SN 2025kg, linked to EP 250108a, is among the brightest broad-lined Type Ic supernova (SN) known, showing unique helium absorptions, a late-time broad H alpha, and an early bump. In this Letter, we propose a jet-cocoon origin to explain EP 250108a as off-axis cooling emission from a mildly relativistic inner cocoon viewed at similar to 45 degrees and the early bump of SN 2025kg as the outer cocoon cooling emission, both constraining an energy of similar to(1-2) x10(52) erg and a progenitor radius of similar to 5 R-circle dot. To explain SN 2025kg's exceptionally luminous peak, potential energy injection into the similar to 2.5 M-circle dot ejecta from a magnetar with initial period similar to 1.7 ms and magnetic field similar to 2 x10(15) G may be required, implying a rapidly rotating similar to 4 M-circle dot progenitor. Thus, the progenitor may be a low-mass helium star with an extended helium envelope, supported by helium absorption lines and an inferred weak pre-SN wind. Hydrogen-rich material may reside in the inner ejecta layers, as suggested by the late-time broad H alpha, possibly originating from main-sequence companion material evaporated by the magnetar wind. Since the observed near-solar metallicity challenges the popular quasi-chemically homogeneous evolution channel, the rapidly rotating helium star progenitor of EP 250108a/SN 2025kg might attain angular momentum by being tidally spun up by a main-sequence companion in a close binary formed through isolated binary evolution.
Using highly irregular agglomerated debris particles, we analyse the polarimetric observations of the second interstellar Comet 3I/ATLAS beyond the snow line. Unlike the vast majority of Solar system comets at shorter heliocentric distance, modelling of the polarization of the inner coma in Comet 3I/ATLAS necessarily requires water-ice particles (30-40 per cent by volume). Our modelling suggests the other two species to be Mg-rich silicate and organics/amorphous carbon, which are common for Solar system comets. The relative abundance of the Mg-rich silicates is lower than what was needed in modelling the polarization of Solar system comets. The modelling suggests that if Comet 3I/ATLAS were to keep its activity at heliocentric distances smaller than that of the snow line, it would be an extremely high P-max comet with P-max approximate to 36-40 per cent in red light.
We reanalysed the Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [O III]lambda 88 mu m emission line in JADES-GS-z14-0, so one of the most distant spectroscopically confirmed galaxies at z = 14.18. Our analysis shows a tentative detection of a velocity gradient of [O III]lambda 88 mu m using three independent tests: (1) construction of moment maps; (2) extraction of integrated spectra from a grid of apertures; and (3) spectro-astrometry in both the image and uv planes, confirming the presence of the velocity gradient at 3 sigma significance. We performed kinematical fitting using the KINMS code and estimated a dynamical mass of log(10)( M-dyn /M-circle dot) = 9.4(-0.4)(+0.8), with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion (sigma(v)) of<40 km s(-1) which results in an estimate of V-rot /sigma> 2.5. This result, if confirmed with higher resolution observations, would imply that kinematically cold discs are already in place at z similar to 14. Comparison with mock observations from the SERRA cosmological simulations confirms that even low-resolution observations are capable of detecting a velocity gradient in z > 10 galaxies as compact as JADES-GS-z14-0. This Letter shows that deeper ALMA or JWST (James Webb Space Telescope)/Near-Infrared Spectrograph integral field spectroscopy observations with high spatial resolution will be able to estimate an accurate dynamical mass for JADES-GS-z14-0, providing an upper limit to the stellar mass of this overluminous galaxy.
We investigate scaling relations for stellar mass, radius, and age in stars exhibiting solar-like oscillations using two observational data sets comprising 110 stars. Using data set 1 (80 stars), we derive empirical scaling relations incorporating asteroseismic parameters - the frequency of maximum oscillation power, large, and small frequency separations - alongside effective temperature and metallicity. To account for non-Gaussian uncertainties in the stellar parameters, we employ an ensemble machine learning approach that combines Ridge, Huber, and Gradient Boosting regressors to predict stellar mass, radius, and age, along with deriving the corresponding coefficients for the scaling relations. We assess coefficient uncertainties by combining jackknife and bootstrap resampling techniques. Using the resulting scaling relations, we predict the mass, radius, and age of 30 stars in data set 2. These predictions closely match observational data, even when the parameters slightly differ from those in the training set. The predicted stellar ages range from 2.29 to 10.09 Gyr, consistent with Solar-like oscillators. Our findings show that combining machine learning regression with resampling-based uncertainty estimation provides an effective and reliable approach for deriving scaling relations, offering valuable insights for stellar characterization in asteroseismic research.
