High Energy Astrophysical Phenomena
Einstein Probe discovery of EP J171159.4-333253: an eclipsing neutron star low-mass X-ray binary with clocked bursts
Y. L. Wang, F. Coti Zelati, E. Parent et al. (+27 more)
EP J171159.4-333253 is a new
neutron-
star low-mass X-ray binary discovered in outburst by the Einstein Probe (EP) on 2025 June 23, exhibiting clocked type-I X-ray bursts, eclipses and dips. In this paper, we report on the results of the X-ray spectral and timing analyses for EP J171159.4-333253 using data collected by EP and NuSTAR during the first 21 days of the outburst. The X-ray burst recurrence time can be characterized over a subset of nine bursts spanning 1.6 days around the NuSTAR observation, and the result is $t_{\rm rec}=8196 \pm 177\,$s with indications of a possible decreasing trend. From the X-ray eclipse events, the binary orbital period and the eclipse duration are estimated to be $P_{\rm orb}=6.48301 \pm 0.00003\,$hr and $D_{\star,X} = 1245.5^{+6.9}_{-6.5}\,$s, respectively. These enable an estimate of the mass and radius of the companion
star and the binary inclination, which are $M_2\approx0.6-0.8\,M_\odot$, $R_2\approx0.7-0.8\,R_\odot$ and $i\approx73-75^\circ$, respectively. We also report on joint ULTRACAM and EP observations on 2025 July 21–22, detecting the source optical counterpart and covering an eclipse in both X-ray and optical bands. The optical eclipse is wavelength-dependent and broader than in X-rays, indicating that part of the optical emission arises from an extended region in the
accretion flow. Despite a moderate variation in the source flux, the properties of the persistent X-ray emission are typical of a hard spectral state. We further evaluated the ratio of the
accretion energy to the thermonuclear energy to be 120–130, implying helium bursts with the accreted hydrogen being depleted in-between bursts.
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All authors Y. L. Wang, F. Coti Zelati, E. Parent, A. Marino, N. Rea, V. S. Dhillon, J. Blanco-Pozo, I. Ribas, S. P. Littlefair, Z. H. Yang, G. B. Zhang, S. Guillot, K. R. Ni, J. H. Wu, A. Patruno, Y. Cavecchi, G. Illiano, A. Papitto, F. Ambrosino, B. F. Liu, H. Q. Cheng, H. Feng, J. W. Hu, C. C. Jin, H. Sun, L. Tao, Y. J. Xu, H. N. Yang, W. Yuan, Q. C. Zhao
Earth and Planetary Astrophysics
A Multi-Wavelength Study of Comet C/2022 E3 (ZTF): Complementary ALMA and JWST Investigations of Water and Methanol in Cometary Comae
K. D. Foster, M. A. Cordiner, Nathan X. Roth et al. (+7 more)
Long-period comets, which are often considered to be representative of material in the protoplanetary disk that formed the
Solar System, are ideal to investigate the question of chemical inheritance in astronomy. Determining the chemistry of comets, both individually and as a population, has become of great importance in comparative studies against sources representative of evolutionary precursors to planetary systems. Contemporaneous observations of long-period comet C/2022 E3 (ZTF) were obtained with the JWST and the Atacama Large Millimeter/submillimeter Array (ALMA) in early 2023 March. This work focuses on \ce{CH3OH} measurements from both ALMA and JWST as well as \ce{H2O} measurements from JWST. Radiative transfer modeling of \ce{CH3OH} and \ce{H2O} was performed to investigate spatial variations in rotational temperature, column density, and production rates, as well as a comparison of derived values between the two
telescopes. Most of the spatial distributions of the modeled values are centrally peaked, and the modeled values from JWST are all within the error bars of the average values from ALMA. C/2022 E3 (ZTF) also displays an enhancement in modeled rotational temperature in the anti-Sunward direction that is shown to be statistically significant. Based on non-LTE radiative transfer modeling, the declining \ce{H2O} rotational temperatures as a function of nucleocentric distance observed by JWST can be explained primarily as a result of rotational line cooling. The values derived in this work are in general agreement with single-dish millimeter-wave observations.
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All authors K. D. Foster, M. A. Cordiner, Nathan X. Roth, S. N. Milam, A. J. Remijan, N. Biver, J. Boissier, J. Crovisier, Y.-J. Kuan, D. C. Lis
Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): VI. Asymmetries and offsets
J. B. Lovell, A. S. Hales, G. M. Kennedy et al. (+33 more)
Asymmetries in debris discs provide unique clues to understand the
evolution and architecture of planetary systems.** The aim of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is to expand our understanding of radial and vertical
dust structures, as well as gas distributions and kinematics, in debris discs.** Here, in ARKS~VI, we present a systematic analysis of the asymmetries and stellocentric offsets present in the ALMA continuum data for the ARKS survey. Our aims are to identify asymmetries in debris disc
dust distributions, quantify debris disc asymmetry properties, and discuss the potential origins of debris disc asymmetries.** We utilised empirical methods to identify emission asymmetries** and the presence of offset emission between disc centres and the locations of the host
stars, via an analysis of their calibration procedures and disc properties. We associated observational asymmetry types** and plausible physical classes** associated with each source. We show that there are ten systems, almost half of the ARKS sample, that host either a continuum emission asymmetry or offset emission. Three systems host offsets (HD15115, HD32297, and HD109573 (HR4796)), four host azimuthal asymmetries (HD9672 (49Ceti), HD92945, HD107146, and HD121617), two host an asymmetry in their major axis (HD10647 (q$^1$ Eri), and HD39060 ($\beta$ Pic)), and one hosts an asymmetry in their minor axis (HD61005). We attribute the offset asymmetries to non-zero eccentricities, and three of the azimuthal asymmetries to arcs. The presence of an asymmetry or offset in the ARKS sample appears to be correlated with the fractional luminosity of cold
dust.** Conclusions: This study demonstrates that debris disc asymmetries in the ARKS sample are common, and plausibly so in the wider population of debris discs at (sub)-millimetre wavelengths.** ** = ABRIDGED FOR ARXIV: FULL ABSTRACT IN PAPER
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All authors J. B. Lovell, A. S. Hales, G. M. Kennedy, S. Marino, J. Olofsson, A. M. Hughes, E. Mansell, B. C. Matthews, T. D. Pearce, A. A. Sefilian, D. J. Wilner, B. Zawadzki, M. Booth, M. Bonduelle, A. Brennan, C. del Burgo, J. M. Carpenter, G. Cataldi, E. Chiang, A. Fehr, Y. Han, Th. Henning, A. V. Krivov, P. Luppe, J. P. Marshall, S. Mac Manamon, J. Milli, A. Moór, M. C. Wyatt, S. Ertel, M. R. Jankovic, Á. Kóspál, M. A. MacGregor, L. Matrà, S. Pérez, P. Weber
Astrophysics of Galaxies
The impact of attenuation on cosmic-ray chemistry: I. Abundances and chemical calibrators in molecular clouds
Arghyadeb Roy, Brandt A. L. Gaches and Jonathan C. Tan
The chemistry of shielded molecular gas is primarily driven by energetic, charged particles dubbed
cosmic rays (CRs), in particular those with energies under 1 GeV. CRs ionize molecular hydrogen and helium, the latter of which contributes greatly to the destruction of molecules. CR ionization initiates a wide range of gas-phase chemistry, including pathways important for the so-called "carbon cycle", C$^+$/C/CO. Therefore, the CR ionization rate, $\zeta$, is fundamental in theoretical and observational astrochemistry. Although observational methods show a wide range of ionization rates – varying with the environment, especially decreasing into dense clouds – astrochemical models often assume a constant rate. To address this limitation, we employ a post-processed gas-phase chemical model of a simulated dense molecular cloud that incorporates CR energy losses within the cloud. This approach allows us to investigate changes in abundance profiles of important chemical tracers and gas temperature. Furthermore, we analyze analytical calibrators for estimating $\zeta$ in dense molecular gas that are robust when tested against a full chemical network. Additionally, we provide improved estimations of the electron fraction in dense gas for better consistency with observational data and theoretical calibrations for UV-shielded regions.
