Observations with the James Webb Space Telescope (JWST) have uncovered a substantial population of high-redshift, broad-line active galactic nuclei (AGNs), whose properties challenge standard models of black-hole growth and AGN emission. We analyzed a spectroscopic sample of 34 Type 1 AGNs from the JWST Advanced Deep Survey (JADES) survey, spanning redshifts 1.7 < z < 9, to constrain the physical nature of the accretion flows powering these sources with broad-line diagnostics statistically for the first time. At z > 5, we find a marked suppression of high-ionization emission lines (HeII, CIV, NV) relative to prominent broad Hα and narrow OIII features. This contrast places strong constraints on the shape of the ionizing spectral energy distribution (SED) and on the physical conditions in the broad-line region (BLR). By comparing the observations to photoionization models based on SEDs of black holes accreting at sub-Eddington ratios, we show that standard AGN continua struggle to reproduce the observed broad-line ratios and equivalent widths (EWs) across a wide ionization parameter range. These results suggest the need for modified SEDs -- either intrinsically softened due to super-Eddington accretion or radiative inefficiencies in the innermost disk, or externally filtered by intervening optically thick gas that absorbs or scatters the highest energy photons before they reach the BLR.

Abstract We report the discovery of a substantial sodium doublet (Na D λλ 5890, 5896)—traced neutral outflow in the quiescent galaxy JADES-GS-206183 at z = 1.317. Its JWST/NIRSpec-Microshutter Array spectrum shows a deep, blueshifted Na D absorption, revealing a neutral outflow with v out = 82 8 − 49 + 79 km s − 1 and a mass outflow rate of log ( M ̇ out / M ⊙ yr − 1 ) = 2.4 0 − 0.16 + 0.11 . This outflow rate exceeds that of any neutral outflows identified beyond z ∼ 1 by the same line and is comparable with those in local galaxies with intensive star formation (SF) or luminous active galactic nuclei (AGN). JADES-GS-206183 is also a peculiar quiescent galaxy with a spiral+bar morphology, high dust attenuation ( A V = 2.27 ± 0.23 mag). Paschen α (Pa α ) emission from the FRESCO NIRCam grism confirms its low star formation rate (SFR Pa α = 10.78 ± 0.55 M ⊙ yr −1 ), placing it 0.5 dex below the main sequence ( log ( sSFR yr − 1 ) = − 10.2 ). Despite the systematics introduced by different SF history priors, the spectral energy distribution modeling, combining Hubble Space Telescope-to-NIRCam photometry with the Very Large Telescope/MUSE spectrum, suggests that JADES-GS-206183 experienced an older episode of SF 0.5–2 Gyr ago and a possible rejuvenation within the recent ∼10 Myr. Moreover, rest-frame optical lines indicate that the current AGN activity of JADES-GS-206183, if present, is also weak. Even though we tentatively detect a broad component of the H α line, it likely traces an ionized outflow rather than an AGN. The results demonstrate that the Na D outflow in JADES-GS-206183 is highly unlikely to be driven by current SF or nuclear activity. Instead, it may represent a long-lasting fossil outflow from past AGN activity, potentially cotriggered with the early phase of rejuvenation.

Abstract The detection of very-high-energy gamma rays from M87 can provide crucial insights into particle acceleration and radiation mechanisms in jets. The recent observations by the Large High Altitude Air Shower Observatory detector extend the energy range of TeV gamma-ray astronomy, and also the variability study to the TeV energy domain. We have modeled the low state and flare state multiwavelength spectral energy distributions of M87 within a time-dependent framework. In our model, the low state gamma-ray flux results from the emissions from the subparsec and the kiloparsec scale jets of M87, whereas the flare state gamma-ray flux is mainly produced in the subparsec scale jet. We have shown that the spectral and temporal features of the TeV gamma-ray spectrum of M87 are consistent with this two-zone model, where the contribution from the subparsec scale jet significantly increases during the flare state.

