Papers for Wednesday, Feb 16 2022

We report on X-ray flares that were observed from the active galactic nucleus I Zwicky 1 (I Zw 1) in 2020 January by the NuSTAR and XMM-Newton observatories. The X-ray spectrum is well-described by a model comprised of the continuum emission from the corona and its reflection from the accretion disc around a rapidly spinning (a > 0.94) black hole. In order to model the broadband spectrum, it is necessary to account for the variation in ionisation across the disc. Analysis of the X-ray spectrum in time periods before, during and after the flares reveal the underlying changes to the corona associated with the flaring. During the flares, the reflection fraction drops significantly, consistent with the acceleration of the corona away from the accretion disc. We find the first evidence that during the X-ray flares, the temperature drops from 140(-20,+100)keV before to 45(-9,+40)keV during the flares. The profile of the iron K line reveals the emissivity profile of the accretion disc, showing it to be illuminated by a compact corona extending no more than 7(-2,+4)rg over the disc before the flares, but with tentative evidence that the corona expands as it is accelerated during the flares. Once the flares subsided, the corona had collapsed to a radius of 6(-2,+2)rg. The rapid timescale of the flares suggests that they arise within the black-hole magnetosphere rather than in the accretion disc, and the variation of the corona is consistent with the continuum arising from the Comptonisation of seed photons from the disc.

The formation and evolution of stellar clusters is intimately linked to that of their host galaxies. To study this connection, we present the EMP-Pathfinder suite of cosmological zoom-in Milky Way-mass simulations. These simulations contain a sub-grid description for stellar cluster formation and evolution, allowing us to study the simultaneous formation and evolution of stellar clusters alongside their host galaxies across cosmic time. As a key ingredient in these simulations, we include the physics of the multi-phase nature of the interstellar medium (ISM), which enables studies of how the presence of a cold, dense ISM affects cluster formation and evolution. We consider two different star formation prescriptions: a constant star formation efficiency per free-fall time, as well as an environmentally-dependent, turbulence-based prescription. We identify two key results drawn from these simulations. Firstly, we find that tidal shock-driven disruption caused by the graininess of the cold ISM produces old ($\tau>10~$Gyr) stellar cluster populations with properties that are in excellent agreement with the observed populations in the Milky Way and M31. Importantly, the addition of the cold ISM addresses the areas of disagreement found in previous simulations that lacked the cold gas phase. Secondly, the formation of stellar clusters is extremely sensitive to the baryonic physics that govern the properties of the cold, dense gas reservoir in the galaxy. This implies that the demographics of stellar cluster populations represent an important diagnostic tool for constraining baryonic physics models in upcoming galaxy formation simulations that also include a description of the cold ISM.

Young stars are highly variable in the X-ray regime. In particular, bright X-ray flares can substantially enhance ionization in the surrounding protoplanetary disk. Since disk chemical evolution is impacted by ionization, X-ray flares have the potential to fundamentally alter the chemistry of planet forming regions. We present 2D disk chemical models that incorporate a stochastic X-ray flaring module, named \xgen, and examine the flares' overall chemical impact compared to models that assume a constant X-ray flux. We examine the impact of 500 years of flaring events and find global chemical changes on both short time scales (days) in response to discrete flaring events and long time-scales (centuries) in response to the cumulative impact of many flares. Individual X-ray flares most strongly affect small gas-phase cations, where a single flare can temporarily enhance the abundance of species such as H$_3^+$, HCO$^+$, CH$_3^+$, and C$^+$. We find that flares can also drive chemistry out of "steady state" over longer time periods, where the disk-integrated abundance of some species, such as O and O$_2$, changes by a few percent over the 500 year model. We also explore whether the specific history of X-ray flaring events (randomly drawn but from the same energy distribution) impacts the chemical evolution and find that it does not. Finally, we examine the impact of X-ray flares on the electron fraction. While most molecules modeled are not highly sensitive to flares, certain species, including observable molecules, are very reactive to the dynamic environment of a young star.

We examine the capacity to identify binary systems from astrometric deviations alone. We apply our analysis to the \textit{Gaia} eDR3 and DR2 data, specifically the \textit{Gaia Catalogue of Nearby Stars}. We show we must renormalize (R)UWE over the local volume to avoid biasing local observations, giving a Local Unit Weight Error (LUWE). We use the simple criterion of LUWE>2, along with a handful of quality cuts to remove likely contaminants, to identify unresolved binary candidates. We identify 22,699 binary candidates within 100 pc of the Sun (just under 10\% of sources in this volume). We find an astrometric binary candidate fraction of around 20\% for giant stars, 10\% on the Main Sequence and lower than 1\% for White Dwarfs. We also look for Variability Induced Movers, by computing the correlation between photometric variability and astrometric noise -- and show that VIMs may dominate the binary population of sub-Solar mass MS stars. We discuss the possibility and limitations of identifying non-luminous massive companions from astrometry alone, but find that our method is insensitive to these. Finally, we compare the astrometric deviations of MS binaries to the simulated sample from paper I, which show excellent agreement, and compute the astrometric candidate binary fraction as a function of absolute magnitude.

We report the discovery and analysis of a massive, compact, hierarchical triple system (TIC 470710327) initially identified by citizen scientists in data obtained by NASA's Transiting Exoplanet Survey Satellite (TESS). Spectroscopic follow-up observations obtained with the HERMES spectrograph, combined with eclipse timing variations (ETVs), confirm that the system is comprised of three OB stars, with a compact 1.10 d eclipsing binary and a non-eclipsing tertiary on a 52.04 d orbit. Dynamical modelling of the system (from radial velocity and ETVs) reveal a rare configuration wherein the tertiary star (O9.5-B0.5V; 14-17 M$_{\odot}$) is more massive than the combined mass of the inner binary (10.9-13.2 M$_{\odot}$). Given the high mass of the tertiary, we predict that this system will undergo multiple phases of mass transfer in the future, and likely end up as a double neutron star gravitational wave progenitor or an exotic Thorne-Zytkow object. Further observational characterisation of this system promises constraints on both formation scenarios of massive stars as well as their exotic evolutionary end-products.

A fundamental prediction of the LambdaCDM cosmology is the hierarchical build-up of structure and therefore the successive merging of galaxies into more massive ones. As one can only observe galaxies at one specific time in cosmic history, this merger history remains in principle unobservable. By using the TNG100 simulation of the IllustrisTNG project, we show that it is possible to infer the unobservable stellar assembly and merger history of central galaxies from their observable properties by using machine learning techniques. In particular, in this first paper of ERGO-ML (Extracting Reality from Galaxy Observables with Machine Learning), we choose a set of 7 observable integral properties of galaxies (i.e. total stellar mass, redshift, color, stellar size, morphology, metallicity, and age) to infer, from those, the stellar ex-situ fraction, the average merger lookback times and mass ratios, and the lookback time and stellar mass of the last major merger. To do so, we use and compare a Multilayer Perceptron Neural Network and a conditional Invertible Neural Network (cINN): thanks to the latter we are also able to infer the posterior distribution for these parameters and hence estimate the uncertainties in the predictions. We find that the stellar ex-situ fraction and the time of the last major merger are well determined by the selected set of observables, that the mass-weighted merger mass ratio is unconstrained, and that, beyond stellar mass, stellar morphology and stellar age are the most informative properties. Finally, we show that the cINN recovers the remaining unexplained scatter and secondary cross-correlations. Our tools can be applied to large galaxy surveys in order to infer unobservable properties of galaxies' past, enabling empirical studies of galaxy evolution enriched by cosmological simulations.

Crustal plateaus are Venusian highlands characterized by tectonized terrains. It is commonly interpreted that their topography is isostatically supported and that they represent fossils of an extinct tectonic regime. Using gravity and topography we perform a comprehensive investigation of the lithospheric structure of six crustal plateaus. We computed the admittance (gravity to topography wavelength-dependent ratio) for each region and compared them to modeled admittances. Three compensation scenarios were tested: Airy isostasy, a surface-loading flexural model, and a flexural model with surface and subsurface loads. Our results show that the topography of most plateaus is supported by crustal thickening and that the addition of a mantle support component is not necessary at the investigated wavelengths. The elastic thickness was constrained to be less than 35 km with a best-fitting average of 15 km, confirming that these regions are consistent with an isostatic regime. The average crustal thickness of the plateaus ranges from 15 to 34 km, and if they are in Airy isostasy, this implies that the global average crustal thickness of Venus is about 20 km. Phoebe Regio is the sole exception of our analysis in that crustal thicknesses that are compatible with the other plateaus are obtained only when a buoyant layer is included. Heat flow estimations computed from the elastic thickness indicate that the plateaus formed under higher heat flow conditions compared to the current global average and could have caused localized melting. Present-day heat flow predictions suggest that eclogitization could occur where the crust is thickest.

