Large Telescope Research Articles

VLTI/GRAVITY interferometric measurements of the innermost dust structure sizes around active galactic nuclei

We present new Very Large Telescope Interferometer (VLTI)/GRAVITY near-infrared interferometric measurements of the angular size of the innermost hot dust continuum for 14 type 1 active galactic nuclei (AGNs). The angular sizes are resolved on scales of ∼0.7 mas and the inferred ring radii range from 0.028 to 1.33 pc, comparable to those reported previously and a factor of 10−20 smaller than the mid-infrared sizes in the literature. Combining our new data with previously published values, we compiled a sample of 25 AGNs with bolometric luminosity ranging from 1042 to 1047 erg s−1, with which we studied the radius-luminosity (R − L) relation for the hot dust structure. Our interferometric measurements of radius are offset by a factor of 2 from the equivalent relation derived through reverberation mapping. Using a simple model to explore the dust structure’s geometry, we conclude that this offset can be explained if the 2 μm emitting surface has a concave shape. Our data show that the slope of the relation is in line with the canonical R ∝ L0.5 when using an appropriately non-linear correction for bolometric luminosity. In contrast, using optical luminosity or applying a constant bolometric correction to it results in a significant deviation in the slope, suggesting a potential luminosity dependence on the spectral energy distribution. Over four orders of magnitude in luminosity, the intrinsic scatter around the R − L relation is 0.2 dex, suggesting a tight correlation between the innermost hot dust structure size and the AGN luminosity.

A Multiwavelength Approach to Constraining the Merger Properties of ACT-CL J0034.4+0225

ACT-CL J0034.4+0225 is a previously unrecognized merging galaxy cluster at z = 0.38588 ± 0.00068. Our primary evidence is provided by a 21 ks Chandra image that shows two surface brightness peaks separated by ∼49″ (259 kpc) surrounded by an extended cluster gas distribution. Each gas peak contains a brightest cluster galaxy, offset from the gas peak. We collect new South African Large Telescope optical spectra that, when augmented by archival data, yield redshifts for the two BGCs and 58 other cluster members. Archival Giant Metrewave Radio Telescope and MeerKAT data reveal a radio halo that encompasses the X-ray peaks. We provide and compare three X-ray-based mass estimates (5.0 × 1014 M ⊙, 6.4 × 1014 M ⊙, and 8.6 × 1014 M ⊙). The Planck and ACT Sunyaev–Zel’dovich masses are ≈5.8 × 1014 M ⊙. We constrain the merger state and properties by comparing them to an existing suite of N-body/hydrodynamical models using the measured gas peak separation (259 kpc, projected) and radial velocity difference (0–1000 km s−1). This constrains the epoch of the merger to be within ∼100 Myr of first pericenter passage. A strong lensing analysis constrains the mass ratio to be in the range 1:1–1:20, while the cluster morphology prefers values near the equal-mass range.

Spectroastrometry and Reverberation Mapping of Active Galactic Nuclei. I. The Hβ Broad-line Region Structure and Black Hole Masses of Five Quasars

We conduct a reverberation mapping (RM) campaign to spectroscopically monitor a sample of selected bright active galactic nuclei with large anticipated broad-line region (BLR) sizes adequate for spectroastrometric (SA) observations by the GRAVITY instrument on the Very Large Telescope Interferometer. We report the first results for five objects, IC 4329A, Mrk 335, Mrk 509, Mrk 1239, and PDS 456, among which Mrk 1239 and PDS 456 are for the first time spectroscopically monitored. We obtain multiyear monitoring data and perform multicomponent spectral decomposition to extract the broad Hβ profiles. We detect significant time lags between the Hβ and continuum variations, generally obeying the previously established BLR size–luminosity relation. Velocity-resolved Hβ time lags illustrate diverse, possibly evolving, BLR kinematics. We further measure the Hβ line widths from mean and rms spectra and the resulting virial products show good consistency among different observing seasons. Adopting a unity virial factor and the FWHM of the broad Hβ line from the mean spectra as a measure of velocity, the obtained black hole masses averaged over seasons are logM•/M⊙=8.02−0.14+0.09 , 6.92−0.12+0.12 , 8.01−0.25+0.16 , 7.44−0.14+0.13 , and 8.59−0.11+0.07 for the five objects, respectively. Black hole mass estimations using other line width measures are also reported. For objects with previous RM campaigns, our mass estimates are in agreement with earlier results. In a companion paper, we will employ BLR dynamical modeling to directly infer the black hole mass and thereby determine the virial factors.

