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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 5 February

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Early-universe constraints on the electron mass

Michela Garramone, Stefano Gariazzo and Nicolao Fornengo

We investigate the impact of a nonstandard electron mass $m_e$ on early-Universe thermal history, focusing on neutrino decoupling and Big Bang Nucleosynthesis (BBN). In the standard cosmology, neutrino–electron interactions keep neutrinos in thermal contact with the electromagnetic plasma until shortly before $e^\pm$ annihilation. Varying $m_e$ shifts the decoupling epoch and the entropy transfer from $e^\pm$ annihilation, thereby modifying the neutrino energy density and the inferred effective number of relativistic species, $N_{\mathrm{eff}}$. Independently, during BBN the rates of charged-current weak processes, and hence the neutron-to-proton ratio, depend on $m_e$. By confronting BBN predictions for the primordial light-element abundances with observations and imposing cosmological constraints on $N_{\mathrm{eff}}$, we obtain the following $1\sigma$ bounds on $m_e$ in the early Universe: $m_e = 0.505^{+0.006}_{-0.007}$ MeV (for the NACRE II nuclear reaction network) or $m_e=0.509^{+0.005}_{-0.004}$ MeV (for the PRIMAT nuclear reaction network). These bounds have been derived by adopting the recent determination of the primordial Helium-4 abundance by the Large Binocular Telescope observations of 54 metal-poor H\,ii regions. If instead we adopt the Particle Data Book Helium-4 abundance, the bounds are: $m_e = 0.503^{+0.011}_{-0.015}$ MeV (NACRE II) or $m_e=0.521^{+0.009}_{-0.007}$ MeV (PRIMAT) The obtained allowed ranges are close to the present laboratory value at the level of $\sim 0.4\%-2\%$, depending on the dataset and nuclear network, thus supporting the constancy of the electron mass over cosmological timescales.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Detecting gravitational wave background with equivalent configurations in the network of space based optical lattice clocks

Mingzhi Lou, Hong Su, Tao Yang et al. (+1 more)

This paper studies the use of optical lattice clock (OLC) detector networks for detecting the stochastic gravitational-wave background (SGWB). Starting from the cross-correlation formalism for two OLC detectors, we analyze how the detector geometry influences the overlap reduction function (ORF) and systematically search for configuration transformations that preserve the modulus of the ORF. We identify an equivalent transformation in which the emitting and receiving ends of both OLC links are exchanged, while the modulus of the ORF remains invariant. We then numerically compare the ORFs of isosceles trapezoidal configurations with different separations and included angles. Based on these results, we design a feasible four-spacecraft orbital configuration and evaluate its strain sensitivity and noise energy-density spectrum in comparison with LISA, Taiji, and TianQin.
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All authors Mingzhi Lou, Hong Su, Tao Yang, Yun-Long Zhang

Cosmology and Nongalactic Astrophysics

The kinematic cosmic dipole beyond Ellis and Baldwin

Albert Bonnefous

The cosmic dipole anomaly, currently detected at a significance exceeding 5$\sigma$ in several independent survey poses a significant challenge to the standard model of cosmology. The Ellis & Baldwin formula provides a theoretical link between the intrinsic dipole anisotropy in the sky distribution of extragalactic light sources and the observer's velocity relative to the cosmic rest frame, under the assumptions that the sources follow a power-law luminosity function and exhibit power-law spectral energy distributions. In this work, we demonstrate that this relation can be generalized to arbitrary luminosity distributions and spectral profiles. We derive the corresponding expression for the effective spectral index and apply it to a sample of quasars observed in the W1 band of the CatWISE survey. We show that the anomalous cosmic dipole persists beyond the power-law assumption. These results provide a more general and robust framework to interpret measurements of the cosmic dipole in future large-scale surveys.
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Earth and Planetary Astrophysics · Cross-listed from physics.flu-dyn

On the stability of viscous Riemann ellipsoids

Joris Labarbe

The present study investigates the linear stability of Riemann ellipsoids in both the inviscid limit and in the presence of weak viscosity. In the inviscid regime, we derive a generalised Poincare equation governing small fluid oscillations and construct a family of polynomial solutions that extends the classical results of Cartan to flows with a uniform strain field. This formulation provides an analytic dispersion relation for three-dimensional ellipsoidal disturbances and remains computationally efficient at arbitrary harmonic degree, in contrast to the virial tensor method or to short-wavelength (WKB) approximations. The viscous effects are incorporated through a boundary-layer analysis based on Prandtls theory, leading to first-order viscous corrections to the inviscid spectrum and allowing a systematic investigation of viscosity-driven instabilities. Stability diagrams are presented over the space of admissible Riemann ellipsoids, illustrating the roles of rotation, internal strain, and diffusion, with implications for rotating shear flows in geophysical and astrophysical contexts.
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High Energy Astrophysical Phenomena

Coalescence Forensics: Weighing the Hosts of Hierarchical Binary Black Hole Mergers

Avinash Tiwari and Shasvath J. Kapadia

We present a novel framework to infer the mass of clusters that host hierarchical binary black hole (BBH) mergers detected with gravitational-waves (GWs), on a single event basis. We show that the requirement that a second-generation (2G) remnant be retained, and subsequently undergo a dynamical encounter, places strong constraints on the mass of the cluster. Using a Plummer model as a readily interpretable baseline, we derive analytic scaling relations between the peak of the inferred host mass posterior, the GW-driven recoil velocity of the remnant, and the parameters that determine the structure of the host. We then perform exact numerical marginalization over thermal and recoil velocities, angles, and cluster structure parameters, to infer the host-mass posterior. We apply our framework to putative hierarchical mergers GW241011 and GW241110, and infer the masses of their hosts on a single-event basis. We find that these are consistent with either heavy globular clusters or nuclear star clusters, with inferred masses spanning $10^{5.7 - 7.7} M_{\odot}$ at $68\%$ confidence depending on the 2G recoil velocity distribution used.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Induced-Gravity Palatini-Like Higgs Inflation in Supergravity Confronts ACT DR6

