Sazuna/UAT_keywords huggingface dataset:
EP250108a/SN 2025kg: A Jet-driven Stellar Explosion Interacting with Circumstellar Material. We present optical, radio, and X-ray observations of EP250108a/SN 2025kg, a broad-line Type Ic supernova (SN Ic-BL) accompanying an Einstein Probe (EP) fast X-ray transient at z = 0.176. EP250108a/SN 2025kg possesses a double-peaked optical light curve, and its spectrum transitions from a blue underlying continuum to a typical SN Ic-BL spectrum over time. We fit a radioactive decay model to the second peak of the optical light curve and find SN parameters that are consistent with the SN Ic-BL population, while its X-ray and radio properties are consistent with those of low-luminosity GRB (LLGRB) 060218/SN 2006aj. We explore three scenarios to understand the system's multiwavelength emission: (a) SN ejecta interacting with an extended circumstellar medium (CSM), (b) the shocked cocoon of a collapsar-driven jet choked in its stellar envelope, and (c) the shocked cocoon of a collapsar-driven jet choked in an extended CSM. Models (b) and (c) can explain the optical light curve and are also consistent with the radio and X-ray observations. We favor model (c) because it can self-consistently explain both the X-ray prompt emission and first optical peak, but we do not rule out model (b). From the properties of the first peak in model (c), we find evidence that EP250108a/SN 2025kg interacts with an extended CSM and infer an envelope mass Me ∼ 0.1 M⊙ and radius Re ∼ 4 × 1013 cm. EP250108a/SN 2025kg's multiwavelength properties make it a close analog to LLGRB 060218/SN 2006aj and highlight the power of early follow-up observations in mapping the environments of massive stars prior to core collapse.

Keywords: Type Ic supernovae, Gamma-ray bursts, Circumstellar matter
Evidence for Evolutionary Pathway-dependent Black Hole Scaling Relations. Recent observations have identified an abundance of high-redshift active galactic nuclei (AGN) with overmassive supermassive black holes (BHs) compared to the local BH mass−total stellar mass (MBH─M⋆) relation for AGN. High-z MBH measurements are critical for probing growth histories of BHs and their host galaxies, including BH seeding and evolution of the MBH─M⋆ relation. However, BH masses in high-z AGN are generally estimated from single-epoch measurements, which carry large systematic uncertainties. More reliable MBH detection methods like dynamical measurements are currently only possible in the local Universe or with strongly lensed systems. Fortunately, new dynamical MBH measurements in a sample of six local galaxies identified as likely relics of common quiescent red nugget galaxies at cosmic noon, as well as a z ∼ 2 lensed red nugget, present a complementary probe of high-z relations. We compare the z ∼ 2 red nugget and relic BHs to recent results for 4 &lt; z &lt; 11 AGN, quasi-stellar objects, and little red dots. Intriguingly, the z ∼ 2 galaxy and local relics all lie on both the local MBH─M⋆ relation for bulges and the 4 &lt; z &lt; 7 MBH─M⋆ AGN relation, although high-z AGN remain overmassive compared to both local relations. We conclude it is unlikely that a uniform MBH─M⋆ redshift evolution applies to all galaxies. Since total M⋆ is affected by growth processes that may not drive BH growth, different evolutionary pathways must be carefully considered when building BH scaling relations.

Keywords: Supermassive black holes, Active galaxies, Scaling relations, Active galactic nuclei, Galaxy evolution, High-redshift galaxies, Early-type galaxies
Microwave Imaging Spectroscopy Diagnosis of the Slow-rise Precursor of a Major Solar Eruption. In this Letter, taking advantage of microwave data from the Expanded Owens Valley Solar Array and extreme-ultraviolet (EUV) data from the Atmospheric Imaging Assembly, we present the first microwave imaging spectroscopy diagnosis for the slow-rise precursor of a major coronal mass ejection (CME) on 2022 March 30. The EUV images reveal that the CME progenitor, appearing as a hot channel above the polarity inversion line, experiences a slow rise and heating before the eruption. The microwave emissions are found to mainly distribute along the hot channel, with high-frequency sources located at the ends of the hot channel and along precursor bright loops underneath the hot channel. The microwave spectroscopic analysis suggests that microwave emissions in the precursor phase are dominated by thermal emission, largely different from the main phase when a significant nonthermal component is present. These results support the scenario that the precursor reconnection, seeming to be moderate compared with the flare reconnection during the main phase, drives the buildup, heating, and slow rise of CME progenitors toward the explosive eruption.