Improved Astrophysical and Computational Oscillator Strengths for Ultraviolet P ii Lines

Abundance measurements for the volatile element phosphorus are important for measuring the metallicity in interstellar and circumgalactic gas, where their accuracies are limited by uncertainties in the oscillator strengths. We report updated oscillator strength values for two resonant transitions of the dominant ion P II, the transitions at 961.041 and 963.801 Å, which have historically shown large uncertainties. Using a combination of observational measurements and highly accurate quasi-relativistic Hartree–Fock theoretical calculations, we present an updated oscillator strength of f = 0.147 ± 0.021 for the poorly constrained P II resonant transition at 961.401 Å, which arises from the ground electronic state 3s 23p 2 3P0 to the excited level 3s 23p3d 3D 1o . This result utilizes archival optical spectra obtained with the Very Large Telescope for the quasar PKS 0528–250, which has a damped Lyα absorber at z = 2.811. We calculate a theoretical f-value = 0.153 for 961.401 Å consistent with our empirically derived value, and calculate a theoretical f-value = 1.79 for 963.801 Å. We also present theoretical oscillator strengths for the P II resonant transitions at 972.779, 1124.945, 1152.818, 1301.874, and 1532.533 Å, as well as for multiple P II fine-structure and excited-level transitions. The updated f-value for the P II 961 Å transition will be useful in future studies of P abundances, especially in sight lines where the 1152 Å line is saturated.

Casting Light on Degeneracies: A Comprehensive Study of Lightcurve Variations in Microlensing Events OGLE-2017-BLG-0103 and OGLE-2017-BLG-0192

This study investigates orbital parallax in gravitational microlensing events, focusing on OGLE-2017-BLG-0103 and OGLE-2017-BLG-0192. For events with timescales ≤60 days, a Jerk-Parallax degeneracy arises due to high Jerk velocity ( vj˜ ), causing a fourfold continuous parallax degeneracy. OGLE-2017-BLG-0103, after incorporating orbital parallax, reveals four discrete degenerate parallax solutions, while OGLE-2017-BLG-0192 exhibits four discrete solutions without degeneracy. The asymmetric lightcurve of OGLE-2017-BLG-0103 suggests a more probable model where Xallarap is added to the parallax model, introducing tension. The galactic model analysis predicts a very low-mass stellar lens for OGLE-2017-BLG-0192. For OGLE-2017-BLG-0103, degenerate solutions suggest a low-mass star or a darker lens in the disk, while the Xallarap+Parallax model also predicts a stellar lens in the bulge, with the source being a solar-type star orbited by a dwarf star. This study presents five degenerate solutions for OGLE-2017-BLG-0103, emphasizing the potential for confirmation through high-resolution Adaptive Optics observations with Extremely Large Telescopes in the future. The complexities of degenerate scenarios in these microlensing events underscore the need to analyze special single-lens events in the Roman Telescope Era.

New γ-Ray Sources Identified in All-sky Surveys Based on Fermipy’s Advanced Algorithm

We employ an efficient method for identifying γ-ray sources across the entire sky, leveraging advanced algorithms from Fermipy, and cleverly utilizing the Galactic diffuse background emission model to partition the entire sky into 72 regions, thereby greatly enhancing the efficiency of discovering new sources throughout the sky through multi-threaded parallel computing. After confirming the reliability of the new method, we applied it for the first time to analyze data from the Fermi Large Area Telescope (Fermi-LAT) encompassing approximately 15.41 yr of all-sky surveys. Through this analysis, we successfully identified 1379 new sources with significance levels exceeding 4σ, of which 497 sources exhibited higher significance levels exceeding 5σ. Subsequently, we performed a systematic analysis of the spatial extension, spectra, and light variation characteristics of these newly identified sources. We identified 21 extended sources and 23 sources exhibiting spectral curvature above 10 GeV. Additionally, we identified 44 variable sources above 1 GeV.

