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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 12 July

Astrophysics of Galaxies

Young star clusters in the extended UV disk of M83

M. Andersen, A. Zavagno, J. Koda et al. (+2 more)

The process of star formation in a low-metallicity environment and whether it differs from star formation in the solar neighbourhood is an open topic. Recently, CO clumps were identified within the extended ultraviolet (XUV) disk of M83 despite the low metallicity and distance from the galaxy center which allows a search for any recent star formation in the clumps. We aim to probe whether active star formation is occurring within the CO clumps in the XUV disk, and to assess its implications for star formation in such environments. We analyse deep Subaru Suprime-Cam Halpha, Hyper Suprime-Cam g, r, & i, and Gemini/FLAMINGOS 2 J and Ks band imaging to search for evidence of star formation within the ALMA-identified CO clumps. We identify sources within the CO clump contours, and we evaluate the probability that these sources are associated with the CO clumps rather than being chance alignments. Based on their magnitudes and adopting single-age stellar population models, we estimate their masses. Four of the clumps have an associated near-infrared counterpart. Based on their magnitude, color, and the general source density in the field, two of these could be chance alignments. One counterpart is associated with the most massive clump in the sample, while another is an unresolved cluster near-infrared source with an estimated age of 5 Myr and a mass of 2000 Msun. The other, an extended complex, is consistent with an age of 6Myr and a mass of 700Msun. The near-infrared photometry is sensitive to young clusters with masses down to a few hundred of Msun for a fully sampled IMF. Star formation is ongoing in a few of the CO clumps, and despite their location on the outskirts of M83, favourable conditions for star formation persist in at least a few clusters. One of the detected sources appears to be interacting with an adjacent molecular clump, which could trigger further star formation.
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All authors M. Andersen, A. Zavagno, J. Koda, S. Boissier, F. Combes

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

The KM3NeT 220 PeV event: a neutrino messenger from the grand unification scale?

Vernon Barger

The 220~PeV neutrino KM3-230213A, in tension with IceCube and Auger unless narrow, admits a two-body reading: relic decay $X \to \nu\bar\nu$ with $m_X \approx 4.4\times10^{8}$~GeV. Consistency with neutrino and $\gamma$-ray bounds sets $\tau/f \approx 10^{29}$–$10^{30}$~s, lifetime over relic fraction. For a flavored $^1S_0$ onium, the operator scale lands in the Majorana-mass range of unified models: one Higgs insertion gives a singlet mediator, $M/|C_7|^{1/3} \approx 10^{14}$–$10^{16}$~GeV across the allowed relic fraction; two give the seesaw window; Dirac or Majorana neutrinos select the branch. We give the construction and its decisive tests.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Scalar-induced gravitational waves from a box-shaped curvature power spectrum

Zu-Cheng Chen and Lang Liu

We compute the stochastic background of gravitational waves (GWs) produced at second order in cosmological perturbation theory by a primordial curvature power spectrum that is flat in $\ln k$ over a finite band $[k_-,k_+]=[k_*e^{-\Delta},k_*e^{+\Delta}]$ and vanishes elsewhere. This logarithmic box interpolates between a monochromatic spectrum as $\Delta\to0$ and a locally scale-invariant plateau as $\Delta\to\infty$, and its sharp boundaries make the geometry of the source convolution unusually transparent. Working in the radiation era, we reduce the convolution to a compact integral over the overlap between the momentum triangle and the box, and evaluate it analytically in two regimes. For a narrow box we show that, to leading order in the width, the spectrum equals the Dirac-spectrum result multiplied by a purely geometric overlap factor $\Phi_{\rm box}(\kappa,\Delta)$; this factor turns the infrared slope from $k^{3}\ln^{2}k$ into $k^{2}\ln^{2}k$ at a break $k_b=2k_*\sinh\Delta$. For a broad box we separate the lower edge, the scale-invariant interior, and the upper edge, derive the leading behaviour in each (an infrared $k^{3}\ln^{2}k$ rise, a scale-invariant plateau, and a quartic cut-off at the hard endpoint $k=2k_+$), and combine them into a single uniform formula cast as a product of two universal, $\Delta$-independent edge functions. We also provide an integral-free closed-form surrogate for these edge functions for use in parameter scans.
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Solar and Stellar Astrophysics

Rediscussion of eclipsing binaries. Paper 32. The eccentric F-type system EY Cephei

John Southworth

EY Cep is a detached eclipsing binary containing two F0 V stars in an orbit with a period of 7.97 d and an eccentricity of 0.440. We determine the physical properties of the system using light-curves from the Transiting Exoplanet Survey Satellite and published spectroscopic measurements. We find masses of 1.523 +/- 0.008 Msun and 1.494 +/- 0.014 Msun, radii of 1.491 +/- 0.004 Rsun and 1.446 +/- 0.004 Rsun, and temperatures of 7070 +/- 170 K and 6990 +/- 150 K. We calculate the system's distance to be 300.3 +/- 3.8 pc, in excellent agreement with the Gaia DR3 parallax, and estimate its age to be 220 Myr. We find no evidence for pulsations, but there are hints of variation in the eclipse times potentially attributable to a third body on a longer-period eccentric orbit.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Do primordial quark pellets solve the dark matter puzzle?