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High Energy Astrophysical Phenomena
Black hole accretion disks with outflows II. Time dependent Green's function solutions in Newtonian gravity
Andrew Mummery
We present Green's function solutions of the Newtonian time-dependent thin disk equations in the presence of
outflows, showing that simple and exact analytical expressions exist in various natural limits of the problem. These Green's functions are mathematically very similar to the classical Lynden-Bell & Pringle solutions in the absence of
outflows, but differ strongly in their precise physical details and observational implications. Solutions are presented for phenomenological radius-dependent
outflows which both do and do not torque the local
accretion flow, and for
outflows which are launched proportional to the local
accretion rate. Generically,
outflows lead to a more rapid decay of the bolometric luminosity of the disk, flatten the radial dependence of the disk temperature, and suppress variability in the
accretion rate at small radii and low frequencies (on long timescales). Observational implications of these four results are discussed in detail.
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Solar and Stellar Astrophysics
Using Astrometry to Break Degeneracies in Stellar Surface Mapping
Jamila Taaki, Lia Corrales and Alfred O. Hero III
Astrometric jitter noise arises when starspots on a rotating
stellar surface move in and out of view, shifting the photocenter. This noise may limit our ability to detect and weigh small, sub-Neptune-sized
planets around active
stars. By deriving a linear forward model for the astrometric jitter signal of a rotating
star in a spherical-harmonic coordinate system, we show that jitter noise can be used to reconstruct surface-brightness maps and, in principle, disentangle jitter from
stellar reflex motion due to an orbiting
planet. Furthermore, we show that astrometry and photometry probe complementary surface information: photometry measures even-degree spherical harmonic surfaces that are symmetric about the equator, while astrometry measures odd-degree modes. Their joint use, therefore, breaks degeneracies in surface mapping. Our model further quantifies the variation in the astrometric signal with inclination angle, which is foundational for studies of worst-case configurations of astrometric
star-spot noise. For example, we show that pole-on
stellar inclinations lead to poorly constrained inversions, as any
stellar surface produces a purely circular astrometric jitter signal. We characterize the degeneracy in jointly identifying the
stellar surface and
stellar inclination, and develop a surface estimation approach. Using this approach, we present example simulations and reconstructions that demonstrate the use of astrometry data alongside light-curve data to improve
stellar surface mapping and localize spot positions in latitude and longitude. With forthcoming high-precision
Gaia astrometry, astrometric surface mapping provides a promising new approach to probe
stellar activity.
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Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS). X. Interpreting the peculiar dust rings around HD 131835
M. R. Jankovic, N. Pawellek, J. Zander et al. (+27 more)
Dusty discs detected around main-sequence
stars are thought to be signs of planetesimal belts in which the
dust distribution is shaped by collisional and dynamical processes, including interactions with gas if present. The debris disc around the young A-type
star HD 131835 is composed of two
dust rings at ~65 au and ~100 au, a third unconstrained innermost component, and a gaseous component centred at ~65 au. New ALMA observations show that the inner of the two
dust rings is brighter than the outer one, in contrast with previous observations in scattered light. We explore two scenarios that could explain these observations: the two
dust rings might represent distinct planetesimal belts with different collisional properties, or only the inner ring might contain planetesimals while the outer ring consists entirely of
dust that has migrated outwards due to gas drag. To explore the first scenario, we employed a state-of-the-art collisional
evolution code. To test the second scenario, we used a simple dynamical model of
dust grain
evolution in an optically thin gaseous disc. Collisional models of two planetesimal belts cannot fully reproduce the observations by only varying their dynamical excitation, and matching the data through a different material strength requires an extreme difference in
dust composition. The gas-driven scenario can reproduce the location of the outer ring and the brightness ratio of the two rings from scattered light observations, but the resulting outer ring is too faint overall in both scattered light and sub-millimetre emission. The
dust rings in HD 131835 could be produced from two planetesimal belts, although how these belts would attain the required extremely different properties needs to be explained. The
dust-gas interaction is a plausible alternative explanation and deserves further study using a more comprehensive model.
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All authors M. R. Jankovic, N. Pawellek, J. Zander, T. Löhne, A. V. Krivov, J. Olofsson, A. Brennan, J. Milli, M. Bonduelle, M. C. Wyatt, A. A. Sefilian, T. Pearce, S. Mac Manamon, Y. Han, S. Marino, L. Matrá, A. Moór, M. Booth, E. Chiang, E. Mansell, P. Weber, A. M. Hughes, D. J. Wilner, P. Luppe, B. Zawadzki, C. del Burgo, Á. Kóspál, S. Pérez, J. M. Carpenter, Th. Henning
High Energy Astrophysical Phenomena
Discovery of High X-Ray Polarization from the Neutron Star Low-Mass X-Ray Binary Cyg X-2 in the Horizontal Branch
Andrea Gnarini, Swati Ravi, Philip Kaaret et al. (+17 more)
We present results from simultaneous X-ray polarimetric and spectroscopic observations of the bright
neutron star low-mass X-ray binary Cyg X-2, performed by the Imaging X-ray Polarimetry Explorer (IXPE) and the
Nuclear Spectroscopic
Telescope Array (NuSTAR). IXPE detected significant polarization (15 sigma) from the source in the 2-8 keV energy band with an average polarization degree (PD) of 4.5% +/- 0.3% and a polarization angle (PA) of 128 +/- 2 degrees as the source moved along the horizontal branch of its Z-track. The PD increases with energy reaching 9.9% +/- 2.8% in the 7-8 keV band, with no evidence for energy-dependent variation in the PA. The PA is roughly consistent with previous measurements obtained during the normal and flaring branches and also with the known
radio jet axis. From spectropolarimetric analysis, the main contribution to the polarized radiation is due to Comptonized
photons, but the polarization is higher than predicted in typical spreading layer geometries. The observed high polarization may be due to a combination of a highly polarized reflected component and a moderately polarized spreading layer on the
neutron star surface or produced by electron scattering in an equatorial wind.