Abstract We report the discovery of LAMOST J0041+3948, the most luminous post-asymptotic giant-branch (AGB) Type II Cepheid known, located in the Andromeda Giant Stellar Stream. Its spectral energy distribution (SED) exhibits a strong near-infrared excess, indicating the presence of a circumbinary dusty disk and hence binarity. SED fitting yields an effective temperature of T eff = 673 8 − 262 + 234 K and a post-AGB luminosity of log ( L / L ⊙ ) = 4.3 2 − 0.08 + 0.07 . Comparison with theoretical evolutionary tracks suggests a ∼2.0–4.0 M ⊙ progenitor when accounting for a possible scattered-light contribution. Zwicky Transient Facility light curves reveal a pulsation period of 89 days that lies close to the period–luminosity relation for long-period RV Tauri stars. Follow-up spectroscopy reveals clear s -process enrichment and signatures consistent with an accretion disk around the companion. The inferred progenitor is significantly younger and more massive than a typical stream member, suggesting that an additional mechanism, such as a stellar merger, is required. We propose a formation channel in which the present post-AGB binary descends from a hierarchical triple system. In this scenario, the inner binary merged after the system was displaced to its current location by the galaxy merger event, and the resulting massive merger remnant subsequently evolved into the extremely luminous post-AGB star observed today.

Abstract Long-duration gamma-ray bursts (GRBs) are believed to occur in star-forming regions. The multiwavelength follow-up observations of the early afterglow of GRB 240825A provided insights into the evolution of the optical-to-X-ray spectral feature of the afterglow. We comprehensively investigate the evolution of X-ray spectral properties through time-resolved spectral analysis and calculate optical darkness ( β OX ) to reveal the physical properties of the afterglow. The X-ray-to-optical spectral energy distributions of afterglow in different time intervals are fitted to derive the extinction curves. The β OX exhibits a trend of decreasing and then increasing, reaching its minimum value at ∼1000 s post-trigger. However, at 11 hr post-trigger, β OX does not meet the criteria for an optically dark burst. The extinction curves in different time intervals indicate that GRB 240825A occurred in a dust-obscured environment.

Abstract Herbig Ae/Be stars (HAeBes) are critical tracers of intermediate- and high-mass star formation, yet their census remains incomplete compared to low-mass young stellar objects like T-Tauri stars. To expand the known population, we systematically searched for HAeBes in LAMOST DR7 low-resolution spectra. Following Sun et al., we applied Uniform Manifold Approximation and Projection for dimensionality reduction and Support Vector Machine classification, identifying ∼240,000 spectra with potential H α emission. After removing contaminants (nonstellar objects, extragalactic sources, cataclysmic variables, and Algol systems) and restricting to B/A-type stars, we obtained 1835 candidates through 2MASS/WISE visual inspection. Spectral energy distribution analysis confirmed 143 sources with infrared excess ( J band or longer wavelengths), including 92 known HAeBes. From the remaining 51 candidates, we classified 26 with strong infrared excess as new HAeBes. Color-index analysis of confirmed HAeBes and classical Ae/Be stars (CAeBes) revealed that the ( K − W 1) 0 versus ( W 2 − W 3) 0 diagram effectively separates these populations: CAeBes predominantly occupy ( K − W 1) 0 ≤ 0.5 and ( W 2 − W 3) 0 ≤ 1.1, while other regions trace transition disks (( K − W 1) 0 < 0.5 and ( W 2 − W 3) 0 > 1.1), globally depleted disks (( K − W 1) 0 > 0.5 and ( W 2 − W 3) 0 < 1.1), and Class I/Flat/II HAeBes (( K − W 1) 0 > 0.5 and ( W 2 − W 3) 0 > 1.1). More importantly, the HAeBes exhibit a clear evolutionary gradient on this diagram, with those in the Class III, Class II, Flat-SED, and Class I evolutionary stages being effectively distinguished by concentric ellipses that are roughly centered at (0, 0) with semimajor axes of a = 1.5, a = 3.0, and a = 4.0, and a semimajor to semiminor axis ratio of 1.6:1.

