High Energy Astrophysical Phenomena
Magnetic field and plasma number density from radio and millimeter core measurements in AGN jets
E.E. Nokhrina, A.P. Lobanov, A.Yu. Istomin et al. (+1 more)
Understanding the mechanism for launching relativistic jets in active
galactic nuclei relies upon measuring the
magnetic field strength and emitting
plasma number density, tracing their
evolution along the jet, and determining the relation between their rest frame energy densities. This can be achieved using measurements of the size and brightness temperature of the compact region at the jet base (the “core”) obtained with very long baseline interferometry (VLBI) across frequencies from 2 to 230~GHz. We develop a framework for independently estimating the
magnetic field B* and the emitting
plasma number density N* as functions of the jet width $d$, using multifrequency VLBI observations of the core size and brightness temperature. We apply the standard model of self-absorbed synchrotron emission, assuming power-law dependencies of the jet Doppler factor, Lorentz factor,
magnetic field strength, and
plasma density on the jet width. For an arbitrary jet boundary shape, we derive the dependencies B*(d) and N*(d), and explore a possible relation between the rest frame energy densities of the
magnetic field and the emitting
plasma. Analysis of core widths and brightness temperatures measured at multiple frequencies points to the possible presence of a
magnetic flux decay and effective
plasma acceleration within the observed cores at least in some sources of the sample.
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All authors E.E. Nokhrina, A.P. Lobanov, A.Yu. Istomin, V.A. Frolova
Astrophysics of Galaxies
Interstellar filament detection and characterization: methods and implications for studies of magnetized interstellar medium
Dana Alina
Filamentary structures are ubiquitous in the interstellar medium and play a key role in the
evolution of molecular clouds and
star formation. Their morphology and relative orientation with respect to
magnetic fields have been widely used as a diagnostic of magnetohydrodynamic processes,
turbulence, and gravitational
accretion. In recent years, the growing availability of large continuum, spectroscopic, and polarization data stimulated the development of various filament detection techniques. In this review, we present a systematic overview of filament detection methods applied to observations of the interstellar medium. We classify the existing approaches into methodological categories, discuss underlying principles, illustrate their application on a same observational field, discuss limitations and advantages, in particular with respect to the studies of the relative
alignment between
magnetic fields and filaments. We conclude with presenting a point of view on the perspectives for filament studies in the era of ever-growing astronomical data volume.
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Cosmology and Nongalactic Astrophysics
The Large-Scale Structure of the Universe through the SKA lenses
Virginia Cuciti, Surajit Paul, Viral Parekh et al. (+11 more)
The large-scale distribution of
galaxies in the Universe forms an intricate, interconnected network known as the
cosmic web. Cosmological simulations within the standard Lambda-CDM framework successfully reproduce this filamentary structure and predict that the nodes and filaments are filled with tenuous
plasma at temperatures ranging from 10^5-10^8 K. The hottest and luminous
plasma in the nodes corresponds to the intra-cluster medium, while the cooler, more tenuous, gas extends along filaments and cluster outskirts.
Galaxies and
galaxy groups form and flow along these filaments before accreting onto
galaxy clusters (the nodes), outlining the dynamical
evolution of large-scale structures. During this process, an enormous amount of energy is dissipated through complex
plasma processes that can be traced by
radio emitting electrons. Despite strong theoretical support for this picture, observational validation remains limited. While massive clusters have been widely detected across various wavelengths, cluster outskirts and the diffuse intergalactic medium within filaments has remained elusive due to their extremely faint emission. The advent of highly sensitive
radio facilities such as LOFAR, uGMRT, and MeerKAT has recently enabled a few successful detections of emission from comparatively denser regions of the
cosmic-web. These include
radio megahalos, permeating the entire cluster volume, as well as bridges of
radio emission connecting cluster pairs. In this chapter, we summarize current theoretical insights into the
cosmic web, discuss observational strategies and recent discoveries, and highlight how the forthcoming Square Kilometre Array (SKA) is expected to transform our understanding of the
cosmic web and the distribution of
baryons in the Universe.
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All authors Virginia Cuciti, Surajit Paul, Viral Parekh, Franco Vazza, M. Brüggen, Prateek Gupta, Sameer Salunkhe, S. Sankhyayan, A. Bonafede, T. Akahori, G. Brunetti, R. Cassano, M. Hoeft, R. Kale
Astrophysics of Galaxies
A simulation-based analytic model of radio galaxies II: self-consistent radiative losses
M. J. Hardcastle
The
evolution of the
radio properties of high-
redshift radio-luminous active
galactic nuclei is well known to be strongly affected by inverse-Compton losses which increase rapidly at higher
redshifts due to the higher energy density in the
cosmic microwave background radiation. Dynamical models of these sources, however, generally neglect the effects of radiative losses on the dynamics and energetics of the sources themselves. In the framework of an analytical model I developed in a previous paper, I show that the assumption that these losses can be neglected becomes unsafe at high
redshifts. The effects on the source dynamics and energetics can result in significantly lower predicted luminosities for high-
redshift sources in both
radio (synchrotron) and X-ray (inverse-Compton) bands. Modelling of the population of these powerful sources needs to take account of these results in order to infer jet powers at high
redshift, and also to make a correct prediction of the number of sources that may be available to provide a background for studies of the 21-cm forest.
