High Energy Astrophysical Phenomena
Advancing Fundamental Physics and Cosmology with high-resolution X-ray imaging
Sara Turriziani, Herman L. Marshall, Daryl Haggard et al. (+4 more)
Black Holes are the key to solving many unanswered questions in fundamental physics: in particular, the very extreme properties shown by supermassive black holes at the centers of
galaxies make them obvious candidates for testing
gravity theories in the strong-field regime. Since X-rays are generated by matter under extreme physical conditions, ultra-high resolution X-ray imaging (uXRI) will directly image the region near the event horizon of black holes in X-rays, similar to the Event Horizon
Telescope in the
radio band, enabling unprecedented tests of General Relativity and alternative theories of
gravity near supermassive black holes. On the other hand, clusters of
galaxies hold the potential of unveiling many unknowns in cosmology. uXRI will unlock this potential by probing small-scale
plasma properties in the intracluster medium, providing the missing link required to establish
galaxy clusters as reliable tools for high-precision cosmology. Moreover, uXRI will enable mapping of Dark Matter from
galaxy cluster dynamics via proper motion measurements. Finally, uXRI will open a new field of precision X-ray astrometry, allowing for measuring
pulsar parallaxes to support nanoHertz gravitational wave searches.
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All authors Sara Turriziani, Herman L. Marshall, Daryl Haggard, Scott Randall, Mayura Balakrishnan, Tom Maccarone, Nicole Ford
Earth and Planetary Astrophysics
The $\gamma$ Cephei System: Updated Orbits, Dynamical Architecture, and Limits on Additional Companions
Judah Van Zandt, Brendan P. Bowler, Michael Endl et al. (+18 more)
The $\gamma$ Cephei system hosts one of the first
exoplanets discovered and is orbited by one of the closest known stellar companions to a
planet-hosting
star. Here, we derive updated orbital fits for $\gamma$ Cep AB, the stellar binary, and Ab, the
planet, by combining literature data with Hipparcos-Gaia astrometry, new radial velocities (RVs), and adaptive optics imaging. We acquired 328 RVs of $\gamma$ Cep A with Keck/HIRES, AFP/Levy, McDonald/Tull, and Whipple/TRES, and eight adaptive optics imaging epochs with Keck/NIRC2, including the earliest spatially resolved image of $\gamma$ Cep B in 2003. These observations extend the precision RV baseline of $\gamma$ Cep to 45 years and the direct imaging baseline to 23 years, improving inferred orbital parameter precisions by a factor of 2–10 compared to previous work. For $\gamma$ Cep B, we derive a semi-major axis of $a_B=20.07 \pm 0.06$ AU, a mass of $M_B=415 \pm 2$ $M_{Jup}$ ($0.396 \pm 0.002$ $M_{\odot}$), an eccentricity of $e_B=0.422 \pm 0.002$, and an inclination of $i_B=119.8^{\circ}\pm0.1^{\circ}$. For $\gamma$ Cep Ab, we find a separation of $a_{Ab}=1.978 \pm 0.007$ AU, a minimum mass of $M_{Ab} \sin i = 1.62 \pm 0.04$ $M_{Jup}$, and an eccentricity of $e_{Ab}=0.07 \pm0.03$. Using the RV residuals and dynamical constraints, we rule out additional Jovians between 2.5–20 AU, and companions more massive than Neptune for $a<1$ AU, both at $>90\%$ confidence. The absence of additional giant
planets over a broad range of orbital separations is consistent with a dynamically sculpted system in which the close stellar companion limited the formation or long-term survival of other distant companions.
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All authors Judah Van Zandt, Brendan P. Bowler, Michael Endl, William D. Cochran, Phillip MacQueen, Artie Hatzes, Guillermo Torres, David W. Latham, Andrew W. Howard, Benjamin Fulton, Howard Isaacson, Michael C. Liu, Samuel A. U. Walker, Jerry W. Xuan, Jingwen Zhang, Rebeca E. Soto Armendariz, Lauren I. Biddle, Kyle Franson, Lillian Jiang, Marvin Morgan, Quang H. Tran
High Energy Astrophysical Phenomena
Vortex pinning and the elastic response of neutron-star crusts - I. Axisymmetric loading
Elia Giliberti and Gabriele Cambiotti
Vortex pinning is central to the standard interpretation of
pulsar glitches, but the mechanical load exerted by a pinned
vortex array on the solid crust has received less
attention than the angular-momentum reservoir itself. We calculate the axisymmetric elastic response of a continuously stratified
neutron-
star crust to this load using realistic SLy4 and BSk21 stellar backgrounds and composition-dependent Coulomb shear moduli. The superfluid-crust lag sets the Magnus force, while the mesoscopic pinning force of Seveso et al. (2016) provides a local upper bound. At low lag the response is linear; progressive local saturation then produces a broad transition and a finite high-lag envelope. The stress maximum is robustly located at the deep crustal boundary towards the rotation axis, although the local Magnus force vanishes on-axis, showing that the localization is produced by global elastic-gravitational redistribution. Realistic elasticity changes the stress amplitude by 10-20 per cent relative to the common mu=10^-2 P prescription and reverses the SLy4-BSk21 ordering. At a Vela-motivated lag of 10^-2 rad s^-1, the maximum strain is only 3.1 x 10^-5 (SLy4) and 4.7 x 10^-5 (BSk21), remaining below 1.4 x 10^-4 on the formal plateau. A 1.2-2.0 solar-mass scan changes the stress amplitude by only about 20 per cent and leaves the deep-polar localization unchanged. Pinning therefore supplies a structured and astrophysically relevant crustal pre-stress, but cannot by itself break an initially relaxed crust.