Domenec Espriu

We show that primordial quark pellets (PQPs) - ultra-dense quark-matter mini-stars formed at $T\sim 1$ GeV - could naturally arise in a radiation dominated early universe if rare baryon overdensities are produced by contracting Peccei-Quinn domain walls or similar super-horizon structures. Solving the Tolman-Oppenheimer-Volkoff equation with a hot quark equation of state, we find stable solutions with a maximum theoretical mass of $10^{-2}$ solar masses and radii of order 100 m, although the formation mechanism favours much lighter objects that would indeed be dominant. Once formed, PQPs cool and evolve into either mini neutron stars or stable strange-matter nuggets, depending on the QCD ground state. The mechanism we present could suffice to reproduce the present dark matter density without altering Big Bang Nucleosynthesis or requiring a posterior entropy injection. PQPs may evade current microlensing constraints if their masses are below $10^{-8}$ solar masses, a range that in view of their mass function could easily accommodate a large fraction of dark matter. PQPs thus potentially constitute a conservative Standars-Model based, and observationally testable candidate.
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Solar and Stellar Astrophysics

SN 2025aico: Early observations of a faint Type IIb supernova with a low-mass envelope

J.-W. Zhao, A. Pastorello, B. Kumar et al. (+45 more)

We aimed to investigate the physical properties and the underlying explosion mechanisms of the Type IIb SN 2025aico. Through a comprehensive analysis of early-phase optical light curves and spectroscopic data, we aim to constrain the fundamental explosion parameters and evaluate the physical state of the event. We present early multi-band optical imaging and low-resolution optical spectroscopic follow-up observations of the Type IIb SN 2025aico, spanning approximately 70 days from the explosion. We constrain the properties of SN 2025aico by utilizing a hybrid model that combines shock-cooling emission and radioactively powered diffusion, as well as by analyzing the spectroscopic evolution. We use various approaches to constrain the 56Ni mixing from early data, and also compared our spectra with models to constrain the properties of the progenitor. The explosion epoch of SN 2025aico is estimated to be MJD 61032.69, while the rise time in the r_M-band is 22.30 +/- 0.70 days. The peak pseudo-bolometric luminosity in the optical bands is L_opt = (4.07 +/- 0.10) x 10^41 erg/s. The fitting yields a moderate to relatively low 56Ni mass of M_Ni = 0.033 +0.006/-0.004 M_sun and an ejecta mass of M_ej = 2.79 +0.21/-0.18 M_sun. The photospheric velocity near the bolometric peak, measured from the Fe II lambda 5169 line, is 6450 +180/-160 km/s. The derived envelope properties suggest a compact He-star progenitor possessing an H-rich envelope of M_env approx. 0.01 M_sun and a radius of R_env approx. 6-10 R_sun. The derived physical properties of SN 2025aico indicate an origin from a moderate-mass, stripped He-star in a compact binary system, characterized by a minimal residual hydrogen envelope. The explosion itself demonstrates weak to moderate 56Ni mixing throughout the ejecta.
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All authors J.-W. Zhao, A. Pastorello, B. Kumar, Y.-Z. Cai, A. Dutta, D. K. Sahu, A. Reguitti, R. S. Teja, H. Das, T. J. Moriya, N. Pyykkinen, K. Valeckas, G. Valerin, X.-Z. Zou, C. Ashall, S. Bijavara Seshashayana, G.-W. Du, G. C. Anupama, A. L. Bouquin, S. Campana, K. Chatterjee, X.-L. Chen, X.-L. Du, N. Elias-Rosa, Y. Fang, M. Fraser, W. Hoogendam, E. Hsiao, E. Kankare, E. P. Lagioia, W.-Y. Li, X.-K. Liu, P. Lundqvist, K. Matilainen, J. Martikainen, K. Medler, N. Morrell, Y. Pan, C. Pfeffer, G. Rameshan, T. M. Reynolds, M. D. Stritzinger, V. Vuolteenaho, Z.-Y. Wang, H.-F. Xiao, J.-H. Zhang, X.-W. Liu, Y.-P. Yang

Instrumentation and Methods for Astrophysics

Detector-level simulation closure of radio air-shower reconstruction with native RF-chain inversion and out-of-fold endpoint interpolation

Xin Xu, Pengfei Zhang, Fufu Yang et al. (+2 more)

Autonomous radio arrays reconstruct air showers from trigger-selected digitized voltage traces rather than ideal electric-field footprints. We present a detector-level simulation-closure test linking RF-chain-triggered ZHAireS event packages to reconstructed direction, energy and quality diagnostics. Voltage amplitudes and station timing determine geometry through a robust joint timing–amplitude axis fit. Native-grid RF-chain inversion recovers 50–200 MHz electric-field peaks along the shower-plane v cross B axis. Symmetric four-arm iron and proton templates generated with 2 ns time bins provide endpoint estimates that are combined by a nested five-fold out-of-fold interpolation estimator. One estimator is used over the full angular range without a fitted multiplicative energy scale. Of 972 triggered event packages, 725 pass common quality selection in raw-noisy weighted, hard-gated denoised equal-weight and clean equal-weight branches. In the primary reconstructed-zenith range 60–85 degrees, 693 common events have mean energy residuals of -0.05, -0.30 and -0.66 percent with standard deviations of 11.04, 10.90 and 10.75 percent. The hard-gated denoised branch has a median angular separation of 0.052 degrees. Boundary zenith ranges are reported separately; the upper boundary has a mean energy residual of +14.2 percent and a 19.9 percent standard deviation. These results describe cross-fitted closure within a matched simulation framework, not deployed-array resolution or independent energy calibration.
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All authors Xin Xu, Pengfei Zhang, Fufu Yang, Xiaosong Liu, Chao Zhang

Solar and Stellar Astrophysics

Nucleosynthesis of Pop III and Fe-enriched Pop II Pair-Instability Supernovae

Wenyu Xin, Ken'ichi Nomoto, Chun-Ming Yip et al. (+4 more)

