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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 22 July

Instrumentation and Methods for Astrophysics

Noise reduction in suspension control with photon-pressure actuator for CHRONOS gravitational wave detector

Daiki Tanabe, Yuki Inoue and Mario Juvenal S. Onglao III

Improving sub-Hz sensitivity of gravitational wave (GW) detectors is important to detect heavier binary black hole mergers and study phenomena in stronger gravity fields. Torsion-bar-based GW detectors have been projected to focus on low-frequency GW. Among noise sources of GW detector, actuation noise induced by vibration of force sources and fluctuation of environmental magnetic fields is one that increases in low frequency. In this study, we propose photon-pressure actuator as a solution to isolate an actuator from seismic and magnetic noise. It can also be used as a photon calibrator. We designed an optical layout of the photon-pressure actuator having four beams independently controlled and applied it to CHRONOS experiment. Based on a realistic power control system, we estimated its maximum torque amplitude around yaw rotation axis as $1.0\times 10^{-8}$ N$\cdot$m and actuation efficiency as $6.6\times 10^{-13}$ rad/V, which are sufficiently large for controlling the CHRONOS torsion bar. The actuation noise was estimated as $5.3\times 10^{-19}$ rad ${\rm Hz}^{-1/2}$ at 1 Hz, lower than the target sensitivity of CHRONOS. Assuming its usage as a photon calibrator, the estimated systematic error was 1.14%.
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Solar and Stellar Astrophysics

Oscillatory reconnection and resonant response to wave excitation in 2D coronal null points

Konstantinos Karampelas and Tom Van Doorsselaere

Null points are magnetic field singularities, where the magnetic field strength rapidly drops to zero. In the solar atmosphere, null points are known sites of magnetic reconnection and wave generation and are associated with highly energetic phenomena, such as flares. The aim of this study is to explore the connection between the properties of oscillatory reconnection at null points and the latter's nature as resonant cavities for waves. We perform a set of 2D and 2.5D magnetohydrodynamics simulations of single null points in a stratified solar atmosphere, using the PLUTO code. We perturb each null point through a single propagating pulse and its reflections from the bottom boundary, hitting the null point in an asymmetrical fashion. This leads to both periodic reconnection events and wave refraction around the null point. We find that each null point imposes frequencies on the reconnection matching those of the waves generated from the individual resonant cavity. These frequencies also differ from those excited by the low frequency driver of the reflected waves returning to the null point, the latter lying outside the $95\%$ confidence interval. As such, excited periodic reconnection can be characterised as oscillatory reconnection, i.e. with properties intrinsic to the null points. Finally, the generated waves at the null propagate across the domain, reminiscent of the observed quasi-periodic fast-propagating waves. We provide results showing a direct connection between oscillatory reconnection and the generated high-frequency wavetrains at null points in the solar corona. The propagating waves generated at the resonant cavity, reminiscent of the observed quasi-periodic fast-propagating waves can provide us a diagnostic tool for the reconnection process at the null point and the coronal plasma conditions.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.acc-ph

Capabilities and Limitations of Non-Redundant Aperture Interferometry for Beam Size Measurements

C. Carilli, U. Iriso, B. Nikolic et al. (+3 more)

Non-Redundant Aperture Interferometry (NRAI) is a beam characterization technique developed at ALBA in collaboration with radio-astronomy institutes. It enables the single-acquisition measurement of the full 2D transverse profile of the electron beam using visible synchrotron radiation. To better understand the technique limitations and performance, we performed extensive SRW simulations and compare them with experimental data. This paper presents the results of these studies, which define the capabilities and limits of NRAI applied to the current ALBA machine.
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All authors C. Carilli, U. Iriso, B. Nikolic, N. Thyagarajan, L. Torino, A. Turull Barot

High Energy Astrophysical Phenomena

Constraints on the VHE counterpart of two binary black hole mergers observed by the MAGIC and CTAO LST-1 telescopes