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Astrophysics of Galaxies
Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7
Gourav Khullar, Rachel Bezanson, Katherine A. Suess et al. (+27 more)
We explore the prevalence of mini-quenched or “napping”
galaxies selected from spectroscopic and photometric samples in the UNCOVER/MegaScience survey. These
galaxies are empirically identified by the presence of moderate Balmer breaks, weak emission lines ($EW(H\alpha) < 100$A) and relatively blue UV continua. We infer the
star formation histories (SFHs) of our sample using flexible non-parametric models with Prospector optimized to capture recent episodes of bursty
star formation and quenching, and find that they are uniquely identifiable in the SFR$_{10}$/SFR$_{100}$ parameter space moving towards (temporary) quiescence. We demonstrate that although spectroscopy is best able to identify rapidly declining SFRs, densely sampled medium-band photometry recover these key spectral features and thus robustly identify pure samples of this transient phase – with imaging alone. We quantify the number density of napping
galaxies at $z=4-7$ in the Abell 2744
lensing field, finding 8 spectroscopically confirmed nappers and 60 photometric candidates spanning log$_{10}$(M$_*$/M$_\odot$) $= 7.5-10$. We verify that the photometry alone can identify a pure sample of nappers, leveraging a smaller high signal-to-noise ratio spectroscopic sample. Consistent with previous studies, we find that nappers are most common at low stellar mass (log$_{10}$(M$_*$/M$_\odot$) $\sim9$). We see a hint that the number densities increase from $z\sim6$ to $z\sim4$, though our small sample is likely affected by
cosmic variance. Our study demonstrates the increasing importance of
stochastic star formation as a regulator of low-mass
galaxy growth in the several hundred Myr after reionization, and offers a direct observational testbed for the strength and duty cycle of stellar feedback in cosmological simulations.
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All authors Gourav Khullar, Rachel Bezanson, Katherine A. Suess, Ikki Mitsuhashi, David J. Setton, Joel Leja, Sedona H. Price, Katherine E. Whitaker, Emilie Burnham, John R. Weaver, Iryna Chemerynska, Lukas J. Furtak, Jenny Greene, Bingjie Wang, Hakim Atek, Gabe Brammer, Olivia R. Cooper, Robert Feldmann, Seiji Fujimoto, Anna de Graaff, Ivo Labbe, Danilo Marchesini, Ian McConachie, Tim B. Miller, Abby Mintz, Themiya Nanayakkara, Pascal Oesch, Richard Pan, Casey Papovich, Yunchong Zhang
Astrophysics of Galaxies
Multiscale Synthetic observations of Polarized dust emission: On the origin of Depolarization effect from Molecular clouds to Starless cores and Constraints on Dust Physics
Nguyen Chau Giang, Thiem Hoang, Blakesley Burkhart et al. (+4 more)
Submillimeter observations of polarized dust emission from molecular clouds to starless cores frequently report a decrease in polarization fraction (p) with increasing dust emission intensity (I). This feature is commonly attributed to the
alignment loss of dust grains or the geometrical effects of
magnetic fields, yet, the detailed contributions remain unclear. To investigate the mechanism responsible for the depolarization, we use POLARIS to perform the multiscale synthetic dust polarization observations at $850\mu m$ from magnetically aligned dust grains by RAdiative Torques (RATs) mechanism. We adopt three collapsing cloud models with different
magnetic energy levels and explore the effects of grain
magnetic properties and grain growth on dust polarization. The field geometrical effect is the dominant depolarization mechanism at $N_{\rm H}<10^{21}-10^{22}\rm cm^{-2}$. We find that if grains grow beyond $>0.5\mu m$ and are superparamagnetic (SPM) with large iron clusters, RATs remain effective at high column densities, and grain
alignment loss contributes to depolarization only at $N_{\rm H} > 10^{23}\rm cm^{-2}$. If neither of these conditions is satisfied, the
alignment loss (in cases of insufficient grain growth); or the reduced grain
alignment efficiency by gaseous damping (for paramagnetic grains or SPM grains with small iron cluster sizes) can become the dominant depolarization mechanism at $N_{\rm H} > 10^{22}\rm cm^{-2}$, regardless of how tangled the
magnetic field lines in our simulation. Finally, we show that the depolarization mechanism and the underlying dust physical properties inside starless cores may be identified through the $p-I$ slope and the mean p at the core center.
