Current date: 2026-04-22

Setting default datestamp limit: 0

Datestamp limit: 2026-04-22 (0 days ago)

Created/updated limit: 2026-04-15 (7 days ago)

Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics

Setting default set: physics

OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-04-22&until=2026-04-22&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 673

Keyword score statistics

score 7 -- 1 abstracts

score 6 -- 1 abstracts

score 5 -- 2 abstracts

score 4 -- 3 abstracts

score 3 -- 6 abstracts

score 2 -- 14 abstracts

in total -- 27 abstracts

Articles that appeared on 2026-04-22

[abstract 1 / 27] Wow! (score: 7)
arXiv:2604.19435 [pdf, ps, other]

Title: SDSSJ110546.07+145202.4: The first long-duration radio changing-look NLS1 galaxy

Authors: S. Komossa, D. Grupe, A. Kraus, P. G. Edwards, E. F. Kerrison, K. Rose, R. Soria, T. An, M. J. Hardcastle, K. E. Gabanyi, S. Panda, D. W. Xu, J. Wang, S. Frey, A. Mezosi,

Comments: 20 pages, accepted for publication in ApJ

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

SDSSJ110546.07+145202.4 stands out as a unique radio changing-look Narrow-line Seyfert 1 (NLS1) galaxy that has brightened dramatically and shows an exceptionally long duration of its "on" phase. We present the first high-frequency radio observations, the first simultaneous radio spectral energy distributions (SEDs), the first optical--UV--X-ray SEDs, and the first X-ray monitoring and spectroscopy of this recently discovered event. Importantly for understanding the nature of the outburst, we show that the X-ray spectrum is soft with a photon index Gamma_X=2.5; line-of-sight absorption and extinction are low or absent; the radio SED is peaked at low frequencies ~2 GHz; and the radio outburst emission is very long-lived (t > 8 yr) and roughly constant. The softness of the X-ray spectrum, low supermassive BLACK HOLE (SMBH) mass, and high Eddington ratio all corroborate the optical NLS1 classification. We discuss multiple outburst scenarios, including lensing, absorption, a binary SMBH merger, a long-duration giant-star tidal disruption, a newly ignited ACTIVE GALACTIC NUCLEus (AGN), and an accretion-rate change. While most of them can be either excluded or are deemed too rare and lack positive evidence so far, most or all types of these transients are expected to be detected in ongoing VLA and upcoming SKA surveys. SDSSJ110546.07+145202.4 itself is well explained by an accretion rate change that triggered the powerful radio JET emission. The low redshift and SMBH mass of this system offer a unique perspective of the physical processes of radio-JET ignition that are expected to operate in the early Universe around growing SMBHs.

[abstract 2 / 27] Yes (score: 6)
arXiv:2510.27399 [pdf, ps, other]

Title: Simulating the late stages of WD-BH/NS mergers: an origin for fast X-ray transients and GRBs with periodic modulations

Authors: Jun-Ping Chen, Rong-Feng Shen, Jin-Hong Chen, Wei-Hua Lei,

Comments: 17 pages, 11 figures, submitted to ApJ, revised version after the reviewer's report

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Recent studies indicate that mergers of a white dwarf (WD) with a neutron star (NS) or a stellar-mass BLACK HOLE (BH) may be a potential progenitor channel for certain merger-kind, but long-duration $γ$-ray bursts (GRBs), e.g., GRBs 230307A and 211211A. The relatively large tidal disruption radius of the WD can result in non-negligible residual orbital eccentricity ($0 \lesssim e \lesssim 0.2$), causing episodic mass transfer, i.e., repeated tidal disruptions (RPDs) of the WD. We perform smoothed-particle-hydrodynamics simulations of RPDs in sixteen WD-BH/NS systems, capturing the subsequent mass transfer and accretion. The WD undergoes RPDs near the orbital periastron, modulating the ensuing accretion process, leading to variations of the accretion rate on the orbital period. Across all simulations, the peak accretion rates range from $4 \times10^{-4}$ to 0.2 $M_{\odot} \rm \ s^{-1}$, while the RPD duration spans from $\sim$ 10 s to an hour. More compact systems, i.e., those with a higher mass ratio (higher WD mass and lower accretor mass), tend to undergo fewer RPD cycles, resulting in shorter durations and higher accretion rates. If such events can launch RELATIVISTIC JETs, three categories of non-thermal X/$γ$-ray transients are predicted, in decreasing order of their mean accretion rates: (1) an X-ray transient with a simultaneous GRB, both lasting for $10^{1-2}$ s; (2) a longer X-ray transient lasting up to $10^{2-3}$ s that has a GRB appearing only at its later phase ; (3) an ultra-long X-ray transient lasting for $\sim 10^{3}$ s without a GRB. A generic feature of these transients is that their prompt emission light curves are probably periodically modulated with periods of a few to tens of seconds.

[abstract 3 / 27] Yes (score: 5)
arXiv:2604.18950 [pdf, ps, other]

Title: Very Long Baseline Interferometry Search for Nuclear Radio Continuum Emission in the Barred Spiral Galaxy NGC 7479

Authors: Seppo Laine, Emmanuel Momjian, Emilia Järvelä, Thomas P. Krichbaum, S. Komossa, Travis C. Fischer, Thomas G. Pannuti,

Comments: 20 pages, 6 figures, 2 tables. Accepted for publication in AJ

Subjects: astro-ph.GA

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We have obtained very high angular resolution (a few milliarcseconds or sub-parsec scale) Very Long Baseline Array (VLBA) and European Very Long Baseline Interferometry (VLBI) Network (EVN) radio continuum images of the nucleus in the barred spiral galaxy NGC 7479, to search for possible nuclear emission on parsec scales. The observations were taken using phase referencing. Previous Karl G. Jansky Very Large Array (VLA) and Multi-Element Radio Linked Interferometer Network (MERLIN) observations revealed a large JET-like structure, apparently emanating from the nucleus, and unresolved nuclear emission at 0.1 arcsecond (about 15 pc at the assumed distance of 32 Mpc) scale, respectively. Our sensitive new VLBA and EVN images resolve the previously unresolved nuclear source and reveal two distinct emission regions (VLBI components) that are separated by about 30 milliarcseconds. We also report an apparent change in separation of the two main emission regions over the ten years between EVN and VLBA observations, implying RELATIVISTIC radio JET motion or changes in shock illumination of gas by a nuclear wind. We measure the spectral indices and brightness temperatures of the VLBI components, and discuss possible physical causes of the observed emission.