K. Abe, S. Abe, J. Abhir et al. (+359 more)

We present very-high-energy gamma-ray observations of two binary black hole merger candidates, GW240615_113620 and GW241125_010116, performed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the first Large-Sized Telescope of the Cherenkov Telescope Array Observatory's (CTAO LST-1). GW240615_113620 was the best localized event of the fourth observing run of the LIGO-Virgo-KAGRA gravitational waves interferometers. GW241125_010116 was temporally and spatially coincident with a sub-threshold short-duration burst detected with the Swift-Burst Alert Telescope (BAT), the Swift-X-Ray Telescope (XRT) and the Einstein Probe Follow-up X-ray Telescope (FXT). We observed the two events in stereoscopic mode, taking advantage of the improved sensitivity of joint MAGIC+LST-1 observations. No detection was achieved in the GeV-TeV gamma-ray band for any of the two sources. The unfavourable observing conditions of both events posed a challenge for a standard analysis and therefore a non standard analysis was necessary for both objects. Owing to the small localization area and the association with a GRB-like burst respectively, these events represented an unprecedented opportunity to study in details the electromagnetic emission from binary black holes merger events and, in particular, we discussed two theoretical models that predict a detectable gamma-ray emission and the possible future applications.
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All authors K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, F. Acero, A. Aguasca-Cabot, I. Agudo, I. Albanese, D. Ambrosino, F. Ambrosino, T. Aniello, S. Ansoldi, L. A. Antonelli, C. Aramo, C. Arauner, A. Arbet-Engels, C. Arcaro, T.T.H. Arnesen, P. Aubert, A. Babić, C. Bakshi, A. Baktash, M. Balbo, A. Bamba, A. Baquero-Larriva, U. Barres-de-Almeida, J. A. Barrio, L. Barrios-Jiménez, I. Batkovic, J. Baxter, J. Becerra-González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, E. Bissaldi, O. Blanch, Ž. Bošnjak, G. Bonnoli, P. Bordas, L. Breton-Zaourat, A. Briscioli, E. Bronzini, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, C. Campa, A. Campoy-Ordaz, M. Cardillo, S. Caroff, A. Carosi, R. Carosi, R. Carraro, M. Carretero-Castrillo, F. Cassol, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, A. Cerviño-Cortínez, Y. Chai, A. Chiavassa, A. Chilingarian, G. Chon, L. Chytka, G. M. Cicciari, A. Cifuentes Santos, J. L. Contreras, J. Cortina, H. Costantini, S. Covino, M. Croisonnier, G. D'Amico, P. Da-Vela, M. Dalchenko, F. Dazzi, A. De-Angelis, M. de-Bony-de-Lavergne, B. De-Lotto, R. de-Menezes, G. De-Palma, V. de-Souza, R. Del-Burgo, L. Del-Peral, M. Delfino, C. Delgado Mendez, J. Delgado-Mengual, D. della-Volpe, L. Di-Bella, C. Di-Domenico, A. Di-Piano, F. Di-Pierro, R. Di-Tria, L. Di-Venere, C. Díaz, A. Dinesh, E. Do Souto Espineira, D. Dominis-Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsässer, G. Emery, J. Escudero, L. Farina, L. Feligioni, F. Ferrarotto, A. Fiasson, L. Foffano, L. Font, F. Frías-García-Lago, Y. Fukazawa, S. Gallozzi, J. Garcia-Garcia, R. J. García López, S. Garcia-Soto, D. Gasparrini, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinovic, T. Gradetzke, R. Grau, J. Green, G. Grolleron, S. Gunji, P. Günther, D. Hadasch, A. Hahn, M. Hashizume, T. -Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera-Llorente, N. Hiroshima, D. Hoffmann, D. Horns, J. Houles, D. Hrupec, T. Inada, S. Inoue, K. Ioka, M. Iori, D. Israyelyan, A. Iuliano, J. Jahanvi, I. Jiménez-Martínez, J. Jiménez-Quiles, I. Jorge-Rodrigo, J. Jurysek, M. Kagaya, S. Kankkunen, V. Karas, H. Katagiri, T. Kayanoki, D. Kerszberg, M. Khachatryan, G. W. Kluge, Y. Kobayashi, K. Kohri, J. Konrad, P. Kornecki, P. M. Kouch, H. Kubo, J. Kushida, B. Lacave, M. Láinez, A. Lamastra, L. Lemoigne, E. Lindfors, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, A. Lorini, J. Lozano-Bahilo, F. Lucarelli, H. Luciani, L. Lulić, P. L. Luque-Escamilla, P. Majumdar, M. Makariev, M. Mallamaci, D. Mandat, G. Maneva, M. Manganaro, S. Mangano, D. K. Maniadakis, G. Manicò, K. Mannheim, F. Marini, M. Mariotti, G. Marsella, J. Martí, D. Martin, G. Martínez, M. Martínez, O. Martinez, P. Maruš, evec, M. Massa, D. Mazin, S. Menchiari, J. Méndez-Gallego, S. Menon, E. Mestre-Guillen, D. Miceli, T. Miener, J. M. Miranda, J. M. Miranda, R. Mirzoyan, M. Mizuno, M. Molero-Gonzalez, E. Molina, H. A. Mondal, T. Montaruli, A. Moralejo, S. Morales-Sanchez-De-Lozada, K. Morita, A. -Morselli, V. Moya, K. Mrakovčić, A. L. Müller, H. Muraishi, T. Nagata, S. Nagataki, T. Nakamori, C. Nanci, A. Negro, A. Neronov, V. Neustroev, D. Nieto-Castaño, M. Nievas-Rosillo, C. Nigro, L. Nikolić, K. Nilsson, K. Noda, V. Novotny, S. Nozaki, M. Ohishi, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, S. Paiano, M. Palatiello, G. Panebianco, D. Paneque, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, F. Perrotta, M. Persic, F. Pfeifle, E. Pietropaolo, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, C. Pozo-Gonzaléz, P. G. Prada Moroni, E. Prandini, S. Rainò, R. Rando, W. Rhode, M. Ribó, J. Rico, V. Rizi, G. Rodriguez-Fernandez, A. Roy, E. Ruiz-Velasco, N. Sahakyan, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos-Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, K. Schmitz, F. Schussler, T. Schweizer, M. Seglar-Arroyo, U. Sharma, T. Siegert, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, I. Sofia, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, R. Takeishi, S. J. Tanaka, J. Tartera Barberà, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, S. Ubach, M. Vacula, M. Vázquez-Acosta, S. Ventura, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, M. Vorbrugg, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, C. Walther, L. Wan, P. Witczak, F. Wersig, T. Yamamoto, R. Yamazaki, Y. Yao, P. K. H. Yeung, T. Yoshida, T. Yoshikoshi, W. Zhang

Astrophysics of Galaxies

Nebular continuum in high-redshift galaxies with JWST

Henrique Miranda, Ciro Pappalardo, José Afonso et al. (+2 more)

Studying the relevance of accounting for both stellar and nebular continuum emission when performing optical spectral fitting has been mainly limited to galaxies in the local Universe. The high-quality spectroscopy provided by JWST is now opening the possibility of carrying out these studies in the younger Universe. We aim to estimate the nebular continuum contribution (X$_{\text{neb}}$) of high-redshift star-forming (SF) galaxies, explore its relation to common tracers and galaxy properties, and test the previously established threshold for significant nebular contribution (X$_{\text{neb}}$ $=$ 8%). We select a sample of 54 SF galaxies from the DAWN JWST Archive meeting quality criteria required for spectral fitting with the population synthesis code FADO. The selected galaxies cover the 1.7 $<$ $z$ $<$ 3.9 range and we fit their rest-frame optical spectra to estimate the stellar and nebular continuum emission, plus the physical and evolutionary properties. We show that the H$\alpha$ and H$\beta$ equivalent widths remain suitable tracers of X$_{\text{neb}}$ at high redshift. We also confirm the X$_{\text{neb}}$ $=$ 8% threshold, above which neglecting the nebular continuum can significantly bias spectral modelling. Galaxies above this threshold are generally less massive, younger, exhibit higher SF activity and lower dust extinction relative to those below it. Moreover, these galaxies are light and mass dominated by stellar populations younger than 20 Myr, although their mass contribution is likely overestimated due to the outshining effect. Considering the growing amount of galaxy spectroscopic data at Cosmic Noon from JWST and future facilities, such as MOONS, this work reveals the importance of properly accounting for both stellar and nebular continuum emission when performing optical spectral fitting to obtain reliable stellar population and physical properties estimates.
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All authors Henrique Miranda, Ciro Pappalardo, José Afonso, Polychronis Papaderos, Rodrigo Carvajal

Cosmology and Nongalactic Astrophysics

Ringing of the Reionization: A first direct measurement of the intergalactic pressure smoothing scale at redshift z>4.2 as imprinted onto small-scale peculiar velocities in the Lyman-alpha forest

Vid Iršič, Matteo Viel, Martin G. Haehnelt et al. (+3 more)

