Locally authored papers of the past 5 days

Amino acids (AAs) are a key target in the search for life beyond Earth due to their extensive role in the machinery of all known life, persistence over geologic timescales, and analytical detectability. However, AAs can also arise from abiotic processes on planets and in space. For example, material from asteroid Bennu contained 33 AAs, including 15 of the 20 proteinogenic AAs that are fundamental to life's functions. Distinguishing life from non-life based on AAs in a sample remains an unsolved problem, particularly when their isotopic and structural signatures (e.g., chirality) could be altered via physicochemical processes. Here we introduce LUMOS (Life Unveiled via Molecular Orbital Signatures), a statistical framework that distinguishes life from non-life by analyzing the distribution of abundance-weighted HOMO-LUMO gap (HLG) values of AAs within a sample. Compilation of AAs datasets from diverse environments and provenances revealed that abiotic samples display highly uniform distributions of AAs HLGs. In contrast, biotic samples show greater variance and preference towards AAs with lower HLG, likely reflecting the need for life to control when, where, and how chemical reactions occur. LUMOS achieves >95% accuracy in distinguishing biotic versus abiotic provenance across diverse environmental and extraterrestrial conditions. These results suggest that varied molecular reactivity within biochemical systems may be a universal feature of life, representing an agnostic biosignature unlinked to the specific set of AAs used by life as we know it. LUMOS is compatible with existing analytical instrumentation, applicable to returned samples or in situ analyses. Broader characterization of abiotic and biotic environments will further refine the chemical boundaries separating biotic from abiotic chemical systems.

We present the first results from the POSEIDON survey, aimed at constraining the dynamical origins of transiting Neptunes through stellar obliquity measurements. We report Rossiter-McLaughlin observations of two Neptunes, TOI-181 b and TOI-883 b, obtained with high-resolution spectroscopy from Magellan/PFS and WIYN/NEID. TOI-181 b is on a 4.5-day orbit with a sky-projected spin-orbit misalignment $\lambda = 32.0_{-6.5}^{+6.3}\,^{\circ}$ and a low eccentricity ($e<0.12$ with $2\sigma$ confidence). TOI-883 b has a longer orbital period of 10 days with $\lambda = 22_{-14}^{+15}\,^{\circ}$ and eccentricity $e = 0.16 \pm 0.03$. The significant misalignment of TOI-181 b and the significant eccentricity of TOI-883 b are suggestive of high-eccentricity migration for both systems. After adding these and other new measurements to the sample, we analyze the obliquity distribution of the host stars of transiting Neptunes. Earlier studies had suggested that the obliquity distribution is bimodal, with peaks corresponding to aligned orbits and polar orbits; the addition of more measurements has weakened the evidence for bimodality. The current sample appears to be consistent with a population of well-aligned systems and a smaller population with nearly random obliquities. This distribution resembles that observed for more massive planets, suggesting that transiting Jupiters and Neptunes originate from similar dynamical processes.