In the vicinity of a supermassive black hole, magnetohydrodynamics (MHD) simulations and models of hot accretion flow predicted a density of injected pairs divided by the Goldreich-Julian density - the pair multiplicity - in the range 1-10(3). When the reconnection mechanism in the magnetosphere is introduced, the multiplicity could reach 10(8) -10(9) and can explain the observed superluminal radio blobs. Here we show that the range 1-10(3) is also difficult to reconcile with observations at the Alfven point of the M87 jet on the polar axis at few tens of gravitational radii. An axisymmetric and frozen flux MHD approach allows to show that the pair multiplicity on the Alfven point only depends on the black hole mass, the fluid temperature and velocity, the magnetic field, and the isorotation frequency. Normalizing our calculations from observational constraints on M87 jet and with reasonable assumptions, we obtain pair multiplicity around 10(9). In conclusion, for a pure pair plasma, the velocity and magnetic field deduced from observations of superalfvenic jets lead to high values of the pair multiplicity at the Alfven point.
Following the work by Rowan et al., I found that a large fraction of systems presented as triple/quadruple stars are in fact only blends. After careful inspection of 225 candidate systems from Rowan et al., I found that one-third of them are, in fact, only blended signals of two different eclipsing binaries, well separated from each other on the sky. Their typical angular separation is dozens of arcsec, reaching up to more than 100 arcsec for some targets. This is probably due to relatively large TESS pixels and insufficient cross-checking of all available catalogues and photometric data. I present a list of 76 confirmed blends with their correct identification and respective periods. Such a high fraction (33.8 per cent) of reported false-positive systems should be taken into account in future studies, when reporting to new discoveries of doubly eclipsing candidates.
The Dark Energy Spectroscopic Instrument (DESI) collaboration, combining their baryon acoustic oscillation (BAO) data with cosmic microwave background (CMB) anisotropy and supernovae data, have found significant indication against the Lambda cold dark matter (Lambda CDM) cosmology. This can also be interpreted as the significance of the detection of the w(a) parameter that measures variation of the dark energy equation of state. DESI's DR2 article quotes exclusion of Lambda CDM for combinations of BAO and CMB data with each of three different and overlapping supernovae compilations (at 2.8 sigma for Pantheon+, 3.8 sigma for Union3, and 4.2 sigma for DESY5). We show that one can neither choose amongst nor average over these three different significances. We demonstrate how a principled statistical combination yields a combined exclusion significance of 3.1 sigma. Further we argue that, faced with these competing significances, the most secure inference from the DESI DR2 results is the 3.1 sigma level exclusion of Lambda CDM obtained from combining DESI + CMB alone, omitting supernovae.
Flat rotational velocity curve out to 1 Mpc has been recently observed applying deprojection formula to infer the gravitational potential around isolated galaxies from weak gravitational lensing. Here, we focus on the theoretical self-consistent non-linear density wave model as an explanation for observed data, as an alternative to Lambda cold dark matter and Modified Newtonian Dynamics. The physics of this model relays on the non-linear soliton solution established in plasma physics applied on the spiral galaxy dynamics resolving several issues including flat rotational curve with baryonic matter only. This novel model is tested by baryonic Tully-Fisher relation (BTFR); expression of the rotational velocity from non-linear model is used to fit observed data by weak gravitational lensing. Fitted parameter, surface mass density, is used to calculate mass of the galaxy and construct BTFR, which agrees with BTFR obtained by weak gravity lensing; slope parameter is similar to 4, while the intercept is slightly higher indicating higher mass of the baryonic matter in the galaxy.