The epoch of reionization leaves detectable imprints in the thermal history of the Universe. In particular, the fast ionization fronts passing over cold gas in the cosmic web overpressurize the gas, leading to the well-established phenomenon of pressure smoothing due to the hydrodynamic response of the gas. Although the effect has been indirectly measured from the power spectra of the Lyman-$\alpha$ forest over the past decades, very few examples exist of directly measuring the typical scale associated with this physical process. This work identifies an acoustic feature in the power spectrum of the projected peculiar velocity gradient $\eta$. Using toy models and linear theory, this work shows that the acoustic feature is likely strongly associated with the pressure smoothing scale. A feature at the same scale is imprinted on the small-scale flux power spectrum of the Lyman-$\alpha$ forest at $k=0.1-1\;\mathrm{s/km}$. A methodology developed for the simulations is applied to the latest measurements of the flux power spectra at $z=4.2-5.0$ to provide the first direct measurements of the pressure smoothing scale at high redshifts, $\lambda_p(z=4.2) > 33.78\;\mathrm{ckpc}\;(1\sigma)$, $\lambda_p(z=4.6) = 32.36\pm8.35\;\mathrm{ckpc}$ and $\lambda_p(z=5.0)=31.27\pm18.28\;\mathrm{ckpc}$. This proof-of-concept study paves the way for future observational programs aimed at recovering the thermal history using small-scale observations of the Lyman-$\alpha$ forest.
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All authors Vid Iršič, Matteo Viel, Martin G. Haehnelt, James S. Bolton, Ewald Puchwein, Luke I. Gilmartin

Instrumentation and Methods for Astrophysics

CATKit2-HCI: a collaborative framework for advancing high-contrast coronagraph testbeds

Rémi Soummer, Iva Laginja, Emiel H. Por et al. (+19 more)

High-contrast exoplanet imaging requires dedicated laboratory testbeds for the development and validation of coronagraph architectures, wavefront sensing and control methods, calibration strategies, and system-level observing concepts. These testbeds often share similar software needs, yet many tools are developed independently at each institution. The CATKit2-High-Contrast-Imaging collaboration, or CATKit2-HCI, addresses this gap by providing a shared software framework for reusable HCI infrastructure. Built on top of CATKit2, an open-source hardware control and synchronization framework originally developed for the High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed at the Space Telescope Science Institute, CATKit2-HCI provides the collaborative layer for HCI-specific algorithms, calibration tools, diagnostics, visualization, and performance metrics. The collaboration currently includes multiple coronagraph testbeds in the United States and Europe. Its goals are to reduce duplicated software development, improve code quality through shared review, enable more direct comparison of results across facilities, and facilitate the movement of students, postdoctoral researchers, and collaborators between laboratories. We describe the motivation, architecture, collaboration model, shared technical capabilities, and early cross-testbed examples of CATKit2-HCI as a framework for accelerating coronagraph technology development.
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All authors Rémi Soummer, Iva Laginja, Emiel H. Por, Raphaël Pourcelot, Sarah Steiger, Bryony Nickson, Alexis Lau, Pierre Baudoz, Clarissa Do Ó, Jules Fowler, Raphaël Galicher, Tyler D. Groff, Rebecca Jensen-Clem, Dimitri P. Mawet, Johan Mazoyer, Michael W. McElwain, Lane Meier, Axel Potier, Laurent A. Pueyo, Susan F. Redmond, Scott D. Will, Neil T. Zimmerman

Cosmology and Nongalactic Astrophysics

QCD CP-violation scenario for a revised cosmological dynamics: analysis of the binned Pantheon Sample of Super Novae Ia

Giovanni Montani, Nakia Carlevaro, Maria Giovanna Dainotti et al. (+1 more)

We investigate a modified cosmological dynamics in which the Universe is composed of baryonic matter and a complex (classical) scalar field. The phase component of this field is identified with the axion field, which accounts for the dark matter contribution, while its modulus follows a $\lambda\phi^4$-like theory, associated with a dominant constant energy density and describing the dark energy component of the Universe. When the potential term of this complex scalar field is studied near its maximum, it naturally provides an interaction term between dark matter and dark energy. The cosmological model that emerges from this physical framework leads to a modified $\Lambda$CDM dynamics, in which the dark matter contribution is slightly and monotonically suppressed. We then construct the effective running Hubble constant associated with this revised cosmological scenario and we compare this diagnostic tool with the binned data of the Pantheon Sample of Type Ia Supernovae. As a result of the fitting procedure, we are able to provide a satisfactory interpretation of the data in terms of our theoretical conjecture that results statistically favored with respect to the $\Lambda$CDM model.
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All authors Giovanni Montani, Nakia Carlevaro, Maria Giovanna Dainotti, Eleonora Giovannetti

Solar and Stellar Astrophysics

Reversive and Non-Reversive Magnetic CP Stars. I. Catalog

I. I. Romanyuk

An analysis of the distribution of signs of the longitudinal magnetic field component $B_z$ is presented for a sample of 307 chemically peculiar (CP) stars with reliably measured magnetic fields. For each star, the root-mean-square field $B_{\rm rms}$ and the extreme values of $B_z$ are used to classify the field configuration as either reversive or non-reversive. Among the 173 non-reversive stars, 100 exhibit a predominantly negative $B_z$ sign, while only 73 display a positive sign, corresponding to an excess of negative polarities by a factor of about 1.37. A subsample of stars with at least five independent measurements (254 objects) yields a similar ratio of 1.38, confirming the robustness of the asymmetry. The observed predominance of negative $B_z$ values among non-reversive CP stars in the solar neighbourhood is statistically significant. Possible origins of this asymmetry remain unclear and will be addressed in future studies.
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High Energy Astrophysical Phenomena

Peculiar Behavior of Optical Polarization in Blazar 1ES 1959+650: Role of Jet Magnetic Field and Geometry

A. Singh, A. Tolamatti, K. K. Singh et al. (+2 more)

Measurements of high degree of optical polarization from blazars provide a strong evidence for the optically thin synchrotron radiation from the relativistic leptons in the jet. This in turn characterizes the presence of a partially ordered magnetic field in the emission region. However, the topology of magnetic field and acceleration of electrons to ultrarelativistic energies within the blazar jet are poorly understood. In this work, we investigate the decade long optical light curve of the well-known blazar 1ES 1959+650 to probe the role of jet magnetic field in the peculiar behavior of the highly varying degree of linear polarization in the wavelength band 500- 700 nm. The optical light curves in V and R-bands exhibit a strong flare without any significant change in the contemporaneous degree of linear polarization. However, the degree of linear polarization shows strong positive and negative/anti-correlations with the V and R-band fluxes measured during the epochs before and after the flare, respectively. This can be satisfactorily explained using the helical magnetic field and transverse shock under the framework of a relativistic jet with modestly varying orientations. During the flare, the fractional linear polarization is explained by the turbulent emission multi-zone model.
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All authors A. Singh, A. Tolamatti, K. K. Singh, A. C. Gupta, K. K. Yadav

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Characterization of the Scattered Light Noise in KAGRA Interferometer

Shih-Hong Hsu, Hirotaka Yuzurihara, Chia-Jui Chou et al. (+1 more)

