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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 21 September

Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics

Real-Time Doppler-Frequency Measurement and Frequency-Pulling Suppression in Arm-locking

Zheng-Rong Xiang, Jun Ke, Tian-Chi Zhu et al. (+3 more)

Arm-locking is an important technique for suppressing laser frequency noise in space-based gravitational-wave detection. However, stronger noise suppression inevitably increases the magnitude of frequency pulling, thereby prolonging the lock-acquisition time and increasing the risk of system instability. To address this issue, this paper proposes a real-time Doppler-frequency measurement and frequency-pulling suppression method based on a linear-quadratic-gaussian controller. To achieve a balance between noise suppression and pulling suppression, a time-varying control strategy is adopted. At the initial stage of the time-varying control process, the primary objective is to rapidly limit frequency pulling. Subsequently, the level of pulling suppression is gradually relaxed while the capability for laser frequency-noise suppression is progressively enhanced, so that the residual frequency noise satisfies the time-delay interferometry (TDI) requirement by the end of the transition. Comprehensive performance simulations are conducted for several arm-locking configurations. The results show that the proposed suppressor can reduce frequency pulling within approximately 1000 s while limiting its magnitude to below 100 MHz, thereby eliminating the need for the conventional Doppler frequency pre-estimation stage. When a Fabry-Perot laser is used, the amplitude spectral density (ASD) of the closed-loop laser frequency noise meets the requirements of second-generation and first-generation TDI after 2000 s and 9200 s of closed-loop operation, respectively. These results demonstrate that the proposed suppressor provides both rapid frequency-pulling suppression and a high level of laser frequency-noise suppression. This new method provide a feasible way for rapid acquisition and locking of arm-locking.
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All authors Zheng-Rong Xiang, Jun Ke, Tian-Chi Zhu, Hao-Xin Xu, Cheng-Gang Shao, Jie Luo

Earth and Planetary Astrophysics

Transit timing variation

Luca Borsato

The transit timing variation (TTV) method is a key approach to the confirmation, detection, and characterisation of exoplanetary systems. This review discusses the detection of TTVs from transit observations and the origins of TTVs, mainly due to gravitational interactions with perturbing planets, whether transiting or not. Additionally, this work details methodologies for deriving planetary parameters, employing quasi-global and local optimisation algorithms within a Bayesian framework. By analysing TTVs, planetary orbital parameters and dynamical properties can be inferred, providing valuable insights into system formation and evolution. The role of resonances and stability in shaping these systems is reviewed, along with sensitivity biases that influence mass determination. Comparative analyses highlight the unique demographic contributions of TTV systems. TTVs offer a window into the dynamical and physical properties of planetary systems, advancing our understanding of their diversity and stability.
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High Energy Astrophysical Phenomena

Multi-wavelength Behaviour and Lepto-hadronic Modeling of PKS 0215+015 Around the Epoch of IceCube-220225A

Athira M Bharathan and Markus Böttcher

The detection of high-energy astrophysical neutrinos has opened a new avenue for identifying cosmic particle accelerators. Blazars, active galactic nuclei (AGN) with relativistic jets oriented close to the observer's line of sight, are promising sites of hadronic interactions capable of producing PeV-scale neutrinos. We investigate the flat-spectrum radio quasar (FSRQ) PKS~0215+015 ($z \simeq 1.715$), positionally consistent with the IceCube-220225A neutrino event of estimated energy $\sim$154~TeV. We combine Fermi-LAT $\gamma$-ray data with Swift-XRT and Swift-UVOT observations to characterise the source around the neutrino epoch. PKS~0215+015 exhibited pronounced $\gamma$-ray, X-ray and optical activity in early 2022, consistent with a disturbance propagating along the jet. We construct broadband spectral energy distributions (SEDs) for the flaring interval and model them using leptonic and lepto-hadronic frameworks. The SED is well reproduced by a leptonic model comprising synchrotron, synchrotron self-Compton and external Compton emission, indicating that electron processes dominate. A co-accelerated proton population remains radiatively subdominant but requires a proton kinetic luminosity roughly two orders of magnitude above equipartition with the magnetic field. The predicted neutrino flux is well below that implied by a single IceCube-220225A-like detection. Independent analysis of short-term $\gamma$-ray variability yields an emission-region size consistent with the SED fit, supporting the model's physical self-consistency. We discuss the temporal and energetic plausibility of the association between PKS~0215+015 and IceCube-220225A and implications for future multimessenger studies of high-redshift FSRQs.
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Astrophysics of Galaxies

Physical conditions in PDRs revealed by IGRINS ro-vibrational H2 observations

Aurélien Piluso, Vincent Maillard, Raphael Meshaka et al. (+10 more)

We compare H2 high ro-vibrational observations of 5 PDRs (S140, IC63, Horsehead Nebula, NGC 2023 and Orion Bar) obtained with the IGRINS spectrograph to PDR models produced with the Meudon PDR code, in order to estimate the physical conditions and to constrain the physical and chemical processes that govern PDRs. We use newly flux-calibrated and extinction-corrected IGRINS H2 observations covering the 1.45-2.45 um range at a resolution of 45000, and adjust Meudon PDR models using both a simple chi2 minimization approach and a robust method using Bayesian inversion followed by posterior exploration via an advanced MCMC technique. The PDR models use specific incident FUV spectra for each PDRs based on theoretical stellar spectra from the Pollux database. The Meudon PDR code is able to reproduce more than 85% of the observed H2 ro-vibrational line intensities within a factor of two. We find that (1) a realistic modeling of the incident FUV field (both in term of geometry and of spectral shape) and (2) the inclusion of recent data on collisional de-excitation rates for high vibrational levels of H2 are key to this success. H2 ro-vibrational emission lines are found to provide good constraints on both the thermal pressure and the incident FUV field strength, G0, although with a non-negligible remaining degeneracy in most PDRs. Additional constraints, such as the spatial scales of the PDR derived from ALMA or JWST observations, are found to be able to lift this degeneracy. For low excitation PDRs, the observations provide evidence that nascent H2 molecules formed on grains have relatively low rotational energy and high vibrational energy, as predicted by theoretical and experimental studies of the surface formation of H2.
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All authors Aurélien Piluso, Vincent Maillard, Raphael Meshaka, Emeric Bron, Franck Le Petit, Kyle Kaplan, Pierre Palud, Emilie Habart, Evelyne Roueff, Jacques Le Bourlot, Aristide Doussot, David Languignon, Nicolas Moreau

