Current date: 2026-04-23

Setting default datestamp limit: 0

Datestamp limit: 2026-04-23 (0 days ago)

Created/updated limit: 2026-04-16 (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=2026-04-23&until=2026-04-23&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 646

Keyword score statistics

score 11 -- 1 abstracts

score 7 -- 1 abstracts

score 6 -- 3 abstracts

score 5 -- 1 abstracts

score 4 -- 5 abstracts

score 3 -- 6 abstracts

score 2 -- 12 abstracts

in total -- 29 abstracts

Articles that appeared on 2026-04-23

[abstract 1 / 29] Wow! (score: 11)
arXiv:2604.19916 [pdf, ps, other]

Title: Search for Anisotropic Pair Halos Associated with Blazar Jets

Authors: Ao Zhang, Wenlei Chen, Manel Errando,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

The origin of intergalactic MAGNETic fields (IGMFs) remains one of the key open questions in cosmology. Gamma-ray pair halos produced by electroMAGNETic cascades from TeV-emitting BLAZARs provide a powerful indirect probe of these fields. In this work, we present a novel search for pair halos that explicitly exploits their expected anisotropic morphology, aligning with the projected orientation of BLAZAR JETs on the sky. Using a Monte Carlo framework to model the spatial distribution of cascade emission, we identify an optimal sample of 21 high-SYNCHROTRON-peaked BL Lac objects with well-constrained JET position angles from radio interferometry. By rotating and stacking \textit{FERMI}-LAT observations of these sources along their JET directions, we enhance sensitivity to anisotropic extended emission that would be diluted in traditional orientation-agnostic analyses. Applying a likelihood analysis to the combined dataset, we find evidence for a non-zero IGMF, excluding the null hypothesis at $3.8σ$ level and obtaining a best-fit field strength of $B_0 = 2.8 \times 10^{-16}\,\mathrm{G}$, with a $99\%$ confidence interval of $0.9 \times 10^{-16}\,\mathrm{G} < B_0 < 8.9 \times 10^{-16}\,\mathrm{G}$. Our result is consistent with previous constraints from spectral, spatial, and temporal studies, while demonstrating that incorporating anisotropic information provides a significant gain in sensitivity. This approach opens a new avenue for probing intergalactic MAGNETism and highlights the potential of future high-angular-resolution gamma-ray observations to directly image pair halos and map MAGNETic fields in cosmic voids.

[abstract 2 / 29] Wow! (score: 7)
arXiv:2604.20768 [pdf, ps, other]

Title: Primordial Magnetogenesis and Gravitational Waves from ALP-assisted Phase Transition

Authors: Pankaj Borah, P. S. Bhupal Dev, Anish Ghoshal,

Comments: 41 pages, 7 figures + References; Comments are welcome !

Subjects: hep-ph astro-ph.CO hep-th

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Sufficiently strong first-order phase transitions (FOPTs) in the early Universe can simultaneously produce an observable stochastic gravitational wave background (SGWB) and a large-scale primordial MAGNETic field (PMF). The recent $3.8σ$ evidence for a non-zero intergalactic MF from anisotropic pair-halo searches using \textit{FERMI}-LAT data further motivates a cosmological origin of this MF. We investigate an FOPT-origin of both cosmic signatures, namely, PMF and SGWB, and the correlation between them, within a minimal axion-like particle (ALP) framework in which a global $U(1)$ symmetry is spontaneously broken through radiative corrections, with the ALP sector coupled to the Standard Model (SM) via Higgs-portal. We compute the present-day PMF amplitude and coherence length for both maximally helical and non-helical configurations, accounting for inverse cascade effects. For maximally helical configurations, we find peak field strengths up to $B_0 \sim 10^{-9}$ G at coherence length $λ_0 \sim 10^{-3}-10^{-1}$ Mpc, consistent with lower bounds on the IGMF inferred from BLAZAR observations by MAGIC, H.E.S.S. and {\it FERMI}-LAT. We show that the ALP parameter region consistent with $γ$-ray BLAZAR data (assuming maximal helicity) simultaneously produces SGWB detectable at future space-based interferometers, such as LISA, etc., over the ALP decay constant range $10^3~\text{GeV} \lesssim f_a \lesssim 10^5~\text{GeV}$. We directly map these onto effective ALP couplings to SM particles, e.g., photons, gluons, and fermions. This establishes a multi-messenger complementarity between cosmological observables and laboratory/astrophysical ALP searches, with the combined constraints preferring relatively heavy ALPs, $m_a \gtrsim 0.1~\text{GeV}$, in a regime accessible to next-generation intensity and energy-frontier experiments.

[abstract 3 / 29] Yes (score: 6)
arXiv:2604.20095 [pdf, ps, other]

Title: Detections of nearly bias-free core shifts with 5-30 $μ$as precisions at 8-43 GHz in BL Lacertae

Authors: Niu Liu, Jun Yang, Xiaopeng Cheng, Ai-Ling Zeng, Wen Chen, Xiao-Long Yang, Xiaoyu Hong, Xia-Xuan Zhang, Jia-Cheng Liu, Zi Zhu,

Comments: 12 pages, 6 figures, accepted for publication in ApJ

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

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

When a radio JET is partially optically thick in the launching region, its apparent compact core may display frequency-dependent positional shifts. High-precision astrometric measurements of core shifts enable astronomers to pinpoint the JET's origin and place tight constraints on the MAGNETic field. BL Lacertae, the archetypal BL Lac object, hosts a highly variable and well-collimated JET. To independently constrain its innermost core shifts, we conducted very long baseline interferometric (VLBI) observations at 8.4, 12.4, 15.2, 23.6, and 43.2 GHz. By exploiting a nearby (13.3 arcmin) steep-spectrum calibrator (NVSS J220340+420839) through inverse phase-referencing VLBI astrometry, we detect nearly unbiased two-dimensional core shift measurements with state-of-the-art precisions of 5-30 $μ$as, which are significant at $>3σ$ confidence. The core shift between 8.4 and 43.2 GHz reaches 250 $μ$as. The apparent core shifts scale with frequency as $ν^{-1/k_r}$, implying the existence of an optically thick region in the upstream of JET. The derived core-shift index, $k_r\!=\!1.18^{+0.59}_{-0.34}$, is consistent, within uncertainties, with the canonical $k_r\!=\!1$ expected under energy equipartition between the JET particle and MAGNETic field energy densities, while allowing for modest deviations given that BL Lacertae was captured in a flaring state.