We present a detailed study of near-infrared (2-4$\rm \mu$m) JWST/NIRSpec spectra of 48 high-redshift ($z=2.53^{+1.32}_{-0.70}$) galaxies detected with ALMA at $>3\sigma$. From a multi-wavelength SED analysis we establish the sample has a a median stellar mass of $\rm\log_{10}(M_\ast/M_\odot)=10.8\pm0.1$ and dust mass of $\rm\log_{10}(M_{\rm d}/M_\odot)=8.7\pm0.1$, covering a broad range of far-infrared luminosity $\rm (\log_{10}(L_{FIR}/L_\odot)=10.9-12.7)$. The majority of sources show no signs of AGN activity, with 40% having either X-ray counterparts $(\rm L_{Xc}>10^{42}erg/s)$, elevated optical line ratios, or broad (FWHM>800 km/s) H$\alpha$ profiles, although we note this is a lower limit due to the stochastic placement of NIRSpec slits. We establish the sample has a median gas-phase metallicity of $12+\log({\rm O/H})=8.71\pm0.02$, as derived from the [NII]/H$\alpha$ ratio, with the most FIR-luminous galaxies ($\rm\log_{10}(L_{\rm FIR}/L_\odot)>12$) falling $0.15\pm0.03$dex above the fundamental metallicity relation. From the [SII] emission-line doublet ratio, we measure a median electron density of $\log_{10}(n_{\rm e}/{\rm cm}^{-3})=2.53\pm0.07$ consistent with less-massive, star-forming, galaxies at the same epoch. For nine galaxies with [OII] and H$\beta$ detections (median $\rm\log_{10}(L_{\rm FIR}/L_\odot)=11.81\pm0.15$), we derive a median observed (dust-uncorrected) ionisation parameter of $\rm\log_{10}(U)=-2.84\pm0.06$. Our results indicate that luminous far-infrared galaxies are massive, chemically evolved systems that appear to deviate from the standard dust and metal production equilibrium observed in less obscured galaxies. This study demonstrates the synergy of JWST and ALMA in unveiling the nature of DSFGs, and highlights the need for a NIRSpec survey of uniformly selected, massive, dust-obscured, galaxies to fully characterise their interstellar medium.

The radiolysis effect of cosmic rays (CRs) plays an important role in the chemistry in molecular clouds. CRs can dissociate the molecules on dust grains, producing reactive suprathermal species and radicals which facilitate the formation of large molecules. We add the radiolysis process and some relevant reactions into the Nautilus astrochemical code. By adjusting some parameters, we investigate the sensitivity of the simulation results of the H2O ice on the removal of reaction-diffusion competition, the removal of non-diffusive chemistry, and the desorption energies of the suprathermal species. We find the model, with a few adjustments of the chemistry, can reproduce the steady-state [H2O2]/[H2O] and [O3]/[O2]_0 abundance ratios in the H2O and O2 radiolysis experiments at any CR flux in the experiments. These adjustments in the model do not fully reproduce the fluence required to reach the steady state. It tends also to overestimate the destruction of H2O as measured in H2O radiolysis experiments. We show that reducing the G-values of H2O radiolysis, which implies an increase in the efficiency of immediate reformation of water locally after ion impact, leads to simulated H2O destruction rates closer to the experiments. The effect of reaction-diffusion competition on the simulation results of H2O ice is significant at $\zeta \lesssim 10^{-14}\ \rm s^{-1}$. The non-diffusive chemistry affects the simulation results at 16 K but not 77K, while the results are sensitive to the desorption energies of suprathermal H, O, O3 and OH at 77 K. Our results show that the steady-state [H2O2]/[H2O] and [O3]/[O2]_0 in experiments can be reproduced by fine-tuning the chemical model, but still call for more constraints on the intermediate pathways in the radiolysis processes, especially the ion chemistry in the ice bulk, as well as activation barriers and branching ratios of the reactions in the network.

Galaxy major mergers are a potential mechanism for triggering active galactic nuclei (AGN) activity, but their role remains debated, particularly beyond the local Universe. We aim to shed light on the merger-AGN connection at $z=0.5$-$2$, exploiting the multi-wavelength datasets and {\it James Webb Space Telescope} (JWST) observations in the COSMOS field. We construct a stellar mass-limited sample and identify AGN via mid-infrared (MIR) colours, X-ray detections, and spectral energy distribution (SED) fitting. We train convolutional neural networks to identify mergers with mock JWST observations. We create non-AGN and non-merger control samples matching the redshift, stellar mass, and star-formation rate distributions of the AGN and mergers. We find AGN to be moderately more frequent in mergers than in non-mergers, with excess ratios ranging from $\sim2.5$ (X-ray AGN) to $\sim1.3$ (MIR) and $\sim 1.1$-1.2 (SED AGN). Similarly, AGN galaxies show a higher merger fraction ($f_{merg}$) than non-AGN controls. We then study $f_{merg}$ as a function of relative and absolute AGN power, utilising the AGN fraction ($f_{AGN}$) and accretion disc luminosity (L$_{disc}$) parameters. We uncover a $f_{merg}$-$f_{AGN}$ relation with two regimes: $f_{merg}$ stays roughly flat for less-dominant AGN ($f_{AGN}<0.8$) but increases at $f_{AGN}>0.8$ for the MIR and X-ray AGN, and more gently for SED AGN, where mergers appear to be the main triggering mechanism. Additionally, $f_{merg}$ increases monotonically as a function of L$_{disc}$, for all AGN types, reaching $f_{merg}>50\%$ for the most luminous AGN (L$_{disc} \gtrsim 10^{46}\,{erg\,s^{-1}}$). Overall, our results suggest that major mergers can trigger AGN out to the cosmic noon at $z\sim2$. Furthermore, the role of major mergers shows a clear dependence on AGN luminosity and remains the principal mechanism for fuelling the most powerful AGN.