Abstract We present new Chandra observations of seven luminous quasars at z > 6.5. Combined with archival Chandra observations of all other known quasars, they form nearly complete X-ray observations of all currently known z ∼ 7 quasars with M 1450 < –26.5, except for J0313−1806 at z = 7.642 and J0910−0414 at z = 6.636. Together with existing ground-based near-infrared spectroscopy and Atacama Large Millimeter Array observations, we investigate the correlations between X-ray emission (the X-ray luminosity L X and the optical/UV-to-X-ray spectral slope α OX ) and various quasar properties (rest-UV luminosity L 2500 Å , bolometric luminosity L bol , C iv blueshift, and infrared luminosity L IR ). We find most z > 6.5 quasars follow a similar α OX – L 2500 Å relation as z ∼ 1–6 quasars, but also display a large scatter. We find a potential correlation between α OX and the C iv blueshift, suggesting a soft optical/UV-to-X-ray spectral energy distribution shape is frequently associated with fast disk winds. Furthermore, we analyze the X-ray spectrum of 11 quasars at z > 6.5 with Chandra detection, and find that the best-fit photon index, Γ, is 2.41 ± 0.27, which is likely driven by high accretion rates of z > 6.5 quasars. In addition, we find there are no significant correlations between either L X and L IR , nor L bol and L IR , suggesting no strong correlations between quasar luminosity and star formation luminosity for the most luminous quasars at z > 6.5.

Abstract Galaxy mergers are key drivers of galaxy formation and evolution, including triggering AGN and star formation to a still unknown degree. We thus investigate the impact of galaxy mergers on star formation and AGN activity using 3,330 galaxies at z = 4.5 − 8.5 from eight JWST fields (CEERS, JADES GOODS-S, NEP-TDF, NGDEEP, GLASS, El-Gordo, SMACS-0723, MACS-0416), covering an unmasked area of 189 arcmin2. We focus on star formation rate (SFR) enhancement, AGN fraction, and AGN excess in close pairs defined by Δz < 0.3 and projected separations rp < 100 kpc, relative to non-merger samples. Close pairs with mass ratios greater than 1:4 are used for the SFR–enhancement analysis, whereas no mass–ratio constraint is applied for the AGN fraction and AGN excess measurements. We find SFR enhancement occurs only at rp < 20 kpc, with values 0.25 ± 0.10 dex and 0.26 ± 0.11 dex above non-merger medians for z = [4.5, 6.5] and z = [6.5, 8.5], respectively. No other statistically significant enhancements in galaxy sSFR or stellar mass are observed at any projected separation or redshift. We also compare observational results with predictions from the SC-SAM simulation, finding no evidence of star formation enhancement in simulations at any separation. Lastly, we examine the fraction and excess of AGNs identified through photometric SED fitting (Type-I) and BPT diagnostics (Type-II). We find $48^{+33}_{-7}\%$ of Type-I and $44^{+26}_{-20}\%$ of Type-II AGNs have a close companion within rp < 50 kpc and Δz < 0.3. Furthermore, $73^{+27}_{-32}\%$ of AGNs have companions within 100 kpc. Relative to isolated galaxies, we measure an AGN excess factor of $1.26^{+0.15}_{-0.04}$ for Type-I and $1.34^{+0.23}_{-0.11}$ for Type-II AGNs in close pairs, suggesting notable AGN enhancement in galaxy pairs at these higher redshifts.

Abstract We present FrankenBlast , a customized and improved version of the Blast web application. FrankenBlast associates transients to their host galaxies, performs host photometry, and runs a innovative spectral energy distribution fitting code to constrain host stellar population properties—all within minutes per object. We test FrankenBlast on 14,432 supernovae (SNe), ≈half of which are spectroscopically classified, and are able to constrain host properties for 9262 events. When contrasting the host stellar masses ( M * ), specific star formation rates (sSFR), and host dust extinction ( A V ) between spectroscopically and photometrically classified SNe Ia, Ib/c, II, and IIn, we determine that deviations in these distributions are primarily due to misclassified events contaminating the photometrically classified sample. We further show that the higher redshifts of the photometrically classified sample also force their M * and sSFR distributions to deviate from those of the spectroscopically classified sample, as these properties are redshift-dependent. We compare host properties between spectroscopically classified SN populations and determine if they primarily trace M * or SFR. We find that all SN populations seem to both depend on M * and SFR, with SNe II and IIn somewhat more SFR-dependent than SNe Ia and Ib/c, and SNe Ia more M * -dependent than all other classes. We find the difference in the SNe Ib/c and II hosts to be the most intriguing and speculate that SNe Ib/c must be more dependent on higher M * and more evolved environments for the right conditions for progenitor formation. All data products and FrankenBlast are publicly available, along with a developing FrankenBlast version intended for Rubin Observatory science products.