[abstract 4 / 29] Yes (score: 6)
arXiv:2604.20142 [pdf, ps, other]

Title: Fast-Cooling Synchrotron in Decaying Magnetic Fields: Implications for the GRB Spectral Distribution

Authors: Jia-Ming Chen, Ke-Rui Zhu, Zhao-Yang Peng, Yong-Gang Zheng, Yun-Lu Gong, Shan Chang, Shi-Ting Tian, Li Zhang,

Comments: 18 pages, 14 figures,accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The prompt-emission spectra of GAMMA-RAY BURSTs (GRBs) are commonly described by the empirical Band function. The typical low-energy spectral index is $\sim -1$, which poses a challenge to standard SYNCHROTRON radiation models. We systematically investigate a fast-cooling SYNCHROTRON model with a decaying MAGNETic field and test, within an observation-consistent pipeline, whether it reproduces the Band-fit parameter distributions in the GBM catalog, in a statistical sense. We solve the electron continuity equation with SYNCHROTRON, adiabatic, and SYNCHROTRON self-Compton cooling to obtain the time-dependent electron distribution and synthetic spectra; we then forward-fold through the GBM response matrices and recover $(α, β, E_p)$ with Band fits. We find that MAGNETic-field decay can harden the recovered $α$ relative to the fast-cooling limit in part of parameter space, but the effect is not robust and is sensitive to the location of $E_p$ within the finite band and to spectral curvature; varying key physical scales reshapes the recovered $α$ distribution, indicating that catalog $α$ often represents an effective in-band slope rather than the asymptotic index. SSC cooling provides modest additional hardening and, in our setups, does not stabilize $α$ near the observed peak. Using Monte Carlo samples designed to mimic the observations, the model yields $α$ mostly between $-1.5$ and $-0.8$, but remains centered around $α\approx -1.5$. Overall, while decaying-field fast-cooling SYNCHROTRON can partially alleviate overly soft spectra expected from standard fast-cooling SYNCHROTRON emission, it still falls short of reproducing the GBM $α$ distribution at the population level, implying that additional physical processes are required.

[abstract 5 / 29] Yes (score: 6)
arXiv:2604.20346 [pdf, ps, other]

Title: XRF 241001A/SN 2024aiiq: A Faint Soft X-ray Transient Detected by SVOM with a Broad-Line Type Ic Supernova Revealed by JWST

Authors: B. Schneider, M. Brunet, B. P. Gompertz, D. Turpin, D. B. Malesani, O. Godet, A. J. Levan, F. Daigne, N. Sarin, N. A. Rakotondrainibe, A. Martin-Carrillo, J. T. Palmerio, C. C. Thöne, H. L. Li, A. Saccardi, A. de Ugarte Postigo, S. Antier, V. Buat, D. Ďurovčíková, L. Izzo, J. K. Leung, G. Mo, Y. L. Qiu, S. D. Vergani, J. Wang, J. Y. Wei, L. P. Xin, R. Mochkovitch, B. Zhang, H. B. Cai, S. Campana, A. Coleiro, B. Cordier, P. D'Avanzo, N. Dagoneau, V. D'Elia, Y. W. Dong, D. Götz, S. Guillot, X. H. Han, D. H. Hartmann, L. Huang, Y. F. Huang, P. Jakobsson, A. Klotz, C. Lachaud, X. M. Lu, P. Maggi, M. De Pasquale, F. Piron, R. Salvaterra, S. Schanne, J. Sollerman, N. R. Tanvir, Z. Vidadi, P. Wang, C. Wu, S. L. Xiong, Y. Xu, T. Zafar, P. P. Zhang, S. N. Zhang, S. J. Zheng,

Comments: 24 pages, 14 figues. Submitted to A&A

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

X-ray flashes (XRFs) are a type of GAMMA-RAY BURSTs (GRBs) with prompt emission predominantly below 30 keV poorly detected by previous missions. The advent of the SVOM mission, with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients such as XRFs. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, sub-luminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigate the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. We analyze the SVOM/ECLAIRs prompt emission and model its afterglow emission from X-ray to-radio. We present JWST/NIRSpec and SVOM/VT observations of the associated SUPERNOVA (SN 2024aiiq), which we model with an Arnett radioactive decay component and compare its properties with previously detected GRB/SNe. XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV with a duration of T90 = 3.14 seconds. Its spectrum can be modeled by non-thermal or thermal models, all pointing towards a low Epeak < 10 keV and Eiso ~ 8x10^49 erg. The X-ray-to-radio afterglow modeling favors an origin from a RELATIVISTIC JET viewed on-axis. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some fast X-ray transients and inconsistent with SYNCHROTRON emission. The JWST/NIRSpec observations firmly established its collapsar origin by revealing a SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events. XRF 241001A is a soft, low-luminosity collapsar event produced by a weak RELATIVISTIC JET observed on-axis, supporting the view that part of the XRF population forms the low-energy tail of the long GRB population. It demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population.

[abstract 6 / 29] Yes (score: 5)
arXiv:2603.02520 [pdf, ps, other]

Title: Observational Properties of Near-Maximally Spinning Supermassive Black Holes

Authors: Tegan A. Thomas, Angelo Ricarte, Cora Prather, Hyerin Cho,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

Black holes described by the Kerr metric can have a theoretical maximum dimensionless spin parameter of $a_\bullet = 1$, but several effects may limit the maximum spin parameter in astrophysical systems. We perform general RELATIVISTIC MAGNETohydrodynamics simulations of accretion flows around BLACK HOLEs with $a_\bullet = 0.9375$ and $a_\bullet = 0.998$, each corresponding to a proposed astrophysical limit in the literature. We then perform full polarized general RELATIVISTIC ray-tracing to produce astrophysical movies of these simulations, as can be spatially resolved by the Event Horizon Telescope (EHT) and its extensions. Although many properties of BLACK HOLEs and accretion flows evolve rapidly as $a_\bullet \to 1$, we find that our $a_\bullet=0.9375$ and $a_\bullet=0.998$ simulations are remarkably similar, both in terms of their GRMHD fluid properties and their full-Stokes, time-variable images. This suggests that previous work using simulations with $a_\bullet \approx 0.9375$ may be representative of models with $a_\bullet \gtrsim 0.9375$ in most practical cases. Our calculations suggest that shape and size constraints on the photon ring, enabled by extensions of the EHT into space by missions such as the Black Hole Explorer (BHEX) may be the only practical way to distinguish between models with different spin parameters as $a\to 1$.