Using the Gaia colour-magnitude diagram, we assign masses to a catalogue of 979 confirmed members of the Hyades cluster and tails. By fitting the cumulative mass profile, stars within the tidal radius have a Plummer-like profile with half-mass radius $r_{\rm h}$ of 5.75 pc. The tails are extended with $r_{\rm h} = 69.35$ pc and fall off more slowly than Plummer with density proportional to distance$^{-1.36}$. The cluster stars are separated into two groups at BP-RP $=2$ or $0.56 M_\odot$ to give a high mass (${\bar M} = 0.95 M_\odot$) and a low mass (${\bar M} = 0.32 M_\odot$) population. We show that: (i) the high mass population has a half-mass radius $r_{\rm h}$ of 4.88 pc, whilst the low mass population has $r_{\rm h} = 8.10$ pc; (ii) despite the differences in spatial extent, the kinematics and binarity properties of the high and low mass populations are similar. They have isotropic velocity ellipsoids with mean 1d velocity dispersions $\sigma$ of 0.427 and 0.415 km s$^{-1}$ respectively. The dynamical state of the Hyades is far from energy equipartition ($\sigma \propto {\bar M}^{-1/2}$). We identify a new mass segregation instability for clusters with escape speed $V$. Populations with $V/\sigma \lesssim 2\sqrt{2}$ can never attain thermal equilibrium and equipartition. This regime encompasses many Galactic open and globular clusters. For the Hyades, there must be an outward energy flux of at least $9.5 \times 10^{-4} M_\odot\,{\rm km^2\, s^{-2} Myr^{-1}}$ to maintain its current configuration. The present mass loss of $0.26 M_\odot {\rm Myr}^{-1}$ due to tidal stripping by itself implies a substantial energy flow beyond the required magnitude.

We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of eleven galaxies with existing ground-based Balmer H$\alpha$ and H$\beta$ measurements from slit spectra, plus space-based grism constraints on Paschen-$\beta$. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best-fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-$\beta$/H$\alpha$ ratios driving these results. We find that galaxies with high Paschen-$\beta$/H$\alpha$ ratios may be explained by slightly sub-unity covering fractions ($>$97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at $z\approx0.3-2$, enabling uniform constraints on the optical-infrared dust attenuation law and its intrinsic variation.

Globular clusters are both primary fossils of galactic evolution and formation and are ideal laboratories for constraining the evolution of low-mass and metal-poor stars. RR Lyrae and type II Cepheid variables are low-mass, radially pulsating stars that trace old-age stellar populations. These stellar standard candles in globular clusters are crucial for measuring their precise distances and, in turn, absolute ages, and for the calibration of the extragalactic distance scale. Herein, the evolutionary stages of RR Lyrae and type II Cepheids are discussed, and their pulsation properties, including the light curves, color-magnitude and period-amplitude diagrams, and period-luminosity relations in globular clusters at optical and infrared wavelengths are presented. The RR Lyrae visual magnitude-metallicity relation and the multiband period-luminosity-metallicity relations in globular clusters covering a wide metallicity range are also discussed in detail for their application to the RR Lyrae-based distance~scale.

NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources (PULXs), and so is thought to contain a neutron star that accretes at highly super-Eddington rates. However, the physics of this accretion remains to be determined. Here we report the results of two simultaneous XMM-Newton and HST observations of this PULX taken to observe two distinct X-ray behaviours as defined from its Swift light curve. We find that the X-ray spectrum of the PULX is best described by the hard ultraluminous (HUL) regime during the observation taken in the lower flux, lower variability amplitude behaviour; its spectrum changes to a broadened disc during the higher flux, higher variability amplitude epoch. However, we see no accompanying changes in the optical/UV fluxes, with the only difference being a reduction in flux in the near-IR as the X-ray flux increased. We attempt to fit irradiation models to explain the UV/optical/IR fluxes but they fail to provide meaningful constraints. Instead, a physical model for the system leads us to conclude that the optical light is dominated by a companion O/B star, albeit with an IR excess that may be indicative of a jet. We discuss how these results may be consistent with the precession of the inner regions of the accretion disc leading to changes in the observed X-ray properties, but not the optical, and whether we should expect to observe reprocessed emission from ULXs.

October 1957, and the successful launch of Sputnik 1 into Earth orbit, marked the dawn of the Space Age. The first of the 'fellow travellers' - humanity's first artificial satellite - orbited for a mere three months before re-entering the Earth's atmosphere, though its mission paved the way for an era of exploration that has endured to the present day. For many, a world without satellites would be a difficult one to imagine. As a society, we have become reliant on them for a vast array of services and applications. With a divine view of large swathes of the Earth's surface, and the ability to relay signals around its curvature, satellites have enabled the fast transfer of data on a global scale, bypassing the challenges associated with ground-based broadcasting, long-distance wiring, and so on. Positioning, Navigation and Timing (PNT) satellites have revolutionised transportation by land, air, and sea, while weather satellites enable scientists to monitor and warn of large-scale phenomena as they develop in near real-time. Satellites have extended the frontiers of observation: looking outwards, astronomers are able to circumvent the Earth's atmosphere to look deeper into the cosmos than ever before; looking inwards, patterns and processes that feed into general circulation models can be monitored on a range of timescales, improving our understanding of climate change. Satellites, and the services they provide, are not going to disappear any time soon. That said, threats to satellite safety do exist, and it is important that they be addressed as soon as possible to avoid long-lasting damage to operations in the space domain. Nearly sixty-five years on from the advent of human activity in space, I chart the evolution of the orbital debris environment and review latest efforts to make space operations more sustainable.

We examine Chandra observations of the powerful Fanaroff-Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central Active Galactic Nucleus (AGN) at a separation of 0.42 arcseconds. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5-7.0 keV flux upper limit of $1.04 \times 10^{-12}\rm\,erg\,cm^{-2}\,s^{-1}$, or a rest-frame 2-10 keV luminosity of $8.6\times 10^{42}\rm\,erg\,s^{-1}$. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival ACIS data from 2016-2017, and both the overall morphology and the flux limits of the AGN complex agree between the two datasets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the datasets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyze its AGN at an unprecedented level of precision.

We present a comprehensive census of X-ray millisecond pulsars (MSPs) in 29 Galactic globular clusters (GCs), including 68 MSPs with confirmed X-ray luminosities and 107 MSPs with X-ray upper limits. We compile previous X-ray studies of GC MSPs, and add new analyses of six MSPs (PSRs J1326$-$4728A, J1326$-$4728B, J1518$+$0204C, J1717$+$4308A, J1737$-$0314A, and J1807$-$2459A) discovered in five GCs. Their X-ray spectra are well described by a single blackbody model, a single power-law model, or a combination of them, with X-ray luminosities ranging from 1.9$\times$10$^{30}$ erg s$^{-1}$ to 8.3$\times$10$^{31}$ erg s$^{-1}$. We find that most detected X-ray MSPs have luminosities between $\sim 10^{30}$ erg s$^{-1}$ to $3 \times 10^{31}$ erg s$^{-1}$. Redback pulsars are a relatively bright MSP population with X-ray luminosities of $\sim2\times10^{31}$--$3\times10^{32}$ erg s$^{-1}$. Black widows show a bi-modal distribution in X-ray luminosities, with eclipsing black widows between $\sim 7\times10^{30}$ and $2\times10^{31}$ erg s$^{-1}$, while the two confirmed non-eclipsing black widows are much fainter, with $L_X$ of $1.5-3\times10^{30}$ erg s$^{-1}$, suggesting an intrinsic difference in the populations. We estimate the total number of MSPs in 36 GCs by considering the correlation between the number of MSPs and stellar encounter rate in GCs, and suggest that between 600--1500 MSPs exist in these 36 GCs. Finally, we estimate the number of X-ray detectable MSPs in the Galactic bulge, finding that 1--86 MSPs with $L_X > 10^{33}$ erg s$^{-1}$, and 20--900 MSPs with $L_X > 10^{32}$ erg s$^{-1}$, should be detectable there.

