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- Cold collapse and bounce of an FLRW cloud(2025) Pradhan, Swaraj; Gabler, Michael; Gaztañaga, EnriqueWe study the collapse of spherical cold clouds beyond black hole formation to investigate the possibility of a bounce in the in-falling matter when a critical density or pressure is reached. As a first step, we analyse the pressureless collapse in general relativity (GR), where an analytic solution exists, and demonstrate that an equivalent Newtonian solution can be derived. Such equivalence also holds for spherically symmetric perfect fluids with uniform density and non-vanishing pressure. We numerically investigate the Newtonian collapse of such clouds with masses of 5, 20, and 1000 M obeying a polytropic equation of state (EoS). By choosing EoS parameters inspired by typical neutron star conditions, we observe bounces at and above nuclear saturation density. Assuming approximate uniformity, we explore the equivalent GR behaviour of the matter during the bounce. Our findings are as follows: (i) A GR bounce occurs around the ground state of the matter, characterized by . (ii) The GR solution differs significantly from the Newtonian result due to the presence of curvature ( ). (iii) Both the curvature and the ground state are crucial factors in allowing a GR bounce to occur.
- Multitemporal assessment of burned areas and fire severity in Ourense (August 2025) using Sentinel-2 imagery(2025) Sobrino Rodríguez, José A.; Llorens Company, RafaelThis study analyzes the burned area and fire severity of the forest fires that occurred in Ourense in August 2025. The analysis was based on Sentinel-2 imagery, which provides near-infrared (NIR) and short-wave infrared (SWIR) bands suitable for distinguishing between burned and unburned surfaces, as well as different severity levels. Several spectral indices widely applied in wildfire remote sensing were employed, including the Normalized Burn Ratio (NBR), the Burned Area Index for Sentinel-2 (BAIS2), and the Relativized Burn Ratio (RBR), together with their differential forms (e.g., dNBR). Temporal comparisons between pre- and post-fire conditions allowed a multitemporal assessment of fire progression and impact. Field plots were compared with the satellite-derived classification to evaluate accuracy (88%). The results demonstrate that Sentinel-2 data enable a precise delineation of burned areas and a reliable classification of severity levels in forest fires in Ourense. This study confirms the potential of satellite-based indices, supported by limited field validation, to provide rapid and accurate information for forest fires assessment and post-fire management.
- Assessing the Potential of Land Surface Emissivity for Land Cover Classification(2025) Li, Xiujuan; Sobrino Rodríguez, José A.; Wu, HuaAs an inherent property of natural materials, Land Surface Emissivity (LSE) varies across different land surface materials, serving as an indicator of the composition and changes in land covers. However, due to the limitations in sensor level, there were few studies on land surface classification based on LSE. With the development of hyperspectral thermal infrared (TIR) remote sensing, research on land surface classification using emissivity spectra is expected to be put on the agenda. Therefore, this study examined the potential of land cover classification using the LSEs of 17 types selected from ECOSTRESS spectral database. The analysis was conducted using the Spectral Angle Mapper (SAM) method and the Munn-Whitney U (MWU) test. Results showed that some land cover types had distinct separability in LSE spectra, particularly for alfisol, entisol, tree, lichen, flower and igneous rock. Moreover, most of the soil and vegetation used in this study exhibited a significant difference (exceeding 70 %) across wavelengths. However, some surfaces remain indistinguishable, such as different types of man-made surfaces. In general, land surface classification using emissivity spectra has great development potential. Nevertheless, this study only analyzes a subset of land surfaces, which is a limitation. In the future, more in-depth analysis should be conducted using a wider variety of data types.
- Ring Asymmetry and Spin in M87*(2026) Bernshteyn, Vadim; Akiyama, Kazunori; Algaba, Juan Carlos; Ros Ibarra, Eduardo; Albentosa Ruiz, Ezequiel; Zhao, Guang-Yao;Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring's peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a*. We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor ∣a*∣ ≲ 0.2. This is consistent with the Blandford─Znajek model for M87's jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.