Recently discovered very metal-poor (VMP) star LAMOST J1010+2358 shows a peculiar abundance pattern that is remarkably well fit by a Pop III pair-instability supernova (PISN) of $\simeq 260$ M$_\odot$. Motivated by this, we investigate the nucleosynthetic characteristics of Pop III and Pop II PISNe to provide theoretical constraints for future observations. This paper is divided into two parts. First, we explore the evolution and nucleosynthesis of Pop III PISNe with initial masses of 130 - 300 M$_\odot$. Our main aim is to investigate how the uncertainty in $^{12}$C$(\alpha,\gamma)^{16}$O and $^{16}$O+$^{16}$O reaction rates affect their explosion properties and nucleosynthesis. We find that the yields of odd-$Z$ elements are particularly sensitive to the $^{12}$C$(\alpha,\gamma)^{16}$O rate, while the production of Fe-peak elements shows significant sensitivity to both rates. Second, we investigate the nucleosynthetic features of Pop II PISNe formed in gas enriched exclusively by Pop III PISN ejecta. By employing a time-dependent convection model during the explosion, we demonstrate that metal enrichment increases opacity and triggers vigorous convective mixing. This hydrodynamic effect significantly enhances the explosion energy and $^{56}\text{Ni}$ production. Consequently, Pop II PISNe exhibit distinct chemical signatures, including a weaker odd-even effect and enhanced Zn-Ge production, providing unique diagnostics for identifying PISN remnants in the early Universe.
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All authors Wenyu Xin, Ken'ichi Nomoto, Chun-Ming Yip, Xianfei Zhang, Qian-Fan Xing, Shaolan Bi, Gang Zhao

Cosmology and Nongalactic Astrophysics

Conformal dark matter and MHz gravitational waves

Imtiaz Khan, Niamat Ullah, Salvatore Capozziello et al. (+2 more)

A localized enhancement of the primordial curvature spectrum can leave two distinct relics: gravitationally produced conformal-fermion dark matter and a scalar-induced stochastic gravitational-wave background. We show that the dark-matter abundance fixes the scalar normalization through the cubic moment of the curvature spectrum, while the induced tensor signal probes its quadratic convolution. This closes the usual normalization freedom in scalar-induced gravitational-wave templates and ties the MHz signal directly to the dark-matter mass, peak scale, and spectral width. A concrete single-field realization demonstrates this mechanism: a Mukhanov–Sasaki evolution produces a broad MHz background that sits safely below the Gaussian primordial-black-hole threshold. In this construction, a null high-frequency search becomes a lower bound on the conformal-fermion mass, while a detection has to reproduce the relic abundance, peak frequency, amplitude, and width from one primordial feature. The result is a testable link between small-scale inflationary structure, superheavy dark matter, and laboratory MHz gravitational-wave searches
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All authors Imtiaz Khan, Niamat Ullah, Salvatore Capozziello, G. Mustafa, Farruh Atamurotov

Astrophysics of Galaxies

Unveiling the enigma of the Nakashima-Deguchi object (IRAS 19312+1950): a candidate Orion KL analog

Y. Gong, K. M. Menten, T. Kamiński et al. (+5 more)

The Nakashima-Deguchi object (NDO; aka IRAS 19312+1950) has been recognized as an enigmatic object, exhibiting characteristics of both an evolved star and a star-forming region. However, the actual nature of this object remains a topic of ongoing debate. We conducted observations of this object in (sub)millimeter continuum and molecular line emission using the IRAM-30m and APEX telescopes as well as the SMA. Based on SED fitting of single-dish continuum observations, we determined that the cloud hosting NDO has a dust temperature of $25\pm2$ K, a source-averaged (24$^{\prime\prime}$) H$_2$ column density of $(4.4\pm 0.6) \times 10^{22}$ cm$^{-2}$, a dust emissivity index of $1.7\pm0.2$, and a total gas mass of $220\pm21 M_{\odot}$. SMA continuum observations resolve the cloud into at least four dust continuum cores. The centrally peaked core MM1, associated with an SiO maser, is the primary mass reservoir. Single-dish spectroscopic observations of NDO led to the detection of 59 spectral lines attributed to 12 species and their isotopologues. This includes the first detection of deuterated molecules, DCO$^{+}$, DCN, DNC, and HDCO, indicating substantial deuterium abundance. SMA spectroscopic observations detected 75 spectral lines toward MM1, assigned to 12 species and their isotopologues. These lines exhibit diverse morphologies on a scale of $\sim$0.1 pc, likely due to outflow feedback. The observed high-velocity outflow is inconsistent with a spherical morphology and rather resembles a wide-angle bipolar outflow. The presence of deuterated species, and the overall large mass of the complex, the surrounding material of NDO appears more naturally associated with a star-forming environment than with a purely evolved-star scenario. Our investigations led us to postulate that this enigmatic object may represent an Orion KL analog about ten times farther away.
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All authors Y. Gong, K. M. Menten, T. Kamiński, F. Schuller, F. Navarete, A. Belloche, P. Schilke, F. Wyrowski

High Energy Astrophysical Phenomena

Wind-driven angular momentum removal and X-ray ionization effects in Roche-lobe overflowing HMXBs

Atsuo T. Okazaki and Stanley P. Owocki

We investigate the dynamical interaction between stellar winds and Roche-lobe overflow (RLO) streams in high-mass X-ray binaries using three-dimensional SPH simulations. We show that the donor wind can exert a strong dynamical influence on the accretion flow. In the absence of X-ray ionization, the wind interacts asymmetrically with the disk and carries retrograde angular momentum, resulting in a net removal of angular momentum and a reduction of the disk size. When X-ray photoionization is included, the response of the system becomes strongly non-monotonic. At high luminosity ($L_X = 10^{38} {\rm erg s}^{-1}$), wind acceleration is suppressed and the flow approaches the no-wind case. In contrast, at moderate luminosity ($L_X = 10^{37} {\rm erg s}^{-1}$), the system enters a qualitatively different accretion regime. In this regime, the partially ionized wind becomes dense and dynamically important, strongly perturbing the RLO stream. As a result, the accretion flow transitions from RLO-dominated to wind-dominated, and the RLO stream undergoes a dynamical bifurcation into low- and high-angular-momentum branches. This leads to suppressed disk formation despite the presence of a strong mass supply. These results demonstrate that moderate ionization can be more disruptive than both weak and strong ionization, providing a new mechanism regulating accretion flows in RLO HMXBs.
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Astrophysics of Galaxies