[abstract 7 / 29] Yes (score: 4)
arXiv:2512.17498 [pdf, ps, other]

Title: High-Resolution Measurements with the CTAO Southern Array: The Case for Pulsar Wind Nebulae

Authors: Georg Schwefer, Jim Hinton,

Comments: 18 pages, 18 figures; Version resubmitted to A&A with minor revisions

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

The advent of the Cherenkov Telescope Array Observatory (CTAO) and recent advances in reconstruction of gamma-ray photons with Cherenkov telescopes are bound to push the limit of angular resolution to an unprecedented precision of less than one arcminute at tens of TeV. Naturally, such instrumental improvements open up possibilities for new and interesting scientific studies. We aim to show that the study of pulsar wind nebulae (PWNe) in particular is bound to profit from these high-resolution measurements. This is because PWNe are the dominant Galactic source population at TeV energies, exhibit hard spectra up to hundreds of TeV and from X-ray observations are known to possess plentiful structure on arcminute scales. Using HESS J1813-178 and MSH 15-52 as examples, we create simple leptonic models of the TeV morphology of these sources based on X-ray observations and existing gamma-ray measurements. Then, assuming different models for the exposure and point spread function of the observatory, we create mock observations with the future CTAO southern array. We use these to assess the ability of these observations to differentiate between models and study the physics of these sources, in particular to infer the structure of the MAGNETic field and electron distributions. We find that future observations with the CTAO southern array at multi-TeV energies - in combination with existing X-ray measurements - will likely be able to constrain the distributions of MAGNETic field and high-energy electrons in these sources. We demonstrate that the sensitivity of these measurements can be significantly enhanced with the improved angular resolution achievable with novel reconstruction algorithms. However, we also show that in the relevant multi-TeV regime, signal-photon statistics remain a limitation and trading event statistics for improved angular resolution is not necessarily advantageous.

[abstract 8 / 29] Yes (score: 4)
arXiv:2604.08020 [pdf, ps, other]

Title: Chromospheric turbulence as a regulator of stellar wind mass flux

Authors: Munehito Shoda, Tom Van Doorsselaere, Allan Sacha Brun,

Comments: accepted for publication in MNRAS

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

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The mass flux of solar and stellar winds is a key quantity for stellar evolution and space weather, yet its physical regulation mechanism remains an unsolved problem. In particular, conventional Alfvén wave--driven models that self-consistently connect the stellar surface to the stellar wind fail to reproduce the observed scaling between stellar X-ray flux and mass-loss rate, a discrepancy that can be largely attributed to the dissipation of a substantial fraction of the wave energy by chromospheric turbulence. To address this issue, we aim to clarify the role of chromospheric turbulence in regulating the stellar wind mass flux. We perform one-dimensional wave-driven wind simulations, comparing cases with and without chromospheric turbulence suppression to assess its impact on coronal and wind properties. We find that suppressing chromospheric turbulence leads to a systematic increase in the coronal particle flux, and hence the wind mass flux, by up to an order of magnitude, particularly in regions of moderately strong MAGNETic field. This behavior arises from a combination of changes in the Poynting flux at the coronal base and in the asymptotic wind speed. Furthermore, the model with chromospheric turbulence suppression reproduces the observed empirical scaling between coronal MAGNETic field strength and mass flux without invoking additional energy input mechanisms such as interchange RECONNECTion. These results identify the chromospheric turbulence as a key factor in regulating stellar wind mass flux and highlight the importance of incorporating its effects in models that connect the stellar surface and the stellar wind.

[abstract 9 / 29] Yes (score: 4)
arXiv:2604.19896 [pdf, ps, other]

Title: HI 21-cm absorption in low- and high-excitation radio-loud AGNs at $z<0.5$ from MALS

Authors: P. P. Deka, N. Gupta, J-. K. Krogager, S. A. Balashev, H. -W. Chen, F. Combes, H. -R. Klöckner, P. Noterdaeme,

Comments: 12 pages, 11 figures, Comments are welcome

Subjects: astro-ph.GA

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

We present results from a search of cold neutral gas associated with radio-loud ACTIVE GALACTIC NUCLEi (AGNs) at $z < 0.5$ using HI 21-cm absorption measurements from the MeerKAT Absorption Line Survey (MALS). Cross-matching the MALS 1006 MHz and SDSS DR18 catalogs yields 1908 radio sources at $z < 0.5$. Of these, 613 are classified as AGNs using BPT diagnostics and radio luminosity criteria. We further classify 426 AGNs into 327 low-excitation RADIO GALAXies (LERGs) and 99 high-excitation RADIO GALAXies (HERGs). We observe a significant ($>3σ$) difference in $k$-corrected $g-r$ color, consistent with LERGs residing in older galaxies with quenched STAR FORMATION. We searched a radio-bright subsample of 79 LERGs and 20 HERGs ($S_{\mathrm{1.4\,GHz}} > 4$ mJy) for associated HI 21-cm absorption. This spans six decades in radio luminosity ($\log L_{\mathrm{1.4\,GHz}}$ (WHz$^{-1}$) $\sim 21.1-27.0$), probing an order of magnitude fainter than previous targeted HI surveys. We report five new detections (4 LERGs, 1 HERG) at $0.29 < z < 0.47$. The overall detection rate of $3^{+3}_{-2}$% (at a $3σ$ threshold of 10.0 kms$^{-1}$) is consistent with sensitivity-matched low-$z$ ($<0.2$) samples, suggesting no significant redshift evolution out to $z \sim 0.5$ or dependence on radio luminosity. Evaluating velocity offset, asymmetry, and width reveals three systems with entirely redshifted absorption and two with predominantly blueshifted absorption. HI profiles in LERGs show diverse asymmetries and velocity offsets exceeding 350 kms$^{-1}$, indicating disturbed cold-gas kinematics likely driven by lobe expansion or JET activity.

[abstract 10 / 29] Yes (score: 4)
arXiv:2604.19897 [pdf, ps, other]

Title: Radio detection of SUPERNOVA remnant G310.7-5.4 with $γ$-ray counterpart: Abeona SNR

Authors: Christopher Burger-Scheidlin, Brianna D. Ball, Sanja Lazarević, Roland Kothes, Robert Brose, Jonathan Mackey, Miroslav D. Filipović, Zachary J. Smeaton, Andrew M. Hopkins, Denis Leahy, Mehrnoosh Tahani, Jennifer L. West, Tayyaba Zafar,