Extreme emission line galaxies (EELGs) are believed to significantly contribute to the star formation activity and mass assembly in galaxies. EELGs likely also play a leading role in the cosmic re-ionization as their interstellar medium may allow a significant fraction of their ionizing photons to escape ( > 5%). Finding low-redshift analogues of these high-z galaxies is therefore essential to characterizing the physical conditions in the interstellar medium of these galaxies and understanding the processes that re-ionized the Universe. We aimed to develop a robust and efficient method for the photometric identification of EELGs using the J-PAS survey. J-PAS will cover approximately 8500 deg2$ of the sky with 54 narrow-band filters in the optical range plus $i-SDSS, enabling detailed studies of the physical properties of these galaxies. In this work we focused on an initial subset of the survey: a 30 square degree area with complete observations in all bands. We combine equivalent width (EW) measurements from J-PAS narrow-band photometry with artificial intelligence techniques to identify galaxies with emission lines exceeding 300 Å. We validated our selection using spectroscopic data from DESI DR1 and characterized the selected sample through spectral energy distribution fitting with . CIGALE We identify 917 EELGs up to z = 0.8 over 30 deg2$, achieving a purity of 95% and a completeness of 96% for i-SDSS < 22.5 mag. Importantly, active galactic nucleus contamination was carefully considered and is estimated to be around 5%. Furthermore, a cross-match with DESI yielded 79 counterparts; their redshifts are in excellent agreement with our photometric estimates, thereby confirming the reliability of our redshift determination. In addition, the derived emission line fluxes are in good agreement with spectroscopic measurements. Moreover, the selected sample reveals strong correlations between the ionizing photon production efficiency (ξ_ ion ) and EW(H$β), which are consistent with previous observational studies at low and high redshifts and theoretical expectations. Finally, most of the sources surpass the ionizing efficiency threshold required for re-ionization, highlighting their relevance as local analogues of early-Universe galaxies.

For atmospheric irradiation experiments, precise particle beam flux attenuation is crucial for dose control, while conventional vacuum windows lack flux control functionality despite providing vacuum isolation. To facilitate atmospheric experiments, including in vitro cell irradiation, detector calibration, and broad-range irradiation studies, a truncated-cone microchannel collimator integrated into a vacuum window structure was designed to provide structural support for vacuum windows. In addition, it attenuates charged particle beam flux in research accelerators, such as electrostatic accelerators, cyclotrons, and synchrotrons. Monte Carlo simulations were employed to quantify energy deposition profiles and spectral distributions of protons, alpha particles, and C6+ ions penetrating the composite structure. An average attenuation of 20% ± 5% was achieved across all tested beam species (protons, α-particles, and C6+ ions) demonstrating the consistent performance of the geometry in reducing beam flux while preserving spectral integrity. These results highlighted the design's potential for applications requiring precise dose modulation and enhanced mechanical stability in beamline engineering.

Abstract We introduce J-HERTz (J-PLUS Heritage Exploration of Radio Targets at z < 5), a new multiwavelength catalog that combines optical narrowband photometry from J-PLUS, infrared observations from the Wide-field Infrared Survey Explorer, and deep low-frequency radio data from LoTSS for nearly 0.5 million sources across 2100 deg 2 of the northern sky. Key innovations of J-HERTz include Bayesian neural network classifications for 390,000 galaxies, 31,000 quasars, and 20,000 stars, along with significantly improved photometric redshifts for 235,000 galaxies compared to previous J-PLUS DR3 and LoTSS DR2 estimates. We identify 831 candidate Galactic radio stars, which, if confirmed, would constitute a significant addition to the number of radio-emitting stars identified to date. Among radio-loud galaxies with spectroscopic observations, ≳20% lack Seyfert or LINER signatures, indicating a substantial population of optically quiescent radio galaxies, in agreement with previous works. Spectral energy distribution fitting of their host galaxies using J-PLUS photospectra reveals systematically low specific star formation rates, consistent with quenched stellar populations. J-HERTz thus provides a powerful data set to exploit radio-optical synergies, enabling studies that span from the origin of stellar radio emission to the active galactic nucleus life cycle and the role of jet activity in shaping host galaxy evolution.