Mapping Dust Attenuation at Kiloparsec Scales. III. The 2175Å\ Bump

Ruonan Guo, Cheng Li, Tao Jing et al. (+3 more)

We combine the SwiM_v4.2 Swift/UVOT+MaNGA catalog with 2MASS $K_s$ imaging to map the 2175Å attenuation bump at kiloparsec scales in nearby galaxies. We use two complementary estimators: an ultraviolet-to-near-infrared attenuation-curve method, yielding $A_{bump}^{UOIR}$ and $B$ for 2487 high-continuum-S/N spaxels, and the NUV-only method of Battisti et al. (2025), yielding $A_{bump}^{NUV}$ and $k_{bump}$ for 7934 spaxels. The two absolute bump estimates agree well where they overlap. We compare bump strength with local stellar-population, emission-line, attenuation-curve, and geometric diagnostics after separating star-forming (SF) and non-SF regions. The strongest bumps occur at low specific H$\alpha$ surface brightness, $\Sigma_{\text{H}\alpha}/\Sigma_\ast$, especially in non-SF regions, where this ratio traces ionized-gas emission per unit stellar mass rather than sSFR. The bump also weakens with EW(H$\alpha$) and strengthens with $D_n4000$ and stellar age. In contrast, metallicity, inclination, galactocentric radius, $A_V$, and optical attenuation-curve slope are secondary predictors. The absolute strength $A_{bump}^{NUV}$ increases with $\Sigma_{\text{H}\alpha}$ and $\Sigma_\ast$, while the relative strengths $k_{bump}$ and $B$ do not, indicating that absolute bump amplitude partly follows dust column whereas normalized strengths better trace effective bump prominence. These results support local radiation-field processing of the 2175Å carriers.
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All authors Ruonan Guo, Cheng Li, Tao Jing, Shuang Zhou, Niu Li, Zhuo Cheng

High Energy Astrophysical Phenomena

Inhibition of Accretion by the Stellar Wind in Misaligned Be/X-ray Binaries

Atsuo T. Okazaki

Be/X-ray binaries (BeXRBs) constitute a major subclass of high-mass X-ray binaries. They show intermittent X-ray activity with $L_X > 10^{36} {\rm erg s}^{-1}$, while remaining quiescent most of the time with $L_X < 10^{34} {\rm erg s}^{-1}$. BeXRBs generally have eccentric orbits as a result of supernova kicks when neutron stars were born. In these systems, the same kicks are also likely to make the binary orbital axis misaligned with the spin axis of the Be star. In such systems, when the neutron star captures gas from the equatorial disk of the Be star, the resulting accretion disk is in general tilted to both the Be disk plane and to the binary orbital plane. This raises an interesting possibility that in misaligned BeXRBs, the polar wind of the Be star collides with the accretion disk and significantly affects its structure by the large ram pressure. In this paper, we study the effects of the stellar wind on the accretion dynamics in misaligned BeXRBs. Using analytical wind and disk models, we first compare the wind's ram pressure with the gas pressures of the accretion flow to derive a condition for the stellar wind to strongly suppress accretion, and then apply the condition to a sample of BeXRBs whose relevant parameters are well determined or constrained. We find that wind-driven inhibition is a plausible mechanism for suppressing accretion in systems with slowly rotating neutron stars in wide orbits, where the classical propeller mechanism is expected to be inefficient. The effect is particularly important if the accretion flow is hot and low-density, or after the accretion rate has declined from the outburst level.
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Cosmology and Nongalactic Astrophysics

Constraining primordial black holes and primordial curvature power spectrum with extragalactic muon neutrino

Yupeng Yang

We investigate a mixed dark matter scenario comprising weakly interacting massive particles (WIMPs) and primordial black holes (PBHs). After PBH formation, WIMPs can accrete onto them, forming ultracompact minihalos (UCMHs). The resulting WIMP number density within UCMHs is significantly enhanced compared to classical dark matter halo models, leading to a higher WIMP annihilation rate. Previous studies have focused mainly on the associated gamma-ray flux, we investigate the extragalactic neutrino flux from such annihilation. Considering the annihilation channels $\mu^{+}\mu^{-}$, $\tau^{+}\tau^{-}$, and $\nu_{\mu}\bar{\nu}_{\mu}$, we analyze two classes of neutrino events: upward and contained events. By requiring the neutrino flux from WIMP annihilation around PBHs does not exceed the atmospheric neutrino background, we derive upper limits on the fraction of dark matter in PBHs ($f_{\rm PBH}$) for a one-year exposure of the IceCube experiment. These limits depend on the annihilation channel, the masses of the WIMP and PBH, and the neutrino event type. The strongest constraints come from the $\nu_{\mu}\bar{\nu}_{\mu}$ channel, yielding $f_{\rm PBH} \sim 10^{-4}$ ($4\times 10^{-5}$) for contained (upward) events with $m_{\chi}=10^{3}$ GeV and $M_{\rm PBH}=10^{3} M_{\odot}$. Based on these bounds on PBHs, we further derive upper limits on the primordial curvature power spectrum $\mathcal{P}_{\mathcal{R}}$. From our strongest constraint, we obtain $\mathcal{P}_{\mathcal{R}} \sim 10^{-1.65}$ at the scale $k\sim 3\times 10^{12}~\mathrm{Mpc^{-1}}$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Quantum corrections as a Bound for Detecting Self-Interacting Ultralight Dark Matter

Jae-Weon Lee and Chueng-Ryong Ji

We investigate the implications of interactions between ultralight dark matter (ULDM) and Standard Model fermions for the radiative stability of the ULDM potential. By matching the heavy fermion onto a low-energy scalar effective field theory, we derive the one-loop threshold corrections to the ULDM mass and self-interaction couplings. We interpret these corrections in terms of radiative naturalness conditions. For the parameter region motivated by cosmological and galactic considerations, the quadratic correction provides the strongest naturalness criterion, while the direct and cubic-induced quartic corrections remain subdominant. Our results illustrate how radiative effects can constrain the parameter space satisfying our radiative-naturalness criterion based on threshold corrections.
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Solar and Stellar Astrophysics