CXOU J005245.0-722844: Discovery of a be star / white dwarf binary system in the SMC via a very fast, super-eddington X-ray outburst event

Abstract CXOU J005245.0-722844 is an X-ray source in the Small Magellanic Cloud (SMC) that has long been known as a Be/X-ray binary (BeXRB) star, containing an OBe main sequence star and a compact object. In this paper, we report on a new very fast X-ray outburst from CXOU J005245.0-722844. X-ray observations taken by Swift constrain the duration of the outburst to less than 16 days and find that the source reached super-Eddington X-ray luminosities during the initial phases of the eruption. The XRT spectrum of CXOU J005245.0-722844 during this outburst reveals a super-soft X-ray source, best fit by an absorbed thermal blackbody model. Optical and Ultraviolet follow-up observations from the Optical Gravitational Lensing Experiment (OGLE), Asteroid Terrestrial-impact Last Alert System (ATLAS), and Swift identify a brief ∼0.5 magnitude optical burst coincident with the X-ray outburst that lasted for less than 7 days. Optical photometry additionally identifies the orbital period of the system to be 17.55 days and identifies a shortening of the period to 17.14 days in the years leading up to the outburst. Optical spectroscopy from the Southern African Large Telescope (SALT) confirms that the optical companion is an early-type OBe star. We conclude from our observations that the compact object in this system is a white dwarf (WD), making this the seventh candidate Be/WD X-ray binary. The X-ray outburst is found to be the result of a very-fast, ultra-luminous nova similar to the outburst of MAXI J0158-744.

A Comprehensive Study on the Mid-Infrared Variability of Blazars

We present a comprehensive investigation of mid-infrared (MIR) flux variability at 3.4 μm (W1 band) for a large sample of 3816 blazars, using Wide-field Infrared Survey Explorer (WISE) data through December 2022. The sample consists of 1740 flat-spectrum radio quasars (FSRQs), 1281 BL Lac objects (BL Lacs), and 795 blazars of uncertain type (BCUs). Considering Fermi Large Area Telescope detection, we classify 2331 as Fermi blazars and 1485 as non-Fermi blazars. Additionally, based on synchrotron peak frequency, the sample includes 2264 low-synchrotron peaked (LSP), 512 intermediate-synchrotron peaked (ISP), and 655 high-synchrotron peaked (HSP) sources. We conduct a comparative analysis of short- and long-term intrinsic variability amplitude (σm), duty cycle (DC), and ensemble structure function (ESF) across blazar subclasses. The median short-term σm values were 0.181−0.106+0.153, 0.104−0.054+0.101, 0.135−0.076+0.154, 0.173−0.097+0.158, 0.177−0.100+0.156, 0.096−0.050+0.109, and 0.106−0.058+0.100 mag for FSRQs, BL Lacs, Fermi blazars, non-Fermi blazars, LSPs, ISPs, and HSPs, respectively. The median DC values were 71.03−22.48+14.17, 64.02−22.86+16.97, 68.96−25.52+15.66, 69.40−22.17+14.42, 71.24−21.36+14.25, 63.03−33.19+16.93, and 64.63−24.26+15.88 percent for the same subclasses. The median long-term σm values were 0.137−0.105+0.408, 0.171−0.132+0.206, 0.282−0.184+0.332, 0.071−0.062+0.143, 0.218−0.174+0.386, 0.173−0.132+0.208, and 0.101−0.077+0.161 mag for the same subclasses, respectively. Our results reveal significant differences in 3.4 μm flux variability among these subclasses. FSRQs (LSPs) exhibit larger σm and DC values compared to BL Lacs (ISPs and HSPs). Fermi blazars display higher long-term σm but lower short-term σm relative to non-Fermi blazars, while DC distributions between the two groups are similar. ESF analysis further confirms the greater variability of FSRQs, LSPs, and Fermi blazars across a wide range of time scales compared to BL Lacs, ISPs/HSPs, and non-Fermi blazars. These findings highlight a close correlation between MIR variability and blazar properties, providing valuable insights into the underlying physical mechanisms responsible for their emission.