Astrophysics of Galaxies

LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744

Mingyu Li, Roberto Maiolino, Zheng Cai et al. (+26 more)

When Population III (Pop III) star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic metallicity constraints, it was identified as an extremely metal-poor or metal-free galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar metallicity to identify Pop III galaxy candidates for spectroscopic follow-up.
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All authors Mingyu Li, Roberto Maiolino, Zheng Cai, Hannah Übler, Boyuan Liu, Qiao Duan, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Eiichi Egami, Bjorn H. C. Emonts, Xiaohui Fan, Yuki Isobe, Lucy R. Ivey, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, J. Xavier Prochaska, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Yunjing Wu, Fujiang Yu, Zijian Zhang

Astrophysics of Galaxies

LATED: Ly$\alpha$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon

Mingyu Li, Zheng Cai, Roberto Maiolino et al. (+24 more)

Cosmological simulations allow a low-level tail of Population III (Pop III) star formation to persist to $z=2-6$. Spectroscopic confirmation is expensive, so an efficient photometric pre-selection is needed. We present LATED (Lyman-Alpha Tomography of Extremely Metal-poor Domains), which selects metal-free and extremely metal-poor candidates from a Ly$\alpha$-emitter parent sample using strong-line diagnostics. The method requires three bands and two colours, $x=m_{\rm OIII}-m_{{\rm H}\alpha}$ and $y=m_{{\rm H}\alpha}-m_{\rm cont}$, which trace oxygen abundance and the H$\alpha$ equivalent width, respectively. Requiring that the filters simultaneously contain [O III]+H$\beta$ and H$\alpha$, together with a Ly$\alpha$ parent selection, defines five windows spanning $z=1.92-6.60$ (four JWST/NIRCam, one Roman/WFI). The criteria, $x\geq x_{\rm min}(z)$ and $y\leq y_{\rm max}(z)$, are set by the per-redshift extrema of a forward-modelled Pop III template locus. Ordinary metal-enriched star-forming and AGN templates fall outside the selection region, and possible contaminants such as little red dots are flagged by their multi-band colours. To check contamination empirically, we apply LATED to 1126 JADES spectroscopic galaxies, and no source is selected in the four NIRCam windows. We release a Python package which converts the same photometry into R3=[O III]/H$\beta$ as a measurement or upper limit, reproducing JADES spectroscopy with small 0.12 dex scatter. Applied to 85 archival MUSE Ly$\alpha$ emitters in Abell 2744, LATED recovers the confirmed extremely metal-poor galaxy AMORE6 and reveals three new candidates at $z=3-5$. Photometry alone cannot establish a metal-free nature. LATED delivers prioritised candidates for spectroscopic follow-up, providing a scalable route toward a systematic census of late-time Pop III star formation.
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All authors Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang

Instrumentation and Methods for Astrophysics

Pushing high angular resolution and high contrast observations on the VLTI from Y to L band with the Asgard instrumental suite: integration status and plans

Marc-Antoine Martinod, Michael J. Ireland, Denis Defrère et al. (+39 more)

ESO's VLTI has a history of record-breaking discoveries in astrophysics using high-angular resolution instrumentation. Its latest visitor instrument, the Asgard instrumental suite, is one key to further enhance the potential of the facility, particularly in the very near-infrared. It comprises four natively collaborating instruments: HEIMDALLR, a K-band fringe tracker, wavefront corrector and stellar interferometer in K band, with the same optics; Baldr, an H-band Zernike wavefront sensor; BIFROST, an Y-J-H-band photonic combiner whose main science case is studying the formation processes and properties of stellar and planetary systems; and NOTT, an L-band nulling interferometer for imaging young planetary systems. Each of these instruments promise significant advances in their respective science goals that scale with their technical challenges and technology innovations. The integration of Asgard is planned in three phases. The first one (integration, commissioning of HEIMDALLR and Baldr) is successfully done. In this paper, we show an overview of the current progress of the integration of Asgard, the first results of the on-sky commissioning of HEIMDALLR and the future steps and observing policies for Asgard to serve the broader community.
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All authors Marc-Antoine Martinod, Michael J. Ireland, Denis Defrère, Stefan Kraus, Frantz Martinache, Peter G. Tuthill, Emilie Bouzerand, Julia Bryant, Sorabh Chhabra, Peter Chingaipe, Benjamin Courtney-Barrer, Fred Crous, Nick Cvetojevic, Daniel S. Dahl, Colin Dandumont, Steve Ertel, Germain Garreau, Adrian M. Glauser, Xavier Haubois, Lucas Labadie, Stéphane Lagarde, Daniel Lancaster, Romain Laugier, Roxanne Ligi, Nathan Long, Alexandra Mazzoli, Thomas Mattheussen, György Medgyesi, Kwinten Missiaen, Sébastien Morel, Daniel J. Ahrer, Barnaby Norris, Jyotirmay Paul, Romain Petrov, Gert Raskin, Sylvie Robbe-Dubois, Gordon Robertson, Muhammad Salman, Ahmed Sanny, Nicolas Schuhler, Owain Snaith, Adam K. Taras

Instrumentation and Methods for Astrophysics

Silencing the stellar glare with kernel-nulling and active phase control on photonic chips

Marc-Antoine Martinod, Vincent Foriel, Nick Cvetojevic et al. (+4 more)

Characterizing exoplanets and finding biosignatures are among the hottest topics in astronomy. This quest is challenged by the brightness contrast between the faint planet and the overwhelming glare of the host star, their small angular separation, and observing conditions degraded by optical aberrations. Nulling interferometry is a promising technique to achieve this goal by fulfilling requirements for both high contrast and high angular resolution. Photonic Integrated Circuits (PICs) provide compactness, design versatility, and scalability needed for nulling. With the PHOTONICS project, we aim to create novel coherent combination architectures, based on a multimode interferometer (MMI) coupler and on-chip active phase control with no moving parts. We present the first lab tests of a four-beam kernel-nuller made out of a single MMI coupler with active phase control: ABCD fringe-tracking and the characterization of the contrast detection limits of a four-beam kernel-nuller.
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All authors Marc-Antoine Martinod, Vincent Foriel, Nick Cvetojevic, Frantz Martinache, Jeronimo Calderon-Gomez, Roxanne Ligi, David Mary