- The persistent shadow of the supermassive black hole of M 87 I. Observations, calibration, imaging, and analysis(2024) Akiyama, Kazunori; Martí Vidal, Iván; Ros Ibarra, Eduardo; Algaba, Juan Carlos; Yu, Chen-YuIn April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3−3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5 × 109 M⊙. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.
- First Very Long Baseline Interferometry Detections at 870 μm(2024) Raymond, Alexander W.; Ros Ibarra, Eduardo; Martí Vidal, Iván; Zhao, Shan-ShanThe first very long baseline interferometry (VLBI) detections at 870 μm wavelength (345 GHz frequency) are reported, achieving the highest diffraction-limited angular resolution yet obtained from the surface of the Earth and the highest-frequency example of the VLBI technique to date. These include strong detections for multiple sources observed on intercontinental baselines between telescopes in Chile, Hawaii, and Spain, obtained during observations in 2018 October. The longest-baseline detections approach 11 Gλ, corresponding to an angular resolution, or fringe spacing, of 19 μas. The Allan deviation of the visibility phase at 870 μm is comparable to that at 1.3 mm on the relevant integration timescales between 2 and 100 s. The detections confirm that the sensitivity and signal chain stability of stations in the Event Horizon Telescope (EHT) array are suitable for VLBI observations at 870 μm. Operation at this short wavelength, combined with anticipated enhancements of the EHT, will lead to a unique high angular resolution instrument for black hole studies, capable of resolving the event horizons of supermassive black holes in both space and time.
- Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode(2024) Algaba, Juan Carlos; Martí Vidal, Iván; Ros Ibarra, Eduardo; Zhong, W.Context. The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio to γ-ray energies) took part in the second M87 EHT campaign. Aims. The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity. Methods. The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high-energy (VHE) γ-rays as well as details of the individual observations and light curves. We also conducted phenomenological modelling to investigate the basic source properties. Results. We present the first VHE γ-ray flare from M87 detected since 2010. The flux above 350 GeV more than doubled within a period of ≈36 hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image. Conclusions. Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHE γ-ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and it emphasises the need for combined image and spectral modelling.
- The putative center in NGC 1052(2024) Baczko, Anne-Kathrin; Kadler, Matthias; Ros Ibarra, Eduardo; Fromm, Christian M.; Wielgus, Maciek; Perucho Pla, Manuel; Martí Vidal, Iván; Zha, Guang-YaoContext. Many active galaxies harbor powerful relativistic jets, however, the detailed mechanisms of their formation and acceleration remain poorly understood. Aims. To investigate the area of jet acceleration and collimation with the highest available angular resolution, we study the innermost region of the bipolar jet in the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 1052. Methods. We combined observations of NGC 1052 taken with VLBA, GMVA, and EHT over one week in the spring of 2017. Our study is focused on the size and continuum spectrum of the innermost region containing the central engine and the footpoints of both jets. We employed a synchrotron-self absorption model to fit the continuum radio spectrum and we combined the size measurements from close to the central engine out to ∼1 pc to study the jet collimation. Results. For the first time, NGC 1052 was detected with the EHT, providing a size of the central region in-between both jet bases of 43 μas perpendicular to the jet axes, corresponding to just around 250 RS (Schwarzschild radii). This size estimate supports previous studies of the jets expansion profile which suggest two breaks of the profile at around 3 × 103 RS and 1 × 104 RS distances to the core. Furthermore, we estimated the magnetic field to be 1.25 Gauss at a distance of 22 μas from the central engine by fitting a synchrotron-self absorption spectrum to the innermost emission feature, which shows a spectral turn-over at ∼130 GHz. Assuming a purely poloidal magnetic field, this implies an upper limit on the magnetic field strength at the event horizon of 2.6 × 104 Gauss, which is consistent with previous measurements. Conclusions. The complex, low-brightness, double-sided jet structure in NGC 1052 makes it a challenge to detect the source at millimeter (mm) wavelengths. However, our first EHT observations have demonstrated that detection is possible up to at least 230 GHz. This study offers a glimpse through the dense surrounding torus and into the innermost central region, where the jets are formed. This has enabled us to finally resolve this region and provide improved constraints on its expansion and magnetic field strength.