We review the latest developments in our X-ray observational and theoretical understanding of the outskirts of galaxy clusters, and their connection to the cosmic web. The faint cluster outskirts are challenging regions to observe in X-rays, requiring highly sensitive telescopes with low and stable background levels. We present our latest understanding of the thermodynamic profiles of clusters in the outskirts, and the biases that gas clumping and non-thermal pressure support can introduce. Features in the outskirts due to merging activity are discussed, along with the chemical enrichment of the outskirts ICM. We describe future prospects for X-ray observations to explore further out in the cluster outskirts and probe their connections to the cosmic web.

Cosmic rays are nowadays a crucial tool to study the astrophysics of extreme objects in the Universe, the cosmic environmental plasma (both Galactic and extra-galactic), the physics of nuclear interactions or the properties of elementary particles at very high energies and even cosmological problems such as the dark matter puzzle. In this thesis, the phenomenology on the transport of Galactic cosmic rays is studied in light of the most recent experimental data in the field and new analyses are presented in order to obtain better constraints. Throughout the thesis, secondary particles produced from collisions of cosmic rays with the interstellar gas, such as secondary cosmic ray nuclei (B, Be and Li), antiprotons and gamma rays, are treated in order to adjust and test our models and probe different scenarios, such as possible signatures of dark matter decay or annihilation. A preliminary version of the upcoming DRAGON2 code has been used to perform the propagation computations. With the increasing accuracy of CR data a number of anomalies have appear with respect to the standard paradigm of propagation of charged particles in the Galaxy. In this thesis, we demonstrate that some of these anomalies disappear by taking into account the systematic uncertainties involving these kind of analyses, specially cross sections uncertainties.

We use ALMA measurements of 870 $\mu$m thermal emission from a sample of mid-sized (15-40 km diameter) Jupiter Trojan asteroids to search for high albedo objects in this population. We calculate the diameters and albedos of each object using a thermal model which also incorporates {contemporaneous} Zwicky Transient Facility photometry to accurately measure the absolute magnitude at the time of the ALMA observation. We find that while many albedos are lower than reported from WISE, several small Trojans have high albedos independently measured both from ALMA and from WISE. The number of these high albedo objects is approximately consistent with expectations of the number of objects that recently have undergone large-scale impacts, suggesting that the interiors of freshly-crated Jupiter Trojans could contain high albedo materials such as ices.

Wind-fed high-mass X-ray binaries are powered by accretion of the radiatively driven wind on the compact star. Accretion-generated X-rays alter the ionization state of the wind. Because higher ionization states drive the wind less effectively, X-ray ionization may brake acceleration of the wind. This causes a decrease in the wind terminal velocity and mass flux in the direction toward the X-ray source. We study the effect of X-ray ionization on the stellar wind of B supergiants. We determine the binary parameters for which the X-ray irradiation significantly influences the stellar wind. This can be studied in diagrams that plot the optical depth parameter versus the X-ray luminosity. For low optical depths or for high X-ray luminosities, X-ray ionization leads to a disruption in the wind aimed toward the X-ray source. Observational parameters of high-mass X-ray binaries with B-supergiant components appear outside the wind disruption zone. The X-ray feedback determines the resulting X-ray luminosity. For low X-ray luminosities, ionization is weak, and the wind is not disrupted by X-rays and flows at large velocities, consequently the accretion rate is relatively low. On the other hand, for high X-ray luminosities, the X-ray ionization disrupts the flow braking the acceleration, the wind velocity is low, and the accretion rate becomes high. These effects determine the X-ray luminosity of individual binaries. Accounting for the X-ray feedback, estimated X-ray luminosities reasonably agree with observational values. We study the effect of small-scale wind inhomogeneities, showing that they weaken the effect of X-ray ionization by increasing recombination and the mass-loss. This effect is particularly important in the region of the bistability jump. We show that ultraluminous X-ray binaries with $L_x<10^{40}$ erg/s may be powered by accretion of a B-supergiant wind on a massive black hole.

In the pursuit of the measurement of the still-elusive ultrahigh-energy (UHE) neutrino flux at energies of order EeV, detectors using the in-ice Askaryan radio technique have increasingly targeted lower trigger thresholds. This has led to improved trigger-level sensitivity to UHE neutrinos. Working with data collected by the Askaryan Radio Array (ARA), we search for neutrino candidates at the lowest threshold achieved to date, leading to improved analysis-level sensitivities. A neutrino search on a data set with 208.7~days of livetime from the reduced-threshold fifth ARA station is performed, achieving a 68\% analysis efficiency over all energies on a simulated mixed-composition neutrino flux with an expected background of $0.10_{-0.04}^{+0.06}$ events passing the analysis. We observe one event passing our analysis and proceed to set a neutrino flux limit using a Feldman-Cousins construction. We show that the improved trigger-level sensitivity can be carried through an analysis, motivating the Phased Array triggering technique for use in future radio-detection experiments. We also include a projection using all available data from this detector. Finally, we find that future analyses will benefit from studies of events near the surface to fully understand the background expected for a large-scale detector.

The detection of Earth-size exoplanets is a technological and data analysis challenge. Future progress in Earth-mass exoplanet detection is expected from the development of extreme precision radial velocity measurements. Increasing radial velocity precision requires developing a new physics-based data analysis methodology to discriminate planetary signals from host-star-related effects, taking stellar variability and instrumental uncertainties into account. In this work, we investigate and quantify stellar disturbances of the planet-hosting solar-type star HD121504 from 3D radiative modeling obtained with the StellarBox code. The model has been used for determining statistical properties of the turbulent plasma and obtaining synthetic spectroscopic observations for several Fe I lines at different locations on the stellar disk to mimic high-resolution spectroscopic observations.

As building blocks of dust, rocky planets, and even complex life, the chemical elements heavier than hydrogen (H) and helium (He) - called "metals" in astronomy - play an essential role in our Universe and its evolution. Up to Fe and Ni, these metals are known to be created by stars and stellar remnants via nuclear fusion and to be ejected into their immediate surroundings to enrich new stellar generations. A spectacular finding, however, is that these processed elements are found even outside stellar systems, in particular in the hot, X-ray atmospheres surrounding early-type galaxies and pervading galaxy clusters and groups. These large-scales structures are thus a remarkable fossil record of the integrated history of the enrichment of our Universe. In this Chapter, we briefly discuss the chemical properties of this intracluster - or intragroup - medium (ICM). After introducing the concept of chemical abundances, and recalling which stellar sources produce which elements, we review the method to derive abundance measurements from observations of the ICM and detail some chemical models implemented in numerical hydrodynamical simulations of cosmic structures. In particular, we explore how synergies between X-ray observations and numerical simulations help us to understand (i) the cosmic epoch at which the bulk of the enrichment occurred, (ii) the physics of these stellar sources responsible for this enrichment, and (iii) the main mechanisms responsible for metal diffusion and mixing outside galaxies.

We present results exploring the role that probabilistic deep learning models can play in cosmology from large scale astronomical surveys through estimating the distances to galaxies (redshifts) from photometry. Due to the massive scale of data coming from these new and upcoming sky surveys, machine learning techniques using galaxy photometry are increasingly adopted to predict galactic redshifts which are important for inferring cosmological parameters such as the nature of dark energy. Associated uncertainty estimates are also critical measurements, however, common machine learning methods typically provide only point estimates and lack uncertainty information as outputs. We turn to Bayesian neural networks (BNNs) as a promising way to provide accurate predictions of redshift values. We have compiled a new galaxy training dataset from the Hyper Suprime-Cam Survey, designed to mimic large surveys, but over a smaller portion of the sky. We evaluate the performance and accuracy of photometric redshift (photo-z) predictions from photometry using machine learning, astronomical and probabilistic metrics. We find that while the Bayesian neural network did not perform as well as non-Bayesian neural networks if evaluated solely by point estimate photo-z values, BNNs can provide uncertainty estimates that are necessary for cosmology

Extreme mass ratio inspirals (EMRIs) are among the most interesting gravitational wave (GW) sources for space-borne GW detectors. However, successful GW data analysis remains challenging due to many issues, ranging from the difficulty of modeling accurate waveforms, to the impractically large template bank required by the traditional matched filtering search method. In this work, we introduce a proof-of-principle approach for EMRI detection based on convolutional neural networks (CNNs). We demonstrate the performance with simulated EMRI signals buried in Gaussian noise. We show that over a wide range of physical parameters, the network is effective for EMRI systems with a signal-to-noise ratio larger than 50, and the performance is most strongly related to the signal-to-noise ratio. The method also shows good generalization ability towards different waveform models. Our study reveals the potential applicability of machine learning technology like CNNs towards more realistic EMRI data analysis.

