Earth and Planetary Astrophysics
Unraveling the Mystery of the Peculiar and Young Hot Jupiter CoRoT-2b. I. H$_2$O and CO Detection from Dayside Observations with Gemini-S/IGRINS
Ying Shu, Lisa Dang, Antoine Darveau-Bernier et al. (+12 more)
We present ground-based high-resolution spectroscopic pre-eclipse observations of the hot Jupiter CoRoT-2b obtained with the IGRINS spectrograph on Gemini South. Using cross-correlation analysis, we detect the Doppler-shifted signature of the
planet's thermal emission with a signal-to-noise ratio of 4.32. Our independent analyses confirm the presence of H$_2$O with a confidence level of 2.6$\sigma$ and an abundance of log$_{10}$$-5.08^{+0.43}_{-0.43}$, as well as CO with 2.3$\sigma$ confidence and an abundance of log$_{10}$$-4.21^{+0.48}_{-0.81}$ in CoRoT-2b's atmosphere, using two fully independent data reduction and
retrieval pipelines. No significant detections of CH$_4$, CO$_2$, TiO, or VO are reported. While our cross-correlation analysis tentatively suggests the presence of HCN and OH,
retrieval analysis does not confirm these molecules. The detected H$_2$O and CO features indicate that CoRoT-2b's dayside spectrum is not featureless, as previously inferred from lower-resolution observations, but instead reveals a complex atmospheric structure. Interestingly, we find a lack of significant molecular features at wavelengths shorter than 1.7 $\mu m$, potentially due to high-altitude absorbers such as H$^-$, clouds, or observational systematics. From our retrieved abundances of CO and H$_2$O, we constrain a supersolar C/O ratio of $0.91^{+0.08}_{-0.17}$ and a subsolar
metallicity. This study provides the first high-resolution constraints on the atmospheric composition of CoRoT-2b and serves as the foundation for future investigations into its peculiar westward hotspot offset. Further phase-resolved observations will be required to explore the underlying atmospheric dynamics in more detail.
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All authors Ying Shu, Lisa Dang, Antoine Darveau-Bernier, Aurora Kesseli, Luc Bazinet, Justin Lipper, Stefan Pelletier, Romain Allart, Nicolas B. Cowan, David Lafreniére, Emily Rauscher, Alejandro Sánchez-López, Björn Benneke, Anne Boucher, René Doyon
High Energy Astrophysical Phenomena
Thermal Structure and Chemical Enrichment of the North and South Polar Spurs: Supersolar N/O and Ne/O in the X-ray Plasma
Anjali Gupta, Smita Mathur, Joshua Kingsbury et al. (+5 more)
The North Polar Spur (NPS) is a prominent diffuse X-ray feature whose origin has remained uncertain for decades. Using a uniform analysis of archival Suzaku and XMM–Newton data with new Chandra observations, we constrain its thermal and chemical properties. The NPS emission is fully absorbed by the neutral interstellar medium, demonstrating that the
plasma lies beyond the
Galactic disk and is not a local
supernova remnant or nearby superbubble. The spectra require a two-temperature model with a warm–hot component ($kT \approx 0.2$ keV) and a hotter component ($kT = 0.4$–$0.5$ keV), with emission measures of $(41.8 \pm 4.9) \times 10^{-3}$ and $(12.9 \pm 2.2) \times 10^{-3} \mathrm{cm^{-6}~pc}$, respectively. A key result is the detection of super-
solar abundance ratios in the warm–hot phase, with N/O $= 3.6 \pm 0.3$ and Ne/O $= 1.9 \pm 0.1$
solar. A Suzaku observation of the outer South Polar Spur (SPS) shows similar absorption, temperatures, and enhanced abundances (N/O $= 2.9 \pm 0.4$, Ne/O $= 1.6 \pm 0.2$), though with lower emission measures. The similar super-
solar abundance ratios suggest a common enrichment history. These properties are consistent with those measured along other sightlines through the X-ray–bright shells of the
Galactic bubbles. Together, these results support that the NPS and SPS trace opposite limbs of the
Galactic bubbles. The chemical properties suggest a strong contribution from
stellar feedback in shaping the
Galactic bubbles.
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All authors Anjali Gupta, Smita Mathur, Joshua Kingsbury, Anthony Taylor, Sanskriti Das, Joy Bhattacharya, Manami Roy, Yair Krongold
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Indirect Parametric Resonance of the Electromagnetic Field Driven by an Oscillating SU(2) Dark Matter Condensate
Tatsuya Daniel, Vahid Kamali and Robert Brandenberger
We study a local patch of an
axion-like dark sector in Minkowski spacetime, containing an initially homogeneous and isotropic non-Abelian $SU(2)$ condensate, and a real pseudoscalar field $\chi$, coupled to an Abelian $U(1)$ gauge field which could be that of usual electromagnetism. The pseudoscalar couples directly to both gauge sectors through Chern-Simons interactions, while the $U(1)$ field couples to the $SU(2)$ condensate only indirectly, through the pseudoscalar. We show analytically that a homogeneous oscillating $SU(2)$ background $Q(t)$ acts as a periodic source for $\chi$, generating a homogeneous oscillatory condensate $\dot{\chi}$ that in turn modulates the frequency of the $U(1)$ helicity modes. In the linear regime this produces a Hill equation, and when the first harmonic dominates it reduces to a Mathieu equation. We derive the approximate resonance conditions, the leading Floquet exponent, and the conditions for a two-stage enhancement $Q \to \chi \to U(1)$. We also highlight an important point: in the exactly periodic, zero-bias limit, the indirect resonance is not intrinsically
chiral, because the two Abelian helicities are related by a half-period time shift.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Model-Building Implications from Light Magnetic Monopoles: A Case Study of Flavour Deconstruction
Marko Pesut, Davide Racco and Yunlong Zhao
We highlight a generic connection between extensions of the Standard Model featuring low-scale semi-simple
embeddings of $\rm{U}(1)_{\rm EM}$ and the phenomenology of light
magnetic monopoles in the early Universe. Combining cosmological, astrophysical, and direct-search constraints, we show that
magnetic monopoles with masses far below the scale of Grand Unified Theories are generically excluded and require low-scale inflation to dilute their abundance, followed by reheating below the monopole-production scale. These constraints are particularly relevant for flavour non-universal models, which provide a well-motivated framework to address the hierarchical structure of Yukawa couplings while allowing new dynamics close to the TeV scale compatible with experimental bounds. In many of these constructions, the sequential breaking of semi-simple gauge groups through intermediate stages containing a $\rm{U}(1)$ factor generically leads to the production of light
magnetic monopoles. We show that the parameter region naturally predicted by these models implies low-scale inflation, with reheating temperature as low as $10^{3}\text{--}10^4 \,\mathrm{TeV}$. These results significantly reduce the otherwise large allowed inflationary window and establish a direct connection between flavour physics and the thermal history of the early Universe: future evidence for a low-scale semi-simple
embedding of $\rm U(1)_{\rm EM}$, in particular through flavour non-universal interactions, would point towards low-scale reheating, while probes of
primordial gravitational waves could directly constrain the scale at which low-scale semi-simple groups can appear.