- Shaping Galactic habitability: Impact of stellar migration and gas giants(2025) Spitoni, E.; Palla, M.; Magrini, L.; Matteucci, F.; Danielski, Camilla; Tsantaki, M.; Sozzetti, A.; Molero, M.; Fontani, F.; Romano, D.; Cescutti, G.; Silva, L.In exoplanet research, studies are increasingly focussed on identifying planets that similar in density and habitability potential to our planet, known as Earth analogs. As the number of known rocky exoplanets grows, parallel discussions have emerged on system architectures and galactic environments that may support life, drawing comparisons to our own planet. This has brought renewed attention to the concept of the Galactic habitable zone (GHZ) as a broader context for interpreting the diversity of planetary environments. This study is the first to use detailed chemical evolution models to investigate the impact of stellar migration, modelled through a parametric approach, on the GHZ. Our findings reveal that stellar migration significantly enhances the number of stars capable of hosting habitable planets in the outer Galactic regions, with an increase of up to a factor of five at 18 kpc relative to a baseline value of unity at 6 kpc. Furthermore, we have explored a novel scenario where the presence of gas giant planets increases the probability for the formation of terrestrial ones. We find that this increased probability is higher in the inner Galactic disc, but is also mitigated by stellar migration. In particular, at the present time, the number of FGK stars hosting terrestrial planets with minimum habitability conditions in the ring centred at 4 kpc is approximately 1.4 times higher than in scenarios where gas giants are assumed to hinder the formation and evolution of Earth-like planets. Without stellar migration, this factor increases to 1.5. Even larger ratios are predicted for terrestrial planets orbiting retired A stars, reaching 2.8 in models with stellar migration and 3.3 in models without it. In conclusion, this study shows that stellar migration predominantly influences the GHZ in the outer Galactic regions, while assuming a positive contribution from gas giants to terrestrial planet formation increases the number of stars capable of hosting habitable planets in the Galactic ring centred at 4 kpc.
- A Gamma-Ray Flare from TXS 1508+572: Characterizing the Jet of a z = 4.31 Blazar in the Early Universe(2024) Gokus, A.; Heßdörfer, J.; Eppel, F.; Kadler, Matthias; Benke, P.; Ros Ibarra, Eduardo; Rösch, F.; Wilms, JörnBlazars can be detected from very large distances due to their high luminosity. However, the detection of γ-ray emission of blazars beyond z = 3 has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 z > 3 blazars with the Fermi Large Area Telescope (Fermi-LAT), we present the first detection of a γ-ray flare from the z = 4.31 blazar TXS 1508+572. This source showed high γ-ray activity from 2022 February to August, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi-LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, the Neil Gehrels Swift Observatory, the Effelsberg 100 m radio telescope, and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and the Near-Earth Object Wide-field Infrared Survey Explorer at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily timescales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the γ-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons.