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High Energy Astrophysical Phenomena
Multi-wavelength Emission Modeling from Accretion Flows around Isolated Black Holes Including Magnetic Flux Transport
Takumi Koshimizu and Shigeo S. Kimura
Isolated
stellar-mass black holes (IBHs) are expected to be abundant in the Milky Way, yet their electromagnetic signatures remain largely undetected. We investigate the detectability of IBHs in molecular clouds using a 1D, multi-wavelength emission model that incorporates
magnetic flux transport controlled by the
magnetic Prandtl number $P_m$. We find that magnetically arrested disks (MADs) form for $P_m\gtrsim 1$, where the
magnetic flux threading the black hole is in a saturation value. On the other hand, MAD formation is restricted to a limited parameter range for $P_m<1$, In our model, outer parts of
accretion disks, around 100 gravitational radii, efficiently emit infrared
photons detectable by WISE. This feature is not captured by the conventional one-zone model. X-ray emission depends strongly on $P_m$; For $P_m=1$ where MAD is formed, X-ray emission is dominated by nonthermal radiation, whereas inverse Compton emission becomes dominant for $P_m=0.5$ where the
magnetic field is weaker than the saturation value. X-ray detection is plausible if they are in dense molecular-cloud filaments for $P_m\ge1$, although it is challenging for $P_m< 1$. These results demonstrate that
magnetic flux transport plays a key role in shaping the multiwavelength observational signatures of IBHs.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Landau-Zener formula and resonant axion conversion in neutron star magnetospheres
Matti Heikinheimo, Topi Sirkiä and Kimmo Tuominen
We investigate the Landau-Zener description of resonant
axion-
photon conversion in
neutron star magnetospheres. We find that this picture often fails for
axion conversions to millimeter-to-optical band
photons due to the characteristic resonance width exceeding the size of the conversion region. This comparison of scales yields a simple criterion for evaluating the validity of the Landau-Zener formula. We verify this criterion numerically, and show that when invalid, the Landau-Zener conversion probability may significantly deviate from the numerical result. In light of these findings, we revise constraints on
axions from
neutron star optical-band polarization searches.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The unavoidable de Sitter fate of a scale-invariant Universe
Chiara Cecchini and Massimiliano Rinaldi
We consider a very general scale-invariant scalar-tensor theory of
gravity and its flat cosmological solutions. We show that any stable configuration with non-degenerate gravitational dynamics carries a non-vanishing cosmological constant, unless the quartic self-coupling of the scalar field vanishes. Since this condition is not protected against radiative corrections, a residual cosmological constant is expected as a generic and robust prediction of this class of theories. This result suggests that dark energy may be a natural consequence of an early scale-invariant phase of the Universe.
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Solar and Stellar Astrophysics
Role of SKA in Advancing Remote Measurements of Magnetic Fields of Solar Coronal Mass Ejections
Devojyoti Kansabanik, Surajit Mondal, Shaheda Begum Shaik et al. (+13 more)
Coronal Mass Ejections (CMEs) are large expulsions of magnetized
plasma from the Sun into interplanetary space and are the primary drivers of extreme space weather variations. The strength and
topology of CME
magnetic fields largely determine their impact on Earth. Although visible-light coronagraphs routinely observe CMEs and provide their
geometric and kinematic properties, they cannot directly measure CME vector
magnetic fields. These fields evolve from initiation through the inner heliosphere due to interactions with other CMEs, coronal structures, and the ambient
solar wind, leading to significant structural deformation. Such
evolution complicates predictions of the CME
magnetic field at Earth. Accurate measurements of CME
magnetic fields in the corona and heliosphere are therefore essential for advancing space weather
forecasting.
Radio observations spanning MHz to GHz frequencies provide a powerful remote-sensing approach for measuring CME
magnetic fields from the ground. Recent observations with Square Kilometre Array (SKA) precursors and pathfinder instruments, as well as other new-generation facilities, have demonstrated the potential of these
radio techniques for CME
magnetic-field diagnostics. At the same time, these studies have highlighted several limitations of current instruments. The higher sensitivity, wider instantaneous bandwidth, and broader frequency coverage of the SKA will open a new observational window, enabling these techniques to be fully exploited for constraining SpWx models and improving predictive accuracy. However, such observations are non-standard and require special consideration in scheduling, calibration, and imaging. Developments achieved with SKA precursors and pathfinders are paving the way for robust CME
magnetic-field measurements with the SKA.
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All authors Devojyoti Kansabanik, Surajit Mondal, Shaheda Begum Shaik, Peijin Zhang, Puja Majee, Angelos Vourlidas, John Morgan, Divya Oberoi, Anshu Kumari, Alec Thomson, Bin Chen, Carl Shneider, Hariharan Krishnan, Kamen Kozarev, Sneha Pandit, Vanessa Moss
High Energy Astrophysical Phenomena
Scattering of Strong Radio Waves by Particles in Strongly Magnetized Plasmas and Implications for Fast Radio Bursts
Yuanhong Qu and Pawan Kumar
Fast
Radio Bursts (FRBs) are millisecond-duration
radio transients that are widely believed to originate within magnetar magnetospheres. Large-amplitude
radio waves associated with FRBs propagate through strongly magnetized
plasmas, where nonlinear scattering can affect their propagation. By solving the relativistic motion of a single particle interacting with electromagnetic waves of arbitrary polarization and propagation angle $\theta_B$, we compute the scattering cross section and the corresponding optical depth. The scattering cross section of the O-mode can exceed that of the X-mode when $a\sin\theta_B < \omega_B/\omega$, and becomes comparable to that of the X-mode when $a\sin\theta_B > \omega_B/\omega$, where $\theta_B$ is the angle between the wave vector and the background field. In the strongly magnetized and quasi-parallel limits, the cross sections asymptotically recover the linear regime scalings and are strongly suppressed by relativistic particle motion, leading to optical depths well below unity. We also show that
curvature radiation losses of O-mode waves are strongly suppressed for quasi-parallel propagation, allowing them to escape from the magnetosphere at moderate multiplicities. We propose that Alfvén waves excited by magnetar crust quakes can reach amplitudes comparable to the background
magnetic field, thus straightening field lines and reducing $\theta_B$. This geometrical
alignment enhances the ability of FRBs to freely propagate through the open field line region. These results suggest that large-amplitude waves propagating quasi-parallel to open
magnetic field lines can avoid significant single-particle scattering losses, providing a possible condition for their escape.