Radial Evolution of Near-Sun Magnetic Switchbacks Alfvenicity, Occurrence Rate, and Size

Xiaolei Li, Chen Shi and Yuliang Ding

Magnetic switchbacks, characterized by reversals of magnetic field direction, are widely observed in the inner heliosphere by Parker Solar Probe (PSP). With PSP reaching perihelia near 10Rs, observations from the first 24 encounters enable studies of near-Sun switchback evolution at r > 10Rs. We construct a switchback catalog within 10 < r < 55Rs by identifying magnetic field reversals with stable field magnitude and strahl-electron polarity. Statistical analysis shows that switchback Alfvenicity decreases with increasing radial distance, consistent with solar wind evolution beyond the Alfven critical point. Meanwhile, switchback occurrence rate and spatial size increase with distance, suggesting continued generation and expansion during solar wind propagation. At a given radial distance, the fraction of solar wind containing switchbacks is positively correlated with background solar wind radial velocity (VR) and Alfven Mach number (MA), while the local occurrence rate is mainly controlled by MA. These results suggest that switchback patches preferentially form in faster and higher-MA solar wind. The spatial size of switchbacks shows no clear dependence on MA or VR, implying that their size evolution is probably not determined by source conditions. Solar activity influences switchback evolution through changes in background solar wind properties, with a larger fraction of higher-MA switchbacks during solar minimum. We further identify anisotropy relative to the background magnetic field direction: the local occurrence rate and spatial size are approximately 1.5 times as large in the perpendicular direction as in the parallel direction, indicating distinct magnetic topology of switchback patches
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Saturday 11 July

Solar and Stellar Astrophysics

Synthetic Observed-Band Light Curves of Delta Cephei from MESA-RSP Models

Zuhoor Elahi, Christopher Sirola and Wafa Gull

Observed-band light curves provide a stronger test of Cepheid pulsation models than period matching alone, because the measured photometric amplitude depends on the phase-dependent luminosity, temperature, radius, and passband transformation. We construct synthetic observed-band light curves for delta Cephei from nonlinear radial pulsation models computed with MESA-RSP and transform the model outputs L(phi), Teff(phi), and R(phi) into bolometric magnitudes and MIST bolometric-correction magnitudes in Bessell and Gaia passbands. The adopted AAVSO Johnson V-band template has peak-to-peak amplitude Delta V_obs = 0.8390 mag. The period-stable reference model with RSP alfam = 0.60 gives a MIST-BC V-band amplitude of only Delta V_syn approximately 0.0106 mag. Amplitude-enhanced models increase the synthetic amplitude, with RSP alfam = 0.425 giving 0.0302 mag, RSP alfam = 0.400 giving 0.0344 mag, and the accepted RSP alfam = 0.400, RSP alfat = 0.095 model giving 0.0367 mag. The final accepted model therefore reaches only 4.4 percent of the observed Johnson V-band amplitude. These results show that MIST-BC transformations are necessary for a physically meaningful observed-band comparison, but they do not remove the amplitude discrepancy in the present model sequence. The remaining mismatch indicates that the dominant limitation is the small nonlinear pulsation amplitude of the models rather than the bolometric-correction transformation itself.
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Solar and Stellar Astrophysics

Nonlinear MESA-RSP Modeling of Delta Cephei: Period Matching, Amplitude Control, and Model-Acceptance Diagnostics

Zuhoor Elahi, Christopher Sirola and Wafa Gull

Delta Cephei is the prototype classical Cepheid and a useful target for testing whether a one-dimensional nonlinear radial-pulsation workflow can satisfy more than a period constraint. We present a target-specific, reproducible workflow using the Modules for Experiments in Stellar Astrophysics (MESA) Radial Stellar Pulsation (RSP) capability, hereafter MESA-RSP, to construct, tune, extend, and classify nonlinear radial-pulsation calculations for Delta Cephei. A tuned 200-period calculation with M = 5.0 solar masses, Teff = 6050 K, L = 2422.5 solar luminosities, X = 0.73, and Z = 0.007 gives P_model = 5.366622 d for the adopted target P_obs = 5.366531 d, a difference of 9.1 x 10^-5 d, or approximately 7.9 s. This agreement shows that the mean-density structure can be tuned successfully, but extended calculations demonstrate that period matching alone is not an adequate nonlinear model-acceptance criterion. When the period-matched model was continued with the default/weak-damping setup, the amplitude and cycle behavior became nonstationary. We therefore explored the MESA-RSP eddy-viscous damping parameter RSP_alfam as a first amplitude-control experiment. The RSP_alfam = 0.60 case is retained as a period-stable reference, while the RSP_alfam = 0.425, 500-period calculation is classified as the clean amplitude-enhanced candidate. A 700-period continuation is retained only as a diagnostic case because it produced an energy-error warning. The main contribution is a reproducible Delta Cephei workflow and a transparent classification scheme showing that acceptable nonlinear Cepheid models require period agreement, interpretable late-cycle amplitude behavior, controlled surface-velocity diagnostics, and the absence of serious numerical warnings.
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Earth and Planetary Astrophysics · Cross-listed from eess.SY