C. Pallis

We formulate within Supergravity a model of induced-gravity inflation, excellently consistent with ACT DR6, inspired by the Palatini gravity. The inflaton belongs in the decomposition of a conjugate pair of Higgs superfields which lead to the spontaneous breaking of a U(1)B-L symmetry at a scale close to the range (0.102-5.85)x10^16 GeV. The inflaton field is canonically normalized thanks to a real and shift-symmetric contribution into the Kaehler potential. It also includes two separate holomorphic and antiholomorphic logarithmic terms, the argument of which can be interpreted as the coupling of the inflaton to the Ricci scalar. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. Embedding the model in a B-L extension of the MSSM we show how the mu parameter can be generated and non-thermal leptogenesis can be successfully realized. An outcome of our scheme is split SUSY with gravitino mass in the range (40-60) PeV, which is consistent with the results of LHC on the Higgs boson mass.
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Solar and Stellar Astrophysics

MESS: Multi-Epoch Spectroscopic Solver for Detecting Double-Lined Systems

Gil Nachmani, Simchon Faigler and Tsevi Mazeh

We present MESS, a fully automated algorithm for identifying and characterizing double-lined spectroscopic binaries (SB2) in large databases of multi-epoch spectra. MESS extends the two-dimensional TODCOR approach to a global multi-epoch formalism, deriving the radial velocities (RVs) of both components at each epoch while optimizing the templates jointly across all observations. Template optimization searches a continuous synthetic-spectra manifold spanning an eight-dimensional parameter space: effective temperature, surface gravity, and rotational broadening for each star, together with a common metallicity and the flux ratio. Single-lined spectroscopic binaries (SB1) and single stars (S1) are handled within the same framework by fitting one optimized template, with either epoch-dependent RVs (SB1) or a single shared RV (S1). Model selection among S1/SB1/SB2 uses the Bayesian information criterion with an effective sample size that accounts for intra-spectrum correlations, and is complemented by the Wilson relation between the two RVs to infer the mass ratio and systemic velocity without a full orbital solution. We validate MESS on 1500 simulated LAMOST MRS systems (SNR=50), with primary RV semi-amplitudes predominantly below the instrumental resolution, achieving an overall classification accuracy of ~95%. We also derive full orbital solutions for two SB2 systems detected in our LAMOST analysis, including a faint-secondary case with flux ratio ~0.1, and present example outputs for one SB1 and three constant-velocity stars. A companion paper will report the survey-wide application to LAMOST DR11 and the resulting SB1/SB2 catalogs.
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Astrophysics of Galaxies

XGAP with uGMRT I: Old AGN plasma in merging galaxy groups

R. Santra, R. Kale, K. Kolokythas et al. (+10 more)

Galaxy groups are affected by outflows from central Active Galactic Nuclei due to the shallower gravitational potential compared to galaxy clusters. The group binding energy is comparable to the energy output from AGN, making it an important factor in mutual evolution. We present a multi-wavelength analysis of three dynamically active groups: SDSSTG8102, SDSSTG16393, and SDSSTG28674, which are part of the XMM-Newton Group AGN Project X-GAP sample, a statistically complete sample of 49 galaxy groups. We combine uGMRT 400 MHz observations with 144 MHz LOFAR and XMM-Newton observations to study the radio sources associated with the Brightest Group Galaxies (BGGs). The BGGs in SDSSTG8102 and SDSSTG16393 have extended radio emission with asymmetric distortions in their morphologies. SDSSTG28674 has a compact flat-spectrum radio source associated with the BGG and an extended lobe on one side, connected by a faint bridge detected with LOFAR. Integrated spectral indices of the three BGGs are $-0.96\pm0.09$ (SDSSTG8102), $-1.35\pm0.09$ (SDSSTG16393), and $-1.6\pm0.02$ (SDSSTG28674). X-ray images reveal elongated morphologies in all three groups, with SDSSTG28674 showing evidence of a binary merger, while thermodynamical maps highlight temperature variations. In SDSSTG8102, lobes are bent and displaced by IGrM flows, while SDSSTG16393 hosts steep-spectrum relic-like plasma coinciding with X-ray emission. SDSSTG28674, with its ultra-steep spectrum lobe and disturbed morphology, likely traces merger-driven activity, consistent with a remnant or revived radio phoenix. The spectral diversity across the systems reflects different stages of AGN fading governed by duty cycle, source age, and confinement by the hot IGrM.
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All authors R. Santra, R. Kale, K. Kolokythas, M. Brienza, E. O'Sullivan, D. Eckert, F. De. Gasperin, T. Pasini, F. Gastaldello, A. Finoguenov, M. Sun, G. Gozaliasl, M. Bourne

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

An approximate Kappa generator for particle simulations

Seiji Zenitani and Takayuki Umeda

A random number generator for the Kappa velocity distribution in particle simulations is proposed. Approximating the cumulative distribution function with the q-exponential function, an inverse transform procedure is constructed. The proposed method provides practically accurate results, in particular for k<4. It runs fast on graphics processing units (GPUs). The derivation, numerical validation, and relevance to GPU execution models are discussed.
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High Energy Astrophysical Phenomena

Particle acceleration signatures in the time-dependent one-zone synchrotron self-Compton model of blazar flares

Paloma Thevenet, Andreas Zech, Catherine Boisson et al. (+1 more)