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High Energy Astrophysical Phenomena
Estimation of black hole spins in low-mass AGNs and comparison with other types of AGNs
M.Yu. Piotrovich, S.D. Buliga and T.M. Natsvlishvili
We estimated the
spins of a sample of 58 low-mass AGNs. Analysis of the obtained
spins showed that they decrease with increasing SMBH mass, leading us to hypothesize that mergers and/or chaotic
accretion are the primary mechanisms for mass growth. In this regard, we proposed a more general hypothesis about the
evolution of AGNs. We assume that early low-mass SMBHs have high
spins, then, during their
evolution, the
spins initially decrease and then begin to increase, with the rate of increase gradually slowing.
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Astrophysics of Galaxies
Unveiling the properties of galaxy cores excavated by supermassive black hole binaries with SHARP
E. Bortolas, E. Portaluri, E. Dalla Bonta' et al. (+3 more)
Massive black hole (MBH) binaries form as a result of
galaxy mergers and can coalesce into a single MBH by emitting gravitational waves detectable by LISA and
pulsar timing array campaigns. Although electromagnetic observations of bound MBH binaries are extremely challenging, an indirect signature of their passage is the core scouring: a bound binary shrinks by ejecting nearby
stars, creating a flat
stellar density core of the size of the binary influence radius. Through this mechanism,
stars on radial orbits are preferentially ejected, resulting in a central tangential anisotropy in the velocity field of
stars that can be identified via IFU observations. At present, the sample of
galaxies with such properties is limited by instrument resolution to the closest
giant ellipticals within the nearest ~100 Mpc. The SHARP-VESPER IFU and MICADO+MORFEO instruments can work in concert to detect both these features: their unprecedented spatial resolution can allow us to detect central scourings with sizes above ~500 pc in principle up to reionization; smaller cores of ~150 pc can be detected up to z~0.14, encompassing a volume that is more than 40 times the one available at present. In addition, they can enable the search for these features in smaller
galaxies, enhancing by a factor 30 the volume over which we can search for pc-size cores around 1-10 million
solar mass MBHs. The fraction of scoured
galaxies, combined with their kinematic and morphological properties, carry information on the amount of merging binaries, their masses and typical environment, thus knowing this will be fundamental to complement the forthcoming gravitational wave data.
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All authors E. Bortolas, E. Portaluri, E. Dalla Bonta', C. Arcidiacono, P. Severgnini, A. Gualandris
High Energy Astrophysical Phenomena · Cross-listed from physics.space-ph
David Pelosi, Fernando Barão, Bruna Bertucci et al. (+3 more)
The modulation of
galactic cosmic rays, driven by the
evolution of the heliospheric
magnetic field, strongly influences the intensity of
cosmic rays reaching near-Earth space. Characterizing this process is crucial both for advancing our understanding of
cosmic-ray transport and for assessing radiation exposure and related hazards in space environments. Here we present a newly developed
forecasting framework built on a numerical description of charged particle transport in the heliosphere and its dependence on
solar activity, designed for the long-term
forecasting of
galactic cosmic-ray fluxes. It solves a one-dimensional, spherically symmetric form of the Parker transport equation, including
diffusion,
solar-wind advection, and adiabatic energy losses. The model has been validated using multi-species flux measurements from space-based experiments: PAMELA, AMS-02, and ACE. Its strategy is based on
Hilbert-Huang transform filtering and cross-correlation between delayed
solar proxies and effective model parameters. Our charge-sign- and
rigidity-dependent parametric description of the
diffusion-advection processes yields good overall agreement with the data, as shown by the reconstruction uncertainty. The robustness of this approach is validated across a broad set of multichannel
datasets covering different particle species, energy ranges, and phases of
solar activity, supporting its applicability to space radiation monitoring and
forecasting. Furthermore, when coupled with
solar-proxy
forecasting models, it enables decadal-scale predictions of
galactic cosmic-ray fluxes, thereby supporting long-term planning and radiation-risk assessment for future space missions.