We introduce a laboratory experiment utilizing a water tornado to model Keplerian flows, which are relevant to astrophysical accretion discs. The tornado is generated by opposing water jet streams, creating a hyperbolic free surface that acts like a gravitational potential. Key findings demonstrate that tracer particles show a Keplerian rotation profile with Omega alpha r(-3/2) and conserved area speed, aligning with Kepler's third and second law. The experiment enables the determination of dimensionless quantities such as the flow's Reynolds number and the tracer particles' Stokes numbers. The effective Reynolds numbers measured, Re = 2 x 10(5), are within the range for turbulent protoplanetary discs of Re = 10(3) - 10(5). The recovered Stokes numbers (ranging between 10(-2) and 10(-1)) show excellent agreement with the major dust component. Furthermore, the set-up's advantages include its ability to achieve a large ratio between inner and outer radii, allowing for the study of global dynamics instead of local shear flows. It is diagnostically very accessible and geometrically flexible. The experiment opens a new avenue for studying the interaction between dust and gas in protoplanetary discs, relevant to grain growth and planet formation.
We analyse the ro-vibrational absorption bands of various molecular cations (HCO+, HCNH+, and N2H+) and neutral species (HCN, HNC, and HC3N) detected in the James Webb Space Telescope/Mid-Infrared Instrument Medium Resolution Spectrometer spectrum (4.9-27.9 mu m) of the local ultraluminous infrared galaxy IRAS 07251-0248. We find that the molecular absorptions are blueshifted by 160 km s(-1) relative to the systemic velocity of the target. Using local thermal equilibrium excitation models, we derive rotational temperatures (T-rot) from 42 to 185 K for these absorption bands. This range of measured T-rot can be explained by infrared radiative pumping as a by-product of the strength, effective critical density, and opacity of each molecular band. Thus, these results suggest that these absorptions originate in a warm expanding gas shell ((M)over dot similar to 90-330 M-circle dot yr(-1)), which might be the base of the larger scale cold molecular outflow detected in this source. Finally, the elevated abundance of molecular cations can be explained by a high cosmic ray ionization rate, with log(zeta(H2)/n(H) [cm(3) s(-1)]) in the range of -18.2 (from H-3(+)) to -19.1 (inferred from HCO+ and N2H+, which are likely tracing denser gas), consistent with a cosmic ray dominated chemistry as predicted by chemical models.
We present the results of a further investigation of the Class II methanol maser emission in the 14(1) - 14(0) A(-+) transition at 349.1 GHz discovered in 2016 in the remarkable core S255IR-SMA1, which harbours a similar to 20-M-circle dot protostar NIRS 3 that exhibited a disc-mediated accretion burst in 2015. The present study is based on observations of this object with Atacama Large Millimeter/submillimeter Array in Band 7 at the largest baselines, which provide an angular resolution of similar to 15 mas. We estimated the physical conditions in the region where the maser emission comes from, and in the surroundings, using the presumably quasi-thermal methanol lines in our bands and the CH3CN 19(K) - 18(K) line series. The total flux density in the 14(1) - 14(0) A(-+) line in 2021 is about two times higher than in 2019. A maser emission of about the same intensity in 2021 is detected for the first time in the 12(1) - 12(0) A(-+) transition at 336.9 GHz. The physical conditions in the masering and non-masering regions are similar. The masers are apparently excited by the radiation of the central source. Unfortunately, the existing models cannot adequately take into account this radiation. The 18(-3) - 17(-4) E transition at 345.919 GHz also shows characteristics of maser emission.
Most little red dots (LRDs) hosting active galactic nuclei (AGNs) show broad H alpha emission, which recent studies ascribe to scattering off free electrons within an ionized medium embedding the broad-line region (BLR), rather than directly from the BLR itself. If correct, this model would imply intrinsically narrower broad line widths, leading to black hole masses that are up to two orders of magnitude smaller than what is inferred when assuming that the whole broad line emission comes from the BLR. To test this, we present a joint analysis of multiple hydrogen recombination lines in the 'Rosetta Stone' AGNs, the brightest known LRD at z = 2.26. We show that H alpha, H beta, and Pa beta have different spectral profiles, which is inconsistent with the predictions of the simple scattering scenario. Additionally, we test a variety of exponential models and show that none of them can simultaneously reproduce all three line profiles with physically plausible parameters. The inadequacy of these models for the Rosetta Stone implies that the scenario of electron scattering by an ionized medium embedding the BLR is not universally applicable to LRDs and AGNs, and therefore provides a counterexample to the claim of a universal and systematic overestimation of black hole masses.