In a gravitational wave (GW) telescope, non-stationary noise can prevent stable interferometer operation and limit the GW analyses. Among the non-stationary noise, we focus on the scattered light noise. It fluctuates across a wide frequency band within a short time. Therefore, the scattered light noise can mimic the GW signal, increase the false alarm rate, or bias the parameter estimation results. In this work, we propose a new analysis method, named f-cluster, to characterize these features without prior assumptions about the scattering source. The scattered light noise shows characteristic arch-shaped features in time-frequency maps. Therefore, the algorithm extracts the periodicity of the arch shapes from the spectrogram. The algorithm detects the occurrence times and periodicity of excess-power regions in the spectrogram to estimate the oscillation frequency of the scattering object. To demonstrate the algorithm, we applied this method to KAGRA data from April 1 to 30, 2025, and successfully identified a scattering frequency of $f_{sc} = 0.432$ Hz. Furthermore, we found a strong correlation between the occurrence rate of the scattered light noise and the amplitude of ground motion in the $0.3-1.0$ Hz band with a Pearson correlation coefficient of 0.82. This correlation showed that the occurrence of scattered light noise can be forecast from the seismic motion. We confirmed that our algorithm identifies the frequency of the scattered light noise and its occurrence time, without making assumptions about the scattering object, thereby contributing to the characterization of the scattered light noise in real data. Our algorithm provides information that leads to further investigation into the noise hunting to specify the source of scattered light noise.
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All authors Shih-Hong Hsu, Hirotaka Yuzurihara, Chia-Jui Chou, Yi Yang

Solar and Stellar Astrophysics

Origin of the Long-Period Radial Velocity Variation in the Red Supergiant HD 216946 (V424 Lac)

Byeong-Cheol Lee and Myeong-Gu Park

We present precise radial-velocity (RV) observations of the K-type red supergiant HD~216946 (V424 Lac) obtained over approximately 22 years with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES). The RV measurements reveal a significant long-period variability with a period of 1365 days. To investigate its origin, we analyzed the RV data together with line-profile variations (LPVs), chromospheric activity indicators, and published photometric variability. The LPVs exhibit periods of approximately 1370–1380 days, while the Na~D lines show a similar periodicity near 1355 days, both comparable to the RV period. In contrast, the H-line indicators display longer periods of 2730–2800 days, approximately twice the RV period. The close correspondence between the RV variations and the activity-related diagnostics strongly suggests that the 1365-day RV signal is primarily linked to chromospheric activity and extended atmospheric variability rather than arising from purely Keplerian motion. Published photometric studies also report additional long-period variability, including a 1601-day long secondary-period (LSP)-like variation. The coexistence of multiple non-identical periods indicates that the observed variability of HD~216946 is unlikely to originate from a single physical mechanism. We therefore interpret HD~216946 as a multiperiodic red supergiant in which several intrinsic stellar processes coexist. The observed variability is most likely dominated by chromospheric activity and large-scale atmospheric dynamics, possibly accompanied by rotational modulation and LSP-like variability, although the presence of a low-mass stellar companion cannot be completely excluded.
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Astrophysics of Galaxies

From Dark Matter to Galaxies: Halo-Free Mock Generation via Conditional Point-Cloud Diffusion

Kana Moriwaki, Ken Osato and Naoki Yoshida

We present a diffusion-based generative model for constructing realistic galaxy catalogues from dark matter density fields. The model takes a three-dimensional dark matter density field as input and generates galaxies directly as a point cloud with positions and physical properties, including star formation rate (SFR), without identifying dark matter haloes or subhaloes. We train the model on galaxy catalogues from the IllustrisTNG hydrodynamical simulation. The generated catalogues reproduce the spatial correspondence between galaxies and the underlying dark matter field, preferentially populating dense regions and filamentary structures. They also accurately reproduce the one- and two-dimensional distributions of SFR and stellar mass, the galaxy auto-power spectrum, and the galaxy–dark matter cross-power spectrum. The model generates galaxies associated with structures below the nominal resolution of the input density field by marginalising over unresolved small-scale structure rather than relying on a resolved halo catalogue. With an optimised diffusion sampling schedule, it generates a catalogue with SFR $> 1 ~\rm M_\odot/yr$ over a $(151.3 ~\rm Mpc)^3$ volume in approximately 10 seconds on a single GPU. Our model therefore provides a practical engine for producing large mock ensembles for upcoming galaxy redshift surveys and line-intensity mapping experiments, and offers a path toward simulation-based inference that bypasses halo finding and directly connects field-level dark matter statistics to observable galaxy populations.
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Cosmology and Nongalactic Astrophysics

Accurate parameter inference for the Light-cone Epoch of Reionization 21-cm signal

Suman Pramanick, Anoop Krishna, Rajesh Mondal et al. (+1 more)

The light-cone (LC) effect introduces line-of-sight (LoS) statistical inhomogeneity into the 21-cm signal. Consequently, the traditional power spectrum (PS) fails to capture the full two-point statistical information. The evolving power spectrum (ePS), $P_e(k, z)$, offers an alternative that accounts for this LoS evolution. We compare the statistical power of three different summary statistics: the standard cylindrical PS $P(k_\perp,k_\parallel)$, slice-wise PS $P_s(k, z)$ (3D PS for small bandwidth LC slices), and ePS $P_e(k, z)$. We first demonstrate that $P_e(k,z)$ successfully recovers the benchmark 3D PS of coeval simulations across most $k$ and $z$, whereas the slice-wise PS recovers only at large $k$. To efficiently perform parameter inference, we train artificial neural network (ANN) emulators on $500$ LC 21-cm signals. Our forecasts incorporate cosmic variance, estimated using $50$ statistically independent realizations of the signal, alongside SKA-Low system noise for integration times of $1000$ and $104$ hrs. We find that ePS outperforms its peers, yielding $3$ and $1.4$ times tighter constraints than $P(k_\perp,k_\parallel)$ and $P_s(k,z)$, respectively. Our results establish the ePS as an optimal summary statistic for interpreting forthcoming data.
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All authors Suman Pramanick, Anoop Krishna, Rajesh Mondal, Somnath Bharadwaj

Solar and Stellar Astrophysics

Metric Type II Radio Emission associated with Coronal Mass Ejections of Large Angular Widths: Some New Insights