Abstract We report the modeling of the millimeter and far-infrared (FIR) spectral energy distributions (SEDs) of 71 dusty star-forming galaxies (DSFGs) selected by the Atacama Cosmology Telescope (ACT) with a 5 σ flux density limit of 8 mJy at 220 GHz (1.4 mm). All sources were cross-identified with Herschel surveys at 500, 350, and 250 μ m, and 19 of our sources were observed with the Submillimeter Array (SMA). A probabilistic cataloging (PCAT) algorithm favors multiple unresolved flux components in the Herschel data for the majority of ACT-selected DSFGs. We compare the derived physical properties of the DSFGs obtained from modeling the flux densities with those from similar studies of DSFG populations. We find the median, 16th, and 84th percentiles for the following SED model parameters: redshift z phot = 3 . 3 − 0.6 + 0.7 , apparent size μ d = 5 . 2 − 2.4 + 0.9 kpc , apparent dust mass log 10 ( μ M d / M ⊙ ) = 9.1 4 − 0.04 + 0.12 , and cutoff temperature T c = 35 . 6 − 1.6 + 4.8 K for a power-law distribution, and the corresponding apparent FIR luminosity log 10 ( μ L IR / L ⊙ ) = 13 . 6 − 0.3 + 0.2 , where μ is the lensing magnification. While many of the properties broadly agree with those of samples of primarily lensed DSFGs, we exercise caution in interpreting them. ACT’s lower flux limit, the PCAT decomposition, and the SMA observations all suggest that some fraction of these DSFGs are likely to be unlensed and possibly multiples. The SMA data indicate that at least 14 out of 19 sources are such, either via “missing” flux in comparison to the model or detection of additional sources in the fields. Additional high-resolution follow-up and redshift determination are needed to better understand this flux-limited sample of DSFGs.

Abstract We report the discovery of 13 broad-line active galactic nuclei (AGNs) at z = 5–8 from the first 10% of JWST Cycle 3 Treasury Program COSMOS-3D. These AGNs are identified by their broad H α or H β emission lines through NIRCam grism slitless spectroscopy. One object at z = 7.646 with broad H β emission has an F444W magnitude of 23.6 mag, making it one of the brightest z > 7.5 broad-line AGNs yet known. Among the 13 AGNs, 10 objects exhibit reddened optical continua with slopes β opt > 0. The remaining three resemble UV-luminous quasars at similar redshift but with β opt less blue than those of typical unobscured quasars. We also obtain MIRI photometry (7.7–18 μ m) for two AGNs and place strong constraints on their rest-frame near-IR spectral energy distribution. We find no significant variability in the rest-frame UV by comparing the COSMOS-3D and COSMOS-Web F115W images taken apart by 60 days in the rest-frame. We compute the H α luminosity function (LF) at z ≈ 5–6 and find potential redshift evolution compared to z ≈ 4–5. We also derive the H β LF at z ∼ 8 by combining our sample with those from the literature. The broad H β emitters in this work suggest a number density 2 orders of magnitude higher than that predicted by the quasar LF based on rest-frame UV-selected samples. As a preview, our work showcases the ability of the COSMOS-3D grism survey to provide a complete view of the properties, growth, and evolution of bright broad-line AGNs at z > 5.