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High Energy Astrophysical Phenomena
On the origin of anomalous dissipation in simulations of tidal disruption events
Chris Nixon, Eric R. Coughlin and Zachary L. Andalman
In a
tidal disruption event (TDE), a
star is destroyed by the
tidal field of a supermassive black hole. The
stellar debris is initially placed on highly elliptical orbits, and a longstanding question in TDE theory is: How does the
stellar debris circularize into a disc and accrete? The originally proposed answer to this question is self-intersection shocks, where relativistic apsidal precession results in a strong collision between the incoming and outgoing material. However, global simulations of TDEs tend to find enhanced hydrodynamical dissipation prior to any intersections of the debris orbits, with the material “fanning out” into a wide-angle and partially-unbound
outflow upon passing through pericenter. We show that this dissipation is numerical in origin and arises from a combination of 1) the change in the kinematics of the debris as it passes through pericenter, with its velocity profile along the stream transitioning from strongly diverging pre-pericenter to strongly converging post-pericenter, and 2) the dependence of numerical
algorithms (viscosity switches for particle-based methods and Riemann solvers for Godunov-based schemes) on the diverging vs. converging nature of the fluid. We support this conclusion with analytical and numerical modeling. We discuss possible resolutions to these issues as well as the implications of our findings in the context of observations.
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Astrophysics of Galaxies
Suppression of Radiative Cooling in Galaxy Cluster Cores by the Combination of AGN Heating and Sloshing
Yutaka Fujita, Tomoaki Matsumoto and Keiichi Wada
Recent XRISM observations suggest that gas mixing induced by sloshing contributes to core heating. We systematically investigate the suppression of cooling flows in
galaxy cluster cool cores through three-dimensional hydrodynamic simulations that incorporate both sloshing-driven
turbulence and active
galactic nucleus (AGN) heating. The AGN heating is modeled as thermal energy input that mimics
cosmic-ray heating. Sloshing is represented by simple waves with amplitudes \alpha = 0, 0.15, and 0.3 times the sound speed and wavelengths \lambda = 200, 1000, and 2000 kpc. We evolve each model from an isothermal initial condition to t = 8 Gyr. Without AGN heating, sloshing suppresses cooling, but it cannot stop it completely unless the core is fully disrupted. Longer wavelengths promote deeper mixing and greater suppression. Sloshing can cause cooler gas to move more quickly than hotter gas. This phenomenon has been observed in a few clusters by XRISM. When AGN heating is included, the dense central gas is heated efficiently, substantially delaying or preventing the onset of a cooling flow. However, for intermediate wave lengths, sloshing can displace the densest gas away from the AGN heating zone, reducing the feedback effect and paradoxically enhancing net cooling relative to the wave-free case. These results highlight a non-trivial coupling between sloshing and AGN feedback, with implications for interpreting XRISM velocity and temperature maps of cool-core clusters.
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Astrophysics of Galaxies
Inferring Globular Cluster Initial Mass Function from Stellar Streams
Claire S. Ye and Raymond G. Carlberg
The
Gaia mission has provided precise astrometry and spectrophotometry for billions of
stars in the Milky Way, enabling the identification and kinematic characterization of
stellar streams. These streams, remnants of disrupted globular clusters and
dwarf galaxies, have revealed the structure of the Milky Way's dark matter
halo. We show that
stellar streams also encode information about the initial mass function of globular clusters. We combine cold dark matter simulations that model the
evolution and disruption of embedded globular clusters with observations of
stellar streams and globular clusters to infer the initial cluster mass function. We find that initially more massive clusters produce more massive streams, but deposit a smaller fraction of their initial mass into those streams. Using stream mass and angular momentum measurements, we recover a declining, power-law-like initial mass function with a slope $\alpha = 1.4\pm0.05$ for streams $\gtrsim 1000\,M_{\odot}$ (with a maximum value of $\sim 1.6$ if we strictly use lower limits of stream mass measurements). This work establishes
stellar streams as a novel probe of the early mass distribution of globular clusters.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Ringdown and lensing of triple systems
Vitor Cardoso, Giuseppe Ficarra, Jaime Redondo-Yuste et al. (+1 more)
Triple systems have progressively been recognized as ubiquitous in our Universe and provide a good testing ground for wave generation and propagation in nontrivial environments. We study the dynamics of triple systems in a fully nonlinear setting. In particular, we analyze numerical relativity simulations of head-on collisions of black holes in the presence of a companion. We show evidence for Doppler and gravitational
redshift in the ringdown, and clear signs of amplification by
lensing. In certain cases, we also show the appearance of a second image, with hints of resonant mode excitation. Our results pave the way for the understanding of mergers in the vicinity of massive companions. Even in extreme setups we do not find collapse to black holes from lensed gravitational radiation.