Instrumentation and Methods for Astrophysics

Premature re-entry of the FACSAT-2 nanosatellite: orbital decay and attribution to the maximum of solar cycle 25

Santiago Vargas Dominguez, Mara Valentina Angel and Brayan Nicolas Buitrago

FACSAT-2 Chiribiquete, the second satellite of the Colombian Aerospace Force and the first South American nanosatellite mission dedicated to greenhouse gases, re-entered on 27 October 2025, 926 days after its deployment into a Sun-synchronous orbit, against a declared service life of at least five years and an estimated orbital lifetime of fifteen. The orbital evolution was built from the epochs of the TLEs (two-line elements) of NORAD ID 56205. We reconstruct its decay using its 3696 orbital elements, the solar and geomagnetic indices from the OMNI2 database, and NRLMSISE-00 densities sampled along the orbit. Inverting the drag yields a ballistic coefficient of 72.3 kg/m2 (6% statistical, 20% systematic), equivalent to an effective area of 0.047 m2, consistent with the declared geometry. With it, the model reproduces the trajectory with a root-mean-square error of 7.4 km and, calibrated on 2023-2024 alone, the re-entry with a 28-day out-of-sample error. F10.7 averaged 170.8 sfu over the mission, against the 139 sfu of the environmental scenario derived from the official 2019 forecast, which lengthens the orbital lifetime by x1.52; two co-launched CubeSats give x1.50 and x1.57, a consistency check across objects rather than independent evidence. Imposing quiet geomagnetic conditions returns 102 days, 22% of the shortening, with strong sensitivity to the adopted threshold; a superposed-epoch analysis over 149 storms gives a median drag enhancement of x1.92 for the intense events. We discuss the consequences for the design of FACSAT-3 and for the public communication of a mission's expected lifetime.
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Instrumentation and Methods for Astrophysics

Natural coordinates for constrained correlation functions: Partial autocorrelations and the geometry of positive power spectra

Thomas Erben

Two-point correlation functions are a standard summary statistic in cosmic shear and large-scale-structure analyses. Their values are, however, constrained: non-negativity of the underlying power spectrum restricts any admissible sequence of correlation coefficients $(r_1,\ldots,r_N)$ to a bounded convex region, described in the one-dimensional case by the recursive interval geometry of Schneider & Hartlap (2009). Their formalism introduces an affine variable $x_n$ that maps the admissible interval for $r_n$, given $r_1,\ldots,r_{n-1}$, to $[-1,+1]$. We identify $x_n$ with the partial autocorrelation coefficient $\alpha_n$ of the associated positive Toeplitz correlation matrix, a classical quantity in time-series analysis. The partial autocorrelations thus provide natural coordinates on the admissible region, each $\alpha_n$ varying independently in $[-1,+1]$. This identification makes the standard partial-autocorrelation toolbox directly applicable. The admissible intervals for $r_n$, cumbersome to obtain at higher order in the original determinant-based formalism, now follow from an $\mathcal{O}(N^2)$ recursion at arbitrary order. The inverse hyperbolic tangent used in the quasi-Gaussian likelihood construction of Wilking & Schneider (2013) becomes Fisher's $z$-transformation of partial autocorrelations, providing a classical statistical interpretation of its empirical Gaussianising effect. Numerical experiments illustrate the practical use of these natural coordinates in the tested one-dimensional settings. Higher-dimensional isotropic constraints require additional geometric input and lie outside the direct scope of this identification.
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Instrumentation and Methods for Astrophysics

Development of a Photonically Generated Frequency Reference for Space VLBI

Hannah Tomio, Kohei Yamamoto, Charlotte Zehnder et al. (+5 more)

Space-based Very Long Baseline Interferometry (VLBI) can improve both the angular and temporal resolution of images over terrestrial VLBI techniques. Future space VLBI (sVLBI) missions are targeting higher observation frequencies than modern, terrestrial VLBI, and therefore these missions will require higher stability frequency references than standard hydrogen masers. While existing frequency references for space-based applications have concentrated on long-term stability, in this effort, we present a frequency reference with high short-term stability intended for sVLBI missions. This reference leverages developments in cavity-stabilized lasers from the Laser Interferometer Space Antenna (LISA) mission and commercial efforts towards a robust, space-qualifiable optical frequency comb. We describe the implementation and experimental results of this system with a path to spaceflight, which demonstrates an Allan deviation of $3.26 \times 10^{-14}$ at 1 second, $6.00 \times 10^{-15}$ at 10 seconds, and $6.73 \times 10^{-15}$ at 30 seconds for the 100 MHz frequency reference signal, and show that this performance meets the needs of future sVLBI missions.
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All authors Hannah Tomio, Kohei Yamamoto, Charlotte Zehnder, Guangning Yang, Kenji Numata, Andrew Attar, Henry Timmers, Holly Leopardi

Solar and Stellar Astrophysics

Oblique kink waves in solar coronal streamers

Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin et al. (+1 more)

Coronal streamer kink waves excited by an impact of coronal mass ejections (CMEs) are routinely used to estimate the coronal Alfvén speed. These estimates generally assume wave propagation parallel to the equilibrium magnetic field directed radially outward to the Sun, in the plane of the sky. However, the geometry of CME impacts naturally allows for oblique propagation. We investigate the properties of obliquely propagating kink waves guided by a plasma slab with a central current sheet representing a coronal streamer stalk. We consider both cold and warm streamer plasmas and analyse influence of propagation obliquity on wave dispersion, eigenfunctions, and seismological diagnostics. We find that increasing the propagation obliquity reduces the phase speed owing to both projection effects and the intrinsic dependence of the phase speed on the propagation angle. The wave structure also undergoes a gradual transition from a body mode to a surface mode, leading to stronger perturbations at the slab boundaries and enhanced wave localization. Consequently, for a given energy deposited by a CME impact, oblique kink waves are expected to produce larger observable amplitudes than field-aligned waves. Applying the developed theory to streamer waves reported previously, we infer Alfvén speeds in the range of 50-500 km/s. We show that neglecting wave propagation obliquity may underestimate the Alfvén speed by up to a factor of 1.5. These results demonstrate that wave propagation obliquity should be taken into account in coronal seismology of streamer waves and that stereoscopic observations will be required to constrain the true propagation direction.
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All authors Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin, Ding Yuan