Planets orbiting intermediate and low-mass stars are in jeopardy as their stellar hosts evolve to white dwarfs (WDs) because the dynamics of the planetary system changes due to the increase of the planet:star mass ratio after stellar mass-loss. In order to understand how the planet multiplicity affects the dynamical stability of post-main sequence (MS) systems, we perform thousands of N-body simulations involving planetary multiplicity as the variable and with a controlled physical and orbital parameter space: equal-mass planets; the same orbital spacing between adjacent planet's pairs; and orbits with small eccentricities and inclinations. We evolve the host star from the MS to the WD phase following the system dynamics for 10 Gyr. We find that the fraction of dynamically active simulations on the WD phase for two-planet systems is $10.2^{+1.2}_{-1.0}$-$25.2^{+2.5}_{-2.2}$ $\%$ and increases to $33.6^{+2.3}_{-2.2}$-$74.1^{+3.7}_{-4.6}$ $\%$ for the six-planet systems, where the ranges cover different ranges of initial orbital separations. Our simulations show that the more planets the system has, the more systems become unstable when the star becomes a WD, regardless of the planet masses and range of separations. Additional results evince that simulations with low-mass planets (1, 10 $\mathrm{M_\oplus}$) lose at most two planets, have a large fraction of systems undergoing orbit crossing without planet losses, and are dynamically active for Gyr time-scales on the WD's cooling track. On the other hand, systems with high-mass planets (100, 1000 $\mathrm{M_\oplus}$) lose up to five planets, preferably by ejections, and become unstable in the first few hundred Myr after the formation of the WD.

We analyze the velocity anisotropy of stars in real and energy space for a sample of Milky Way-like galaxies in the TNG50 simulation. We employ different selection criteria, including spatial, kinematic and metallicity cuts, and make three halo classes ($\mathcal{A}$-$\mathcal{C}$) which show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16% and 36% of halos, respectively. We analyze the $\beta$ radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing $\beta$ profiles are mostly from class $\mathcal{A}$, whilst those with peaks/troughs are part of classes $\mathcal{B}$-$\mathcal{C}$. This means that care must be taken as the observationally reported peaks/troughs might be a consequence of different selection criteria. We infer the anisotropy parameter $\beta$ energy space and compare that against the $\beta$ radial profile. It is seen that 65% of halos with very mild sensitivity to different selections in real space, are those for which the $\beta$ radial and energy profiles are closely related. Consequently, we propose that comparing the $\beta$ radial and energy profiles might be a novel way to examine the sensitivity to different selection criteria and thus examining the robustness of the anisotropy parameter in tracing stellar kinematics. We compare simulated $\beta$ radial profiles against various isolated and extended observations and demonstrate that, in most cases, the model diversity is comparable with the error bars from different observations, meaning that the TNG50 models are in good overall agreement with observations.

As one of the best ground-based photometric dataset, Pan-STARRS1 (PS1) has been widely used as the reference to calibrate other surveys. In this work, we present an independent validation and re-calibration of the PS1 photometry using spectroscopic data from the LAMOST DR7 and photometric data from the corrected Gaia EDR3 with the Stellar Color Regression (SCR) method. Using per band typically a total of 1.5 million LAMOST-PS1-Gaia stars as standards, we show that the PS1 photometric calibration precisions in the $grizy$ filters are around $4\sim 5$ mmag when averaged over $20'$ regions. However, significant large- and small-scale spatial variation of magnitude offset, up to over 1 per cent, probably caused by the calibration errors in the PS1, are found for all the $grizy$ filters. The calibration errors in different filters are un-correlated, and are slightly larger for the $g$ and $y$ filters. We also detect moderate magnitude-dependent errors (0.005, 0.005, 0.005, 0.004, 0.003 mag per magnitude in the 14 -- 17 magnitude range for the $grizy$ filters, respectively) in the PS1 photometry by comparing with the Gaia EDR3 and other catalogs. The errors are likely caused by the systematic uncertainties in the PSF magnitudes. We provide two-dimensional maps to correct for such magnitude offsets in the LAMOST footprint at different spatial resolutions from $20'$ to $160'$. The results demonstrate the power of the SCR method in improving the calibration precision of wide-field surveys when combined with the LAMOST spectroscopy and Gaia photometry.

On 1 June 2019, just before 7:30 PM local time, the Desert Fireball Network detected a -9.3 magnitude fireball over South Australia near the Western Australia border. The event was observed by six fireball observatories, and lasted for five seconds. One station was nearly directly underneath the trajectory, greatly constraining the trajectory solution. This trajectory's backward numerical integrations indicate that the object originated from the outer main belt with a semi-major axis of 2.75 au. A light curve was also extracted and showed that the body experienced very little fragmentation during its atmospheric passage. A search campaign was conducted with several Desert Fireball Network team members and other volunteers. One 42 g fragment was recovered within the predicted fall area based on the dark flight model. Based on measurements of short-lived radionuclides, the fragment was confirmed to be a fresh fall. The meteorite, Arpu Kuilpu, has been classified as an H5 ordinary chondrite. This marks the fifth fall recovered in Australia by the Desert Fireball Network, and the smallest meteoroid ($\simeq 2$ kg) to ever survive entry and be recovered as a meteorite.

In the past decade, significant efforts have been made in developing physics-based solar wind and coronal mass ejection (CME) models, which have been or are being transferred to national centers (e.g., SWPC, CCMC) to enable space weather predictive capability. However, the input data coverage for space weather forecasting is extremely limited. One major limitation is the solar magnetic field measurements, which are used to specify the inner boundary conditions of the global magnetohydrodynamic (MHD) models. In this study, using the Alfven wave solar model (AWSoM), we quantitatively assess the influence of the magnetic field map input (synoptic/diachronic vs. synchronic magnetic maps) on the global modeling of the solar wind and the CME-driven shock in the 2013 April 11 solar energetic particle (SEP) event. Our study shows that due to the inhomogeneous background solar wind and dynamical evolution of the CME, the CME-driven shock parameters change significantly both spatially and temporally as the CME propagates through the heliosphere. The input magnetic map has a great impact on the shock connectivity and shock properties in the global MHD simulation. Therefore this study illustrates the importance of taking into account the model uncertainty due to the imperfect magnetic field measurements when using the model to provide space weather predictions.

We performed a multi-wave study of the oscillation dynamic in short-lived facula regions during their lifetime. We studied oscillations in five regions, three of which belonged to the beginning of the current solar activity cycle, and two of them existed at the end of the previous cycle. We found that in the facula regions of the current cycle, low-frequency 1-2 mHz oscillation dominated at the early stages of the faculae formation, while in the regions of the previous cycle, five-minute oscillations dominated at this stage. At the maximal development phase of all the facula regions, the locations of observed low frequencies are closely related to those of the coronal loops. These results support the version that the sources of the low-frequency oscillations in loops lie loops' foot points.

Dark matter can be characterized by the mass and size of its smallest constituents, which are challenging to be directly probed and detected. We present a new approach to predict the mass and properties of dark matter particles based on the nature of dark matter flow. The self-gravitating collisionless dark matter flow exhibits an inverse mass and energy cascade from small to large mass scales with a scale-independent constant energy flux (the rate of energy transfer $\epsilon_u$). In this paper, we study the simplest case with only gravitational interaction involved. In the absence of viscosity, the energy cascade leads to a two-thirds law for pairwise velocity that extends down to the smallest length scale, where quantum effects are dominant. Combining the energy flux $\epsilon_u$, Planck constant $\hbar$, and gravitational constant $G$ on that scale, the mass of dark matter particles is found to be around $10^{12}$GeV and size is on the order of $10^{-13}$m. This suggests a heavy dark matter scenario with a mass much greater than standard thermal WIMPs.

Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.