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All authors Vitor Cardoso, Giuseppe Ficarra, Jaime Redondo-Yuste, João Sieiro dos Santos
High Energy Astrophysical Phenomena
Guide-Field-mediated Multiscale Instabilities in Relativistic Reconnection
Pranab J Deka, Fabio Bacchini, Muni Zhou et al. (+1 more)
We investigate
magnetic-energy dissipation, current-sheet dynamics, and nonthermal particle acceleration in three-dimensional relativistic reconnection in an electron–ion
plasma with a realistic mass ratio. Using particle-in-
cell simulations of a double Harris current sheet, we explore a range of ion magnetisations and guide-field strengths to determine how guide fields regulate the overall
magnetic energy dissipation. At low magnetisation, $\sigma_i=0.1$, increasing the guide field suppresses reconnection:
magnetic-energy dissipation decreases, the growth of tearing modes is weakened, and nonthermal particle acceleration remains inefficient. At higher magnetisations, $\sigma_i=1$ and $\sigma_i=5$, the behaviour changes qualitatively. In the zero-guide-field case, strong drift-kink activity corrugates and broadens the current sheet, inhibiting efficient tearing-mediated reconnection. A weak guide field suppresses this drift-kink-driven disruption, allowing the current sheet to remain laminar and more coherent and thereby enhancing
magnetic-energy dissipation. However, once the guide field becomes too strong, reconnection is again suppressed: the onset is delayed, tearing activity weakens, current-sheet compression is reduced, and the system retains a larger fraction of its initial
magnetic energy. This non-monotonic behaviour is reflected consistently in
magnetic-energy
evolution,
Fourier analysis of the tearing and kink modes, current-sheet thickness, and nonthermal particle acceleration. The most dissipative cases are not necessarily the zero-guide-field runs, but rather those in which the guide field balances drift-kink suppression without strongly impeding the tearing modes. Our results show that the overall system
evolution is controlled not only by the available
magnetic energy, but also by the guide-field-regulated morphology and stability of the reconnecting current sheet.
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All authors Pranab J Deka, Fabio Bacchini, Muni Zhou, Camille Granier
High Energy Astrophysical Phenomena
Simulation-Based Prediction of Black Hole Fe K$\alpha$ Line Profiles
Chris Nagele, Julian H. Krolik, Brooks E. Kinch et al. (+1 more)
One of the most useful spectral diagnostics of accreting black hole systems is the Fe K$\alpha$ fluorescence line. Detected in many systems, it is often used to estimate the black hole
spin, as its breadth is attributed to relativistic kinematics near the
spin-dependent innermost stable circular orbit (ISCO). In a companion paper, we showed how continuum spectra emitted by accreting black holes can be derived from snapshots of general relativistic magnetohydrodynamics simulations by combining radiation transfer solutions for the disk body and the corona. In this paper, we focus on the Fe K$\alpha$ line, solving its transfer problem on the basis of local ionization and thermal balance. Its equivalent width is $\sim 25-225$ eV, depending mainly on viewing angle, for an
accretion rate of 1$\%$ Eddington. Contrary to common assumptions, the illuminating X-ray spectrum and ionization parameter $\xi$ can be strong functions of radius; e.g. $\xi \propto r^{-1.5}$ in this simulation. Consequently, the region of the disk near the ISCO is completely ionized and contributes almost no Fe K$\alpha$
photons; most of the flux is made at radii $\gtrsim 10 r_g$. The lines are broadened by a combination of relativistic Doppler shifts, Compton broadening in the disk atmosphere, and the differing line energies emitted by different Fe ions. These new mechanisms expand the parameter space of acceptable models, including the possibility of broad line profiles without large black hole
spin; physical trends revealed by the simulations can refocus fitting efforts on the most relevant sections of the parameter space.
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All authors Chris Nagele, Julian H. Krolik, Brooks E. Kinch, Jeremy D. Schnittman
Instrumentation and Methods for Astrophysics · Cross-listed from physics.pop-ph
The Era of Extremely Large Optical Telescopes: The ELT
Priya Hasan
The advent of Extremely Large
Telescopes ELTs, ground-based optical or infrared observatories with primary mirrors exceeding 20 m heralds a transformative epoch in observational astronomy. This article examines the dawn of this new era and the three upcoming facilities in the optical infrared band the
Giant Magellan
Telescope GMT, the Thirty Meter
Telescope TMT, and the European Extremely Large
Telescope ELT. This article will focus on the ELT, while a sequel will cover GMT and TMT. We describe the key technological breakthroughs enabling its construction, most notably the segmented mirror design, advanced adaptive optics AO, and
laser guide
star systems. These innovations will deliver more than an order of magnitude leap in light-gathering area and spatial resolution, providing image sharpness exceeding that of spacebased
telescopes for widefield observations. The scientific impact of the ELT is profound and multifaceted. We discuss its inception and construction milestones and explore its potential to directly image and characterize the atmospheres of Earth like
exoplanets, searching for biosignatures, and trace the formation of the first
stars,
galaxies, and supermassive black holes. This paper concludes that ELTs are not mere incremental improvements but foundational instruments that will redefine the frontiers of astrophysics, address some of science's most enduring questions, and inevitably lead to discoveries beyond current prediction.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
WIMP-like Dark Matter Without Thermalization At Freeze-Out
Dan Hooper, Gordan Krnjaic and Gabriele Montefalcone
In the standard thermal relic scenario, dark matter remains in chemical
equilibrium with the Standard Model radiation bath until freeze-out occurs at $T \sim m_X/20$, where $m_X$ is the dark matter mass. In this familiar class of models, the observed relic density is obtained for annihilation cross sections of order $\sigma v \sim 10^{-26}$ cm$^3$/s. We show that comparable cross sections can naturally be realized in hidden-sector models in which the dark matter and Standard Model sectors decouple at a very high temperature, $T \gg m_X$, and subsequently evolve with separate thermal histories. Despite this decoupling, the two sectors have similar temperatures during freeze-out, leading to the usual thermal relic abundance. As a consequence, the coupling between the Standard Model and hidden sectors can be extremely small, potentially placing direct detection and
collider signals far below foreseeable sensitivities.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Dark Matter Interpretation of the Super-Kamiokande Antineutrino Excess and Predictions for JUNO
Alessandro Granelli, Silvia Pascoli and Salvador Rosauro-Alcaraz
Super-Kamiokande has reported a small excess of electron antineutrino events in the 20 MeV energy range, in the search for the diffuse
supernova neutrino background. We interpret this signal as a possible indication of dark matter that annihilates dominantly into
neutrinos, pointing to a thermal dark matter candidate with $s$-wave annihilation and with mass in the tens of MeV range. This mass scale naturally fits into rich dark sector extensions of the Standard Model.