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All authors Nguyen Chau Giang, Thiem Hoang, Blakesley Burkhart, Doris Arzoumanian, Nguyen Bich Ngoc, Jihye Hwang, Aran Lyo
Astrophysics of Galaxies
The Structural Abundance Crisis of Massive Galaxies in Current Cosmological Simulations
Hassen M. Yesuf, Connor Bottrell, Luis C. Ho et al. (+5 more)
The internal structure of
galaxies encodes the complex baryon cycle driven by gas
accretion,
star formation, and feedback, together with secular
evolution and environmentally driven processes such as mergers and tidal interactions. We present a population-level census of massive nearby
galaxies ($\log(M_\star/M_\odot) > 10$) by comparing Hyper Suprime-Cam Subaru Strategic Program observations with matched mock images from IllustrisTNG, EAGLE, and SIMBA. Using a consistent, like-for-like imaging pipeline, we construct structural abundance functions (SAFs) for key morphological parameters, revealing a structural abundance crisis. Across Sérsic index, concentration, size, and ellipticity, all simulations exhibit large, systematic discrepancies ($>5\sigma$; RMSE $\sim 0.2$–$1.8$\,dex), typically corresponding to abundance differences of factors of several. While individual simulations display diverse failures—underproducing or overproducing compact spheroids, extended or round
galaxies —all underproduce highly flattened disks. Although TNG shows the closest agreement and SIMBA the largest offsets, this shared failure indicates that current models—despite matching global demographics such as the stellar mass function—do not uniquely constrain internal
galaxy structure. Our results demonstrate that agreement in integrated observables can mask fundamental shortcomings in the modelling of mass and angular momentum redistribution. We therefore establish SAFs as a stringent, multidimensional, and observationally accessible
benchmark for testing and calibrating next-generation
galaxy formation models in the era of upcoming deep, wide-field surveys.
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All authors Hassen M. Yesuf, Connor Bottrell, Luis C. Ho, Aaron S. G. Robotham, Sabine Bellstedt, Robin H. W. Cook, Lei Hao, Fengshan Liu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Anamaria Hell, Lincoln da S. Pereira and Tsutomu T. Yanagida
The No-Scale
gravity is a compelling framework to describe particle physics,
gravity and cosmology, in which all mass scales are an illusion given by the value of a scalar field $\phi$. This theory, however, falls under the umbrella of more general scalar-tensor theories, which propagate different modes depending on the scalar field, and faces the extensive debate regarding the equivalence between its Jordan and Einstein frame descriptions. In this work we advocate that by excluding the singular point in the transformation between the two frames (e.g., $\phi=0$) we can have the classical equivalence between them. To show the merit of removing this singular point, we argue the Jordan frame makes the
symmetries of the model manifest, which creates a suitable playground for the particle-physics model building which we illustrate by showing the emergence of discrete
symmetries which leads to a high-quality
axion and also naturally incorporate the seesaw mechanism.
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Earth and Planetary Astrophysics
Probing Triton's Space Environment and Internal Structure: An Integrated Detection-and-Interpretation Framework
Jiansen He, Chuanpeng Hou, Haoen Xie et al. (+10 more)
Triton, Neptune's largest moon, is a
prime ocean-world target. Constraining ocean thickness, composition, and conductivity is essential for habitability assessment, but
magnetic induction alone cannot resolve the thickness-conductivity degeneracy, and
magnetic perturbations from Triton's space currents can obscure the internal induction signal. We present an integrated detection-and-interpretation concept linking four physically consistent calculations. Using `PlanetProfile', we construct a common radial interior structure (temperature, density, conductivity, seismic-wave speed). We then use `MoonMag' to compute the degree-one
magnetic-induction response from that conductivity profile at the synodic, rotational, and orbital periods. We perform a multi-fluid `SWMF' simulation with the induced dipole as the inner-boundary condition and develop a Coulomb-gauge Poisson reconstruction to isolate space-current
magnetic fields. Finally, we develop the `TritonSeis' workflow, three-dimensional seismic forward modeling plus hierarchical travel-time inversion, to constrain the ice-ocean and ocean-rock interface depths. We find that induction is substantially more sensitive to ocean conductivity than to layer thickness, and that space-current fields are comparable in amplitude to the internal induction signal. A five-station synthetic recovery test resolves both interfaces to first order, with errors of +8.4% for the ice shell and -12.5% for the ocean. Under a conservative noise assumption, the minimum detectable magnitudes are approximately 3.8-4.6 at epicentral distances of 100-1000 km. The Poisson reconstruction and end-to-end seismic recovery are, to our knowledge, the first such quantitative demonstrations for Triton. Coordinated
magnetic,
plasma, and seismic measurements are complementary and can break the conductivity-thickness degeneracy, providing a framework for future Triton exploration.