Comments: 11 pages, 4 figures, 3 tables. Accepted in A&A

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

G310.7-5.4 is a SUPERNOVA remnant (SNR) candidate identified as a faint shell in the second epoch Molonglo Galactic Plane Survey (MGPS-2), but this has not been followed up with multi-wavelength observations until now. It is an example of an SNR at high Galactic latitude showing spatially coinciding $γ$-ray emission. Here, we make the first detailed investigation of the radio emission from the G310.7-5.4 region, aiming to characterise the radio structure, polarisation measurements and the coinciding GeV emission. We used recent radio continuum observations at 943.5 MHz from the EMU and the POSSUM surveys with ASKAP, as well as 16.5 years of FERMI-LAT observations. We furthermore considered the multiwavelength context of the object by investigating observations previously conducted with other instruments, such as infrared and X-ray surveys. We confirm the SNR candidate as a new SUPERNOVA remnant, dubbed Abeona. We detect the presence of a faint, extended, bilateral radio shell of the size of around 30' diameter and ASKAP radio flux density of $1.5^{+1.5}_{-0.1}$ Jy with no obvious infrared counterparts. With a radio surface brightness of about $2.4^{+2.4}_{-0.1}\times10^{-22}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$, this SNR is one of the faintest radio SNRs known. The northern part of the shell shows linearly polarised radio emission, characteristic of SYNCHROTRON emission in SNRs. The physical size of the SNR is estimated to be around $42^{+42}_{-21}$ pc, which would give a distance of around $4.9^{+4.9}_{-2.5}$ kpc. Furthermore, the spatially coincident $γ$-ray source 4FGL J1413.9-6705 shows an energy flux of $1.26\pm0.35\times 10^{-6}$ MeV cm$^{-2}$ s$^{-1}$ with a significance of 5.7 $σ$ between 100 MeV and 100 GeV. The SNR is also put in context with known high-latitude SNRs with $γ$-ray counterparts and compared with their observational properties.

[abstract 11 / 29] Yes (score: 4)
arXiv:2604.20480 [pdf, ps, other]

Title: The January 2010 flare of Mrk421: Insights from a stochastic acceleration model

Authors: MAGIC collaboration, K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, I. Albanese, T. Aniello, L. A. Antonelli, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, A. Babić, C. Bakshi, U. Barres de Almeida, J. A. Barrio, L. Barrios-Jiménez, I. Batković, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž. Bošnjak, E. Bronzini, I. Burelli, A. Campoy-Ordaz, A. Carosi, R. Carosi, M. Carretero-Castrillo, D. Cerasole, G. Ceribella, A. Cerviño, Y. Chai, G. Chon, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, R. de Menezes, M. Delfino, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, L. Foffano, L. Font, F. Frías García-Lago, Y. Fukazawa, S. García Soto, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, T. Gradetzke, R. Grau, J. G. Green, P. Günther, D. Hadasch, A. Hahn, G. Harutyunyan, T. Hassan, J. Herrera Llorente, D. Hrupec, D. Israyelyan, J. Jahanvi, I. Jiménez Martínez, J. Jiménez Quiles, J. Jormanainen, S. Kankkunen, T. Kayanoki, G. W. Kluge, J. Konrad, P. M. Kouch, H. Kubo, J. Kushida, M. Láinez, A. Lamastra, E. Lindfors, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, L. Lulić, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, G. Maneva, M. Manganaro, S. Mangano, M. Mariotti, M. Martínez, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez Gallego, S. Menon, D. Miceli, J. M. Miranda, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, C. Nanci, A. Negro, V. Neustroev, M. Nievas Rosillo, C. Nigro, L. Nikolić, K. Nilsson, S. Nozaki, A. Okumura, J. Otero-Santos, S. Paiano, D. Paneque, R. Paoletti, J. M. Paredes, M. Peresano, M. Persic, M. Pihet, G. Pirola, F. Podobnik, P. G. Prada Moroni, E. Prandini, W. Rhode, M. Ribó, J. Rico, A. Roy, N. Sahakyan, F. G. Saturni, F. Schiavone, K. Schmitz, F. Schmuckermaier, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, Y. Suda, M. Takahashi, R. Takeishi, J. Tartera Barberà, P. Temnikov, T. Terzić, M. Teshima, A. Tutone, S. Ubach, M. Vazquez Acosta, S. Ventura, G. Verna, I. Viale, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, M. Vorbrugg, I. Vovk, R. Walter, C. Walther, F. Wersig, P. K. H. Yeung, M. Perri, A. Tramacere,

Comments: Accepted for publication in A&A. Corresponding Authors: : J. Abhir, A. Arbet-Engels, A. Tramacere

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

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Mrk421 displayed its highest flux state ever observed in February of 2010 with very high TeV fluxes and interesting cross-band correlations and a spectral energy distribution (SED) evolution not entirely consistent with the standard single zone leptonic SYNCHROTRON self-Compton model. The source was already in a high state in January 2010 and displayed strong variability in the days preceding the highest state. We study the temporal evolution of the spectra in January to extract information about the particle dynamics and the physical properties of the emission region. We build up on the temporal variability and correlations studied in the previous work (MAGIC collaboration - Abe et al. 2025) and attempt to improve the SED model fits with a physics oriented approach. The multi-wavelength data was processed and the SEDs were fit using JetSeT. The SED evolution and cross band correlations were modelled using leptonic log-parabola with a low energy power-law branch (LPPL) and pile-up distributions that are predicted in a stochastic acceleration scenario. A simplified temporal evolution model was developed and fit to the SEDs and the resulting trends and phenomenology were characterised in context of theoretical literature. An expanding emission region model was also tested. We find the spectral variability to be well in agreement with stochastic acceleration. Our analysis suggests that the standard LPPL distribution develops a Maxwellian pile-up component at the transition from acceleration to cooling dominated phase on 3 nights in the dataset, as also hinted by the very-high energy and X-ray light curves. The resulting phenomenology of our sequential snapshot evolution SED model agrees well with theoretical and numerical simulation studies on temporal evolution using the diffusion equation approach.

[abstract 12 / 29] (score: 3)
arXiv:2604.19865 [pdf, ps, other]

Title: A population-based approach to understanding radio AGN feedback with LOFAR: The LoTSS Deep Fields

Authors: J. C. S. Pierce, F. Sweijen, M. J. Hardcastle, L. K. Morabito, H. J. A. Röttgering, R. D. Baldi,

Comments: Accepted for publication in MNRAS. 14 pages, 6 figures

Subjects: astro-ph.GA

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

Feedback from radio AGN JETs is regularly implemented into contemporary models of galaxy evolution to offset radiative cooling in the large-scale environments in which they typically reside. While previous studies suggest that the total kinetic power output from radio AGN is sufficient for this purpose, many have relied on JET-power estimation from radio luminosities using generalised scaling relations that neglect additional information such as source size and environment. We here infer the cosmic evolution of radio AGN kinetic JET powers using a physically motivated semi-analytic model for the first time. Initial analysis on a sample of 619 radio AGN at $z < 2.5$ from LoTSS Deep Field and International LOFAR Telescope images of the Lockman Hole implies a population dominated by short-lived sources typically of lower JET power. After incorporating weighting towards shorter lifetimes in the inference models, we utilise ELAIS-N1 and Boötes LoTSS Deep Field data to expand our analysis to a much larger sample of 5,187 objects, deriving JET kinetic luminosity functions and integrated kinetic luminosity densities for the radio AGN population out to $z = 2.5$. In broad agreement with previous results in the literature, we find the total power output per comoving volume to be $\sim$10$^{32}-$10$^{33}$ W Mpc$^{-3}$ across the full redshift range, with some suggestions of moderate positive evolution from $z$ = 0$-$1 and little evolution from $z$ = 1$-$2. These values are compatible with expectations from some cosmological models, providing strong evidence for the viability of feedback from radio AGN JETs across cosmic time.