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All authors Andrea Gnarini, Swati Ravi, Philip Kaaret, Anna Bobrikova, Juri Poutanen, Sofia V. Forsblom, Francesco Ursini, Maria Cristina Baglio, Stefano Bianchi, Fiamma Capitanio, Massimo Cocchi, Maria Alejandra Diaz Teodori, Sergio Fabiani, Ruben Farinelli, Giorgio Matt, Mason Ng, Alexander Salganik, Paolo Soffitta, Antonella Tarana, Silvia Zane
Astrophysics of Galaxies
Blobs and Blurs: A Citizen Science-Identified Catalog of Diffuse Galaxies in the Fornax Cluster
Nicolas Mazziotti, Michael G. Jones, Donghyeon J. Khim et al. (+2 more)
We present a catalog of 643 diffuse
galaxies identified through a citizen science search of the Fornax cluster, of which we estimate 21.8% are nucleated (139/637; 6 inconclusive). This marks the first crowd-sourced effort to construct a cluster-scale census of diffuse
galaxies. These objects were visually identified using a combination of the Fornax Deep Survey and Dark Energy Camera Legacy Survey imaging across 26 deg$^2$. Over 1,400 volunteers cataloged the candidates within this sky area at a rate of 1.15 days/deg$^2$. Our catalog is highly complete relative to existing
dwarf catalogs of Fornax ($> 80\%$ of objects recovered) down to an effective radius $r_{\mathrm{eff}} = 5^{\prime \prime}$, the minimum size we suggested volunteers classify, and to an effective r-band surface brightness as faint as $\langle \mu_r \rangle \simeq26$ mag arcsec$^{-2}$. We detect 97 candidates that existing automated searches of Fornax did not find and three candidates not found by any prior search, automated or visual. The
stellar mass distribution of our sample is consistent with similar
dwarf studies of Fornax, with the nucleated fraction peaking at 80% for a host
galaxy mass of $\sim$10$^{8.5}M_{\odot}$. The efficiency and completeness of our catalog thus establishes citizen science as a valuable tool for mapping diffuse
galaxy populations in future sky surveys, such as the Legacy Survey of Space and Time.
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All authors Nicolas Mazziotti, Michael G. Jones, Donghyeon J. Khim, David J. Sand, Paul Bennet
Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) IV: CO gas imaging and overview
S. Mac Manamon, L. Matrà, S. Marino et al. (+29 more)
CO gas is detected in a significant number of debris discs, but its origin and
evolution remains unclear. Key constraints are its mass and spectro-spatial distribution, which are coupled through optical depth and have only been analysed at low to moderate resolution so far. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is the first ALMA large program to target debris discs at high spectro-spatial resolution. We used $^{12}$CO and $^{13}$CO J=3-2 line data of 18 ARKS debris belts, 5 of which were already known to host gas, to analyse the spectro-spatial distribution of CO, constrain the gas masses, and to search for gas in the remaining systems. We developed a line-imaging pipeline and produced line cubes for each disc, with a spatial resolution down to $\sim$70 mas and spectral resolution of 26 m s$^{-1}$. Using spectro-spatial shifting and stacking, we produced high signal-to-noise maps, and radial and spectral profiles that reveal the distribution and kinematics of gas in 5 gas-bearing discs. For these discs, we constrained the inner radius of the $^{12}$CO, and found the radial brightness profile of CO peaked interior to the
dust ring, but that CO was more radially extended than the
dust. We present the first radially resolved $^{12}$CO/$^{13}$CO isotopologue flux ratios in gas-bearing debris discs, which are constant with radius for the majority of systems, indicating $^{12}$CO and $^{13}$CO are both optically thick or thin throughout the discs. We report CO line fluxes/upper limits for all systems and optical depth dependant masses for the 5 gas-bearing systems. Finally, we analysed the $^{12}$CO J=3-2 line luminosities for the ARKS debris discs and discs from the literature. We confirm that gas is mostly detected in young systems. However, the high scatter seen in young/high fractional luminosity systems indicates no trend within the systems with detected gas.
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All authors S. Mac Manamon, L. Matrà, S. Marino, A. Brennan, Y. Han, M. R. Jankovic, P. Weber, M. Bonduelle, J. M. Carpenter, G. Cataldi, A. M. Hughes, A. Kóspál, J. P. Marshall, B.C. Matthews, J. Milli, A. Moór, K. Öberg, S. Pérez, A. A. Sefilian, D. J. Wilner, M. C. Wyatt, E. Chiang, A. S. Hales, J. B. Lovell, P. Luppe, M. A. MacGregor, T. Pearce, M. Booth, C. del Burgo, A. Fehr, E. Mansell, B. Zawadzki
Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) VIII: A dust arc and non-Keplerian gas kinematics in HD 121617
S. Marino, V. Gupta, P. Weber et al. (+25 more)
ExoKuiper belts around young A-type
stars often host CO gas, whose origin is still unclear. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) includes 6 of these gas-bearing belts, to characterise their
dust and gas distributions and investigate the gas origin. As part of ARKS, we observed the gas-rich system HD121617 and discovered an arc of enhanced
dust density. In this paper, we analyse in detail the
dust and gas distributions and the gas kinematics of this system. We extracted radial and azimuthal profiles of the
dust (in the millimetre and near-infrared) and gas emission ($^{12}$CO and $^{13}$CO) from reconstructed images. To constrain the morphology of the arc, we fitted an asymmetric model to the
dust emission. To characterise the gas kinematics, we fitted a Keplerian model to the velocity map and extracted the azimuthal velocity profile by deprojecting the data. We find that the
dust arc is narrow (1-5 au wide at a radius of 75 au), azimuthally extended, and asymmetric; the emission is more azimuthally compact in the direction of the system's rotation, and represents 13% of the total
dust mass (0.2$M_\oplus$). The arc is much less pronounced or absent for small grains and gas. Finally, we find strong non-Keplerian azimuthal velocities at the inner and outer wings of the ring, as was expected due to strong pressure gradients. The
dust arc resembles the asymmetries found in protoplanetary discs, often interpreted as the result of
dust trapping in
vortices. If the gas disc mass is high enough ($\gtrsim20M_\oplus$, requiring a
primordial gas origin), both the radial confinement of the ring and the azimuthal arc may result from
dust grains responding to gas drag. Alternatively, it could result from
planet-disc interactions via mean motion resonances. Further studies should test these hypotheses and may provide a dynamical gas mass estimate in this CO-rich exoKuiper belt.
