Papers for Monday, Jan 25 2021

Light curves of the accreting white dwarf pulsator GW Librae spanning a 7.5 month period in 2017 were obtained as part of the Next Generation Transit Survey. This data set comprises 787 hours of photometry from 148 clear nights, allowing the behaviour of the long (hours) and short period (20min) modulation signals to be tracked from night to night over a much longer observing baseline than has been previously achieved. The long period modulations intermittently detected in previous observations of GW Lib are found to be a persistent feature, evolving between states with periods ~83min and 2-4h on time-scales of several days. The 20min signal is found to have a broadly stable amplitude and frequency for the duration of the campaign, but the previously noted phase instability is confirmed. Ultraviolet observations obtained with the Cosmic Origin Spectrograph onboard the Hubble Space Telescope constrain the ultraviolet-to-optical flux ratio to ~5 for the 4h modulation, and <=1 for the 20min period, with caveats introduced by non-simultaneous observations. These results add further observational evidence that these enigmatic signals must originate from the white dwarf, highlighting our continued gap in theoretical understanding of the mechanisms that drive them.

We study the halo mass function and inner halo structure at high redshifts ($z\geq5$) for a suite of simulations within the structure formation ETHOS framework. Scenarios such as cold dark matter (CDM), thermal warm dark matter (WDM), and dark acoustic oscillations (DAO) of various strengths are contained in ETHOS with just two parameters $h_{\rm peak}$ and $k_{\rm peak}$, the amplitude and scale of the first DAO peak. The Extended Press-Schechter (EPS) formalism with a smooth-$k$ filter is able to predict the cut-off in the halo mass function created by the suppression of small scale power in ETHOS models (controlled by $k_{\rm peak}$), as well as the slope at small masses that is dependent on $h_{\rm peak}$. Interestingly, we find that DAOs introduce a localized feature in the mass distribution of haloes, resulting in a mass function that is distinct in shape compared to either CDM or WDM. We find that the halo density profiles of ${\it all}$ ETHOS models are well described by the NFW profile, with a concentration that is lower than in the CDM case in a way that is regulated by $k_{\rm peak}$. We show that the concentration-mass relation for DAO models can be well approximated by the mass assembly model based on the extended Press-Schechter theory, which has been proposed for CDM and WDM elsewhere. Our results can be used to perform inexpensive calculations of the halo mass function and concentration-mass relation within the ETHOS parametrization without the need of $N-$body simulations.

Magnitude-limited samples have shown that 20-25 per cent of cataclysmic variables contain white dwarfs with magnetic fields of Mega Gauss strength, in stark contrast to the approximately 5 per cent of single white dwarfs with similar magnetic field strengths. Moreover, the lack of identifiable progenitor systems for magnetic cataclysmic variables leads to considerable challenges when trying to understand how these systems form and evolve. Here we present a sample of six magnetic white dwarfs in detached binaries with low-mass stellar companions where we have constrained the stellar and binary parameters including, for the first time, reliable mass estimates for these magnetic white dwarfs. We find that they are systematically more massive than non-magnetic white dwarfs in detached binaries. These magnetic white dwarfs generally have cooling ages of more than 1 Gyr and reside in systems that are very close to Roche-lobe filling. Our findings are more consistent with these systems being temporarily detached cataclysmic variables, rather than pre-cataclysmic binaries, but we cannot rule out the latter possibility. We find that these systems can display unusual asymmetric light curves that may offer a way to identify them in larger numbers in future. Seven new candidate magnetic white dwarf systems are also presented, three of which have asymmetric light curves. Finally, we note that several newly identified magnetic systems have archival spectra where there is no clear evidence of magnetism, meaning that these binaries have been previously missed. Nevertheless, there remains a clear lack of younger detached magnetic white dwarf systems.

We present a detailed X-ray spectral analysis of the nearby Seyfert 2 galaxy MCG-01-24-12 based on a multi-epoch data set. Data have been taken with different X-ray satellites, namely XMM-Newton, NuSTAR, Swift and Chandra and cover different time intervals, from years down to a few days. From 2006 to 2013 the source had a 2-10 keV flux of $\sim$1.5$\times$10$^{-11}$ erg cm$^{-2}$ s$^{-1}$, consistent with archival observations based on \textit{HEAO} and \textit{BeppoSAX} data, though a 2019 \textit{Chandra} snapshot caught the source in an extreme low flux state, a factor of $\sim$10 fainter than its historical one. Based on phenomenological and physically motivated models, we find the X-ray spectrum of MCG-01-24-12 to be best modelled by a power-law continuum emission with $\Gamma$=1.76$\pm$0.09 with a high energy cut-off at E$_{\rm c}=70^{+21}_{-14}$ keV that is absorbed by a fairly constant column density of N$_{\rm H}$=(6.3$\pm$0.5)$\times10^{22}$ cm$^{-2}$. These quantities allowed us to estimate the properties of the hot corona in MCG-01-24-12 for the cases of a spherical or slab-like hot Comptonising plasma to be kT$_{\rm e}$=27$^{+8}_{-4}$ keV, $\tau_{\rm e}$=5.5$\pm$1.3 and kT$_{\rm e}$=28$^{+7}_{-5}$ keV, $\tau$=3.2$\pm$0.8, respectively. Finally, despite the short duration of the exposures, possible evidence of the presence of outflows is discussed.

We revisit Bondi accretion - steady-state, adiabatic, spherical gas flow onto a Schwarzschild black hole at rest in an asymptotically homogeneous medium - for stiff polytropic equations of state (EOSs) with adiabatic indices $\Gamma > 5/3$. A general relativistic treatment is required to determine their accretion rates, for which we provide exact expressions. We discuss several qualitative differences between results for soft and stiff EOSs - including the appearance of a minimum steady-state accretion rate for EOSs with $\Gamma \geq 5/3$ - and explore limiting cases in order to examine these differences. As an example we highlight results for $\Gamma = 2$, which is often used in numerical simulations to model the EOS of neutron stars. We also discuss a special case with this index, the ultra-relativistic `causal' EOS, $P = \rho$. The latter serves as a useful limit for the still undetermined neutron-star EOS above nuclear density. The results are useful, for example, to estimate the accretion rate onto a mini-black hole residing at the center of a neutron star.

Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent method using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM$_{\rm IGM}$) is an indicator of the amount of ionised material in the IGM. Since the differential of DM$_{\rm IGM}$ against redshift is proportional to the ionisation fraction, our method allows us to directly measure the reionisation history without any assumption on its functional shape. As a proof of concept, we constructed mock non-repeating FRB sources to be detected with the Square Kilometre Array, assuming three different reionisation histories with the same optical depth of Thomson scattering. We considered three cases of redshift measurements: (A) spectroscopic redshift for all mock data, (B) spectroscopic redshift for 10% of mock data, and (C) redshift estimated from an empirical relation of FRBs between their time-integrated luminosity and rest-frame intrinsic duration. In all cases, the reionisation histories are consistently reconstructed from the mock FRB data using our method. Our results demonstrate the capability of future FRBs in constraining the reionisation history.

