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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 12 December

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitational Foundations and Exact Solutions in $n$-Dimensional Fractional Cosmology

S. M. M. Rasouli, J. Marto, D. A. V. Oliveira et al. (+1 more)

Three theoretically plausible techniques to developing a fractional scalar field cosmological model are pointed in this paper; the time-dependent kernel weighted action being then selected. Upon this choice, we proceed to establish (i) a time weighted action associated with the generalized scalar field cosmology; and (ii) a fractional cosmological model in $n$ dimensions considering the FLRW metric and a generalized version of the Sáez-Ballester (SB) theory. Our study focuses on the following purposes. Firstly, to investigate the fundamental gravitational structural features of the model, we analyze the dynamical behavior of the field equations, the fulfillment of the Bianchi identities, the associated conservation laws, and the application of the second Noether theorem at the background and first-order perturbation levels. Moreover, the model's distinguishing characteristics and theoretical differences from the corresponding standard scenarios are also investigated. Secondly, we aim to obtain exact analytical solutions and analyze the time evolution of key cosmological quantities, considering the fractional parameter effects. Furthermore, the model's predictions are compared with those of the corresponding standard models. Lastly, we propose new ideas to further generalize our model, with a focus on constructing an effective potential and investigating the conditions under which bounce solutions may emerge.
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All authors S. M. M. Rasouli, J. Marto, D. A. V. Oliveira, P. Moniz

High Energy Astrophysical Phenomena

JWST and HST observations of the host galaxy and supernova, SN 2024aihh in EP240801a at z=1.67

Agnes P.C. van Hoof, Andrew J. Levan, Peter G. Jonker et al. (+15 more)

We present James Webb Space Telescope (JWST) and Hubble Space Telescope (HST) observations of the counterpart of EP240801a, at z=1.67, the first fast X-ray transient (FXT) identified as an X-ray flash (XRF) by the Einstein Probe (EP) and Fermi-GBM. Our observations reveal strong photometric and spectroscopic evidence for an associated broad-lined Type Ic supernova (SN) SN 2024aihh, the most distant spectroscopically identified gamma ray-burst (GRB)-SN to date. The SN exhibits similar luminosity and light curve evolution to the proto-type GRB-SN 1998bw with an absolute magnitude of the SN at $\sim$23 days rest-frame of $M_{F140W} \approx$-19 mag. The SN is located in a host galaxy with complex morphology at a large ($\sim$6 kpc) offset in a region of relatively low surface brightness. The region around the SN has a modest star formation rate and is dominated by an intermediate mass-weighted age (1.4$\pm$0.3 Gyr) population, despite the apparent presence of a young, massive broad-lined Type Ic SN progenitor. These observations demonstrate that observations with HST and JWST can greatly extend the redshift range over which the GRB/FXT-SN connection can be studied, including in relatively low luminosity, X-ray rich events. They demonstrate little apparent evolution in the SN properties from local examples despite EP240801a originating from an epoch 10 Gyr ago.
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All authors Agnes P.C. van Hoof, Andrew J. Levan, Peter G. Jonker, Morgan Fraser, Luca Izzo, Andrew S. Fruchter, Joyce N. D. van Dalen, Nial R. Tanvir, Jens Hjorth, Antonio Martin-Carrillo, Nikhil Sarin, Laura C. Cotter, Jonathan A. Quirola-Vásquez, Maria E. Ravasio, Javi Sánchez-Sierras, Manuel A. P. Torres, Shuai-Qing Jiang, Dong Xu

Cosmology and Nongalactic Astrophysics

The magnitude of the dark ages 21-cm signal in the context of existing early and late time constraints on $\Lambda$CDM

H. T. J. Bevins

The dark ages 21-cm signal is a promising probe of the currently unobserved infant universe between the formation of the Cosmic Microwave Background around $z \approx 1100$ and the first galaxies around $z\approx 30$. A detection of the signal will help researchers understanding the nature of dark matter and dark energy, the expansion of the universe and any extensions to the concordance $\Lambda$CDM model that could explain the reported Cosmic Dawn 21-cm signal from EDGES and the Hubble tension. In this letter we take existing constraints on the $\Lambda$CDM cosmological model from two early time probes, Planck and WMAP, and two late time probes, DES galaxy lensing and clustering and Baryon Acoustic Oscillations, and propagate these through to constraints on the magnitude of the dark ages 21-cm signal. We constrain the magnitude and central frequency of the signal while methodically accounting for uncertainties in the cosmological parameters. We find that within the context of our modelling assumptions and the $\Lambda$CDM paradigm, the depth of the dark ages 21-cm signal is known to better than 1 mK and the central frequency to within 0.05 MHz.
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Earth and Planetary Astrophysics

Dynamical evolution of massless particles in star clusters with NBODY6++GPU-MASSLESS: II. The long-term evolution of free-floating comets

Francesco Flammini Dotti, M.B.N. Kouwenhoven, Kai Wu et al. (+5 more)

Context. Comets, asteroids, planetesimals, free-floating planets and brown dwarfs, are continuously injected into the intra-cluster environment after expulsion from their host planetary systems or binary system. The dynamics of large populations of such free-floating comets (ffcs) in a star cluster environment is not yet fully understood. Aims. We investigate the dynamical evolution of comet populations in star clusters, and characterize the kinematics and ejection rates of ffc in a star cluster. Moreover, we determine whether a different initial energy distribution affects the mass segregation of the less massive population. Methods. We carry out simulations using the N-body code NBODY6++GPU-MASSLESS (Flammini Dotti et al. 2025), which allows fast integration of star clusters that contain large numbers of massless particles, to characterize the dynamics of populations of low-mass particles with sub-virial and super-virial distributions. Results. Comets do not participate in the mass segregation process, similarly to planet-size objects, regardless of their initial energy distribution. The latter is slightly changing the whole dynamical evolution at the start of the simulation. We only observe an initial relaxation or collapse of the objects for super-virial and sub-virial ratios, respectively. The external regions of the ffcs population tend to be pulled back in the cluster core at the end of the simulation, suggesting the gravitational pull of the stars is pulling them back in the core. This phenomenon occurs at later times if the system in virial equilibrium. Compared to less massive bodies, brown dwarfs experiences more mass segregation the inner regions tend to be more mixed with the stellar population
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All authors Francesco Flammini Dotti, M.B.N. Kouwenhoven, Kai Wu, Abbas Askar, Peter Berczik, Mirek Giersz, Rainer Spurzem, Ian Dobbs-Dixon