[abstract 4 / 27] Yes (score: 5)
arXiv:2604.19210 [pdf, ps, other]

Title: VLTI-GRAVITY observations of BLAZARs

Authors: Talvikki Hovatta, Elina Lindfors, Heidi Korhonen, Preeti Kharb, Markus Wittkowski, Aaron Labdon, Tapio Pursimo, Kaj Wiik,

Comments: Accepted for publication in A&A. 6 pages of main text with 4 figures

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Parsec-scale JETs of BLAZARs have so far been spatially resolved only in mm- and submm wavelengths, where very long baseline interferometry can be used to obtain milliarcsecond-scale images of the JETs. We have attempted to spatially resolve the near-infrared emission in JET-dominated BLAZARs for the first time. We used the VLTI-GRAVITY instrument to obtain milliarcsecond-scale near-infrared interferometric observations of a flaring BLAZAR Ton 599. Additionally, we observed four non-flaring BLAZARs using the GRAVITY-wide mode, where a nearby bright star is used as a fringe tracker. We modeled the squared visibilities of Ton 599, and find that they are incompatible with a single unresolved point source unless there is a significant amount of additional unknown coherence loss in the instrument. With the present data, we cannot distinguish between a model with an unresolved point source and extended emission or coherence loss and a model with a single Gaussian component. This suggests that we are seeing the unresolved or only partially resolved JET-base in near-infrared wavelengths. The wide-field mode of GRAVITY was challenging for the additional relatively faint targets resulting in either non detections or poor quality data that could not be modeled. Our observations demonstrate that it is possible to detect the compact JET emission in BLAZARs with near-infrared interferometry, suggesting that with the improved GRAVITY+ instrument it will be possible to spatially resolve and image the near-infrared emission of BLAZAR JETs.

[abstract 5 / 27] Yes (score: 4)
arXiv:2604.15575 [pdf, ps, other]

Title: Mechanism Behind the Recombination Requirement for Benign Termination of Relativistic Electron Beams

Authors: George Su, Carl Friedrich Benedikt Zimmermann, Carlos Paz-Soldan, Matthias Hoelzl, Pavel Aleynikov,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We present a first-principles explanation of the recombination requirement for benign termination of RELATIVISTIC electron (RE) beams in tokamaks. Kinetic modeling including neutrals shows that the injection of neutrals over a finite quantity window, together with recombination, increases bulk resistivity. Nonlinear MHD simulations using the JOREK code demonstrate that this preferentially amplifies edge tearing modes, producing a more stochastic edge MAGNETic field during RE deconfinement, resulting in a larger RE wetted area. We identify resistivity, not the free electron density, to govern access to benign termination. This provides the first broadly applicable and experimentally consistent picture of the MHD mechanisms behind the benign scenario, critical to its extrapolation to next-step devices.

[abstract 6 / 27] Yes (score: 4)
arXiv:2604.18787 [pdf, ps, other]

Title: System Size Dependence of Collisionless Reconnection Rate

Authors: Yi-Min Huang, Naoki Bessho, Li-Jen Chen, Judith T. Karpen, Amitava Bhattacharjee,

Comments:

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

Created: 2026-04-20; Updated: 2026-04-22; Datestamp: 2026-04-22

It is a widely accepted paradigm that collisionless MAGNETic RECONNECTion proceeds at a universal fast rate of $\sim0.1$ when normalized to a properly defined RECONNECTing MAGNETic field and Alfvén speed, effectively independent of the macroscopic system size. This conclusion, derived primarily from kinetic simulations of classical Harris current sheets with kinetic-scale thickness, stands in contrast to results from forced RECONNECTion and island coalescence, where the rate significantly depends on the system size. Here, we reconcile this disparity by performing a rigorous scaling study using both particle-in-cell and Hall MAGNETohydrodynamic simulations. We demonstrate that when the global MAGNETic configuration is self-consistently preserved by scaling the initial current sheet thickness proportionally with the system size, the ``universal'' fast rate disappears. Instead, the RECONNECTion rate decreases as the system size increases. These results indicate that dependence on macroscopic scales is not peculiar to specific geometries but is a fundamental property of collisionless RECONNECTion, effectively unifying the Harris sheet with other configurations exhibiting size-dependence.