The analysis of the APOGEE DR16 data suggests the existence of a clear distinction between two sequences of disc stars at different Galactocentric distances in the [$\alpha$/Fe] vs. [Fe/H] abundance ratio space: the so-called high-$\alpha$ sequence, classically associated to an old population of stars in the thick disc, and the low-$\alpha$ sequence, which mostly comprises relatively young stars in the thin disc. We perform a Bayesian analysis based on a Markov Chain Monte Carlo method to constrain a multi-zone two-infall chemical evolution model designed for regions at different Galactocentric distances using measured chemical abundances from the APOGEE DR16 sample. An inside-out formation of the Galaxy disc naturally emerges from the best fit of our two-infall chemical-evolution model to APOGEE-DR16: inner Galactic regions are assembled on shorter time-scales compared to the external ones. In the outer disc (with radii $R>6$ kpc), the chemical dilution due to a late accretion event of gas with primordial chemical composition is the main driver of the [Mg/Fe] vs. [Fe/H] abundance pattern in the low-$\alpha$ sequence. In the inner disc, in the framework of the two-infall model, we confirm the presence of an enriched gas infall in the low-$\alpha$ phase as suggested by chemo-dynamical models. Our Bayesian analysis of the recent APOGEE DR16 data suggests a significant delay time, ranging from $\sim$3.0 to 4.7 Gyr, between the first and second gas infall events for all the analyzed Galactocentric regions. Our results propose a clear interpretation of the [Mg/Fe] vs. [Fe/H] relations along the Galactic discs. The signatures of a delayed gas-rich merger which gives rise to a hiatus in the star formation history of the Galaxy are impressed in the [Mg/Fe] vs. [Fe/H] relation, determining how the low-$\alpha$ stars are distributed in the abundance space at different Galactocentric distances.

In star formation process, the vital role of environmental factors such as feedback from massive stars and stellar density on the form of the Initial Mass Function (IMF) at low-mass end is yet to be understood. Hence a systematic, high sensitive observational analysis of a sample of regions under diverse environmental conditions is essential. We analyse the IMF of eight young clusters ($<$5 Myr) namely IC1848-West, IC1848-East, NGC1893, NGC2244, NGC2362, NGC6611, Stock8 and Cygnus OB2 which are located at the Galactocentric distance ($R_g$) range $\sim$6-12 kpc along with nearby cluster IC348 using deep near-IR photometry and Gaia-DR2. These clusters are embedded in massive stellar environments of radiation strength $log(L_{FUV}/L_{\odot})$ $\sim$2.6 to 6.8, $log(L_{EUV})$ $\sim$42.2 to 50.85 photons/s, with stellar density in the range of $\sim$170 - 1220 stars/pc$^2$. After structural analysis and field decontamination we obtain an unbiased, uniformly sensitive sample of Pre-Main Sequence members of the clusters down to brown-dwarf regime. The log-normal fit to the IMF of nine clusters gives the mean characteristic mass ($m_c$) and $\sigma$ of 0.32$\pm$0.02 $M_\odot$ and 0.47$\pm$0.02, respectively. We compare the IMF with that of low and high mass clusters across the Milky Way. We also check for any systematic variation with respect to the radiation field strength, stellar density as well with $R_g$. We conclude that there is no strong evidence for environmental effect in the underlying form of IMF of these clusters.

We report the validation of a recently proposed infrared selection criterion for symbiotic stars (SySts). Spectroscopic data were obtained for seven candidates, selected from the SySt candidates of Akras et al. (2019, MNRAS, 483, 5077) by employing the new supplementary infrared selection criterion for SySts in the VST/OmegaCAM Photometric H-Alpha Survey (VPHAS+). Five of them turned out to be genuine SySts after the detection of H$\alpha$, He II and [O III] emission lines as well as TiO molecular bands. The characteristic O VI Raman-scattered line is also detected in one of these SySts. According to their infrared colours and optical spectra, all five newly discovered SySts are classified as S-type. The high rate of true SySts detections of this work demonstrates that the combination of the H$\alpha$-emission and the new infrared criterion improves the selection of target lists for follow-up observations by minimizing the number of contaminants and optimizing the observing time.

Determining the mechanism by which high-mass stars are formed is essential for our understanding of the energy budget and chemical evolution of galaxies. By using the New IRAM KIDs Array 2 (NIKA2) camera on the Institut de Radio Astronomie Millim\'etrique (IRAM) 30-m telescope, we have conducted high-sensitivity and large-scale mapping of a fraction of the Galactic plane in order to search for signatures of the transition between the high- and low-mass star-forming modes. Here, we present the first results from the Galactic Star Formation with NIKA2 (GASTON) project, a Large Programme at the IRAM 30-m telescope which is mapping $\approx$2 deg$^2$ of the inner Galactic plane (GP), centred on $\ell$=23.9$^\circ$, $b$=0.05$^\circ$, as well as targets in Taurus and Ophiuchus in 1.15 and 2.00 mm continuum wavebands. In this paper we present the first of the GASTON GP data taken, and present initial science results. We conduct an extraction of structures from the 1.15 mm maps using a dendrogram analysis and, by comparison to the compact source catalogues from Herschel survey data, we identify a population of 321 previously-undetected clumps. Approximately 80 per cent of these new clumps are 70 $\mu$m-quiet, and may be considered as starless candidates. We find that this new population of clumps are less massive and cooler, on average, than clumps that have already been identified. Further, by classifying the full sample of clumps based upon their infrared-bright fraction - an indicator of evolutionary stage - we find evidence for clump mass growth, supporting models of clump-fed high-mass star formation.

In preparation for the Dark Energy Spectroscopic Instrument (DESI), a new top end was installed on the Mayall 4-meter telescope at Kitt Peak National Observatory. The refurbished telescope and the DESI instrument were successfully commissioned on sky between 2019 October and 2020 March. Here we describe the pointing, tracking and imaging performance of the Mayall telescope equipped with its new DESI prime focus corrector, as measured by six guider cameras sampling the outer edge of DESI's focal plane. Analyzing ~500,000 guider images acquired during commissioning, we find a median delivered image FWHM of 1.1 arcseconds (in the r-band at 650 nm), with the distribution extending to a best-case value of ~0.6 arcseconds. The point spread function is well characterized by a Moffat profile with a power-law index of $\beta$ ~ 3.5 and little dependence of $\beta$ on FWHM. The shape and size of the PSF delivered by the new corrector at a field angle of 1.57 degrees are very similar to those measured with the old Mayall corrector on axis. We also find that the Mayall achieves excellent pointing accuracy (several arcseconds RMS) and minimal open-loop tracking drift (< 1 milliarcsecond per second), improvements on the telecope's pre-DESI performance. In the future, employing DESI's active focus adjustment capabilities will likely further improve the Mayall/DESI delivered image quality.

We use Pantheon Type Ia supernova (SN Ia) apparent magnitude, DES-3yr binned SN Ia apparent magnitude, Hubble parameter, and baryon acoustic oscillation measurements to constrain six spatially flat and non-flat cosmological models. These sets of data provide mutually consistent cosmological constraints in the six cosmological models we study. A joint analysis of these data sets provides model-independent estimates of the Hubble constant, $H_0=68.8\pm1.8\ \rm{km \ s^{-1} \ Mpc^{-1}}$, and the non-relativistic matter density parameter, $\Omega_{\rm m_0}=0.294\pm0.020$. Although the joint constraints prefer mild dark energy dynamics and a little spatial curvature, they do not rule out dark energy being a cosmological constant and flat spatial hypersurfaces. We also add quasar angular size and HII starburst galaxy measurements to the combined data set and find more restrictive constraints.