Astrophysics of Galaxies

Laboratory rotational spectroscopy and interstellar search for the protein precursor 4-oxobutanenitrile (HCOCH$_2$CH$_2$CN)

V. M. Rivilla, E. R. Alonso, W. Song et al. (+6 more)

Understanding the presence and distribution of prebiotic precursors in the interstellar medium (ISM) is key to tracing the chemical origins of life. Among them, 4-oxobutanenitrile (\ch{HCOCH2CH2CN}) has been identified in laboratory simulations as a plausible intermediate in the formation of glutamic acid, a proteinogenic amino acid. Here, we report its gas-phase rotational spectrum, measured using two complementary techniques: chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy (2$-$18 GHz) and free-jet millimeter-wave (FJ$-$AMMW) absorption spectroscopy (59.6$-$80 GHz). Quantum chemical calculations revealed nine low-energy conformers, of which the TC conformer was assigned based on the measured spectra. The resulting spectroscopic parameters were used to search for the molecule in the ultradeep spectral survey of the G+0.693-0.027 molecular cloud, located in the Galactic Center. No signal attributable to 4$-$oxobutanenitrile was detected. A stringent upper limit to its column density was derived ($N<$ 4 $\times$10$^{12}$ cm$^{-2}$), corresponding to a molecular abundance of $<$ 2.9 $\times$10$^{-11}$ relative to H$_{2}$. This upper limit lies well below the observed abundances of simpler structurally related species containing $-$HCO and $-$CN groups, underscoring the challenge of detecting increasingly complex prebiotic molecules in the ISM and the need for future, more sensitive astronomical facilities.
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All authors V. M. Rivilla, E. R. Alonso, W. Song, A. Insausti, A. Maris, F. J. Basterretxea, S. Melandri, I. Jiménez-Serra, E. J. Cocinero

High Energy Astrophysical Phenomena

The Polarized X-ray Universe: Insights and Discoveries

Arbind Pradhan, Sree Bhattacherjee and Biplob Sarkar

Polarization is one of the fundamental natures of electromagnetic radiation. The detection of polarization or polarized photons from distant X-ray radiating systems (such as X-ray binaries (XBs), active galactic nuclei (AGN), pulsars, and stars) complements the timing, spectral, and imagining analysis to better understand the physical mechanisms taking place in these sources. Polarization has enhanced the understanding of the internal geometry of these systems and their vicinity. Polarized X-rays can be generated either directly through non-thermal physical processes in the presence of a magnetic field(B) or through the scattering of unpolarized thermal radiation within plasma structures such as an accretion disk. X-ray polarization can measure the two important independent parameters, the polarization degree (PD) and polarization angle (PA) of the X-ray photons. These parameters are crucial as they reveal the characteristics of particles in such a strong magnetic and gravitational field. In this chapter, we have discussed (i) the basic idea of polarization, (ii) some distant sources radiating polarized X-ray photons, (iii) missions dedicated to observing polarized X-ray photons, and (iv) recent breakthroughs and upcoming missions.
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Solar and Stellar Astrophysics

Type II and Type III Solar Radio Burst Classification Using Transfer Learning

Herman le Roux, Ruhann Steyn, Du Toit Strauss et al. (+6 more)

The Sun periodically emits intense bursts of radio emission known as solar radio bursts (SRBs). These bursts can disrupt radio communications and be indicative of large solar events that can disrupt technological infrastructure on Earth and in space. The risks posed by these events highlight the need for automated SRB classification, providing the potential to improve event detection and real-time monitoring. This would advance the techniques used to study space weather and related phenomena. A dataset containing images of radio spectra was created using data recorded by the Compound Astronomical Low frequency Low cost Instrument for Spectroscopy and Transportable Observatory (e-Callisto) network. This dataset comprises three categories: empty spectrograms; spectrograms containing Type II SRBs; and spectrograms containing Type III SRBs. These images were used to fine-tune several popular pre-trained deep learning models for classifying Type II and Type III SRBs. The evaluated models included VGGnet-19, MobileNet, ResNet-152, DenseNet-201, and YOLOv8. Testing the models on the test set produced F1 scores ranging from 87% to 92%. YOLOv8 emerged as the best-performing model among them, demonstrating that using pre-trained models for event classification can provide an automated solution for SRB classification. This approach provides a practical solution to the limited number of data samples available for Type II SRBs.
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All authors Herman le Roux, Ruhann Steyn, Du Toit Strauss, Mark Daly, Peter T. Gallagher, Jeremiah Scully, Shane A. Maloney, Christian Monstein, Gunther Drevin

Earth and Planetary Astrophysics · Cross-listed from cond-mat.stat-mech

A mini-review on combinatorial solutions to the Marcus-Lushnikov irreversible aggregation

Michał Łepek, Agata Fronczak and Piotr Fronczak

Over the past decade, a combinatorial framework for discrete, finite, and irreversibly aggregating systems has emerged. This work reviews its progress, practical applications, and limitations. We outline the approach's assumptions and foundations, based on direct enumeration of system states, contrasting with classical Smoluchowski and Marcus-Lushnikov methods. Using the constant kernel as an example, we derive combinatorial expressions for the average number of clusters of a given size and their standard deviation, and present the complete probability distribution for cluster counts. The method is then extended to several kernels (additive, product, linear-chain, condensation) by explicitly enumerating ways to form clusters of a given size. For general kernels, approximate solutions are obtained via recursive expressions, enabling predictions without explicit solutions. Applications to aerosol growth and planetesimal formation are demonstrated, with comparisons to numerical results. We summarize issues of validity and precision and propose open problems. The appendix includes partial Bell polynomials, generating functions, Lagrange inversion, potential applications, and links between combinatorial and scaling solutions of the Smoluchowski equation.
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Solar and Stellar Astrophysics