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All authors Jiansen He, Chuanpeng Hou, Haoen Xie, Jiaqi Li, Tianhang Chen, Hong Zou, Xuzhi Zhou, Hui Li, Yan Li, Fuchuan Pang, Bingkun Yu, Hui Huang, Tong Wang
Instrumentation and Methods for Astrophysics
A generalized likelihood model for segmented muon counters
Joaquín de Jesús, Juan Manuel Figueira, Federico Sanchez et al. (+1 more)
Measurements of the muonic component of extensive air showers constrain
cosmic-ray mass composition and hadronic interactions at energies beyond those accessible at accelerators. Arrays of segmented detectors with binary readout are widely used for this purpose: they sample the
muon density at different distances from the shower core to reconstruct the
muon lateral distribution function (LDF). Each detector response is summarized by the number of activated segments, $k$, whose probability distribution provides the likelihood relating the observation to the expected
muon content. Signal pile-up, detector inefficiency, corner-clipping
muons, and background signals shape this distribution, and neglecting them can bias the reconstruction. Existing analytical models include pile-up but otherwise assume an ideal detector response. In this work, we develop a unified statistical framework that incorporates inefficiency, corner clipping, and background through a small set of physically interpretable parameters. We derive exact expressions for the detector response and the likelihood required for
muon-LDF reconstruction, together with a simple binomial approximation that preserves the main statistical properties of the exact distribution. Dedicated Monte Carlo simulations are used to assess the impact of the assumptions underlying the analytical treatment and show that it is negligible over the parameter range considered. They also show that the exact and approximate likelihoods yield similar performance in terms of
estimator bias and confidence-interval coverage. Although motivated by the Underground
Muon Detector of the Pierre Auger Observatory, the framework applies more broadly to segmented particle detectors with binary readout in which particle content is inferred from the number of activated segments.
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All authors Joaquín de Jesús, Juan Manuel Figueira, Federico Sanchez, Darko Veberic
Solar and Stellar Astrophysics
Ion-Scale Waves Regulated by Plasma Beta and Cross Helicity: Observational Evidence for the Helicity Barrier in Imbalanced Solar Wind Turbulence
G. Q. Zhao, R. Meyrand, H. Q. Feng et al. (+3 more)
Ion-scale waves are believed to play an important role in heating of the solar corona and wind, though their generation mechanism remains unclear. Based on Parker Solar Probe observations, this Letter investigates the occurrence of ion-scale waves in the near-Sun solar wind with heliocentric distances between 0.1 and 0.2 au. Results show that the occurrence rate of left-handed polarized waves significantly depends on the
plasma beta ($\beta$) and cross helicity ($\sigma_c$). The occurrence rate rapidly increases with decreasing $\beta$ and increasing $\sigma_c$. Overall, the occurrence rate exceeds 45$\%$ when $\beta<0.2$ and $\sigma_c > 0.7$ are satisfied. These observations are consistent with the direct predictions of the helicity barrier theory that suggests the generation of ion cyclotron waves via imbalanced magnetized
turbulence.
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All authors G. Q. Zhao, R. Meyrand, H. Q. Feng, H. F. Yang, L. Xiang, Z. Wang
Solar and Stellar Astrophysics
Type I Solar Radio Bursts Modulated by Solar Flares
Yutong Li, Chuanyang Li, Yanke Tang et al. (+7 more)
Type I solar
radio bursts (noise storms) are persistent meter-wave nonthermal emissions above active regions, with their occurrence and proper?ties closely related to the local
magnetic configuration and nonthermal electron acceleration. This study examines a type I noise storm on 24 December 2023 and its relation to
flare activity. The noise-storm source was co-spatial with active region AR 3529 and showed frequency-dependent spatial dispersion. The associated M2.9
flare strongly modulated the emission, with the storm intensity decreasing at
flare onset, recovering afterward, and shifting to higher frequencies. Based on multiwavelength observations, we suggest that pre-
flare small-scale reconnection supplied nonthermal electrons to overlying closed
magnetic struc?tures and maintained the storm. During the
flare,
magnetic reconnection above the active region produced bidirectional
plasma ejections and type III bursts with bidirectional frequency drifts; the gradually decreasing starting frequency of these bursts may indicate an upward-moving reconnection site. The resulting
magnetic reconfiguration disrupted electron trapping and suppressed the storm, whereas post-
flare magnetic recovery allowed the emission to resume. These results show that
flares can modulate type I noise storms through
magnetic restructuring and provide insight into the generation mechanism of noise storms.