Radio interferometers are phased arrays producing high-resolution images from the covariance matrix of measurements. Calibration of such instruments is necessary and is a critical task. This is how the estimation of instrumental errors is usually done thanks to the knowledge of referenced celestial sources. However, the use of high sensitive antennas in modern radio interferometers (LOFAR, SKA) brings a new challenge in radio astronomy because there are more sensitive to Radio Frequency Interferences (RFI). The presence of RFI during the calibration process generally induces biases in state-of-the-art solutions. The purpose of this paper is to propose an alternative to alleviate the effects of RFI. For that, we first propose a model to take into account the presence of RFI in the data across multiple frequency channels thanks to a low-rank structured noise. We then achieve maximum likelihood estimation of the calibration parameters with a Space Alternating Generalized Expectation-Maximization (SAGE) algorithm for which we derive originally two sets of complete data allowing close form expressions for the updates. Numerical simulations show a significant gain in performance for RFI corrupted data in comparison with some more classical methods.

With ever increasing pressure from collider physics and direct detection experiments, particle physics models of TeV scale dark matter are gaining more attention. In this work, we consider two realizations of the class of scalar portal dark matter scenarios -- the inverse seesaw model and the inert doublet model. Observations by the Cherenkov Telescope Array (CTA) of very-high-energy $\gamma$ rays from dark matter annihilation in the context of these models are simulated for the Draco and Sculptor dwarf spheroidal galaxies, and later analyzed using ctools. We study the potential of CTA for the 5$\sigma$ detection of a dark matter annihilation signal. In the absence of a signal, we also derive the 2$\sigma$ upper limits on the annihilation cross-section. We compare our projected CTA sensitivity against the projected sensitivity of the next generation of direct detection experiment, i.e. XENONnT. Although the limits from CTA are significantly improved compared with the previous generations of $\gamma$-ray experiments, they are still $\sim2$ orders of magnitude above the thermal relic cross-section for the considered targets. In the case of the inverse seesaw model, the constraint from the future direct detection experiment XENONnT is much weaker than the CTA sensitivity, whereas for the inert doublet model, XENONnT gives a bound an order of magnitude stronger compared to the CTA limits.

We report the results of a search for MeV-scale astrophysical neutrinos in KamLAND presented as an excess in the number of coincident neutrino interactions associated with the publicly available high-energy neutrino datasets from the IceCube Neutrino Observatory. We find no statistically significant excess in the number of observed low-energy electron antineutrinos in KamLAND, given a coincidence time window of +/-500s, +/-1,000 s, +/-3,600 s, and +/-10,000 s around each of the IceCube neutrinos. We use this observation to present limits from 1.8 MeV to 100 MeV on the electron antineutrino fluence, assuming a mono-energetic flux. We then compare the results to several astrophysical measurements performed by IceCube and place a limit at the 90% confidence level on the electron antineutrino isotropic thermal luminosity from the TXS 0506+056 blazar.

We model hypothetical bio-dispersal within a single Galactic region using the stochastic infection dynamics process, which is inspired by these local properties of life dispersal on Earth. We split the population of stellar systems into different categories regarding habitability and evolved them through time using probabilistic cellular automata rules analogous to the model. As a dynamic effect, we include the existence of natural dispersal vectors (e.g., dust, asteroids) in a way that avoids assumptions about their agency. By assuming that dispersal vectors have a finite velocity and range, the model includes the parameter of 'optical depth of life spreading'. The effect of the oscillatory infection rate on the long-term behavior of the dispersal flux, which adds a diffusive component to its progression, is also taken into account. We found that phase space is separated into subregions of long-lasting transmission, rapidly terminated transmission, and a transition region between the two. We observed that depending on the amplitude of the oscillatory life spreading rate, life-transmission in the Galactic patch might take on different geometrical shapes. Even if some host systems are uninhabited, life transmission has a certain threshold, allowing a patch to be saturated with viable material over a long period. Although stochastic fluctuations in the local density of habitable systems allow for clusters that can continuously infect one another, the spatial pattern disappears when life transmission is below the observed threshold, so that transmission process is not permanent in time. Both findings suggest that a habitable planet in a densely populated region may remain uninfected.

We present the results obtained from our campaign to characterize the intra-night-optical variability properties of blazars detected by the {\it Fermi} Large Area Telescope. This involves R-band monitoring observations of a sample of 18 blazars, that includes five flat-spectrum radio quasars (FSRQs) and thirteen BL Lac objects (BL Lacs) covering the redshift range z = 0.085$-$1.184. Our observations, carried out using the 1.3 m J.C. Bhattacharya Telescope cover a total of 40 nights ($\sim$200 hrs) between the period 2016 December and 2020 March. We characterized variability using the power enhanced $F-$test. We found a duty cycle (DC) of the variability of about 11\% for FSRQs and 12\% for BL Lacs. Dividing the sample into different sub-classes based on the position of the synchrotron peak in their broadband spectral energy distribution (SED), we found DC of $\sim$16\%, $\sim$10\% and $\sim$7\% for low-synchrotron peaked (LSP), intermediate synchrotron peaked (ISP) and high synchrotron peaked (HSP) blazars. Such high DC of variability in LSP blazars could be understood in the context of the R-band tracing the falling part (contributed by high energy electrons) of the synchrotron component of the broadband SED. Also, the R-band tracing the rising synchrotron part (produced by low energy electrons) in the case of ISP and HSP blazars, could cause lesser variability in them. Thus, the observed high DC of variability in LSP blazars relative to ISP and HSP blazars is in accordance with the leptonic model of emission from blazar jets.

We present CO(1--0) observations of the high-redshift quasar SDSS J160705+533558 ($z=3.653$) using the Karl G. Jansky Very Large Array (VLA). We detect CO emission associated with the quasar and at $\sim16.8\,\rm kpc$ projected distance from it, separated by $\sim800\,\rm km\,s^{-1}$ in velocity. The total molecular gas mass of this system is $\sim5\times10^{10}\,\rm M_{\odot}$. By comparing our CO detections with previous submillimetre (submm) observations of the source, an offset between the different emission components is revealed: the peak of the submm emission is offset from the quasar and from the CO companion detected in our VLA data. To explain our findings, we propose a scenario similar to that for the Antennae galaxies: SDSS J160705+533558 might be a merger system in which the quasar and the CO companion are the merging galaxies, whose interaction resulted in the formation of a dusty, star-forming overlap region between the galaxies that is dominant at the submm wavelengths.

We report results from the spectro-timing analysis of the atoll source 4U 1636$-$536 observed with NuSTAR and AstroSat during its hard spectral state. In three observations of 207 ks total exposure, we identify 31 thermonuclear X-ray bursts including five doublets and a triplet. Recurrence time as short as 3.8 minutes is seen in one of the doublets. To the best of our knowledge, this is the shortest recurrence time known for this source. Our time-averaged spectroscopy during the bursts indicate the presence of an additional powerlaw or a blackbody component in a few cases, perhaps due to varying temperatures during bursts or plausible deviation from ideal blackbody behavior, however, it is difficult to probe this using the time-resolved spectroscopy owing to limited statistics. Time-resolved bursts are well fit using an absorbed blackbody model with temperatures varying between 1.7 and 2.2 keV. Burst oscillations around 581 Hz are detected with 3$\sigma$ confidence during the decay phase in two of the X-ray bursts. One of the burst oscillations is seen at 582 Hz, a frequency observed during the 2001 superburst in this source.

Here we study the nature and characteristics of waves propagating in partially ionised plasmas in the weakly ionised limit, typical for the lower part of the solar atmosphere. The framework in which the properties of waves are discussed depends on the relative magnitude of collisions between particles, but also on the relative magnitude of the collisional frequencies compared to the gyro-frequency of charged particles. Our investigation shows that the weakly ionised solar atmospheric plasma can divided into two regions and this division occurs, roughly, at the base of the chromosphere. In the solar photosphere the plasma is non-magnetised and the dynamics can described within the three-fluid framework where acoustic waves associated to each species can propagate. Due to the very high concentration of neutrals, the neutral sound waves propagates with no damping, while for the other two modes the damping rate is determined by collisions with neutrals. The ion and electron-related acoustic modes propagate with a cut-off determined by the collisional frequency of these species with neutrals. In the weakly ionised chromosphere only electrons are magnetised, however, the strong coupling of charged particles reduces the working framework to a two-fluid model. The disassociation of charged particles creates electric currents that can influence the characteristic of waves. The propagation properties of waves with respect to the angle of propagation are studied with the help of polar diagrams.