The study of multiwavelength flux and spectral variations during rapid flares from blazars provides strong constraints on the physical parameters of the compact emission regions responsible for these still poorly understood events. Although a full description of the continuous and transient emission from blazars seems to require more sophisticated scenarios, particle acceleration and loss mechanisms can be approximately described within the simple leptonic one-zone framework, enabling a systematic study of their impact on the observable properties of multiwavelength flare light curves. Our goal is to identify characteristic signatures in these light curve profiles that permit one to discriminate between the main physical processes situated inside the relativistic jet and commonly invoked to explain blazar flares. The present study exclusively focuses on modeling rapid flares from BL Lac type objects, which can be described within the synchrotron self-Compton (SSC) emission scenario. Combinations of several commonly employed mechanisms to describe the gain and loss of energetic particles in onezone models during flaring events are studied in a systematic way: particle injection; diffusive shock and stochastic acceleration and reacceleration; particle escape; adiabatic losses; radiative losses through synchrotron and inverse-Compton radiation. The current study is limited to the case of "hard-sphere" scattering. A large variety of light curve shapes arises from the different scenarios under study. Characteristic signatures, in particular energy-dependent time delays and differences in the shapes of the rising part of the flare, should allow the distinction to be made between different injection and acceleration scenarios, given the availability of sufficiently high-quality multiwavelength data sets. This is illustrated with a simplified application to a flare event from the blazar Mrk 421.
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All authors Paloma Thevenet, Andreas Zech, Catherine Boisson, Anton Dmytriiev

High Energy Astrophysical Phenomena

Exploring the central engines of gamma-ray bursts from prompt light curves

Xue Zhang, Shuang-Xi Yi, Wei-Hua Lei et al. (+6 more)

Hyperaccreting stellar-mass black hole systems are leading candidates for the central engines of gamma-ray bursts (GRBs). Their jets are thought to be powered by either the Blandford-Znajek (BZ) process or neutrino-dominated accretion flows (NDAFs), but discriminating between these mechanisms remains challenging. To address this, we propose using the luminosity decay slope (parameter d) of GRB light curves to distinguish between the BZ and NDAF mechanisms, thereby linking the light-curve morphology to the central engine physics. By analysing 85 single-peaked GRBs with fast-rise, exponential-decay (FRED) profiles observed by Swift/BAT using 64 ms background-subtracted light curves, we fit the decay slope (parameter d) with the empirical Kocevski-Ryde-Liang (KRL) function and compare the results with theoretical predictions for the BZ (d approximately 1.67) and the NDAF (d approximately 3.7 to 7.8) mechanisms. We find that the decay slope (parameter d) can differentiate central engine mechanisms, with 15 GRBs consistent with the BZ mechanism and 22 supporting the NDAF mechanism. However, most events exhibit slopes within the range between 2 and 4, suggesting a hybrid of mechanisms, with NDAF being dominant.
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All authors Xue Zhang, Shuang-Xi Yi, Wei-Hua Lei, Tong Liu, Yu-Peng Yang, Ying Qin, Yan-Kun Qu, Qing-Wen Tang, Fa-Yin Wang

Cosmology and Nongalactic Astrophysics

Forecast on $f(R)$ Gravity with HI 21cm Intensity Mapping Surveys

Yanling Song, Yu Sang, Linfeng Xiao et al. (+1 more)

Modified gravity theories offer a well-motivated extension of General Relativity and provide a possible explanation for the late-time accelerated expansion of the Universe. Among them, $f(R)$ gravity represents a minimal and theoretically appealing class, characterized by the Compton wavelength parameter $B_0$, which quantifies deviations from General Relativity. In this work, we explore the capability of future neutral hydrogen (HI) 21-cm intensity mapping (IM) observations to constrain $f(R)$ gravity at low redshifts. We perform Fisher-matrix forecasts for $B_0$ and standard cosmological parameters using upcoming 21-cm IM experiments, including BINGO and SKA1-MID (Band 1 and Band 2), both individually and in combination with Planck cosmic microwave background (CMB) priors. For the phenomenological HI treatment, we obtain $\sigma(B_0)=3.73\times10^{-6}$, $5.98\times10^{-6}$, and $6.78\times10^{-8}$ for BINGO, SKA1-MID Band 1, and Band 2, respectively, and the tightest bound is improved to $3.95\times10^{-8}$ when Planck priors are included. We further consider a redshift-dependent HI model with fixed $\Omega_{\rm HI}(z)$ and $b_{\rm HI}(z)$, and find that the constraints remain of similar order, confirming the robustness of the results. In both cases, SKA1-MID Band 2 provides the strongest sensitivity, while foreground residuals degrade the constraints but do not change the main conclusion that future HI intensity mapping, especially combined with CMB data, can provide stringent tests of General Relativity on cosmological scales.
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All authors Yanling Song, Yu Sang, Linfeng Xiao, Bin Wang

Solar and Stellar Astrophysics

Effects of Dynamo-Generated Large-Scale Magnetic Fields on the Surface Gravity ($f$) Mode