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All authors Yutong Li, Chuanyang Li, Yanke Tang, Ning Gai, Zichuan Li, Zhe Cui, Yang Gao, Yifan Wang, Xiaodong Xu, Xiaodi Huo
Instrumentation and Methods for Astrophysics
Soft proton experiments supporting the development of astronomical X-ray instrumentation
S.J. Diebold, B. Heß, F. Pfeifle et al. (+11 more)
Orbital soft
protons can severely degrade the performance of astronomical X-ray observatories. On the one hand, they may cause permanent radiation damage to X-ray detectors; on the other hand, they introduce an irreducible background component. Our low-energy grazing-incidence scattering setup provides experimental data for the validation of radiation transport simulations used in the assessment of future X-ray missions. Recent measurements indicate that a significant fraction of
protons scattered from X-ray optics undergo charge exchange and therefore cannot be mitigated by
magnetic diverters. In addition, we present initial
proton-transmission measurements through a thin X-ray filter and compare them qualitatively with TRIM simulations. Quantitative measurements of energy loss and charge-exchange fractions, together with comparisons with TRIM and Geant4, are planned. In this publication, we present the upgraded experimental setup together with commissioning measurements for grazing-incidence scattering and
proton transmission through thin X-ray filters.
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All authors S.J. Diebold, B. Heß, F. Pfeifle, L.Ph.H. Schmidt, C. Tenzer, T. Wildfang, D. Ferreira, M. Freyberg, S. Massahi, D. Paredes-Sanz, E. Perinati, A. Santangelo, B. Stelzer, S. Svendsen
Astrophysics of Galaxies
Primordial Black Hole Seeds for Little Red Dots in $f(R)$ Gravity
Saeed Fakhry
The discovery by the James Webb Space
Telescope (JWST) of an abundant population of compact little red dots (LRDs) and supermassive black holes at high
redshifts poses a severe timing challenge for standard Eddington-limited growth from stellar remnants. In this work, we present a unified hybrid assembly framework in which intermediate-mass seed black holes are formed via hierarchical primordial black hole (PBH) mergers within dense clusters in Hu-Sawicki $f(R)$
gravity, followed by galactic gas
accretion. We demonstrate that the screened $f(R)$ fifth force nonlinearly accelerates early seed formation through a quadratic enhancement of the gravitational-wave radiation-capture kernel, while environmental chameleon screening dynamically self-regulates the growth. Because subsequent gas
accretion scales multiplicatively with seed mass, the $f(R)$ seed enhancement is preserved throughout the
accretion history, drastically reducing the time-averaged Eddington ratios required to assemble $10^{6}\text{-}10^{9}\,M_{\odot}$ LRDs by
cosmic dawn. Confronting our active mass functions with JWST data reveals that a small clustered PBH fraction ($f_{\rm PBH} \lesssim 10^{-3}$) under a realistic active galactic
nucleus duty cycle ($\delta \approx 10^{-2}$) naturally matches observed LRD space densities at $z \sim 5.5\text{-}6.5$ while remaining fully compliant with LIGO-Virgo-KAGRA limits, with modified
gravity naturally driving the high-mass tail. Finally, we show that parameter degeneracies between modified
gravity and cluster density can be cleanly broken by combining three multi-messenger diagnostics: remnant
spin state signatures, a
stochastic GW background cutoff, and a scale-dependent inversion in the PBH spatial correlation function.
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Earth and Planetary Astrophysics
Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS)
Carl Ingebretsen, Bryce T. Bolin, Meredith A. MacGregor et al. (+8 more)
We present results from multi-band g, r, and i, observations of C/2025 K1 (ATLAS) taken with the Gemini North 8.1-m/GMOS imager on 2025 December 6 and December 24, and u, g, r, i, and z observations with the Astrophysical Research Consortium (ARC) 3.5-m/ARCTIC imager on 2025 December 8. We identify at least four distinct fragments in the Gemini and ARC images, designated as A, C, D, and E in these data taken between 2025 December 6 and 24. Color indices are determined from the December 8 ARC observations of fragments A and C, and from the Gemini observations on December 24 for A, C, and D. K1 has an unusually blue g-r color of $\sim$0.40. The color difference between the comet and its fragments at the two epochs may be explained by particle size and light-scattering effects. We used the Gemini observations to calculate dust mass-loss rates for fragments A, C, and D. We conclude that C/2025 K1 has moderate dust mass-loss rates for millimeter-sized dust of $\sim$50 kg/s for the A and C fragments.
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All authors Carl Ingebretsen, Bryce T. Bolin, Meredith A. MacGregor, Carey M. Lisse, Matthew Belyakov, Gracyn Jewett, Mukremin Kilic, Marco Micheli, Davide Farnocchia, Brian Lemaux, Hyewon Suh
Instrumentation and Methods for Astrophysics · Cross-listed from quant-ph
Imaging Stars at the Quantum Compatibility Limit
Xinyao Guo, Haixing Miao, Zheng Cai et al. (+1 more)
Imaging astrophysical sources with a multi-station interferometer is intrinsically a multiparameter
quantum-estimation problem. {Using tools from multiparameter
quantum metrology,} we show that time-resolved repetitive or adaptive measurements in an \(N\)-station array suffer a fundamental array-level incompatibility among visibility
estimators. Collective measurements, {which coherently process the received starlight across multiple time bins in a single joint readout}, remove the array-size penalty up to an order-unity factor, yielding an asymptotic \(O(\sqrt{N})\) enhancement for the {directional-averaged} SNR of visibility measurement. We then propose a
memory-assisted interferometric architecture designed to implement collective readout through coherent storage and joint
quantum processing. Imaging simulations and Fisher-information analyses demonstrate that collective measurements improve image reconstruction in near-term arrays and enhance the resolving power of future long-baseline architectures, with pronounced benefits for representative AGN targets such as NGC~4151 and 3C~273. These results highlight collective measurement as a promising building block for future
quantum-assisted interferometric arrays for stellar imaging.