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All authors David Pelosi, Fernando Barão, Bruna Bertucci, Emanuele Fiandrini, Miguel Orcinha, Nicola Tomassetti
Cosmology and Nongalactic Astrophysics
One Feature, Three Clocks: Phase-Locked Gravitational Waves, Primordial Black Holes, and Non-Gaussianity from Periodic Warm Inflation
Mayukh R. Gangopadhyay
A shift-symmetric inflaton dissipating into a thermal bath couples to that bath periodically, so its friction oscillates as the field rolls. We follow what this does to warm inflation when a thermal channel opens midway through the rolling: the friction surges, and the
curvature spectrum grows a sharp, log-periodically modulated peak at small scales while the CMB scales stay untouched. It saturates
Primordial Black Holes (PBHs) formation in the asteroid-mass window, where the PBHs can make up an order-unity fraction of the dark matter, and it sources a scalar-induced gravitational-wave background in two bands at once – a peak at $h^2\Omega_{\rm GW}\simeq10^{-8}$ near $3$~mHz for LISA, and a second band at $h^2\Omega_{\rm GW}\sim10^{-11}$ from deci-hertz to a hundred hertz, within reach of DECIGO and the Einstein
Telescope, fed by the friction's continued growth toward smaller scales. And a separate-universe computation places its equilateral bispectrum a quarter cycle ahead of the power spectrum – an offset fixed by the running of the spectrum and so robust to the equilateral-shape coefficient. The two GW bands carry the same underlying log-period and freeze-out phase to leading order, and the bispectrum is expected to share them: a modulation seen at two widely separated frequencies, plausibly accompanied by a $\pi/2$-shifted bispectrum, is not something a single-scale feature can fake. Because the feature is localized in the field, it imprints the same log-periodic structure on multiple observables, tying the gravitational-wave bands, black-hole mass, and bispectrum phase to a single underlying clock. We derive the freeze-out transfer function in closed form and use it to cap the first two harmonics at one quarter, and we show that the high-frequency band is itself bounded by PBHs overproduction, which turns it into a constraint on how far the friction can grow.
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Solar and Stellar Astrophysics
Impact of Sub-2.5 MeV 12C+12CResonances on the Production of Elements from C to Pd in Core-Collapse Supernovae
L. Roberti, S. Palmerini, A. Falla et al. (+10 more)
We explore the impact of a more efficient 12C+12C reaction on the structure and nucleosynthesis of massive
stars. We calculate non-rotating
stellar models with initial masses of 15, 16, 18, 20, 22, 25, and 40 Msun and
solar metallicity by means of the FRANEC code. Furthermore, we simulate the core-collapse
supernova of these models with the thermal bomb technique, using two different approaches to inject the thermal energy into the pre-
supernova structure. Our results show that a more efficient 12C+12C rate extends the duration of the central carbon burning phase, developing more massive convective cores and leading to a different and less compact pre-
supernova structure with respect to models calculated with a standard 12C+12C rate. These structural differences significantly impact nucleosynthesis. In particular, an increased rate enhances the production of elements heavier than Fe, produced by the s-process nucleosynthesis and driven by the more efficient activation of the 13C($\alpha$,n)
neutron source in the early carbon burning shells. We find that the differences in the chemical composition of the core-collapse
supernova ejecta are primarily determined by these pre-
supernova structural changes, which dominate over the effects of different explosion prescriptions.
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All authors L. Roberti, S. Palmerini, A. Falla, L. Boccioli, F. Andreis, A. Chieffi, M. La Cognata, M. Limongi, M. Masci, A. Nurmukhanbetova, A. Oliva, R. Spartá, A.Tumino
Astrophysics of Galaxies
Boosting Water Maser Studies in AGN with the SKA
Andrea Tarchi, Paola Castangia and Elisabetta Ladu
Extragalactic water maser sources are unique tools to derive fundamental physical quantities of the host
galaxies. In nearby and distant active
galactic nuclei (AGN), water masers are used to determine the geometry of
accretion disks around super-massive black holes, precise black hole masses, and standard-candles-independent distances to the host
galaxy. In addition, they allow detailed studies of the interaction between
nuclear jets/
outflows and the interstellar medium, providing clues on AGN feedback mechanisms. So far, however, extragalactic maser searches have yielded detection rates of few percent, and only relatively few maser sources have been found, mostly in the nearby Universe. Because of its unprecedented sensitivity, the SKA will allow to significantly increase the number of known water maser sources especially in the more distant Universe. This will lead to the chance of performing statistically-relevant studies of the maser phenomenon (and its occurrence), derive extragalactic maser luminosity functions and, ultimately, to perform the aforementioned studies for larger samples and up to cosmological distances. In this Chapter, we will provide a quantitative analysis of the expected number of new extragalactic water maser sources already at the reach of the SKA-Mid
telescope (in AA4 configuration) through targeted and blinds surveys. In addition, we will discuss the main requirements for the upcoming SKA design, in terms of baselines and frequency coverage, that may maximize the exploitation of such wealth of new targets, allowing a true step forward in AGN-related maser science.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Cooling of Hybrid Stars with a 2SC+$<dd>$ Phase
Tsuneo Noda, Akira Dohi, Nobutoshi Yasutake et al. (+3 more)
Recently, Fujimoto, Fukushima & Weise (2019) have proposed a new colour-superconductive state, 2SC+$<dd>$ phase, which can be smoothly connected to the low-density
baryon superfluidity in contrast to the 2SC phase. In this scenario, the
neutron ${}^3P_2$ superfluidity on the low-density side of the phase transition is inherited by unpaired $d$-
quarks in the 2SC phase on the high-density side. Since this could be realized in hybrid
stars (
neutron stars containing hadronic and
quark matter), the 2SC+$<dd>$ phase may change the properties of
neutron stars compared to the traditional 2SC phase. In this work, we study the thermal
evolution of hybrid
stars with the 2SC+$<dd>$ phase for the first time. We find that NSs with the 2SC+$<dd>$ phase become hotter than those with the 2SC phase, and are close to the CFL phase. The ${}^{3}P_2$ superfluidity plays an important role in cooling curves with not the 2SC but 2SC+$<dd>$ phases due to the suppression of
quark $\beta$ decay. We therefore point out that, if the scenario of 2SC+$<dd>$ phase is true, it could be specified through low-temperature observations such as Vela, 3C58, Vela Jr., and Vela-like
pulsar.