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All authors S. Marino, V. Gupta, P. Weber, T. D. Pearce, A. Brennan, S. Pérez, S. Mac Manamon, L. Matrà, J. Milli, M. Booth, C. del Burgo, G. Cataldi, E. Chiang, Y. Han, Th. Henning, A. M. Hughes, M. R. Jankovic, Á. Kóspál, J. B. Lovell, P. Luppe, E. Mansell, M. A. MacGregor, A. Moór, J. Olofsson, A. A. Sefilian, D. J. Wilner, M. C. Wyatt, B. Zawadzki
Astrophysics of Galaxies
Resonant Scattering of the He I 1.0833$\mu$m Triplet in H II Regions: Emission Spectra
B.T. Draine
Resonant scattering of He I 1.0833$\mu$m triplet
photons by metastable He 2 $^3$S$_1$ is studied for optical depths characteristic of H II regions. Regions with large He 2 $^3$S$_1$ column densities are predicted to have unusually broad, multi-peaked 1.0833$\mu$m emission profiles, with the centroid blue-shifted by up to $\sim$14 km/s relative to other lines. The feature FWHM can exceed 100 km/s for some regions. Resonant trapping enhances
dust absorption and reduces the He I 1.0833$\mu$m emission. Care must be taken when using the He I 1.0833$\mu$m/H I 1.0941$\mu$m (Pa$\gamma$) ratio to estimate the He$^+$/H$^+$ ratio. Predicted spectra are computed for examples, including M-17B and NGC3603 in the
Galaxy, and a
star-forming region in M51. Observations of the 1.0833$\mu$m triplet with spectrometers such as NIRSPEC, CARMENES, or X-Shooter can confirm the predicted effects of resonant scattering in H II regions, and constrain the nebular conditions.
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Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) IX: Gas-driven origin for the continuum arc in the debris disc of HD 121617
Philipp Weber, Sebastián Pérez, Clément Baruteau et al. (+24 more)
Debris discs were long considered to be largely gas-free environments governed by collisional fragmentation, gravitational stirring, and radiative forces. Recent CO detections show that gas is present, but its abundance and origin remain uncertain. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) revealed a narrow gas and
dust ring in the disc HD 121617 with an asymmetric arc 40% brighter than the rest of the ring. We aim to constrain the total gas mass in HD 121617 assuming the
dust arc is produced by hydrodynamical gas-
dust interactions. We used the Dusty FARGO-ADSG code, modelling
dust as Lagrangian particles, including radiation pressure and
dust feedback, and varying the total gas mass. Simulations were compared to observations using radiative transfer. An unstable gas ring creates a size-dependent radial and azimuthal
dust trap whose efficiency depends on gas mass. Two models, with 50 and 5 Earth masses of gas, reproduce both the ALMA band 7 arc and the outward offset of the VLT/SPHERE scattered-light ring via gas drag and radiation pressure. We infer a conservative gas-mass range of 2.5 to 250 Earth masses. If the ALMA asymmetry is caused by gas drag, the required gas mass compared with the observed CO implies substantial H2, consistent with
primordial gas. HD 121617 would then be a hybrid disc between protoplanetary and debris stages. Since a
planet could also create an arc, future observations are needed to distinguish these scenarios.
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All authors Philipp Weber, Sebastián Pérez, Clément Baruteau, Sebastian Marino, Fernando Castillo, Marija R. Jankovic, Tim Pearce, Mark C. Wyatt, Antranik A. Sefilian, Johan Olofsson, Gianni Cataldi, Joshua B. Lovell, Carlos del Burgo, A. Meredith Hughes, Sorcha Mac Manamon, Aoife Brennan, Luca Matrà, Julien Milli, Brianna Zawadzki, Eugene Chiang, Meredith MacGregor, David J. Wilner, Myriam Bonduelle, John Carpenter, Yinuo Han, Ágnes Kóspál, Patricia Luppe
Earth and Planetary Astrophysics
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) I: Motivation, sample, data reduction, and results overview
S. Marino, L. Matrà, A. M. Hughes et al. (+39 more)
The outer regions of planetary systems host dusty debris discs analogous to the Kuiper belt (exoKuiper belts), which provide crucial constraints on
planet formation and
evolution processes. ALMA
dust observations have revealed a great diversity, and that some belts contain CO gas, whose origin and implications are uncertain. Most of this progress, however, has been limited by low-resolution observations. We conducted the first ALMA large programme dedicated to debris discs: the ALMA survey to Resolve exoKuiper belt Substructures (ARKS). We selected the 24 most promising belts to constrain their detailed radial and vertical structure, and to characterise the gas content. We constrained the radial and vertical distribution of
dust, as well as the presence of asymmetries. For a subset of six belts with CO gas, we constrained the gas distribution and kinematics. To interpret these observations, we used a wide range of dynamical models. The first ARKS results are presented as a series of ten papers. We discovered that up to 33% of our sample exhibits multiple dusty rings. For highly inclined belts, we found that non-Gaussian vertical distributions are common and are indicative of multiple dynamical populations. We also found that 10 of the 24 belts present asymmetries. We find that the CO gas is radially broader than the
dust, but this could be an effect of optical depth. At least one system shows non-Keplerian kinematics due to strong pressure gradients, which may have triggered a
vortex that trapped
dust in an arc. Finally, we find evidence that the micron-sized grains may be affected by gas drag in gas rich systems. ARKS has revealed a great diversity of structures in exoKuiper belts that may arise when they are formed in protoplanetary discs or subsequently via interactions with
planets and/or gas. We encourage the community to explore the reduced data and data products.