We characterize the radius-dependent eccentricity distribution of 347 warm (P = 8-200 days) systems with only one transiting planetary candidate identified during Sectors 1-69 of the TESS mission. Using the ``photoeccentric effect'' in a hierarchical Bayesian framework, we first model the population using discrete planetary size bins (sub-Neptunes, sub-Saturns, and Jovians). We then develop a continuous mixture model with weights governed by a logistic sigmoid function of radius. We find that the warm-single population is best described by two components: a dominant low-eccentricity mode ( <e_low> = 0.070-0.068+0.026) and a secondary dynamically excited mode (<e_high> = 0.616-0.075+0.091). The fraction of planets belonging to this high-eccentricity component increases strongly with planet radius, characterized by a transition at a break radius of R_br = 9.8-1.1+1.4 R_e. This trend places warm sub-Saturns predominantly on the same low-eccentricity track as sub-Neptunes. In contrast, warm Jovians (8--16 R_e) are frequently eccentric, with 59+-13% of the population in the high eccentricity mode. We detect this bimodality at >4sigma, providing statistically significant evidence that warm gas giants are sculpted by two distinct pathways, or a single mechanism with subsequent eccentricity excitation. Finally, we identify a non-negligible tail of highly eccentric sub-Neptunes (1--4 R_e), which comprise 14.9-6.5+5.1% of the population, consistent with excitation by non-transiting external companions.

Many post-starburst galaxies at $z\sim0.7$ have been shown to retain substantial molecular gas reservoirs yet host low ongoing star formation, suggesting that the remaining gas may be inefficient at forming stars during the early post-burst phase. We present new Atacama Large Millimeter/submillimeter Array CO(5-4) observations of nine gas-rich post-starburst galaxies at $z\sim0.7$ from the Studying Quenching in Intermediate-z Galaxies: Gas, angu$\vec{L}$ar momentum, and Evolution (SQuIGG$\vec{L}$E) survey, providing a view of the molecular gas excitation in these systems. Combined with existing CO(2-1) data, we detect CO(5-4) in 8/9 targets and find that most have moderate CO excitation with $r_{52}\equiv L'_{\rm CO(5-4)}/L'_{\rm CO(2-1)}\approx0.1-0.3$. These systems show no clear trend between $r_{52}$ and either total or surface-density of star formation. Specifically, all objects have $\Sigma_{\mathrm{SFR}} \sim 0.01-1\ \text{M}_\odot\ \text{yr}^{-1}\ \text{kpc}^{-2}$, consistent with compact, modest star formation, even when allowing for buried activity, as these galaxies decline from their peak. One object J1448+1010, which has clear optical, mid-infrared, and radio indicators of an active galactic nucleus, is an outlier with $r_{52}\approx0.6$; its elevated excitation likely requires significant non-stellar heating, with a contribution from potentially obscured star formation. Together, most gas-rich SQuIGG$\vec{L}$E post-starbursts have moderately excited molecular gas alongside little to modest star-forming activity, indicating that the remaining gas hosts relatively suppressed star formation efficiencies instead of strong buried starburst activity.