There had been recent advancement toward the detection of ultra-faint dwarf galaxies, which may serve as a useful laboratory for dark matter exploration since some of them contains almost 99$\%$ of pure dark matter. The majority of these galaxies contain no black hole that inhabits them. Recently, there had been reports that some dwarf galaxies may have a black hole within. In this study, we construct a black hole solution combined with the Dehnen dark matter halo profile, which is commonly used for dwarf galaxies. We aim to find out whether there would be deviations relative to the standard black hole properties which might allow determining whether the dark matter profile in ultra-faint dwarf galaxies is cored or cuspy. To make the model more realistic, we applied the modified Newman-Janis prescription to obtain the rotating metric. We analyzed the black hole properties such as the event horizon, ergoregion, geodesics of time-like and null particle, and the black hole shadow. To broaden the scope of this study, we also calculated the weak deflection angle to examine the effect of the Dehnen profile. Results revealed that the Dehnen profile causes some tiny but interesting deviations to the known black hole properties. It is shown that the radius of the innermost stable circular orbit decreases, while the photonsphere radius increases. We also found out that the size of the shadow decreases due to the Dehnen profile and the extent depends on whether the profile is cored or cuspy. Overall, the deviation caused by the Dehnen profile relative to the known black hole properties are so tiny, that one needs a very sophisticated and ultra-sensitive space detectors to help distinguish whether this profile for ultra-faint dwarf galaxy is cored or cuspy.

Detection of bending waves is a highly challenging task even in nearby disc galaxies due to their sub-kpc bending amplitudes. However, simulations show that the harmonic bending of a Milky Way like disc galaxy is associated with a harmonic fluctuation in the measured line of sight (los) velocities as well, and can be regarded as a kinematic signature of a manifested bending wave. Here, we look for similar kinematic signatures of bending waves in \HI discs, as they extend to much beyond the optical radii. We present a multipole analysis of the \HI los residual velocity fields of six nearby spiral galaxies from the THINGS sample, which uncovers the bending wave-induced velocity peaks. This allows us to identify the radial positions and amplitudes of the different bending modes present in the galaxies. We find that all of our sample discs show a combined kinematic signature of superposition of a few lower-order bending modes, suggesting that bending waves are a common phenomenon. The identified velocity peaks are found to be of modes $m=2,3$ and $4$, not more than 15 km s$^{-1}$ in amplitude and spread across the entire \HI disc. Interestingly, they appear to be concentrated near the optical edge of their host galaxies. Also, $m=2$ appears to be more common than the other two modes.

Europa's surface composition and evidence for cryovolcanic activity can provide insight into the properties and composition of the subsurface ocean, allowing the evaluation of its potential habitability. One promising avenue for revealing the surface processing and subsurface activity are the relative fractions of crystalline and amorphous water-ice observed on the surface, which are influenced by temperature, charged particle bombardment, vapor deposition, and cryovolcanic activity. The crystallinity observed on Europa's leading hemisphere cannot be reproduced by thermophysical and particle flux modeling alone, indicating that there may be additional processes influencing the surface. We performed a spectral mixture analysis on hyperspectral image cubes from the Galileo Near-Infrared Mapping Spectrometer (NIMS) to identify how surface crystallinity is influenced by physical processing at a high spatial resolution scale. We focus specifically on two image cubes, 15e015 closer to the equator and 17e009 closer to the south pole, both on the leading hemisphere. We performed a nonnegative least-squares spectral mixture analysis to reveal both the non-ice composition and the water-ice crystallinity of the surface. We found that amorphous water-ice dominates the spectrum at the equator and the south pole. We estimated a mean crystallinity of ~35% within the 15e015 NIMS cube and a mean crystallinity of ~15% within the 17e009 NIMS cube, which is consistent with ground-based spectroscopically derived crystallinities. We also identified a correlation of magnesium sulfate, magnesium chloride, and hydrated sulfuric acid with lineae and ridges, which may provide evidence for surface processing by upwelling subsurface material.

We study the role of nonlinear effects on tidally-excited internal gravity waves in stellar radiation zones in exoplanetary or binary systems. We are partly motivated to study tides due to massive short-period hot Jupiters, which preferentially orbit stars with convective cores, for which wave breaking near the stellar centre cannot operate. We develop a theory (and test it with numerical calculations) for the nonlinear excitation of super-harmonic "secondary" waves (with frequencies $2\omega_p$) by a "primary" tidal wave (with frequency $\omega_p$) near the interface between the radiation zone and convective envelope. These waves have the same horizontal phase speeds to leading order, and this nonlinear effect could contribute importantly to tidal dissipation if the secondary waves can efficiently damp the primary. We derive criteria involving the orbital and stellar parameters required to excite these secondary waves to large amplitudes using a local model of the radiative/convective interface, which we convert to apply to tides in a spherical star. We numerically evaluate the critical amplitudes required for this new nonlinear effect to become important using stellar models, comparing them to the "conventional" criteria for wave breaking in radiative cores and the application of WKBJ theory near convective cores. The criteria for this new effect are easier to satisfy than the conventional measures of nonlinearity in $1.4$ and $2M_\odot$ stars on the main-sequence. We predict nonlinear effects to be important even for planetary-mass companions around the latter, but this effect is probably less important in stars with radiative cores.

We present a new analysis of the diffuse soft $\gamma$-ray emission towards the inner Galaxy as measured by the SPectrometer aboard the INTEGRAL satellite (SPI) with 16 years of data taking. The analysis implements a spatial template fit of SPI data and an improved instrumental background model. We characterize the contribution of Primordial Black Holes (PBH) as dark matter (DM) candidates evaporating into $\mathcal{O}$(1) MeV photons by including, for the first time, the spatial distribution of their signal into the fitting procedure. No PBH signal is detected, and we set the strongest limit on PBH DM for masses up to $4 \times 10^{17}$ g, significantly closing in into the so-called asteroid mass range.

Neutron stars in low-mass X-ray binaries are thought to be heated up by accretion-induced exothermic nuclear reactions in the crust. The energy release and the location of the heating sources are important ingredients of the thermal evolution models. Here we present thermodynamically consistent calculations of the energy release in three zones of the stellar crust: at the outer-inner crust interface, in the upper layers of the inner crust (up to the density $\rho \leq 2\times 10^{12}$ g cm$^{-3}$), and in the underlying crustal layers. We consider three representative models of thermonuclear ashes (Superburst, Extreme rp, and Kepler ashes). The energy release in each zone is parametrized by the pressure at the outer-inner crust interface, which encodes all uncertainties related to the physics of the deepest inner-crust layers. Our calculations allow us, in particular, to set new lower limits on the net energy release (per accreted baryon): $Q\gtrsim0.28$ MeV for Extreme rp ashes and Q~0.43-0.51 MeV for Superburst and Kepler ashes.

Introduced in 1998 to attempt a first unified view of the broad-band emission properties of blazars, the blazar sequence has been extensively used in the past 25 years to guide observations as well as physical interpretation of the overall emission from these galaxies. In this review, we describe the evolution of the sequence along with the tremendous advances in the observational field, in particular in the gamma-ray band. A new version of the sequence built on TeV-detected objects is also presented. Two extreme classes of objects (MeV and hard-TeV blazars) are included in the discussion, given their relevance for future observatories. Finally, the current physical understanding at the base of the sequence is presented along with the major criticisms to the blazar sequence.

We present in here the exploration of the physical properties of the sample of HII regions and aggregations of the last HII regions catalog of the CALIFA survey. This sample comprises the optical spectroscopic properties of more than ~26,000 ionized regions corresponding to 924 galaxies from the Integral Field Spectroscopy data, including the flux intensity and equivalent widths and the properties of their underlying stellar population. In the current study we derive a set of physical quantities for all these regions based on those properties, including (i) the fraction of young stars; (ii) the ionization strength (using six different estimations); (iii) the oxygen abundance (using 25 different calibrators); (iv) the nitrogen and nitrogen-to-oxygen abundance; (v) the dust extinction and (vi) the electron density. Using this dataset we explore how the loci in the classical diagnostic diagrams are connected with those quantities, the radial distributions of these parameters, and the inter-relations between themselves and with the properties of the underlying stellar populations. We conclude that many properties of the HII regions are tightly related to the galactic stellar evolution at the location where those regions are observed. Those properties are modulated only as a second-order effect by the properties of the ionizing stars and the ionized nebulae that do not depend on the astrophysical context in which they are formed. Our results highlight the importance of HII regions to explore the chemical evolution in galaxies, clarifying which of their properties can be used as proxies of that evolution.