[abstract 13 / 29] (score: 3)
arXiv:2604.19988 [pdf, ps, other]

Title: Pulsational mass loss from supermassive stars creates the compact shells of Little Red Dots

Authors: Devesh Nandal, Igor Chilingarian, Chris Nagele, John Chisholm, Franz E. Bauer, Abraham Loeb,

Comments: 19 pages, 6 figures. Submitted to ApJL. Comments are welcome !

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

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

Little Red Dots (LRDs) have emerged as one of the central puzzles of the JWST era. Their spectra increasingly require dense gas close to the source, yet the physical origin of that cocoon-like structure remains unclear. We examine whether late pulsational mass loss from supermassive stars (SMS)leads to dense gas cocoons. We analyze five accreting GENEC models at different metallicities with characteristic masses of order $10^5\,M_\odot$, following them through post-accretion evolution with radial pulsation calculations and general RELATIVISTIC (GR) stability diagnostics. Mass loss during the final stages of evolution occurs not as a steady wind, but through discrete strange-mode ejection episodes. In the $Z=10^{-2}\,Z_\odot$ model, which provides the clearest LRD analogue, four late episodes last $41$--$282$ yr and eject $10$--$348\,M_\odot$ each, for a total loss of $(4.8-10)\times10^2\,M_\odot$; the final episode alone contributes $\simeq 73\%$ of that budget. Since the last episode dominates the mass-loss, it is the only event sufficiently massive enough to leave behind a compact, optically thick shell extending out to 0.4 pc that reproduces the LRD dense gas cocoon. The final ejecta are H/He dominated but chemically distinctive, with a robust nitrogen-rich composition, $\log(\mathrm{N/O})\simeq0.13$ and $\log(\mathrm{C/O})\simeq-0.23$. The SMS reaches GR instability at an age of $\sim 1$ Myr and collapses in $\sim10^4$ s, retaining $\sim 99\%$ all of its mass. Across the full metallicity range from Pop III to $10^{-2}\,Z_\odot$, this shell-ejection channel persists. Pulsational mass-loss from SMSs therefore provides a physically motivated origin for the compact cocoon-like structure implied by LRDs, while remaining the natural progenitors of the massive BLACK HOLE seeds invoked in direct collapse scenario.

[abstract 14 / 29] (score: 3)
arXiv:2604.20085 [pdf, ps, other]

Title: A Physics-Informed Neural Network for Solving the Quasi-static Magnetohydrodynamic Equations

Authors: Jonathan S. Arnaud, Christopher J. McDevitt, Golo Wimmer, Xian-Zhu Tang,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

A physics-informed neural network (PINN) is developed, for the first time, to learn the time-dependent quasi-static MAGNETohydrodynamic (MHD) equations in axisymmetric tokamak geometry, without any experimental or synthetic data. The initial study considered an ITER-like tokamak and found that a PINN, after careful treatment, was capable of learning the solution to the MHD system and predict a vertically displacing plasma, where general agreement with ground truth simulation was observed. The proof-of-principle demonstration highlights the potential of physics-constrained deep learning to learn complex plasma behavior.

[abstract 15 / 29] (score: 3)
arXiv:2604.20484 [pdf, ps, other]

Title: The physics of ELM-free regimes in EUROfusion tokamaks

Authors: M. G. Dunne, M. Faitsch, O. Sauter, E. Viezzer, B. Labit, A. Kappatou, D. Keeling, B. Vanovac, I. Balboa, P. Bilkova, P. Bohm, D. Kos, J. Hobirk, E. Lerche, P. Lomas, S. Menmuir, T. Pütterich, L. Radovanovic, S. Saarelma, S. Silburn, D. Silvagni, E. R. Solano, H. J. Sun, A. Tookey, The ASDEX Upgrade Team, The TCV Team, The EUROfusion Tokamak Exploitation Team, JET contributors,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The development of operational scenarios without large Type-I ELMs is of utmost importance for the stable operation and longevity of future tokamaks. The EUROfusion tokamak exploitation program has therefore made the understanding of ELM-free regimes a major topic of exploration across all its contributing devices (ASDEX Upgrade, JET, MAST-Upgrade, TCV, and WEST). An integrated program to investigate a range of Type-I ELM-free regimes has been developed covering the enhanced D-alpha (EDA), MAGNETic perturbations (MP), negative triangularity (NT), quasi-continuous exhaust (QCE), quiescent H-mode (QH), the baseline small ELMs (SE), I-mode, and X-point radiator (XPR) regimes. This contribution focuses on the development and understanding of the NT and QCE regimes on ASDEX Upgrade, JET, and TCV. The importance of transport via ballooning modes in both regimes is highlighted, as well as the progress in developing access models based on ideal-MHD. In the case of the QCE, this can also be expressed as a minimum separatrix density, which corresponds well to experimentally measured separatrix densities. Particular focus is paid to the performance of the QCE in terms of the achieved pedestal top values, which, when appropriately normalised, do not differ significantly from ELMy H-mode plasmas. This, combined with the predicted minimum separatrix density for the 15 MA ITER baseline plasma, highlight the relevance of the QCE as a potential operational scenario for both ITER and future reactors.

[abstract 16 / 29] (score: 3)
arXiv:2604.20499 [pdf, ps, other]

Title: Reshaping the inner shadow of a Kerr BLACK HOLE by a torn accretion disk

Authors: Shiyang Hu, Dan Li, Chen Deng, Kejian He,

Comments: 23 pages, 9 figures

Subjects: gr-qc astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

When an accretion flow extends to the event horizon, their intersection defines the contour of the inner shadow. However, the morphological evolution of this critical feature remains largely unexplored within a torn accretion disk system, a configuration comprising distinct sub-disks formed when a tilted disk is disrupted by frame-dragging. To address this, we phenomenologically construct a torn accretion disk model and numerically simulate the inner shadow of a Kerr BLACK HOLE using RELATIVISTIC backward ray-tracing. We discover that the torn disk geometry profoundly alters the BLACK HOLE's observational signatures, inducing severe erosion of the inner shadow and generating novel features such as bifurcated shadows, crescent-like structures, and multiple orders of shadow rings. These exotic morphologies, which are predominantly governed by the spatial discontinuity between the sub-disks and the tilt angle of the outer sub-disk, are exceedingly difficult to replicate within standard equatorial accretion paradigms. Our findings demonstrate that these distinctive shadow structures hold significant potential to serve as robust diagnostic probes for torn accretion environments, simultaneously implying that relying solely on the inner shadow to test gravity theories is fundamentally insufficient.