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All authors Tsuneo Noda, Akira Dohi, Nobutoshi Yasutake, Huan Chen, Toshiki Maruyama, Toshitaka Tatsumi
Astrophysics of Galaxies
GSED: The Galactic Stellar Extinction Database
Baisong Zhang, Bingqiu Chen, Dongwei Fan et al. (+9 more)
Reliable extinction correction is essential for nearly all astrophysical studies within the
Galaxy. We present the
Galactic Stellar Extinction Database (GSED, https://nadc.china-vo.org/data/gsed/), a homogenised database that unifies six representative 3D extinction
datasets under a common $E(B-V)$ and parallax-distance baseline. A six-layer multilayer perceptron is designed to correct the systematic differences in both extinction and distance across the heterogeneous input catalogues. Applying the trained models yields a catalogue of over 1.9 billion homogenised entries, which is built into a publicly accessible, real-time query service: a user supplies a coordinate and a search radius, the system retrieves the data, fits the distance–extinction relation, returns $E(B-V)$ together with $E(G_{\rm BP}-G_{\rm RP})$ and $A_V$, and allows the raw catalogue and the fitted curve to be downloaded. By delivering extinction as raw
stellar measurements rather than voxelised map products and retaining the capacity to incorporate future
datasets, GSED provides a flexible, traceable, and extensible new tool for
Galactic extinction correction and
dust-structure studies.
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All authors Baisong Zhang, Bingqiu Chen, Dongwei Fan, Haibo Yuan, Pinjian Chen, Helong Guo, Lin Zhang, Baokun Sun, Xingzhu Zou, Lunwei Zhang, Yanan Cao, Longfei Ding
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Establishing Compactness as a Population Observable in Gravitational-Wave Astronomy
Shrobana Ghosh, Charlie Hoy, Mark Hannam et al. (+1 more)
Classically, black holes (BHs) are the most compact objects predicted in nature with C=0.5 in the Schwarzschild limit; C is defined as the mass-to-radius ratio in
geometric units. In this work we perform a novel measurement on the nature of putative BH mergers in the gravitational wave (GW) data by directly probing the binary's closest approach through an effective compactness parameter. We confidently show all such high-significance signals in GWTC-3 are consistent with the BH hypothesis for the first time. Our hierarchical analysis yields $C_{\rm eff} = 0.5^{+0.3}_{-0.1}$, and we further limit the merger rate of low-compactness exotic binaries to $< 0.7\,{\rm Gpc}^{-3}\,{\rm yr}^{-1}$. This work establishes compactness as a key observable in GW astronomy.
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All authors Shrobana Ghosh, Charlie Hoy, Mark Hannam, Frank Ohme
Cosmology and Nongalactic Astrophysics
Running into tension: primordial black holes from ultra-slow-roll inflation, spectral running, and the Hubble tension
Miguel A. Sabogal, Antonio J. Iovino and Sunny Vagnozzi
Single-field ultra-slow-roll (USR) inflation is among the most studied mechanisms for
primordial black hole (PBH) formation. When a non-stationary inflection point close to CMB scales is present, these models predict a negative spectral running ($\alpha_s<0$), whose magnitude increases with the PBH mass. This is in tension with recent hints for positive running from Atacama Cosmology
Telescope (ACT)
Cosmic Microwave Background (CMB) data. However, inflationary parameters inferred from CMB data are sensitive to the assumed pre-recombination expansion history, which is precisely where new physics motivated by the Hubble tension should operate. Focusing on
axion-like early dark energy (EDE) as a
benchmark, we investigate the effect of such pre-recombination new physics on $\alpha_s$, and hence on the viability of USR PBH models, in light of state-of-the-art CMB data from Planck, ACT, and the South Pole
Telescope, together with
Baryon Acoustic Oscillation data from DESI DR2. Our analysis therefore provides an updated set of constraints on $\alpha_s$ and the running of the running $\beta_s$. For most
dataset combinations, moving from $\Lambda$CDM to EDE increases the inferred $\alpha_s$: once the acoustic angular scale $\theta_s$ is fixed, EDE increases the
diffusion-to-acoustic angular scale ratio $\theta_d/\theta_s$, and the shift in $\alpha_s$ compensates this extra damping by increasing small-scale power. In this sense, tension calls for tension: taking the Hubble tension seriously as an indication for new physics strengthens the challenges faced by USR PBH models. More broadly, our analysis stresses that inflationary model selection using CMB-inferred inflationary parameters such as $n_s$ and $\alpha_s$ may be premature, especially until the Hubble tension, and more generally the pre-recombination expansion history, is understood.
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Instrumentation and Methods for Astrophysics
Combining a Diffraction-Limited Coronagraph with Fiber Nulling: A Demonstration of Serially Coupling Different Nullers
Satoshi Itoh, Taro Matsuo, Reiki Kojima et al. (+3 more)
We present experimental results of an efficient small-IWA ($\sim$1 $\lambda/D$) high contrast imaging approach realized by co-optimizing a coronagraph front-end with a fiber nulling 2nd stage. The setup includes the one-dimensional diffraction-limited coronagraph (1DDLC) and Parity Fiber Nuller (PFN). The 1DDLC has promising features (binary nuller, small inner working angles (IWAs)). Although the 1DDLC has the 2nd/4th-order sensitivity to spectral bandwidth and tilt aberrations, it outputs
stellar leak due to wavelengths other than the design wavelength only as a flat wavefront on the Lyot-stop plane, preserving the same complex amplitude profile as an on-axis point source. The PFN after the 1DDLC erases the leak from the 1DDLC. For the wavelength 6% less than the coronagraph's design-center wavelength, we confirmed the contrast mitigation ability of $3.5\times10^{-5}$, which is about 1/20 times the value of the case with only 1DDLC, suggesting that the combined system works robustly against the broad spectral bandwidth. Future work needs to address the demonstration of the anticipated broadband robustness for the contrast level lower than about $10^{-5}$.