[abstract 7 / 27] Yes (score: 4)
arXiv:2604.19534 [pdf, ps, other]

Title: The swept-back multipolar MAGNETic field of neutron stars: Application to NICER MSP J0030+0451

Authors: Anu Kundu, Constantinos Kalapotharakos, Zorawar Wadiasingh, Greg Olmschenk, Wendy F. Wallace, Alice K. Harding, Christo Venter, Demosthenes Kazanas,

Comments: 27 pages, 13 figures, 3 tables. Submitted. Comments are welcome

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

NICER observations of millisecond pulsars (MSPs) suggest that non-dipolar MAGNETic fields are required to explain their surface X-ray hotspots. C. Kalapotharakos et al. (2021) modeled the NICER light curve of MSP J0030+0451 (J0030) using a static vacuum offset dipole-plus-quadrupole field and corresponding force-free (FF) solutions to jointly reproduce the X-ray and FERMI-LAT $γ$-ray emission. We substitute their static vacuum field model with a more realistic swept-back configuration that accounts for rotational effects. This field more closely resembles the corresponding FF solutions, making it a more physically motivated choice for future multiwavelength modeling. We adopt a centered swept-back vacuum multipolar MAGNETic field (SVM2F; J. Pétri 2015), expressed as a complete expansion in vector spherical harmonics, enabling flexible descriptions of arbitrary MAGNETic field geometries. We introduce a metric to quantify the complexity among different field prescriptions, illustrated for the static offset vacuum field. To efficiently explore parameter space, we train a neural network surrogate (G. Olmschenk et al. 2025) on SVM2F light curves including components up to the octupole, accelerating Markov chain Monte Carlo sampling by $\sim 10^3$ compared to direct physical model evaluations. Applying this framework to J0030, we constrain the field parameter space and find that a centered swept-back multipolar field including terms up to the octupole adequately reproduces the bolometric thermal X-ray light curve. Our study highlights the importance and inherent complexity of prescribing different multipolar MAGNETic field models for rotating stars, and can be extended to other MSPs to ultimately constrain the masses and radii of neutron stars, and hence their equation of state.

[abstract 8 / 27] (score: 3)
arXiv:2604.16191 [pdf, ps, other]

Title: High-Frequency Gravitational Waves from the Galactic Pulsar Population

Authors: Anne S. Freise, Jamie I. McDonald, Kirill Riabtsev, Samuel J. Witte,

Comments: This manuscript was submitted without knowledge or consent of ASF, JIM, or SJW. In addition, content of manuscript was plagarised from draft of ASF, JIM, and SJW

Subjects: astro-ph.HE

Created: 2026-04-20; Updated: 2026-04-22; Datestamp: 2026-04-22

The high-frequency gravitational-wave band is often discussed primarily in the context of new physics, but realistic Standard-Model foregrounds remain incompletely characterized. We investigate pulsar polar caps as a physically motivated astrophysical source of high-frequency gravitational waves, generated by repeated discharge cycles in compact near-surface plasma gaps. Our baseline result is population-level: we construct the signal from the Galactic normal-pulsar population rather than from a single especially favorable object. To do so, we calibrate the source dynamics with particle-in-cell simulations performed at real physical scales, with physical pulsar parameters mapped directly onto numerical scales, and then lift the resolved longitudinal discharge to a cap-scale emission model. The gravitational-wave signal is computed in a full Fourier-space framework, retaining finite-source, geometric, and POLARIZATION effects explicitly. Within this treatment, the dominant contribution is not the purely electric channel emphasized in some earlier simplified approaches, but a source channel involving the large background MAGNETic field and discharge-induced transverse fluctuations of MAGNETic field. Integrating this description over a normal-pulsar population, we find an astrophysical foreground in the MHz-scale high-frequency band that can overlap with and partially obscure the thermal gravitational-wave signal sourced by the plasma of the early Universe. At the same time, the normalization remains sensitive to the modeled assumptions. Although the predicted strain remains far below current experimental sensitivity, pulsar polar caps provide a concrete Standard-Model foreground benchmark in a band often treated as nearly background-free. Alternative source configurations further broaden the plausible signal range around this baseline.

[abstract 9 / 27] (score: 3)
arXiv:2604.18735 [pdf, ps, other]

Title: Magnetic properties of the Abell 3391-3395 system revealed using wide-field MeerKAT polarimetry

Authors: V. Gustafsson, M. Brüggen, C. Tasse, S. P. O'Sullivan,

Comments:

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

Created: 2026-04-20; Updated: 2026-04-22; Datestamp: 2026-04-22

Magnetic fields in cluster outskirts and the intercluster medium are poorly constrained because diffuse SYNCHROTRON emission is hard to detect at low surface brightness. Faraday rotation measures (RMs) of polarized background sources can probe foreground large-scale structure. The nearby interacting Abell 3391-3395 system hosts a well-established X-ray bridge, making it an excellent target for studying MAGNETization in the intercluster environment. We characterize the MAGNETized environment of Abell 3391/95 and its surroundings by constructing a dense RM grid from wide-field polarimetry. We observed Abell 3391/95 with MeerKAT in full POLARIZATION using a three-pointing mosaic. The data were calibrated with direction-independent and direction-dependent techniques and imaged using visibility-plane mosaicing for a large field of view at high sensitivity. Using Faraday synthesis, we formed Faraday cubes and measured RMs for polarized background sources. We defined on- and off-target regions using contours from a wavelet-filtered eROSITA image. We identified 434 polarized sources within the field, with a polarized source density ranging from about 30 sources per square degree in the outer regions to about 110 sources per square degree in the central field, and a field-averaged density of 73 sources per square degree. The clusters show a statistically significant enhancement of RM scatter relative to the off-target region. In contrast, the bridge shows comparatively low RM scatter, while an RM structure-function analysis on matched angular scales yields a tentative indication of larger RM differences in the bridge than off-target. Combined with low per-source dePOLARIZATION, this suggests a bridge MAGNETic field relatively ordered on ~10 kpc scales, but less ordered on larger scales. The non-detection of diffuse SYNCHROTRON emission in the bridge yields improved upper limits on the emissivity.