Since the asteroseismic revolution, availability of efficient and reliable methods to extract stellar-oscillation mode parameters has been one of the keystone of modern stellar physics. In the helio- and asteroseismology fields, these methods are usually referred as peakbagging. We introduce in this paper the apollinaire module, a new Python 3 open-source Markov Chains Monte Carlo (MCMC) framework dedicated to peakbagging. The theoretical framework necessary to understand MCMC peakbagging methods for integrated helio- and asteroseismic observations are extensively described. In particular, we present the models that are used to compute the posterior probability in a peakbagging framework. A description of the apollinaire module is then provided. We explain how the module enables stellar background, p-mode global pattern and individual-mode parameters extraction. By taking into account instrumental particularities, stellar inclination angle, rotational splittings, and asymmetries, the module allows fitting a large variety of p-mode models suited for solar as well as stellar data analysis with different instruments. After having been validated through a Monte Carlo fitting trial on synthetic data, the module is benchmarked by comparing its outputs with results obtained with other peakbagging codes. An analysis of the PSD of 89 one-year subseries of GOLF observations is performed. Six stars are also selected from the Kepler LEGACY sample in order to demonstrate the code abilities on asteroseismic data. The parameters we extract with apollinaire are in good agreement with those presented in the literature and demonstrate the precision and reliability of the module.

Estimating the horizontal irradiance from measurements of the zenith night sky radiance is a useful operation for basic and applied studies in observatory site assessment, atmospheric optics and environmental sciences. The ratio between these two quantities, also known as Posch ratio, has been previously studied for some canonical cases and reported for a few observational sites. In this work we (a) generalize the Posch ratio concept, extending it to any pair of radiance-related linear indicators, (b) describe its main algebraic properties, and (c) provide analytical expressions and numerical evaluations for its three basic nighttime components (moonlight, starlight and other astrophysical light sources, and artificial light). We show that the horizontal irradiance (or any other linear radiance indicator) is generally correlated with the zenith radiance, enabling its estimation from zenith measurements if some a priori information on the atmospheric state is available.

A sample of $60,410$ bona fide optical quasars with astrometric proper motions in Gaia EDR3 and spectroscopic redshifts above 0.5 in an oval 8400 square degree area of the sky is constructed. Using orthogonal Zernike functions of polar coordinates, the proper motion fields are fitted in a weighted least-squares adjustment of the entire sample and of six equal bins of sorted redshifts. The overall fit with 37 Zernike functions reveals a statistically significant pattern, which is likely to be of instrumental origin. The main feature of this pattern is a chain of peaks and dips mostly in the R.A. component with an amplitude of 25~$\mu$as yr$^{-1}$. This field is subtracted from each of the six analogous fits for quasars grouped by redshifts covering the range 0.5 through 7.03, with median values 0.72, 1.00, 1.25, 1.52, 1.83, 2.34. The resulting residual patterns are noisier, with formal uncertainties up to 8~$\mu$as yr$^{-1}$ in the central part of the area. We detect a single high-confidence Zernike term for R.A. proper motion components of quasars with redshifts around 1.52 representing a general gradient of 30 $\mu$as yr$^{-1}$ over $150\degr$ on the sky. We do not find any small- or medium-scale systemic variations of the residual proper motion field as functions of redshift above the $2.5\,\sigma$ significance level.

We report on the the long term monitoring campaign of the seemingly youngest magnetar Swift~J1818.0-1607 at radio and X-ray wavelengths over a span of one year. We obtained a coherent timing solution for the magnetar over the same time span. The frequency derivative of the magnetar shows systematic variation with the values oscillating about a mean value of $-$1.37$\times$10$^{-11}$ Hz s$^{-1}$. The magnitude of the variation in the frequency derivative reduces with time before converging on the mean value. We were able to identify four states in the spin-frequency derivative that were quantified by the amount of modulation about the mean value and the transition between these states seem to be correlated with the change in the radio emission of the magnetar while no correlation is seen in the average radio profile variability on a shorter timescale (days). The 0.5--12 keV X-ray flux shows a monotonic decrease that can be attributed to thermal emission from a hot-spot on the surface of the neutron star that is reducing in size. Such decrease is consistent with what is seen in other magnetars. The potential correlation between the radio emission mode and the behaviour of the spin-down rate hints to a global change in the magnetopshere of the magnetar akin to the correlation seen in a subset of mode-changing radio pulsars and suggests a physical link between the two sub-populations.

In this paper we present an extension to the $\texttt{matryoshka}$ suite of neural network based emulators. The new editions have been developed to accelerate EFTofLSS analyses of galaxy power spectrum multipoles in redshift space. They are collectively referred to as the $\texttt{EFTEMU}$. We test the $\texttt{EFTEMU}$ at the power spectrum level and achieve a prediction accuracy of better than 1\% with BOSS-like bias parameters and counterterms on scales $0.001\ h\ \mathrm{Mpc}^{-1} \leq k \leq 0.19\ h\ \mathrm{Mpc}^{-1}$. We also run a series of mock full shape analyses to test the $\texttt{EFTEMU}$ at the inference level. Through these mock analyses we verify that the $\texttt{EFTEMU}$ recovers the true cosmology within $1\sigma$ at several redshifts ($z=[0.38,0.51,0.61]$), and with several noise levels (the most stringent of which being a Gaussian covariance associated with a volume of $5000^3 \ \mathrm{Mpc}^3 \ h^{-3}$). We compare mock inference results from the $\texttt{EFTEMU}$ to those obtained with a fully analytic EFTofLSS model and again find no significant bias, whilst speeding up the inference by three orders of magnitude. The $\texttt{EFTEMU}$ is publicly available as part of the $\texttt{matryoshka}$ $\texttt{Python}$ package https://github.com/JDonaldM/Matryoshka.

The Brans-Dicke (BD) theory is the simplest Scalar-Tensor theory of gravity, which can be considered as a candidate of modified Einstein's theory of general relativity. In this work, we forecast the constraints on BD theory in the CSST galaxy clustering spectroscopic survey with a magnitude limit $\sim 23$ AB mag for point-source 5$\sigma$ detection. We generate mock data based on the zCOSMOS catalog and consider the observational and instrumental effects of the CSST spectroscopic survey. We predicate galaxy power spectra in the BD theory from $z=0$ to 1.5, and the galaxy bias and other systematical parameters are also included. The Markov Chain Monte Carlo (MCMC) technique is employed to find the best-fits and probability distributions of the cosmological and systematical parameters. A Brans-Dicke parameter $\zeta$ is introduced, which satisfies $\zeta=\ln \left(1+\frac{1}{\omega}\right)$. We find that the CSST spectroscopic galaxy clustering survey can give $|\zeta|<10^{-2}$, or equivalently $|\omega|>\mathcal{O}(10^2)$ and $|\dot{G}/G|<10^{-13}$, under the assumption $\zeta = 0$. These constraints are almost at the same order of magnitude compared to the joint constraints using the current cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and Type Ia supernova (SN Ia) data, indicating that the CSST galaxy clustering spectroscopic survey would be powerful to constrain the BD theory and other modified gravity theories.

Dark matter particles near the center of a blazar, after being accelerated by the elastic collisions with relativistic electrons and protons in the blazar jet, can be energetic enough to trigger detectable signals at terrestrial detectors. In this work, focusing on the blazars TXS 0506+056 and BL Lacertae, we derive novel limits on the cross section of the elastic scattering between dark matter and electrons by means of the available Super-Kamiokande data. Thanks to the large blazar-boosted dark matter flux, the limit on the dark matter-electron scattering cross section for dark matter masses below 100 MeV can be as low as $\sim10^{-38}~\text{cm}^2$, that is about 5 orders of magnitude stronger than the analogous results from galactic cosmic rays.

Asteroseismology is used to infer the interior physics of stars. The \textit{Kepler} and TESS space missions have provided a vast data set of red-giant light curves, which may be used for asteroseismic analysis. These data sets are expected to significantly grow with future missions such as \textit{PLATO}, and efficient methods are therefore required to analyze these data rapidly. Here, we describe a machine learning algorithm that identifies red giants from the raw oscillation spectra and captures \textit{p} and \textit{mixed} mode parameters from the red-giant power spectra. We report algorithmic inferences for large frequency separation ($\Delta \nu$), frequency at maximum amplitude ($\nu_{max}$), and period separation ($\Delta \Pi$) for an ensemble of stars. In addition, we have discovered $\sim$25 new probable red giants among 151,000 \textit{Kepler} long-cadence stellar-oscillation spectra analyzed by the method, among which four are binary candidates which appear to possess red-giant counterparts. To validate the results of this method, we selected $\sim$ 3,000 \textit{Kepler} stars, at various evolutionary stages ranging from subgiants to red clumps, and compare inferences of $\Delta \nu$, $\Delta \Pi$, and $\nu_{max}$ with estimates obtained using other techniques. The power of the machine-learning algorithm lies in its speed: it is able to accurately extract seismic parameters from 1,000 spectra in $\sim$5 seconds on a modern computer (single core of the Intel Xeon Platinum 8280 CPU).