[abstract 17 / 29] (score: 3)
arXiv:2604.20814 [pdf, ps, other]

Title: A Search for Rotation Measure Flare Candidates in Repeating Fast Radio Bursts

Authors: Ye Li,

Comments: 13 pages, 5 figures

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of unknown origin. Rotation measures (RMs) probe their local MAGNETo-ionic environments and provide important clues to their nature. While RM variability has been observed in several repeating FRBs, it is typically gradual or stochastic. Recently, observations of FRB~20220529 revealed an abrupt RM excursion followed by rapid recovery on week-long timescales, termed an ``RM flare'', suggesting a potentially distinct form of RM variability associated with localized MAGNETized plasma. In this work, we perform a systematic search for RM flare candidates in repeating FRBs with multi-epoch RM measurements. Using a $3σ$ significance threshold, we identify two candidates with multiple observational epochs (FRB~20121102A and FRB~20201124A) and two additional single-epoch candidates (FRB~20180916B), in addition to the event in FRB~20220529A. Our results suggest that RM flares, if confirmed, may not be rare among repeating FRBs and point to highly dynamic MAGNETized environments local to the sources. Future high-cadence polarimetric observations, particularly following the discovery of RM excursions, will be essential for confirming these candidates and constraining their physical origin.

[abstract 18 / 29] (score: 2)
arXiv:1706.00895 [pdf, ps, other]

Title: Basic geometric and kinematic features of the Standard Cosmological Model

Authors: D. I. Nagirner, S. G. Jorstad, A. V. Dementyev,

Comments: Published in the Journal of Advance Research in Applied Science

Subjects: gr-qc

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

We present a brief history of the construction of models of the universe, followed by calculations of quantitative characteristics of basic geometric and kinematic properties of the Standard Cosmological Model ($Λ$CDM). Using the Friedmann equations of uniform space, we derive equations characterizing a $Λ$CDM model that describes a universe corresponding to current observational data. The equations take into account the effects of radiation and ultra-RELATIVISTIC neutrinos. It is shown that the universe at very early and late stages can be described to sufficient accuracy by simple formulas. Certain important moments of cosmic evolution are determined: the times when densities of the gravitational components of the universe become equal, when they contribute equally to the gravitational force, when the accelerating expansion of space begins, and several others. The dependences of different distances on redshift and the scale factor of space are derived. The distance to the sphere that expands with the speed of light (the Hubble distance), and its current and future acceleration, are found. Concepts of a horizon, second inflation, and second horizon are discussed. We consider the remote future of the universe and the opportunity, in principle, of connection with extraterrestrial civilizations.

[abstract 19 / 29] (score: 2)
arXiv:2507.23663 [pdf, ps, other]

Title: Disentangling spinning and nonspinning binary BLACK HOLE populations with spin sorting

Authors: Lillie Szemraj, Sylvia Biscoveanu,

Comments: matches published version

Subjects: gr-qc astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The individual component spins of binary BLACK HOLEs (BBHs) are difficult to resolve using gravitational-wave observations but carry key signatures of the processes shaping their formation and evolution. Recent analyses have found conflicting evidence for a sub-population of BLACK HOLEs with negligible spin, but the Default spin magnitude population model used in LIGO-Virgo-KAGRA analyses cannot formally accommodate an excess of systems with zero spin. In this work, we analyze several different simulated BBH populations to demonstrate that even in the face of this mismodeling, spinning and nonspinning populations can be reliably distinguished using the Default spin magnitude population model coupled with spin sorting. While typical analyses sort the binary components by their masses, sorting the components by their spin magnitudes instead offers a complementary view of the properties of individual systems consistent with equal mass and of population-level properties, given binary evolution processes like tidal-spin up that predict asymmetric spin magnitudes among the binary components. We conclude that current observations of the BBH population are inconsistent with a fully nonspinning population, but could be explained by a population with only one spinning BLACK HOLE per binary or a population with up to 80% nonspinning sources.

[abstract 20 / 29] (score: 2)
arXiv:2601.03337 [pdf, ps, other]

Title: AT2024wpp: An Extremely Luminous Fast Ultraviolet Transient Powered by Accretion onto a Black Hole

Authors: Daniel A. Perley, Anna Y. Q. Ho, Zoë McGrath, Michael Camilo, Cassie Sevilla, Ping Chen, Genevieve Schroeder, Taya Govreen-Segal, Aleksandra Bochenek, Yu-Jing Qin, James H. Gillanders, Benjamin Amend, Joseph P. Anderson, Igor Andreoni, Amar Aryan, Eric C. Bellm, Joshua S. Bloom, Thomas de Boer, Jonathan Carney, Ilaria Caiazzo, Ken C. Chambers, Panos Charalampopoulos, Ting-Wan Chen, Tracy X. Chen, Eric R. Coughlin, Michael Coughlin, Michel Dennefeld, Georgios Dimitriadis, Christoffer Fremling, Danielle Frostig, Avishay Gal-Yam, Lluís Galbany, Anjashay Gangopadhyay, Melzie Ghendrih, Matthew J. Graham, Mariusz Gromadzki, Steven L. Groom, Claudia P. Gutiérrez, K. -Ryan Hinds, Mark E. Huber, Cosimo Inserra, Benjamin C. Kaiser, Mansi M. Kasliwal, Niilo E. Koivisto, Chien-Cheng Lin, Chang Liu, Thomas B. Lowe, Eugene Magnier, Ashish A. Mahabal, Andrew Milligan, Paloma Minguez, Geoffrey Mo, Tomás E. Müller-Bravo, Matt Nicholl, Priscila J. Pessi, Giuliano Pignata, Josiah Purdum, Nabeel Rehemtulla, R. Michael Rich, Anwesha Sahu, Avinash Singh, Stephen J. Smartt, Jesper Sollerman, Gokul Srinivasaragavan, Shubham Srivastav, Robert D. Stein, Steve Schulze, Jack W. Tweddle, Richard Wainscoat, Jacob L. Wise, Lin Yan, David R. Young,

Comments: Accepted to MNRAS. Machine-readable radio and optical photometry tables included as ancillary files

Subjects: astro-ph.HE

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

We present the discovery of AT 2024wpp ("Whippet"), a fast and luminous 18cow-like transient. At a redshift of z=0.0868, revealed by Keck Cosmic Web Imager spectroscopy of its faint star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity (2x10^45 erg/s), maximum photospheric radius (10^15 cm), and total radiated energy (10^51 erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-UV spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending >100 days post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly-accreting central engine blows a fast (~0.2c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent identifiable spectroscopic features from appearing in the ejecta or in the surrounding circumstellar material. Weak H and He signatures do emerge in the spectra after 35 days in the form of double-peaked narrow lines. Each peak is individually narrow (full width ~3000 km/s) but the two components are separated by ~6600 km/s, indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.