[abstract 10 / 27] (score: 3)
arXiv:2604.18985 [pdf, ps, other]

Title: The Gamma-Ray Monitor onboard the SVOM satellite

Authors: Jian-Chao Sun, Yong-Wei Dong, Jiang He, Jiang-Tao Liu, Lu Li, Rui-Jie Wang, Xin Liu, Li Zhang, Min Gao, Yue Huang, Hao-Li Shi, Li-Ming Song, Wen-Jun Tan, Chen-Wei Wang, Jin Wang, Jin-Zhou Wang, Ping Wang, Xing Wen, Bo-Bing Wu, Shao-Lin Xiong, Juan Zhang, Shuang-Nan Zhang, Xiao-Yun Zhao, Shi-Jie Zheng,

Comments: 13 pages, 15 figures, 4 tables, SVOM special issue (RAA), accepted by RAA

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

The Gamma-Ray Monitor (GRM) is a key scientific payload onboard the Space-based Multi-band Variable Object Monitor (SVOM) satellite, designed specifically for the detection and study of GAMMA-RAY BURSTs (GRBs). Launched into a 625 km low-Earth orbit on 22 June 2024, GRM serves as a large-area, wide-field-of-view instrument capable of observing the hard X-ray and soft gamma-ray emissions in the energy range of 15 keV to 5 MeV. Its primary scientific objectives include: promptly triggering and localizing GRBs (with particular sensitivity to short-hard GRBs), measuring spectral and temporal properties of bursts, monitoring charged particle fluxes in orbit. GRM successfully detected its first GRB (GRB 240627B) on 27 June 2024, and has since maintained a detection rate of more than 100 GRBs per year. Cross-instrument comparisons with detectors such as GECAM and FERMI/GBM have validated the performance and data quality of GRM. This paper provides a comprehensive overview of GRM instrument design, reliability verification through ground testing, in-orbit triggering and localization algorithms, performance calibration, and preliminary in-orbit results, demonstrating its capability as a versatile gamma-ray all-sky monitor.

[abstract 11 / 27] (score: 3)
arXiv:2604.19182 [pdf, ps, other]

Title: Identifying Merger-Driven and Collapsar-Driven Gamma-Ray Bursts with Precursor based Solely on Prompt Emission

Authors: Si-Yuan Zhu, Pak-Hin Thomas Tam, Fu-Wen Zhang, Hui-Ying Deng, Bing Zhang,

Comments: 13 pages, 6 figures, 1 table, Accepted for publication in the ApJ

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Gamma-ray bursts (GRBs) are generally classified as Type~I GRBs, which originate from compact binary mergers, and Type~II GRBs, which originate from massive collapsars. The traditional correspondence between short--Type~I GRBs and long--Type~II GRBs, separated by a duration of 2 seconds, has been challenged by recent observations of long GRBs associated with kilonovae (i.e., Type~I-L GRBs) and a short GRB associated with a SUPERNOVA. In this paper, we focus on GRBs with precursor emission (PE) and compile 366 GRBs detected by FERMI/GBM. Applying the unsupervised machine learning methods t-SNE and UMAP, we are able to distinguish Type~I (including subclass Type~I-L) and Type~II GRBs for the first time and identify PE as a key feature for distinguishing GRBs of different origins. Inspired by results of machine learning, we propose a diagnostic parameter, the $E_{\rm p,ME}$-precursor index ($EPI$), defined as ${\rm log_{10}}(E_{\rm p,ME}^{2}/(T_{\rm 100,PE}T_{\rm 100,QE1}^{1/2}T_{\rm MVT,PE}))$, where most Type~I GRBs have $EPI > 6.2$ and most Type~II GRBs have $EPI < 6.2$. This parameter can help the community to diagnose the origin of any GRB with PE based solely on its prompt emission and rapidly plan for follow-up observations. The validation using SWIFT GRBs provides illustrative evidence that our method may also be applicable to GRBs observed by instruments other than FERMI.

[abstract 12 / 27] (score: 3)
arXiv:2604.19607 [pdf, ps, other]

Title: Are X-ray Atmospheres Heated by Turbulent Dissipation? XRISM Constraints

Authors: B. R. McNamara, A. C. Fabian, H. R. Russell, P. E. J. Nulsen, A. Simionescu, A. Majumder, E. D. Miller, A. Sarkar,

Comments: Submitted to ApJ. Comments are welcome!

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We evaluate whether dissipation of turbulence injected into hot cluster atmospheres by JETs and bubbles can offset radiative cooling flows. No trends are found between atmospheric velocity dispersion, $σ_v$, and either the ratio of kinetic to thermal energy or JET power over nearly four decades of JET power. Apparently, JETs disperse their energy gently at roughly constant energy per gram of gas. Assuming the velocity dispersions at the centers of Perseus, Virgo, and Hydra A reflect JETted turbulence, up to roughly half the bubble enthalpy could be dissipated by turbulent motion. A model is presented that balances radiation losses and turbulent power injected by radio bubbles rising at their terminal speeds. The model is anchored by XRISM measurements of $σ_v$ and is governed by the ratio of the bubble's terminal speed to the atmospheric sound speed. Bubbles must rise close to the sound speed and impart energy with a broad range of injection scales to heat the entire cooling volume. The level of turbulence in the powerful Hydra A system may offset cooling over some of the cooling volume. However, turbulent dissipation would struggle and probably fail to balance cooling in Perseus and Virgo, except perhaps in their inner regions. Several factors including, low velocity dispersions, small injection scales, short duty cycles, anisotropic turbulence injection, and long turbulent diffusion timescales present severe challenges for JETted turbulence heating models. A larger sample of spatially resolved cluster atmospheres is needed to reach a definitive conclusion.