Neutrino experiments, including JUNO, will be able to test this hypothesis in the coming years.
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High Energy Astrophysical Phenomena
The exceptional 2017 gamma-ray flare of the radio galaxy NGC 1275: VERITAS and Multiwavelength Observations
A. Acharyya, A. Archer, P. Bangale et al. (+66 more)
The
radio galaxy NGC 1275 is the Brightest Cluster
Galaxy in the Perseus cluster. It is well-studied across all wavebands, including Very High Energy (VHE; E>100GeV gamma-rays, and with
radio observations over the last 20 years tracking an unusual
radio component, "C3". NGC 1275 was observed in an exceptional VHE flaring state between 2016 December 31 and 2017 January 3. The
flare peak reached ~1.5 Crab units as measured by the MAGIC observatory. We report on the observations of NGC~1275 conducted by VERITAS and multi-wavelength data collected during this flaring state, and for context, data taken between 2009 and 2017 inclusive. VERITAS detected the declining state of the
flare on 2017 January 2 (MJD 57755) and 3 (MJD 57756) at an average flux state of 0.5 Crab units. VERITAS spectra show an overall long-term trend of harder-when-brighter. During the
flare, the gamma-ray spectrum obtained from the combined
Fermi-LAT, MAGIC, and VERITAS observations, changes from a power law with an exponential cut-off on January 1 to a log-parabola on January 2. To study the
evolution of the
flare in more detail, multi-band spectral energy distributions (SEDs) were constructed for the nights of 2017 January 1 and 2 corresponding to the shift from the peak to the decline of the
flare. A blob-in-jet modeling of the SEDs results in support for a two-component model with a jet angle of 10 degrees to the line of sight and the gamma-ray emission zone located in the vicinity of the C3
radio component.
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All authors A. Acharyya, A. Archer, P. Bangale, J. T. Bartkoske, W. Benbow, Y. Chen, J. L. Christiansen, A. J. Chromey, A. Duerr, M. Errando, M. Escobar Godoy, A. Falcone, S. Feldman, Q. Feng, S. Filbert, L. Fortson, A. Furniss, W. Hanlon, O. Hervet, C. E. Hinrichs, J. Holder, Z. Hughes, M. Iskakova, W. Jin, M. N. Johnson, P. Kaaret, M. Kertzman, M. Kherlakian, D. Kieda, T. K. Kleiner, N. Korzoun, F. Krennrich, S. Kundu, M. J. Lang, M. Lundy, G. Maier, E. Meyer, P. Moriarty, R. Mukherjee, W. Ning, M. Ohishi, R. A. Ong, A. Pandey, J. Escudero Pedrosa, M. Pohl, E. Pueschel, J. Quinn, P. L. Rabinowitz, K. Ragan, P. T. Reynolds, D. Ribeiro, E. Roache, C. Rulten, I. Sadeh, L. Saha, M. Santander, G. H. Sembroski, R. Shang, M. Splettstoesser, D. Tak, A. K. Talluri, J. V. Tucci, J. Valverde, V. V. Vassiliev, D. A. Williams, S. L. Wong, T. Yoshikoshi, P. S. Smith, J. Kataoka
Solar and Stellar Astrophysics
Spectral classification of brown dwarfs using machine learning
A.R. Callen, I.H. Bustos Fierro and M. Gómez
Brown
dwarfs are compact objects that do not reach temperatures high enough to produce sustained hydrogen fusion. Consequently, they cool over time, gradually evolving through later spectral types. In fact, three new spectral types (L, T, and Y) were added to the Harvard sequence to accommodate the spectral features of brown
dwarfs. During the cooling process, some brown
dwarfs unexpectedly become bluer instead of redder (at optical and near-infrared wavelengths). This phenomenon, known as the bluing effect, is particularly noticeable at the L/T spectral transition. The aim of this work is to approximate the spectral type of brown
dwarfs using only photometric data, in particular 2MASS and WISE magnitudes. We used two machine learning
algorithms, Random Forest and Gaussian Processes, which were evaluated using a 70/30 train/test split. Both models were trained using 5-fold cross-validation and achieved F1-scores of 0.84 and 0.87, respectively, on the test set. After validating the reliability of the
algorithms, we applied them to 21 isolated brown
dwarfs without prior spectral type determinations. Our results indicate that 5 of these objects have a spectral type between L0 and L4, while the remaining 16 fall within the M6-M9 range. Machine learning
algorithms, combined with multi-band photometry, are a powerful tool for estimating the spectral types of brown
dwarfs.