- The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. VI. Evidence for Radially Evolving Icy Grains in the HD 141569A Disk via NIRCam Coronagraphic Imaging(2025) Choquet, Elodie; Kammerer, Jens; Hinkley, Sasha; Booth, Mark; Biller, Beth A.; Skemer, Andrew; Meyer, Michael R.; Boccaletti, Anthony; Perrin, Marshall D.; Absil, Olivier; Balmer, William O.; Calissendorff, Per; Cugno, Gabriele; Currie, Thayne; Danielski, Camilla; Lagage, Pierre-Olivier; Ray, ShrishmoyWe present JWST NIRCam coronagraphic observations of the HD 141569A circumstellar disk, obtained as part of the JWST Early Release Science program. The observations recover the multi-ringed structure seen in previous shorter-wavelength observations, but at filters centered on the ∼3 μm water ice absorption feature and a complementary continuum region (F300M and F360M, respectively). The observations reveal apparent absorption between the F300M and F360M filters that decreases with radius, with a notable change around 200 au, between the innermost and outermost two rings. These results are consistent whether the data is reduced via deconvolution or through a forward-modeling approach. We demonstrate that these changes suggest a radial decrease in the water ice mass fraction by a factor of ∼3-10 and possibly a change in minimum grain size. We do not detect any point sources within the system and can exclude planetary companions 2 Jupiter masses and greater beyond 1″ radius (∼111 au). These observations and the subsequent analysis illustrate a robust pathway for using JWST/NIRCam to characterize the distribution of water ice in other circumstellar disks. We highlight some of the early lessons learned from this work that we hope will be useful for future circumstellar disk observation planning and analysis.
- A JWST/MIRI view of κ Andromedae b: Refining its mass, age, and physical parameters(2025) Godoy, N.; Choquet, Elodie; Serabyn, Eugene; Mâlin, Mathilde; Tremblin, Pascal; Danielski, Camilla; Lagage, Pierre-Olivier; Boccaletti, Anthony; Charnay, Benjamin; Ressler, M. E.Context. κ And b is a substellar companion with a mass near the planet-brown dwarf boundary orbiting a B9IV star at ~50-100 au. Estimates of its age and mass vary, which has fueled a decade-long debate. Additionally, the atmospheric parameters (Teff 1650-2050 K and log(g) 3.5-5.5 dex) remain poorly constrained. The differences in atmospheric models and inhomogeneous datasets contribute to the varied interpretations. Aims. We aim to refine the characterization of κ And b by using mid-infrared data to capture its full bolometric emission. Combined with near-infrared (NIR) measurements, we aim to constrain Teff, log(g), and the radius to narrow down the uncertainties in age and mass. Methods. We obtained JWST/MIRI coronagraphic data in the F1065C, F1140C, and F1550C filters and recalibrated existing NIR photometry using an updated ATLAS stellar model. We used MIRI color-magnitude diagrams to probe the likelihood of species (e.g., CH4, NH3, and silicates). We compared the H and F1140C colors and magnitudes of the companion to isochrones to constrain the age and mass. We then modeled its spectral energy distribution with atmospheric models to refine the estimates of Teff, radius, and log(g) and to constrain age and mass using evolutionary models. Results. Cloudy atmosphere models fit the spectral energy distribution of κ And b best. This is consistent with its L0/L2 spectral type and its position near silicate-atmosphere field objects in the MIRI color-magnitude diagram. We derived an age of 47 ± 7 Myr and a mass of 17.3 ± 1.8 MJup by weight-mean combining the models. Atmospheric modeling yielded Teff = 1791 ± 68 K and a radius of 1.42 ± 0.06 RJup. This improves the precision by ~30% over previous estimates. log(g) was constrained to 4.35 ± 0.07 dex, which is an improvement in the precision by ~70% relative to the most precise literature value of 4.75 ± 0.25 dex. Conclusions. Our new mass estimate places κ And b slightly above the planet-brown dwarf boundary determined by the deuterium-burning limit. Our age estimate is ~75% more precise than previous values and aligns the object with the Columba association (42 Myr). The derived Teff suggests silicate clouds, but this needs to be confirmed spectroscopically. MIRI data were crucial to refine the radius and temperature, which led to stronger constraints on the age and mass (both dependent on the model) and improved the overall characterization of κ And b.