High fidelity adaptive mirror simulations with reduced order models

In the design process of large adaptive mirrors numerical simulations represent the first step to evaluate the system design compliance in terms of performance, stability and robustness. For the next generation of Extremely Large Telescopes increased system dimensions and bandwidths lead to the need of modeling not only the deformable mirror alone, but also all the system supporting structure or even the full telescope. The capability to perform the simulations with an acceptable amount of time and computational resources is highly dependent on finding appropriate methods to reduce the size of the resulting dynamic models. In this paper we present a framework developed together with the company Microgate to create a reduced order structural model of a large adaptive mirror as a preprocessing step to the control system simulations. The reduced dynamic model is then combined with the remaining system components allowing to simulate the full adaptive mirror in a computationally efficient way. We analyze the feasibility of our reduced models for Microgate’s prototype of the adaptive mirror of the Giant Magellan Telescope.

Revisit of GeV Gamma-Ray Emission from Orion B with the Fermi Large Area Telescope

We revisit the γ-ray emission above 300 MeV towards the massive star-forming region of Orion B by adopting 14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools. The extended γ-ray emission region around Orion B is resolved into two components (region I and region II). The γ-ray spectrum of region I agrees with the predicted γ-ray spectrum assuming the cosmic ray (CR) density is the same as that of Alpha Magnetic Spectrometer (AMS-02) measured locally. The γ-ray emissivity of region II appears to be deficit at low energy band (E < 3 GeV). Through modeling we find that CR densities exhibit a significant deficit below 20 GeV, which may be caused by a slow diffusion inside the dense region. This is probably caused by an increased magnetic field whose strength increases with the gas density.

Scientific preparation for JRT: Wind pressure prediction model for large radio telescope based on real data from multi-sensors

Jingdong 120-meter radio telescope (JRT) is poised to become the world's largest single-aperture fully steerable medium-low frequency radio telescope. However, like other large-aperture radio telescopes, the JRT is vulnerable to wind loads, which can cause structural deformation and pointing errors. Addressing this challenge requires the ability to predict dynamic winds in real-time. This study developed a wind pressure preprocessing and prediction model using sensor data collected from the Kunming 40-meter radio telescope (KRT), enabling real-time prediction of wind pressure on the telescope. The model employs adaptive noise and Variational Mode Decomposition (VMD) techniques to eliminate random noise from the original wind pressure data. Subsequently, wind pressure predictions are made using a Bidirectional Long Short-term Memory (BiLSTM) model. By conducting predictions under various stabilization conditions and conducting a thorough analysis of measurement data from five sensors, the study has achieved impressive results in predicting wind pressure on the KRT reflector surface. The proposed model demonstrates the lowest MAE, RMSE, and MAPE, while achieving the highest R2 across various data sets. Where the average R2 of the proposed model is 0.9392 at 45° pitch angle attitude and the RMSE, MAE and MAPE values are 1.4923, 1.2377 and 1.82% respectively. This model helps wind load monitoring of real-time wind pressure monitoring of the telescope surface, to study the effects of wind load on pointing accuracy. By adjusting the control parameters to reduce wind load interference, to ensure the high-precision work of a large radio telescope, such as JRT.

Redshifts of candidate host galaxies of four fast X-ray transients using VLT/MUSE

