitive to the local radial profile of the wave and not only to its amplitude at the resonance.

[abstract 31 / 35] (score: 2)
arXiv:2609.39399 [pdf, ps, other]

Title: The impact of primordial MAGNETic fields on the formation of galaxies

Authors: Yao-Yu Li, Shihong Liao, Yue-Lin Sming Tsai, Yi-Zhong Fan,

Comments: 23pages, 12figures, Accepted for publication in Physical Review D

Subjects: astro-ph.GA astro-ph.CO

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

Primordial MAGNETic fields (PMFs), potentially generated during cosmic inflation or early-universe phase transitions, can modify cosmic structure formation by enhancing the post-recombination matter power spectrum. In this work, we investigate the impact of PMFs on galaxy formation using a suite of high-resolution cosmological hydrodynamical simulations evolved to $z=0$. Our simulations are initialized with PMF-induced enhancements to the matter power spectrum and include more comprehensive baryonic subgrid models than previous work, incorporating both stellar and AGN feedback. We find that PMFs systematically accelerate early structure formation, producing more abundant halos and galaxies, higher baryon fractions, enhanced STAR FORMATION rates, and rapid growth of supermassive BLACK HOLEs at high redshifts ($z \sim 10$). However, the resulting enhanced stellar and AGN feedback efficiently processes and expels gas, reducing the late-time differences between PMF and standard $Λ$CDM models. The PMF signatures are therefore strongest at high redshift and gradually weaken toward low redshift as nonlinear evolution and baryonic feedback dominate over the initial PMF-induced enhancements. The impact of PMFs depends strongly on the characteristic peak scale, $k_{\rm peak}$, of the initial power enhancement, with models yielding similar non-linear evolution if they share a similar $k_{\rm peak}$, even when other PMF parameters differ. Our results highlight the critical role of comprehensive baryonic physics in accurately quantifying PMF signatures.

[abstract 32 / 35] (score: 2)
arXiv:2609.39428 [pdf, ps, other]

Title: Correlating Surface Magnetic Field Decay with Internal Field Depth of Isolated Neutron Stars

Authors: Kathleen Sellick, Subharthi Ray,

Comments: 9 pages, 13 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

Subjects: astro-ph.HE

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The long-term evolution of neutron star crustal MAGNETic fields through Ohmic decay is governed by the transport properties of the crust. In this work, we demonstrate that the depth at which the MAGNETic flux is anchored plays a significant role in the dissipation timescale. We study the evolution of the MAGNETic field at the surface of the neutron star due to the crustal field evolution, under the assumption of Ohmic diffusion in a curved spacetime. We employ a cumulative distribution function to parameterise the initial current distribution and explore the effects of varying the equation of state and crustal impurity. We compare results across three neutron star models representing varying degrees of compactness. We find that MAGNETic fields anchored deeper within the inner crust experience negligible decay over timescales up to $10^{10}$ years. Significant field evolution, necessary to explain the deficit of high-field pulsars at advanced ages, is possible if the MAGNETic currents are confined to the shallow outer crust. This result holds true regardless of the impurity concentration or the specific geometric thickness of the crust determined by the equation of state.

[abstract 33 / 35] (score: 2)
arXiv:2609.39515 [pdf, ps, other]

Title: Probing JET quenching via the correlation of groomed JET substructure observables in Pb$-$Pb and pp collisions

Authors: ALICE Collaboration,

Comments: 26 pages, 7 captioned figures, authors from page 21, submitted to Journal of High Energy Physics, figures at http://alice-publications.web.cern.ch/node/13655

Subjects: nucl-ex hep-ex

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

A measurement of the correlation between the splitting angle $θ_{\rm g}$ and the momentum-sharing fraction $z_{\rm g}$ of the first hard splitting in a parton shower in pp collisions and 0$-$10% central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5 TeV with the ALICE detector is reported. Charged-particle JETs are reconstructed using the anti-$k_{\rm T}$ algorithm with a JET resolution parameter $R$ = 0.2, in the transverse-momentum range $60 \leq p_{\rm T,ch\;JET} < 80$ GeV/$c$. The Soft Drop grooming algorithm is used to identify the first splitting in the parton shower. Jets observed in Pb$-$Pb collisions are narrower than in pp collisions. This effect is more pronounced for balanced than for unbalanced JETs. No significant modification of the momentum-sharing fraction is observed for JETs with small opening angles. In contrast, there is a hint that JETs with a large opening angle may be less balanced in transverse momentum in Pb$-$Pb collisions compared to pp collisions. The correlations between $θ_{\rm g}$ and $z_{\rm g}$ are well described in pp collisions by PYTHIA 8 and POWHEG while HERWIG shows too few JETs with large opening angle. In Pb$-$Pb collisions the measurement is compared to a variety of models. The measurement is insensitive to the different implementations of medium response. Inclusion of elastic scatterings, as implemented in the HYBRID model is preferred to describe the unbalanced JETs with large $θ_{\rm g}$ in Pb$-$Pb collisions. The balanced JETs, however, are less sensitive to elastic scatterings.