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All authors Xinyao Guo, Haixing Miao, Zheng Cai, Huan Yang
Cosmology and Nongalactic Astrophysics
Spheroidal Resampling Analysis of High-Redshift Gamma-Ray Burst Spatial Densities
Istvan Horvath, Zsolt Bagoly, Lajos G. Balazs et al. (+6 more)
Gamma-ray bursts (GRBs) are bright transient sources that can be observed at high
redshift. They can therefore be used as tracers of the distant large-scale structure, although the GRB
redshift sample is sparse and affected by strong selection effects. We analyze the three-dimensional distribution of 542 GRBs with spectroscopic
redshifts. The method extends our earlier spherical-window search by replacing spherical counting volumes with axisymmetric spheroids. The angular positions of the observed GRBs are kept fixed in the Monte-Carlo null samples, while the
redshifts are shuffled within each Galactic hemisphere. In the Northern Galactic hemisphere, the overdensity associated with the Hercules–Corona Borealis Great Wall remains significant for a range of spheroidal shapes. This supports the stability of the previously reported signal and shows that it is not only a consequence of using spherical counting volumes. In the Southern Galactic hemisphere, the same method finds no structure with comparable significance. A small candidate grouping is present, but its significance is only marginal, and it is sensitive to the small number of events. We conclude that spheroidal resampling is a useful check of GRB overdensity searches, but the physical nature of any candidate structure still requires confirmation with independent tracers such as
galaxy or
quasar samples.
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All authors Istvan Horvath, Zsolt Bagoly, Lajos G. Balazs, Jon Hakkila, Janos Horvath, Sandor Pinter, Istvan I. Racz, Peter Veres, Bendeguz Koncz
Astrophysics of Galaxies
The multi-frequency radio light curve of the sub-pc SMBH binary candidate PG 1302-102
Sayan Basu, Roger P. Deane and Keith W. Bannister
Supermassive black hole binary (SMBHB) candidates with sub-parsec (sub-pc) orbital separations are rare, high-value systems, thought to be the dominant sources of the recently detected nanoHertz (nHz) gravitational wave (GW) background. Alongside
pulsar-timing-array searches for localized nHz GW sources from SMBHBs, an increasing number of candidates have been identified from synoptic surveys of large
quasar optical light curves over increasingly long baselines. The optical light curve of the
quasar PG~1302-102 at a
redshift of $z=0.278$ exhibits a pronounced, smoothly varying periodic signal of ~5.2 years over approximately 20 years. Although the cause of this periodicity remains debated, a plausible explanation is a binary system of two SMBHs with a sub-pc separation. At this close distance, the $10^{8.3-9.4} M_{\odot}$ nuclear black holes in PG 1302-102 are expected to merge within $\sim$$10^{5}$ yr solely due to GW emission. We present a multi-frequency
radio light curve analysis of PG~1302-102 spanning a $\sim$19-year baseline, with observations between 2005 and 2024 drawn from the Australian
Telescope Compact Array (ATCA). The ATCA
radio light curve is highly variable at 5.5~GHz but shows no significant evidence of the periodicity seen at optical wavelengths. However, we report fractionally stronger evidence of periodicity in the in-band spectral index time-series at 5.5~GHz, with a period consistent with the optical periodicity. Furthermore, the recently reported change in optical periodicity is also present in the
radio in-band spectral index light curve. These two results suggest that
radio and optical periodicity may be physically coupled despite very different emission mechanisms. We argue that this
radio-optical coupling reinforces the SMBHB interpretation, despite the optical periodicity change, and provides an intriguing case study ahead of the LSST-SKAO era.
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Instrumentation and Methods for Astrophysics
Microchannel plate detector development for ultraviolet astronomy
S. Diebold, J. Barnstedt, J. Bayer et al. (+8 more)
Observational data from the UV wavelength range is crucial to solve several astrophysical puzzles. Consequently, there are a number of upcoming UV missions from CubeSats up to the future flagship Habitable Worlds Observatory. Besides novel instrument concepts and improved coatings, advanced detectors are key for the success of these missions. The microchannel plate (MCP) detector technology offers a unique asset in the UV: the combination of single-
photon counting and visible-blindness. The UV hardware group at the Institut für Astronomie und Astrophysik Tübingen (IAAT) develops a versatile MCP detector system that addresses the complete UV band. While a sealed-tube design is limited to wavelengths above 118\,nm, an open-face variant also covers the whole far- and extreme-UV. Both use the same readout: a coplanar cross-strip anode and FPGA-based electronics. In this contribution, we report on the status of the detector development, present the latest characterization results, and give an outlook on the mission prospects.