Using data from the Sloan Digital Sky Survey Moving Object Catalog, we study color as a function of size for C-complex families in the Main Asteroid Belt to improve our understanding of space weathering of carbonaceous materials. We find two distinct spectral slope trends: Hygiea-type and Themis-type. The Hygiea-type families exhibit a reduction in spectral slope with increasing object size until a minimum slope value is reached and the trend reverses with increasing slope with increasing object size. The Themis family shows an increase in spectral slope with increasing object size until a maximum slope is reached and the spectral slope begins to decrease slightly or plateaus for the largest objects. Most families studied show the Hygiea-type trend. The processes responsible for these distinct changes in spectral slope affect several different taxonomic classes within the C-complex and appear to act quickly to alter the spectral slopes of the family members.

There is a broad consensus that accretion onto supermassive black holes and consequent jet formation power the observed emission from active galactic nuclei (AGNs). However, there has been less agreement about how jets form in accretion flows, their possible relationship to black hole spin, and how they interact with the surrounding medium. There have also been theoretical concerns about instabilities in standard accretion disk models and lingering discrepancies with observational constraints. Despite seemingly successful applications to X-ray binaries, the standard accretion disk model faces a growing list of observational constraints that challenge its application to AGNs. Theoretical exploration of these questions has become increasingly reliant on numerical simulations owing to the dynamic nature of these flows and the complex interplay between hydrodynamics, magnetic fields, radiation transfer, and curved spacetime. We conclude the following: The advent of general relativistic magnetohydrodynamics (MHD) simulations has greatly improved our understanding of jet production and its dependence on black hole spin. Simulation results show both disks and jets are sensitive to the magnetic flux threading the accretion flow as well as possible misalignment between the angular momentum of the accretion flow and the black hole spin. Radiation MHD simulations are providing new insights into the stability of luminous accretion flows and highlighting the potential importance of radiation viscosity, UV opacity from atoms, and spiral density waves in AGNs.

Debris disks are tenuous, dusty belts surrounding main sequence stars generated by collisions between planetesimals. HD 206893 is one of only two stars known to host a directly imaged brown dwarf orbiting interior to its debris ring, in this case at a projected separation of 10.4 au. Here we resolve structure in the debris disk around HD 206893 at an angular resolution of 0.6" (24 au) and wavelength of 1.3 mm with the Atacama Large Millimeter/submillimeter Array (ALMA). We observe a broad disk extending from a radius of <51 au to 194^{+13}_{-2} au. We model the disk with a continuous, gapped, and double power-law model of the surface density profile, and find strong evidence for a local minimum in the surface density distribution near a radius of 70 au, consistent with a gap in the disk with an inner radius of 63^{+8}_{-16} au and width 31^{+11}_{-7} au. Gapped structure has been observed in four other debris disks -- essentially every other radially resolved debris disk observed with sufficient angular resolution and sensitivity with ALMA -- and could be suggestive of the presence of an additional planetary-mass companion.

In this paper we present a two-step neural network model to separate detections of solar system objects from optical and electronic artifacts in data obtained with the "Asteroid Terrestrial-impact Last Alert System" (ATLAS), a near-Earth asteroid sky survey system [arXiv:1802.00879]. A convolutional neural network [arXiv:1807.10912] is used to classify small "postage-stamp" images of candidate detections of astronomical sources into eight classes, followed by a multi-layered perceptron that provides a probability that a temporal sequence of four candidate detections represents a real astronomical source. The goal of this work is to reduce the time delay between Near-Earth Object (NEO) detections and submission to the Minor Planet Center. Due to the rare and hazardous nature of NEOs [Harris and D'Abramo, 2015], a low false negative rate is a priority for the model. We show that the model reaches 99.6\% accuracy on real asteroids in ATLAS data with a 0.4\% false negative rate. Deployment of this model on ATLAS has reduced the amount of NEO candidates that astronomers must screen by 90%, thereby bringing ATLAS one step closer to full autonomy.

Normal-mode helioseismic data analysis uses observed solar oscillation spectra to infer perturbations in the solar interior due to global and local-scale flows and structural asphericity. Differential rotation, the dominant global-scale axisymmetric perturbation, has been tightly constrained primarily using measurements of frequency splittings via "$a$-coefficients". However, the frequency-splitting formalism invokes the approximation that multiplets are isolated. This assumption is inaccurate for modes at high angular degrees. Analysing eigenfunction corrections, which respect cross coupling of modes across multiplets, is a more accurate approach. However, applying standard inversion techniques using these cross-spectral measurements yields $a$-coefficients with a significantly wider spread than the well-constrained results from frequency splittings. In this study, we apply Bayesian statistics to infer $a$-coefficients due to differential rotation from cross spectra for both $f$-modes and $p$-modes. We demonstrate that this technique works reasonably well for modes with angular degrees $\ell=50-291$. The inferred $a_3-$coefficients are found to be within $1$ nHz of the frequency splitting values for $\ell > 200$. We also show that the technique fails at $\ell < 50$ owing to the insensitivity of the measurement to the perturbation. These results serve to further establish mode coupling as an important helioseismic technique with which to infer internal structure and dynamics, both axisymmetric (e.g., meridional circulation) and non-axisymmetric perturbations.

The asteroid exploration project "Hayabusa2" has successfully returned samples from the asteroid (162173) Ryugu. In this study, we measured the linear polarization degrees of Ryugu using four ground-based telescopes from 2020 September 27 to December 25, covering a wide-phase angle (Sun-target-observer's angle) range from 28$^\circ$ to 104$^\circ$. We found that the polarization degree of Ryugu reached 53$\%$ around a phase angle of 100$^\circ$, the highest value among all asteroids and comets thus far reported. The high polarization degree of Ryugu can be attributed to the scattering properties of its surface layers, in particular the relatively small contribution of multiply-scattered light. Our polarimetric result indicates that Ryugu's surface is covered with large grains. On the basis of a comparison with polarimetric measurements of pulverized meteorites, we can infer the presence of millimeter-sized grains on the surface layer of Ryugu. We also conjecture that this size boundary represents the grains that compose the aggregate. It is likely that a very brittle structure has been lost in the recovered samples, although they may hold a record of its evolution. Our data will be invaluable for future experiments aimed at reproducing the surface structure of Ryugu.

A cosmological model with an energy transfer between the dark matter (DM) and dark energy (DE) can give rise to comparable energy densities at the present epoch. The present work deals with the perturbation analysis of interacting models with dynamical coupling parameter that determines the strength of the interaction. We considered two cases, where the interaction is a more recent phenomenon, and where the interaction is a phenomenon in the distant past. Using the perturbation analysis, we have shown that interaction present as the brief early phenomenon is preferred over a recent interaction and a constant coupling interaction.