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Astrophysics of Galaxies
Galaxy Proximate Damped Lyman-Alpha Systems and HI Reionization Topology in TECHNICOLOR DAWN
Maya Steen, Kristian Finlator, Samir Kušmić et al. (+1 more)
Recent observations from the James Webb Space
Telescope (JWST) have revealed proximate damped Lyman-$\alpha$ systems (PDLAs) in the foreground of high
redshift galaxies ($z \gt 5$), which have been interpreted as neutral circumgalactic media (CGM). The ionization state of the CGM, potentially inferred from DLA strength, may serve as a probe to trace the progress of reionization, similarly to the ionization state of the intergalactic medium (IGM). To determine if this method has merit, we use the cosmological hydrodynamical simulation TECHNICOLOR DAWN to study simulated gas
halos at
redshifts $z = 10, 8, 6,$ and $5.5$. We investigate the reionization
topology to determine whether the CGM and IGM have similar ionization histories, and we study the relation between column density of neutral hydrogen (observationally measured by DLA strength), neutral fraction, and gas mass fraction of the foreground gas to determine whether PDLAs can be used to trace the progress of reionization. We find an inside-out-middle reionization
topology, where the CGM reionizes after the IGM and remains partially neutral at $ z= 5.5$. The foreground column density of neutral hydrogen depends mostly on
halo mass, with a weak dependence on neutral fraction or
redshift. Therefore, provided precise estimates of
halo or
stellar mass, PDLAs may be used to trace the progress of reionization particularly at high
redshifts.
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All authors Maya Steen, Kristian Finlator, Samir Kušmić, Ezra Huscher
High Energy Astrophysical Phenomena
The potential of diffuse Galactic Ridge neutrino measurements to constrain dark matter
Jaume Zuriaga-Puig, Pedro de la Torre Luque and Viviana Gammaldi
We use the latest ANTARES
Galactic Ridge
neutrino measurements to investigate their implications for indirect dark matter (DM) searches. We consider both annihilating and decaying DM scenarios, spanning a wide range of masses and final states, and systematically compare the resulting
neutrino fluxes with the expected astrophysical
Galactic diffuse emission. Furthermore, we compare the results for different DM density profiles allowed by the observations, from spike and cuspy to cored profiles. We do so for the WIMP model-independent scenario and explore two more specific models: branons and very heavy sterile
neutrinos, where a cold DM candidate arises naturally from the theory. We show the potential
neutrino measurements in the
Galactic Ridge for DM and make predictions for future
neutrino observatories.
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Cosmology and Nongalactic Astrophysics
Gravitational-wave constraints on $H_0$ are robust to putative redshift evolution in the binary black hole mass spectrum at current sensitivity
Alessandro Agapito, Viola De Renzis and Michele Mancarella
Spectral-siren cosmology constrains the Hubble constant $H_0$ using gravitational-wave observations of compact-binary coalescences. The method combines luminosity distances inferred from the waveform with
redshift information statistically encoded in population features of the source-frame mass spectrum. Because the detector measures redshifted masses, structure in the intrinsic mass distribution acts as an internal “ruler,” making the inference sensitive to assumptions about the population model. In particular,
redshift evolution of the mass spectrum is widely discussed as a potential systematic for $H_0$ measurements. We revisit spectral-siren constraints with the GWTC-4.0 binary black hole catalog, explicitly allowing the main mass scales of a standard parametric mass model to evolve with
redshift. We find no compelling evidence for
evolution at current sensitivity. Allowing
evolution produces a modest, nonstatistically significant shift of the $H_0$ posterior toward lower values, which we interpret with targeted posterior and event-level diagnostics. Importantly, the associated systematic uncertainty is subdominant to that induced by alternative
redshift-independent descriptions of the mass spectrum, such as the number of spectral features and the functional form used to model them. Our results indicate that, at current sensitivity, spectral-siren constraints on $H_0$ are robust to
redshift evolution of the mass spectrum within the flexibility explored here. Using injection studies, we show that this mild $H_0$ shift is reproduced when a nonevolving underlying population is analyzed with an evolving model, consistent with an overflexible population description at the present signal-to-noise. The sign and magnitude of the shift can, however, depend on detector sensitivity and
redshift reach as the population features become increasingly constrained directly by the data.
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Solar and Stellar Astrophysics
TIC 295741342: A Triply-Eclipsing Triple Star System with a Giant Tertiary
Brian P. Powell, Guillermo Torres, Veselin B. Kostov et al. (+4 more)
We present the discovery and characterization of TIC 295741342, a triply-eclipsing triple
star system with a
giant tertiary. The eclipsing binary consists of two similar main-sequence
stars in a 4.75-day orbit. The binary is in a 412.8-day orbit with the
giant tertiary. We found two degenerate solutions for the system: one where the tertiary is ascending the Red
Giant Branch (RGB), and the other where the tertiary is on the Horizontal Branch (HB) and will eventually ascend the Asymptotic
Giant Branch (AGB). In both solutions, the system is near-perfectly coplanar. In TESS Sector 33, the binary passes behind the
giant tertiary, producing a distinctive "head-and-shoulders" eclipse that directly constrains the relative flux contributions and radii of all three
stars. We modeled the system using a comprehensive spectro-photodynamical model that simultaneously fits the TESS lightcurve, eclipse times, spectral energy distribution, and radial velocities from 48 TRES spectra obtained over four years of observation resolving all three components. Evolutionary analysis using MIST tracks indicates that, in both solutions, the tertiary will overflow its Roche lobe, one in the RGB and the other in the AGB. The Roche lobe overflow will initiate either a stable mass transfer to the binary or a common envelope
evolution that will likely result in ejections and/or mergers. Our models predict the midpoint of the next outer eclipse will occur on September 1, 2026 and we encourage follow-up observations with a $\pm$3 day window to observe the full event and further constrain the system parameters.