The hydrogen-free circumstellar interaction in the Type Ib supernova 2021efd: A clue to the mechanism of the helium-layer stripping

N. Pyykkinen, T. Nagao, H. Kuncarayakti et al. (+27 more)

Stripped-envelope supernovae (SESNe), including Type IIb, Ib, and Ic supernovae (SNe), originate from the explosions of massive stars whose outer envelopes have been largely removed during their lifetimes. The main stripping mechanism for the hydrogen (H) envelope in the progenitors of SESNe is often considered to be interaction with a binary companion, while that for the helium (He) layer is unclear. We conducted photometric and spectroscopic observations of the Type Ib SN 2021efd, which shows signs of interaction with H-free circumstellar material (CSM). Around 30 days after the r-band light curve (LC) peak, until at least ~ 770 days, its LCs display excessive luminosity compared to regular SESNe and at least three distinct peaks. The light curve evolution is similar to that of SN 2019tsf, whose previously unpublished spectrum at 400 days is also presented here. The nebular spectrum of SN 2021efd shows narrow emission lines (~ 1000 km/s) in various species. Our observations suggest that SN 2021efd is a Type Ib SN interacting with CSM with the following parameters: The estimated CSM mass, composition, and distribution are at least a few times 0.1 M_sun, H-free, and clumpy, respectively. Based on the estimated ejecta properties, we conclude that this event is a transitional SN whose progenitor was experiencing He-layer stripping at the epoch of the explosion, and was on the way to becoming a carbon-oxygen star from a He star. The estimated CSM properties suggest that the progenitor had some episodic mass ejections with a rate of ~ 0.001-0.01 M_sun/yr for the last decade and slightly smaller before this final phase at least from ~ 200 years before the explosion, for the assumed CSM velocity of 100 km/s. For the case of ~ 1000 km/s, the necessary mass-loss rate would be increased by a factor of ten, and the timescales decreased by a factor of ten.
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All authors N. Pyykkinen, T. Nagao, H. Kuncarayakti, M.D. Stritzinger, T. Kangas, K. Maeda, P. Chen, J. Sollerman, C. Burns, S. Bose, G. Folatelli, L. Ferrari, N. Morrell, A. Reguitti, I. Salmaso, S. Mattila, A. Gal-Yam, C. Fremling, S. Anand, M. Kasliwal, C.P. Gutiérrez, L. Galbany, W. Hoogendam, S. Schulze, C. Ashall, K. Medler, C.M. Pfeffer, P. Lundqvist, B. Rusholme, J. Adler

High Energy Astrophysical Phenomena

Measurement of the cosmic ray nickel energy spectrum from 10 GeV/n to 2 TeV/n with the DAMPE

F. Alemanno, Q. An, P. Azzarello et al. (+145 more)

Nickel, one of the most tightly bound nuclei alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index -2.60 +/- 0.03 from 40 GeV/n to 1 TeV/n. This work provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time.
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All authors F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. V. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan, K. K. Duan, R. R. Fan, Y. Z. Fan, F. Fang, K. Fang, C. Q. Feng, L. Feng, S. Fogliacco, J. M. Frieden, P. Fusco, M. Gao, F. Gargano, E. Ghose, K. Gong, Y. Z. Gong, D. Y. Guo, J. H. Guo, S. X. Han, Y. M. Hu, G. S. Huang, X. Y. Huang, Y. Y. Huang, M. Ionica, L. Y. Jiang, W. Jiang, Y. Z. Jiang, J. Kong, A. Kotenko, D. Kyratzis, S. J. Lei, B. Li, M. B. Li, W. L. Li, W. H. Li, X. Li, X. Q. Li, Y. M. Liang, C. M. Liu, H. Liu, J. Liu, S. B. Liu, Y. Liu, F. Loparco, M. Ma, P. X. Ma, T. Ma, X. Y. Ma, G. Marsella, M. N. Mazziotta, D. Mo, Y. Nie, X. Y. Niu, A. Parenti, W. X. Peng, X. Y. Peng, C. Perrina, E. Putti Garcia, R. Qiao, J. N. Rao, Y. Rong, A. Serpolla, R. Sarkar, P. Savina, Z. Shangguan, W. H. Shen, Z. Q. Shen, Z. T. Shen, L. Silveri, J. X. Song, H. Su, M. Su, H. R. Sun, Z. Y. Sun, A. Surdo, X. J. Teng, A. Tykhonov, G. F. Wang, J. Z. Wang, L. G. Wang, S. Wang, X. L. Wang, Y. F. Wang, D. M. Wei, J. J. Wei, Y. F. Wei, D. Wu, J. Wu, S. S. Wu, X. Wu, Z. Q. Xia, Z. Xiong, E. H. Xu, H. T. Xu, J. Xu, Z. H. Xu, Z. Z. Xu, Z. L. Xu, G. F. Xue, M. Y. Yan, H. B. Yang, P. Yang, Y. Q. Yang, H. J. Yao, Y. H. Yu, Q. Yuan, C. Yue, J. J. Zang, S. X. Zhang, W. Z. Zhang, Y. Zhang, Y. P. Zhang, Y. Zhang, Y. J. Zhang, Y. Q. Zhang, Y. L. Zhang, Z. Zhang, Z. Y. Zhang, C. Zhao, H. Y. Zhao, X. F. Zhao, C. Y. Zhou, X. Zhu, Y. Zhu

Astrophysics of Galaxies

The Influential Roles of Gravity, Turbulence, and Magnetic Fields in Shaping the Physical Evolution of Dense Massive Clumps