[abstract 13 / 27] (score: 3)
arXiv:2604.19674 [pdf, ps, other]

Title: Resolved UV-Optical HST Imaging and Spectral Energy Distribution Modeling of Nearby BAT Active Galactic Nuclei

Authors: Connor Auge, Michael Koss, Kriti K. Gupta, Claudio Ricci, Benny Trakhtenbrot, Franz E. Bauer, Ezequiel Treister, Alessandro Peca, Brad Cenko, Kohei Ichikawa, Arghajit Janna, Darshan Kakkad, Richard Mushotzky, Kyuseok Oh, Alejandra Rojas Lilayú, David Sanders, Roberto Serafinelli, Matilde Signorini, Alessia Tortosa, C. Megan Urry,

Comments: 14 pages, 8 figures, accepted to ApJ

Subjects: astro-ph.GA

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We use high-resolution UV-to-optical imaging from the Hubble Space Telescope (HST) to construct spatially resolved spectral energy distributions (SEDs) for seven nearby ($z<0.07$) hard (14--195$\,$keV) X-ray-selected broad-line ACTIVE GALACTIC NUCLEi (AGN) with $L_{\rm bol}=10^{43.26}-10^{45.34}\,\rm{erg\,s^{-1}}$. The high spatial resolution of HST, which physically resolves structures on the scale of $\sim$50$\,$pc at $z=0.05$, enables the separation of AGN and host-galaxy emission through morphological decomposition with GALFIT, yielding improved measurements of AGN properties compared to those obtained with lower-resolution SWIFT UV/Optical Telescope (UVOT) data. AGN UV magnitudes derived from HST imaging (e.g., F225W) can differ by more than a magnitude from those from SWIFT/UVOT UVM2 due to extended nuclear emission. Additionally, the inclusion of high-resolution data at longer wavelengths (e.g., F814W) can significantly affect the resulting SED fit. Comparing fits of accretion disk and extinction models using HST and SWIFT/UVOT data, we find significant differences in the resulting parameters, with average differences of 2.0$\,$eV in the maximum disk temperature and 2.2$\,$mag in the AGN host-galaxy extinction. These differences ultimately lead to significant changes in bolometric luminosities and X-ray bolometric corrections, with the HST-based fits yielding average increases of $\sim$0.57$\,$dex and $\sim$0.66$\,$dex respectively. This demonstrates host-galaxy contamination in unresolved UV--optical data can strongly bias SED-based estimates of disk temperatures, extinction, bolometric luminosities, and X-ray bolometric corrections in AGN. Large-area, high-resolution imaging surveys from Euclid and the Nancy Grace Roman Space Telescope will extend these techniques to much larger AGN samples, enabling uniform, high-precision SED measurements in the near-IR.

[abstract 14 / 27] (score: 2)
arXiv:2107.13736 [pdf, ps, other]

Title: Turbulence closure in the light of phase transition

Authors: Mohammed A. Azim,

Comments: Manuscript has 14 pages and 16 figures

Subjects: physics.flu-dyn

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

In this study, new turbulence closure equations are derived in the light of turbulence as a continuous phase transition phenomenon. Closed-form Reynolds averaged Navier-Stokes equations due to those closure equations are solved numerically by treating turbulent viscosity as a tensor, unlike the eddy viscosity, for a plane turbulent JET. Overall agreement between the obtained results and the existing literature for the JET flow demonstrates the effectiveness of the new closure equations. Besides, turbulent stresses as a function of the normalized mean velocity exhibit their odd and even symmetries in the flow, which are manifestations of the free energy symmetry of continuous phase transition.

[abstract 15 / 27] (score: 2)
arXiv:2507.19319 [pdf, ps, other]

Title: Enhanced performance in quasi-isodynamic max-$J$ stellarators with a turbulent particle pinch

Authors: G. G. Plunk, A. G. Goodman, P. Xanthopoulos, P. Costello, H. M. Smith, K. Aleynikova, C. D. Beidler, M. Drevlak, S. Stroteich, P. Helander,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Recent stellarator reactor designs demonstrate mostly outward turbulent particle transport, which, without advanced fueling technology, inhibits the formation of density gradients needed for confinement. We introduce ``SQuID-$τ$'', a self-fueling quasi-isodynamic stellarator capable of sustaining density peaking through inward particle transport caused by turbulence. Temperature and density profile predictions based on high-fidelity gyrokinetic simulations demonstrate enhanced performance, significantly relaxing constraints on the size and MAGNETic field strength for reactor designs.

[abstract 16 / 27] (score: 2)
arXiv:2602.11274 [pdf, ps, other]

Title: Evolution of the transitional millisecond pulsar PSR J1023+0038 from Aqueye+ and NICER observations

Authors: Silvia Conforti, Luca Zampieri, Michele Fiori, Alessia Spolon, Giampiero Naletto, Aleksandr Burtovoi,

Comments: 8 pages, 4 figures. Accepted for publication in A&A

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Transitional millisecond pulsars (tMSPs) are old neutron stars spun up by accretion from a low-mass companion. These objects can switch between two emission regimes: rotation-powered radio pulsar and accreting X-ray pulsar. The origin of their optical and X-ray pulsations is still debated, although one model attributes them to SYNCHROTRON emission produced in a shock between the pulsar wind and the accretion flow. The small phase lag observed between optical and X-ray pulses in PSR J1023+0038 supports a common origin. We present a new measurement of the phase lag between optical and X-ray pulse profiles of PSR J1023+0038 and investigate the evolution of the time of passage at the ascending node ($T_{\rm{asc}}$) up to 2023. We performed a timing analysis of optical observations obtained with Aqueye+ between 2021 and 2023 and of X-ray data from NICER in 2023. We derive updated values of $T_{\rm{asc}}$ and measure the optical - X-ray phase lag from simultaneous observations. We find that $T_{\rm{asc}}$ increases by about 20 s per year. In January 2023, we measure a phase lag of $0.067 \pm 0.018$, corresponding to $112.3 \pm 30.7\,μ$s. Since 2017, the evolution of $T_{\rm{asc}}$ follows a parabolic trend, indicating an increase in the orbital period and orbital separation of the system. This behaviour is consistent with non-conservative Roche-lobe overflow, with the donor losing mass at a rate much higher than the accretion rate. The phase lag measurement further supports a common origin of the optical and X-ray pulsations.