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All authors S. Marino, L. Matrà, A. M. Hughes, J. Ehrhardt, G. M. Kennedy, C. del Burgo, A. Brennan, Y. Han, M. R. Jankovic, J. B. Lovell, S. Mac Manamon, J. Milli, P. Weber, B. Zawadzki, R. Bendahan-West, A. Fehr, E. Mansell, J. Olofsson, T. D. Pearce, A. Bayo, B. C. Matthews, T. Löhne, M. C. Wyatt, P. Ábrahám, M. Bonduelle, M. Booth, G. Cataldi, J. M. Carpenter, E. Chiang, S. Ertel, A. S. Hales, Th. Henning, Á. Kóspál, A. V. Krivov, P. Luppe, M. A. MacGregor, J. P. Marshall, A. Moór, S. Pérez, A. A. Sefilian, A. G. Sepulveda, D. J. Wilner
Solar and Stellar Astrophysics
Inferring hemispheric asymmetries of stellar active regions through the information content of astrometric signals
Conaire Deagan and Benjamin T. Montet
Photometric light curves suffer from fundamental degeneracies that limit surface information recovery. We demonstrate that astrometry enables access to complementary information through photocentre variations induced by rotating surface features. The forthcoming commissioning of microarcsecond-precision astrometric missions presents an opportunity to improve
stellar surface mapping. This paper extends a previous theoretical framework for
stellar surface mapping, along three primary directions: (1) we derive analytical selection rules showing that astrometry is sensitive to spherical harmonic modes not detectable via photometry, particularly odd-$\ell$ modes that encode north-south asymmetries; (2) we quantify the information content of combined photometric and astrometric observations, showing that the rank of observable modes grows faster for combined observations than for either technique alone, though the fraction of recoverable modes still decreases asymptotically with increasing spatial resolution; and (3) we reframe astrometric jitter-traditionally treated as noise in
exoplanet studies-as a signal encoding
stellar surface structure. Given the limited proposed target lists of high-precision astrometric missions, this capability is particularly valuable: understanding host
star surfaces is crucial for both removing
stellar signals from
exoplanet detections and characterising
star-
planet interactions. We show that while Sun-like
stars require sub-microarcsecond precision, evolved
stars with angular diameter and larger spots present immediate opportunities with current technology, such as the
Gaia mission.
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Astrophysics of Galaxies
Hedorah, the first yellow supergiant Kaiju star candidate at $z=3.7$ revealed by JWST behind AS1063
J.M. Diego, J.M. Palencia, C. Goolsby et al. (+8 more)
We present a new free-form lens model for the $z=0.348$
galaxy cluster AS1063, based on previously spectroscopically confirmed lensed
galaxies and new JWST images from the GLIMPSE program. We use the ultra-deep JWST data to identify new counterimages for previously confirmed (spectroscopically) lensed systems. We use the full set of spectroscopically confirmed systems to derive a new lens model, which is later used to confirm many of the previous lensed system candidates and discover new lensed system candidates in the JWST images. We compute the
geometric redshifts, time delays, and magnification for all counterimages (confirmed and not confirmed). Among the new systems, and based on photometry, we find a peculiar multiply lensed
galaxy with a strong emission line at $\approx 4\, \mu$m that likely corresponds to H$-\beta$ and/or OIII at $z\approx 7.5$. This
galaxy could be a little-red-dot or an extreme emission line
galaxy. We also identify a yellow supergiant lensed
star candidate at $z\approx 3.7$. This
star shows some similarities with previous Kaiju
stars and we nickname it "Hedorah", in honor of the famous yellow-eyed Kaiju. Previous lensed
stars at $z>0.1$ are either blue supergiants or red supergiants, making Hedorah the first yellow supergiant discovered beyond $z=0.1$ and confirming that, despite their rarity, they can also be found at these
redshifts. Since many Cepheid
stars are yellow supergiants, we consider the possibility that Hedorah could also be the first Cepheid discovered at cosmological distances, but we conclude that Hedorah is more likely a hypergiant yellow
star approaching the end of its life. Alternatively, Hedorah could be a small group of
stars, although this is less likely based on Hedorah's peculiar colors and additionally may require the more exotic fuzzy dark matter to help explain the lack of counterimage.
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All authors J.M. Diego, J.M. Palencia, C. Goolsby, C.J. Conselice, D. Perera, L.L.R. Williams, D.J. Lagattuta, G. Mahler, J. Richard, K. Sharon, M. Struble
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Probing super-heavy dark matter with ultra-high-energy gamma rays
Marco Chianese, Ninetta Saviano, Sara Cesare et al. (+4 more)
We refine the constraints on the lifetime of decaying super-heavy dark matter particles (SHDM), with masses ranging from $10^7$ to $10^{15}$ GeV, by analyzing ultra-high-energy (UHE) gamma-ray data. Our approach involves an accurate comparison of the primary gamma-ray emissions resulting from
prompt SHDM decays in the
galactic halo with the most recent upper limits on isotropic UHE gamma-ray fluxes provided by various extensive air shower experiments. We demonstrate that a precise consideration of the field of view and the
geometric acceptance of different UHE gamma-ray observatories has significant implications for the inferred limits of dark matter lifetime. In addition, we examine the influence of uncertainties linked to the current models of the
galactic dark matter distribution, employing diverse
halo density profiles while varying both their radial extent and the local dark matter density. Our findings indicate that the newly established UHE gamma-ray constraints are marginally less stringent than earlier evaluations, thereby revisiting the SHDM parameter space and allowing for observable
neutrino fluxes.
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All authors Marco Chianese, Ninetta Saviano, Sara Cesare, Vincenzo M. Grieco, Valentina Nasti, Francesca Spinnato, Alessandro Tiano
Instrumentation and Methods for Astrophysics
Exoplanet atmospheres and demographics in the 2040s
Jens Kammerer, Sydney Vach, Sylvestre Lacour et al. (+7 more)
Direct observations of
exoplanets probe the demographics and atmospheric composition of young self-luminous companions, yielding insight into their formation and early
evolution history. In the near future,
Gaia will reveal hundreds of nearby young
exoplanets amenable to direct follow-up observations. Long-baseline interferometry with current and future facilities is best capable of exploiting this unique synergy which is poised to deliver a statistical sample of
benchmark planets with precise dynamical masses and in-depth atmospheric characterization. This will enable tackling the longstanding question of how
giant planets form from multiple angles simultaneously, shining light on the complex physical processes underlying
planet formation.