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All authors Brian P. Powell, Guillermo Torres, Veselin B. Kostov, Saul A. Rappaport, Tamás Borkovits, Robert Gagliano, David W. Latham
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
A novel pre-inflationary model in view of the lack of angular correlation of CMB
M. Montes, José Edgar Madriz Aguilar, A. Bernal et al. (+1 more)
In this paper we propose a novel unified cosmological model that connects a pre-inflationary epoch, starting at the Planckian time, with the onset of inflation within a single scalar-field framework. The pre-inflationary phase is characterized by a decelerated expansion with an increasing comoving Hubble horizon, followed by a gradually transition to an accelerated inflationary regime. This early dynamics leads to a modified causal structure that naturally accounts for the suppression of large-angle $(\theta \gtrsim 60^\circ)$ correlations in the
cosmic microwave background (CMB) reported by the satellite PLANCK. We study the
quantum fluctuations of the scalar field using the Mukhanov-Sasaki formalism and a canonical quantization procedure based on energy minimization. We find that the
vacuum state is well-defined only for sub-horizon modes at the onset of inflation, which induces a natural cutoff in the
primordial power spectrum. The resulting spectrum exhibits a suppression at large scales while remaining nearly scale-invariant at small scales. In the appropriate limit, the model recovers the standard de Sitter result, in agreement with current observational constraints. These results highlight the relevance of pre-inflationary dynamics for addressing large-scale anomalies within a consistent inflationary framework.
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All authors M. Montes, José Edgar Madriz Aguilar, A. Bernal, Diego Allan Reyna
Cosmology and Nongalactic Astrophysics
Interacting Dark Sector field theory with phantom crossing
E. Abdalla, O. P. F. Piedra, A. A. Escobal et al. (+4 more)
Recent results from the Dark Energy Spectroscopic Instrument (DESI) provide evidence for a dynamical dark-energy component, whose equation of state appears to have recently crossed the phantom divide. In this Letter, we present an interacting dark-energy model, grounded in field theory, that naturally accommodates such a double crossing. In our framework, fermionic dark matter is coupled via a Yukawa interaction to a tachyonic scalar field governed by Born-Infeld dynamics. The phantom crossing arises at the level of the effective dark-energy equation of state, while the underlying scalar-field dynamics remains nonphantom and well bounded. We confront our model with data including BAO from the DESI (DR2) survey, CMB distance priors from Planck 2018, and the latest Type Ia
supernovae compilations, obtaining robust constraints across the different data combinations and reconstructing a recent double crossing of the phantom divide. Furthermore, under naturalness assumptions, the model expects an ultralight fermionic dark matter mass of order $1.9\times10^{-3}\,\mathrm{eV}$, suggesting a possible connection with new light particles in the dark sector and motivating future tests with cosmological perturbations.
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All authors E. Abdalla, O. P. F. Piedra, A. A. Escobal, A. M. Vicente, F. B. Abdalla, B. Wang, A. Marins
Cosmology and Nongalactic Astrophysics
ComPACT: Mass-Redshift Properties of the galaxy cluster catalogue
S. Voskresenskaia, N. Lyskova, I. Zaznobin et al. (+1 more)
Machine-learning methods are increasingly applied to astronomical surveys, providing powerful tools for detecting and studying
galaxy clusters. We investigate the mass-
redshift properties and completeness of the ComPACT
galaxy cluster catalogue, constructed using a convolutional neural network applied to publicly available combined ACT+Planck maps. The ComPACT catalogue contains 2,962 SZ-selected
galaxy cluster candidates. We confirm clusters by estimating
redshifts using literature information and photometric techniques based on DESI Legacy Imaging Surveys data. Cluster masses are derived from ACT+Planck and Planck Compton-y maps via SZ scaling relations. The completeness is assessed using simulated cluster injections into real microwave maps. We confirm approximately $\sim$60 % of the ComPACT candidates as
galaxy clusters. The
redshifts span the range $0.007 < z < 1.7$, including approximately 116 new measurements. Masses are obtained for 56 % of the sample, covering the range $(0.25 - 13.1) \times 10^{14} ~M_\odot$ and including 158 new mass determinations. We identify five previously unreported massive clusters ($M_{500c} > 6 \times 10^{14}~M_\odot$) at $z > 0.7$, increasing the known population of such systems by approximately 10 %. The ComPACT catalogue expands the SZ-selected Planck-like cluster population, especially at high
redshift and high mass, demonstrating the effectiveness of deep-learning approaches for cluster detection in microwave data.
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All authors S. Voskresenskaia, N. Lyskova, I. Zaznobin, A. Meshcheryakov
Solar and Stellar Astrophysics
Simulating the Convective Urca Process with Multiple Urca Pairs in a Simmering White Dwarf
Brendan Boyd, Ferran Poca-Amorós, Alan Calder et al. (+1 more)
Type Ia
supernovae are bright thermonuclear explosions of one or more white
dwarf stars. The exact origin and explosion mechanism for these
supernovae is still poorly understood. In the near-Chandrasekhar mass progenitor model, a simmering phase precedes the explosion. During this simmering phase, central carbon burning heats the core and drives convection. A poorly understood aspect of this phase is the convective Urca process, a linking of weak
nuclear reactions and convective mixing. Convective Urca has the potential to alter characteristics of the convection zone and thus alter the
evolution of the white
dwarf. To study the convective Urca process, we use the low Mach number hydrodynamic code MAESTROeX to run 3D simulations of the convection zone. We build off previous work to implement a more comprehensive carbon burning network and include the A=21, A=23, and A=25 Urca pairs in the simulations. We compare simulations with and without the convective Urca process to isolate the direct effects the process has on the convection zone. We find the convective Urca process reduces the efficiency of convective mixing near the the convective boundary, but does not restrict the size of the convection zone. We additionally find the A=23 Urca pair to be the most important Urca pair to the convective Urca process in these simulations. All together, our results better inform our understanding of this complex phenomena as well as demonstrates the range of potential convective structures, particularly at the convective boundary, of a simmering white
dwarf.