Cosmology and Nongalactic Astrophysics

Biases from Astrophysical Environmental Effects in Standard-Siren Cosmology

Ioannis Liodis, Rodrigo Vicente, Soumen Roy et al. (+1 more)

Next-generation ground based gravitational wave detectors will enable precision standard-siren cosmology, making systematics increasingly important. We investigate how line-of-sight acceleration, as may arise for compact binaries in dense astrophysical environments, biases measurements of the Hubble constant $H_0$. We simulate a catalogue of 50 binary neutron star bright sirens with known host redshifts, assuming the signals have been impacted by line-of-sight acceleration and analysing them with vacuum waveforms. Unmodelled line-of-sight acceleration biases the inferred luminosity distances and shifts the individual $H_0$ posteriors systematically towards lower values. Consequently, combining events narrows the posterior around a biased value rather than averaging away the systematic, even when the acceleration signs are assigned randomly. For our 50-event catalogues, affected fractions of approximately $10\%$ at $|a_\parallel|/c=10^{-6}\,\mathrm{s^{-1}}$, or $30\%$ at $|a_\parallel|/c=10^{-7}\,\mathrm{s^{-1}}$, produce offsets exceeding three posterior standard deviations in at least one quarter of the realisations. Considering larger catalogues further increases the significance of the effect. Our results indicate that environmental effects may constitute an important systematic for precision standard-siren cosmology and should be incorporated into future population analyses.
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All authors Ioannis Liodis, Rodrigo Vicente, Soumen Roy, Samaya Nissanke

Solar and Stellar Astrophysics

Streamer slab eigenmode analysis with the Legolas code

Jordi De Jonghe, Daria Sorokina and Tom Van Doorsselaere

Context. Helmet streamers are large ray-like structures extending from the solar corona that thin further away from the solar surface, forming an extended current sheet. These structures are quasi-stable, and are observed to support kink waves travelling outward from the Sun, called helmet streamer waves. Aims. Limited analytical models identify streamer waves as fast body kink eigenmodes of the streamer slab. To bridge the gap between analytical models and numerical simulations, we investigate the eigenmode spectrum of more realistic streamer slab configurations, obtained from simulations, to retrieve the kink profiles and firmly establish that streamer waves are eigenmodes of the streamer. Methods. Using a streamer slab model extracted from numerical simulations, the Legolas code is applied to compute the eigenmode spectrum, for wavelengths observed in the simulation. In the spectrum we identify the mode matching the behaviour in the non-linear simulations by comparing to analytical and numerical results for the established Epstein profile. The identified modes's phase speeds are then compared to analytical, simulation, and observational results. Results. For each case, the spectrum is found to contain a mode matching the properties of a streamer wave. The phase speeds of the identified modes are compatible with those measured in observations, strongly suggesting that the observed streamer waves are fast body kink modes. Comparison to the analytical slab model is difficult due to the sensitivity of the analytical dispersion relation to the internal values.
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Earth and Planetary Astrophysics

How dust particles orbiting white dwarfs can reveal undetected co-orbiting exoplanets I. Exoplanet on a circular orbit

Kyriaki I. Antoniadou and Dimitri Veras

Abridged. Mounting observations of transiting dusty debris orbiting WDs display complex signatures that often feature orbital period drifts. The asteroid or planet progenitor of this debris might still be partly intact on a near-circular orbit that is inclined or coplanar, with a period that is similar to that of the dust. Alternatively, the debris could persist concurrently with other intact asteroids or planets that had tidally circularised around the WD at a later time, but still remain directly unobservable. We sought to first improve the identification of this detectability threshold by expanding our previous investigation of the WD-secondary-dust co-orbital circular restricted three-body problem (CRTBP) to higher secondary masses corresponding to Ceres, Mercury, Earth, and Neptune. Next, we continued to explore the link between the analytic and numerical characterisations of the CRTBP. First, we computed families of periodic orbits in the 1/1 mean-motion-resonance (MMR) in both the planar and spatial CRTBP cases, where the dust is on an arbitrarily eccentric orbit. Second, we generated global phase space portraits. Third, we determined observational links with debris located in very close proximity to WDs via N-body simulations. For each method we applied, we report a novel set of results. These include 3 newly discovered bifurcation points, $B_T^4, B_{cs}^4$, and $B_{cs}^5$, 2 branches of asymmetric periodic orbits, called $A_2$ and $A_3$, at high dust eccentricity regime in the 2D-CRTBP, and 2 families of symmetric orbits in the 3D-CRTBP. The maps reveal stability domains as a function of the dust's eccentricity, argument of pericentre, and slight semi-major axis deviations from the 1/1 MMR. The N-body simulations reveal that over 10 yr, mass analogues of Mercury, Earth, and Neptune generate orbital period deviations in the dust of, respectively, 1-10 s, 10-100 s, and over 100 s.
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Instrumentation and Methods for Astrophysics

IceCube Upgrade status and perspectives

Anna Eimer

The IceCube Neutrino Observatory instruments one cubic kilometer of deep-glacial ice between 1450 m and 2450 m below the surface at the geographic South Pole to detect neutrinos via Cherenkov radiation of relativistic charged particles produced in their interactions. This detector is responsible for a number of key observations in neutrino astrophysics, which include the discovery of a high-energy astrophysical neutrino flux and, more recently, the galactic plane. During the austral summer of 2025/26, five new strings equipped with new photosensor designs were deployed as a dense infill in the middle of the existing detector. The science goals of this detector are twofold: Firstly, given the higher photocathode density, an improved atmospheric neutrino event selection and reconstruction at a few GeV can be achieved for enhanced capabilities to study neutrino oscillations. Secondly, novel calibration devices will improve the knowledge of the optical properties of the glacial ice and the detector response. These new calibration results will be applied to archival IceCube data, improving angular and spatial resolution of all detected astrophysical neutrino events. The IceCube Upgrade also serves as a first step towards the next-generation neutrino telescope at the South Pole, called IceCube-Gen2.
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Cosmology and Nongalactic Astrophysics

Probing modified gravity with galaxy-cluster-lensed gravitational-wave time delays: impact of systematic effects

Eleni Tsaprazi, Ettore Delpogetto, Federico Marulli et al. (+1 more)