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All authors Satoshi Itoh, Taro Matsuo, Reiki Kojima, Motohide Tamura, Takahiro Sumi, Oliver Guyon
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Relativistic magnetohydrodynamics from kinetic theory
Khwahish Kushwah
This thesis develops a kinetic-theory framework for relativistic dissipative magnetohydrodynamics under strong electromagnetic fields, motivated by
quark-
gluon plasma in heavy-ion collisions. Starting from the relativistic Boltzmann-Vlasov equation and using the method of moments within the 14-moment approximation, it derives causal second-order hydrodynamic equations for relativistic
plasmas with increasing generality. The work first review relativistic dissipative hydrodynamics and its kinetic foundations, emphasizing the need for Israel-Stewart-type transient theories to preserve causality and stability. Electromagnetic fields are then introduced at the microscopic level, where the Lorentz force modifies the moment hierarchy and produces anisotropic transport effects absent in field-free fluids. Next, it develops relativistic dissipative magnetohydrodynamics for a non-resistive two-component
plasma of oppositely charged particles. Here, the
magnetic field couples the dissipative sectors of the two species, generating relative dissipative currents and coupled shear dynamics. For Bjorken expansion, the theory predicts damped oscillations in the transverse shear sector associated with cyclotron motion. Finally, the thesis treats the resistive two-component case, where the electric field evolves dynamically and couples to charge
diffusion and shear stress. The resulting theory reveals current-shear feedback, transient electromagnetic generation of momentum anisotropy, and underdamped dissipative oscillations. Applications to homogeneous and Bjorken-expanding
plasmas show how resistive and electromagnetic effects modify
evolution beyond standard hydrodynamics. Overall, the thesis extends relativistic dissipative hydrodynamics to magnetized and resistive
plasmas, providing a microscopic foundation for future studies of strongly magnetized
quark-
gluon plasma and astrophysical systems.
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Cosmology and Nongalactic Astrophysics
Cosmological Viability of Exponential Infrared $f(T)$ Gravity
Mahmoud Hashim, Eleonora Di Valentino, Jackson Levi Said et al. (+1 more)
We investigate the cosmological viability of exponential infrared $f(T)$ teleparallel
gravity using current cosmological observations. This framework realizes late-time
cosmic acceleration through torsional modifications of
gravity without enlarging the six-parameter cosmological parameter space of spatially flat $\Lambda$CDM, and admits two distinct solution branches: a phantom-like model (Model I) and a model featuring a negative-to-positive transition in the effective torsional dark-energy density (Model II). We constrain both branches using CMB observations from Planck, ACT, and SPT together with DESI BAO and Pantheon+ Type Ia
supernovae. We find that the principal branch (Model I) alleviates the Hubble tension relative to $\Lambda$CDM, but remains statistically disfavoured by the combined
dataset. The secondary branch (Model II) is decisively ruled out. We show that the failure of Model II originates from the interplay between background and perturbation constraints: once late-time distance measurements constrain the expansion history, the model becomes overconstrained, forcing correlated shifts in $\Omega_{\rm m}h^2$, $A_s$, $n_s$, and $\tau_{\rm reio}$, degrading the fit to the CMB damping tail and driving the optical depth to unphysical values. Our results demonstrate that perturbation observables provide stringent and complementary tests of teleparallel
gravity beyond the background expansion history.
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All authors Mahmoud Hashim, Eleonora Di Valentino, Jackson Levi Said, Waleed El Hanafy
Astrophysics of Galaxies
Dissecting the Obscured Core of GN20: an Active Galactic Nucleus Outshone by Young Stars
M. Hamed, L. Colina, P. G. Pérez-González et al. (+17 more)
We investigate the relative contributions of
star formation and AGN activity to the total energy budget of GN20, one of the most luminous dusty
star-forming
galaxies known at $z>4$, through spatially resolved spectral energy distribution decomposition. We perform
Bayesian SED fitting with CIGALE on two spatially distinct apertures: the
nuclear core (r=0.14", $\sim$1kpc physical) and the full
galaxy (r=1.4", 9.9 kpc), combining JWST/NIRCam and MIRI broadband imaging, JWST/NIRSpec PRISM IFU pseudo-continuum photometry spanning 42 wavelength bins across rest-frame $0.12$–$1.05\mu$m, and archival HST and millimeter interferometry data from NOEMA and PdBI. The integrated SED is dominated by
stellar-heated
dust, with only a marginal AGN contribution at
galaxy-wide scales ($f_\mathrm{AGN}^\mathrm{int}=0.09\pm0.02$). The
nuclear core, however, requires a significant AGN component ($f_\mathrm{AGN}=0.34\pm0.05$) to account for a mid-infrared excess at rest-frame $\sim$2.5–3.6$\mu$m characteristic of AGN-heated
torus dust. The AGN accounts for $\sim34\%$ of the
nuclear infrared luminosity but only $\sim9\%$ of the total integrated $L_\mathrm{IR}$, explaining its weak signature in integrated diagnostics and its consistency with existing upper limits from Spitzer spectroscopy. The inferred black hole mass places GN20 within the local $M_\mathrm{BH}$–$M_\mathrm{bulge}$ relation at the Eddington limit, and in the overmassive regime at sub-Eddington
accretion rates, suggesting early and rapid black hole assembly concurrent with the dominant starburst. GN20 exemplifies a class of systems where
nuclear-scale SED decomposition, enabled by the angular resolution and infrared sensitivity of JWST, is the only means to uncover a buried AGN overwhelmed by
galaxy-wide
star formation.