[abstract 21 / 29] (score: 2)
arXiv:2603.17505 [pdf, ps, other]

Title: Optical transients from non-explosive double white-dwarf mergers: the case of a central neutron star remnant

Authors: M. M. Ridha Fathima, Alexandre M. R. Almeida, Mattia Bulla, Jaziel G. Coelho, Cristiano Guidorzi, Jorge A. Rueda,

Comments: 12 pages, 6 figures, 3 tables, Published in JHEAP. Version 3 includes corrigenda

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Discoveries of ultra-massive MAGNETic white dwarfs (WDs) and peculiar pulsars have been proposed to originate in double white dwarf (DWD) mergers. There are three possible post-merger central remnants of non-explosive mergers: 1) a stable sub-Chandrasekhar WD; 2) a rapidly rotating super-Chandrasekhar WD; 3) a neutron star (NS). In this work, we explore the thermal transient arising from non-explosive DWD mergers that leave an NS remnant from the prompt collapse of the merged core. The transient is powered by the cooling of the expanding dynamical ejecta, with energy injection from MAGNETic dipole radiation, which depends on the dipole factor $D = B_d^2/P_0^4$, with $B_d$ and $P_0$ being the surface MAGNETic field strength and initial rotation period of the newborn NS. We simulate lightcurves in the Legacy Survey of Space and Time (LSST) bands and estimate the horizon and detection rates for these transients across a range of model parameters. We find LSST detection horizons upper limits ranging $30$--$820$ Mpc and corresponding detection rates $10^2$--$10^6$ yr$^{-1}$ for $\log D = 24$--$40$. Accounting for the survey cadence, we find that only configurations with $\log D = 36$--$40$ are detectable within $240$--$760$ Mpc, with detection rates $10^4$--$10^5$ yr$^{-1}$. Combined searches across surveys can compensate for the low cadence and improve the detection rates of fast and less energetic sources. Multi-wavelength campaigns can aid in detecting the spindown radiation at higher energies observable after the optical transient. Observations of these transients will provide direct evidence of the non-explosive DWD mergers, characterise the remnants and progenitor parameters, and the fraction of explosive and non-explosive mergers.

[abstract 22 / 29] (score: 2)
arXiv:2604.12521 [pdf, ps, other]

Title: POLARIS: A Sparse Radial Neutrino Telescope Design for the Pacific Ocean

Authors: Karolin Hymon, Alexander Chen, Meng-Xue Tsai, Wan-Ting Hseu, Tzu-Hsuan Su, Anatoli Fedynitch,

Comments: Submission to JCAP

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The cubic-kilometer neutrino telescopes have opened neutrino astronomy as an observational discipline. The recent detection of KM3-230213A, the highest-energy neutrino ever observed at ~220 PeV, as a near-horizontal muon track underscores that the ultra-high-energy frontier is accessed through horizontal directions where the Earth's opacity above ~100 TeV confines the observable sky to a narrow band around and above the horizon. Yet extending general-purpose detector architectures into this regime requires disproportionate increases in instrumentation, cost, and logistical complexity. A compelling alternative is to deploy specialized detectors that target this natural geometry. POLARIS (Pacific Ocean Large Area Radial Instrumented Sparse array) is a sparse planar deep-water Cherenkov array optimized for neutrino-induced muon tracks from horizontal directions in the multi-TeV to PeV regime. By rotating the conventional vertical string layout into a radial planar configuration, the detector presents maximal cross-section to horizontal tracks while naturally suppressing the down-going atmospheric background. With only 1100 optical modules, the five-arm design reaches point source and diffuse flux sensitivities at PeV energies competitive with detectors deploying several times more instrumentation. As a dedicated $ν_μ$ track detector, POLARIS provides the muon-flavor channel that tau-optimized experiments such as TAMBO and Trinity do not cover, enabling full flavor composition measurements from astrophysical sources. Using the Prometheus simulation framework, this study demonstrates that targeted sparse geometries can open new discovery space at the high-energy frontier at a fraction of the cost of general-purpose arrays.

[abstract 23 / 29] (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: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

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 24 / 29] (score: 2)
arXiv:2604.19927 [pdf, ps, other]

Title: Experimental observation of drift acoustic cnoidal waves in a MAGNETized plasma

Authors: Tanmay Karmakar, Rosh Roy, Lavkesh Lachhvani, Raju Daniel, Bhoomi Khodiyar, Prabal K. Chattopadhyay, Abhijit Sen, Sayak Bose,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

We report the experimental observation of highly nonlinear coherent structures in a linear MAGNETtized plasma characterized by a strong background density gradient and significant ExB velocity shear under high ion-neutral collisionality. These structures, identified as drift acoustic waves, exhibit large normalized density fluctuations reaching amplitudes of up to ~10% and show periodic sawtooth-like waveforms. These observed waveforms are well described by cnoidal functions, corresponding to stationary nonlinear wave trains. Cnoidal waves are exact solutions of the Korteweg-de Vries (KdV)-type equations, alongside the more commonly studied soliton solutions. To the best of our knowledge, this work presents the first controlled experimental observation of cnoidal wave trains in a highly collisional MAGNETized plasma through systematic variation of profile gradients. These findings provide important new insights into the nonlinear evolution and saturation of drift acoustic waves in inhomogeneous, sheared, and collisional MAGNETized plasmas.

[abstract 25 / 29] (score: 2)
arXiv:2604.19967 [pdf, ps, other]

Title: The curved JET in the young star FN Tau

Authors: M. A. Burlak, A. V. Dodin, A. V. Zharova, N. P. Ikonnikova, V. A. Kiryukhina, S. A. Lamzin, D. A. Lashin, B. S. Safonov,

Comments: 20 pages, 7 figures, Accepted in Astrophysics

Subjects: astro-ph.SR

Created: 2026-04-21; Updated: 2026-04-23; Datestamp: 2026-04-23

In the vicinity of the young star FN Tau, we have detected a microJET and four Herbig-Haro objects, whose positions and kinematics indicate the presence of a bipolar collimated outflow from the star - HH 1267. The stellar JET does not propagate rectilinearly, and we discuss the possibility that the curved shape of the JET, whose axis is inclined to the line of sight at an angle $<20^\circ$, results from the precession of the inner regions of the FN Tau protoplanetary disk. Approximately 60 years ago, the star underwent outbursts with an amplitude of $Δm_{\rm pg} \sim 2^{\rm m}$ lasting several months, which we associate with the onset of the microJET.