Quasars at the dawn of cosmic time (z>6) are fundamental probes for investigating the early coevolution of supermassive black holes and their host galaxy. Nevertheless, their infrared spectral energy distribution currently remains poorly constrained because the photometric coverage that probes the far-infrared wavelength range in which the dust modified blackbody is expected to peak (sim80 _158μ m deficit. Most remarkably, we note that the average value of T_d of this sample does not differ from the one that is observed in luminous, ultraluminous and hyperluminous infrared galaxies at different redshifts that show no signs of hosting a quasar. Finally, our findings suggest that the presence of a bright AGN does not significantly bias the derived infrared properties, although further high frequency observations with a high spatial resolution might reveal more subtle effects on subkiloparsec scales. m) is limited. We studied the high-frequency dust emission via a dedicated ALMA Band 8 (∼400 GHz) campaign targeting 11 quasar host galaxies at 6<z<7. Combined with archival observations in other ALMA bands, this program enables a detailed characterization of their infrared emission, which allowed us to derive dust masses (M_d), dust emissivity indexes (β), dust temperatures (T_d), infrared luminosities (L_IR), and associated star formation rates (SFRs). Our analysis confirmed that dust temperature is higher in this sample (34-65 K) than in local main-sequence galaxies, and this finding can be linked to the increased star formation efficiency we derived, as also suggested by the CII

Abstract The currently known compact extreme emission-line galaxies (the “Green Peas” (GPs)) in the Sloan Digital Sky Survey (SDSS) are rare and were mostly found among serendipitous spectroscopic targets, thus leaving open the possibility that a substantial population of GPs is missed. A significantly larger number of identified GPs in the Local Universe might provide a better characterization of their high-redshift analogs and Lyman continuum escape. In this paper, we confront the challenges of robustly identifying GPs without spectroscopic information, a needed approach considering the incompleteness of spectroscopic surveys for compact sources. The principal difficulty stems from a significant contamination of photometric candidates by stars and quasars of similar color. To solve this, we introduce a spectral energy distribution matching method, which separates candidate GPs from contaminants on the basis of SDSS and Wide-field Infrared Survey Explorer photometry of spectroscopically confirmed stars, quasars, and galaxies. The method has an effectiveness of 85% and a contamination rate of ∼10%. With it, we identify ∼9600 GP candidates expected to lie in the 0.12 < z < 0.36 range—a tenfold increase over what would be selected using SDSS DR18 spectra. Some of the new GPs are as bright as r ∼ 19, and 1200 are predicted to have [O III ]5007 equivalent widths in excess of 500 Å. The new population contains many “Extended Peas,” which are absent among known GPs and possibly represent merging systems. We provide catalogs containing 8313 newly identified GP candidates, as well as 917 GPs confirmed using SDSS spectroscopy and 521 GPs with spectroscopic redshifts from LAMOST and other sources.

Abstract In this paper, we present a detailed analysis of the light variation of KIC 5623923 using high-precision time-series data from the Kepler mission. The analysis reveals this target is an eclipsing binary system with δ Scuti-type pulsations from the primary component, rather than from the secondary as previously reported. The frequency analysis of three short-cadence data reveals 41 significant frequencies, including the orbital frequency ( f orb = 0.827198 day −1 ) due to orbital motion from the binary system and the pulsational frequencies. Most of the pulsational signal lies in the frequency range of 20–32 day −1 , with amplitude between 0.3 and 8.8 mmag, in which seven peaks are identified as “independent” modes. The strongest one ( f 3 = 28.499399 day −1 ) likely corresponds to a high-order radial mode. In other peaks ( f 7 , f 10 , and f 18 ), several pairs of multiplet structures centered on them are found. The fitting of spectral energy distribution using the collected photometry measurement of multiple bands reveals the effective temperatures of the primary and secondary components as 834 8 − 225 + 230 K and 475 3 − 229 + 237 K, respectively, which place the primary star in the classical pulsating instability zone. The characteristic light-curve morphology and short orbital period are consistent with a tidally locked system. Based on the characteristics of amplitude spectra of pulsating stars in close binaries, the analysis of the multiplet structures reveals that three independent frequencies (i.e., f 7 , f 10 , and f 18 ) correspond to nonradial modes with l = 2, while the associated sidelobes are produced by the orbital motion. We highlight the potential of this method in future studies of pulsating binary stars.