Rajesh Mondal and Nishant K. Singh

By modelling the upper layers of the Sun in terms of a two-layer setup where a free-surface exists within the computational domain, we numerically study the interaction between the surface gravity, or the fundamental ($f$) mode, and the magnetic fields. Earlier such works were idealized in the sense that the static magnetic fields were imposed below the photosphere, i.e., the free-surface, to detect signatures of sub-surface magnetic fields and flows on the $f$-mode. In this work, we perform three-dimensional (3D) numerical simulations where the interior fluid below the photosphere is stirred helically at small scales, thus facilitating an $\alpha^2$-dynamo. This allows us to investigate how these self-consistently generated large-scale magnetic fields influence the properties of the $f$-mode. We find that when the magnetic fields saturate near the equipartition values with the turbulent kinetic energy of the flow, the $f$-mode is significantly perturbed. Compared to the non-magnetic case, or the kinematic phase of the dynamo when fields are too weak, we note that the frequencies and the strengths of the $f$-mode are enhanced in presence of saturated magnetic fields, with these effects being larger at larger wavenumbers. This qualitatively confirms the earlier findings from observational and numerical works which reported the $f$-mode strengthening due to strong sub-surface magnetic fields.
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Instrumentation and Methods for Astrophysics

Nano-particle Transition Matrix code implementation

G. La Mura, G. Mulas, G. Aresu et al. (+4 more)

Electromagnetic scattering and absorption by material particles is a fundamental physical problem with a broad range of applications, going from laboratory experiments, biology and material sciences, all the way up to environmental studies and astrophysical investigations. In spite of its primary importance, an exact theoretical treatment is only possible for a limited range of ideal cases, while realistic situations require the development of numerical solutions. In the course of the years, several techniques were developed to model the effects of scattering and absorption in more general cases, using approaches such as the Discrete Dipole Approximation (DDA), the Finite Difference Time Domain (FDTD) method, the Transition Matrix formalism (T-matrix) or the Mean Field Theory (MFT). Among these possibilities, the T-matrix approach grants the highest degree of flexibility in modeling aggregates of spherically symmetric particles with arbitrary overall morphology and composition, but its application has been limited by the challenging computational requirements of the method in realistic cases. This paper describes the Nano-Particle Transition Matrix Code project (NP_TMcode), a new implementation of the T-matrix formalism that, taking advantage of high performance parallel hardware architectures, allows the solution of increasingly complex models, while substantially reducing the computing time. The paper describes the code structure, with a particular focus on the algorithm optimization, and it presents the results of the performance analysis for a set of development applications.
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All authors G. La Mura, G. Mulas, G. Aresu, M. A. Iatì, C. Cecchi-Pestellini, S. Rezaei, R. Saija

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Simulating first-order phase transition during inflation

Jintao Zou, Ligong Bian and Shao-Jiang Wang

Ending the inflation by vacuum decay is considered infeasible due to the graceful exit problem. Even if considering an alternative field other than the inflaton to realize a first-order phase transition (FoPT) during inflation, it is usually challenging for concrete model building, as bubble nucleations might not be fast and dense enough to successfully end the inflation. In this work, we propose a FoPT at the grand-unification-theory (GUT) scale within the Starobinsky inflation. The key construction is an exponentially evolving potential barrier dynamically controlled by the rolling inflaton, so that almost no bubble is nucleated during the early inflationary era, but with massive bubble nucleations near the end of inflation. With lattice numerical simulations, we have successfully tested this GUT-FoPT during Starobinsky inflation, and the resulting gravitational-wave energy density spectrum reproduces previous analytical estimation with a distinctive oscillation feature at high frequencies.
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Solar and Stellar Astrophysics

The Correlation Length of Turbulence in Magnetic Clouds

S. W. Good, J. Lalueza Puértolas, A.-S. M. Jylhä et al. (+1 more)

The large-scale limit or outer scale of turbulence in the solar wind is associated with the correlation length of the magnetic field. Determining correlation lengths from magnetic field time series in magnetic clouds is complicated by the presence of the global flux rope: without removal of the flux rope trend, correlation length measurements will be sensitive to the flux rope as well as the turbulence, and give overestimates of the outer scale when turbulence amplitudes at the outer scale are small relative to the flux rope amplitude. We have used force-free flux rope fits to detrend magnetic field time series measured by Parker Solar Probe in two magnetic clouds and calculated the turbulence correlation length in the clouds using the detrended data. The detrended correlation length in terms of the proton inertial length, $d_p$, was $2.7\times10^{4} d_p$ in one cloud (observed at 0.77 au) and $1.6\times10^{4}d_p$ in the other (observed at 0.39 au), significantly smaller than the values obtained without detrending. Increments in the flux rope fits scaled equivalently to a $k^{-3}$ wavenumber power spectrum; this contribution from the flux rope considerably steepened the total spectrum at the largest scales but had a negligible effect in the inertial range, where scaling in both clouds equivalent to $\sim$$k^{-5/3}$ was observed. Finally, we discuss the possible relation of turbulence correlation lengths to mesoscale structure in magnetic clouds.
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All authors S. W. Good, J. Lalueza Puértolas, A.-S. M. Jylhä, E. K. J. Kilpua

Solar and Stellar Astrophysics

Probing Compact Objects in Wide-Orbit Binaries with Joint LAMOST LRS and MRS

Hao-Bin Liu and Wei-Min Gu

Wide-orbit binaries serve as crucial laboratories for understanding stellar evolution and identifying quiescent compact objects. In this work, we search for compact objects in wide-orbit binaries by merging the LAMOST multi-epoch catalogs from LRS and MRS in the 12th data release. We specifically focus on sources with at least 20 observation epochs that clearly exhibit long-term radial velocity (RV) variations while remaining essentially stationary over short time scales. By constraining the mass function with Lomb-Scargle periods and RV ranges, we identified 74 single-lined spectroscopic binary candidates harboring potential compact objects with robust orbital solutions. These systems exhibit orbital periods ranging from 10 to 1000 days, with semi-amplitudes of velocity $K_1 \lesssim 50$ ${\rm km\,s^{-1}}$ and mass functions $f(M_2)$ between 0.03 and 0.94 $M_{\odot}$. Combining $f(M_2)$ with SED-derived stellar parameters, we identify four strong compact object candidates with main-sequence companions (Class A), 9 systems likely consisting of either compact objects with giant/subgiant companions or mass-inverted Algol-type binaries (Class B), and 61 candidates with relatively lower mass ratios (Class C). Cross-matching with the Gaia DR3 nss\_two\_star\_orbit catalog yields 16 sources, all of which exhibit orbital solutions consistent with our results. This study demonstrates the essential role of long-term spectroscopic monitoring in searching for compact objects in wide-orbit binaries and validating orbital solutions. The strategy of leveraging extended time baselines will be increasingly effective as spectroscopic databases continue to grow, enabling the systematic discovery of compact objects in wide orbits across the Galaxy.
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Astrophysics of Galaxies