Strongly lensed gravitational waves provide exceptionally precise measurements of relative macroimage arrival times, making their time delays a promising time-domain probe of gravity on galaxy-cluster scales. This precision places stringent demands on the control of lensing systematic effects. We present a proof-of-concept pipeline for constraining a phenomenological modification, $D$, of the galaxy cluster Weyl potential using the macroimage time-delay span of a simulated sample of binary neutron star (BNS) sources and cluster lenses described by a Navarro–Frenk–White cluster halo and a singular isothermal sphere for the brightest cluster galaxy (BCG). Closure tests recover the injected general-relativistic (GR) limit. Adopting a fiducial 5 per cent precision on the reconstructed time-delay span, we assess controlled mis-specifications of the halo mass and concentration, BCG contribution, source and lens positions, redshifts, line-of-sight environment, projected ellipticity and secondary cluster-scale structure. Within the adopted gravity model, neglecting halo ellipticity, secondary cluster-scale structure, cluster mis-centring and line-of-sight perturbations can induce significant, strongly configuration-dependent biases in the inferred parameter $D$. Biased estimates of the cluster halo mass and concentration, as well as systematic BNS source-position errors at the level considered here, produce significant coherent shifts. By contrast, uncertainties in the BCG contribution and in the lens and source redshifts are comparatively subdominant. These results highlight the need for explicit treatment of the above uncertainties before cluster-lensed gravitational wave time delays can be used as precision tests of gravity.
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All authors Eleni Tsaprazi, Ettore Delpogetto, Federico Marulli, Amandine M. C. Le Brun

Solar and Stellar Astrophysics

Stellar flare detection and characterization in ZTF High-cadence light curves

Aratrika Ghosh, Shravan Hanasoge, Matthew J. Graham et al. (+1 more)

Stellar flares are brief, intense increases in brightness resulting from magnetic reconnection events in stellar atmospheres. In this paper, we have developed a pipeline to detect and characterize flares in short-duration (approximately 6.2-hour) light curves from the Zwicky Transient Facility (ZTF) Extended Deep-Drilling survey. This method involves robust detrending with Tukey's biweight estimator, followed by sigma-based thresholding and visual scrutiny to identify flare candidates. It is applied to 28 million light curves, and we found 331 flaring events from 310 stars across evolutionary stages and spectral types. We estimated flare energies by assuming a blackbody emission model for 234 flares with reliable distance, and flare morphologies were classified based on flare modeling using the template by Mendoza et al.(2022). We obtained a power law correlation between energy and duration with an index of $0.19 \pm 0.01$. We also find similar power law correlation between the flare energy and $T_{decay}$, $T_{rise}$ and FWHM. This study demonstrates the power of high-cadence ground-based surveys for statistical and morphological flare studies across a broad stellar sample.
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All authors Aratrika Ghosh, Shravan Hanasoge, Matthew J. Graham, Ashish Mahabal

Earth and Planetary Astrophysics

Impact of accretion variability on the CO emission of a disk around a very-low-mass star with JWST

C. Bergez-Casalou, B. Tabone, Y. Aoyama et al. (+14 more)

Studying the structure of very-low-mass stars ($M_\star<0.2M_\odot$) protoplanetary disk is crucial to understand the formation of Earth-like planets. In this paper, we characterize the innermost regions of the disk around a known very-low-mass star, 2MASS J16053215-1933159 (J1605 hereafter), by analyzing new JWST/NIRSpec observations taken in 2024, 2 years after a first observation with JWST/MIRI. We find that between the two epochs (2022 & 2024), the CO flux is reduced by a factor $\sim 3$, the flux of the HI 10-6 line seen by both NIRSpec and MIRI is reduced by a factor $\sim13$, and the total continuum density flux is reduced by $\sim 15 \%$. The accretion rate derived from individual HI lines is consistent with a decrease of a factor $\sim13$ in 2 years. After correcting the spectrum from the CO absorption present in J1605 stellar photosphere, we find that the decrease of the disk's CO emission is consistent with a CO gas of same column density and temperature at each epoch, but originating from a smaller emitting area when the accretion rate is low. While warm hydrocarbons ($\simeq 500~$K) are detected with MIRI-MRS with extremely high column densities of $\rm C_2H_2$, no hydrocarbons features are seen with NIRSpec. We propose that non-LTE effects quench the near-IR emission of hydrocarbons in the warm reservoir. The variation of the accretion luminosity of J1605 correlates with the variation of its fundamental CO luminosity in a similar way as in T-Tauri stars, supporting the idea that very-low-mass stars could be seen as scaled-down versions of T-Tauri stars. The detection of the emission of the fundamental band of CO in disks around cold objects is challenging because of the presence of CO absorption in their photosphere. Future observations (e.g., with ELT/METIS) looking for such emission will require robust ways to constrain the photosphere emission.
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All authors C. Bergez-Casalou, B. Tabone, Y. Aoyama, G. Herczeg, A. Caratti o Garatti, E. Habart, E. F. van Dishoeck, I. Chemerynska, T. Henning, S. L. Grant, M. Guedel, A. M. Arabhavi, J. Kanwar, G. Olofsson, G. Perotti, L. Tychoniec, L. B. F. M. Waters

Solar and Stellar Astrophysics

Companion masses of Gaia DR3 AstroSpectroSB1 binaries: a Bayesian forward-modelling framework

Prasid Sandave and Raghuveer Garani

Gaia Data Release 3 (DR3) has substantially expanded the study of unresolved binaries by providing combined astrometric and spectroscopic orbital solutions for a large sample of non-single stars. We present a Bayesian forward-modelling framework for estimating companion masses in Gaia DR3 AstroSpectroSB1 systems. The method samples the physical parameters of each binary, predicts the corresponding astrometric Thiele-Innes constants and spectroscopic orbital coefficients, and evaluates their likelihood using the full covariance matrix published by Gaia. An external prior on the primary mass is incorporated to resolve the remaining degeneracy between the component masses and orbital inclination in single-lined systems. We apply this framework to 1035 AstroSpectroSB1 systems with primary-mass estimates drawn from the Gaia DR3 astrophysical\_parameters table. Of these, 760 systems also have Gaia-reported estimates for both component masses and are used as a validation sample. The remaining 275 systems constitute an inference sample for which the mass of the fainter, unresolved companion is estimated. For systems with well converged posteriors, the inferred parameters reproduce the Gaia orbital observables, while the companion masses recovered for the validation sample are consistent with the Gaia estimates. In the inference sample we find 113 well converged systems for which the companion masses are meaningfully inferred. We find that the population is dominated by ordinary stars, together with a smaller high-mass tail that may contain massive white dwarfs or other compact-object candidates. Our framework provides a scalable approach for converting Gaia AstroSpectroSB1 solutions into companion-mass posterior distributions, identifying promising systems for targeted follow-up, and preparing for the larger and more precise orbital samples anticipated with Gaia DR4.
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Astrophysics of Galaxies