- The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. III. Aperture Masking Interferometric Observations of the Star HIP 65426 at 3.8 μm(2025) Ray, Shrishmoy; Sallum, Steph; Hinkley, Sasha; Sivaramkrishnan, Anand; Cooper, Rachel; Kammerer, Jens; Greebaum, v; Thatte, Deeparshi; Stolker, Tomas; Lazzoni, Cecilia; Tokovinin, Andrei; Furio, Matthew de; Factor, Samuel; Meyer, Michael R.; Stone, Jordan M.; Carter, Aarynn; Biller, Beth A.; Skemer, Andrew; Suárez, Genaro; Leisenring, V.; Perrin, Marshall D.; Kraus, Adam L.; Absil, Olivier; Balmer, William O.; Boccaletti, Anthony; Bonavita, Mariangela; Bonnefoy, Mickael; Booth, Mark; Bowler, Brendan P.; Briesemeister, Zackery W.; Bryan, Marta L.; Calissendorff, Per; Faustine Cantalloube; Gael Chauvin; Christine H. Chen; Elodie Choquet; Christiaens, Valentin; Cugno, Gabriele; Currie, Thayne; Danielski, CamillaWe present aperture masking interferometry (AMI) observations of the star HIP 65426 at 3.8 μm, as part of the JWST Direct Imaging Early Release Science program, obtained using the Near Infrared Imager and Slitless Spectrograph instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of 0.5λ/D for an interferometer), which are inaccessible with the classical inner working angles of the JWST coronagraphs. When combined with JWST's unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a 5σ contrast of ΔmF380M ∼ 7.62 ± 0.13mag relative to the host star at separations ≥.07, and the contrast deteriorates steeply at separations ≤.07. However, we detect no additional companions interior to the known companion HIP65426b (at separation ∼0 '82 or+ 87 108 31 au ). Our observations thus rule out companions more massive than 10-12MJup at separations ∼10-20 au from HIP65426, a region out of reach of ground- or space-based coronagraphic imaging. These observations confirm that the AMI mode on JWST is sensitive to planetary mass companions at close-in separations (≥.07), even for thousands of more distant stars
- First unambiguous detection of ammonia in the atmosphere of a planetary mass companion with JWST/MIRI coronagraphs(2025) Mâlin, Mathilde; Boccaletti, Anthony; Perrot, Clément; Baudoz, Pierre; Rouan, Daniel; Lagage, Pierre-Olivier; Waters, Rens; Güdel, Manuel; Henning, Thomas; Vandenbussche, Bart; Absil, Olivier; Barrado, David; Charnay, Benjamin; Choquet, Elodie; Cossou, Christophe; Danielski, Camilla; Decin, Leen; Glauser, Adrian M.; Pye, John; Olofsson, Goran; Glasse, Alistair; Patapis, Polychronis; Royer, Pierre; Scheithauer, Silvia; Serabyn, Eugene; Tremblin, Pascal; Whiteford, Niall; Dishoeck, Ewine F. van; Ostlin, Göran; Ray, Tom P.; Wright, GillianContext. The newly accessible mid-infrared (MIR) window offered by the James Webb Space Telescope (JWST) for exoplanet imaging is expected to provide valuable information to characterize their atmospheres. In particular, coronagraphs on board the JWST Mid-InfraRed instrument (MIRI) are capable of imaging the coldest directly imaged giant planets at the wavelengths where they emit most of their flux. The MIRI coronagraphs have been specially designed to detect the NH3 absorption around 10.5 µm, which has been predicted by atmospheric models and should be detectable for planets colder than 1200 K. Aims. We aim to assess the presence of NH3 while refining the atmospheric parameters of one of the coldest companions detected by directly imaging GJ 504 b. Its mass is still a matter of debate and depending on the host star age estimate, the companion could either be placed in the brown dwarf regime of ∼20 MJup or in the young Jovian planet regime of ∼4 MJup. Methods. We present an analysis of new MIRI observations, using the coronagraphic filters F1065C, F1140C, and F1550C of the GJ 504 system. We took advantage of previous observations of reference stars to build a library of images and to perform a more efficient subtraction of the stellar diffraction pattern. We used an atmospheric grid from the Exo-REM model to refine the atmospheric parameters by combining archival near-infrared (NIR) photometry with the MIR photometry. Results. We detected the presence of NH3 at 12.5 σ and measured its volume mixing ratio of 10−5.3±0.07 in the atmosphere of GJ 504 b. These results are in line with atmospheric model expectations for a planetary-mass object and observed in brown dwarfs within a similar temperature range. The best-fit model with Exo-REM provides updated values of its atmospheric parameters, yielding a temperature of Teff = 512 ± 10 K and radius of R = 1.08−0.03+0.04 RJup. Conclusions. These observations demonstrate the capability of MIRI coronagraphs to detect NH3 and to provide the first MIR observations of one of the coldest directly imaged companions. Overall, NH3 is a key molecule for characterizing the atmospheres of cold planets, offering valuable insights into their surface gravity. These observations provide valuable information for future spectroscopic observations planned with JWST, in particular, with the MIRI medium-resolution spectrometer (MRS), which will allow us to characterize the atmosphere of GJ 504 b in depth.
- Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations(2026) Saurabh; Ros Ibarra, Eduardo; Shan-Shan, ZhaoWe investigate the presence and spatial characteristics of the jet base emission in M87* at 230 GHz, enabled by the significantly enhanced (u,v) coverage in the 2021 Event Horizon Telescope (EHT) observations. The integration of the 12−m Kitt Peak Telescope (USA) and NOEMA (France) stations into the array introduces two critical intermediate-length baselines to SMT (USA) and IRAM 30−m (Spain), providing sensitivity to emission structures at spatial scales of ∼250 μas and ∼2500 μas (∼ 0.02 pc and ∼ 0.02 pc). Without these new baselines, previous EHT observations of the source in 2017 and 2018 lacked the capability to constrain emission on large scales, where a 'missing flux' of order ∼1 Jy is expected to reside. To probe these scales, we analyzed closure phases─robust against station-based gain calibration errors─and model the jet base emission using a simple Gaussian component offset from the compact ring emission at spatial separations > 100 μas. Our analysis revealed a Gaussian feature centered at (∆RA ≍ 320 μas, ∆Dec. ≍ 60 μ as), projected separation of ≍ 5500 AU, with an estimated flux density of only ∼60 mJy, implying that most of the missing flux identified in previous EHT studies had to originate from different, larger scales. Brighter emission at the relevant spatial scales is firmly ruled out, and the data do not favor more complex models. This component aligns with the inferred position of the large-scale jet and is therefore physically consistent with the emission of the jet base. While our findings point to detectable jet base emission at 230 GHz, the limited coverage provided by only two intermediate baselines limits our ability to robustly reconstruct its morphology. Consequently, we treated the recovered Gaussian as an upper limit on the jet base flux density. Future EHT observations with expanded intermediate baseline coverage will be essential to constrain the structure and nature of this component with higher precision.