Context. Fast X-ray transients (FXTs) are X-ray flares that last from minutes to hours. Multi-wavelength counterparts to these FXTs have proven hard to find. As a result, distance measurements are made through indirect methods such as a host galaxy identification. Of the three main models proposed for FXTs, that is, supernova shock breakout emission (SN SBO), binary neutron star (BNS) mergers, and tidal dirsuption events (TDEs) of an intermediate-mass black hole (IMBH) disrupting a white dwarf (WD), the SN SBO predicts a much lower maximum peak X-ray luminosity (LX, peak). If the distance to FXTs were to be obtained, it would be a powerful probe for investigating the nature of these FXTs. Aims. We aim to obtain distance measurements to four FXTs by identifying candidate host galaxies. Through a redshift measurement of the candidate host galaxies, we derive LX, peak and the projected offset between the candidate host galaxy and the FXT. Methods. We obtained Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE) observations of a sample of FXTs. We report the redshift of between 13 and 22 galaxies per FXT. We used these redshifts to calculate the distance, LX, peak and the projected offsets between the FXT position and the position of the sources. Additionally, we computed the chance alignment probabilities for these sources with the FXT postitions. Results. We find LX, peak &gt; 1044 erg s−1 when we assume that any of the sources with a redshift measurement is the true host galaxy of the corresponding FXT. For XRT 100831, we find a very faint galaxy (mR, AB = 26.5 ± 0.3, z ∼ 1.22, LX, peak ∼ 8 × 1045 erg s−1 if the FXT is at this distance) within the 1σ uncertainty region with a chance alignment probability of 0.04. For XRT 060207, we find a candidate host galaxy at z = 0.939 with a low chance alignment probability within the 1σ uncertainty region. However, we also report the detection of a late-type star within the 3σ uncertainty region with a similar chance alignment probability. For the remaining FXTs (XRT 030511 and XRT 070618), we find no sources within their 3σ uncertainty regions. The projected offsets between the galaxies and the FXT positions is &gt; 33 kpc at 1σ uncertainty. Therefore, if one of these candidate host galaxies turns out to be the true host galaxy, it would imply that the FXT progenitor originated from a system that received a significant kick velocity at formation. Conclusions. We rule out an SN SBO nature for all FXTs based on LX, peak and the projected offsets between the FXT position and the sources, assuming any of the candidate host galaxies with a redshift determination is the true host galaxy to the FXT. For XRT 100831, we conclude that the detected galaxy within the 1σ uncertainty position is likely to be the host galaxy of this FXT based on the chance alignment probability. From the available information, we are not able to determine whether XRT 060207 originated from the galaxy found within 1σ of the FXT position or was due to a flare from the late-type star detected within the 3σ uncertainty region. Based on LX, peak and the offsets within our sample, we are not able to distinguish between the BNS merger and the IMBD-WD TDE progenitor model. However, for the candidate host galaxies with an offset ≳30 kpc, we can conclude that the IMBH-WD TDE is unlikely due to the large offset.

From gas to stars: MUSEings on the internal evolution of IC 1613

Context. The kinematics and chemical composition of stellar populations of different ages provide crucial information on the evolution of the various components of a galaxy. Aim. Our aim is to determine the kinematics of individual stars as a function of age in IC 1613, a star-forming, gas-rich, and isolated dwarf galaxy of the Local Group (LG). Methods. We present results of a new spectroscopic survey of IC 1613 conducted with MUSE, an integral field spectrograph mounted on the Very Large Telescope. We extracted ∼2000 sources, from which we separated stellar objects for their subsequent spectral analysis. The quality of the dataset allowed us to obtain accurate classifications (Teff to better than 500 K) and line-of-sight velocities (with average δv ∼ 7 km s−1) for about 800 stars. Our sample includes not only red giant branch (RGB) and main sequence (MS) stars, but also a number of probable Be and C stars. We also obtained reliable metallicities (δ[Fe/H] ∼ 0.25 dex) for about 300 RGB stars. Results. The kinematic analysis of IC 1613 revealed for the first time the presence of stellar rotation with high significance. We found general agreement with the rotation velocity of the neutral gas component. Examining the kinematics of stars as a function of broad age ranges, we find that the velocity dispersion increases as a function of age, with the behaviour being very clear in the outermost pointings, while the rotation-to-velocity dispersion support decreases. On timescales of &lt; 1 Gyr, the stellar kinematics still follow very closely that of the neutral gas, while the two components decouple on longer timescales. The chemical analysis of the RGB stars revealed average properties comparable to other Local Group dwarf galaxies. We also provide a new estimation of the inclination angle using only independent stellar tracers. Conclusions. Our work provides the largest spectroscopic sample of an isolated LG dwarf galaxy. The results obtained seem to support the scenario in which the stars of a dwarf galaxy are born from a less turbulent gas over time.