Keywords: Solar flares
A Transiting Giant on a 7.7 yr Orbit Revealed by Transit Timing Variations in the TOI-201 System. We report the detection and characterization of TOI-201 c, a long-period transiting companion to the warm Jupiter TOI-201 b. Its presence was first inferred from high-amplitude transit timing variations (TTVs) in TOI-201 b, pointing to a massive outer body on a  7.7−0.6+1.0  yr eccentric orbit. This prediction was confirmed when Transiting Exoplanet Survey Satellite observed a transit of TOI-201 c, precisely constraining its orbital geometry. A joint fit to TTVs, transit photometry, and archival radial velocities yields a mass of  14.2−1.2+1.0  MJup and an eccentricity of  0.643−0.021+0.009 . The mutual inclination between planets b and c is  2.°9−4.4+4.8 , indicating a nearly coplanar architecture. Long-term numerical integrations confirm dynamical stability over gigayear timescales and predict that transits of TOI-201 b will cease within a few thousand years. TOI-201 c ranks among the longest-period transiting planets with well-constrained properties. Its detection via TTVs, followed by a confirmed transit, represents a rare observational sequence and highlights the power of TTVs and photometric monitoring to uncover distant companions. The TOI-201 system offers a valuable laboratory for testing models of giant planet formation, migration, and secular evolution in multiplanet systems.

Keywords: Exoplanet dynamics, Exoplanets, Transit timing variation method, Radial velocity, Transit photometry
Cosmological Evolution of Fast Radio Bursts and the Star Formation Rate. We investigate the cosmological evolution of the luminosity and redshift of fast radio bursts (FRBs). As is the case for all extragalactic sources, we are dealing with data that are truncated by observational selection effects, the most important being the flux limit, which introduces the so-called Eddington-Malmquist bias. In addition, for FRBs, there is a significant uncertainty in the redshifts obtained from the observed dispersion measures (DMs). To correct for the truncation we use the nonparametric, nonbinning Efron–Petrosian and Lynden-Bell methods, which give unbiased distributions of luminosities and redshifts and their cosmological evolution. To quantify the redshift uncertainty, we use a data set that accounts for uncertainties of contribution to the DM of the host galaxy, and DM uncertainties due to fluctuation in the intergalactic medium. These data, in addition to a mean redshift, give the 1σ errors. We construct three samples with lower, mean, and upper redshifts and apply the above methods to each. For the three samples, we find (1) similar ∼3σ evidence for luminosity evolution, (2) a luminosity function that can be fit by a simple broken power law, and (3) a comoving density formation rate that decreases rapidly with redshift, unlike the cosmic star formation rate (SFR). This rate is similar to that of short gamma-ray bursts, which are believed to result from compact star mergers with a formation rate delayed relative to the SFR. This may further support the hypothesis that magnetars are the progenitors of FRBs.

Keywords: Luminosity function, Cosmological evolution, Radio bursts, Star formation, Magnetars, Radio transient sources
Dynamics of Reconnection Nanojets in Eruptive and Confined Solar Flares. Recent observations reveal small-scale reconnection-driven plasma ejections, often termed nanojets, triggered by magnetic field interactions at slight misalignment angles. These fast, collimated plasma ejections are ∼1.5 Mm long and ∼0.5 Mm wide. In this study, we analyze two high-resolution extreme ultraviolet imaging data sets from the Extreme Ultraviolet Imager on board the Solar Orbiter mission, corresponding to an eruptive (M7.6) and a confined (C1.2) flare, to investigate the dynamics of nanoflare ejections and, for the first time, compare their properties in distinct magnetic environments. We identified 59 nanoflare ejections: 44 in the eruptive flare and 15 in the confined flare event. Our analysis reveals that these events form two distinct classes: confined events exhibit lower speeds (41–174 km s‑1) and lower kinetic energies (1020–1022 erg), placing them closely in or near the picoflare energy regime, while eruptive events show higher speeds (131–775 km s‑1) and higher kinetic energies (1022–1024 erg), falling within the nanoflare regime. Furthermore, magnetic field extrapolations reveal a highly sheared arcade with greater twist and higher magnetic energy density in the eruptive event, compared to the less twisted configuration in the confined event. We infer that this sheared arcade configuration in the eruptive event creates favorable conditions for higher speeds and kinetic energies, unlike the less braided structure in the confined event. Our findings highlight the crucial role of the surrounding magnetic environment in regulating the energetics of nanoflare ejections in the solar atmosphere.