Tulip-Shaped Orbits for Lunar South-Pole PNT and Direct-to-Earth Relay Missions

Darin C. Koblick and Michael Casey

This geometric study evaluates a compact seven-petal, 6:5-resonant tulip-shaped orbit constellation for lunar south-pole positioning, navigation, and timing (PNT) and direct-to-Earth relay services. The tulip-shaped orbits are compared against elliptical lunar frozen orbit (ELFO) constellations over the NASA LunaNet Service Volume 2 (SV2), covering lunar latitudes south of -75 degrees. We compare a six-satellite tulip baseline with a minimum-cost five-satellite variant; both use the same shared three-body orbit and differ only in satellite count and along-track phasing. Performance is scored against three Initial Operating Capability C (IOC-C) metrics: line-of-sight (LOS) link availability, Lunar Augmented Navigation System (LANS) geometric dilution of precision (GDOP) below 6, and daily extravehicular activity (EVA) usable-PNT windows. Both tulip constellations satisfy all three IOC-C metrics across SV2. The six-satellite configuration meets requirements with wide margin: 75% worst-point daily GDOP availability and 18 hours of daily EVA support. The five-satellite variant also passes, but with thinner margin: 44% availability and 10 hours of EVA support. Unlike the ELFO configurations, each spacecraft in the tulip-shaped constellation maintains continuous Earth line of sight, providing persistent geometric opportunity for direct single-hop Earth relay. Because all spacecraft share a single three-body orbit, initial phasing and post-failure reconstitution reduce to along-track drift maneuvers between neighboring orbits, with screening-level estimates indicating low maneuver cost.
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Solar and Stellar Astrophysics

Explosive Molecular Outflows

Luis A. Zapata

About fifteen years ago a new type of extreme (with kinetic energies of $\mathrm{E}_k \sim 10^{47-49}\, \mathrm{erg}$) molecular outflows associated with very luminous ($\geq 10^5\, \mathrm{L}_\odot$) and massive (10$^3$ M$_\odot$) young clusters was confirmed, the Explosive Molecular Outflows. This new class of outflows is largely different from the classical bipolar protostellar flows, with spatial distributions made of numerous narrow straight filament- or streamer-like ejections in an almost isotropic arrangement and with clear Hubble–Lemaître-like expansion motions. Straight filaments point directly to the center of expanding molecular or ionized shells, which exhibit expansion velocities of about 10–50 km s$^{-1}$. However, no young massive stars are clearly located there, probably because they moved to other places. These physical characteristics suggest that explosive outflows are short-lived in nature and possibly generated by an energetic single and brief disrupting event. The most up-to-date theoretical model for explaining their nature involves the disruption of non-hierarchical massive protostellar systems, where members may either form a close binary (with separations of a few au) or merge into a single massive star, as recently proposed for the nearest high-mass star-forming region, Orion BN/KL.
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Earth and Planetary Astrophysics

The dynamical surface of Phobos: a morphodynamic atlas

Isabel Herreros and Sébastien Charnoz

Phobos evolves in a highly dynamical environment where surface-material motion is controlled by the combined effects of self-gravity, time-dependent Martian tides, and inertial forces. In such a low-gravity regime, the displacement of loose material, cannot be inferred from topographic slope alone, making a dynamical approach essential for interpreting Phobos' surface morphology and for supporting the Martian Moons eXploration (MMX) mission led by JAXA. Here, using our RAVEL code, we apply a dynamical model that combines the surface acceleration field with friction on a digital terrain model of Phobos to compute surface regolith trajectories. The model does not aim to predict the triggering of slope failure. Instead, it addresses where material would preferentially move once motion is initiated. This reveals large scale coherent dynamical regions and a sparse network of preferred regolith transport routes, termed here Regolith Migration Pathways (RMPs). The final positions of the RMPs correlate with smooth, low-relief terrains and spectrally neutral units, consistent with depositional mantles formed by long-term regolith infill, whereas rough, high-standing areas with abundant small craters and blue spectral slopes tend to correspond to dynamically active or denuded source regions. In contrast, spectrally red terrains are generally associated with dynamically quiet, morphologically rough surfaces where our model predicts negligible regolith motion, suggesting older, less frequently reworked units. Taken together, these patterns indicate that much of Phobos' surface morphology and spectral heterogeneity can be explained by long-term regolith redistribution driven by the surface acceleration field along RMPs. We provide a 3D morphodynamic atlas of RMPs across Phobos' surface, which will be useful for constraining the geographical provenance of samples to be collected by the MMX spacecraft.
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Astrophysics of Galaxies

Diffhalos: A Generative Model of Cosmological Lightcones of Dark Matter Halos

Georgios Zacharegkas, Andrew P. Hearin, Alan Pearl et al. (+3 more)

We present a generative model of cosmological lightcones of dark matter halos, Diffhalos. In our model, we draw Monte Carlo samples of the halo mass function in a lightcone with a JAX-based implementation of the halo model, Halox, and we generate samples of subhalos by drawing from a model for the conditional subhalo mass function. We generate mass assembly histories (MAHs) using a normalizing flow trained on merger trees in cosmological N-body simulations. We show that Diffhalos can generate samples of halos, subhalos, and their MAHs with a statistical distribution that accurately approximates populations in simulated lightcones. As an example application, we use Diffhalos to calculate gradients of the halo and subhalo mass functions with respect to cosmological parameters. We conclude with a discussion of ongoing work using Diffhalos together with models of the galaxy–halo connection to make theoretical predictions for cosmological populations of galaxies, and to generate mock galaxy catalogs.
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All authors Georgios Zacharegkas, Andrew P. Hearin, Alan Pearl, Matthew R. Becker, Florian Kéruzoré, Sara Ortega-Martinez

High Energy Astrophysical Phenomena

Fermi-Large Area Telescope Detection of Very High Energy (>100 GeV) Emission from Compton-Dominated Blazars