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All authors Jens Kammerer, Sydney Vach, Sylvestre Lacour, Mathias Nowak, Thomas Winterhalder, Antoine Mérand, Akke Corporaal, Guillaume Bourdarot, Stefan Kraus, Sasha Hinkley
Earth and Planetary Astrophysics
Orbital Stability of Closely-Spaced Four-planet Systems
Bennet Outland, Gretchen Noble, Andrew W. Smith et al. (+1 more)
We investigate the orbital dynamics of four-
planet systems consisting of Earth-mass
planets on initially-circular, coplanar orbits around a
star of one
solar mass. In our simulations, the innermost
planet's semimajor axis is set at 1 AU, with subsequent semimajor axes spaced equally in terms of
planets' mutual Hill radii. Several sets of initial planetary longitudes are investigated, with integrations continuing for up to $10^{10}$ orbits of the innermost
planet, stopping if a pair of
planets pass within 0.01 AU of each other or if a
planet is ejected from the system. We find that the simulated lifetimes of four-
planet systems follow the general trend of increasing exponentially with planetary spacing, as seen by previous studies of closely-spaced
planets. Four-
planet system lifetimes are intermediate between those of three- and five-
planet systems and more similar to the latter. Moreover, as with five-
planet systems, but in marked contrast to the three-
planet case, no initial semimajor axes spacings are found to yield systems that survive several orders of magnitude longer than other similar spacings. First- and second-order mean-motion resonances (MMRs) between
planets correlate with reductions in system lifetimes. Additionally, we find that third-order MMRs between
planets on neighboring orbits also have a substantial, though smaller, destabilizing effect on systems very near resonance that otherwise would be very long-lived. Local extrema of system lifetimes as a function of planetary spacing occur at slightly smaller initial orbital separation for systems with
planets initially at conjunction relative to those in which the
planets begin on widely-separated longitudes. This shift is produced by the asymmetric mutual planetary perturbations as the
planets separate in longitude from the initial aligned configuration that cause orbits to spread out in semimajor axis.
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All authors Bennet Outland, Gretchen Noble, Andrew W. Smith, Jack J. Lissauer
High Energy Astrophysical Phenomena
X-ray Polarization of the Intrabinary Shock in Redback Pulsar J1723$-$2837
Andrew G. Sullivan, Jack T. Dinsmore and Roger W. Romani
The intrabinary shocks (IBS) in spider
pulsars emit non-thermal synchrotron X-rays from accelerated electrons and positrons in the shocked
pulsar wind, likely energized by
magnetic reconnection. The double-peaked X-ray light curves from these shocks have been well characterized in several spider systems. In this paper, we analyze Imaging X-ray Polarimetry Explorer (IXPE) observations of the redback
pulsar J1723$-$2837 to examine the expected synchrotron polarization. Using advanced extraction methods that include spatial, temporal, and particle background weights, we constrain the polarization of the IBS. We compare different models for the
magnetic field in the radiation zone and find that the best fit prefers a striped
pulsar wind model over other polarized models, with maximum polarization degree of the IBS emission component $\Pi_{\rm IBS}=36^{+16}_{-15}\%$, in addition to an unpolarized non-IBS component. Since this is only 2.4$\sigma$, we cannot claim strong preference over an unpolarized model; we report a $99\%$ confidence level upper limit on the total polarization of both IBS and non-IBS components $\Pi_{99}<36\%$, which is improved over the $50\%$ limit obtained in previous work. The best-fit polarization of the IBS component is consistent with numerical simulations. Detailed tests of such models are accessible to future measurements.
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Astrophysics of Galaxies
Spectroscopic confirmation of a large and luminous galaxy with weak emission lines at $\mathbf{z = 13.53}$
Callum T. Donnan, Derek J. McLeod, Ross J. McLure et al. (+15 more)
We present JWST/NIRSpec PRISM observations of a robust
galaxy candidate at $z\simeq14$, selected from pure-parallel NIRCam imaging; PAN-z14-1. The NIRSpec spectrum allows confirmation of this source at $z_{\rm spec}=13.53^{+0.05}_{-0.06}$ through modeling of the Lyman-$\alpha$ break. PAN-z14-1 is the fourth most distant
galaxy known to date and is extremely luminous ($M_{\rm UV}=-20.6\pm0.2$), with a blue UV-continuum slope ($\beta=-2.26\pm0.08$) and a large physical size ($r_{\rm c}=233\pm10\, \rm pc$). We fail to detect any rest-frame UV emission lines at $\geq 2\sigma$ significance, with upper limits sufficiently constraining to exclude the possibility of strong line emission. In terms of its physical properties, PAN-z14-1 is remarkably similar to the previously confirmed $z_{\rm spec}=14.18$
galaxy GS-z14-0. The lack of strong emission lines and large physical size is consistent with an emerging picture of two potentially distinct
galaxy populations at $z>10$, distinguished by
star-formation rate surface density. In this scenario, PAN-z14-1 is a second example of a “normal”, extended, luminous,
star-forming
galaxy at $z \simeq 14$, and differs markedly from the other class of extremely compact
galaxies with strong emission lines recently uncovered at extreme
redshifts with JWST. These results highlight the importance of further spectroscopic confirmation of $z>10$
galaxy candidates in order to fully understand the diversity of properties displayed by the first
galaxies.
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All authors Callum T. Donnan, Derek J. McLeod, Ross J. McLure, James S. Dunlop, Fergus Cullen, Mark Dickinson, Pablo Arrabal Haro, Anthony J. Taylor, Cecilia Bondestam, Feng-Yuan Liu, Karla Z. Arellano-Córdova, Laia Barrufet, Ryan Begley, Adam C. Carnall, Hanna Golawska, Ho-Hin Leung, Dirk Scholte, Thomas M. Stanton
High Energy Astrophysical Phenomena
Analytical approaches to the study of the phase of the visibility function
S.V. Chernov
In
radio interferometric observations, the main source of information is the complex visibility function, which includes amplitude and phase. In this paper, the dependence of the phase of the visibility function on the base projection is investigated when used in
radio interferometry with space bases up to six Earth diameters. The dependence of the phase of the visibility function on the projection of the base and direction is obtained. It is shown that for small values of the base projections, this dependence has a universal character and is consistent with the results of numerical magnetohydrodynamic models.
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Astrophysics of Galaxies
Galactic core-tail structure in BEC dark matter with Kapitza potential
Itauany do Nascimento Barroso and Hermano Velten
Recently, the experimental realization of a Kapitza potential in a Bose-Einstein Condensate (BEC) has been reported for the first time in literature, motivating further theoretical investigations of such system. At the same time, in the astrophysical context, BEC dark matter models have been widely studied as a possible phenomenological explanation for the dark matter phenomena. We model the
galactic structure with an inner cored profile obtained from the ground state
equilibrium solution of the Schroedinger-Poisson together with a Kapitza-BEC like interaction for the tail region. We find reasonable agreement of the model with representative
galaxy rotation curves available in the SPARC catalogue.