[abstract 26 / 29] (score: 2)
arXiv:2604.20101 [pdf, ps, other]

Title: Gyrokinetic simulations on zonal flow-turbulence spreading coupling

Authors: Min Ki Jung, Sumin Yi, Taik Soo Hahm, Yong-Su Na,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Zonal flows and turbulence spreading play important roles in MAGNETic fusion plasma confinement, yet their coupling mechanisms remain elusive. Using global nonlinear gyrokinetic simulations, we show that turbulence spreading transports zonal flow radially, extending into the linearly stable regions after local nonlinear saturation of turbulence. Theoretical understanding has been gained by analyzing the simulation results in the context of a momentum theorem in toroidal plasmas [T.S. Hahm \textit{et al.}, Phys. Plasmas \textbf{31}, 032310 (2024)] which is an extension of the Charney-Drazin non-acceleration theorem [J.G. Charney and P.G. Drazin, J. Geophys. Res. \textbf{66}, 83 (1961)]. It indicates a direct relation between turbulence-driven enstrophy transport and perpendicular momentum generation.

[abstract 27 / 29] (score: 2)
arXiv:2604.20163 [pdf, ps, other]

Title: A Spatial-Resolved Proton Energy Spectrometer Based on a Scintillation-Fiber Cube

Authors: Tan Song, Ying Gao, Di Wang, Yujia Zhang, Jiarui Zhao, Qingfan Wu, Zhuo Pan, Shirui Xu, Ziyang Peng, Yulan Liang, Tianqi Xu, Zihao Zhang, Haoran Chen, Qihang Han, Xuan Liu, Ye Yang, Maocheng Wang, Siguang Wang, Yihua Yan, Zhongming Wang, Wenjun Ma,

Comments: 21 pages, 12 figures

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

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

Advanced particle acceleration methods have produced high-peak-current ion beams with broad energy spread and complex spatial distribution. There is an urgent need to develop online spatial-resolved energy spectrometers for high-energy pulsed ions. This paper introduces a novel spectrometer based on a scintillation-fiber cube for online diagnosis of proton beams with broadband energy spread and complex spatial distribution. We present its working principles, experimental setup, and comprehensive calibration using monoenergetic and spatially uniform proton beams generated by a SYNCHROTRON accelerator. Calibration results confirm an energy measurement range of 6-93 MeV, a relative energy uncertainty of 0.6% at 80 MeV, and a pixel size of 0.5 mm for beam profile reconstruction. By exploiting a custom-designed energy degrader, we generated a complex proton beam and measured it with the scintillation-fiber cube spectrometer (SFICS). The results demonstrate the spectrometer's potential for online measurement of the energy spectrum and spatial distribution of complex proton beams.

[abstract 28 / 29] (score: 2)
arXiv:2604.20609 [pdf, ps, other]

Title: Deep VLBI constraints on compact radio cores in four ultraluminous X-ray sources

Authors: Ailing Wang, Hua Feng, Tao An, Yijia Zhang, Jun Yang, Roberto Soria, Lian Tao, Thomas Russell, Jing Guo, Liang Zhang,

Comments: This paper has been accepted for publication in The Astrophysical Journal

Subjects: astro-ph.HE

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

We present high-sensitivity Very Long Baseline Interferometry (VLBI) observations of four ultraluminous X-ray sources (ULXs): Holmberg II X-1, IC 342 X-1, NGC 6946 X-1, and NGC 925 X-1. No compact emission was detected on milliarcsecond scales, with rms noise levels reaching approximately 5--20 $μ$Jy. The corresponding $5σ$ flux density upper limits reach $\sim 26\,μ\mathrm{Jy}$, implying radio luminosity limits $L_{\rm R} \lesssim 2 \times 10^{33}\,\mathrm{erg\,s^{-1}}$. This disfavors any persistently bright hard-state-like compact core at our sensitivity level. The previously reported VLBI core in Holmberg II X-1 exhibits significant long-term variability, broadly consistent with an overall decline over the past decades. This behavior is consistent with emission from optically-thin ejecta undergoing adiabatic expansion. The VLBI non-detections may reflect intrinsically weak/intermittent compact emission, and/or low--surface--brightness structure that is resolved out by VLBI, and/or absorption/propagation effects such as free--free absorption in dense, ionized winds.

[abstract 29 / 29] (score: 2)
arXiv:2604.20699 [pdf, ps, other]

Title: Forecasts of CMB $E$-mode anomalies for AliCPT-1

Authors: Jiazheng Dou, Wen Zhao,

Comments: 25 pages, 7 figures, 5 tables

Subjects: astro-ph.CO

Created: 2026-04-22; Updated: 2026-04-23; Datestamp: 2026-04-23

The standard $Λ$CDM model has been highly successful in describing cosmic microwave background (CMB) observations. Nevertheless, a set of large-scale statistical anomalies persists in temperature anisotropies across WMAP and Planck. CMB $E$-mode POLARIZATION offers an independent probe of these anomalies, circumventing the look-elsewhere effect inherent in temperature-only analyses. In this paper, we forecast the capability of the Ali CMB Polarization Telescope (AliCPT), a ground-based CMB experiment in the Northern Hemisphere, to detect such anomalies in large-scale $E$-mode POLARIZATION. Using 1000 unconstrained simulations processed with the NILC component separation method, we evaluate four anomaly estimators: dipole modulation, lack of large-angle correlations, quadrupole-octopole alignment, and point-parity asymmetry. Our analysis considers two noise levels for AliCPT, as well as a joint configuration with Simons Observatory (SO) Large Aperture Telescope (LAT). For dipole modulation, we validate the local variance estimator on modulated simulations with an input amplitude $A_d = 0.07$, and find that the combined AliCPT+SO dataset is likely to detect the injected $E$-mode modulation at a 99% confidence level. Tests of the full suite of anomaly statistics on unconstrained isotropic simulations indicate that AliCPT alone, owing to its limited sky coverage, might introduce systematic biases or enlarged uncertainties, especially for quadrupole-octopole alignment and point-parity asymmetry. The combination with SO largely restores the statistical distributions to those expected in an ideal full-sky scenario, thereby establishing a near-cosmic-variance benchmark for upcoming anomaly investigations.