- Ariel stellar characterisation III. Fast rotators and new FGK stars in the Ariel mission candidate sample(2025) Tsantaki, M.; Magrini, L.; Danielski, Camilla; Bossini, D.; Turrini, D.; Moedas, D.; Folsom, C. P.; Ramler, H.; Biazzo, K.; Campante, T. L.; Delgado-Mena, E.; Da Silva, R.; Sousa, S. G.; Benatti, S.; Casali, G.; Helminiak, K.G; Rainer, M.; Sanna, N.Context. The next mission dedicated to the study of planetary atmospheres is the Ariel space mission, planned for launch in 2029, which will observe a variety of planetary systems belonging to different classes around stars with spectral types from M to A. To optimise the scientific outcome of the mission, such stars need to be homogeneously characterised beforehand. Aims. In this work, we focus on a methodology based on spectral synthesis for the characterisation of FGK-type stars from the Ariel Tier 1 mission candidate sample (MCS) that exhibit fast rotation. In addition, we analyse 108 slow-rotating FGK-type stars, with either new observations or archival spectra available, consistently as in our previous work using the equivalent width (EW) analysis. Methods. To ensure consistency between our methods, we re-analysed a sample of FGK-type stars with the spectral synthesis method and compared it to our previous work. The results of our analysis show excellent agreement with the previous set of derived parameters. Results. We provide homogeneous effective temperature, surface gravity, metallicity, projected rotational velocity, and stellar mass for a sample of 36 fast rotators with the spectral synthesis technique, and we include 108 FGK-type dwarfs with the EW analysis. An additional 25 stars were analysed with the spectral synthesis method because their EW analysis did not converge on the final parameters.We computed their orbital parameters establishing whether they belong to the Galactic thin or thick discs.With the current set of stellar parameters, we almost double the analysed hosts in the Ariel MCS to 353 stars in total. Conclusions. Using our homogeneous set of stellar parameters, we studied the correlations between stellar and planetary properties for the Ariel MCS analysed so far. We confirmed a close relationship between stellar mass (up to 1.8M⊙) and giant planet radius, with more inflated planets at lower metallicity. We confirm that giant planets are more frequent around more metal-rich stars that belong to the thin disc, while lower-mass planets are also found in more metal-poor environments, and are more frequent than giant planets in the thick disc as also seen in other works in the literature. © The Authors 2025.
- TANAMI: Tracking active galactic nuclei with austral milliarcsecond interferometry. III. First-epoch S band images(2024) Benke, P.; Rösch, F.; Ros Ibarra, Eduardo; Kadler, Matthias; Ojha, R.; Edwards, P. G.; Horiuchi, S.; Stevens, J.; Phillips, C.; Tzioumis, A. K.; Weston, S.Context. With the emergence of very high energy astronomy (VHE; E > 100 GeV), new open questions were presented to astronomers studying the multi-wavelength emission from blazars. Answers to these open questions, such as the Doppler crisis, and finding the location of the high-energy activity have eluded us thus far. Recently, quasi-simultaneous multi-wavelength monitoring programs have shown considerable success in investigating blazar activity. Aims: Such quasi-simultaneous observations across the electromagnetic spectrum became possible thanks to the launch of the Fermi Gamma-ray Space Telescope in 2008. In addition, with very long baseline interferometry (VLBI) observations, we can resolve the central parsec region of active galactic nuclei (AGN) and compare morphological changes to γ-ray activity in order to study high-energy-emitting blazars. To achieve our goals, we need sensitive, long-term VLBI monitoring of a complete sample of VHE-detected AGN. Methods: We performed VLBI observations of TeV-detected AGN and high-likelihood neutrino associations as of December of 2021 with the Long Baseline Array (LBA) and other southern-hemisphere radio telescopes at 2.3 GHz. Results: In this paper, we present first light TANAMI S-band images, focusing on the TeV-detected subsample of the full TANAMI sample. In addition to these VHE-detected sources, we show images of two flux density calibrators and two additional sources included in the observations. We study the redshift, 0.1-100 GeV photon flux, and S-band core brightness temperature distributions of the TeV-detected objects, and find that flat-spectrum radio quasars and low-synchrotron-peaked sources on average show higher brightness temperatures than high-synchrotron-peaked BL Lacs. Sources with bright GeV γ-ray emission also show higher brightness temperature values than γ-low sources. Conclusions: Long-term monitoring programs are crucial for studying the multiwavelength properties of AGN. With the successful detection of even the faintest sources, with flux densities below 50 mJy, future work will entail kinematic analysis and spectral studies both at 2.3 and 8.4 GHz to investigate the connection between the radio and γ-ray activity of these objects.