Moses Onyemaechi Asogwa, Seblu Humne Negu, Gemechu Muleta Kumssa et al. (+1 more)

We explore the roles of the three competitors, namely, gravity, turbulence, and magnetic fields, in controlling star formation (SF) within dense, massive clumps identified in the ATLASGAL survey. By examining scaling relations, virial parameters, and turbulent energy spectra, we evaluate the dynamical state of these clumps. We observe a weak velocity dispersion-size relation (sigma proportional to L^0.11), which is much shallower than the classical Larson-like relations, suggesting that turbulence does not mainly drive internal dynamics. The turbulent energy spectrum, E(k) proportional to k^-1.21, is also less steep than what is expected for both incompressible and compressible turbulence. We equally observe a decreasing trend in the virial parameter with increasing mass (alpha_vir proportional to M^-0.37), indicating that more massive clumps are increasingly gravitationally bound. These trends indicate an increasing relative dominance of gravity over turbulence at smaller scales, aligning with multiscale collapse scenarios; however, the absolute energy balance remains unquantifiable with the current data. Although magnetic fields are not directly measured, their potential influence is considered in the interpretation of pressure balance and dynamical support. Our findings imply that gravitational processes appear to primarily regulate the structure and evolution of massive clumps.
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All authors Moses Onyemaechi Asogwa, Seblu Humne Negu, Gemechu Muleta Kumssa, Innocent Okwudili Eya

High Energy Astrophysical Phenomena

Impacts of hydrogen envelope on supernova fallback and the resulting compact remnant masses

Kengo Shinoda, Yudai Suwa, Ryosuke Hirai et al. (+4 more)

Fallback in core-collapse supernovae plays a central role in setting compact-remnant masses and may produce late-time emission. In hydrogen rich progenitors, the reverse shock arising at the hydrogen-helium interface has the potential to dramatically enhance fallback, yet its overall impact across a broad explosion-energy range has not been systematically quantified. Using one-dimensional hydrodynamic simulations for metal-poor progenitors with $M_{\rm ZAMS}=18$-$28\,M_\odot$ and models with and without hydrogen envelopes, we explore fallback over explosion energies of $10^{48}$-$10^{52}\,{\rm erg}$. We find a robust and universal mass-transition behaviour: when the explosion energy reaches only $2$-$3$ times the binding energy of the hydrogen envelope, the reverse shock returns to the centre and sharply increases the remnant mass by $\gtrsim 2\,M_\odot$. Above this threshold, the reverse shock escapes and hydrogen-rich and stripped-envelope progenitors yield nearly identical remnant masses. By normalizing the results with the envelope binding energy, we show that all progenitor models converge to a common fallback relation. We further provide a simple analytic prescription that connects explosion energy, hydrogen-envelope binding energy, and final compact-remnant mass. This relation provides an important link between progenitor properties and compact-remnant masses, and is useful for population-synthesis and galactic chemical-evolution studies.
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All authors Kengo Shinoda, Yudai Suwa, Ryosuke Hirai, Ryo Sawada, Kengo Tomida, Kazunari Iwasaki, Takeru K. Suzuki

High Energy Astrophysical Phenomena

Intergalactic magnetic field lower limits up to the redshift $z\approx3$

Ievgen Vovk

Large-scale intergalactic magnetic fields may contain a mixture of galactic and cosmogenic contributions, that can be probed via observations of $\gamma$-ray "echo" - a delayed emission from electromagnetic cascades initiated by the highest energy photons from the sources at cosmological distances. While these fields contributions may be disentangled based on the difference in their redshift evolution, thus far indications of non-negligible magnetic field have been found only at low redshifts. This work aims at extending the intergalactic magnetic field constraints to redshifts $z\gtrsim 1$ using 17-year long all-sky observations of high-redshift active galactic nuclei with Fermi/LAT $\gamma$-ray telescope. Combing the Fermi/LAT measurements in the 0.1 GeV - 1 TeV energy range with the Monte Carlo simulations of the $\gamma$-ray "echo", it is shown that the zero field strength hypothesis at $z = [0.5; 3]$ is disfavoured at the $\approx 8.6\sigma$ significance level, yielding the lower limit of $B \gtrsim 1\times10^{-18}$ cG for the magnetic field correlation length above 1 Mpc. It is further shown that the same data put a lower limit on the volume-filling fraction of this field of $f\gtrsim 90\%$ in the redshift range considered. It is also demonstrated that the derived limits are not substantially affected by either source flux variability or the assumed $\gamma$-ray emission attenuation model. Implications of these limits for intergalactic magnetic field origin are discussed.
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Cosmology and Nongalactic Astrophysics

A high-significance detection of primordial tidal torque imprints

Ming-Jie Sheng, Hao-Ran Yu, Min Bao et al. (+8 more)

Tidal-torque theory predicts that galaxy angular momenta are imprinted by the primordial tidal field acting on proto-structures and that they can retain information about the early Universe through cosmic evolution. Here we test this prediction by comparing observed galaxy angular momentum vectors with those predicted from the primordial density field reconstructed by ELUCID for the nearby Universe. Among the galaxy populations considered, the gas component of central massive elliptical galaxies provides the clearest signal, exhibiting a strong direction correlation at a significance of about $7\sigma$. These results provide a robust observational evidence for tidal-torque theory and open a window for cosmological measurements of neutrino mass and other cosmological parameters.
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All authors Ming-Jie Sheng, Hao-Ran Yu, Min Bao, Bing-Hang Chen, Fang-Na Shao, Qi Guo, Yan-Mei Chen, Huiyuan Wang, Ue-Li Pen, Jie Wang, Xiaohu Yang

Solar and Stellar Astrophysics

Varying core-envelope coupling efficiency identified from stellar rotation–activity relation

Henggeng Han, Song Wang, Huiqin Yang et al. (+5 more)