[abstract 17 / 27] (score: 2)
arXiv:2602.17511 [pdf, ps, other]

Title: The Stark effect in molecular Rydberg states: Calculation of Rydberg-Stark manifolds of H$_2$ and D$_2$ including fine and hyperfine structures

Authors: Ioana Doran, Leon Jeckel, Maximilian Beyer, Christian Jungen, Frédéric Merkt,

Comments: 30 pages, 16 figures

Subjects: physics.atom-ph

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We present a general theoretical treatment and calculations of the fine and hyperfine structures in the spectra of high-$n$ molecular Rydberg states in static uniform electric fields. The treatment combines (i) multichannel quantum-defect theory and long-range POLARIZATION models to determine the field-free energies of $n\ell$ Rydberg states of the molecules ($\ell$ is the orbital-angular-momentum quantum number of the Rydberg electron), (ii) a matrix-diagonalization approach to calculate the Stark shifts including their hyperfine structure, and (iii) sequences of angular-momentum frame transformations to predict the line positions and intensities in Stark spectra as they would be observed in single or multiphoton excitation sequences. To clarify how the molecular rotation and the nuclear spins influence the fine and hyperfine structure of molecular Rydberg-Stark spectra, we compare calculated spectra of ortho-D$_2$ with a D$_2^+$ ion core in the rotational ground state ($N^+=0$) for total nuclear spins $I$ of 0 (i.e., without hyperfine structure) and 2 (i.e., with hyperfine structure) with the corresponding spectra of para-H$_2$ with an H$_2^+$ ion core in the first excited rotational state ($N^+=2$) but zero nuclear spin ($I=0$). The calculations show that the hyperfine interaction alone does not significantly modify the Stark effect, but splits each Stark state by almost exactly the hyperfine FERMI-contact splitting of the ion core. In contrast, the effect of the molecular rotation, which is coupled both to the ion-core electron spin by the MAGNETic spin-rotation interaction and to the Rydberg-electron orbital motion by the core-POLARIZATION and charge-quadrupole interactions, induces Stark-state specific splittings that significantly differ from the spin-rotation splitting of the ($N^+=2$) ion core.

[abstract 18 / 27] (score: 2)
arXiv:2604.17352 [pdf, ps, other]

Title: Assessment of Reynolds-Averaged Navier-Stokes Modeling of Jet Interaction in Fan-Array Wind Generator Flows

Authors: M. Hosein Niroomand, Utku Şentürk,

Comments:

Subjects: physics.flu-dyn

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Fan-array wind generators (FAWGs) provide controlled turbulent inflow conditions that cannot be reproduced in conventional wind tunnels. Despite their increasing use in experimental studies, numerical modeling of FAWG-generated flows remains largely unexplored. The present study assesses the capability of Reynolds-Averaged Navier-Stokes (RANS) modeling to predict JET interaction in a 10x10 fan-array wind generator. Numerical predictions are compared against experimental measurements of axial velocity and turbulence intensity from a reference configuration. Individual fan units are represented using a pressure-jump boundary condition based on a reconstructed performance curve derived from manufacturer data. Grid convergence is verified, and the influence of fan representation, operating point and inflow turbulence conditions is examined. The results show that RANS modeling captures the global JET interaction topology and downstream velocity decay with reasonable accuracy. However, systematic magnitude discrepancies are observed in the near-field injection region and peripheral shear layers. Turbulence intensity predictions exhibit larger deviations, reflecting limitations of the eddy-viscosity closure in highly mixing-dominated flows. A low-aspect-ratio flat plate is included as a demonstrative application to illustrate the aerodynamic impact of FAWG-generated inflow. Overall, the study shows that RANS modeling, combined with a pressure-jump fan representation, provides a computationally efficient framework for predicting the mean-flow structure of FAWG systems, while exhibiting clear limitations in resolving localized turbulence characteristics.

[abstract 19 / 27] (score: 2)
arXiv:2604.18628 [pdf, ps, other]

Title: Visual Characteristics of a Rotating Black Hole in $4$D Einstein-Gauss-Bonnet Gravity with Thin Accretion Disk Under EHT Constraints

Authors: Muhammad Israr Aslam, Manahil Ali, Abdul Malik Sultan, Xiao-Xiong Zeng, Sultan Hussain,

Comments: This article contains 32 pages, 25 equations, 13 figures and 82 references

Subjects: astro-ph.HE gr-qc

Created: 2026-04-18; Updated: 2026-04-22; Datestamp: 2026-04-22

This study investigates the visual characteristics of a rotating BLACK HOLE (BH) within the fabric of $4$D Einstein-Gauss-Bonnet gravity illuminated with two illumination models, such as a celestial light sphere and a thin accretion disk. To visualize the BH shadow images, we use a recent fisheye camera model and ray-tracing method. And then, we focus on investigating the impact of the coupling parameter $α$ and the spin parameter $a$ on the shadow images. The results exhibit that the shadow radius decreases, while the shadow deviation increases with the aid of $α$. However, with respect to $a$, the shadow radius is slightly increased compared to the corresponding shadow deviation. For a celestial light sphere, the increasing values of $α$, lead to a decrease in the corresponding photon ring, while the space-dragging effect becomes more prominent with increasing $a$. For a thin accretion disk, we enhance its inner edge to the BH event horizon, and the particle motion is different in the regions inside and outside the innermost stable circular orbit. The result demonstrates that the shadow becomes progressively asymmetric with $a$, while the overall size of the inner shadow gradually decreases with the variations of $α$. Subsequently, we also investigated the distinct features of red-shift configurations on the disk for both direct and lensed images. Additionally, we used the latest observational data from M87* and Sgr A* to impose certain parameter constraints on $α$; the results depict the consistency of our considering the BH model.