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All authors M. Hamed, L. Colina, P. G. Pérez-González, J. Álvarez Márquez, A. Crespo Gómez, L. A. Boogaard, A. Bik, H. Übler, S. E. I. Bosman, A. Alonso-Herrero, M. Perna, S. Arribas, L. Ulivi, M. Annunziatella, L. Costantin, A. Labiano, C.-L. Liao, C. Prieto-Jiménez, P. van der Werf, F. Walter
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
A parametric signal plus noise inference framework for short duration non-Gaussian noise transients
Charlie Hoy, Ruxandra Bondarescu, Andrew Lundgren et al. (+1 more)
Gravitational waves are now routinely detected with ground-based observatories, and, through a process known as
Bayesian inference, their source properties are inferred. However, terrestrial noise artifacts, often referred to as glitches, commonly overlap astrophysical signals. This invalidates a fundamental assumption of gravitational wave analyses: the noise is no longer stationary and Gaussian. As a result, traditional techniques can provide biased inferences in realistic data. One method for mitigating the effect of glitches is to jointly analyse both the signal and noise in a single framework. In this work, we introduce bilby-antiglitch to infer the astrophysical signal properties in non-Gaussian noise. By additionally including a quasi-physical glitch model to describe short duration non-Gaussian noise transients, we show that unlike traditional techniques, we infer the true source properties of simulated signals contaminated with loud glitches. We also show that bilby-antiglitch prevents false violation claims of General Relativity, and validates the exceptional nature of gravitational wave signals in spurious data.
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All authors Charlie Hoy, Ruxandra Bondarescu, Andrew Lundgren, Laura K. Nuttall
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Distance duality relation in symmetric teleparallel gravity
Rocco D'Agostino
In this work, we investigate the distance duality relation (DDR) in symmetric teleparallel theories, where
gravity is mediated by nonmetricity. Starting from the general metric-affine formulation and adopting the geometrical optics approximation, we show that the standard Etherington reciprocity relation remains valid in the presence of nonmetricity when electromagnetism is minimally coupled and the
photon number is conserved. We then extend the analysis to a class of $f(Q)$ theories with a nonminimal coupling between the electromagnetic field and the nonmetricity scalar. We demonstrate that such an interaction modifies the conservation of the
photon number current, leading to a dynamical violation of the DDR. Focusing on a homogeneous and isotropic spacetime background in the coincident gauge, we derive a generalized DDR formula that directly relates observational distance measures to the Hubble expansion rate. Furthermore, we discuss the link between the deviations from Etherington's relation and variations of the effective fine-structure constant. Specific illustrative examples of the coupling function are also analyzed, showing that phenomenologically viable models predict only small deviations from the standard DDR. Our results provide a unified framework to distinguish between the
geometric and dynamical origins of DDR violations, opening new avenues for testing non-Riemannian
gravity with future high-precision astrophysical and cosmological observations.
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High Energy Astrophysical Phenomena
Multi-band power color-color diagrams of three black hole X-ray binaries observed with Insight-HXMT
Shao-Feng Liu, Long Ji and Yanan Wang
Power color-color diagrams (PCCDs) provide a useful diagnostic tool for studying the
evolution of outbursts in black hole X-ray binaries. In this paper, we present power color-color diagrams of three sources (MAXI J1348-630, MAXI J1820+070 and Swift J1727.8-1613) observed with Insight-HXMT in a wide energy range of 2-80 keV. We compared the hue regions defined by RXTE, which are associated with different spectral states, with the Insight-HXMT results. We find that, for hard and hard-intermediate states, the trajectories of Insight-HXMT in the power color-color diagrams are generally consistent with those of RXTE. In the soft and soft-intermediate states, weak variability generally prevents robust hue constraints. Nevertheless, a few points in MAXI J1348-630 deviate from the RXTE-defined regions, possibly because of averaged variable power spectra and the presence of a type-A QPO. The trajectories of MAXI J1348-630 and MAXI J1820+070 exhibited roughly consistent patterns over different energy bands, whereas Swift J1727.8-1613 was an exception during its very high state, caused by an additional low-frequency component in the low-energy band. We found that the very high state can be identified through the power color-color diagram, exhibiting a hue similar to that of the hard-intermediate state but not forming a loop pattern. We also investigated the relationship between hue and hardness and found that, although they are generally anti-correlated, they provide consistent timing for the spectral state transitions.
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Earth and Planetary Astrophysics
The HST/WFC3 Transmission Spectrum of AU Mic b Part I: An Atmosphere Obscured by Contamination and Systematics
William C. Waalkes, Peter Gao, Elisabeth Newton et al. (+10 more)
Young sub-Neptune progenitors around M
dwarfs offer an excellent opportunity to probe the formation of their abundant, older cousins. At $\sim$20 Myr and only 9.7 pc away, AU Mic b is an ideal candidate for this effort, with its density and observations of escaping hydrogen pointing to a significant
primordial atmosphere. Here we present the 0.8-1.6 $\micron$ transmission spectrum of AU Mic b observed with the Wide Field Camera 3 on the Hubble Space
Telescope (HST). We find that HST experienced unstable scanning during its visits, resulting in a variable PSF that dramatically affects the orbit-to-orbit baseline of the observations. While we were able to somewhat mitigate this problem through spectral binning, the effects cannot be completely eliminated, limiting the precision of our results. Our data is further impacted by the intense
magnetic activity of AU Mic, which introduced significant rotational variability along with spot crossings and the transit light source (TLS) effect into the light curves and spectrum, respectively. Through decomposition of the out-of-transit
stellar SED, we are able to constrain AU Mic's photospheric and spot temperatures to 3891$\pm$37 and 3020$\pm$69 K, respectively, with a spot filling factor of $0.33\pm0.05$. Using
Bayesian atmospheric
retrievals, we show that the spectrum is dominated by the TLS effect with weak atmospheric constraints, with the data preferring a relatively small scale height of $<$185 km to 3$\sigma$. Extrapolation of our retrieved spectra shows that the TLS effect dominates over atmospheric features at optical and infrared wavelengths.