Gravity-driven Emergence of Multi-fractal Density Structure in the Orion A Integral Shaped Filament

Mengke Zhao, Guang-Xing Li, Keping Qiu et al. (+1 more)

Molecular clouds are often described as self-similar structures, although spatially averaged measures do not retain local variations in density scaling. We use the density exponent $\kappa_\rho$ ($\rho \propto r^{\kappa_\rho}$) to characterize the density structure of the Integral Shaped Filament (ISF) in Orion\,A. Applying the Multiscale Decomposition Reconstruction method to the Herschel column-density map, we find distinct density–scale relations across the connected filament. Their slopes steepen from $\kappa_\rho \approx -1.7$ to $-1.9$ in the quiescent OMC-4/5 regions, through $\approx -2.1$ in the star-forming OMC-2/3, to $\approx -2.3$ in OMC-1, which hosts massive star formation. The ISF therefore does not follow a single local density-scaling exponent but exhibits multi-fractal density scaling. The pixel-level distributions show the same progression toward higher volume density and more negative $\kappa_\rho$. Since $\kappa_\rho$ measures the concentration of gas toward smaller scales, we interpret this sequence as gravity-driven differential collapse: denser regions have shorter free-fall times and develop steeper density profiles. Longitudinal gas motions toward OMC-1 may limit the mass supply available for large-scale growth in the outer sub-regions and help maintain the observed range of local exponents. These results link local density scaling to gravitational concentration within a single connected filamentary system.
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All authors Mengke Zhao, Guang-Xing Li, Keping Qiu, Guangya Zeng

Instrumentation and Methods for Astrophysics

Fast and accurate astronomical source deblending with Density-Peak Clustering

M. D. Lepinzan, F. Tomba, E. Romelli et al. (+2 more)

Source deblending is a fundamental challenge for current and forthcoming astronomical surveys, where increasing source density and image depth lead to a growing number of overlapping detections. Accurate deblending is essential for reliable measurements of source morphology and photometry, as well as for cosmological analyses. We present a redesign of the Advanced Density Peak (ADP) clustering algorithm, tailored to the identification and separation of blended astronomical sources within detection regions. We develop a validation framework combining realistic image simulations, automatically generated ground-truth segmentation, and label-invariant metrics. ADP is assessed against ASTErIsM, an established density-based astronomical deblender, using pairwise simulations, synthetic multi-source images, and Euclid Q1 public data. In pairwise simulations, the methods show comparable performance across a broad range of source separations and flux ratios, with photometric differences typically below 1% and reaching 5-7% in the most challenging cases, without systematic bias. In multi-source simulations, ADP recovers approximately 8% more ground-truth sources, while the positions of sources identified by both methods agree at the sub-pixel level. On Euclid Q1 public data, the methods show strong agreement in segmentation area, ellipticity, position angle, and photometry, with the largest differences for the smallest and faintest sources. ADP also provides a substantial computational advantage: end-to-end benchmarks on 19200 x 19200 pixel Euclid images require approximately 16-200 s, corresponding to speedups of 12-156x relative to ASTErIsM, with median and mean improvements of 36x and 54x, respectively. These results show that ADP provides scientifically competitive deblending at substantially lower computational cost, making it a promising approach for large-scale astronomical imaging surveys.
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All authors M. D. Lepinzan, F. Tomba, E. Romelli, A. Rodriguez, L. Tornatore

Instrumentation and Methods for Astrophysics

Scale-Vector Alignment: A Scale-Aware Framework for Spatially Resolved Morphological Similarity in Astronomical Images

Mengke Zhao, Guang-Xing Li, Keping Qiu et al. (+1 more)

Astronomical maps made with different tracers are not expected to have identical morphology. Excitation, optical depth, chemistry, radiation, and ISM phase alter the response of a tracer, and the resulting differences can depend on both position and spatial scale. We propose scale-vector alignment, a scale-aware method based on Constrained Diffusion Decomposition (CDD). CDD decomposes an image into localized scale components; at each position, their amplitudes define a scale vector that describes how the measured intensity is distributed over spatial scale. We define the pixel-wise similarity $\Spix(x,y)$ as the normalized alignment of two local scale vectors. The normalization removes the overall amplitude, so $\Spix$ compares relative scale composition rather than absolute flux. We also define the scale-wise similarity $\Sscale(l)$ by comparing the two CDD component maps at each spatial scale. Spatial shifts are used to construct an empirical shifted reference distribution for $\Spix$. In Orion~A, the tracer with the highest similarity to the dust-derived column-density map changes from $^{12}$CO to $^{13}$CO to C$^{18}$O toward higher column density. In NGC~6334I(N), the line–continuum similarity decreases locally around the brightest compact structures, where radiative-transfer effects can alter the observed line morphology. In NGC~3627, CO is most similar to 21~$\mu$m emission, and $\Sscale$ reaches its maximum at an intermediate sub-kpc scale. The method measures where two tracers have similar multiscale structure and at which scales their spatial distributions agree. The implementation is publicly available at https://github.com/meng-ke/Scale-Vector-Alignment.
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All authors Mengke Zhao, Guang-Xing Li, Keping Qiu, Shanghuo Li

High Energy Astrophysical Phenomena

Rotating Radio Transient Phases of Isolated Neutron Star Systems and Descendants of Central Compact Objects