[abstract 20 / 27] (score: 2)
arXiv:2604.18899 [pdf, ps, other]

Title: Application of Metric-Based Mesh Adaptation to Hypersonic Aerothermal Simulations Using US3D

Authors: Dirk Ekelschot,

Comments: 21 pages

Subjects: physics.flu-dyn

Created: 2026-04-20; Updated: 2026-04-22; Datestamp: 2026-04-22

The main goal of this paper is to demonstrate the application of metric-based mesh adaptation to real gas problems and highlight the benefits particularly when complex geometries are considered. We use the Hessian of the temperature solution as an indicator to dictate where the mesh needs refinement or coarsening. In the context of hypersonic flow simulations, these methods are not widely adopted since unstructured meshes often result in poor surface heating predictions. The present work aims to demonstrate the great flexibility metric-based mesh adaptation provides when it comes to predicting complex flow features while still maintaining comparable surface heating predictions. We consider two test cases: (a) a supersonic flow over a hemisphere and show that comparable surface heating is obtained by applying mesh adaptation and by employing hexahedra instead of prisms in the boundary layer mesh; (b) we consider a more realistic test case of a hypersonic flow of a C02-N2 mixture past a 70 degree sphere cone atmospheric entry capsule. For the second test case, similar surface heating predictions are obtained compared to more conventional block structured DPLR simulations. Furthermore, for the adapted unstructured simulations, the geometries of the eight Reaction Control System (RCS) JET on the back shell were taken into account. This highlights the ability of these methods to deal with complex geometries that are typically out of reach for block structured approaches.

[abstract 21 / 27] (score: 2)
arXiv:2604.18906 [pdf, ps, other]

Title: Instability-Aware Steering of an Extreme Atmospheric River in an AI Weather Foundation Model

Authors: Moyan Liu, Qin Huang, Upmanu Lall,

Comments:

Subjects: physics.ao-ph

Created: 2026-04-20; Updated: 2026-04-22; Datestamp: 2026-04-22

Advances in deep learning methods for weather forecasting are creating opportunities to computationally explore the potential for steering or control of extreme weather trajectories for societal risk reduction. We present initial investigations into the feasibility of redirecting extreme atmospheric rivers (ARs) through small, instability-aware perturbations. Using the Aurora AI weather foundation model, we identify sensitive upstream locations using finite-time Lyapunov exponents and JET-eddy interaction criteria. We apply an idealized cloud-seeding operator that mimics latent heat release to assess whether these Lyapunov-guided interventions can influence downstream evolution. In a case study of a severe California AR, perturbations induce coherent downstream shifts in moisture transport, reducing intensity at landfall under favorable kinematic conditions. The response is nonlinear and contingent on the local flow geometry. These initial results suggest that the atmosphere's intrinsic chaotic sensitivity could be leveraged for dynamical control, offering a new research direction for extreme event risk mitigation.

[abstract 22 / 27] (score: 2)
arXiv:2604.19236 [pdf, ps, other]

Title: Numerical Studies of Accretion Flows onto a Neutron Star Engulfed in a Massive Star

Authors: Daiyu Sakurai, Ryuichiro Akaho, Shoichi Yamada,

Comments: 20 pages, submitted to MNRAS, comments welcome

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

Massive stars commonly form binaries that can evolve into compact systems via common envelope evolution (CEE), a critical but poorly understood phase -- especially when the companion is a neutron star. Understanding the drag force exerted on a neutron star during CEE is a key to the quantitative evaluation of orbital decay, merger timescale, and compactness of the resultant binary. In this paper, we conduct general-RELATIVISTIC hydrodynamical simulations under a novel strategy of multi-layer domain-decomposition to treat the vast disparity of $10^4$--$10^7$ between the neutron star radius and the accretion radius. Our 10-model survey spans diverse physical conditions that the neutron star encounters in the envelope of a massive star. We find that nested bow shocks with alternating orientations commonly form. This configuration is qualitatively different from those in the conventional picture and results in an enhancement of the drag force by one to two orders of magnitude from what the Bondi--Hoyle--Lyttleton formula predicts. Moreover, the direction of the net force can reverse depending on the envelope conditions, contrary to the standard picture in which the drag always decelerates the companion. These results will serve as a basis for improvements of the drag force prescription in CEE modeling, and have implications for binary evolution theory.

[abstract 23 / 27] (score: 2)
arXiv:2604.19375 [pdf, ps, other]

Title: On the Relation Between Diffusion and Shear Viscosity in Two-Dimensional Magnetized Yukawa Liquids

Authors: N. Kh. Bastykova, T. S. Ramazanov, S. K. Kodanova,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We investigate the interplay between shear viscosity and diffusion in a 2D Yukawa liquid subjected to an external MAGNETic field.

[abstract 24 / 27] (score: 2)
arXiv:2604.19495 [pdf, ps, other]

Title: Search for quantum BLACK HOLEs in lepton+JET final states using proton-proton collisions at $\sqrt{s}=13.6$ TeV with the ATLAS detector

Authors: ATLAS Collaboration,

Comments: 36 pages in total, author list starting page 19, 4 figures, 2 tables, submitted to PLB. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2024-32

Subjects: hep-ex

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

A search for quantum BLACK HOLEs in electron+JET or muon+JET final states with high invariant mass is performed. The analysis uses data from $\sqrt{s}=13.6~\textrm{TeV}$ $pp$ collisions recorded by the ATLAS detector between 2022 and 2024 during Run~3 of the Large Hadron Collider, corresponding to an integrated luminosity of $164~\mathrm{fb}^{-1}$. This search is strongly motivated by a dramatic increase of the production cross-section by up to an order of magnitude for the highest masses considered, thanks to the small increase of $0.6~\textrm{TeV}$ in centre-of-mass energy between Run~2 and Run~3. No significant excess above the Standard Model background is observed, and 95\% CL upper limits are set on the production cross-section times branching ratio in several benchmark models, reaching a mass scale of $9.4~\textrm{TeV}$. These represent the strongest exclusion limits to date on quantum BLACK HOLE production.