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All authors Brendan Boyd, Ferran Poca-Amorós, Alan Calder, Dean M. Townsley
Cosmology and Nongalactic Astrophysics
Probing String-Theory-Inspired Topologies of the Early Universe through CMB Temperature and Polarization Anisotropies
Nick E. Mavromatos and Miguel-Angel Sanchis-Lozano
TeV string-mass-scale strings have been excluded experimentally at
colliders, as their effects have not been observed at the Large
Hadron Collider (CERN). On the other hand, higher-scale string theory, with mass scales typically close to the Planck scale, is often regarded as experimentally inaccessible due to the enormous energies required for direct tests, and far beyond the reach of present or foreseeable particle accelerators. Nevertheless, the early Universe may provide an indirect observational window for high-string scale through imprints left on the
Cosmic Microwave Background (CMB). In this work, building on previous studies, we reexamine temperature and polarization angular correlations as probes of the geometry and
topology of the pre-inflationary Universe. We focus in particular on two-point correlation functions at large angular scales, where signatures of nontrivial spatial
topology may survive as relics of
primordial physics. We investigate the observational consequences of toroidal compactification and analyze their impact on the
primordial power spectrum of the CMB provided by the Planck satellite. Within the current experimental and theoretical uncertainties, we identify a possible indication closely related to spatial-parity breaking, consistent with the presence of six spatial extra dimensions in the early Universe, compactified at the GUT epoch before the start of inflation. Finally, we extend our framework to B-mode polarization, highlighting its potential as a sensitive probe in forthcoming ground-based and space-borne experiments with unprecedented precision.
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Solar and Stellar Astrophysics · Cross-listed from nucl-th
A new analysis of the "hep" S-factor and the "hen" cross section
Michele Viviani, Alex Gnech, Laura Elisa Marcucci et al. (+2 more)
We present a new accurate analysis of the $^3$He$(p,e^+\nu_e)$${}^4$He (”hep”) reaction at astrophysical energies. The S-factor is computed using a state-of-the-art method to calculate the four-nucleon scattering and bound-state wave functions (the hyperspherical harmonic expansion), and by using
nuclear interactions and accompanying electroweak
nuclear currents obtained within the
chiral effective field theory framework. Our analysis includes a detailed examination of the theoretical uncertainties coming from two different sources: the truncation of the interaction and current
chiral expansions, and the model dependence. Our recommended final theoretical value for the hep S-factor at zero energyis $S(0)=(8.7\pm 0.9)\times 10^{-20}$ keV b. We provide also the energy spectrum of the outgoing hep positrons which may be measured in future experiments. We include also an analysis of the ”sister” reaction $^3$He$(n,\gamma)$${}^4$He (”hen”) at low energies, showing that the calculation well reproduce the total cross section from thermal energies to few MeV, validating our results on the hep reaction.
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All authors Michele Viviani, Alex Gnech, Laura Elisa Marcucci, Alejandro Kievsky, Luca Girlanda
Solar and Stellar Astrophysics
New NanoSIMS Multielement Isotope Data Reveal CO Novae As Key Sources Of 13C-rich Presolar Silicon Carbide Grains
Jordi José, Nan Liu, Conel M. O'D. Alexander et al. (+1 more)
We present new multielement NanoSIMS isotopic measurements (C, N, Si, Mg-Al, Ti, and Ni) for four putative nova SiC grains and 79 AB SiC grains from the Murchison meteorite to reassess their
stellar origins. High-resolution imaging and a revised Mg/Al relative sensitivity factor for SiC yield substantially improved 26Al/27Al ratios and the most reliable multielement characterization to date for 13C-rich presolar SiC grains. To interpret these data, we computed an expanded suite of hydrodynamic CO, ONe, and recurrent nova models spanning a range of white-
dwarf masses and pre-enrichment parameters. When all isotopic systems are considered together (C, N, Mg-Al, Si, Ti, and Ni), the CO nova models provide the closest and most self-consistent match to both the putative nova grains and the subset of AB grains lacking s-process signatures. CO novae of low- to intermediate-mass naturally reproduce the observed 14N/15N-26Al/27Al trend, the Si isotope compositions of AB grains which dominantly reflect
Galactic chemical
evolution (GCE), and the mild Si isotope shifts in putative nova grains relative to the GCE trend defined by AB grains. In contrast, ONe and recurrent nova models fail multiple isotopic constraints simultaneously. These results demonstrate that low- to intermediate-mass CO novae (0.6-1.0 Msun) are the most plausible
stellar sources of 13C-rich SiC
dust lacking s-process signatures (1-2% of all presolar SiC), and they establish a multielement, model-anchored framework for quantifying nova contributions to the
dust reservoir in the interstellar medium.
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All authors Jordi José, Nan Liu, Conel M. O'D. Alexander, Jianhua Wang
Astrophysics of Galaxies
Arm morphology in off-centre barred galaxies
P. Sánchez-Martín, M. López-Vilamajó, M. Romero-Gómez et al. (+1 more)
Many barred
galaxies, including the Large Magellanic Cloud (LMC), display strong lopsidedness and off-centre bars. The dynamical connection between bar-disc misalignments, internal mass asymmetries, and arm morphology is not yet fully characterised. We investigate how internal mass imbalances within the bar and global offsets between the bar and the centre of mass of the system modify the
equilibrium-point structure and the invariant
manifolds that organise arms. We construct a barred
galaxy model which includes an off-centred and asymmetric in shape bar. Using numerical continuation, we track the position, stability, and bifurcations of the Lagrangian
equilibrium points as functions of the displacement of the asymmetric mass component along the bar and of the offset between the bar and the system's centre of mass. For representative configurations we compute the invariant
manifolds of planar Lyapunov orbits around unstable points and analyse the resulting arm structures. Internal bar lopsidedness and modest bar-disc offsets that keep the centre of mass inside the bar preserve the classical configuration with five
equilibrium points, but strongly distort the associated invariant
manifolds, producing two arms with different densities and shapes. The bar-disc offset reaches a threshold at the point at which the
galactic centre of mass exits the bar ellipsoid, in which a pitchfork bifurcation removes the collinear unstable points and the system transitions to a three-
equilibrium-point configuration in which a single unstable point and its associated
manifold supports one arm. This framework is compatible with the observed correlation between off-centre bars and photometric lopsidedness, and it provides a dynamical explanation for the strongly asymmetric arm morphology of
galaxies such as the LMC.