P N Naseef Mohammed, Vaidehi S. Paliya and C D Ravikumar

The observation of broad emission lines in the optical spectra of flat-spectrum radio quasars (FSRQs) suggests radiatively efficient accretion powering these objects. In such broad emission line blazars, the intense broad-line region (BLR) radiation can provide seed photons for inverse Compton scattering, leading to a Compton-dominated spectral energy distribution. Interestingly, the same BLR photon field can also absorb very high-energy (VHE; E>100 GeV) $\gamma$-ray radiation, thus explaining the paucity of VHE-detected FSRQs. Here we report the results of a systematic search to identify VHE-emitting sources in a sample of 626 Compton-dominated blazars (Compton dominance > 1), using $\sim$17.5 years of Fermi-Large Area Telescope observations. We identified 14 blazars at greater than 4$\sigma$ confidence level, including 4 sources detected in the VHE band at high significance (> 5$\sigma$) for the first time. We also found 21 objects from which at least one VHE photon was detected, thus substantially expanding the known VHE FSRQ population. Investigating the temporal coincidence of the VHE photons with the $\gamma$-ray activity, we noticed the VHE emission to be detected during flaring as well as low jet activity epochs. By estimating the optical depth for the $\gamma$$\gamma$ absorption due to the BLR photon field, we constrained the VHE-emitting region to be located outside BLR (>1.1-1.4$\times$ BLR radius). We conclude that multi-wavelength followup observations of these enigmatic VHE-detected broad line blazars will permit us to constrain the radiative processes responsible for the GeV-TeV emission, and will set the benchmark for their observations with the upcoming Cherenkov Telescope Array Observatory.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Lorentz-Violating Photon Decay into Neutrinos and Constraints from PeV Photon Stability

Zurab Kepuladze

We study the vacuum decay of a Lorentz-violating photon into a neutrino-antineutrino pair. Lorentz-violating corrections to the photon dispersion relation are parametrized through an effective invariant mass $m_{\mathrm{eff}}^{2}=k_{\alpha}k^{\alpha}$. This makes the otherwise forbidden decay $\gamma\to\nu\bar{\nu}$ kinematically allowed. The process proceeds through the Standard Model one-loop neutrino electromagnetic vertex and is therefore strongly suppressed. Using the low-$q^{2}$ anapole form factor, we derive the decay rate and apply it to TeV and PeV photons. We find that below the electron-positron threshold the neutrino channel is open but generally too slow to provide stronger constraints than existing bounds. Above the threshold, $\gamma\to e^{+}e^{-}$ dominates unless the relative photon-electron LIV parameter closes this channel. In that case, the neutrino decay gives an independent constraint on photon-neutrino relative LIV parameters.
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Earth and Planetary Astrophysics

The muon Moonshot: Moon subsurface tomography with upward-going muons

Zimo Hu, Leyun Gao, Zhengyun You et al. (+6 more)

We propose a novel muon Moonshot concept for lunar subsurface tomography based on upward-going muons originated from the lunar regolith. Unlike the Earth, the Moon lacks an atmosphere, leaving a dense regolith below and a near-vacuum environment above. Consequently, while most downward-going hadrons are absorbed before decaying, upward-going hadrons escaping the regolith can decay in flight, producing a significant source of lunar muons. These muons are detectable by instruments on the lunar surface or in near-lunar orbit. We perform Monte Carlo simulations to investigate their energy spectra, angular distributions, and integrated fluxes under various theoretical and detector configurations. The results indicate that the lunar muon flux is sensitive to detector altitude under a flat-terrain assumption, demonstrating its potential as a novel non-invasive probe of shallow subsurface voids. We also present case studies on the detection of underground cavities and water resources, with cavity-induced flux variations observable in less than two minutes and weaker water signals distinguishable after about 36 minutes of data collection with a $1~\mathrm{m^2}$ detector, and discuss potential implementations in future lunar missions.
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All authors Zimo Hu, Leyun Gao, Zhengyun You, Qite Li, Qiang Li, Yuhong Yu, Liangwen Chen, Xueheng Zhang, Zhiyu Sun

High Energy Astrophysical Phenomena

Strongly interacting matter with criticality induced by modified excluded volume in core-collapse supernova simulations

Anil Kumar, Noshad Khosravi Largani, Stefan Typel et al. (+3 more)

This article reviews critically the core-collapse supernova explosion mechanism associated with a sufficiently strong first-order phase transition from normal nuclear, in general hadronic matter to deconfined quark matter, which commonly assumes Gibbs conditions for the coexistence of phases and a phase transition construction accordingly. To this end, a novel class of multi-purpose equation of state (EOS) is developed, based on the modified excluded volume (MEV) approach employing a medium-dependent excluded-volume functional within the relativistic mean field framework with density-dependent meson-nucleon couplings. The chosen MEV parametrisation features the change in the number of degrees of freedom, mimicking the EOS softening in excess of nuclear saturation density, featuring a first-order phase transition with van der Waals like behaviour and the presence of a critical point at high temperatures. Simulations of core-collapse supernovae are performed, based on general relativistic neutrino radiation hydrodynamics in spherical symmetry, in order to explore the previously reported supernova explosion scenario within this class of phenomenological modified microscopic hadronic EOS. A burst-like neutrino signature is released, substantially longer than previously reported based on common hadron-quark hybrid model EOS with two-phase approach and Gibbs phase-transition construction, as observable signal, which is complemented by a gravitational wave mode analysis.
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All authors Anil Kumar, Noshad Khosravi Largani, Stefan Typel, Pablo Cerdá-Durán, Alejandro Torres-Forné, Tobias Fischer

Astrophysics of Galaxies

Magnetically Arrested Discs Powering Jets in a Large Sample of Low-Accretion FR I Radio Galaxies

Huibo Fei, Han He, Bei You et al. (+4 more)

We study a sample of 289 Fanaroff-Riley type I (FR I) radio galaxies selected from the LOFAR Two-Metre Sky Survey (LoTSS) DR1, identified by their edge-darkened radio morphologies. Using Sloan Digital Sky Survey (SDSS) DR17 optical photometry and spectroscopy, we derive Eddington-scaled accretion rates spanning -6.84 < log $\dot{m}$ < -0.87 (median $\approx$ -2.84). The vast majority of sources lie below $\dot{m}$ = 0.01, indicating that their central engines are well described by advection-dominated accretion flows (ADAFs). However, even for a rapidly spinning black hole with a = 0.95, the maximum jet power predicted by the Blandford-Znajek mechanism in the standard ADAF regime is lower than the observed jet power (estimated from 151 MHz radio luminosity) for approximately 70% of the sample. We demonstrate that the magnetically arrested disc (MAD) scenario, in which large-scale poloidal magnetic flux accumulates near the event horizon, can fully account for the powerful jets observed in these low-accretion systems. Within the MAD framework, the data are consistent with slow-spinning black holes with $a < 0.5$. This large, uniformly selected LoTSS sample extends the MAD requirement previously established for the bright 3CR FR I population, indicating that magnetically arrested discs are common in FR I radio galaxies across a wide range of luminosities.
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All authors Huibo Fei, Han He, Bei You, MinFeng Gu, Liang Chen, Xuheng Ding, Leyi Wang