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All authors S. Diebold, J. Barnstedt, J. Bayer, L. Conti, H.R. Elsener, C. Kalkuhl, D. Rau, D. Schaadt, T. Schanz, B. Stelzer, K. Werner
Solar and Stellar Astrophysics
Origin of small-scale evaporation flows deep in the chromosphere during a solar flare
L. P. Chitta, H. N. Smitha, F. A. Iglesias et al. (+29 more)
Flares are caused by an abrupt release of
magnetic energy in the solar atmosphere.
Plasma heated to well over 10 MK filling the post-
flare corona originates from a rapid heating and ablation of the cooler chromospheric material. This chromospheric evaporation is thought to be facilitated primarily by nonthermal electrons impinging on to the lower atmosphere. Questions on when and where in the chromosphere these upflows originate, however, are not fully resolved. Here we report on unprecedented high-resolution observations of an M-class
flare recorded by the Sunrise Ultraviolet Spectropolarimeter and Imager on board the balloon-borne SUNRISE observatory, that reveal highly structured upflows on spatial scales of ~100 km originating deep in the chromosphere. The flows even precede the onset of nonthermal electrons by about 10 minutes and last through the impulsive phase of the
flare. Our observations shed new light on the lower atmospheric heating and mass circulation in
flares that are challenging to reconcile with the standard solar
flare model.
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All authors L. P. Chitta, H. N. Smitha, F. A. Iglesias, T. L. Riethmüller, A. Feller, W. Chen, A. Lagg, A. Gandorfer, J. Hölken, S. K. Solanki, J. C. del Toro Iniesta, Y. Katsukawa, P. Bernasconi, T. Berkefeld, A. Álvarez-Herrero, M. Kubo, D. Orozco Suárez, B. Grauf, M. Carpenter, A. Bell, Valentín Martínez Pillet, F. J. Bailén, J. Blanco Rodríguez, J. Sebastián Castellanos Durán, E. Harnes, R. T. Ishikawa, Y. Kawabata, T. Matsumoto, T. Oba, A. L. Siu-Tapia, H. Strecker, D. Vukadinović
Astrophysics of Galaxies
Tracing Radial Migration in the Outer Disk: A Comprehensive Analysis of the Old Open Cluster Berkeley 36
Deniz Cennet Ç{\i}nar, D. Bisht, Ing-Guey Jiang et al. (+2 more)
We present a chemo-kinematical, structural, and photometric analysis of the old open cluster Berkeley 36 using Gaia DR3 astrometry and photometry together with high-resolution spectroscopy from the Gaia-ESO Survey DR5.1. Applying a Gaussian Mixture Model to Gaia astrometry, we identify 946 high-probability cluster members. We derive a core radius of 2.63 +/- 0.21 arcmin and a tidal radius of 14.84 +/- 0.47 arcmin, indicating a moderately concentrated and dynamically relaxed system. By fixing the cluster
metallicity to the spectroscopic value of [Fe/H] = -0.19 +/- 0.02 dex and adopting an independently determined
geometric distance of 4377 +/- 510 pc, we minimize the classical age-reddening-
metallicity degeneracy and derive a robust isochrone age of 6.8 +/- 0.5 Gyr. Independent Ba-based chemical clocks yield a mean age of 7.75 +/- 1.94 Gyr, supporting the isochrone solution. The cluster exhibits a high main-sequence binary fraction of 48.0 +/- 1.7% and hosts 83 blue straggler
star candidates with an extended spatial distribution, contrary to classical mass segregation. Orbit integration shows that Berkeley 36 follows a nearly circular orbit in the outer Galactic disc at R_GC = 11.42 +/- 0.44 kpc. Accounting for the Galactic warp and disc
flare increases the cluster's maximum vertical excursion by 86% and the local disc scale height by 17%, respectively. Comparison with its chemically inferred birth radius at R_b = 6.71 +/- 0.66 kpc indicates an outward radial migration of approximately 5 kpc, predominantly driven by churning. These results establish Berkeley 36 as a
benchmark for investigating radial migration, secular
evolution, and the dynamical history of old Galactic open clusters.
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All authors Deniz Cennet Ç{\i}nar, D. Bisht, Ing-Guey Jiang, K. Belwal, Selçuk Bilir
Instrumentation and Methods for Astrophysics
Self-calibration of adaptive optics systems. Application to the THEMIS solar telescope
Clementine Bechet, Eric Thiebaut, Michel Tallon et al. (+3 more)
The interaction
matrix models the effects of deformable mirror (DM) commands as perceived by the wavefront sensor (WFS) and is the cornerstone of the Adaptive Optics (AO) control. Difficulties to calibrate this
matrix arise due to the number of degrees of freedom, the non-linearity, and temporal
evolution of the AO system. An affine approximation of the unknown mapping between the DM commands and the WFS measurements is considered. Optimal
estimators of the parameters of this affine model are obtained by fitting, in the weighted least squares sense, WFS data acquired with random probe commands sent to the DM. Several calibration methods are being considered depending on whether the model is directly fit to the WFS data or to the differences between successive WFS data. We derive closed-form expressions of the
estimators of the components of the model. The proposed calibration methods can be applied under different conditions: before observing, on an internal source, or on-sky in open- or closed-loop. By introducing forgetting factors to reduce the weight of data as they age, we show that the model can be learned continuously using simple recurrence rules. The low computational complexity of these rules makes them suitable for real-time at the same frequency as the AO loop. We derive simple expressions for the mean squared errors (MSE) of the proposed
estimators. We apply the proposed calibration methods to real telemetry data from the AO system of the THEMIS solar
telescope. Our results show that the simple differences method is the method of choice: not only does it produce
estimators with the least MSE, but it is also very simple to implement compared to the push-pull method which is widely used in AO systems.