Mayank Rajput, Susanta Kumar Bisoi and Janardhan Padmanabhan

Solar Type II radio bursts are manifestations of shocks produced by explosive and eruptive solar activities, such as solar flares and coronal mass ejections (CMEs). Metric range or coronal Type II bursts are interesting because of their association with CME-driven shocks. It is therefore important to examine the correlation between the properties of Type II bursts and the associated CMEs. This, in turn, would be useful in understanding the impact of CMEs on space weather and geomagnetic activity. We conducted a statistical study of 23 coronal Type II radio bursts in the frequency range 150-20 MHz, for the period spanning 2007-2024. We correlated the frequency bandwidth of coronal Type II bursts with the angular width of the associated CMEs. Our investigation showed an anti-correlation between the two quantities with a correlation coefficient of $\approx$ -0.62. We further deduced the height of the Type II bursts (r$_{Type II}$) at the onset time of the burst and compared them with the estimated height of the associated CMEs/shocks (r$_{CME}$). With the exception of one event, for the rest of the Type II burst events, r$_{Type II}$ was $<$ r$_{CME}$. The results suggest that the CMEs with large angular widths produce narrow-band Type II emissions, and these Type II emissions could possibly be produced in the flank region of the CME-driven shock rather than at the shock front.
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Solar and Stellar Astrophysics

Boundary conditions for radial pulsations in AGB envelopes

Jan Zalewski

We present a formulation of outer and inner boundary conditions for radial non-adiabatic pulsations in AGB/post-AGB envelopes in terms of local structure of pulsation equations. This approach provides a framework to construct classes of boundary condition selectors. We show that the pulsation spectrum is primarily determined by the choice of the outer boundary selector. Different choices of the two-dimensional subspace at the outer boundary lead to different types of pulsation spectra ranging from p-mode like spectra to ones including strongly excited and damped strange modes. Our results show that the outer boundary conditions control the degree of coupling between acoustic and entropy components in the solution. Selectors dominated by slow (non-acoustic) branches lead to strongly non-adiabatic behavior and emergence of strongly excited/damped strange modes, while selectors including acoustic branches result in weaker coupling and more classical looking spectra. At the inner boundary we found that it is sufficient to enforce that the solution resides in a two-dimensional subspace allowed by the local pulsation equations. This ensures regular behavior and compatibility with WKB asymptotics in deep parts of the envelope. Once this condition is met the detailed form of the inner boundary selector has only minor influence on the resulting pulsation spectrum. We also compare the obtained spectra with those obtained using standard boundary conditions to show that the variations in excitation rates of strange modes reported previously may be interpreted in terms of the subspaces selected by the outer boundary.
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Solar and Stellar Astrophysics

A Search for Exoplanets around Northern Circumpolar Stars X. The origin of radial velocity variations in the evolved star HD 216595

Sang-Hee Kim, Byeong-Cheol Lee, Shenghong Gu et al. (+9 more)

Detecting planetary companions around evolved stars, particularly asymptotic giant branch (AGB) stars, is challenging due to intrinsic stellar variability such as surface convection, pulsations, and mass loss, which can produce radial velocity (RV) signals that mimic Keplerian motion. We investigate the origin of long-period, low-amplitude RV variations observed in the AGB star HD 216595 based on high-resolution spectroscopic data spanning approximately 16 years obtained with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES) and the Las Cumbres Observatory Network of Robotic Echelle Spectrographs (NRES) instruments. The RV measurements reveal a statistically significant periodic signal at 567 days that can be described by a Keplerian model consistent with a substellar companion. However, no strong correlations are found between the RV variations and stellar activity indicators, including line bisectors, chromospheric activity, and photometric variability, although weak signals at similar timescales are present in some diagnostics. Given the stellar properties of HD 216595 and similarities to previously reported cases, the observed RV variations are likely related to intrinsic stellar processes, although a companion-induced origin cannot be definitively ruled out. Further progress will require improved diagnostics and more sophisticated modeling to disentangle stellar variability from genuine orbital signals.
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All authors Sang-Hee Kim, Byeong-Cheol Lee, Shenghong Gu, Jae-Rim Koo, Beomdu Lim, Myeong-Gu Park, Huan-Yu Teng, Yeon-Ho Choi, David Mkrtichian, Tae-Yang Bang, Hyeong-Ill Oh, Heon-Young Chang

Solar and Stellar Astrophysics

2D hydrodynamical simulations of Be star decretion disc formation through boundary layer effects

Madeline Overton, Zhaohuan Zhu, Rebecca G. Martin et al. (+1 more)

Be stars are massive main-sequence stars rotating close to their breakup rate. They possess a decretion disc of material built up due to mass loss from the star, however, there is not a consensus to the mechanism responsible for the formation of the disc because of their sub-breakup spin rates. We present the first 2D hydrodynamical simulations of the formation of a Be star decretion disc from a rapidly rotating star due to boundary layer effects that reduce the rotation rate of the disc close to the star. In our simulations with a disc aspect ratio of $h/r=0.1$, a decretion disc forms around a star rotating with $80 \%$ of the breakup rate, but fails when rotating at $70 \%$ of the breakup rate. For a thinner disc, a faster stellar spin may be needed to form a dynamically important decretion disc. We also demonstrate good agreement between 1D and 2D models. Although this work does not consider the presence of magnetic fields and the angular momentum transport is through viscosity, our results robustly show a Be star disc may be built up hydrodynamically through boundary layer effects, and may play an essential role in regulating the stellar spin.
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All authors Madeline Overton, Zhaohuan Zhu, Rebecca G. Martin, Jiayin Dong

Earth and Planetary Astrophysics

CAFE follow-up of TESS hot Jupiter candidates left behind: I. Five newly confirmed planets and a false positive