[abstract 25 / 27] (score: 2)
arXiv:2604.19497 [pdf, ps, other]

Title: Design and preliminary performance study of the broad-band spectrometer detector for POLAR-2

Authors: Jian-Chao Sun, Jiang He, Shuang-Nan Zhang, Shao-Lin Xiong, Jiang-Tao Liu, Yan-Bing Xu, Jia Ma, Shuo Wang, Lei Shuai, Xiu-Zuo Liang, Hong-Bang Liu, Fei Xie, Ming Zeng, Philipp Azzarello, Joerg Bayer, Franck Cadoux, Nicolas De Angelis, Huan-Bo Feng, Zu-Ke Feng, Min Gao, Ramandeep Gill, Jonathan Granot, Jochen Greiner, Alejandro Guzman, Jin-Xiu Hu, Yue Huang, Johannes Hulsman, Zheng-Huo Jiang, Merlin Kole, Dao-Wu Li, Han-Cheng Li, Tong-Lei Liao, Long Peng, Agnieszka Pollo, Nicolas Produit, Dominik Rybka, Andrea Santangelo, Li-Ming Song, Chris Tenzer, Xiao-Ming Wang, Yuan-Hao Wang, Bo-Bing Wu, Pei-Lian Wu, Xin Wu, Shuo Xiao, Sheng Yang, Lai-Yu Zhang, Lei Zhang, Yong-Jie Zhang,

Comments: 60 pages, 24 figures, accepted for publication in Exp. Astron

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

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

POLAR-2, the successor of the POLAR experiment aboard China's Tiangong-2 space lab, is set to be deployed on the China Space Station. The POLAR-2 mission aims to conducting high-precision POLARIZATION measurements of high-energy transients with a primary focus on Gamma-Ray Bursts (GRBs), following POLAR's pioneering accurate POLARIZATION measurements of GRB prompt emission. One of the key advancements in POLAR-2 is the inclusion of a dedicated Broad-band Spectrometer Detector (BSD) instrument, designed to provide precise measurements of GRB location and spectral parameters, which are critical inputs for accurate POLARIZATION analysis of POLAR-2's dedicated High-energy Polarimetry Detector (HPD), which is made of plastic scintillator bars array. BSD employs a coded-aperture mask imaging technique and pixelated GAGG scintillation crystals, offering a wide half-coded field of view of ~132° x 125° and an operational energy range of 10-1000 keV. Simulation results indicate that the instrument can achieve a localization accuracy of approximately 1.5° for faint GRBs similar to GRB 170817A, satisfying the core requirements of GRB polarimetry with HPD. BSD also has moderate capability for GRB polarimetry, particularly at several hundred keV energy. This paper outlines the preliminary design of BSD and presents an overall evaluation of its expected scientific performance, based on extensive Monte Carlo simulations and preliminary ground-based calibration tests.

[abstract 26 / 27] (score: 2)
arXiv:2604.19585 [pdf, ps, other]

Title: Centrality Dependence of the Balance Functions for Identified Particles in Pb--Pb Collisions Using Pythia + Angantyr

Authors: Rashi Gupta, Ankhi Roy,

Comments:

Subjects: hep-ph

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

In this paper, we study the balance functions for pions, kaons, and protons in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV using the PYTHIA 8.3 + Angantyr model. The balance function is evaluated through two-particle azimuthal angular correlations $(Δϕ, Δη)$ between particle and antiparticle. Correlations are constructed for $ππ$, $KK$, and $pp$, and their dependence on collision centrality is investigated. The results indicate that the balance function for pions is narrower compared to kaons and protons. Notably, the pion balance function width decreases from peripheral to central collisions, while the widths for kaons and protons remain nearly unchanged. For the Monash 2013 tune used in this study, PYTHIA 8.3 + Angantyr describes peripheral collisions reasonably well but does not quantitatively reproduce central Pb--Pb data. This suggests that an improved description of central Pb--Pb collisions may require a dedicated heavy-ion tuning of the Angantyr framework. We further explore the influence of resonance decays and collective effects by incorporating multi-parton interactions and color RECONNECTion into the analysis. Owing to resonance effects and Bose--Einstein correlations, a dip at $Δη= 0$ and $Δϕ= 0$ is observed for pions and kaons.

[abstract 27 / 27] (score: 2)
arXiv:2604.19692 [pdf, ps, other]

Title: QPOs from the Viscous Transonic Accretion Flow Around a Spinning Black Hole

Authors: Sanjit Debnath, Indranil Chattopadhyay, Soumyadip Mandal, Raj Kishor Joshi, Priyesh Kumar Tripathi, M. Saleem Khan,

Comments: 13 pages, 8 figures

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-22; Datestamp: 2026-04-22

We investigate the dynamics of transonic advective accretion flows around spinning BLACK HOLEs in the presence of viscosity. The spacetime of a Kerr BLACK HOLE is approximated using a pseudo-potential. We study viscously driven shock oscillations over a range of BLACK HOLE spin parameters. Our results show that the frequency range of quasi-periodic oscillations (QPOs) obtained from the power density spectra depends strongly on the BLACK HOLE spin. Low-spin systems predominantly exhibit low-frequency QPOs, whereas rapidly rotating BLACK HOLEs (0.9) produce QPOs spanning a broad range from low to high frequencies, comparable to those observed in BLACK HOLE X-ray binaries. We further obtain a correlation between the QPO frequency and the power-law photon index by computing the spectrum for a 10 solar mass BLACK HOLE.