The dynamics of both the preinflationary and the preheating epochs for a model consisting of a Higgs inflaton plus an additional auxiliary field are studied in full General Relativity. The minimally coupled auxiliary field allows for parametric-type resonances that successfully transfer energy from the inflaton condensate to particle excitations in both fields. Depending on the interaction strengths of the fields, the broad resonance periods lead to structure formation consisting of large under/over-densities, and possibly the formation of compact objects. Moreover, when confronting the same model to multi-field inhomogeneous preinflation, the onset of inflation is shown to be a robust outcome. At relatively large Higgs values, the non-minimal coupling acts as a stabilizer, protecting the dynamics of the inflaton, and significantly reducing the impact of perturbations in other fields and matter sectors. These investigations further confirm the robustness of Higgs inflation to multi-field inhomogeneous initial conditions, while putting in evidence the formation of complex structures during the reheating.

Stellar-mass binary black holes (BBHs) embedded in active galactic nucleus (AGN) discs are possible progenitors of black-hole mergers detected in gravitational waves by LIGO/VIRGO. To better understand the hydrodynamical evolution of BBHs interacting with the disc gas, we perform a suite of high-resolution 2D simulations of binaries in local disc (shearing-box) models, considering various binary mass ratios, eccentricities and background disc properties. We use the $\gamma$-law equation of state and adopt a robust post-processing treatment to evaluate the mass accretion rate, torque and energy transfer rate on the binary to determine its long-term orbital evolution. We find that circular comparable-mass binaries contract, with an orbital decay rate of a few times the mass doubling rate. Eccentric binaries always experience eccentricity damping. Prograde binaries with higher eccentricities or smaller mass ratios generally have slower orbital decay rates, with some extreme cases exhibiting orbital expansion. The averaged binary mass accretion rate depends on the physical size of the accretor. The accretion flows are highly variable, and the dominant variability frequency is the apparent binary orbital frequency (in the rotating frame around the central massive BH) for circular binaries but gradually shifts to the radial epicyclic frequency as the binary eccentricity increases. Our findings demonstrate that the dynamics of BBHs embedded in AGN discs is quite different from that of isolated binaries in their own circumbinary discs. Furthermore, our results suggest that the hardening timescales of the binaries are much shorter than their migration timescales in the disc, for all reasonable binary and disc parameters.

We study the detection prospects of relatively light charged scalars in radiative Majorana neutrino mass models, such as the Zee model and its variants using scalar leptoquarks, at current and future neutrino telescopes. In particular, we show that these scalar mediators can give rise to Glashow-like resonance features in the ultra-high energy neutrino (UHE) event spectrum at the IceCube neutrino observatory and its high-energy upgrade IceCube-Gen2. The same scalars can also give rise to observable non-standard neutrino interactions (NSI), and we show that the UHE neutrinos provide a complementary probe of NSI. We also discuss an interesting possibility of producing such resonances by incoming sterile neutrino components in the case where neutrinos are pseudo-Dirac particles.

We extend General Relativity by adding $4$-form field strengths to the gravitational sector of the theory. This promotes Planck scale and the cosmological constant into integration constants of these $4$-forms. When we include the charges of the $4$-forms, these constants can jump discretely from region to region. We explain how the cosmological constant problem can be solved in this framework. When the cosmological constant picks up contributions from two different $4$-forms, with an irrational ratio of charges, the spectrum of its values is a very fine discretuum. If the distribution of values is controlled by the Euclidean path integral, the theory exponentially favors a huge hierarchy $\Lambda/M_{Pl}^4 \ll 1$ instead of $\Lambda/M_{Pl}^4 \simeq 1$.

Brief recollections by the author about how he and Stephen Hawking arrived at the theory of the No-Boundary Quantum State of the Universe

Recently, it was shown that the gravitational field undergoes exponential cutoff at large cosmological scales due to the presence of background matter. In this article, we demonstrate that there is a close mathematical analogy between this effect and the behavior of the magnetic field induced by a solenoid placed in a superconductor.

We present a successful realization of supersymmetric $\mu$-hybrid inflation model based on a gauged $U(1)_{B-L}$ extension of the minimal supersymmetric standard model, with the soft supersymmetry breaking terms are playing an important role. Successful non-thermal leptogenesis with gravitino dark matter yields a reheat temperature in the range $2 \times 10^{7} \lesssim T_R \lesssim 5 \times 10^{9}$ GeV. This corresponds to the predictions $2 \times 10^{-18} \lesssim r\lesssim 4 \times 10^{-13}$ for the tensor to scalar ratio, and $-2 \times 10^{-6} \lesssim dn_s/d\ln k \lesssim -5 \times 10^{-11}$ for the running of the scalar spectral index. The $B-L$ breaking scale is estimated as $ 6 \times 10^{14}\lesssim M/ \text{GeV}\lesssim 10^{16}$, calculated at the central value of the scalar spectral index, $n_s =0.9655$, reported by Planck 2018. Finally, in a grand unified theory setup the dimensionless string tension parameter associated with the metastable strings is in the range $ 10^{-9} \lesssim G\mu_\text{cs} \lesssim 10^{-6}$ corresponding to a stochastic gravitational wave background lying within the 2$\sigma$ bound of the recent NANOGrav 12.5-yr data.

We describe a case study of translational research, applying interpretability techniques developed for computer vision to machine learning models used to search for and find gravitational waves. The models we study are trained to detect black hole merger events in non-Gaussian and non-stationary advanced Laser Interferometer Gravitational-wave Observatory (LIGO) data. We produced visualizations of the response of machine learning models when they process advanced LIGO data that contains real gravitational wave signals, noise anomalies, and pure advanced LIGO noise. Our findings shed light on the responses of individual neurons in these machine learning models. Further analysis suggests that different parts of the network appear to specialize in local versus global features, and that this difference appears to be rooted in the branched architecture of the network as well as noise characteristics of the LIGO detectors. We believe efforts to whiten these "black box" models can suggest future avenues for research and help inform the design of interpretable machine learning models for gravitational wave astrophysics.

As Earth's orbits fill with satellites and debris, debris-producing collisions between orbiting bodies become more likely. Runaway space debris growth, known as Kessler Syndrome, may render Earth's orbits unusable for centuries. We present a dynamic physico-economic model of Earth orbit use under rational expectations with endogenous collision risk and Kessler Syndrome. When satellites can be destroyed in collisions with debris and other satellites, the open-access equilibrium manifold allows for multiple steady states. When debris can collide to produce more debris, at least one steady state may be a tipping point and Kessler Syndrome can occur along equilibrium paths. We show open access is increasingly and inefficiently likely to cause Kessler Syndrome as satellites become more profitable. Calibrated simulations reveal Kessler Syndrome is expected to occur in low-Earth orbit around 2048 under recent historical sectoral growth trends, and may occur as early as 2035 if the space economy grows consistent with projections by major investment banks. These results highlight the urgent need for modeling and policy approaches which incorporate open access and positive feedbacks in debris growth.

We consider inhomogeneous spherically symmetric models based on the Lema\^{i}tre-Tolman-Bondi (LTB) metric, assuming as its source an interactive mixture of ordinary baryonic matter, cold dark matter and dark energy with a coupling term proportional to the addition of energy densities of both dark fluids. We reduce Einstein's field equations to a first order 7-dimensional autonomous dynamical system of evolution equations and algebraic constraints. We study in detail the evolution of the energy density and spatial curvature profiles along the phase space by means of two subspace projections: a three-dimensional projection associated with the solutions of the Friedman-Lema\^\i tre-Robertson-Walker metric (invariant subspace) and a four-dimensional projection describing the evolution of the inhomogeneous fluctuations. We also classify and study the critical points of the system in comparison with previous work on similar sources, as well as solving numerically the equations for initial energy density and curvature profiles that lead to a spherical bounce whose collapsing time we estimate appropriately.