We studied the general advective accretion solutions around the Kerr black hole (BH) with investigating two types of inflow gases at the outer accretion boundary (AB). We classified these two types of gases as a \cm and a \hm inflow gas at the outer AB on the basis of their temperatures and solutions. We found that the \hm gas is more efficient for angular momentum transportation around the outer AB than the \cm gas. The \hm gas can give global multiple \cite[popular as shock solution][]{c89} or single sonic point solutions and the \cm can give smooth global solution \cite[popular as ADAF][]{ny94} or two sonic point solutions. These solutions also represented on a plane of energy and angular momentum ($\be-L_0$) parameter space. Theoretically for the first time, we explored the relation between the nature of accretion solutions with the nature of initial accreting gas at the AB with detail computational and possible physical analysis. We also found that the surface density of the flow is highly affected with changing of the temperature at the AB, which can alter the radiative emissivities of the flow. The flow variables of various advective solutions also compared. On the basis of those results, we plotted some inner disk structures around the BHs. Doing so, we conjectured about the persistent/transient nature of spectral states, soft-excess and time scales of variabilities around the black hole $X-$ ray binaries (BXBs) and active galactic nuclei (AGNs).

In this letter, we note that the observed in the LIGO / Virgo experiment ratio of the detection rate of black holes to the rate of detection of binary neutron stars requires the assumption of a "conservative" collapse of massive stars into a black hole: almost all the mass of the collapsing star goes under the horizon. This is consistent with the large masses of black holes detected by LIGO/Virgo. On the other hand, the assumption of a small loss of matter during the collapse into a black hole is in good agreement with the small eccentricity of Single-lined Binaries. At the same time, the absence of X-rays from most black holes in binary systems with blue stars is explained. We argue that three sets of LIGO / Virgo observations and data on the Single-lined Binary with a Candidate Black Hole Component confirm the scenario of the evolution of massive field binaries.

We present an improved framework for estimating the growth rate of large-scale structure, using measurements of the galaxy-velocity cross-correlation in configuration space. We consider standard estimators of the velocity auto-correlation function, $\psi_1$ and $\psi_2$, the two-point galaxy correlation function, $\xi_{gg}$, and introduce a new estimator of the galaxy-velocity cross-correlation function, $\psi_3$. By including pair counts measured from random catalogues of velocities and positions sampled from distributions characteristic of the true data, we find that the variance in the galaxy-velocity cross-correlation function is significantly reduced. Applying a covariance analysis and $\chi^2$ minimisation procedure to these statistics, we determine estimates and errors for the normalised growth rate $f\sigma_8$ and the parameter $\beta = f/b$, where $b$ is the galaxy bias factor. We test this framework on mock hemisphere datasets for redshift $z < 0.1$ with realistic velocity noise constructed from the L-PICOLA simulation code, and find that we are able to recover the fiducial value of $f\sigma_8$ from the joint combination of $\psi_1$ + $\psi_2$ + $\psi_3$ + $\xi_{gg}$, with 15\% accuracy from individual mocks. We also recover the fiducial $f\sigma_8$ to within 1$\sigma$ regardless of the combination of correlation statistics used. When we consider all four statistics together we find that the statistical uncertainty in our measurement of the growth rate is reduced by $59\%$ compared to the same analysis only considering $\psi_2$, by $53\%$ compared to the same analysis only considering $\psi_1$, and by $52\%$ compared to the same analysis jointly considering $\psi_1$ and $\psi_2$.

Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. Up to date, the detection in the ALMA data of a feature somehow compatible with the emission arising from a proto Pulsar Wind Nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33-years old issue by analyzing archived observations of SN87A performed Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the $10-20$ kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magneto-hydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is the PWN emission.

The transmission of Lyman-{\alpha} (Ly{\alpha}) in the spectra of distant quasars depends on the density, temperature, and ionization state of the intergalactic medium (IGM). Therefore, high-redshift (z > 5) Ly{\alpha} forests could be invaluable in studying the late stages of the epoch of reionization (EoR), as well as properties of the sources that drive it. Indeed, high-quality quasar spectra have now firmly established the existence of large-scale opacity fluctuations at z > 5, whose physical origins are still debated. Here we introduce a Bayesian framework capable of constraining the EoR and galaxy properties by forward-modelling the high-z Ly{\alpha} forest. Using priors from galaxy and CMB observations, we demonstrate that the final overlap stages of the EoR (when >95% of the volume was ionized) should occur at z < 5.6, in order to reproduce the large-scale opacity fluctuations seen in forest spectra. However, it is the combination of patchy reionization and the inhomogeneous UV background that produces the longest Gunn-Peterson troughs. Ly{\alpha} forest observations tighten existing constraints on the characteristic ionizing escape fraction of galaxies, with the combined observations suggesting f_{\rm esc} \approx 7^4_3%, and disfavoring a strong evolution with the galaxy's halo (or stellar) mass.

Recent high precision meteoritic data improve constraints on the formation timescale and bulk composition of the terrestrial planets. High resolution N-body simulations allow direct comparison of embryo growth timescale and accretion zones to these constraints. In this paper, we present results of high resolution simulations for embryo formation from a disc of up to 41,000 fully-self gravitating planetesimals with the GPU-based N-body code GENGA. Our results indicate that the growth of embryos are highly dependent on the initial conditions. More massive initial planetesimals, a shorter gas disc decay timescale and initially eccentric Jupiter and Saturn (EJS) all lead to faster growth of embryos. Asteroid belt material can thereby be implanted into the terrestrial planet region via sweeping secular resonances. This could possibly explain the rapid growth of Mars within 10 Myr inferred from its Hf-W chronology. The sweeping secular resonance almost completely clears the asteroid belt and deposits this material in the Mercury-Venus region, altering the composition of embryos there. This could result in embryos in the Mercury-Venus region accreting an unexpectedly high mass fraction from beyond 2 AU. Changing the initial orbits of Jupiter and Saturn to more circular (CJS) or assuming embryos formed in a gas free environment removes the sweeping secular resonance effect and thus greatly decreases material accreted from beyond 2 AU for Mercury-Venus region embryos. We therefore propose that rock samples from Mercury and Venus could aid greatly in deducing the condition and lifetime of the initial protoplanetary gas disc during planetesimal and embryo formation, as well as the initial architecture of the giant planets.

The INTEGRAL hard X-ray surveys have proven to be of fundamental importance. INTEGRAL has mapped the Galactic plane with its large field of view and excellent sensitivity. Such hard X-ray snapshots of the whole Milky Way on a time scale of a year are beyond the capabilities of past and current narrow-FOV grazing incidence X-ray telescopes. By expanding the INTEGRAL X-ray survey into shorter timescales, a productive search for transient X-ray emitters was made possible. In more than fifteen years of operation, the INTEGRAL observatory has given us a sharper view of the hard X-ray sky, and provided the triggers for many follow-up campaigns from radio frequencies to gamma-rays. In addition to conducting a census of hard X-ray sources across the entire sky, INTEGRAL has carried out, through Earth occultation maneuvers, unique observations of the large-scale cosmic X-ray background, which will without question be included in the annals of X-ray astronomy as one of the mission's most salient contribution to our understanding of the hard X-ray sky.