SFNet: Stellar Feature Network with CWT for Stellar Spectra Recognition

Stellar spectral classification is crucial in astronomical data analysis. However, existing studies are often limited by the uneven distribution of stellar samples, posing challenges in practical applications. Even when balancing stellar categories and their numbers, there is room for improvement in classification accuracy. This study introduces a Continuous Wavelet Transform using the Super Morlet wavelet to convert stellar spectra into wavelet images. A novel neural network, the Stellar Feature Network, is proposed for classifying these images. Stellar spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope DR9, encompassing five equal categories (B, A, F, G, K), were used. Comparative experiments validate the effectiveness of the proposed methods and network, achieving significant improvements in classification accuracy.

Evidence for hybrid gamma-ray emission from the supernova remnant G150.3+4.5

The supernova remnant (SNR) G150.3+4.5 was first identified in radio, exhibiting a hard GeV spectrum and a ~1.5º radius. Radio observations revealed a bright arc with an index of ~−0.40, which stands in contrast to the index of ~−0.69 for the rest. This arc is coincident with the point-like Fermi source 4FGL J0426.5+5434 and KM2A source 1LHAASO J0428+5531. The rest of the SNR has a hard GeV spectrum and a soft TeV spectrum, implying a spectral cut-off or break near 1 TeV. Since there is no X-ray counterpart and no pulse signal detected, the gamma-ray (γ-ray) emission mechanism from the SNR and the point-like source appear puzzling. In this work, we reanalyse the γ-ray emission using 14 yr data recorded by Fermi Large Area Telescope and find that the spectrum of the northern half-sphere is compatible with a broken power law with a break at 146 ± 11 eV and photon indices of ΓNorthlobe = 1.54 ± 0.04stat ± 0.07syst (2.28 ± 0.08stat ± 0.12syst) below (above) the break. In addition, the southern half-sphere can be described well with a single power law with ΓSouthlobe =1.95 ± 0.07stat ± 0.09syst. Since the southern half-sphere is well correlated with CO emission, we propose that the γ-ray emission of the northern half-sphere could be dominated by relativistic electrons via inverse-Compton processes, while the southern half-sphere is dominated by cosmic rays via hadronic processes. 4FGL J0426.5+5434 may result from the illumination of a cloud by escaping cosmic rays or recent shock-cloud interaction. Observations from LHAASO-KM2A thus favour the possibility of a cosmic-ray PeVatron candidate, however, leptonic scenarios cannot be ruled out. Further multi-wavelength observations are warranted to confirm the hadronic nature of 1LHAASO J4028+5531.

On the Correlation between Young Massive Star Clusters and Gamma-Ray Unassociated Sources

Star clusters (SCs) are potential cosmic-ray accelerators and therefore are expected to emit high-energy radiation. However, a clear detection of gamma-ray emission from this source class has only been possible for a handful of cases. This could in principle result from two different reasons: either detectable SCs are limited to a small fraction of the total number of Galactic SCs, or gamma-ray-emitting SCs are not recognized as such and therefore are listed in the ensemble of unidentified sources. In this Letter we investigate this latter scenario by comparing available catalogs of SCs and H ii regions, obtained from Gaia and Wide-field Infrared Survey Explorer observations, to the gamma-ray GeV and TeV catalogs built from Fermi Large Area Telescope (LAT), H.E.S.S., and LHAASO data. The significance of the correlation between catalogs is evaluated by comparing the results with simulations of synthetic populations. A strong correlation emerges between Fermi-LAT-unidentified sources and H ii regions that trace massive SCs in the earliest (≲1–2 Myr) phase of their life, where no supernova explosions have happened yet, confirming that winds of massive stars can alone accelerate particles and produce gamma-ray emission at least up to GeV energies. The association with TeV energy sources is less evident. Similarly, no significant association is found between Gaia SCs and GeV nor TeV sources. We ascribe this fact to the larger extension of these objects but also to an intrinsic bias in the Gaia selection toward SCs surrounded by a lower target gas density, which would otherwise hinder the detection in the optical wave band.