Ş. Demirok, Ü. Ertan and A.A. Gençali

Rotating radio transients (RRATs) form an isolated neutron star (INS) population characterized by their sporadic and short radio bursts. In the fallback disc model, it was suggested that most INS populations pass through an RRAT phase during their evolution, and the mechanism producing these bursts could be the enhancement of the flux of open magnetic field lines through the poles of dead pulsars due to penetration of the inner disc into the light cylinder. To test this idea, we determine the RRAT phases that could be produced by this mechanism along the evolutionary curves of the INS families on the period-period derivative ($P$–$\dot{P}$ diagram). These RRAT phases form an RRAT region in the $P$–$\dot{P}$ diagram, which is in agreement with the known RRAT distribution. Using our results, we also investigate the descendants of central compact objects (CCOs). We estimate that the CCOs similar to the three CCOs with measured $P$ and $\dot{P}$ are not likely to become radio pulsars (RPs). The situation is rather different for Calvera, a recently identified CCO. In the model, Calvera-like sources become RPs with lifetimes $ > 10^{8}$ yr. Indeed, there is a cluster of RPs in the region of \PPdot~diagram where descendants of Calvera-like CCOs evolve in our model. We also estimate that they have a very low birth rate, and therefore their immediate descendants may not currently exist in our Galaxy.
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Astrophysics of Galaxies

Gas phase Elemental abundances in Molecular cloudS (GEMS) XII. First look into the para-to-ortho ratio of c-C3D2 towards prestellar cores

J. Ferrer Asensio, A. Fuente, E. Roueff et al. (+3 more)

Symmetric molecules with identical nuclei form distinct nuclear spin isomers (ortho and para) that cannot interconvert via radiative or inelastic transitions, preserving clues about formation conditions. In the interstellar medium, cyclopropenylidene (c-C3H2) and its doubly-deuterated isotopologue (c-C3D2) provide a prime laboratory for studying these ratios. While measured for the main species, spin ratios for c-C3D2 remain unavailable. We present new detections of ortho and para transitions of c-C3D2 toward three Taurus molecular cloud sources from the GEMS Large program, and revisit four literature cores to investigate the para-to-ortho ratio of c-C3D2 for the first time. Column densities were computed using RADEX with dedicated collision rate coefficients, yielding total c-C3D2 column densities of (2.5-5.3) x 10e11 cm-2 for the new sources. The derived para-to-ortho ratios are 1.5(+0.7-0.6) (B213-C16-1), 1.3(+1.3-0.7) (TMC1-C), and 1.0(+1.4-0.7) (TMC1-NH3, statistical). For revisited sources L1544, TMC-1C, TMC-2, and L1517B, ratios are 0.4(+0.1-0.1), 0.5(+0.1-0.1), 0.6(+0.2-0.1), and 1.4(+0.7-0.5), respectively. Overall, four sources show statistical ratios and three show higher non-statistical values. This is the first observational determination of the para-to-ortho ratio in a doubly deuterated molecule using a detailed radiative transfer tool. The elevated ratios in some sources likely stem from p-D2H+ or D3+ driven reactions, and are independent of H2 and c-C3H2 ortho-to-para ratios. These findings offer an essential benchmark for chemical models investigating c-C3D2 formation pathways.
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All authors J. Ferrer Asensio, A. Fuente, E. Roueff, K. Furuya, B. Tercero, N. Sakai

Earth and Planetary Astrophysics

Feasibility of the Phobos 1 Hypothesis for Dark Comet 1998 KY$_{26}$

Adam Hibberd, Adam Crowl and Abraham Loeb

The asteroid 1998 KY$_{26}$ has been the subject of thorough observation, both optical and radar, from shortly following its discovery on 28 May 1998, through 2 further close apparitions in 2020 and 2024. This has previously allowed an accurate characterization of the object, including an unusually rapid spin-rate with period 5.3516 $\pm$ 0.0001 minutes, a diameter of 11 $\pm$ 2 m, and a high albedo of $\sim{0.52}$. Furthermore, the presence of significant nongravitational accelerations (NGAs), with no detectable shedding of gas or dust, has stimulated the 'dark comet' categorization, with JAXA repurposing their Hayabusa2$\sharp$ spacecraft to rendezvous with the object in 2031. We follow-up the astrodynamical evidence pointing to the possibility this may actually be the lost Soviet Phobos 1 probe, and analyse various photometry and astrometry associated with 1998 KY$_{26}$ to further investigate the feasibility of this hypothesis. We find a first order approximation of the Phobos 1 spacecraft provides compelling agreement to 8 light curves of the object and further that modelling NGAs as solar radiation pressure (SRP) on a cylinder or solar panels provide significant reductions in residual of $\sim{11} \%$ with respect to the 260 astrometric and radar measurements. Although an investigation of this kind cannot be conclusive, nevertheless the results here add strong weight to the Phobos 1 hypothesis, and we find no clear contradictory evidence. The spin pole in Ecliptic J2000 coordinates, calculated from photometry based on the Phobos 1 assumption is $(\lambda,\beta)=({151^{+1}_{-2}}^{\circ},{+11^{+12}_{- 3}}^{\circ})$ , where the quoted ranges represent approximate 68.3% confidence levels.
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High Energy Astrophysical Phenomena

Fast Radio Bursts Associated with Persistent Radio Sources Prefer Hydrogen-poor Superluminous Supernova Host Environments

Fujia Li, Fei Liu, Di Li et al. (+3 more)

A subset of repeating fast radio bursts (FRBs) is associated with compact persistent radio sources (PRSs). The FRB-PRS hosts differ dramatically from the general FRB host population: they do not follow the distribution of localized non-PRS FRB hosts, nor the SFR-weighted or mass-weighted mock host distributions expected for the general star-forming galaxy population, instead occupying the extreme low-mass, high-sSFR, and low-metallicity end of host-galaxy parameter space. We compare these hosts with well-defined samples of hydrogen-poor superluminous supernovae (SLSNe-I), hydrogen-rich superluminous supernovae (SLSNe-II), and Type II core-collapse supernovae (CCSNe). Using cumulative distribution functions and statistical tests, we find that FRB-PRSs tend to reside in dwarf galaxies with high specific star formation rates and low gas-phase metallicities, even relative to galaxies of similar stellar mass. Their hosts are most similar to those of SLSNe-I, but differ significantly from CCSN hosts, with SLSN-II hosts lying between these populations. These results suggest that FRB-PRSs do not simply trace star formation activity or the general FRB host population, but instead favor SLSN-I-like environments. This preference is consistent with young magnetars formed through low-metallicity massive-star channels, for which SLSN-I-like ejecta imply a characteristic free–free transparency time of ~29 yr at 600 MHz.
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All authors Fujia Li, Fei Liu, Di Li, Dongzi Li, Ziheng Ding, Ran Gao