- Lost in the curve: Investigating the disappearing knots in blazar 3C 454.3(2024) Traianou, Efthalia; Krichbaum, T. P.; Gómez, José L.; Lico, Rocco; Paraschos, G. F.; Cho, Ilje; Ros Ibarra, Eduardo; Zhao, Guang-Yao; Liodakis, Ioannis; Dahale, Rohan; Toscano, Teresa; Fuentes, Antonio; Foschi, Marianna; MacDonald, Nicholas R.; Jorstad, Svetlana; Lobanov, Andrei P.One of the most well-known extragalactic sources in the sky, quasar 3C 454.3, shows a curved parsec-scale jet that has been exhaustively monitored with very-long-baseline interferometry (VLBI) over the recent years. In this work, we present a comprehensive analysis of four years of high-frequency VLBI observations at 43 GHz and 86 GHz, between 2013-2017, in total intensity and linear polarization. The images obtained from these observations enabled us to study the jet structure and the magnetic field topology of the source on spatial scales down to 4.6 parsec in projected distance. The kinematic analysis reveals the abrupt vanishing of at least four new superluminal jet features in a characteristic jet region (i.e., region C), which is located at an approximate distance of 0.6 milliarcsec from the VLBI core. Our results support a model in which the jet bends, directing the relativistic plasma flow almost perfectly toward our line of sight, co-spatially with the region where components appear to stop.
- Evidence of a toroidal magnetic field in the core of 3C 84(2024) Paraschos, G. F.; Krichbaum, T. P.; Ros Ibarra, Eduardo; Bach, U.; Lisakov, M.; MacDonald, N. R.; Zensus, Anton J.The spatial scales of relativistic radio jets, probed by relativistic magneto-hydrodynamic (RMHD) jet launching simulations and by most very long baseline interferometry (VLBI) observations differ by an order of magnitude. Bridging the gap between these RMHD simulations and VLBI observations requires selecting nearby active galactic nuclei (AGN), the parsec-scale region of which can be resolved. The radio source 3C 84 is a nearby bright AGN fulfilling the necessary requirements: it is launching a powerful, relativistic jet powered by a central supermassive black hole, while also being very bright. Using 22 GHz globe-spanning VLBI measurements of 3C 84 we studied its sub-parsec region in both total intensity and linear polarisation to explore the properties of this jet, with a linear resolution of ∼0.1 parsec. We tested different simulation set-ups by altering the bulk Lorentz factor Γ of the jet, as well as the magnetic field configuration (toroidal, poloidal, helical). We confirm the persistence of a limb brightened structure, which reaches deep into the sub-parsec region. The corresponding electric vector position angles (EVPAs) follow the bulk jet flow inside but tend to be orthogonal to it near the edges. Our state-of-the-art RMHD simulations show that this geometry is consistent with a spine-sheath model, associated with a mildly relativistic flow and a toroidal magnetic field configuration.
- First very long baseline interferometry detection of Fornax A(2024) Paraschos, G. F.; Benke, P.; Rösch, F.; Ros Ibarra, Eduardo; Kadler, Matthias; Ojha, R.; Edwards, P. G.; Weston, S.Radio galaxies harbouring jetted active galactic nuclei are a frequent target of very long baseline interferometry (VLBI) because they play an essential role in our exploration of how jets form and propagate. Hence, only a few have not yet been detected with VLBI; Fornax A was one of the most famous examples. Here we present the first detection of the compact core region of Fornax A with VLBI. At 8.4 GHz the faint core is consistent with an unresolved point source. We constrained its flux density to be S0 = 47.5 − 62.3 mJy and its diameter to be D0min ≤ 70 μas. The high values of the measured brightness temperature (TB ≳ 1011 K) imply that the observed radiation is of non-thermal origin, likely associated with the synchrotron emission from the active galactic nucleus. We also investigated the possibility of a second radio source being present within the field of view. Adding a second Gaussian component to the geometrical model fit does not significantly improve the quality of the fit, and we therefore, conclude that our detection corresponds to the compact core of Fornax A. Analysis of the non-trivial closure phases provides evidence for the detection of a more extended flux density, on the angular scale of ∼4000 μas. Finally, the fractional circular polarisation of the core is consistent with zero, with a conservative upper limit being mcirc ≤ 4%.