Keywords: Solar flares, Solar magnetic reconnection, Plasma jets, The Sun, Solar coronal heating, Solar physics
Spectral Evolution of Pickup Ions across Interplanetary Shocks in the Outer Heliosphere: Observational Constraints and Transport Simulations. Pickup ions (PUIs) often experience acceleration and heating as they traverse interplanetary shocks, leading to the formation of a distinct suprathermal tail in their energy spectra downstream of the shock. Combining in situ observations and numerical simulations, we investigate how interplanetary shocks shape the energy spectra of PUIs in the outer heliosphere. In this study, we propose a PUI velocity distribution model by incorporating a power-law tail to account for suprathermal ions. By analyzing 18 shock events observed by New Horizons between 20 au and 45 au, we find that, after crossing the shock, the power-law index η of the suprathermal PUI energy spectrum decreases, and this decrease is positively correlated with the shock compression ratio rc and the downstream subadiabatic index βd. To explore the acceleration mechanism of PUIs, we conduct numerical simulations of the shock transport equation, which incorporates the three acceleration-related mechanisms (shock drift acceleration, diffusive shock acceleration, and stochastic acceleration). Our simulations show that when the perpendicular mean free path of PUIs is within 10‑3 ∼ 10‑2 au and the velocity diffusion coefficient is within 10‑9 ∼ 10‑8 s‑1, the shock transport model can reproduce energy spectra consistent with observations. Both the observed and simulated suprathermal power-law spectra exhibit a steeper spectral profile than predictions from first-order Fermi shock acceleration theory. Most PUIs cross the shock less than three times, resulting in low acceleration efficiency, mainly due to weak spatial and velocity diffusion.

Keywords: Pickup ions, Solar wind, Interplanetary shocks, Heliosphere
Formation of Supersonic Turbulence in the Primordial Star-forming Cloud. We present new simulations of the formation and evolution of the first star-forming cloud within a massive minihalo of mass of 1.05 × 107 M⊙, carried out using the GIZMO code with detailed modeling of primordial gas cooling and chemistry. Unlike previous studies that simulated the formation of the first stars within a smaller cosmological box size of ∼0.3–2 Mpc, our work adopts initial conditions from the large-scale cosmological simulations, IllustrisTNG spanning ∼50 Mpc to study the formation of primordial clouds that give birth to the first stars. We increase the original resolution of IllustrisTNG by a factor of ∼105 using a particle-splitting technique, achieving an extremely high resolution that allows us to resolve turbulence driven by gravitational collapse during early structure formation. We find that strong supersonic turbulence with a characteristic Mach number of ∼5.2 naturally develops within the collapsing halo. This turbulence efficiently stirs the gas, promoting fragmentation of the star-forming cloud into multiple dense clumps. Among them, we identify a gravitationally bound core with a mass of 8.07 M⊙ and a size of 0.03 pc, which exceeds its local Jeans mass and is on the verge of collapsing into a star. Our results indicate that supersonic turbulence may be common in primordial halos and can play a crucial role in cloud-scale fragmentation, providing an alternative channel to form less massive first stars and strengthens the argument of lowering the characteristic mass for the first stars found in previous studies.

Keywords: Cosmology, Early universe, Hydrodynamical simulations, Dark matter distribution, Population III stars, Stellar mass functions, Primordial galaxies, James Webb Space Telescope, Star formation, CEMP stars, Collapsing clouds
Cooling Regimes of Nonthermal Electrons: The Slow, the Fast, and the Very Fast. In many astrophysical systems, nonthermal radiation is emitted by accelerated charged particles, whose cooling rates play a crucial role in determining their luminosity and spectral properties. We consider synchrotron radiation from a power-law energy distribution of relativistic electrons and provide a comprehensive framework for understanding particle cooling regimes, focusing on the fast cooling (FC) and very fast cooling (VFC) regimes. In FC, all electrons cool significantly on the dynamical time but remain relativistic. In VFC, all electrons cool to nonrelativistic speeds much faster than the dynamical time. The VFC regime is realized only in highly relativistic sources, with no Newtonian counterpart. It is highly relevant for the prompt phase of gamma-ray bursts (GRBs), where it can naturally occur regardless of the dissipation mechanism and with weak dependence on the degree of magnetization. We find that the FC and VFC regimes are satisfied in a broad range of parameters, under which bright optical emission can be observed during the prompt GRB phase. The brightest optical emission corresponds to an unbroken power-law spectrum extending from the sub-MeV peak of the bolometric luminosity to optical/UV frequencies. Additionally, we propose that VFC in the Thomson-thick regime is necessary for producing a bright and narrow electron–positron annihilation line, as was observed in the B.O.A.T. event, GRB 221009A.