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Solar and Stellar Astrophysics
Fundamental Properties of Novae in M31
Allen W. Shafter and Kamil Hornoch
The peak luminosities and rates of decline for a large sample of novae recently published by Clark et al. have been analyzed using the Yaron et al. nova models to estimate fundamental properties of the M31 nova population. The apparent white
dwarf (WD) mass distribution is approximately Gaussian with a mean $\langle M_\mathrm{WD} \rangle = 1.16\pm0.14~M_{\odot}$. When corrected for recurrence-time bias, the mean drops to $\langle M_\mathrm{WD} \rangle = 1.07~M_\odot$. The average WD mass of the M31 nova sample is found to be remarkably similar to that found by Shara et al. in their study of 82
Galactic novae, but $\sim0.15~M_\odot$ more massive than the mean recently determined by Schaefer in his comprehensive study of more than 300 systems. As expected, the average WD mass for the recurrent novae included in the M31 sample, $\langle M_\mathrm{WD} \rangle = 1.33\pm0.08~M_{\odot}$, is significantly higher than that for novae generally. Other parameters of interest, such as the
accretion rate, velocity of the ejecta, and the predicted recurrence time, are characterized by skewed distributions with large spreads about means of $\langle \log \dot M ~(M_\odot~\mathrm{yr}^{-1}) \rangle \simeq -9.27$, $\langle V_\mathrm{max} \rangle \simeq 1690~\mathrm{km~s}^{-1}$, and $\langle \log P_\mathrm{rec}~\mathrm{(yr)} \rangle \simeq 4.39$, respectively. The role of hibernation in affecting the $\dot M$ and $P_\mathrm{rec}$ distributions is briefly discussed. Finally, the nova properties were studied as a function of apparent position (isophotal radius) in M31, with the preponderance of evidence failing to establish any clear dependence on
stellar population.
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Earth and Planetary Astrophysics
KMT-2025-BLG-1616Lb: First Microlensing Bound Planet From DREAMS
Hongjing Yang, Weicheng Zang, Yoon-Hyun Ryu et al. (+60 more)
We present observations and analysis of the bound planetary microlensing event KMT-2025-BLG-1616. The planetary signal was captured by the Korea Microlensing
Telescope Network (KMTNet) and the DECam Rogue Earths and Mars Survey (DREAMS). DREAMS's minute-cadence observations break the central/resonant degeneracy in the binary-lens models. The color of the faint source
star ($I=22$) is measured from the DREAMS's $r - z$ color. The planetary system has a
planet-host mass ratio of $q \sim 5 \times 10^{-4}$. A
Bayesian analysis yields a host-
star mass of $\sim 0.3\,M_\odot$, a planetary mass of $\sim 40\,M_{\oplus}$, a projected
planet-host separation of $\sim 1.6~\mathrm{au}$, and a lens distance of $\sim 7.5~\mathrm{kpc}$. Based on the photometric precision achieved by DREAMS for this event, we simulate free-floating
planet (FFP) detections and find that DREAMS is sensitive to Mars-mass FFPs in the
Galactic bulge and Moon-mass FFPs in the
Galactic disk.
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All authors Hongjing Yang, Weicheng Zang, Yoon-Hyun Ryu, Takahiro Sumi, Jiyuan Zhang, Hongyu Li, Cheongho Han, Yuchen Tang, Qiyue Qian, Zhixing Li, Yuxin Shang, Xikai Shan, Shude Mao, Guillermo Damke, Alfredo Zenteno, Steve Heathcote, Konstantina Boutsia, Przemek Mróz, Xiurui Zhao, Matthew Penny, Sean Terry, Patrick Tamburo, Timothy Cunningham, Quanzhi Ye, Eric W. Peng, Rachel Street, Katarzyna Kruszyńska, Etienne Bachelet, Yiannis Tsapras, Markus Hundertmark, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Kyu-Ha Hwang, Youn Kil Jung, In-Gu Shin, Yossi Shvartzvald, Jennifer C. Yee, Dong-Jin Kim, Chung-Uk Lee, Byeong-Gon Park, David P. Bennett, Ian A. Bond, Giuseppe Cataldo, Ryusei Hamada, Yuki Hirao, Asahi Idei, Shuma Makida, Shota Miyazaki, Tutumi Nagai, Togo Nagano, Seiya Nakayama, Mayu Nishio, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Yui Okumoto, Nicholas J. Rattenbury, Yuki K. Satoh, Daisuke Suzuki, Motohide Tamura, Takuto Tamaoki, Hibiki Yama
Astrophysics of Galaxies
Pseudo Little Red Dot: an Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z=5.96
Karina I. Caputi, Ryan A. Cooper, Pierluigi Rinaldi et al. (+3 more)
We present a study of Pseudo-LRD-NOM (Pseudo little red dot with no metal lines), a highly magnified low-mass
galaxy behind the
lensing cluster Abell 370 at z=5.96. We classify this object as a pseudo-LRD because its red rest-frame optical colour is contaminated by a prominent Halpha line (with EW0 >~ 800 Angstroms) present in its JWST NIRSpec spectrum. Halpha is dominated by a narrow component and also has a minor broad component indicative of an active black hole with M_BH = 5.6x10^6 Msun. A narrow Hbeta emission line is also detected (with S/N = 8), producing a Balmer decrement (narrow) Halpha/Hbeta = 11. The rest-frame UV spectral slope is beta_UVspec = -1.20 +/-0.28. All these features can be ascribed to high
dust attenuation. However, no [OIII]5007 or any other metal lines are detected in the spectrum, so [OIII]5007/Hbeta < 0.25, at odds with a simple
dust-attenuation explanation. Accounting for all the spectral properties requires the model of a starburst with moderate colour excess E(B-V)=0.2-0.5, high gas density (n_H >~ 10^6 cm^{-3}) and low to extremely low gas/
stellar metallicities (Z = 0.01-0.1 Zsun). The demagnified
stellar mass is 2.25^{+1.30}_{-0.83} x10^7 Msun and the
stellar-mass surface density is Sigma* = 418^{+725}_{-310} Msun/pc^2, similar to that of massive/
nuclear star clusters. Pseudo-LRD-NOM provides evidence of massive black-hole growth occurring in a high-density, dusty starburst which is at the early stages of its chemical enrichment, and is likely a precursor to a real LRD.