Core-envelope coupling provides a reasonable explanation of the spin-down stalling of stars in open clusters, which was not predicted by classical gyrochronology. However, it remains an open question whether the coupling efficiency is constant or variable. M dwarfs, possessing thicker convective envelopes and thus longer coupling timescales than other late-type stars, are ideal objects for this investigation. In this work, based on the $R_{\rm{HK}}^{'}$ measurements from LAMOST and DESI spectra, we construct new rotation–activity relations for M dwarfs. Unlike the traditional picture, we suggest that the new relation consists of three distinct regimes of fast, intermediate, and slow rotation, closely matching the three sequences of gyrochronology, namely the “Convective” sequence, “Gap”, and “Interface” sequence. Our study reveals, for the first time, a variable activity decay rate in the intermediate-rotation regime (i.e., the “Gap” region). This implies a varying core-envelope coupling efficiency, peaking towards the end of this region. It also coincides with the well-known stage of stalled stellar spin-down.
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All authors Henggeng Han, Song Wang, Huiqin Yang, Xue Li, Chuanjie Zheng, Xiangyu Li, Cunshi Wang, Jifeng Liu

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

Temporal Substepping Scheme for Magnetohydrodynamics with Cell-based Adaptive Mesh Refinement on Staggered Grid

Ilja Honkonen, Riku Jarvinen and David Phillips

We present a new algorithm for numerical magnetohydrodynamics on staggered meshes preserving $\nabla \cdot B = 0$. Our algorithm is based on the constrained transport method and supports both cell-based adaptive mesh refinement and temporal substepping. We handle resolution changes directly on the logically Cartesian grid without needing interpolation or projection between nested or neighboring grids, nor coupling the solution between refinement levels.
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Cosmology and Nongalactic Astrophysics

Cosmological Implication of Cross-correlation between Galaxy Clustering and 21-cm Line Intensity Mapping

Yong-Seon Song, Minji Oh, Kyungjin Ahn et al. (+1 more)

The apparent anisotropies of galaxy clustering and 21-cm mapping in redshift space offer a unique opportunity to simultaneously probe cosmic expansion and gravity on cosmological scales through the Alcock-Paczynski (AP) effect and redshift-space distortions (RSD). Although improved theoretical models exist for anisotropic clustering, their applicability is limited by the non-perturbative smearing effect caused by the randomness of relative velocities. Here, we consider an alternative approach using the statistical power of cross-correlation between galaxy clustering and 21-cm line intensity mapping. Based on Fisher matrix analysis, fully incorporating nonlinear RSD, we estimate the benefit of combining both observables. We find that, for spectroscopy surveys like DESI combined with 21-cm line-intensity mapping surveys, constraints on the growth of structure and the cosmic expansion rate are improved by a factor of two relative to the galaxy auto-correlation. Crucially, such an observation can strongly constrain the neutral hydrogen (HI) content Omega_HI to a sub-percent level. This level of precision unlocks the potential of this method to probe post-reionization astrophysics with enhanced precision. It would far surpass existing constraints from stacked 21-cm emission and break the degeneracy between Omega_HI and the HI bias b_HI inherent in the linear-regime power-spectrum analysis. This cross-correlation approach effectively compensates for the loss of constraining power when using galaxy clustering alone.
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All authors Yong-Seon Song, Minji Oh, Kyungjin Ahn, Feng Shi

Instrumentation and Methods for Astrophysics

The Simons Observatory: Development of a Pipeline to Detect Rapid Transients in Time-Ordered Data

Justin Clancy, Carlo Baccigalupi, Josh Borrow et al. (+14 more)

We introduce a method for detecting astrophysical transients evolving on timescales of milliseconds to minutes using cosmic microwave background (CMB) survey telescopes. While previous transient searches in CMB data operate in map space, our pipeline directly processes the raw time-ordered data, enabling sensitivity to fast, dynamic signals. We integrate our detection approach into the Simons Observatory time-domain pipeline and assess the performance by injecting symmetric, stellar flare-like light curves into simulated observations. For events flaring with a timescale of 0.5 s, the pipeline detects $\gtrsim90$ % of events at flux densities of 800, 1150, 1650, and 4250\,mJy when measured in the 93, 145, 225, and 280 GHz bands respectively. At a fixed peak flux density, the pipeline more readily detects longer flares. The limiting flux density for 90 % completeness is four times lower for a $\ge5$ s flare than for a 0.5 s flare, while the flux density limits for $\gtrsim50$ % detection efficiency are comparable to the rms noise of the time-ordered data. We are able to determine the position of detected events in each observing band, with a positional uncertainty at the detection threshold comparable to the telescope resolution at that band. These results demonstrate the readiness of this pipeline for incorporation into upcoming Simons Observatory data analyses.
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All authors Justin Clancy, Carlo Baccigalupi, Josh Borrow, Nadia Dachlythra, Allen M. Foster, Yilun Guan, Carlos Hervias-Caimapo, Adam D. Hincks, Renee Hlozek, Erika Hornecker, Kevin M. Huffenberger, Reijo Keskitalo, Simran K. Nerval, John Orlowski-Scherer, Mike W. Peel, Christian L. Reichardt, Cristian Vargas

Astrophysics of Galaxies

Kennicutt-Schmidt relation of galaxies over 13 billion years in the COLIBRE hydrodynamical simulations

Claudia del P. Lagos, Joop Schaye, Matthieu Schaller et al. (+16 more)