We present the first detailed case study using quadratic estimators (QE) to diagnose and remove systematics present in observed Cosmic Microwave Background (CMB) maps. In this work we focus on the temperature to polarization leakage. We use an iterative QE analysis to remove systematics, in analogy to de-lensing, recovering the primordial B-mode signal and the systematic maps. We introduce a new Gaussian filtering scheme crucial to stable convergence of the iterative cleaning procedure and validate with comparisons to semi-analytical forecasts. We study the limitations of this method, by examining its performance on idealized simulations and we apply this method on realistic simulations generated for a LiteBIRD like experiment, where we assume varying de-lensing efficiencies. Finally, we quantify the systematic cleaning efficiency by presenting a likelihood analysis on the tensor to scalar ratio, $r$, and demonstrate that the blind cleaning results in an un-biased measurement of $r$, reducing the systematic induced B-mode power by nearly two orders of magnitude.

We used data from the near-infrared VISTA survey of the Magellanic Cloud system (VMC) to measure proper motions (PMs) of stars within the Small Magellanic Cloud (SMC). The data analysed in this study comprise 26 VMC tiles, covering a total contiguous area on the sky of ~40 deg$^2$. Using multi-epoch observations in the Ks band over time baselines between 13 and 38 months, we calculated absolute PMs with respect to ~130,000 background galaxies. We selected a sample of ~2,160,000 likely SMC member stars to model the centre-of-mass motion of the galaxy. The results found for three different choices of the SMC centre are in good agreement with recent space-based measurements. Using the systemic motion of the SMC, we constructed spatially resolved residual PM maps and analysed for the first time the internal kinematics of the intermediate-age/old and young stellar populations separately. We found outward motions that point either towards a stretching of the galaxy or stripping of its outer regions. Stellar motions towards the North might be related to the "Counter Bridge" behind the SMC. The young populations show larger PMs in the region of the SMC Wing, towards the young Magellanic Bridge. In the older populations, we further detected a coordinated motion of stars away from the SMC in the direction of the Old Bridge as well as a stream towards the SMC.

Collisions electrically charge grains which promotes growth by coagulation. We present aggregation experiments with three large ensembles of basalt beads ($150\,\mu\mathrm{m} - 180\,\mu\mathrm{m})$, two of which are charged, while one remains almost neutral as control system. In microgravity experiments, free collisions within these samples are induced with moderate collision velocities ($0 - 0.2 \,\mathrm{m\,s}^{-1}$). In the control system, coagulation stops at (sub-)mm size while the charged grains continue to grow. A maximum agglomerate size of 5\,cm is reached, limited only by bead depletion in the free volume. For the first time, charge-driven growth well into the centimeter range is directly proven by experiments. In protoplanetary disks, this agglomerate size is well beyond the critical size needed for hydrodynamic particle concentration as, e.g., by the streaming instabilities.

The precision measurement of the primordial helium abundance $Y_p$ is a powerful probe of the early Universe. The most common way to determine $Y_p$ is analyses of observations of metal-poor \HII regions found in blue compact dwarf galaxies. We present the spectroscopic sample of 100 \HII regions collected from the Sloan Digital Sky Survey. The final analysed sample consists of our sample and HeBCD database from Izotov et al. 2007. We use a self-consistent procedure to determine physical conditions, current helium abundances, and metallicities of the \HII regions. From a regression to zero metallicity, we have obtained $Y_p = 0.2462 \pm 0.0022$ which is one of the most stringent constraints obtained with such methods up to date and is in a good agreement with the Planck result $Y_{\rm p}^{\it {Planck}} = 0.2471 \pm 0.0003$. Using the determined value of $Y_p$ and the primordial deuterium abundance taken from Particle Data Group (Zyla et al. 2020) we put a constraint on the effective number of neutrino species $N_{\rm eff} = 2.95 \pm 0.16$ which is consistent with the Planck one $N_{\rm eff} = 2.99 \pm 0.17$. Further increase of statistics potentially allows us to achieve Planck accuracy, which in turn will become a powerful tool for studying the self-consistency of the Standard Cosmological Model and/or physics beyond.

Extreme Mass Ratio Inspirals (EMRIs) are important sources for space-borne gravitational wave detectors, such as LISA (Laser Interferometer Space Antenna). Previous EMRI rate studies have focused on the "loss cone" scenario, where stellar-mass black holes (sBHs) are scattered into highly eccentric orbits near the central massive black hole (MBH) via multi-body interaction. In this work, we calculate the rate of EMRIs of an alternative formation channel: EMRI formation assisted by the accretion flow around accreting massive black holes. In this scenario, sBHs and stars on inclined orbits are captured by the accretion disk, and then subsequently migrate towards the MBH, under the influence of density wave generation and head wind. By solving the Fokker-Planck equation incorporating both sBH-sBH/sBH-star scatterings and sBH/star-disk interactions, we find that an accretion disk usually boosts the EMRI formation rate per individual MBH by $\mathcal O(10^1-10^3)$ compared with the canonical "loss cone" formation channel. Taking into account that the fraction of active galactic nucleus (AGNs) is $\sim \mathcal O(10^{-2}-10^{-1})$, where the MBHs are expected to be rapidly accreting, we expect EMRI formation assisted by AGN disks to be an important channel for all EMRIs observed by LISA. These two channels also predict distinct distributions of EMRI eccentricities and orbit inclinations, which can be tested by future gravitational wave observations.

The earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. One group of young stellar objects, the FU Orionis-type stars exhibit accretion rate peaks accompanied by bright eruptions. The occurrence of these outbursts might solve the luminosity problem of protostars, play a key role in accumulating the final star mass, and have a significant effect on the parameters of the envelope and the disk. In the framework of the Structured Accretion Disks ERC project, we are conducting a systematic investigation of these sources with millimeter interferometry to examine whether they represent normal young stars in exceptional times or they are unusual objects. Our results show that FU Orionis-type stars can be similar to both Class I and Class II systems and may be in a special evolutionary phase between the two classes with their infall-driven episodic eruptions being the main driving force of the transition.

We conducted global hydrodynamic simulations of protoplanetary disk evolution with an adaptive Shakura-Sunyaev {\alpha} prescription to represent the layered disk structure, and starting with the collapse phase of the molecular cloud. With the canonical values of model parameters, self-consistent dead zones formed at the scale of a few au. The instabilities associated with the dead zone and corresponding outbursts, similar to FUor eruptions, were also observed in the simulations.