Abstract We present a comparative study of carbon-rich asymptotic giant branch (CAGB) stars in the Large Magellanic Cloud (LMC; 7347 stars) and the Milky Way (7163 stars) using infrared color–magnitude diagrams, spectral energy distributions (SEDs), two-color diagrams, and variability data. Observed SEDs are compared with theoretical models to characterize the central stars and their circumstellar dust envelopes and to estimate distances. For the LMC, a set of best-fitting CAGB models is derived by fitting observed SEDs with radiative transfer models, utilizing the galaxy’s well-established distance. For Galactic CAGB stars, where Gaia DR3 parallaxes are uncertain, we estimate distances by fitting observed SEDs with the CAGB models validated against LMC stars and for Mira variables, from the period–magnitude relation calibrated with LMC Miras. A comparison of these approaches demonstrates that the SED-based distances are both reliable and practical for a large sample of Galactic CAGB stars. We find that CAGB stars in both galaxies show broadly similar infrared properties, although the LMC sample lacks stars with extremely thick dust envelopes.

Abstract We present the discovery of the radio afterglow of the most distant ultralong gamma-ray burst (GRB) detected to date, GRB 220627A at redshift z = 3.084. Its prompt gamma-ray light curve shows a double-pulse profile, with the pulses separated by a period of quiescence lasting ∼15 minutes, leading to early speculation it could be a strongly gravitationally lensed GRB. However, our analysis of the Fermi Gamma-ray Burst Monitor spectra taken during the time intervals of both pulses show clear differences in their spectral energy distributions, disfavouring the lensing scenario. We observed the radio afterglow from 7 to 456 days postburst: an initial, steep decay ( F ν ∝ t −2 ) is followed by a shallower decline ( F ν ∝ t −1/2 ) after ∼20 days. There are three scenarios that could explain these radio properties: (i) energy injection from an additional, slower ejecta component catching up to the external shock; (ii) a stratified density profile going as n ∝ r −8/3 ; or alternatively, (iii) the presence of a slow, wide ejecta component in addition to a fast, narrow ejecta component. We also conducted an independent test of the lensing hypothesis via very long baseline interferometry (VLBI) observations at ∼12 days postburst by searching, for the first time, for multiple images of the candidate lensed GRB afterglow. Our experiment highlighted the growing need for developments in real-time correlation capabilities for time-critical VLBI experiments, particularly as we advance towards the SKA and ngVLA era of radio astronomy.

We present a detailed analysis of J154506, a strongly lensed submillimetre galaxy (SMG) behind the Lupus-I molecular cloud, and a characterisation of its physical properties using a combination of new and archival data, including VLT/MUSE and FORS2 optical data. We identify two high-significance (S/N >5) emission lines at 97.0 and 145.5 GHz, corresponding to CO(4-3) and CO(6-5), respectively, in spectral scans from the Atacama Compact Array (ACA) and the Large Millimetre Telescope (LMT), as well as the CII 158 μm fine-structure line at 400 GHz observed with the Atacama Pathfinder Experiment (APEX). These detections yield a spectroscopic redshift of z_ spec =3.7515± 0.0005. We also report the detection of CI , HCN(4-3), and two H_2 ^+ transitions, further confirming the redshift and providing insights into the physical properties of J154506. By modelling sub-arcsecond resolution ( _⊙yr^ O ALMA Band 6 and 7 continuum data in the uv-plane, we derive an average magnification factor of 6.0 ± 0.4, and our analysis reveals a relatively cold dust (38 K) in a starburst galaxy (sim900 M -1 ) with a high intrinsic dust mass (sim2.5 9 M _⊙) and infrared (IR) luminosity (sim6 12 L _⊙). Non-local thermodynamic equilibrium radiative transfer modelling of the joint dust spectral energy distribution (SED) and CO line excitation suggests the dust continuum emission is primarily associated with relatively diffuse regions with molecular gas densities of 10^2-10^4 ^ cm -3 , rather than compact, high-pressure environments typical of extreme starbursts or active galactic nuclei (AGNs). This interpretation is supported by the close-to-unity ratio between the dust and gas kinetic temperatures, which argues against highly energetic heating mechanisms. The CO excitation ladder peaks close to CO(5-4) and is dominated by slightly denser molecular gas. Our results underscore the unique power of far-IR and submillimetre observations to both uncover and characterise scarce, strongly lensed, high-redshift galaxies, even when they are obscured by foreground molecular clouds.