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All authors William C. Waalkes, Peter Gao, Elisabeth Newton, Brett M. Morris, Zachory K. Berta-Thompson, Hannah R. Wakeford, Lili Alderson, Andrew W. Mann, Peter Plavchan, Patrick J. Lowrance, Natasha E. Batalha, Eric D. Lopez, Roxana Lupu
Cosmology and Nongalactic Astrophysics
Galaxy bias renormalization: Two-loop Power Spectrum, One-loop Trispectrum and Bispectrum
Thomas Bakx, Mathias Garny, Henrique Rubira et al. (+1 more)
We present a complete treatment of fifth-order renormalized
galaxy bias at the one- and two-loop level in real space, including gradient corrections to deterministic bias operators at next-to-leading order. We then provide a complete computation of the two-loop power spectrum as well as the one-loop bispectrum and trispectrum of biased tracers, and demonstrate how to jointly model these statistics in a fully renormalized framework. These statistics also require
stochastic renormalization of products of two, three or four operators at coincidence, which we include at leading order in gradients by means of an operator product expansion. We verify that all UV limits of loop integrals are absorbed by the counterterms we consider. Upon solving the resulting renormalization group equations, we find a pronounced scale-dependence of higher-gradient bias coefficients. Since our renormalization prescription is performed manifestly at the operator level, our results can also easily be extended to higher $N$-point functions, higher loop orders and field-level analyses.
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All authors Thomas Bakx, Mathias Garny, Henrique Rubira, Zvonimir Vlah
Solar and Stellar Astrophysics
Bolometric correction for cosmologically redshifted stars with dust: an update to the YBC database
Yang Chen, Xiaoting Fu, Léo Girardi et al. (+2 more)
Observations from HST & JWST continue to reveal gravitationally magnified high-
redshift star candidates, resulting in increasing demand for accurate
stellar bolometric corrections to compare
stellar models with observational data. We update YBC
stellar bolometric correction database by incorporating bolometric corrections for cosmologically redshifted
stars, called zYBC. The bolometric corrections are derived by redshifting
stellar spectra from libraries, attenuated by extinction curves for both the
dust in the host
galaxy and the Milky Way, and followed by convolution with the transmission curves of photometric filters. Our methodology incorporates the effects due to the cosmological K-correction and the
dust. Besides the spectral libraries in earlier YBC, we add NLTE-based spectral libraries for O, B
stars, which are better suited for hot massive
stars, particularly wind-included PoWR and CMFGEN models. The database supports key photometric systems for high-
redshift studies, such as HST/WFC3, JWST/NIRCam, and CSST's MSC and MCI, and maintains the flexibility to incorporate additional photometric systems upon request. As examples, we present colors as functions of Teff at various
redshifts for several photometric systems, which exhibit non-monotonic behaviors and demonstrate the necessity for a dedicated modelling. In particular, we find that the relations show larger dispersions at high
redshift than the zero
redshift case. This indicates that the
stellar parameters of high
redshift stars can be better determined than those of their local counterparts, given their
redshifts reliably determined through other methods and their photometric data are of high enough quality for physical parameter determination through spectral-fitting. We also show the difference in the effect brought by the different amount of extinctions. zYBC represents a valuable resource for high-
redshift star research.
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All authors Yang Chen, Xiaoting Fu, Léo Girardi, Helge Todt, Alessandro Bressan
Astrophysics of Galaxies
Cosmic Rulers: Masers as Tools for Probing Structure in the Galaxy and Beyond, from AU to kpc
Kazi L. J. Rygl, Anna Bartkiewicz, Olga Bayandina et al. (+9 more)
Maser emission provides an unique window into astronomical sources across vast spatial scales - from tens to hundreds of astronomical units around protostars and evolved
stars up to kiloparsecs in distant
galaxies. These natural microwave amplifiers penetrate
dust shells in
star-forming regions, revealing the dynamics of
accretion disks and
outflows, trace envelopes and winds of evolved
stars, map
Galactic structure, while also allowing us to follow the
evolution of all these systems. Owing to their compactness and brightness masers provide precise astrometry as
cosmic rulers: measuring positions, structures and kinematics in dense regions, not easily accessible at other wavelengths. SKA-Mid will observe hydroxyl, methanol, and formaldehyde masers using bands 2, 5a and 5b, and later methylidyne radical masers in band 4. SKA-Mid's sensitivity and broad frequency coverage will support discoveries of new maser types and allow for simultaneous multi-transition and multi-species maser observations. In addition, bright masers can serve in the science verification of the SKA-Mid array during the deployment phase.
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All authors Kazi L. J. Rygl, Anna Bartkiewicz, Olga Bayandina, Andreas Brunthaler, Sandra Etoka, Simon Ellingsen, Dieter Engels, Tomoya Hirota, Arshia Maria Jacob, Jacco Th. van Loon, Alberto Sanna, Lucero Uscanga