Comets and small planetesimals are believed to contain primordial building blocks in the form of millimeter to centimeter sized pebbles. One of the viable growing mechanisms to form these small bodies is through the streaming instability (SI) in which pebbles cluster and gravitationally collapse towards a planetesimal or comet in the presence of gas drag. However, most SI simulations are global and lack the resolution to follow the final collapse stage of a pebble cloud within its Hill radius. We aim to track the collapse of a gravitationally bound pebble cloud subject to mutual collisions and gas drag with the representative particle approach. We determine the radial pebble size distribution of the collapsed core and the impact of mutual pebble collisions on the pebble size distribution. We find that virial equilibrium is never reached during the cloud evolution and that, in general, pebbles with given Stokes number (St) collapse towards an optically thick core in a sequence from aerodynamically largest to aerodynamically smallest. We show that at the location for which the core becomes optically thick, the terminal velocity is well below the fragmentation threshold velocity. While collisional processing is negligible during cloud evolution, the collisions that do occur are sticking. These results support the observations that comets and small planetary bodies are composed of primordial pebbles in the milimeter to centimeter size range

The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet imager and spectrograph instrument concept for tracking coronal mass ejections through the region where they experience the majority of their acceleration: the difficult-to-observe middle corona. It contains a wide field of view (0-4~\Rs) imager and a 1~\AA\ spectral-resolution-irradiance spectrograph spanning 170-340~\AA. It leverages new detector technology to read out different areas of the detector with different integration times, resulting in what we call "simultaneous high dynamic range", as opposed to the traditional high dynamic range camera technique of subsequent full-frame images that are then combined in post-processing. This allows us to image the bright solar disk with short integration time, the middle corona with a long integration time, and the spectra with their own, independent integration time. Thus, SunCET does not require the use of an opaque or filtered occulter. SunCET is also compact -- $\sim$15 $\times$ 15 $\times$ 10~cm in volume -- making it an ideal instrument for a CubeSat or a small, complementary addition to a larger mission. Indeed, SunCET is presently in a NASA-funded, competitive Phase A as a CubeSat and has also been proposed to NASA as an instrument onboard a 184 kg Mission of Opportunity.

The Transiting Exoplanet Survey Satellite (TESS) has now been operational for a little over two years, covering the Northern and the Southern hemispheres once. The TESS team processes the downlinked data using the Science Processing Operations Center pipeline and Quick Look pipeline to generate alerts for follow-up. Combined with other efforts from the community, over two thousand planet candidates have been found of which tens have been confirmed as planets. We present our pipeline, Nigraha, that is complementary to these approaches. Nigraha uses a combination of transit finding, supervised machine learning, and detailed vetting to identify with high confidence a few planet candidates that were missed by prior searches. In particular, we identify high signal to noise ratio (SNR) shallow transits that may represent more Earth-like planets. In the spirit of open data exploration we provide details of our pipeline, release our supervised machine learning model and code as open source, and make public the 38 candidates we have found in seven sectors. The model can easily be run on other sectors as is. As part of future work we outline ways to increase the yield by strengthening some of the steps where we have been conservative and discarded objects for lack of a datum or two.

We investigate the impact on cosmological observables of $f(Q)$-gravity, a specific class of modified gravity models in which gravity is described by the non-metricity scalar, $Q$. In particular we focus on a specific model which is indistinguishable from the $\Lambda$-cold-dark-matter ($\Lambda$CDM) model at the background level, while showing peculiar and measurable signatures at linear perturbation level. These are attributed to a time-dependent Planck mass and are regulated by a single dimensionless parameter, $\alpha$. In comparison to the $\Lambda$CDM model, we find for positive values of $\alpha$ a suppressed matter power spectrum and lensing effect on the Cosmic Microwave Background radiation (CMB) angular power spectrum and an enhanced integrated-Sachs-Wolfe tail of CMB temperature anisotropies. The opposite behaviors are present when the $\alpha$ parameter is negative. We also investigate the modified Gravitational Waves (GWs) propagation and show the prediction of the GWs luminosity distance compared to the standard electromagnetic one. Finally, we infer the accuracy on the free parameter of the model with standard sirens at future GWs detectors.

We study the timing properties of XTE J1858+034 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and Burst Alert Telescope onboard Swift during the outburst in October--November 2019. We have investigated for Quasi-Periodic Oscillation (QPO) during the outburst and detected a low-frequency QPO at $\sim$196 mHz with $\sim$6% RMS variability from the NuSTAR observation. The QPO is fitted and explained with the model - power law and a Lorentzian component. We have also studied the variation of QPO frequency with energy. The beat frequency model and Keplerian frequency model both are suitable to explain the origin of the QPOs for the source. Regular pulsations and QPOs are found to be stronger in high energy which suits the beat frequency model. The variation of the hardness ratio is studied over the outburst which does not show any significant variation.

Particle acceleration and heating at mildly relativistic magnetized shocks in electron-ion plasma are investigated with unprecedentedly high-resolution two-dimensional particle-in-cell simulations that include ion-scale shock rippling. Electrons are super-adiabatically heated at the shock, and most of the energy transfer from protons to electrons takes place at or downstream of the shock. We are the first to demonstrate that shock rippling is crucial for the energization of electrons at the shock. They remain well below equipartition with the protons. The downstream electron spectra are approximately thermal with a limited supra-thermal power-law component. Our results are discussed in the context of wakefield acceleration and the modelling of electromagnetic radiation from blazar cores.

We study the evolutionary and physical properties of evolved O stars in the Small Magellanic Cloud (SMC), with a special focus on their surface abundances to investigate the efficiency of rotational mixing as a function of age, rotation and global metallicity. We analyse the UV + optical spectra of thirteen SMC O-type giants and supergiants, using the stellar atmosphere code CMFGEN to derive photospheric and wind properties. We compare the inferred properties to theoretical predictions from evolution models. For a more comprehensive analysis, we interpret the results together with those we obtained for O-type dwarfs in a former study. Most dwarfs lie in the early phases of the main-sequence. For a given initial mass, giants are further along the evolutionary tracks, confirming that they are more evolved than dwarfs. Supergiants have larger initial masses and are located past the terminal age main-sequence. We find no clear trend of a mass discrepancy, independent of the diagram used to estimate the evolutionary mass. CNO abundances are consistent with nucleosynthesis from the CNO cycle. Comparisons to theoretical predictions reveal the importance of the initial mixture for reproducing the observed trends in the N/C versus N/O diagram. A trend for stronger chemical evolution for more evolved objects is observed. More massive stars, are on average, more chemically enriched at a given evolutionary phase, qualitatively consistent with evolutionary models. Abundance ratios supports the theoretical prediction that massive stars at low metallicity are more chemically processed than their Galactic counterparts. Finally, models including rotation generally reproduce both the surface abundances and rotation rates, provided different initial rotational velocities are considered. Nevertheless, there are objects for which a stronger braking and/or more efficient mixing is required.

The mechanism of thermal driving for launching accretion disk winds is interconnected with classical thermal instability (TI). Indeed, the effective scale height of irradiated accretion disk atmospheres is determined by the extent of the cold branch of the S-curve demarcating thermally unstable zones. In a recent paper, we demonstrated that as a result of this interconnectedness, radial wind solutions of X-ray heated flows are prone to becoming clumpy. In over two decades of numerical work, however, only smooth thermally driven disk wind solutions that approach a steady state have been found. In this paper, we show that the Bernoulli function determines whether or not the entropy mode can grow due to TI in dynamical flows. Based on this finding, we identify a critical radius, $R_{\rm u}$, beyond which TI should accompany thermal driving, resulting in clumpy disk wind solutions. Our numerical simulations reveal that clumpiness is a consequence of buoyancy disrupting the stratified structure of smooth solutions. Namely, instead of a thin transition layer separating the highly ionized disk wind from the cold phase atmosphere below, TI seeds the formation of hot spots below the transition layer that rise up, fragmenting the atmosphere. This results in the continual production of characteristic cold phase structures that we refer to as irradiated atmospheric fragments (IAFs). These IAFs resemble tsunamis upon interacting with the disk wind, as crests develop as they are advected outwards. The multiphase character of these solutions results from the subsequent disintegration of the IAFs, which takes place within a turbulent wake that reaches high enough elevations in the wind so as to be observable from sightlines as high as $45^{\degree}$. We discuss the properties of the AMD in detail, showing that dips in the AMD are not expected within TI zones.