Neutral gas outflows play a crucial role in the baryon cycle of galaxies, their properties provide key insights into the transition from star formation to quiescence. In this work, we investigate the neutral gas outflow of 23 massive ($M_\star = 10^{10.1-11.6}\,\rm M_\odot$) quiescent galaxies (QGs) at z=2.82--4.61, selected from the JWST NIRSpec (R~1000) and NIRCam program DeepDive. We trace the neutral gas outflows using the NaI Doublet absorption lines and detect excess NaI D in 13/23 (57%) targets, of which 7/23 (30%) show blueshifted absorption with velocity offsets $|{\Delta}v|$ >~ 150 km/s. The z ~ 3.5 targets have ${\Delta}v$ similar to those of their local counterparts; they are also equivalent when compared in SFR--${\Delta}v$ space. We derive mass outflow rates and identify the most extreme neutral gas outflow rate $\log(\dot M_{\rm out} / \mathrm{M_\odot \, yr}^{-1})=2.68\pm0.27$ beyond the local Universe, coincident with an X-ray AGN. For all NaI D detected systems, the inferred mass outflow rate can, in principle, suppress ongoing star formation; however, the outflows are unlikely to escape their hosts, suggesting recycling on relatively short timescales (~3--180 Myr), depending on the assumed potential and launching radius. All NaI D detected targets occupy the LI(N)ER region of the BPT diagram and/or are X-ray detected, but we find no strong correlation between ongoing AGN and the neutral outflow: 2/4 broad-line/X-ray AGNs are NaI D undetected -- yet, the outflows can be powered by fossil/episodic AGNs, and one broad-line target shows a possible P-Cygni profile that indicates strong outflows. As neutral outflows alone are not able to permanently quench star formation by removing gas in our sample at z ~ 3.5, the presence of gas cycling in and out of massive passive systems may instead be the signature of feedback-regulated quenching-maintenance processes.

The Vera C. Rubin observatory is expected to produce 10 million transient alerts per night in ugrizy filters, whilst Euclid is a visible to near-infrared space telescope engaged in a wide field survey. We present a prototype system to automatically match the transient alerts from Rubin to Euclid observations. The system produces joint light-curves containing both visible and near-infrared photometry, and joint image cutouts. Using Zwicky Transient Facility alerts as a proxy for Rubin, we demonstrate the system in use in cases where Euclid did and did not detect the transient and highlight the value that can be added in each case. For transients detected by Euclid these benefits include identifying the supernovae (SNe) in observations taken prior to ground-based detection, thereby better constraining the explosion time, such as SN 2024pvw detected ~3 d prior to ground based detections. In cases where Euclid did not detect the transient, we demonstrate the benefit of adding Euclid observations to improve host morphology measurements and associations.

We present the results of the Exploration of Local VolumE Survey - Field (ELVES-Field), a survey of the dwarf galaxies in the Local Volume (LV; $D<10$ Mpc) over roughly $3,000$ square degrees, focusing on the field dwarf population. Candidates are detected using a semi-automated algorithm tailored for low surface brightness dwarfs. Using tests with injected galaxies, we show the detection is $50\%$ complete to $m_g\sim20$ mag and $M_\star \sim 10^6$ $M_\odot$. Candidates are confirmed to be true nearby dwarfs through distance measurements including redshift, tip of the red giant branch, and surface brightness fluctuations. We identify isolated, field dwarfs using various environmental criteria. Over the survey footprint, we detect and confirm 95 LV dwarfs, 44 of which we consider isolated. Using this sample, we infer the field dwarf mass function and find good agreement at the high-mass end with previous redshift surveys and with the predictions of the IllustrisTNG simulation. This sample of isolated, field dwarfs represents a powerful dataset to investigate aspects of small-scale structure and the effect of environment on dwarf galaxy evolution.