Astrophysics of Galaxies

StAGE: Stellar Archaeology-driven Galaxy Evolution II. Binary Black Hole Mergers in Quiescent Galaxies and their Star-forming Progenitors

Irene Iorio, Andrea Lapi, Lumen Boco et al. (+5 more)

We apply StAGE, a data-driven galaxy-evolution framework based on stellar archaeology, to study binary black hole (BBH) mergers in quiescent galaxies (QGs) and their star-forming progenitors. We combine StAGE star-formation and chemical-enrichment histories with pre-computed SEVN binary population-synthesis catalogs to derive the BBH merger-rate density, its dependence on intrinsic binary and host-galaxy properties, and the associated stochastic gravitational-wave (GW) background. We assess uncertainties related to stellar-archaeology prescriptions, common-envelope evolution, and $\alpha$-enhanced abundances. We find that QGs and their progenitors can contribute a sizeable fraction of the cosmic BBH merger rate. For most of the binary-evolution prescriptions explored here, we highlight a tension with the local LVK-inferred merger rates, underscoring the need to revisit some assumptions in the underlying modeling. Most BBHs form at moderately subsolar metallicities, $Z\lesssim Z_\odot/3$, while their merger-time hosts typically have stellar masses $M_\star\lesssim10^{11}\,M_\odot$. At $z\gtrsim2$, hosts lie mainly on the galaxy main sequence, whereas starbursting and quenching descendants contribute increasingly toward lower redshift. Isolated binaries broadly reproduce the observed bulk of the primary- and chirp-mass distributions, but the predictions decline rapidly above $\sim 40-50\,M_\odot$, providing little support for the highest-mass systems inferred by LVK. Dynamical formation in young and globular clusters can populate this regime, but also increases the total merger-rate density, exacerbating the tension with LVK for the fiducial cluster normalizations adopted here. Finally, the predicted stochastic background approaches the projected sensitivity of planned LVK upgrades and lies within reach of the Einstein Telescope.
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All authors Irene Iorio, Andrea Lapi, Lumen Boco, Giovanni Antinozzi, Michele Bosi, Cecilia Sgalletta, Mario Spera, Luigi Danese

Cosmology and Nongalactic Astrophysics

Sound-Horizon-Independent Test of Cosmic Distance Duality Relation Using Artificial Neural Networks and Gaussian Processes

Bo-Hao Jiang, Guo-Jian Wang and Tao Yang

The cosmic distance duality relation (CDDR), $D_L(z)(1+z)^{-2}/D_A(z) \equiv 1$, is a fundamental relation in modern cosmology linking luminosity distance $D_L$ and angular diameter distance $D_A$. We define $\eta(z) \equiv D_L(z)(1+z)^{-2}/D_A(z)$ and reconstruct the relevant quantities over $0 < z < 2.5$ using two independent non-parametric methods: Gaussian processes (GP) and artificial neural networks (ANN). Specifically, we reconstruct $D_L$ from three different Type Ia supernovae (SNe$~$Ia) compilations (PantheonPlus, Union3, and DES-Dovekie), the baryon acoustic oscillation distance ratio $D_M/D_H$ from SDSS and DESI, and the Hubble function $H(z)$ from cosmic chronometer (CC) data. Our CDDR test is independent of both the cosmological model and the sound horizon $r_d$ calibration, as $D_M/D_H$ naturally eliminates $r_d$. We render our GP reconstructions insensitive to mean-function and kernel choices via full Bayesian marginalization over hyperparameters, with ANN as a cross-check$-$revealing the impact of data sparsity on the latter. Our results show no significant deviation from the CDDR exceeding $2\sigma$, and for the CC+BAO+DES-Dovekie combination it remains within $1\sigma$ over most of the redshift range. With $r_d$ eliminated, varying the only remaining external parameter $M_B$ systematically shifts $\eta(z)$ through the $M_B$-$H_0$ degeneracy, indicating that the observed $\eta\neq1$ signal is closely tied to $H_0$ tension among datasets and is likely driven by $M_B$ systematics rather than a true CDDR violation. Future high-quality CC, BAO, and SNe$~$Ia data$-$with either improved $M_B$ calibration or $M_B$-free distance measurements$-$will be essential for extending this calibration-free approach.
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High Energy Astrophysical Phenomena

Constraints on Axion-like Dark Matter from Cosmic Birefringence with a Polarization Array of Repeating Fast Radio Bursts

Xiaohui Liu, Zi-Yan Yuwen, Yun-Long Zhang et al. (+5 more)

Axion-like dark matter (ALDM) is a well-motivated dark matter candidate whose Chern-Simons coupling to photons can induce cosmic birefringence, producing temporal oscillations and spatial correlation in polarization angle (PA) signals from different sources. Hyperactive repeating fast radio bursts (FRBs) with high linear polarization are a particularly promising probe of such signatures. We develop a Bayesian framework to search for PA oscillations caused by ALDM in individual repeating FRBs, and combine multiple sources in an FRB polarization array (FRBPA) by exploiting correlations arising from the common Earth term. We apply this framework to PA datasets from three well-studied hyperactive repeating FRBs, and constrain the Chern-Simons coupling over a broad range of ALDM masses. For each FRB, we estimate the dark matter density at its host location using a simulation-calibrated halo profile. The inferred dark matter densities are comparable to the fiducial local density $\rho_0 = 0.4~\mathrm{GeV/cm^3}$. The comparable source and Earth dark matter densities, together with the redshift-induced difference between the frequencies of the source and Earth terms, motivate our adoption of the full two-component birefringence model. We find no compelling evidence for ALDM-induced PA oscillations in either the individual source analyses or the joint FRBPA analysis. We place 95% credible upper limits on the Chern-Simons coupling strength as a function of ALDM mass. Across the axion mass from $10^{-23}$ to $10^{-18}~\mathrm{eV}$, the resulting upper limits of the coupling strength of FRBPA lie between $10^{-12.6}$ and $10^{-7.9}~\mathrm{GeV}^{-1}$. Our results establish long-term polarimetric monitoring of hyperactive repeating FRBs as a promising and independent probe of ALDM, with sensitivity expected to improve with longer observational baselines and larger source samples.
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All authors Xiaohui Liu, Zi-Yan Yuwen, Yun-Long Zhang, Zerui Liu, Shiqian Zhao, Shuai Feng, Wei-Yang Wang, Xuelei Chen