It has been recently claimed that primordial magnetic fields could relieve the cosmological Hubble tension. We consider the impact of such fields on the formation of the first cosmological objects, mini-halos forming stars, for present-day field strengths in the range of $2\times 10^{-12}$ - $2\times 10^{-10}$ G. These values correspond to initial ratios of Alv\'en velocity to the speed of sound of $v_a/c_s\approx 0.03 - 3$. We find that when $v_a/c_s\ll 1$, the effects are modest. However, when $v_a\sim c_s$, the starting time of the gravitational collapse is delayed and the duration extended as much as by $\Delta$z = 2.5 in redshift. When $v_a > c_s$, the collapse is completely suppressed and the mini-halos continue to grow and are unlikely to collapse until reaching the atomic cooling limit. Employing current observational limits on primordial magnetic fields we conclude that inflationary produced primordial magnetic fields could have a significant impact on first star formation, whereas post-inflationary produced fields do not.

The Planck mass and the cosmological constant determine the minimum and the maximum distances in the physical universe. A relativistic theory that takes into account a fundamental distance limit $\ell$ on par with the fundamental speed limit $c$, is based on the de Sitter extension of the Lorentz symmetry. This article proposes a new de Sitter gauge theory of gravity which allows the consistent cosmological evolution of the $\ell$. The theory is locally equivalent to Dirac's scale-invariant version of general relativity, and suggests a novel non-singular extension of cosmology.

The physical and mathematical properties of the non-linearly coupled black-hole-orbiting-ring system are studied analytically to second order in the dimensionless angular velocity $M_{\text{ir}}\omega_{\text{H}}$ of the black-hole horizon (here $M_{\text{ir}}$ is the irreducible mass of the slowly rotating central black hole). In particular, we determine analytically, to first order in the dimensionless ring-to-black-hole mass ratio $m/M_{\text{ir}}$, the shift $\Delta\Omega_{\text{mb}}/\Omega_{\text{mb}}$ in the orbital frequency of the {\it marginally bound} circular geodesic that characterizes the composed curved spacetime. Interestingly, our analytical results for the frequency shift $\Delta\Omega_{\text{mb}}$ in the composed black-hole-orbiting-ring toy model agree qualitatively with the recently published numerical results for the corresponding frequency shift in the physically related (and mathematically much more complex) black-hole-orbiting-particle system. In particular, the present analysis provides evidence that, at order $O(m/M_{\text{ir}})$, the recently observed positive shift in the angular frequency of the marginally bound circular orbit is directly related to the physically intriguing phenomenon of dragging of inertial frames by orbiting masses in general relativity.

We review the calculation of the solar axion flux from axion-photon and axion-electron interactions and survey the available solar models and opacity codes. We develop a publicly available C++/Python code to quantify the associated systematic differences and statistical fluctuations. The number of axions emitted in helioseismological solar models is systematically larger by about 5% compared to photospheric models, while the overall statistical uncertainties in solar models are typically at the percent level in both helioseismological and photospheric models. However, for specific energies, the statistical fluctuations can reach up to about 5% as well. Taking these uncertainties into account, we investigate the ability of the upcoming helioscope IAXO to discriminate KSVZ axion models. Such a discrimination is possible for a number of models, and a discovery of KSVZ axions with high $E/N$ ratios could potentially help to solve the solar abundance problem. We discuss limitations of the axion emission calculations and identify potential improvements, which would help to determine axion model parameters more accurately.

Ghost-free bimetric theory describes two nonlinearly interacting spin-2 fields, one massive and one massless, thus extending general relativity. We confront bimetric theory with observations of Supernovae type 1a, Baryon Acoustic Oscillations and the Cosmic Microwave Background in a statistical analysis, utilising the recently proposed physical parametrisation. This directly constrains the physical parameters of the theory, such as the mass of the spin-2 field and its coupling to matter. We find that all models under consideration are in agreement with the data. Next, we compare these results to bounds from local tests of gravity. Our analysis reveals that all two- and three-parameter models are observationally consistent with both cosmological and local tests of gravity. The minimal bimetric model (only $\beta_1$) is ruled out by our combined analysis.

Ghost-free bimetric gravity is an extension of general relativity, featuring a massive spin-2 field coupled to gravity. We parameterize the theory with a set of observables having specific physical interpretations. For the background cosmology and the static, spherically symmetric solutions (for example approximating the gravitational potential of the solar system), there are four directions in the parameter space in which general relativity is approached. Requiring that there is a working screening mechanism and a nonsingular evolution of the Universe, we place analytical constraints on the parameter space which rule out many of the models studied in the literature. Cosmological solutions where the accelerated expansion of the Universe is explained by the dynamical interaction of the massive spin-2 field rather than by a cosmological constant, are still viable.

Ghost-free bimetric gravity is a theory of two interacting spin-2 fields, one massless and one massive, in addition to the standard matter particles and fields, thereby generalizing Einstein's theory of general relativity. To parameterize the theory, we use five observables with specific physical interpretations. We present, for the first time, observational constraints on these parameters that: (i) apply to the full theory, (ii) are consistent with a working screening mechanism (i.e., restoring general relativity locally), (iii) exhibit a continuous, real-valued background cosmology (without the Higuchi ghost). For the cosmological constraints, we use data sets from the cosmic microwave background, baryon acoustic oscillations, and type Ia supernovae. Bimetric cosmology provides a good fit to data even for large values of the mixing angle between the massless and massive gravitons. Interestingly, the best-fit model is a self-accelerating solution where the accelerated expansion is due to the dynamical massive spin-2 field, without a cosmological constant. Due to the screening mechanism, the models are consistent with local tests of gravity such as solar system tests and gravitational lensing by galaxies. We also comment on the possibility of alleviating the Hubble tension with this theory.

We study cosmological inflation and its dynamics in the framework of the Randall-Sundrum II brane model. In particular, we analyze in detail four representative small-field inflationary potentials, namely Natural inflation, Hilltop inflation, Higgs-like inflation, and Exponential SUSY inflation, each characterized by two mass scales. We constrain the parameters for which a viable inflationary Universe emerges using the latest PLANCK results. Furthermore, we investigate whether or not those models in brane cosmology are consistent with the recently proposed Swampland Criteria, and give predictions for the duration of reheating as well as for the reheating temperature after inflation. Our results show that (i) the distance conjecture is satisfied, (ii) the de Sitter conjecture and its refined version may be avoided, and (iii) the allowed range for the five-dimensional Planck mass, $M_5$, is found to be between $10^5~\textrm{TeV}$ and $10^{12}~\textrm{TeV}$. Our main findings indicate that non-thermal leptogenesis cannot work within the framework of RS-II brane cosmology, at least for the inflationary potentials considered here.