ATAT: Astronomical Transformer for time series and Tabular data

Context. The advent of next-generation survey instruments, such as the Vera C. Rubin Observatory and its Legacy Survey of Space and Time (LSST), is opening a window for new research in time-domain astronomy. The Extended LSST Astronomical Time-Series Classification Challenge (ELAsTiCC) was created to test the capacity of brokers to deal with a simulated LSST stream. Aims. Our aim is to develop a next-generation model for the classification of variable astronomical objects. We describe ATAT, the Astronomical Transformer for time series And Tabular data, a classification model conceived by the ALeRCE alert broker to classify light curves from next-generation alert streams. ATAT was tested in production during the first round of the ELAsTiCC campaigns. Methods. ATAT consists of two transformer models that encode light curves and features using novel time modulation and quantile feature tokenizer mechanisms, respectively. ATAT was trained on different combinations of light curves, metadata, and features calculated over the light curves. We compare ATAT against the current ALeRCE classifier, a balanced hierarchical random forest (BHRF) trained on human-engineered features derived from light curves and metadata. Results. When trained on light curves and metadata, ATAT achieves a macro F1 score of 82.9 ± 0.4 in 20 classes, outperforming the BHRF model trained on 429 features, which achieves a macro F1 score of 79.4 ± 0.1. Conclusions. The use of transformer multimodal architectures, combining light curves and tabular data, opens new possibilities for classifying alerts from a new generation of large etendue telescopes, such as the Vera C. Rubin Observatory, in real-world brokering scenarios.

The Carousel Lens: A Well-modeled Strong Lens with Multiple Sources Spectroscopically Confirmed by VLT/MUSE

Over the past few years alone, the lensing community has discovered thousands of strong lens candidates, and spectroscopically confirmed hundreds of them. In this time of abundance, it becomes pragmatic to focus our time and resources on the few extraordinary systems, in order to most efficiently study the Universe. In this paper, we present such a system: DESI-090.9854-35.9683, a cluster-scale lens at z l = 0.49, with seven observed lensed sources around the core, and additional lensed sources further out in the cluster. From the number and the textbook configuration of the lensed images, a tight constraint on the mass potential of the lens is possible. This would allow for detailed analysis on the dark and luminous matter content within galaxy clusters, as well as a probe into dark energy and high-redshift galaxies. We present our spatially resolved kinematic measurements of this system from the Very Large Telescope Multi Unit Spectroscopic Explorer, which confirm five of these source galaxies (in ascending order, at z s = 0.962, 0.962, 1.166, 1.432, and 1.432). With previous Hubble Space Telescope imaging in the F140W and F200LP bands, we also present a simple flux-based lens model consisting of two power-law profiles that, for a cluster lens, well models the five lensed arc families with redshifts. We determine the mass to be M(< θ E) = 4.78 × 1013 M ⊙ for the primary mass potential. From the model, we extrapolate the redshift of one of the two source galaxies not yet spectroscopically confirmed to be at zs=4.52−0.71+1.03 .

Vibration-attitude integrated control of large membrane diffraction space telescope

The development of telescopes with large apertures is driven by the increasing demand for higher imaging resolution and coverage. Large membrane diffraction space telescopes are particularly attractive due to their lightweight nature, ease of folding and unfolding, and high-precision imaging capabilities. However, their substantial size and flexibility make them susceptible to long-duration, low-frequency vibrations during attitude maneuvers, which degrade attitude and imaging accuracy and risk instrument damage. Consequently, an urgent need exists for a high-precision integrated control scheme. In this paper, the integrated control of vibration and attitude in a large space telescope is studied using cable actuators and control moment gyroscopes (CMGs). Since cables can only withstand limited tension, the unilateral and constrained characteristics of the control input are taken into account during the control design process. Firstly, a rigid-flexible coupling dynamic model of the space telescope is established using the velocity variation principle with hybrid coordinates. Additionally, a two-body astrodynamic model is developed to assess the impact of gravity gradient torque. Next, combining the computational torque method and H∞ control theory, an integrated control scheme is proposed, which achieves vibration and attitude control during maneuvers. Then, this paper optimizes the cable actuator positions via the discrete particle swarm optimization (PSO) algorithm and plans various attitude maneuver paths. Finally, numerical simulations are adopted to demonstrate the effectiveness of the control scheme. The results show that this integrated control scheme swiftly suppresses structural vibrations during attitude maneuvers, enabling high-precision attitude control of the space telescope.

Simulation study of the performance of the Very Large Area gamma-ray Space Telescope

Simulation study of the performance of the Very Large Area gamma-ray Space Telescope