Keywords: Optical observation, Relativistic jets, Non-thermal radiation sources, Gamma-ray bursts
The Importance of Dust Distribution in Ionizing-photon Escape: NIRCam and MIRI Imaging of a Lyman Continuum-emitting Galaxy at z ∼ 3.8. We present deep JWST/NIRCam and MIRI imaging of Ion1, a previously confirmed Lyman continuum (LyC)-emitting galaxy at zspec = 3.794. Together with existing Hubble Space Telescope imaging, these new observations from the JWST Advanced Deep Extragalactic Survey program enable a joint analysis of Ion1's LyC, rest-frame UV, stellar, and dust emission with unprecedented detail. We report the first detection of dust emission at rest-frame ∼3 μm in a high-redshift LyC-emitting galaxy using MIRI/F1500W. Our analysis suggests a porous distribution of dust in Ion1, with regions exhibiting evidence of dust deficit coinciding both with LyC-emitting regions and with the peak of Hα emission. Furthermore, multiband NIRCam imaging reveals a strong far-UV-to-optical color gradient, where LyC-emitting regions appear significantly bluer than the rest of Ion1. Spatially resolved spectral energy distribution fitting confirms that this color gradient is primarily driven by spatially varying dust attenuation. Together, these findings suggest that Ion1's LyC emission originates from a compact star-forming complex near its stellar-light centroid, where stellar feedback carves out low-H I-column-density channels, facilitating LyC escape. However, only a fraction of these LyC photons—specifically those along sightlines with minimal H I obscuration—ultimately escape and reach observers. This work underscores the critical role of dust and neutral gas geometry in shaping LyC escape in galaxies at high redshifts. Anisotropic LyC escape may be a common feature in the early Universe, which must be properly incorporated to constrain the epoch of reionization.

Keywords: Extragalactic astronomy, Reionization, High-redshift galaxies
A North–South Metallicity Asymmetry in the Outer Galactic Disk—Evidence for the Pericentric Passage of the Sagittarius Dwarf Galaxy. We present maps of the mean metallicity distributions on the Galactocentric R–Z plane at different azimuthal angles using red clump stars selected from the LAMOST and APOGEE surveys. In the inner disk (R &lt; 11 kpc), the metallicity distribution is symmetric between the upper and lower disk. However, we find a north–south metallicity asymmetry in the outer disk (R &gt; 11 kpc), especially toward the anti-Galactic center (‑5∘ &lt; Φ &lt; 15°) direction. By further dissecting the map in age space, we detect this asymmetry across all mono-age stellar populations. However, the asymmetry is less pronounced in older populations (τ &gt; 8 Gyr) compared to younger ones (τ &lt; 6 Gyr). This reduced significance likely stems from three factors: larger age uncertainties, fewer stars in the outer disk, and the kinematically hotter nature of older populations. The observed metallicity asymmetry may be the consequence of the perturbation of the recent pericentric passage through the Galactic disk and tidal force of the well-known Sagittarius dwarf galaxy.

Keywords: Milky Way disk, Galaxy chemical evolution
Prospects for the Detection of High-redshift Gamma-Ray Bursts in the Era of EP and SVOM. Gamma-ray bursts (GRBs) are a promising probe of the high-redshift Universe, but their detection remains observationally challenging. In this work, we explore the detectability of high-z GRBs by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) and the coded-mask gamma-ray imager (ECLAIRs) on board the Space-based multi-band astronomical Variable Objects Monitor (SVOM). Using a population synthesis model calibrated to Swift GRB observations, we develop a tool to estimate high-z GRB detection rates for instruments with specific energy bands and sensitivities. Our results indicate that EP/WXT could detect  ∼5.1‑2.4+3.4  (with 68% confidence level) GRBs annually at z &gt; 6, compared to  ∼0.7‑0.4+1.0  events per year at z &gt; 6 for SVOM/ECLAIRs. While EP cannot independently determine redshifts (requiring optical/near-infrared, NIR, follow-up), its assumed ∼30% follow-up efficiency yields  ∼1.5‑0.7+1.0  confirmed z &gt; 6 GRBs annually. SVOM, equipped with dedicated follow-up telescopes, will promptly identify high-z candidates deserving deep NIR spectroscopy to ensure robust confirmation of high-z GRBs. We anticipate that EP and SVOM will open new avenues for utilizing enlarged samples of high-z GRBs to explore the early Universe. Moreover, EP will assemble a substantial sample of soft, low-luminosity GRBs at low-to-intermediate redshifts, providing critical insights into the structure of GRB jets.