Mergers Drive Structural Complexity but Not Starbursts in Lyman-$\alpha$ Emitters at $3 < z < 4$: A JWST Spatially Resolved View

Qi Song, F. S. Liu, Jian Ren et al. (+6 more)

Recent observations with the James Webb Space Telescope (JWST) reveal that the merger fraction among Ly$\alpha$ emitters (LAEs) at redshifts $z > 3$ is significantly higher than previously estimated. In this study, we focus on three high signal-to-noise merging LAE systems at $3 < z < 4$, selected from the VLT/MUSE-Deep survey in the GOODS-S field. We combine new JWST/NIRCam broadband and medium-band imaging with archival HST/ACS data to perform spatially resolved spectral energy distribution (SED) fitting using the Bagpipes software package. Our analysis reveals that two of the systems are minor mergers, while the third is a major merger. The close agreement between spatially resolved and integrated stellar mass estimates indicates that recent star formation does not significantly outshine the light from older stellar populations in these systems. Moreover, both the individual components and the systems as a whole lie on the star-forming main sequence, further supporting the conclusion that these mergers have not yet triggered substantial starburst activity. Furthermore, we detect prominent color gradients and disturbed dust distributions in these merging systems, indicating that the mergers have already induced significant internal structural perturbations. These morphological and dust-related changes may facilitate the escape of Ly$\alpha$ photons – potentially through mechanisms such as gas redistribution or a reduced covering fraction of neutral hydrogen – thereby playing a key role in shaping the observed properties of LAEs.
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All authors Qi Song, F. S. Liu, Jian Ren, Tianfu Gao, Pinsong Zhao, Qifan Cui, Yubin Li, Hao Mo, Guanghuan Wang

High Energy Astrophysical Phenomena

The Double-Burst Nature and Early Afterglow Evolution of Long GRB 110801A

Qiu-Li Wang, Hao Zhou, Yun Wang et al. (+3 more)

We present a comprehensive temporal and spectral analysis of the long-duration gamma-ray burst GRB 110801A, utilizing multi-band data from the Neil Gehrels Swift Observatory and ground-based telescopes. The $\gamma$-ray emission exhibits a distinct two-episode (“double-burst”) structure. Rapid follow-up observations in the optical and X-ray bands provide full coverage of the second burst. The optical light curve begins to rise approximately 135 s after the trigger, significantly preceding the second emission episode observed in X-rays and $\gamma$-rays at $\sim 320$ s. This chromatic behavior suggests different physical origins for the optical and high-energy emissions. Joint broadband spectral fitting (optical to $\gamma$-rays) during the second episode reveals that a two-component model, consisting of a power-law plus a Band function, provides a superior fit compared to single-component models. We interpret the power-law component as the afterglow of the first burst (dominating the optical band), while the Band component is attributed to the prompt emission of the second burst (dominating the high-energy bands). A physical synchrotron model is also found to be a viable candidate to explain the high-energy emission. Regarding the afterglow, the early optical light curve displays a sharp transition from a rise of $\sim t^{2.5}$ to $\sim t^{6.5}$, which is well-explained by a scenario involving both reverse shock (RS) and forward shock (FS) components. We constrain the key physical parameters of the burst, deriving an initial Lorentz factor $\Gamma_0 \sim 60$, a jet half-opening angle $\theta_j \sim 0.09$, and an isotropic kinetic energy $E_{\rm k,iso} \sim 10^{54.8}$ erg.
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All authors Qiu-Li Wang, Hao Zhou, Yun Wang, Jia Ren, Zhi-Ping Jin, Da-Ming Wei

Astrophysics of Galaxies

ELFO: A Python Package for Emission Line Fitting Optimization in Integral Field Spectroscopy Data

Hui Guo, Guilin Liu, Jianghui Xu et al. (+4 more)

Integral field spectroscopy (IFS) provides spatially resolved spectra, enabling detailed studies that address the physical and kinematic properties of the interstellar medium. A critical step in analyzing IFS data is the decomposition of emission lines, where different velocity components are often modeled with Gaussian profiles. However, conventional fitting methods that treat each spectrum independently often yield spatial discontinuities in the fitting results. Here, we present Emission Line Fitting Optimization (ELFO), a Python package for IFS spectral fitting. ELFO uses the results of neighboring spectra to determine multiple initial guesses and selects the result that exhibits spatial smoothness. We tested ELFO on IFS data of two quasars obtained from the Multi-Unit Spectroscopic Explorer, where it successfully corrected anomalous fits, revealed previously unresolved substructures, and made large-scale kinematic structures more evident. With minor modifications, this method can also be easily adapted to other IFS data and different emission lines.
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All authors Hui Guo, Guilin Liu, Jianghui Xu, Chao Geng, Zhicheng He, Shiyin Shen, Lei Hao

Astrophysics of Galaxies

A Chemistry-First Centered Icy Chemical Inventory of Protostellar Sources with JWST

Andrew M. Turner, Yao-Lun Yang, Rachel Gross et al. (+2 more)