Far-ultraviolet (UV) radiation from massive stars launches photoevaporative winds from the outer regions of protoplanetary discs around other stars, removing gas and dust. Observations have identified a relation between the median dust disc mass and the external UV field strength. Here, we use disc evolutionary models to explore how this relation evolves over time, and with respect to other stellar and disc properties. We find that the slope for the relationship lambda(UV) flattens over time as populations age, possibly explaining the differences seen between the L1641-N and L1641-S clusters in Orion A. We determine that lambda(UV) depends on the stellar mass, where more massive stars exhibit steeper gradients than their lesser counterparts, in agreement with the differences seen between Herbig and T Tauri stars. Additionally, the strength of the mechanism for angular momentum transport, either viscosity or magnetohydrodynamic disc winds, is found to significantly affect lambda(UV) with stronger avalues reducing lambda(UV) due to more material accreting onto the central stars in weaker UV environments. Estimates of lambda(UV) from observations of L1641 place preliminary constraints on alpha to be between 10(-3.5) and 10(-2.5), consistent with literature estimates. Further observations in different regions and better classifications of stellar masses will allow us to place stringent constraints on disc evolution properties, improving our understanding of how protoplanetary discs evolve.
A major attraction of diffusive shock acceleration is the prediction of power-law spectra for energetic particle distributions. However, this property is not fundamental to the theory. We demonstrate that for planar shocks with an oblique magnetic field the generation of power-law spectra critically requires the particles' scattering rate to be both directly proportional to their gyro radius (Bohm scaling) and spatially uniform. Non-Bohm scaling results in curved spectra at oblique shocks, while abrupt changes in the spatial profile of the scattering upstream introduces spectral breaks. Using the publicly available code Sapphire++, we numerically explore the magnitude of these effects, which are particularly pronounced at fast shocks, as expected in active galactic nuclei and microquasar jets, or young supernova remnants.
Multiple populations (MPs) is a intra-star cluster phenomenon consisting in star-to- star variation of the abundance of some light chemical elements. They have been observed in many star clusters, most of them old globular clusters, populating the Milky Way and other satellite galaxies. Since the study of MPs became more system- atic, different astrophysical parameters have been claimed to be the main responsible for its occurrence. However, at the present time, no attempt would seem to have solved this conundrum. This work deals with a potential trigger of the MPs phenomenon, based on the gathered observational evidence of the existence of MPs in some star clusters and the absence of its in others. We found that star clusters with MPs mostly formed during time intervals of intense star formation activity in a galaxy, for instance during the galaxy formation epoch, a close galaxy encounter, etc. At those time inter- vals where relative peaks in the galaxy star formation rate occur, star clusters with masses above a lower mass limit harbour MPs. This lower star cluster mass limit would marginally depend on the star cluster age.
Eclipsing brown dwarfs are important calibrators of substellar evolution models used to infer the characteristics of directly imaged brown dwarfs and giant exoplanets. Only two double brown dwarf eclipsing binary systems are known, among them 2MASS J15104786-2818174 (2M1510 AB), published in 2020 with a poorly constrained orbital period. Here, we analyse the Transiting Exoplanet Survey Satellite (TESS) full-frame image photometry of this faint (T-mag = 15.9) binary and detect a significant (>10 sigma) periodic signal spanning TESS Cycles 1-7, consistent with previous data. We refine the orbital period to 20.897782 +/- 0.000036 d, reducing its present-day uncertainty from 18 h to 8 min. Our work is crucial for scheduling follow-up observations of this system for a detailed study with other photometric facilities. We also find that a recent orbital solution from Doppler data is inconsistent with existing photometry. A timing offset in the Doppler data may have produced a spurious signal mimicking retrograde apsidal precession, from which the claimed circumbinary planet 2M1510 ABb was inferred. From our best attempt at correcting the data, we were unable to reconcile the radial velocity data with the photometry, suggesting that the radial velocity uncertainties are underestimated, and that the circumbinary planet 2M1510 ABb may be a false positive.