We investigate the correlation between star formation rate (SFR) surface density and gas surface density (known as the Kennicutt-Schmidt, KS, relation) at kiloparsec (kpc) scales across cosmic time ($0\le z \le 8$) for galaxies with stellar masses $>10^9\,\rm M_{\odot}$, using the COLIBRE state-of-the-art cosmological hydrodynamical simulations. These simulations feature on-the-fly non-equilibrium chemistry coupled to dust grain evolution and detailed radiative cooling down to $\approx 10$~K, enabling direct predictions for the atomic (HI) and molecular (H$_2$) KS relations. At $z\approx 0$, COLIBRE reproduces the observed (spatially-resolved) KS relations for HI and H$_2$, including the associated scatter, which we predict to be significantly correlated with stellar surface density, local specific SFR (sSFR), and gas metallicity. We show that the HI KS relation steepens for lower-mass galaxies, while the H$_2$ KS relation shifts to higher normalisation in galaxies with higher sSFRs. The H$_2$ depletion time decreases by a factor of $\approx 20$ from $z = 0$ to $z = 8$, primarily due to the decreasing gas-phase metallicity. This results in less H$_2$ and more HI being associated with a given SFR at higher redshift. We also find that galaxies with higher sSFRs have a larger molecular gas content and higher star formation efficiency per unit gas mass on kpc scales. The predicted evolution of the H$_2$ depletion time and its correlation with a galaxy's sSFR agree remarkably well with observations in a wide redshift range, $0\le z\le 5$.
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All authors Claudia del P. Lagos, Joop Schaye, Matthieu Schaller, Danail Obreschkow, Yannick M. Bahe, Alejandro Benitez-Llambay, Evgenii Chaikin, Camila Correa, Timothy A. Davis, Carlos S. Frenk, Filip Husko, Melanie Kaasinen, Robert J. McGibbon, Kyle Oman, Sylvia Ploeckinger, Alexander J. Richings, James W. Trayford, Jing Wang, Ruby J. Wright

Earth and Planetary Astrophysics

CPI-C: Cool Planet Imaging Coronagraph on Chinese Space Station Survey Telescope

Jiangpei Dou, Xi Zhang, Gang Zhao et al. (+23 more)

Cool Planet Imaging Coronagraph (CPI-C) on Chinese Space Station Survey Telescope (CSST) is proposed to direct image the cool planets around nearby solar-type stars (within 40 pc). The core scientific objective of CPI-C is to conduct high-contrast directly imaging surveys of exoplanets ranging in size from Neptune-like to Jupiter-like, located at separations of 0.5 to 5 AU from their host stars, and to perform systematic spectroscopic analysis of the detected planets through high-precision multi-band photometry. CPI-C employs a step-transmission apodization technique to suppress the diffraction noises from the telescope pupil and a precise phase correction technique to eliminate the speckle noises due to imperfections of the optical surfaces. The contrast requirement is better than $10^{-8}$ at an inner working angle (IWA) of $3-4\lambda/D$, in the visible wavelength from 600 nm to 900 nm. CPI-C will be the first space-based instrument capable of directly imaging the reflection light from the cool exoplanets in the visible wavelength enabling the measurement of key physical parameters such as the effective temperature, surface gravity, radius, mass, and other key parameters. The potential observation results will significantly contribute to further understand the formation and evolution mechanisms of planets, which will also lay a solid foundation for future confirmation of the Earth-twins in the next generation space flagship missions.
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All authors Jiangpei Dou, Xi Zhang, Gang Zhao, Mingming Xu, Zhen Wu, Gang Wang, Baoning Yuan, Lingyi Kong, Yiming Zhu, Bingli Niu, Zhonghua Lv, Yongjun Qi, Shu Jiang, Bo Chen, Wei Guo, Di Wang, Yinglu Lin, Liping Zheng, Jing Guo, Ruokun Li, Liyan Xu, Huihai Wu, Cheng Wen, Shuwei Miao, Boyang Lv, Weimiao Li

High Energy Astrophysical Phenomena

The energy structure function of fast radio bursts supports a stochastic origin model

Yi-Nan Chen, Yong-Kun Zhang and Zi-Gao Dai

The origin of fast radio bursts (FRBs) has remained a mystery up to now. There are two kinds of process invoking neutron stars as an origin of FRBs, namely inner-driven starquakes and outer-driven collisions with interstellar objects (ISOs). The former origin should exhibit an earthquake-like statistical behavior while the latter should show a stochastic process. In this paper, we introduce a new statistical method by making use of the energy structure function of active repeating FRBs and earthquakes. We find that the energy structure function of FRBs exhibits a very different statistical behavior compared to that of earthquakes. On small time-interval scales, the energy of an earthquake show a tendency to decay with time-interval and the energy difference of a pair of events increases with time-interval. Such a behavior is not found in FRBs, whose energy function is very similar to those of a stochastic process. Our result shows that repeating FRBs may have an origin process differing from that of earthquakes, i.e., FRBs arise from a series of unrelated events such as collisions of a neutron star with ISOs.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Vibration Isolation for the Laser Interferometer Lunar Antenna

Brett N. Shapiro

The Laser Interferometer Lunar Antenna (LILA) presents a novel concept for observing gravitational waves from astrophysical sources at sub-Hertz frequencies. Compared to the Earth, the seismic environment of the moon, while uncertain, is known to be orders of magnitude lower, opening the possibility for achieving this sub-Hz band. This band fills the gap between space-based detectors (mHz) and Earth-based detectors (10 Hz to a few kHz). The initial version of LILA, known as LILA Pioneer, calls for non-suspended optics, relying on the moon's resonant modes to respond to gravitational waves. However, the follow-on design, LILA Horizon, requires suspensions to realize in-band free floating test masses and to filter the residual seismic background. This paper will establish baseline designs for these suspensions for different assumptions of the seismic background.
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High Energy Astrophysical Phenomena

Probable Quasi-Periodic Oscillations in the TESS observations of blazars in the Swift X-ray Survey

Ashutosh Tripathi, Paul J. Wiita and Krista Lynne Smith

This work presents possible quasi-periodic oscillations in the Transiting Exoplanet Survey Satellite observations of blazars that are in the 157-month hard X-ray survey done by Swift's Burst Alert Telescope. We report observations from four sources, J1104.4+3812, J1654.0+3946, J0353.4-6830, and J1941.3-6216, that show at least 3$\sigma$ local significance in generalized Lomb-Scargle periodogram and weighted wavelet Z-transform methods. These results are also checked using a continuous autoregressive moving average analysis that also predicts the absent data tentatively using stochastic differential equations. Each of these four sources exhibits a nominal QPO signal frequency in the range of 0.5–1.1 d$^{-1}$, resulting in at least 5 putative cycles. However, when the number of frequencies examined and the number of sources examined are both taken into account, the global significances are reduced to $\approx2.2\sigma$ for J1654.0+3964 (Mrk 501), and to $\approx1.9\sigma$ for other sources. These QPOs are thought to arise from the processes within the relativistic jet. Plausible explanations include the kink instability, which arises due to current-driven instabilities in the plasma or the precession of substructures, or mini-jets, within the jets.
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Solar and Stellar Astrophysics