The chemical evolution in star forming regions is driven by the interplay between gas and ice mantles. Identifying the ice compositions at the early stage of star formation thus provides constraints on the chemical processes inaccessible from gas-phase characterizations. As part of the CORINOS program, spectra from the James Webb Space Telescope (JWST) MIRI MRS were taken toward four Class 0 protostars: IRAS 15398-3359, Ser-emb7, L483, and B335. The spectra were processed with simultaneous fitting of a continuum and silicate absorption to produce optical depth mid-infrared spectra of the ices at 5-28 $\mu$m (360-2000 cm$^{-1}$) toward these four sources. Simple molecules such as water (H$_2$O), carbon dioxide (CO$_2$), methanol (CH$_3$OH), formic acid/formate (HCOOH/HCOO$^-$), ammonia/ammonium (NH$_3$/NH$_4$$^+$), and formaldehyde (H$_2$CO) are the most abundant features in these ices, while complex organic molecules (COMs) represent a smaller contribution. Likely COMs include hydroxylamine (NH$_2$OH), methylamine (CH$_3$NH$_2$), and ethanol (CH$_3$CH$_2$OH). Absorption features belonging to functional groups such as -CH$_3$ and -OH suggest that additional COMs are present, but these cannot be unambiguously assigned due to overlapping bands. Formation pathways toward these COMs utilizing radical-radical combination reactions based on laboratory simulation experiments is presented. By extension, COMs predicted by these reactions, but absent from the spectra, are discussed. The results provide insight into the chemical environment of these ices and also highlight the critical need for caution and sufficient evidence in order to confidently identify COMs in ice.
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All authors Andrew M. Turner, Yao-Lun Yang, Rachel Gross, Nami Sakai, Ralf I. Kaiser

Earth and Planetary Astrophysics

Habitability of Tidally Heated H$_2$-Dominated Exomoons around Free-Floating Planets

David Dahlbüdding, Tommaso Grassi, Karan Molaverdikhani et al. (+4 more)

Exomoons around free-floating planets (FFPs) can survive their host planet's ejection. Such ejections can increase their orbital eccentricity, providing significant tidal heating in the absence of any stellar energy source. Previous studies suggested that liquid water could exist on such moons under thick CO$_2$-dominated atmospheres, but these models faced challenges with CO$_2$ condensation and atmospheric collapse, particularly in the high-pressure regimes that favoured long-term habitability. To address this, we employ a self-consistent model, including radiative transfer and equilibrium chemistry with condensation, to simulate a more stable hydrogen-dominated atmosphere for a range of initial chemical compositions, including C, O, and N. We find that such atmospheres can effectively trap heat via collision-induced absorption of H$_2$, maintaining surface temperatures suitable for liquid water for time-scales of up to 4.3 Gyr, depending on the surface pressure, while not prone to condensation-induced collapse. Wet-dry cycling caused by the strong tides together with the alkalinity of dissolved NH$_3$ could create favourable conditions for RNA polymerisation and thus support the emergence of life.
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All authors David Dahlbüdding, Tommaso Grassi, Karan Molaverdikhani, Giulia Roccetti, Barbara Ercolano, Dieter Braun, Paola Caselli

Cosmology and Nongalactic Astrophysics

Dark Energy After DESI DR2: Observational Status, Reconstructions, and Physical Models

Slava G. Turyshev

We review late-time cosmic acceleration after DESI Data Release 2 (DR2), emphasizing the interplay between Type Ia supernovae (SNe Ia), anisotropic BAO, CMB calibration, and perturbation-sensitive probes (RSD and weak lensing). DESI DR2 delivers percent-level BAO distance ratios over $0\lesssim z\lesssim2.5$, including a Ly$\alpha$-forest anchor at $z_{\rm eff}=2.33$. In CMB-calibrated combinations, flat $\Lambda$CDM exhibits a mild parameter mismatch, while allowing evolving dark energy (e.g.\ CPL $w_0$–$w_a$) can improve the fit; the preference is dataset-dependent and is particularly sensitive to redshift-dependent SN calibration/selection residuals at the few$\times10^{-2}$\,mag level. To sharpen likelihood-level interpretation, we provide two diagnostics: (i) an $r_d$-independent BAO-shape observable, $F_{\rm AP}(z)\equiv D_{\rm M}(z)/D_{\rm H}(z)$, constructed directly from published $(D_{\rm M}/r_d,\,D_{\rm H}/r_d)$ with covariance propagation; and (ii) a linear-response map from SN Hubble-diagram systematics $\delta\mu(z)$ to induced biases in $(w_0,w_a)$, yielding an explicit calibration requirement for DESI-era claims of evolving $w(z)$. We synthesize parametric and non-parametric reconstructions of $w(z)$ and $\rho_{\rm DE}(z)$ and map the resulting phenomenology to microphysical dark-energy and modified-gravity models subject to perturbation stability and gravitational-wave propagation constraints.
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Astrophysics of Galaxies

The sub-arcsecond ILT view of the Boötes Deep Field: A link between low-frequency kiloparsec radio morphology and AGN driven ionised outflows

Emmy L. Escott, Leah K. Morabito, Frits Sweijen et al. (+8 more)