J. Lillo-Box, C. Cifuentes, O. Balsalobre-Ruza et al. (+56 more)

Hot Jupiters are key targets for understanding planet formation, migration, and atmospheres. Yet, most ground-based follow-up resources for the TESS mission are focused on confirming low-mass planet candidates, leaving many giant planets without mass determinations or definitive confirmation. We use the \cafe{} spectrograph at Calar Alto Observatory to monitor the radial velocity of stars hosting hot-Jupiter candidates that have received little follow-up, aiming to confirm their planetary nature. We present results for seven candidates. We monitored the radial velocity of TOI-603, TOI-1137, TOI-1837, TOI-2114, TOI-4492, TOI-5806, and TOI-5811, jointly modeling the CAFE radial velocities and TESS photometry to determine the nature and properties of the transiting objects. We confirm five new planets: TOI-603 b ($33.0^{+6.5}_{-6.2}$ M$_{\oplus}$, $16.2$ d), TOI-2114 b ($1.01^{+0.14}_{-0.12}$ M$_{\rm Jup}$, $6.2$ d), TOI-4492 b ($5.92^{+0.67}_{-0.64}$ M$_{\rm Jup}$, $4.4$ d), TOI-5806 b ($2.77^{+0.34}_{-0.32}$ M$_{\rm Jup}$, $3.2$ d), and TOI-5811 B b ($0.81^{+0.11}_{-0.10}$ M$_{\rm Jup}$, $6.3$ d). TOI-603 b lies in the "Neptune savanna", whereas the other four are hot Jupiters orbiting slightly evolved stars. We find TOI-5811.01 to be a planet transiting the nearby bound companion TOI-5811 B (hence TOI-5811 B b), and identify a stellar companion to TOI-5806 at a projected separation of 248 au, making both S-type planetary systems. TOI-1837.01 is an eclipsing binary, while TOI-1137.01 remains inconclusive. The five confirmed planets orbit bright stars (${\rm G}=8.6-10.2$~mag), and four are excellent targets for atmospheric studies, with transmission spectroscopy metrics above 90. These results highlight the importance of intensive follow-up observations to establish the nature of transiting planet candidates.
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All authors J. Lillo-Box, C. Cifuentes, O. Balsalobre-Ruza, B. Montesinos, D. Latham, K. A. Collins, D. Ciardi, G. Hébrard, S. W. Yee, E. W. Guenther, H. Bouy, J. N. Winn, S. B. Howell, C. Ziegler, M. E. Everett, B. Safonov, F. Murgas, N. Narita, L. D. Nielsen, A. Abreu, J. Aceituno, J. F. Agüí Fernández, M. Azzaro, D. Barrado, P. Benni, A. Bieryla, A. Chontos, C. A. Clark, E. Delgado-Mena, S. J. Deveny, R. Forés-Toribio, J. Flores-Martín, A. Garmash, S. Góngora, J. D. Hartman, C. Haukes, N. Heidari, I. J. Helm, J. F. Kielkopf, J. Köhler, C. Littlefield, M. B. Lund, B. Massey, A. Masson, J. McCormac, M. Morales-Calderón, M. Mori, J. A. Muñoz, E. Pallé, P. Plavchan, M. Reefe, J. E. Schlieder, G. Srdoc, C. Stockdale, J. C. van Eyken, R. G. West, F. P. Wilkin, J. Wittrock, D.-V. Zora

Cosmology and Nongalactic Astrophysics

Constraining Effective Viscosity in the Intracluster Medium via the Thermal Sunyaev-Zeldovich Effect – Predictions from the SLOW Constrained Coma Cluster Simulations

Frederick Groth, Yuan Li, Joseph Golec et al. (+4 more)

We study the effect of viscosity on the Sunyaev-Zeldovich signal in a simulated constrained Coma cluster analog. We aim to provide alternative constraints on the amount of viscosity in the ICM. We use the Coma cluster realization with different levels of viscosity from the LOWER DECKS zoom-ins of the SLOW constrained simulations. We generate mock thermal and kinetic Sunyaev-Zeldovich maps and and analyze their statistics. We compare them to Planck observations. Viscosity shows a consistent trend in thermal SZ (tSZ) profiles, increasing the signal in the center and suppressing it in the outskirts. Viscosity also has a strong effect on the tSZ power spectrum, elevating its amplitude on all scales. Comparisons with Planck observations suggest that the effective ICM viscosity is below $5\%$ of the Spitzer value. Unsharp masking reveals an effect on small scales, which are, however, not yet detectable with current observational data. The thermal Sunyaev-Zeldovich effect shows clear and consistent trends that allow us to probe the effective viscosity of the ICM. Our analysis suggests suppressed ICM viscosity below $5\%$ of the Spitzer value, consistent with previous X-ray analysis. Our results validate the strength of the SZ effect as an independent method to constrain ICM viscosity.
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All authors Frederick Groth, Yuan Li, Joseph Golec, Benjamin A. Seidel, Jenny G. Sorce, Tirso Marin-Gilabert, Klaus Dolag

Solar and Stellar Astrophysics

One cluster, two clusters, no cluster? – The curious case of HSC 2686 and Lynga 3

Andreas Ritter, Quentin A. Parker, Xizhe Xie et al. (+1 more)

This study was motivated by the search for Planetary Nebulae (PNe) and Open Cluster (OCs) associations. Only 5 PNe are currently in Galactic OCs among the previous $\sim4,800$ OCs known. They are valuable because as cluster members their properties can be linked to their progenitor stars, something not possible for general field PNe. Since the GAIA astrometric satellite first data release, thousands of new OC candidates have been identified. This offers fresh motivation to search them as hosts for known PNe. Statistically we expect 30 OC-PN pairs to be present. We searched these GAIA candidate OCs, found by Hunt & Reffert (2023), for known central stars of PNe (CSPNe) as a practical proxy for the PNe themselves and one suited to automated searches. We identified 1 potential CSPN (IRAS 15127-5811) of "Likely" PN [GKF2010] MN18 in the HASH database, as a claimed member of the putative cluster HSC~2686. A second cluster (Lynga~3) with similar parameters and in very close angular proximity could also be a potential host. Here we reclassify CSPN IRAS 15127-5811 as a blue supergiant with a surrounding bi-polar nebula. Nevertheless, we collected all available information on proposed member stars for both these clusters. We conclude that neither claimed cluster is real. Our results shed considerable doubt on the veracity of many newly identified OCs that have modest numbers of stellar members.
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All authors Andreas Ritter, Quentin A. Parker, Xizhe Xie, Xingyi Guo

Solar and Stellar Astrophysics

Solar differential rotation driven by baroclinic forcing

L. S. Menicucci, G. Guerrero, M. Dikpati et al. (+3 more)

A combination of recent observations and numerical simulations has called into question whether Sun's interior is characterized by strong turbulent convection, a problem known as convective conundrum. In light of a possible absence of vigorous convective motions, we examine whether the Sun's differential rotation, previously assumed to be tightly coupled to Reynolds stresses, may instead be sustained by the presence of a background latitudinal entropy gradient in thermal wind balance. By performing global hydrodynamical simulations of a rotating spherical shell representing the bulk of the solar convection zone, we demonstrate that solar-like differential rotation can be generated under a variety of thermal stratifications. This work proposes an alternative scenario for the origin of solar differential rotation that accommodates the previously reported discrepancies.
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All authors L. S. Menicucci, G. Guerrero, M. Dikpati, R. Hester, J. Zhang, P. K. Smolarkiewicz

Solar and Stellar Astrophysics

Exploring the Small-scale Magnetic Fields in the Atmosphere of HD 49385 by Asteroseismic Analysis

Yuetong Wang, Yaguang Li, Yan Li et al. (+2 more)