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All authors Clementine Bechet, Eric Thiebaut, Michel Tallon, Isabelle Tallon-Bosc, Bernard Gelly, Richard Douet
Instrumentation and Methods for Astrophysics
AO3k + SCExAO: on-sky wavefront quality and demonstration of novel WFS techniques with the double XAO system
Julien Lozi, Kyohoon Ahn, Vincent Deo et al. (+5 more)
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, fed by its upstream 3000-actuator "woofer" (AO3k), serves both as a platform for high contrast imaging (HCI) technology maturation and as a science instrument for imaging, spectroscopy, and polarimetry of
exoplanets and disks. SCExAO operates in the visible and near-IR and offers a wide choice of instrument configurations. Over the last year, AO3k/SCExAO underwent significant upgrades to bring improved capabilities and support new developments, all while easing science operations. The new configuration features a beam switcher so that light can be shared between several instrument modules. The system is evolving toward a tighter integration between multiple WFSs and AO stages of correction, with the first stage (AO3k) providing visible and nearIR WFSing, as well as
laser tomography. AO3k+SCExAO has been fully operational since October 2025, demonstrating very high stability on-sky, even in bad seeing conditions up to 2". Having two XAO in series allows us to deploy advanced wavefront control techniques optimized for high-contrast imaging (e.g. speckle nulling, EFC, Coronagraphic LOWFS, Fast and Furious) on the second-stage XAO loop, as AO3k by itself delivers high-contrast PSFs already. Areas of active ongoing research include use of photonic devices for spectrally dispersed interferometric sensing, PSF reconstruction from WFS telemetry, and non-linear sensors (focal plane and
curvature). Recent upgrades to the computer infrastructure are aimed at supporting these R&D efforts and providing a rich collaborative environment for experimentation. In this paper, we will present on-sky high-contrast performance characterization of AO3k, AO3k+SCExAO, and on-sky demonstrations of novel wavefront control techniques to improve the contrast behind the coronagraph.
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All authors Julien Lozi, Kyohoon Ahn, Vincent Deo, Olivier Guyon, Sandrine Juillard, Yoshito Ono, Garima Singh, Sébastien Vievard
High Energy Astrophysical Phenomena
Photon–Dark Matter Elastic Scattering: An Effective-Operator Scan and First Operator-Resolved Sensitivity Estimates from the Galactic Halo
Trinity Rosebud Stenhouse, Asli Acar, Mikhail Bashkanov et al. (+3 more)
Elastic
photon–dark matter scattering attenuates gamma-ray spectra along a line of sight, probing the same operators as dark matter annihilation to
photons but at a rate linear, rather than quadratic, in dark matter density. We consider Standard Model gauge-invariant effective operators of mass-dimension 5 to 7, suppressed by a cutoff scale $\Lambda$, coupling scalar, Majorana or Dirac dark matter to the
photon. The leading operators with non-vanishing real-
photon amplitudes enter at dimension-5 for Dirac dark matter and dimension-7 for Majorana dark matter. In the electroweak-doublet dipole portal, the inelastic splitting invoked to evade direct detection also closes the CMB annihilation bound, leaving attenuation the only one of the three
photon-sector probes that survives. Applying this to a pixel-level reanalysis of 17 years of Fermi–LAT Pass~8 data toward the Galactic centre, we derive the first operator-resolved sensitivity estimates for
photon–dark matter scattering from the Galactic
halo: $\Lambda \simeq 0.32~\mathrm{GeV}$ for the dimension-5 Dirac dipoles, $0.21~\mathrm{GeV}$ for the dimension-6 scalar Rayleigh operator and $0.79$–$1.06~\mathrm{GeV}$ for the dimension-7 Rayleigh family. The reach is weak: it lies below the EFT-validity threshold across the cold dark matter mass range, and is superseded on the dipole plane by CMB and direct-detection constraints. The framework is calibrated against pseudo-experiments, and recomputes the sensitivity for any instrument that provides a per-bin spectrum with uncertainties and a line-of-sight column density.
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All authors Trinity Rosebud Stenhouse, Asli Acar, Mikhail Bashkanov, Frank F. Deppisch, Chamkaur Ghag, Dan P. Watts