We report the first direct measurement of the period derivative in a quasi-periodic eruption (QPE), finding a smoothly increasing period with $\dot{P}\approx (1.7\pm 0.02)\times10^{-2}$ d d$^{-1}$ in the source ZTF19acnskyy/"Ansky". Most models for QPEs invoke repeated interactions of a stellar-mass orbiting companion around the supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI). In these scenarios, a positive $\dot{P}$ is surprising, but not impossible to produce. We explore several possible explanations for the observed $\dot{P}$, including stable mass-transfer driven by impulsive mass loss events in an EMRI, velocity kicks at pericenter due to tidal interactions with the SMBH, apparent period changes due either to general relativistic precession effects in an EMRI or light travel-time delays in a hierarchical SMBH binary, and mass-transfer variations in a thermal/viscous disk instability model. We find that none of the considered models provides a complete explanation for the data, motivating further work on physical explanations for positive period derivatives in QPEs.

We use a new sample of low-mass ($M_* < 10^9$ $M_\odot$) isolated galaxies from the Exploration of Local VolumE Survey - Field (ELVES-Field) to examine the star formation properties and sizes of field dwarf galaxies in the Local Volume (LV; $D<10$ Mpc). This volume-limited sample was selected from nearly 3,000 square degrees of imaging, relying on surface brightness fluctuations to determine distances to the majority of the systems and is complete to $M_* \approx 10^6$ $M_\odot$. Across the surveyed area, we catalog over 2300 candidate LV dwarfs, of which we confirm 95 as genuine LV members and reject over 1600 as background contaminants, with the remaining 600 candidates still requiring a distance measurement. Of the confirmed LV dwarfs, 46 are either new discoveries or confirmed via a distance measurement for the first time here. We explore different environmental criteria to select isolated dwarfs but primarily focus on dwarfs that are $>2\times R_{\mathrm{vir}}$ in projection from any known group with $M_\star > 10^9$ $M_\odot$. We find that, at higher dwarf masses ($M_\star \gtrsim 10^7$ $M_\odot$), essentially all field dwarfs are star-forming as has been found before. In contrast, at $M_\star \lesssim 10^7$ $M_\odot$, $\sim30\%$ of field dwarfs appear to be quenched. Finally, we find that isolated dwarfs are noticeably smaller ($\sim 20\%$) than satellite dwarfs of the same stellar mass, regardless of quenched status.

Neutrino emission from astrophysical sources has long been considered a signature of cosmic-ray acceleration. The IceCube neutrino observatory has observed a diffuse flux of TeV-PeV neutrinos, but very few confirmed sources have emerged. With the recent publication of IceCube Event Catalog (IceCat-1), IceCube has released a list of the most promising astrophysical neutrino events since May 2011. Using the archival data from the High Altitude Water Cherenkov (HAWC) $\gamma$-ray observatory, we perform a coincidence search for gamma rays and neutrinos using a Bayesian Block algorithm with the public IceCube alerts from IceCat-1, along with additional alerts issued later. In this work, we consider 368 alerts, up to July 8, 2025, that are within HAWC's field of view. We observe approximately a 5\% coincident detection rate, which is consistent with expectations from background. Two of these detections contain the Active Galactic Nuclei (AGN) Markarian 421 and Markarian 501. We discuss the likelihood that the neutrino/$\gamma$-ray coincidences are false positives and a brief overview of the results.

Feedback from active galactic nuclei (AGN) is widely acknowledged to regulate the growth of massive galaxies, though its driving mechanisms are debated. Prevailing theories suggest that AGN-driven outflows are driven either by radiation pressure acting directly on the dusty interstellar medium (ISM) or by hot winds entraining cooler ISM gas, but the relative contribution of each mechanism remains uncertain. By combining optical emission line measurements with highly ionized UV emission lines, it is possible to constrain whether the pressure source applied to ionized clouds is primarily radiation or primarily hydrodynamic, and thus constrain the dominant driver. This study presents the first multi-object analysis of far-ultraviolet (FUV) spectra from galactic-scale AGN-driven outflows in obscured quasars, based on Cosmic Origins Spectrograph observations of five low-redshift targets. By comparing narrow-line region UV emission line ratios to theoretical models that vary the importance of the two pressure sources, we find three out of five targets fall within the radiation pressure-dominated regime. A fourth target exhibits intermediate emission-line ratios that suggest radiation pressure and pressure from a hot wind are both dynamically important. Finally, the lowest-luminosity object in our sample may have a dynamically important hot wind component, but non-detections prevent a clear conclusion in this case. These results suggest radiation pressure dominates circum-nuclear narrow-line region cloud dynamics, but pressure from a hot wind also plays a role in some cases. This is consistent with AGN feedback scenarios mediated by radiation pressure or a short-lived hot wind phase that dissipates after initially accelerating outflows.