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All authors Karina I. Caputi, Ryan A. Cooper, Pierluigi Rinaldi, Rafael Navarro-Carrera, Edoardo Iani, Abigail A. Tumborang
Instrumentation and Methods for Astrophysics
Five Years of Mini-EUSO Observations from the ISS: Summary of Key Results
Matteo Battisti
Mini-EUSO is the first space-borne detector of the JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) program, operating on the International Space Station (ISS) since October 2019. Designed to search for Ultra-High Energy
Cosmic Rays (UHECRs) above 10$^{21}~$eV and capable of placing a stringent upper limit on their flux at these extreme energies, paving the way to future space-based UHECR observatories, Mini-EUSO has completed more than 150 observation sessions over five years, accumulating approximately 750 hours of data. The mission has produced the first global UV emission maps of Earth and provided valuable insights into lightning phenomena and Transient Luminous Events (TLEs), such as elves, as well as artificial light sources and meteors. Notably, Mini-EUSO has conducted the first systematic space-based meteor survey, detecting over 22,000 meteors and identifying three interstellar candidates. Among the observed TLEs, the most interesting class of phenomena are elves, which appear as expanding ring-shaped structures occurring at $\sim$90 km altitude. Mini-EUSO has detected elves with varying structures and different numbers of concentric rings, from single-ring up to five rings. Thanks to its imaging capabilities, fast time resolution, and favorable observational geometry, Mini-EUSO is uniquely suited to studying this kind of lightning phenomena, providing unprecedented insight into their dynamics. Additionally, the instrument has demonstrated the capability of a space-based detector to identify short light transients resembling extensive air shower signals while distinguishing them from those produced by UHECRs. This contribution presents a comprehensive summary of the Mini-EUSO mission, its status, and main results.
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Astrophysics of Galaxies
Impact of baryons on the population of Galactic subhalos and implications for dark matter searches
Sara Porras-Bedmar, Miguel Á. Sánchez-Conde and Alejandra Aguirre-Santaella
We have used Auriga –a set of state-of-the-art cosmological hydrodynamical simulations of Milky Way-size systems– to study the impact of
baryons on the
Galactic subhalo population. A DM-only run counterpart of Auriga allows us to compare results with and without
baryons. We repopulate the original suites with low-mass subhalos orders of magnitude lighter than the mass resolution limit, starting from a detailed characterization of Auriga data in the well-resolved subhalo mass range. The survival of low-mass subhalos to
tidal forces is unclear and under debate nowadays, thus in our study we stay agnostic and consider two different levels of subhalo resilience to
tidal stripping ('fragile' and 'resilient' subhalos). We find
baryons to alter the
Galactic substructure significantly, by decreasing its overall abundance by a factor $\sim2.4$ (fragile) and $\sim1.9$ (resilient) and subhalo concentration –here defined in terms of maximum circular velocity– by $\sim1.5$ with respect to the DM-only scenario. This has important consequences for indirect searches of DM. As an example, we investigated the case of using unidentified gamma-ray sources to set constraints on the DM particle properties, assuming some of them may be dark satellites. Our results show the importance of including
baryons to properly characterize the
Galactic subhalo population, as well as to propose the most optimal subhalo search strategies, not only via its potential DM annihilation products but also through their gravitational signatures (e.g.~
stellar streams, strong
lensing).
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Astrophysics of Galaxies
FEAST: Probing Hierarchical Star Formation with the Spatial Distributions of Young Star Clusters
Drew Lapeer, Daniela Calzetti, Kathryn Grasha et al. (+19 more)
We apply the angular two-point correlation function (TPCF) to the spatial distribution of young
star clusters (YSCs) in four nearby
star forming
galaxies (NGC 628, NGC 4449, M51, and M83) in order to investigate their underlying hierarchical structuring. Using newly constructed catalogs of YSCs in the emerging phase (eYSCs), identified in the infrared with JWST, and optical YSCs detected in archival HST data, we compute TPCFs for various cluster samples and age bins across the four
galaxies as part of the FEAST (Feedback in Emerging extrAgalactic
Star ClusTers) program. We find clear evidence of hierarchical structuring, especially in eYSCs and YSCs with ages < 10 Myr (referred to as oYSCs), which show similar TPCFs within each
galaxy. NGC 628 exhibits a clear distinction between the TPCFs of eYSCs and oYSCs, implying a shorter randomization timescale. In contrast, clusters aged 10 to 300 Myr exhibit progressively more random spatial distributions, becoming effectively random after $\sim$ 100 Myr, consistent with earlier studies. The two-dimensional fractal index $D_2$ of the YSCs underlying distribution is calculated from model fits to TPCFs. Our values of $D_2$ derived from the youngest YSC populations align better with the expected value of $D_2 \sim $1.3 for a universal
star formation process compared to previous findings.
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All authors Drew Lapeer, Daniela Calzetti, Kathryn Grasha, Angela Adamo, Bruce G. Elmegreen, Arjan Bik, Giacomo Bortolini, Anne Buckner, Michele Cignoni, Matteo Correntim, Debra Meloy Elmegreen, H. Faustino Vieira, Max Hamilton, Kelsey Johnson, Thomas S.-Y Lai, Sean T. Linden, Subhransu Maji, Matteo Messa, Göran Östlin, Alex Pedrini, E. Sabbi, Linda J. Smith
Instrumentation and Methods for Astrophysics
Auditing Frozen-Encoder Anomaly Detection Across Mechanical Systems: Representation Provenance, Calibration, and Protocol Effects
Jose Sánchez Andreu
This version reports a reproducibility audit of the frozen-encoder experiments presented in version 1. The numerical discrimination results are reproducible from the preserved artifacts, but their original attribution to interferometric pretraining is not supported. The released checkpoint contains a nested model state that loads without missing parameters, whereas loading the outer checkpoint dictionary leaves almost the entire EfficientNet-B0 feature stack uninitialized. Preserved
embeddings labelled as interferometric have norms of order $10^{-12}$, matching freshly initialized EfficientNet-B0 networks and differing by more than twelve orders of magnitude from the preserved ImageNet
embeddings. A second, separately preserved near-zero
embedding set produces almost the same IMS 4th-test anomaly scores ($r=0.987$) and record-level discrimination (AUC $0.9812$ versus $0.9818$). We therefore withdraw the causal claim that IMS performance demonstrates a morphological prior transferred from gravitational-wave instrumentation. We reanalyse the controlled IMS splits at matched observed false-positive rates and add multivariate classical signal baselines. The near-zero representations retain strong tail separation, particularly in the 2nd and 4th IMS runs, but this is now interpreted as an exploratory architecture-and-initialization effect coupled to Mahalanobis scoring. A separate PRONOSTIA audit shows that the original large warning times were induced by a lifetime-fraction baseline; under fixed-time evaluation, a ten-feature classical baseline outperforms the preserved encoder scores. These results illustrate how checkpoint provenance, finite-sample calibration, architecture, and target-domain baselines can create an appearance of cross-domain transfer. They also define the controls required before assigning physical meaning to frozen-representation anomaly scores.
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