[abstract 34 / 35] (score: 2)
arXiv:2609.39746 [pdf, ps, other]

Title: Generalised Mixing-Plane Method for Compressible Reacting-Mixture Flows in Steady Multiphysics Turbomachinery Simulations

Authors: Yifeng Wang, Lin Shi, Fenglai Huang, Rui Wang, Feng Wang, Hui Xu,

Comments:

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

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

The mixing-plane method plays a pivotal role in steady simulations of multiple turbomachinery components. With advances in computational power, a whole-engine gas turbine simulation is no longer an elusive approach. However, whole-engine simulations require simultaneous coupling of the compressor, turbine and combustor. A key challenge is that the working fluid after the combustor can no longer be treated as a perfect gas, since the combustion introduces composition variations and combustion products. Conventional mixing-plane methods based on a fixed-composition gas cannot guarantee a thermodynamically consistent mixed-out state. To overcome the difficulty, this paper extends the classic mixing-plane approach to handle compressible reacting flows. The nonlinearity in the thermodynamic closure is addressed using a novel nested algorithm combining an outer pressure-root search with an inner enthalpy inversion. Physical state checks and power-law pressure sampling are incorporated to improve numerical robustness at low normal velocities where the pressure root approaches its upper physical bound. The performance of the method is demonstrated in three configurations: a quasi-1D interface test elucidating the thermodynamic stiffness of the proposed mixing-plane formulation for different fuel types and flow conditions; the Darmstadt transonic compressor case that verifies the proposed method reduces to the classic mixing-plane formulation when the mixture fraction reduces to zero; and a whole-engine simulation of the KJ66 micro-turboJET is used to demonstrate the performance of the method for multiphysics turbomachinery simulations. Good agreement with experimental data is observed, and the maximum relative mass-flow error across the mixing planes remains below 0.11%, demonstrating conservative and thermodynamically consistent interface coupling for compressible reacting turbomachinery flows.

[abstract 35 / 35] (score: 2)
arXiv:2609.39864 [pdf, ps, other]

Title: Testing charged bumblebee BLACK HOLEs through high-frequency quasi-periodic oscillations in X-ray binaries

Authors: Qi-Qi Liang, De-Jiang Yin, Zi-Qiang Cai, Zheng-Wen Long,

Comments:

Subjects: gr-qc

Created: 2026-09-30; Updated: 2026-10-01; Datestamp: 2026-10-01

We investigate strong-field orbital dynamics for static spherically symmetric charged bumblebee BLACK HOLEs featuring spontaneous Lorentz-violating effects. Analysis of null and timelike circular geodesics yields the photon-sphere radius, the innermost stable circular orbit (ISCO) radius, and characteristic orbital frequencies for test particles. Within the RELATIVISTIC precession model for high-frequency quasi-periodic oscillations (HFQPOs), observed twin-peak frequencies are governed by the full set of fundamental parameters $M$, $X=r/M$, $l_1$, $l_2$, and $Q_0/M$. Among them, $l_1$, $l_2$, and $Q_0/M$ enter frequency expressions only in combined forms, giving rise to intrinsic parameter degeneracy. An effective-parameter set $Θ=(M,X,C,β)$ is accordingly introduced to characterize these composite contributions. Bayesian MCMC parameter inference is carried out using HFQPO observational data from three black-hole X-ray binaries: GRO J1655--40, XTE J1550--564, and GRS 1915+105. The 68\% credible intervals of composite parameter $C$ all contain the Reissner--Nordström limit $C=1$, revealing no statistically significant net Lorentz-violating correction under our model assumptions. Distinct triples $(l_1,l_2,Q_0/M)$ yield identical QPO predictions, so HFQPO observations alone cannot disentangle Lorentz-violating and charge-related effects; precise constraints on these fundamental quantities require additional, more precise observational data.