In this work, we develop, for the first time, a supervised classification framework with class-dependent rewards (CDR) to predict $\geq$MM flares within 24 hr. We construct multiple datasets, covering knowledge-informed features and line-of sight (LOS) magnetograms. We also apply three deep learning models (CNN, CNN-BiLSTM, and Transformer) and three CDR counterparts (CDR-CNN, CDR-CNN-BiLSTM, and CDR-Transformer). First, we analyze the importance of LOS magnetic field parameters with the Transformer, then compare its performance using LOS-only, vector-only, and combined magnetic field parameters. Second, we compare flare prediction performance based on CDR models versus deep learning counterparts. Third, we perform sensitivity analysis on reward engineering for CDR models. Fourth, we use the SHAP method for model interpretability. Finally, we conduct performance comparison between our models and NASA/CCMC. The main findings are: (1)Among LOS feature combinations, R_VALUE and AREA_ACR consistently yield the best results. (2)Transformer achieves better performance with combined LOS and vector magnetic field data than with either alone. (3)Models using knowledge-informed features outperform those using magnetograms. (4)While CNN and CNN-BiLSTM outperform their CDR counterparts on magnetograms, CDR-Transformer is slightly superior to its deep learning counterpart when using knowledge-informed features. Among all models, CDR-Transformer achieves the best performance. (5)The predictive performance of the CDR models is not overly sensitive to the reward choices.(6)Through SHAP analysis, the CDR model tends to regard TOTUSJH as more important, while the Transformer tends to prioritize R_VALUE more.(7)Under identical prediction time and active region (AR) number, the CDR-Transformer shows superior predictive capabilities compared to NASA/CCMC.

This report presents the design, characterization, and application of a high-sensitivity optical detection system based on plastic scintillators coupled to Multi-Pixel Photon Counters (MPPCs). The primary objective was to evaluate the performance of MPPCs (Silicon Photomultipliers) as robust, low-voltage alternatives to traditional photomultiplier tubes for detecting faint scintillation light. The optoelectronic properties of the sensors were analyzed, including single-photoelectron gain calibration and dark count rate measurements, to optimize the signal-to-noise ratio. By embedding wavelength-shifting fibers to enhance light collection efficiency, the system was configured into a three-fold coincidence telescope. The angular distribution of the cosmic ray muon flux was measured to validate the detector's stability and geometric acceptance. Fitting the experimental data to a $\bm{\cos^n(\theta)}$ distribution yielded an angular exponent of $\bm{n = 1.44 \pm 0.06}$, consistent with literature values. These results demonstrate the efficacy of the MPPC-scintillator coupling for precise photon counting and timing applications in high-energy physics instrumentation.

The Euclid galaxy survey will provide unprecedented constraints on cosmology, but achieving unbiased results will require an optimal characterisation and mitigation of systematic effects. Among these, the intrinsic alignments (IA) of galaxies are one of the dominant contaminants of the weak lensing (WL) and galaxy-galaxy lensing (GGL) probes. In this work, we assess IA modelling choices for Euclid DR1 3x2pt analyses by comparing the performance of the two most commonly used IA models, nonlinear alignment (NLA) and tidal alignment tidal torquing (TATT), along with several variations. Our analyses combine three perspectives: i) the constraining power on the IA and cosmological parameters for each IA model, ii) the bias that results when the IA analysis model differs from the model used to generate the synthetic data vector, and iii) the degeneracies between IA and photometric redshift (photo-z) nuisance parameters. Among the IA models analysed, the redshift-dependent TATT model (zTATT) provides the most flexible description of IA, with a similar constraining power compared to simpler IA models, making it a well-motivated choice for Euclid DR1 3x2pt analyses.