Recent asteroseismic studies have shown convincing evidences that magnetic fields may exist in the interior of some pulsating red giants. Inspired by this breakthrough, we explored the effect of small-scale magnetic fields on the p-mode oscillations in an evolved star, HD 49385. {\bf We incorporate a modified Eddington $T$-$\tau$ equation that phenomenologically mimics the effect of the magnetic fields in the atmosphere of HD 49385,} and calculate the frequencies of p-modes with $l=0$, 1, and 2. By comparing the calculated frequencies with the observed ones, we select two best-fit models with either GS98 or A09 chemical composition. Our best-fit models not only fit satisfactorily the observed frequencies, but also well reproduce some spectroscopically observed stellar parameters such as effective temperature and log\,$g$. Based on the two best-fit models, we have estimated that the small-scale magnetic fields possess a strength of approximately 80\,G and spread concentratively at approximately a height of 1850 km in the atmosphere. By selecting the best-fit models with special requirement on the avoided-crossing mode, we have confirmed that the frequency of the avoided-crossing mode is tightly related to the helium core of the star, and determined the size of the helium core as 0.117${\rm M}_\odot$ in mass and 0.078${\rm R}_\odot$ in radius. Based on the improvements of previous two sides, we can accurately determine the mass of HD 49385 to be $1.25\pm 0.02\,{\rm M}_\odot$ with an age of 4.1\,Gyr for GS98 composition and 4.5\,Gyr for A09 composition.
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All authors Yuetong Wang, Yaguang Li, Yan Li, Guifang Lin, Tao Wu

Solar and Stellar Astrophysics

Asteroseismic Analysis of a Red Giant KIC 9145955 by Including the Small-scale Magnetic Fields in the Atmosphere

Yuetong Wang, Guifang Lin, Yan Li et al. (+2 more)

Recent convincing evidence is found within asteroseismology that suggests the magnetic fields exist in three red giants. Research on small-scale magnetic fields in the Sun and HD 49385 has shown that they have a certain corrective effect on the systematic discrepancies between observed and theoretical frequencies. Here we apply a similar method applied for the Sun to a red giant, KIC 9145955, to explore the impact of small-scale magnetic fields in the photosphere on its frequencies. We find that the calculated frequencies of our best-fit model, which simulates the effect of the magnetic fields by artificially modifying the Eddington $T-\tau$ relation, perfectly match those of the observed l = 0, 1, and 2 modes, indicating the existence of small-scale magnetic fields with an upper strength limit of 65 G and concentrating at a height 13,100 km in the photosphere. Based on the best-fit model, we revise the stellar parameters of KIC 9145955 as: $M = 1.23\pm0.04\,M_\odot$, $R = 5.57\pm0.06\,R_\odot$, $L = 19.85\pm0.5\,L_\odot$, $Age = 3.83\pm0.5$\,Gyr, $M_{\rm He} = 0.2108\pm0.0005M_\odot$, and $R_{\rm He} = 0.0306\pm0.0001R_\odot$.
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All authors Yuetong Wang, Guifang Lin, Yan Li, Tao Wu, Yaguang Li

Astrophysics of Galaxies

When Galaxies Refuel: Evolution of the Perturbed Spiral Galaxy NGC1385

Xiaoyu Kang, Eva Sextl, Rolf-Peter Kudritzki et al. (+5 more)

The spiral galaxy NGC 1385 is characterized by a vigorous and protracted history of star formation, particularly in its central regions, leading to a current star formation rate that surpasses those of comparable systems. We analyze the evolution history of the galaxy using spatially resolved optical and submillimeter spectroscopy obtained from the PHANGS survey combined with WALLABY radio survey data. We construct radial distributions of star formation rate and the interstellar medium (ISM) neutral and molecular gas mass surface densities and measure the metallicity distribution of the stellar populations using a refined full-spectral fitting population synthesis method together with a determination of ISM oxygen abundances using H\,II region emission lines. The metallicities of the young stars and the ISM are similar and show an almost flat distribution. This is crucially different from previous work which had found a positive gradient for the average metallicities of the stars. We fit a chemical evolution model (incorporating gas infall, outflow, and radial inflow) to the observed data of NGC\,1385. Based on this fit, the evolution of NGC\,1385 is characterized by the typical inside-out disk formation of spiral galaxies – even though our model does not assume an a priori shorter gas infall timescale for the inner disk than for the outer disk. However, the galaxy has experienced sustained star formation over gigayear timescales with a star formation efficiency a factor of two higher than normal. This explains the high metallicity of the young stars of 0.15 to 0.2\,dex higher than solar and the flat distribution of metallicity across the disk. The model predictions for the metallicities of the stars align well with the observed values, supporting the robustness of both our refined spectral fitting analysis and the inferred evolutionary scenario.
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All authors Xiaoyu Kang, Eva Sextl, Rolf-Peter Kudritzki, Hassen M. Yesuf, Fenghui Zhang, Ruixiang Chang, Xiejin Li, Yunkun Han

High Energy Astrophysical Phenomena

No Surviving Companion to the Galactic SN 1181: Evidence for a Double-Degenerate Channel for Type Iax Supernovae

Kohki Uno, Daichi Tsuna, Daichi Hiramatsu et al. (+2 more)

Type Iax supernovae (SNe Iax) are the recently-established, yet peculiar subclass of thermonuclear supernovae, whose progenitor systems and explosion mechanisms remain debated. A leading scenario is a single-degenerate channel, in which a white dwarf accreting from a He-star companion undergoes a pure deflagration, leaving both a bound remnant and surviving companion. The Galactic SN 1181, whose distinctive properties are consistent with an SN Iax involving a weak explosion and bound white dwarf remnant, offers a unique opportunity to test this scenario. Here, we perform a deep search for a surviving He-star companion, a hallmark of the single-degenerate He-donor channel, within $30^{\prime\prime}$ ($\sim 0.3$ pc) of the remnant using archival Gaia and Pan-STARRS1 data. The parallaxes and proper motions exclude all Gaia sources, while the spectral energy distributions of the remaining Pan-STARRS1 sources are inconsistent with both the He-star spectral templates and known hot-subdwarf population. Binary evolution calculations predict a minimum mass of a companion with an absolute $g$-band magnitude of $M_{g} \lesssim 6.5$ mag, much brighter than the Pan-STARRS1 detection limit of $M_{g} > 8$ mag. Our non-detection rules out He-star and luminous hydrogen-rich companions for SN 1181, favoring a double-degenerate channel (i.e., a white dwarf merger). Adding to the luminous He-star companion identified in the pre-explosion imaging of SN 2012Z, our results provide direct evidence for multiple progenitor channels leading to SNe Iax.
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All authors Kohki Uno, Daichi Tsuna, Daichi Hiramatsu, Tomoya Kinugawa, Takatoshi Ko

Cosmology and Nongalactic Astrophysics

Dynamical Test of Cosmic Acceleration: $k$-nearest Neighbor Cross Correlation of Cosmic Microwave Background and Cosmic Infrared Background