Astrophysics of Galaxies

Spectral Energy Distributions of Globular Clusters in VV191a

Ashton Cardona, Timothy Carleton, Jessica Berkheimer et al. (+9 more)

We investigate globular cluster (GC) candidates associated with the elliptical galaxy VV191a using JWST NIRCam and archival HST imaging. Beginning with an initial catalog of over 500 candidate sources, we apply morphological filtering, photometric redshift selection, and spectral energy distribution (SED) fitting using BAGPIPES to isolate a refined sample of 61 probable GCs, including a high-confidence subset of 20 objects. The derived age distribution is concentrated between ~ 6-10 Gyr, with a peak near ~ 8 Gyr, while metallicities are predominantly near and super-solar. Unlike many GC systems in elliptical galaxies, the VV191a sample does not exhibit a clear bimodal metallicity distribution. Derived stellar masses span a broad range and suggest significant degeneracies related to dust attenuation and foreground contamination from the overlapping spiral galaxy VV191b. These results support the presence of an evolved GC population in VV191a while highlighting limitations imposed by broadband SED fitting and foreground contamination
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All authors Ashton Cardona, Timothy Carleton, Jessica Berkheimer, Rogier A. Windhorst, Seth Cohen, Rolf Jansen, Anton M. Koekemoer, Gibson Bowling, Patrick Kamieneski, Jakob Perivolotis, Tyler Hinrichs, Christopher Willmer

High Energy Astrophysical Phenomena

Magnetospheric flows in X-ray pulsars II: Heating, cooling and ionization degree at sub-critical accretion

Alexander A. Mushtukov, Alexander Y. Potekhin, Valery F. Suleimanov et al. (+2 more)

Magnetospheric accretion flows in X-ray pulsars shape their spectra, polarization, and variability. We model the thermal balance of the flow enveloping the neutron star magnetosphere in the sub-critical regime ($L \lesssim 10^{37}\,\mathrm{erg\,s^{-1}}$), where radiation forces do not control the dynamics and single Compton scatterings dominate. The energy budget includes Compton heating by surface X-rays, compressional (adiabatic) heating in the converging flow, and radiative cooling dominated by free-free emission and contributed also by cyclotron emission. We show that the interplay of these processes leads to efficient cooling of the flow in the inner magnetosphere. We compute the flow temperature profile as a function of luminosity and find that near the stellar surface the temperature can fall to a few tens of eV at $L < 10^{35}\,\mathrm{erg\,s^{-1}}$. Under such conditions, the accreting plasma, modelled here as pure hydrogen, is no longer fully ionized. In the strong magnetic fields typical for X-ray pulsars, such temperatures permit partial recombination of electrons and protons into neutral hydrogen. As a result, a significant fraction of the flow becomes weakly ionized, while external illumination ionizes this gas only partially within a geometrically thin layer immediately above the neutron star surface. This implies that magnetospheric accretion at low luminosities proceeds through a partially ionized medium, in contrast to the commonly assumed fully ionized flow.
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All authors Alexander A. Mushtukov, Alexander Y. Potekhin, Valery F. Suleimanov, Andrew Yu, Sergey S. Tsygankov

Cosmology and Nongalactic Astrophysics

Radio Halos in Galaxy Clusters as unveiled by the SKA telescope

R. Cassano, G. Di Gennaro, V. Cuciti et al. (+24 more)

Giant radio halos (RHs) are diffuse, Mpc-scale synchrotron sources observed in a growing fraction of galaxy clusters. They trace relativistic particles and magnetic fields in the intracluster medium (ICM), providing a unique window into non-thermal processes and their role in cluster evolution. RHs are primarily found in merging systems, supporting models in which turbulence generated during cluster collisions re-accelerates pre-existing electrons to the energies required for the observed radio emission. In this scenario, the occurrence, power, and spectral properties of RHs depend on the energetics of cluster mergers, with the most massive and dynamically disturbed clusters hosting the most powerful halos. Low-frequency observations are crucial to uncover ultra-steep-spectrum RHs, a key prediction of turbulent re-acceleration models, and are expected to arise from less energetic merger events. LOFAR has enabled statistical studies of large cluster samples, placing robust constraints on RH occurrence and spectral trends. In this Chapter, we model RH formation and evolution using Monte Carlo simulations calibrated on LoTSS-DR2 findings, and we present predictions for SKA-Low in the AA4 configuration. Our results show that SKA will probe an unprecedented region of cluster mass and redshift space, detecting at least $\sim 2500$ RHs up to $z \approx 0.6$, including $\gtrsim 1000$ ultra-steep-spectrum systems, and revealing halos in clusters down to $\sim 10^{14}\, M_\odot$ and out to $z \approx 1$. These surveys will provide stringent tests of turbulent re-acceleration models and significantly advance our understanding of non-thermal processes in galaxy clusters.
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All authors R. Cassano, G. Di Gennaro, V. Cuciti, A. Datta, M. Balboni, G. Bernardi, A. Bonafede, A. Botteon, M. Brüggen, G. Brunetti, S. Chatterjee, K. Dolag, S. Ettori, F. Gastaldello, S. Giacintucci, C. Giocoli, M. Gitti, R. Kale, M. Pandey-Pommier, G. W. Pratt, M. Rahaman, M. Rossetti, H. J. A. Röttgering, R. Santra, K. S. L. Srikanth, R. J. van Weeren, T. Venturi