White dwarfs (WDs), the evolutionary endpoints of most stars, can form through both single-star and binary channels. While single-star evolutionary models enable reliable WD age estimates, binary evolution introduces interactions that can accelerate WD formation and result in a variety of exotic WDs, which may exhibit strong magnetic fields, rapid rotation, or even serve as potential gravitational wave sources. Such systems offer valuable insights into magnetic field generation, angular momentum evolution, and compact object physics. Star clusters, with their approximately coeval populations, allow precise age determination of member WDs. If a WD's total age derived from single-star evolution exceeds that of its host cluster, it likely indicates a binary origin. In this study, we use \textit{Gaia} 5D astrometry to identify 439 WD candidates in 117 open clusters, with 244 likely formed via binary evolution. We discuss the possibility of dynamical ejection for WDs meeting only 2D (proper motion space) membership criteria. Spectroscopic observations further reveal a subset with strong magnetic fields and rapid rotation, supporting their binary evolutionary origin.

Rapid localisation and follow-up of gamma-ray bursts (GRBs) increasingly rely on low-latency triggers from new missions coupled to wide-field robotic optical facilities. We present the discovery and multi-wavelength follow-up of GRB 250818B, detected by the Space Variable Objects Monitor (SVOM) and localised optically by the Gravitational-wave Optical Transient Observer (GOTO). We compile and homogenise X-ray, optical/NIR, and radio data to build broadband light curves and spectral energy distributions. The afterglow is unusually luminous for a nominal short GRB, lying on the bright end of the short-GRB population in X-rays and optical and among the most luminous high-redshift short-GRB afterglows in the radio. MeerKAT detects the source at 3.1 GHz, while ALMA provides deep higher-frequency limits. Keck/LRIS spectroscopy shows continuum and metal absorption (Fe II, Mg II, Mg I), giving $z=1.216$. Synchrotron forward-shock modelling favours a constant-density medium and strongly prefers refreshed (energy-injection) emission, well described by a two-component jet with $E_{K,iso} \sim 4\times10^{52}$ erg, $n_0 \sim 3.6$ cm$^{-3}$, $\theta_j \simeq 0.10$ rad ($\sim 5.7$ deg), and $p \simeq 1.64$. The host association is ambiguous: the nearest LS DR10 galaxy candidate ($r_{AB} \sim 24.7$) is offset by $\sim 4$ arcsec ($\sim 34$ kpc) with chance-alignment probability $P_{cc} \sim 0.2$, and current imaging does not exclude a fainter, near-coincident host. SED fitting of the candidate host suggests a low-mass galaxy. GRB 250818B highlights the power of rapid wide-field counterpart identification in the SVOM era, while host-association uncertainty can still limit offset-based interpretation.

Context. Characterization of warm giants is crucial to constrain giant planet formation and evolution. Measuring the mass and radius of these planets, combined with their moderated irradiation, allows us to estimate their planetary bulk composition, which is a key quantity to comprehend giant planet formation and structure. Aims. We present the discovery of two transiting warm giant planets orbiting solar-type stars from the Transiting Exoplanet Survey Satellite (TESS), which were characterized by further spectroscopic and photometric ground-based observations. Methods. We performed a joint analysis of photometric data with radial velocities to confirm and characterize TOI-883 b and TOI-899 b, two sub-Saturns orbiting solar-like stars. Results. TOI-883 b and TOI-899 b have masses of $0.123 \pm 0.012$ $M_J$ and $0.213 \pm 0.024$ $M_J$, radius of $0.604 \pm 0.028$ $R_J$ and $0.991 \pm 0.044$ $R_J$, periods of $10.06$ d and $12.85$ d and equilibrium temperature of $1086 \pm 19$ K and $1040 \pm 19$ K, respectively. Conclusions. While having similar masses, orbital periods and stellar host properties, these planets seem to have different internal compositions, which could point to distinct formation histories. Both planets are suitable targets for atmospheric studies to further constrain formation scenarios of planets in the Neptune-Saturn mass range