Keywords: Observational cosmology, Gamma-ray bursts, Star formation
Central Concentration and Escape of Ionizing Photons in Galaxies at the Epoch of Reionization. Compact, low-mass galaxies with strong nebular emission are considered promising candidates for efficient ionizing photon production and escape. We present a spatially resolved analysis of 189 galaxies at redshifts z ∼ 6.7–7.6 in JADES GOODS-N and GOODS-S fields and selected via JWST/NIRCam F410M filter. By employing annular photometry and spectral energy distribution fitting across rest-frame UV to optical wavelengths, we investigate the internal structure of star formation, ionizing photon production and escape, as well as the resolved star formation histories within these galaxies. We find that these galaxies exhibit compact, centrally concentrated, and bursty star formation, especially in lower-mass systems ( logM*/M⊙&lt;9.0 ). The central regions of them display extreme [O III]+Hβ equivalent widths (&gt;1000 Å), high ionizing photon production efficiencies (ξion ∼ 1025.6 Hz erg‑1), steep UV slopes (∼‑2.3), and elevated escape fractions (fesc &gt; 0.08), with all these properties peaking in the inner regions. These findings reveal outside-in growth and rising star formation histories at z ∼ 7, with the central regions of them playing a pivotal role in driving cosmic reionization.

Keywords: Star formation, Reionization, High-redshift galaxies, Galaxy properties
First Robust Detection of Linear Polarization from Metric Solar Emissions: Challenging Established Paradigms. Polarimetric radio observations of the Sun can provide rich information about emission mechanisms and the propagation medium. For the past five decades, solar polarimetric studies at low radio frequencies have almost always assumed the absence of linear polarization. This has been based on the expectations from coronal propagation effects. Here we present the first robust evidence of linear polarization from solar emissions at meter wavelengths using simultaneous measurements with two telescopes of very different designs separated by thousands of kilometers—the Murchison Widefield Array and the upgraded Giant Metrewave Radio Telescope. Both data sets show consistent linear polarization fractions, confirming this detection. Rapid changes in morphology, as well as the fractional linear polarization at small time and frequency spans, further rule out any possibilities of an instrumental origin. Assuming the absence of linear polarization in solar radio emissions can result in incorrect interpretation of solar observations as well as those of other flare stars, which are often guided by learnings from solar studies. This discovery highlights the need for relaxing this assumption and is essential for precise estimation of polarization signatures, ultimately leading to a better understanding of the plasma conditions in the Sun and other stars.

Keywords: Solar coronal radio emission, Spectropolarimetry, Solar physics, Solar radio emission, Radio bursts, Solar corona, Active solar corona, Polarimetry
Central Cluster Galaxies: A Hot Spot for Detectable Gravitational Waves from Black Hole Mergers. Since pulsar timing arrays (PTAs) announced the evidence for a low-frequency gravitational-wave (GW) background, continuous waves (CWs) have been the next anticipated GW signals. In this work, we model CW sources detectable by PTAs based on the massive black hole (MBH) merger population in the ASTRID cosmological simulation. We evolve MBH binaries, simulate their GW emissions, and calculate their detection probability (DP) for PTAs. The most detectable CW sources are produced by MBH mergers with masses MBH &gt; 1010 M⊙ in the lowest-frequency bins with f &lt; 10 nHz. Remarkably, these mergers occur within massive galaxies with stellar mass M* &gt; 1012 M⊙ located at the center of galaxy clusters. Particularly striking in ASTRID is a triple merger event, wherein two consecutive mergers occur within 500 Myr interval in the same cluster core, generating high-DP CW signals at ∼2 and ∼10 nHz. We also investigate the electromagnetic signatures associated with these events: either single or dual active galactic nuclei in the massive host galaxies that are undergoing star formation. This research provides new insights into the low-frequency GW sky and informs future multimessenger searches for PTA CW sources.

Keywords: Supermassive black holes, Gravitational wave sources