The Response of Rotating Stellar Convection to Latitudinally-Varying Heat Flux

Kinfe Teweldebirhan, Rituparna Curt and Nicholas A. Featherstone

We investigate how rotating convection responds to the imposition of a latitudinally-varying heat flux at the base of the convective layer. This study is motivated by the solar near-surface shear layer, whose flows are thought to transition from a buoyancy-dominated regime near the photosphere to a rotation-dominated regime at depth. Here, we conduct a suite of spherical 3-D, nonlinear simulations of rotating convection that operate in either the buoyancy-dominated (high-Rossby-number, high-Ro) or rotation-dominated (low-Rossby-number, low-Ro) regime. At the base of each model convection zone, we impose a heat flux whose latitudinal variation is opposite to the variation that the system would ordinarily develop. In both the low- and high-Ro regimes, a strong thermal wind balance is sustained in the absence of forcing. With a larger flux variation, this balance becomes stronger at high latitudes and weaker at low latitudes. The resulting differential rotation weakens in response and, at sufficiently high forcing, its latitudinal variation reverses for both low- and high-Ro systems. At fixed forcing, there exists a Rossby number above which the convective flows efficiently mix heat laterally, and the imposed flux variation does not imprint to the surface. At sufficiently high-Ro, thermal wind balance is no longer satisfied. We discuss these results within the context of the Sun's near-surface region, which possesses a weakened differential rotation when compared to the deep convection, along with little-to-no variation of photospheric emissivity in latitude.
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Astrophysics of Galaxies

Synthetic polarization observations of magnetized pillars in HII regions: Assessing the reliability of the Davis-Chandrasekhar-Fermi method

Luis Andrés Hernández-Cruz, Manuel Zamora-Avilés, Abraham Luna et al. (+6 more)

We investigated the morphology and strength of magnetic fields in pillar-shaped structures at the boundaries of HII regions by combining three-dimensional radiation-magnetohydrodynamic (R-MHD) simulations with synthetic polarimetric and molecular-line observations. Our analysis focuses on a self-consistently formed pillar as a proof of concept to test the Davis-Chandrasekhar-Fermi (DCF) method under externally driven conditions. The pillar arises as an ionization front compresses a dense clump, producing a magnetically aligned, elongated structure whose morphology and field configuration resemble systems such as the pillars in M16. Synthetic 850 {\mu}m dust-polarization maps reproduce the pillar's large-scale magnetic-field morphology, confirming polarimetry as a reliable tracer of magnetic-field geometry. To evaluate DCF-based methods, we extract local density and velocity dispersion self-consistently from synthetic 13CO observations and measure polarization-angle dispersion using single-Gaussian fits to the synthetic polarization-angle distributions. We find that DCF-based methods systematically overestimate the intrinsic plane-of-sky magnetic-field strength by average factors of ~7 for the classical DCF method and ~5 for the modified Skalidis & Tassis formulation. This overestimation is already present in the full-pillar measurement and is not removed by applying polarimetric S/N cuts or by excluding the dynamically complex head. We attribute the discrepancy to external compression by the expanding H II region, which organizes the magnetic field on pillar scales while driving non-thermal gas motions. Consequently, the measured velocity and polarization-angle dispersions no longer trace the same turbulence-driven perturbation field assumed by DCF. Our results highlight the need for caution when applying DCF-based analyses to pillars or other externally compressed structures.
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All authors Luis Andrés Hernández-Cruz, Manuel Zamora-Avilés, Abraham Luna, Raúl Naranjo-Romero, José Franco, Aina Palau, Alejandro García-Pérez, Javier Ballesteros-Paredes, Marcial Becerril-Tapia

Earth and Planetary Astrophysics

On the Border: Searching for Cometary Activity Near the Centaur-JFC Transition Line

A. Fraser Gillan, Alan Fitzsimmons, Colin Orion Chandler et al. (+2 more)

Current wide-field surveys discover ~15 Jupiter-family comets (JFCs) each year, typically identified via visual detection of a dust coma or tail. The same surveys also discover many asteroids that have distant JFC-like orbits, but with no reported activity. We observed asteroids on Jupiter-crossing orbits beyond the depth of typical survey imaging using the 2.5 m Isaac Newton Telescope. We used deep imaging to observe 16 asteroids in this region, plus 7 known comets for comparison. Three asteroids (2011 WM183, (669525) 2012 XO144, and 2020 RX133) showed surface brightness profiles consistent with low-level activity, equating to ~19% of our total sample. We note that 2020 RX133 is a Jupiter Trojan. When we considered the heliocentric distance range of the asteroids at the time they showed activity, this fraction increased to 33% of the targets in the 3.16 \leq Rh \leq 4.56 au region, and therefore it is possible to infer that at least ~30 asteroids with Tj \leq 3.05 and in the 4.05 < a < 5.05 au parameter space may potentially exhibit low-level activity. We also estimated nuclear radii for the three active targets of r_n = 1.8 \pm 0.2 km, r_n \leq 0.8 km, and r_n \leq 0.5 km for (669525) 2012 XO144, 2011 WM183, and 2020 RX133 respectively. The median color index for the observed asteroids is (g-r)_{PS1} = 0.52 \pm 0.13, aligning with those expected for D-type asteroids.
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All authors A. Fraser Gillan, Alan Fitzsimmons, Colin Orion Chandler, Colin Snodgrass, Joseph Murtagh