Dongkok Kim, Donghui Jeong, Yi-Kuan Chiang et al. (+1 more)

The physical origin of cosmic acceleration remains one of the central questions in modern cosmology. The integrated Sachs-Wolfe (ISW) and Rees-Sciama (RS) effects, which arise from the evolution of gravitational potentials, provide a dynamical test of cosmic acceleration. We measure the cross correlation between the Planck temperature map of the cosmic microwave background (CMB) and a foreground-free map of the $100\,\mu\mathrm{m}$ cosmic infrared background (CIB) from Y.-K. Chiang (2023), using the $k$-nearest neighbor cumulative distribution function ($k$NN-CDF). As the CIB map is reconstructed from ${\sim}600$ million Wide-field Infrared Survey Explorer galaxies extending to $z\approx2.5$, the measurement is equivalent to a galaxy-CMB cross correlation. We find evidence for a positive cross correlation, rejecting the null hypothesis of no correlation at $p=0.02~(2.3\sigma)$ using the $\chi^2$ test. We further quantify its amplitude with $A_{k\mathrm{NN}}$, defined relative to an assumed cosmological model, and obtain $A_{k\mathrm{NN}}=0.95\pm0.20~(4.8\sigma)$ with respect to $\Lambda\mathrm{CDM}$ mock data including the ISW and RS effects. The $k$NN-CDF analysis improves the detection significance by ${\sim}20\%$ over the two-point correlation function. We also explore evolving dark energy by constructing two tomographic maps from the full CIB map; the results are consistent with $\Lambda$CDM. Finer tomographic reconstruction of the CIB, for example from multiband data of SPHEREx, would further tighten constraints on evolving dark energy.
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All authors Dongkok Kim, Donghui Jeong, Yi-Kuan Chiang, Ho Seong Hwang

Solar and Stellar Astrophysics

The magnetic field strength of a methane dwarf measured from its radio spectral cutoff

Timothy W. H. Yiu, Harish K. Vedantham, Joseph R. Callingham et al. (+1 more)

Brown dwarfs and gas-giant planets are expected to emit coherent radio emission via the electron cyclotron maser instability (ECMI) mechanism powered by non-thermal electrons in their magnetospheres. Detection of a characteristic spectral cutoff in their cyclotron emission is likely to be the only feasible route to measure their magnetic field strengths. Previous radio measurements of a subset of cold brown dwarfs (spectral type T or methane dwarfs) have not shown such a cutoff at frequencies as high as $\gtrsim 10\,{\rm GHz}$, implying field strengths far higher than canonical expectations from dynamo scaling laws. However, it is also possible that these high-frequency emissions did not originate in the large-scale magnetic field but rather from small high-field-strength loops at the surface, which the scaling laws are not designed to predict. Here we present radio observations of a methane dwarf binary (WISEP J101905.63+652954.2) whose radio emission was first detected in an untargeted low-frequency survey, making it more likely that the emission traces the object's large-scale magnetic field. The object's spectrum shows a clear radio spectral cutoff whose location yields a polar surface field strength of around 126 gauss. Canonical dynamo scaling laws based on energy balance now over-predict the field strength for this object, but the scaling law based on Lorentz-Coriolis force balance (Elsasser number rule) is consistent with the measurement. Our results suggest that multi-frequency (MHz to GHz) monitoring of brown-dwarf electron cyclotron maser emission is essential to separately measure the `mean field' on large scales and `fluctuating' fields on smaller spatial scales in order to determine the dynamo scaling law that most accurately predicts field generation in the metallic hydrogen layer of gas giants and cold brown dwarfs.
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All authors Timothy W. H. Yiu, Harish K. Vedantham, Joseph R. Callingham, Timothy W. Shimwell

Astrophysics of Galaxies

AGNFormer I: Reconstruction of AGN spectra using a probabilistic transformer model

Benedict L. Rouse, Franz E. Bauer, Tomasz Różański et al. (+8 more)

We explore how an uncertainty-aware transformer-based architecture can leverage information embedded across the entire observed optical spectra of AGN, focusing on the algorithm's ability to predict unseen or masked parts of luminous AGN spectra. This provides a direct probe of the learnable correlations between AGN continua and broad lines. We introduce AGNFormer, a transformer model trained to predict the mean expected flux and variance in masked spectral regions (major broad lines to ${\pm}10^{4}$kms$^{-1}$; missing halves), inputting rest-frame spectral fluxes and uncertainties across the entire redshift range of the SDSS DR16 Quasar Catalogue. We evaluate the performance of the model on both full (no S/N limit) and high-quality (S/N > 10) spectral samples using the negative-log likelihood, and via comparisons with existing C IV and ly-a reconstruction algorithms. The model successfully reconstructs unseen AGN broad lines to better than 10-16% (4-8%) of the flux for the full (S/N > 10) test sets, up to an error floor of $\approx$2-6% of the flux at S/N $\approx$ 40, while predictions for larger unseen halves grow to 12-25% (5-15%) of the flux the further away they are from the cut-off wavelength of the seen input spectrum. Predictions faithfully reproduce the broad AGN spectral diversity across the entire optical and UV QSO main sequence parameter spaces, including both Gaussian and Lorentzian profile regimes, Feii complexes, and narrow emission lines. Performance is similar or better compared to previous spectral reconstruction algorithms. The high precision of the broad-line region reconstruction demonstrates that the method successfully aggregates information across the spectrum and highlights how the AGN continuum and weaker lines/complexes have the potential to assist astronomers in the extraction of the entire wealth of information embedded in AGN spectra.
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All authors Benedict L. Rouse, Franz E. Bauer, Tomasz Różański, Guillermo Cabrera-Vives, Patricia Arévalo, Cristóbal Rodrigo Donoso Oliva, Pavlos Protopapas, Gordon T. Richards, Paula Sánchez-Sáez, Ezequiel Treister, Christian Wolf

Tuesday 21 July

High Energy Astrophysical Phenomena

Chaotic cosmic ray acceleration in nonlinear Alfven waves

Maxim Lyutikov

We demonstrate that motion of a particle in a single coherent linearly polarized (LP) Alfven wave with relative amplitude $\delta = B_w /B_0 \gtrsim 0.25 $ becomes chaotic. As a result, a sufficiently strong, near resonant Alfven waves ($r_L k_\parallel \sim 1$, $r_L $ is relativistic cyclotron radius, $k_\parallel$ is wavevector) can lead to transient trapping and phase mixing, imitating classical scattering. Evolution of pitch angle via Alfven chaos is non-diffusive - a particle on trapped trajectory can reverse its velocity in one scattering event. This both avoids the problem of the 90$^\circ$ barrier, and increases the acceleration rate for those special particle.
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