We review the effective field theory associated to the superfluid phonons that we use for the study of transport properties of superfluid neutrons stars in their low temperature regime. We then discuss the shear and bulk viscosities together with the thermal conductivity coming from the collisions of superfluid phonons in neutron stars. With regards to shear, bulk and thermal transport coefficients, the phonon collisional processes are obtained in terms of the equation of state and the superfluid gap. We compare the shear coefficient due to the interaction among superfluid phonons with other dominant processes in neutron stars, such as electron collisions. We also analyze the possible consequences for the r-mode instability in neutron stars. As for the bulk viscosities, we determine that phonon collisions contribute decisively to the bulk viscosities inside neutron stars. For the thermal conductivity resulting from phonon collisions, we find that it is temperature-independent well below the transition temperature. We also obtain that the thermal conductivity due to superfluid phonons dominates over the one resulting from electron-muon interactions once phonons are in the hydrodynamic regime. As the phonons couple to the Z electroweak gauge boson, we estimate the associated neutrino emissivity. We also briefly comment on how the superfluid phonon interactions are modified in the presence of a gravitational field, or in a moving background.

The absolute electron capture cross sections for single and double charge exchanges between the highly charged ions O6+ and CO2, CH4, H2, N2, the dominant collision processes in the solar wind, have been measured in the energy from 7 keV*q (2.63 keV/u) to 52 keV*q (19.5 keV/u). These measurements were carried out in the new experimental instrument set up at Fudan University, and the error of cross sections for single and double charge exchanges at the 1{\sigma} confidence level are about 11% and 16%, respectively. Limited agreement is achieved with single electron capture results calculated by the classical over-barrier model. These cross sections data are useful for simulation ion-neutral processes in astrophysical environments and to improve the present theoretical model of fundamental atomic processes.

Accurate atomic data are essential for opacity calculations and for abundance analyses of the Sun and other stars. The aim of this work is to provide accurate and extensive results of energy levels and transition data for C I - IV. The Multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods were used in the present work. To improve the quality of the wave functions and reduce the relative differences between length and velocity forms for transition data involving high Rydberg states, alternative computational strategies were employed by imposing restrictions on the electron substitutions when constructing the orbital basis for each atom and ion. Transition data, e.g., weighted oscillator strengths and transition probabilities, are given for radiative electric dipole (E1) transitions involving levels up to 1s$^2$2s$^2$2p6s for C I, up to 1s$^2$2s$^2$7f for C II, up to 1s$^2$2s7f for C III, and up to 1s$^2$8g for CIV. Using the difference between the transition rates in length and velocity gauges as an internal validation, the average uncertainties of all presented E1 transitions are estimated to be 8.05%, 7.20%, 1.77%, and 0.28%, respectively, for C I - IV. Extensive comparisons with available experimental and theoretical results are performed and good agreement is observed for most of the transitions. In addition, the C I data were employed in a reanalysis of the solar carbon abundance. The new transition data give a line-by-line dispersion similar to the one obtained when using transition data that are typically used in stellar spectroscopic applications today.

We study the viability conditions for the absence of ghost, gradient and tachyonic instabilities, in scalar-torsion $f(T,\phi)$ gravity theories in presence of a general barotropic perfect fluid. To describe the matter sector, we use the Sorkin-Schutz action and, then, we calculate the second order action for scalar perturbations. For the study of ghost and gradient instabilities, we have shown that the gravity sector keeps decoupled from the matter sector, applying in this way the viability conditions for each one separately. Particularly, we verified that this theory is free from ghost and gradient instabilities, obtaining the standard results for matter, and for the gravity sector we checked that the speed of propagation satisfies $c_{s,g}^2=1$. On the other hand, in the case of tachyonic instability, we obtained the general expressions for the mass eigenvalues and then we evaluated them in the scaling matter fixed points of a concrete model of dark energy. Thus, we found a space of parameters where it is possible to have a stable configuration respecting the constraints from CMB measurements and the BBN constraints for early dark energy. Finally, we have numerically corroborated these results by solving the cosmological equations for a realistic cosmological evolution with phase space trajectories undergoing scaling matter regimes, and then showing that the system present a stable configuration throughout cosmic evolution.

While the front of a fluid shock is a few mean-free-paths thick, the front of a collisionless shock can be orders of magnitude thinner. By bridging between a collisional and a collisionless formalism, we assess the transition between these two regimes. We consider non-relativistic, un-magnetized, planar shocks in electron/ion plasmas. In addition, our treatment of the collisionless regime is restricted to high Mach number electrostatic shocks. We find that the transition can be parameterized by the upstream plasma parameter $\Lambda$ which measures the coupling of the upstream medium. For $\Lambda \lesssim 1.12$, the upstream is collisional, i.e. strongly coupled, and the strong shock front is about $\mathcal{M}_1 \lambda_{\mathrm{mfp},1}$ thick, where $\lambda_{\mathrm{mfp},1}$ and $\mathcal{M}_1 $ are the upstream mean-free-path and Mach number respectively. A transition occurs for $\Lambda \sim 1.12$ beyond which the front is $\sim \mathcal{M}_1\lambda_{\mathrm{mfp},1}\ln \Lambda/\Lambda$ thick for $\Lambda\gtrsim 1.12$. Considering $\Lambda$ can reach billions in astrophysical settings, this allows to understand how the front of a collisionless shock can be orders of magnitude smaller than the mean-free-path, and how physics transitions continuously between these 2 extremes.

Recent observations made with Advanced LIGO and Advanced Virgo have initiated the era of gravitational-wave astronomy. The number of events detected by these "2nd Generation" (2G) ground-based observatories is partially limited by noise arising from temperature-induced position fluctuations of the test mass mirror surfaces used for probing space time dynamics. The design of next-generation gravitational-wave observatories addresses this limitation by using cryogenically cooled test masses; current approaches for continuously removing heat (resulting from absorbed laser light) rely on heat extraction via black-body radiation or conduction through suspension fibers. As a complementing approach, we investigate cooling via helium gas impinging on the test mass in free molecular flow. We present analytical models for cooling power and related displacement noise, validated by comparison to numerical simulations. Applying this theoretical framework with regard to the conceptual design of the Einstein Telescope (ET), we find a cooling power of 10 mW at 18 K for a gas pressure that increases the ET design strain noise goal by at most a factor of $\sim 3$ in a 8 Hz wide frequency band centered at 7 Hz. A cooling power of 100 mW at 18 K corresponds to a gas pressure that increases the ET design strain noise goal by at most a factor of $\sim 11$ in a 26 Hz wide frequency band centered at 7 Hz.

The extension of the Standard Model with two gauge-singlet Majorana fermions can simultaneously explain two beyond-the-Standard-model phenomena: neutrino masses and oscillations, as well as the origin of the matter-antimatter asymmetry in the Universe. The parameters of such a model are constrained by the neutrino oscillation data, direct accelerator searches, big bang nucleosynthesis, and requirement of successful baryogenesis. We show that the combination of all these constraints still leaves an allowed region in the parameter space below the kaon mass. This region can be probed by the further searches of NA62, DUNE, or SHiP experiments.