Instrumentation and Methods for Astrophysics

amc: The Automated Mission Classifier for Telescope Bibliographies

John F. Wu, Joshua E. G. Peek, Sophie J. Miller et al. (+3 more)

Telescope bibliographies record the pulse of astronomy research by capturing publication statistics and citation metrics for telescope facilities. Robust and scalable bibliographies ensure that we can measure the scientific impact of our facilities and archives. However, the growing rate of publications threatens to outpace our ability to manually label astronomical literature. We therefore present the Automated Mission Classifier (amc), a tool that uses large language models (LLMs) to identify and categorize telescope references by processing large quantities of paper text. A modified version of amc performs well on the TRACS Kaggle challenge, achieving a macro $F_1$ score of 0.84 on the held-out test set. amc is valuable for other telescopes beyond TRACS; we developed the initial software for identifying papers that featured scientific results by NASA missions. Additionally, we investigate how amc can also be used to interrogate historical datasets and surface potential label errors. Our work demonstrates that LLM-based applications offer powerful and scalable assistance for library sciences.
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All authors John F. Wu, Joshua E. G. Peek, Sophie J. Miller, Jenny Novacescu, Achu J. Usha, Christopher A. Wilkinson

Solar and Stellar Astrophysics

Free Energy Sources of Ion-scale Waves Observed by Parker Solar Probe

Niranjana Shankarappa, Kristopher G. Klein, Mihailo M. Martinović et al. (+6 more)

Parker Solar Probe (PSP) observes abundant circularly polarized ion-scale waves throughout the inner heliosphere. These waves are a signature of the interplay between plasma microinstabilities and turbulent dissipation. We perform a mission-wide statistical survey of ion-scale waves observed by PSP, investigating if the waves correspond to specific free energy sources in the measured proton velocity distributions. We find that left-handed waves (LHWs) are frequently observed, with the fraction of time they are observed increasing closer to the Sun, reaching $\sim$30%. Right-handed waves (RHWs) are less frequently observed, with the associated time fraction decreasing closer to the Sun. The observed LHWs are generally consistent with parallel propagating ion cyclotron wave (ICW) storms that occur continuously for extended periods of time. Turbulent energy spectra are consistently steeper when LHW storms are observed; these wave storms mediate the spatial transport of the free energy associated with temperature anisotropy. The observed RHWs are generally consistent with oblique and parallel fast magnetosonic waves (FMWs), and their observation is well correlated with enhanced proton parallel heat flux, which quantifies the presence of secondary proton populations. Using observations and the SAVIC machine learning instability identification algorithm, we identify a threshold on the proton heat flux beyond which FMWs are likely to be driven unstable by the proton beams. We are thus able to associate trends in the observed ion-scale waves with known sources of free energy for Encounters 3 through 24 of the PSP's prime science phase.
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All authors Niranjana Shankarappa, Kristopher G. Klein, Mihailo M. Martinović, Trevor A. Bowen, Davin E. Larson, Roberto Livi, Ali Rahmati, Phyllis L. Whittlesey, Michael L. Stevens

Earth and Planetary Astrophysics

Mantle Differentiation, Mixing and Interior-Exterior Exchange

Takashi Nakagawa, Charitra Jain, Diogo L. Lourenco et al. (+2 more)

We review the formation of large-scale heterogeneity in the solid Earth from the magma ocean phase to the present day, focusing on lower-mantle structure and evolution, as well as continental formation and its impact on interior-exterior volatile exchange. The solidification of the magma ocean sets the "initial condition" for solid-state mantle structure and evolution, partitioning volatiles between the surface and interior, and differentiating major and trace elements between mantle reservoirs. A possibly long-lived basal magma ocean is a potential reservoir for iron and incompatible trace elements with important implications for the present-day structure of the lowermost mantle and the distribution of heat-producing elements. With emergent plate tectonics and mantle convection, the production of oceanic crust is the dominant differentiation mechanism, and may contribute to lower-mantle heterogeneity. In turn, convection acts to re-mix heterogeneity. Thus, the structure of the lower mantle records the early differentiation of our planet, as well as long-term evolution. The formation of continental crust and lithosphere has also an important influence on deep-mantle structure and composition, because the distribution of continents can control the scale of plate tectonics, and thus affect mantle convection patterns. While the formation of continental crust and lithosphere, scenarios can be tested by self-consistent long-term evolution models. The exchange of water between the surface and mantle also plays an important role in the dynamics of Earthś deep interior. By using relative sea-level change as a proxy for the interior-exterior exchange of water, it is possible to constrain the deep-mantle water cycle. Based on a comprehensive review of these topics, we conclude with several open questions that should be addressed by future studies.
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All authors Takashi Nakagawa, Charitra Jain, Diogo L. Lourenco, Maxim D. Baller, Paul J. Tackley

Thursday 11 December

Solar and Stellar Astrophysics · Cross-listed from gr-qc

Self-gravitating equilibrium with slow steady flow and its consistent form of entropy current

Shuichi Yokoyama

A relativistic self-gravitating equilibrium system with spherical symmetry as well as with steady energy flow is investigated perturbatively around the hydrostatic limit, where the radial component of the fluid velocity field $u^\mu$ is sufficiently small. Each component of vectors and tensors consisting of the system is expanded in different powers, which makes the covariant perturbation approach ineffective. The differential equations to determine the subleading correction of the structure variables are presented. The system retains the current $j^\mu$ accounting for the steady flow, which contributes to the entropy current $s^\mu$ in such a general covariant form that $s^\mu=au^\mu+ bj^\mu$ with $a, b$ unknown parametric functions. To determine them, a new condition is proposed. This condition imposes the entropy current to be of an unconventional form $s^\mu=(s-bj^0)u^\mu/u^0+ bj^\mu$, where $s$ is the entropy density. The remaining parameter $b$ is fixed by the current conservation equation. The perturbative analysis shows that $b$ starts with the quadratic order and its leading term is determined explicitly.
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