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All authors P. Sánchez-Martín, M. López-Vilamajó, M. Romero-Gómez, J. J. Masdemont
High Energy Astrophysical Phenomena
The first IXPE view of the eclipsing ADC source 4U 1822-37
A. Anitra, A. Gnarini, T. Di Salvo et al. (+16 more)
Accretion-disc corona sources are high-inclination low-mass X-ray binaries in which the innermost regions are hidden and the observed X-ray emission is dominated by radiation scattered above the disc. 4U 1822-37 is a key binary system of this class, but its geometry is still debated. X-ray polarimetry offers a direct probe of the scattering structure. We present the first X-ray spectro-polarimetric study of 4U 1822-37 and test whether its spectrum and polarisation can be explained within the
accretion-disc-corona scenario. We analysed a coordinated campaign with IXPE, XMM-Newton, NuSTAR, and Swift. We performed broadband spectral modelling and model-independent, energy-resolved, and orbital-phase-resolved polarimetric analyses. The broadband spectrum requires a soft thermal component, a Comptonised continuum, a hard power-law tail, and relativistically blurred reflection. The observed 0.1-100 keV luminosity, $L_{\rm obs}\simeq6.1\times10^{36}\ {\rm erg\,s^{-1}}$, is far below the intrinsic luminosity expected from the orbital
evolution, supporting a geometry in which only a small fraction of the intrinsic emission is scattered into the line of sight by an extended, optically thin corona. In the 2-8 keV band, IXPE measures ${\rm PD}=7.9\pm0.6\%$ and ${\rm PA}=-24^\circ\pm2^\circ$. The PD increases with energy, while the PA remains approximately constant. During eclipse, the PD decreases to ${\rm PD}=5.5\pm1.7\%$, with no significant PA variation. This behaviour is consistent with the companion occulting the most polarimetrically efficient part of the extended corona. The high PD, stable PA, energy-dependent polarisation, and eclipse behaviour support a picture in which 4U 1822-37 is observed in an extreme high-inclination, scattering-dominated regime. The extended corona is the main structure shaping both the observed X-ray emission and its polarisation.
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All authors A. Anitra, A. Gnarini, T. Di Salvo, R. Iaria, A. Marino, F. Barra, L. Burderi, A. Sanna, L. Marra, S. Bianchi, G. Matt, F. Ursini, C. Miceli, A. Miraval Zanon, W. Leone., F. Capitanio, S. Fabiani, P. Kaaret, A. Tarana
Earth and Planetary Astrophysics
Latitudinal variations in Neptune's temperature profile observed with ALMA
Óscar Carrión-González, Raphael Moreno, Emmanuel Lellouch et al. (+5 more)
Despite the low
solar irradiation it receives, Neptune shows a very active atmosphere with some of the most intense dynamics observed in
Solar System atmospheres. Characterizing the atmospheric temperature profiles of the
planet is a key to understand these observed processes. In this work, we derived the Neptune pressure-latitude thermal field, using 2016 ALMA measurements of the CO(3-2) spectral line at 345.796 GHz, with a spatial resolution of about 0.37" on Neptune's 2.24" disk. To analyse the data, we developed MCMC
retrieval methods to derive both the temperature profiles and the CO abundance profile. We find that our data probes the upper troposphere and the lower stratosphere of the
planet, between 2 bar and 0.1 mbar. Although temperature and CO profile are strongly correlated, simultaneous
retrievals of both parameters for disk-integrated observations reveal a factor of 2-3 larger CO abundance in the stratosphere than in the troposphere, reinforcing the hypothesis of CO delivery by a recent cometary impact. CO
retrievals with fixed temperature profile do not fit the spatially-resolved observations, implying underlying temperature variations. By performing temperature
retrievals with spatially constant CO, we find distinct trends of the thermal profile between the southern polar region, mid-latitudes and the equator. At 10–100 mbar, this structure is consistent with that observed by Voyager 2 in 1989, i.e. colder mid-latitudes, with a warmer equator and south polar regions. At 300-600 mbar, however, we find a cold layer of about 45 K at Southern polar regions (-80{\deg}) which disappears towards mid-latitudes and the equator. By probing pressure levels not easily accessible to other observing methods e.g. infrared sounding, submillimeter observations offer a new view of the complex thermal structure in the upper troposphere and lower stratosphere of the Icy
Giants.
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All authors Óscar Carrión-González, Raphael Moreno, Emmanuel Lellouch, Thibault Cavalié, Sandrine Guerlet, Gwenaël Milcareck, Noé Clément, Jérémy Leconte
Solar and Stellar Astrophysics
Facing the phase: Gravity-mode offset and buoyancy glitches in red–giant branch stars
T. van Lier, J. Müller and S. Hekker
With the increasing precision of asteroseismic observations, it becomes possible to reliably measure oscillation properties of an increasing number of
stars. Interpreting these measurements requires a good theoretical understanding of their link to fundamental
stellar properties. In this study, we focus on the phase offset in
gravity(g)-mode frequencies, which is imprinted in the asymptotic eigenfrequency pattern of mixed dipole modes observed in red–
giant branch
stars. We aim to unravel its physical origin and thus enable an informed interpretation of observations. Using
stellar models, we empirically test the contribution of the g-mode offset $\varepsilon_\mathrm{g}$ (which is related to the wave reflection at cavity boundaries and commonly considered to be the dominant phase term) and glitches to the total observable phase. We find that, additionally to $\varepsilon_\mathrm{g}$, buoyancy glitches play an important role in the correct interpretation of the g–mode frequency phase. We further find that glitches in the evanescent zone also contribute to the phase, and we present a formalism to quantify this contribution. Finally, we propose a modification to the widely used formula for $\varepsilon_\mathrm{g}$. The g–mode frequency phase carries more information than previously considered. It has large analytic potential to study not only the reflection properties of the buoyancy cavity, but also the properties of glitches in the Brunt-Väisälä frequency.
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