Active Galactic Nuclei (AGN) outflows can regulate host galaxy evolution via AGN feedback. Ionised gas outflows have been linked to enhanced radio emission. In the first paper of this series, AGN detected with the International LOFAR Telescope (ILT) at 6" were more likely to host an [O III] 5007 outflow than AGN not detected, although only high-powered jets were ruled out as the origin of radio emission. New wide-field, sub-arcsecond resolution imaging at 144 MHz with the ILT now enables a resolved morphological study of this sample. We present the first wide-field, sub-arcsecond images of the Boötes Deep Field at 144 MHz, detecting 4074 sources in the $\sim$0.3" image with a central sensitivity of 33.8 uJy $\mathrm{beam^{-1}}$. For 47 AGN matched in AGN luminosity, we probe radio emission on kiloparsec-scales to investigate correlations with [O III] outflows. This sample spans $z<0.83$, $10^{40}<L_{\mathrm{[O III]}}<10^{43}~\mathrm{erg~s^{-1}}$, and $10^{21}<L_{\mathrm{144MHz}}<10^{24.5}~\mathrm{W~Hz^{-1}}$. We find that if we detect an AGN on both large-scales (6") and small-scales (0.3"), 90$\pm$7 per cent have an [O III] outflow, compared to 63$\pm$9 per cent of sources detected on large-scales, but undetected on small-scales. Furthermore, 17$\pm$6 per cent of sources without an [O III] outflow are detected on kiloparsec-scales, compared to 51$\pm$12 per cent of sources with an [O III] outflow. This implies a connection between [O III] outflows and kiloparsec-scale radio emission, which is likely AGN-driven. In contrast, AGN without an [O III] outflow are dominated by diffuse radio emission, likely to be associated with star formation.
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All authors Emmy L. Escott, Leah K. Morabito, Frits Sweijen, Chris M. Harrison, James Petley, Jurjen M. G. H. J. de Jong, Reinout J. van Weeren, Thomas S. Higginson, Isabella Prandoni, George Miley, Huub J. A. Röttgering

Astrophysics of Galaxies

B-field Orion Protostellar Survey (BOPS). IV: The Relative Orientation Between Magnetic Fields and Density Structures in Young Protostellar Envelopes

Kexin Cai, Bo Huang, Josep Miquel Girart et al. (+7 more)

We investigate the relative alignment between density structures and magnetic fields in eight young protostars from the ALMA B-field Orion Protostellar Survey. Column density maps are derived from 870 $\mu$m dust continuum emission, and the Histogram of Relative Orientations (HRO) method is applied to quantify the correlation between magnetic field orientations and density structures on envelope scales ($\sim$10$^{3}$~au). We find that the relative alignment shows overall weak evidence of systematic evolution with column density, suggesting that column density alone does not fully determine the alignment. The magnetization level also plays a crucial role, with weakly magnetized envelopes exhibiting predominantly parallel or random alignment, whereas strongly magnetized ones show perpendicular configurations even at moderate densities. These results reveal that density and magnetization jointly shape the morphology of protostellar envelopes and the coupling between gravity and magnetic fields during early stages of star formation.
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All authors Kexin Cai, Bo Huang, Josep Miquel Girart, Ian W. Stephens, Álvaro Sánchez-Monge, Valentin J. M. Le Gouellec, Wenyu Jiao, Qianru He, Zu-Jia Lu, Enwei Liang

Cosmology and Nongalactic Astrophysics

Fractal dimension of the cosmic web with different galaxy types

Ana Elisa Lima, Julianne C. Soares, Ana Carolina S. Tavares et al. (+4 more)

The fractal dimension $D$ is used to map the large-scale galaxy distribution in the Universe by color types: blue, green and red. Using a $NUVrK$-complete COSMOS2020 subsample of 618,952 galaxies observed up to $z=4$, number densities were derived and plotted against two cosmological distance measures, the luminosity and comoving (galaxy area) distances, in order to estimate $D$ for each galaxy color type in two redshift intervals: $z\gtrless1$. We found a general gradient $D_{\mathrm{blue}}> D_{\mathrm{red}}>D_{\mathrm{green}}$ with $D=1.40-2.03$ for $z<1$. For $1<z\leq4$, the gradient changes to $D_{\mathrm{blue}}>D_{\mathrm{green}}>D_{\mathrm{red}}$, and the fractal dimension values are lower, $D=0.03-0.44$. These results suggest that the fractal dimension is a sensitive diagnostic for how galaxy populations trace the evolving cosmic web, and confirm the fractal dimension as a useful tool for observational mapping of large-scale structure by galaxy color.
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All authors Ana Elisa Lima, Julianne C. Soares, Ana Carolina S. Tavares, Mariana V. Taveira, Sharon Teles, Amanda R. Lopes, Marcelo B. Ribeiro

Earth and Planetary Astrophysics

Sulfur Enrichment in Close-in Exoplanet Atmospheres Induced by Pebble Drift across the Salt Line

Kanon Nakazawa and Kazumasa Ohno

Observations of JWST have revealed that several close-in exoplanets have sulfur-rich atmospheres through SO$_2$ detections. Atmospheric sulfur is often thought to originate from solid accretion during planet formation, whereas recent simultaneous detections of SO$_2$ and NH$_3$ challenge this conventional scenario. In this study, we propose that ammonium salts, such as NH$_4$SH tentatively detected in comets and molecular clouds, play a significant role in producing sulfur-rich disk gases, which serve as the ingredient of giant planet atmospheres. We simulated the radial transport of dust containing volatile ices and ammonium salts, along with the dissociation, sublimation, and recondensation of these materials, thereby predicting the atmospheric chemical structures and transmission spectra of planets inheriting these compositions. Assuming that ammonium salts sequester 20% of the elemental nitrogen and sulfur budgets, our results reveal that they enhance sulfur and nitrogen abundances in disk gases to 2-10 times the solar values near the salt dissociation line. Photochemical simulations demonstrate that SO$_2$, NS, H$_2$S, NO, and NH$_3$ become the dominant N and S chemical species in the atmospheres on planets that inherited the gas compositions inside H$_2$O snowline. SO$_2$ features clearly appear in the infrared transmission spectra when the salt-bearing grains enhance the sulfur abundance of disk gas by pebble drift. Our model provides a novel scenario that explains the SO$_2$ detected in some exoplanet atmospheres solely from disk gas accretion. Volatile-element ratios, particularly N/S and C/O, would provide a key to disentangle our scenario from the conventional solid-accretion scenario.
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Astrophysics of Galaxies

Galactic seismology: can a disc-crossing impulse explain the large-scale perturbations in the Milky Way's disc?