The luminous fast blue optical transient (LFBOT) AT 2018cow is the prototype of its class with an extensive set of multiwavelength observations. Despite a rich data set there is, still, no consensus about the physical nature and origin of this event. AT 2018cow remained UV bright 2-4 yr after the explosion, which points at an additional energy injection source, most likely from an accretion disc. We present additional late time ultraviolet (UV) data obtained with the Hubble Space Telescope, to show there is no significant fading in the optical since the last epoch and only marginal fading in the UV. The new UV data points match the predictions of previously published accretion disc models, where the disc is assumed to form from the tidal disruption of a low-mass star by an intermediate-mass black hole. This consistency provides evidence that AT 2018cow could indeed be a tidal disruption event. The marginal decay is in contrast with the predictions of light curves produced by interacting supernovae. The difference between expectations for disc emission and interacting supernovae will further increase with time, making data at even later times a route to robustly rule out interaction between supernova ejecta and circumstellar material.
Compact symmetric objects (CSOs) are thought to be short-lived radio sources with two lobes of emission that are separated by less than a kpc in projection. However, studies of such systems at high redshift are challenging due to the limited resolution of present-day telescopes, and can be biased to the most luminous objects. Here, we report imaging of a gravitationally lensed CSO at a redshift of 2.059 using very long baseline interferometry at 1.7 GHz. The data are imaged using Bayesian forward modelling deconvolution, which reveals a spectacularly extended and thin gravitational arc, and several resolved features within the lensed images. The surface brightness of the lensing-corrected source shows two mini-lobes separated by 642 pc in projection, with evidence of multiple hotspots that have brightness temperatures of 10(8.6) to 10(9.2) K, and a total luminosity density of 10(26.3) W Hz(-1). By combining the well-resolved radio source morphology with previous multiwavelength studies, we conclude that this object is likely a CSO of type 2, and that the properties are consistent with the bow-shock model for compact radio sources. Our analysis highlights the importance of combining high-quality data sets with sophisticated imaging and modelling algorithms for studying the high-redshift Universe.
The October Draconid meteor shower, produced by comet 21P/Giacobini-Zinner, is notorious for rare but intense outbursts, some exceeding rates of similar to 10(4) meteors per hour. In 2025, Earth will encounter young trails ejected by the comet in 2005 and 2012, producing a meteor outburst and providing a rare opportunity to probe their structure and benchmark meteoroid stream models. We present predictions from three independent dynamical models (NIMS, MSFC, Sisyphus), calibrated against updated activity profiles including the newly observed 2019 and 2024 outbursts. All simulations predict enhanced activity on 2025 October 8, dominated by faint meteors (m < 10(-5) kg; +4 mag and fainter) primarily detectable by radar. Our best estimate is a radar outburst near 15:00-16:00 UT, driven mainly by the 2012 trail with a possible minor contribution from 2005. The 2025 Draconids may represent one of the strongest radar dominated outbursts of the decade. Coordinated observing campaigns, especially radar measurements across the Northern Hemisphere and optical coverage from Asia, will be essential to validate these forecasts, constrain the dust environment of comet 21P, and improve future predictions of young meteoroid trails.
Active galactic nuclei (AGNs) exhibit stochastic optical variability, commonly characterized by a damped random walk. The damping time-scale is of particular interest because it is related to fundamental properties of the central black hole, such as its mass and accretion rate. However, the systematic underestimation of damping time-scales caused by limited observational baselines makes it difficult to exhaustively utilize all available data. Many previous efforts have relied on strict selection criteria to avoid biased measurements, and such criteria inevitably constrain the range of AGN physical parameter space and therefore hinder robust inference of the underlying dependencies of damping time-scale on AGN properties. In contrast, we introduce a novel forward modelling approach, Baseline-Aware Dependence fitting for DAmping Timescales (BADDAT), which explicitly accounts for these biases and leverages the information contained in underestimated time-scale measurements. Rather than attempting to correct individual time-scale measurements, BADDAT robustly constrains the population-level dependence of damping time-scale on AGN physical properties. We demonstrate its effectiveness using mock light curves and show that it successfully reconciles previous inconsistent results based on two independent AGN samples. Our BADDAT method will have broad applications in AGN variability studies during the era of time-domain astronomy.