Pavadol Yamsiri, Joss Bland-Hawthorn and Thor Tepper-Garcia

Prior to its infall, the Sagittarius (Sgr) dwarf galaxy was a major satellite with a mass of $M_{\rm sgr}\sim 10^{11}$ M$_\odot$. For the past $5-6~\mathrm{Gyr}$ , it has been heavily stripped by the Milky Way (MW), losing most of its mass while crossing the MW disc multiple times. Recent models of Milky Way disc perturbations $-$ including the spiral arms, the stellar bar, the Gaia phase spiral, and stellar and gaseous disc corrugations $-$ have identified these crossings as possible formation triggers, but have generally treated each perturbation in isolation. Here, we adopt a holistic perspective and ask whether a single disc-crossing impulse can simultaneously account for these features as observed today. We focus on simulations of single disc-crossing events by a Sgr-like perturber, and present a forensic analysis of the role of the powerful impulse in forming spiral arms, disc corrugations, the phase spiral and the `$L_{z}-\bar{V}_{R}$ wave', determined from a star's angular momentum and radial velocity, respectively. We find that a single disc crossing can reproduce reasonably well (e.g. structure, amplitude, phase) the observed local disc corrugation, and the Outer, Local and Sagittarius-Carina arm segments, implying that the last significant impulse due to a transit took place $700-1200~\mathrm{Myr}$ ago. Moreover, the $L_{z}-\bar{V}_{R}$ wave and phase spiral appear within the simulations over the same epoch and their general structure is reasonably well replicated, but not in detail. We conclude that Sgr's last significant crossing roughly a Gyr ago could be the primary cause of large-scale MW disc perturbations, but it cannot fully account for the $L_{z}-\bar{V}_{R}$ wave. Consequently, other triggers, possibly the Galactic bar or interactions with other satellites, must be considered in order to fully explain the current dynamical state of the MW's disc.
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Solar and Stellar Astrophysics

First Detailed MeerKAT Imaging Spectroscopy of a Solar Flare

Yingjie Luo, Eduard P. Kontar, Roelf Du Toit Strauss et al. (+5 more)

Radio observations provide powerful diagnostics of energy release, particle acceleration, and transport processes in solar flares. However, despite recent progress in radio interferometric imaging spectroscopy, current instruments still face limitations in image fidelity and resolution, restricting detailed spectroscopic studies of flaring regions. Here we present high-fidelity imaging spectroscopy of a M1.3 GOES class flare with MeerKAT, a precursor to the future-generation array SKA-Mid. Radio emissions at the observed frequencies typically originate in the low corona, offering valuable insights into magnetic reconnection and primary energy-release sites. The obtained images achieve an unprecedented dynamic range exceeding 10^3, enabling simultaneous analysis of bright coherent bursts and faint incoherent emission from the active region. Multiple spatially distinct coherent sources are identified, implying contributions from different populations of accelerated electrons. The incoherent emission extends beyond AIA structures, highlighting MeerKAT's ability to detect dilute but hot plasma invisible to Extreme Ultraviolet instruments. Combined with co-temporal Hard X-ray images and magnetic field extrapolations, the radio sources are located within distinct magnetic structures, further revealing their association with different populations of accelerated electrons. These results demonstrate MeerKAT imaging spectroscopy as powerful diagnostics of solar flares and pave the way for future solar flare studies with SKA-Mid.
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All authors Yingjie Luo, Eduard P. Kontar, Roelf Du Toit Strauss, Gert J. J. Botha, Tomasz Mrozek, Gelu M. Nita, Sarah Buchner, James O. Chibueze

High Energy Astrophysical Phenomena

An Accretion-Modulated Internal Shock Model for Long GRBs

R. Moradi, C. W. Wang, E. S. Yorgancioglu et al. (+1 more)

We introduce the Accretion-Modulated Internal Shock model (AMIS) as a possible framework for explaining the observational properties of long gamma-ray burst (GRB) prompt emission. In this scenario, the envelope of the prompt light curve follows the time-dependent mass-supply history to the central engine, associated with stellar collapse and, where applicable, fallback accretion, whose early-time onset can be approximated by $\dot{M}\propto t^{0-1/2}$ and which subsequently may decay as $\dot{M}\propto t^{-5/3}$, producing a photon count rate with a single fast-rise-exponential-decay (FRED)-like profile. In general, the prompt-emission envelope is regulated by a time-dependent mass supply to the central engine, while internal shocks produce the rapid variability. Since we only aim to introduce this framework here, we focus on the simplest single-FRED shape of the prompt emission profiles, while more complex cases involving multiple episodes and interacting shocks will be explored in forthcoming studies. The model indicates correlations between spectral evolution, FRED-pulse narrowing at high energies, and the mass-supply-controlled envelope. Stochastic Lorentz factor variations of ejected mass- or rate-driven shells, superimposed on the Accretion-Modulated envelope, explain the coexistence of smooth global trends and irregular short-timescale features, such as the widths of individual pulses in long GRB light curves, offering diagnostic tools for probing the inner engine activity.
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All authors R. Moradi, C. W. Wang, E. S. Yorgancioglu, S. N. Zhang