Papers for Tuesday, Mar 02 2021

Dust grains play a major role in many astrophysical contexts. They influence the chemical, magnetic, dynamical and optical properties of their environment, from galaxies down to the interstellar medium, star-forming regions, and protoplanetary disks. Their coagulation leads to shifts in their size distribution and ultimately to the formation of planets. However, although the coagulation process is reasonably uncomplicated to implement numerically by itself, it is difficult to couple it with multi-dimensional hydrodynamics numerical simulations because of its high computational cost. We propose here a simple method to track the coagulation of grains at far lower cost. Given an initial grain size distribution, the state of the distribution at time t is solely determined by the value of a single variable integrated along the trajectory, independently of the specific path taken by the grains. Although this method cannot account for other processes than coagulation, it is mathematically exact, fast, inexpensive, and can be used to evaluate the impact of grain coagulation in most astrophysical contexts. Although other processes modifying the size-distribution, as fragmentation cannot be coupled to this method, it is applicable to all coagulation kernels in which local physical conditions and grain properties can be separated. We also describe another method to calculate the average electric charge of grains and the density of ions and electrons in environments shielded from radiation fields, given the density and temperature of the gas, the cosmic-ray ionization rate and the average mass of the ions. The equations we provide are fast to integrate numerically, and can be used in multidimensional numerical simulations to self-consistently calculate, on-the-fly, the local resistivities needed to model non-ideal magnetohydrodynamics.

Powerful new, high resolution, high sensitivity, multi-frequency, wide-field radio surveys such as the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) are emerging. They will offer fresh opportunities to undertake new determinations of useful parameters for various kinds of extended astrophysical phenomena. Here, we consider specific application to angular size determinations of Planetary Nebulae (PNe) via a new radio continuum Spectral Energy Distribution (SED) fitting technique. We show that robust determinations of angular size can be obtained, comparable to the best optical and radio observations but with the potential for consistent application across the population. This includes unresolved and/or heavily obscured PNe that are extremely faint or even non-detectable in the optical.

The field of exoplanet atmospheric characterization is trending towards comparative studies involving many planets, and using hierarchical modelling is a natural next step. Here we demonstrate two use cases. We first use hierarchical modelling to quantify variability in repeated observations, by reanalyzing a suite of ten Spitzer secondary eclipse observations of the hot Jupiter XO-3b. We compare three models: one where we fit ten separate eclipse depths, one where we use a single eclipse depth for all ten observations, and a hierarchical model. By comparing the Widely Applicable Information Criterion (WAIC) of each model, we show that the hierarchical model is preferred over the others. The hierarchical model yields less scatter across the suite of eclipse depths, and higher precision on the individual eclipse depths, than does fitting the observations separately. We do not detect appreciable variability in the secondary eclipses of XO-3b, in line with other analyses. Finally, we fit the suite of published dayside brightness measurements from Garhart (2020) using a hierarchical model. The hierarchical model gives tighter constraints on the individual brightness temperatures and is a better predictive model, according to the WAIC. Notably, we do not detect the increasing trend in brightness temperature ratios versus stellar irradiation reported by Garhart (2020) and Baxter (2020). Although we tested hierarchical modelling on Spitzer eclipse data of hot Jupiters, it is applicable to observations of smaller planets like hot neptunes and super earths, as well as for photometric and spectroscopic transit or phase curve observations.

We present a spectroscopic and imaging study of an abnormal active galactic nucleus (AGN), 2MASX J00423991+3017515. This AGN is newly identified in the hard X-rays by the Swift BAT All-Sky survey and found in an edge-on disk galaxy interacting with a nearby companion. Here, we analyze the first optical spectra obtained for this system (taken in 2011 and 2016), high-resolution imaging taken with the Hubble Space Telescope and Chandra X-ray Observatory, and 1" imaging with the Very Large Array. Two unique properties are revealed: the peaks of the broad Balmer emission lines (associated with gas orbiting very near the supermassive black hole) are blue shifted from the corresponding narrow line emission and host galaxy absorption by 1540 km/s, and the AGN is spatially displaced from the apparent center of its host galaxy by 3.8 kpc. We explore several scenarios to explain these features, along with other anomalies, and propose that 2MASX J00423991+3017515 may be an AGN with an unusually strong wind residing in a uniquely configured major merger, or that it is an AGN recoiling from either a gravitational "slingshot" in a three-body interaction or from a kick due to the asymmetric emission of gravitational waves following the coalescence of two progenitor supermassive black holes.

We present the first results from the Quasar Feedback Survey, a sample of 42 z<0.2, [O III] luminous AGN (L[O III]>10^42.1 ergs/s) with moderate radio luminosities (i.e. L(1.4GHz)>10^23.4 W/Hz; median L(1.4GHz)=5.9x10^23 W/Hz). Using high spatial resolution (~0.3-1 arcsec), 1.5-6 GHz radio images from the Very Large Array, we find that 67 percent of the sample have spatially extended radio features, on ~1-60 kpc scales. The radio sizes and morphologies suggest that these may be lower radio luminosity versions of compact, radio-loud AGN. By combining the radio-to-infrared excess parameter, spectral index, radio morphology and brightness temperature, we find radio emission in at least 57 percent of the sample that is associated with AGN-related processes (e.g. jets, quasar-driven winds or coronal emission). This is despite only 9.5-21 percent being classified as radio-loud using traditional criteria. The origin of the radio emission in the remainder of the sample is unclear. We find that both the established anti-correlation between radio size and the width of the [O III] line, and the known trend for the most [O III] luminous AGN to be associated with spatially-extended radio emission, also hold for our sample of moderate radio luminosity quasars. These observations add to the growing evidence of a connection between the radio emission and ionised gas in quasar host galaxies. This work lays the foundation for deeper investigations into the drivers and impact of feedback in this unique sample.

A new technique to detect protoplanets is by observing the kinematics of the surrounding gas. Gravitational perturbations from a planet produce peculiar `kinks' in channel maps of different gas species. In this paper, we show that such kinks can be reproduced using semi-analytic models for the velocity perturbation induced by a planet. In doing so we i) confirm that the observed kinks are caused by the planet-induced wake; ii) show how to quantify the planet mass from the kink amplitude; in particular, we show that the kink amplitude scales with the square root of the planet mass for channels far from the planet velocity, steepening to linear as the channels approach the planet; iii) show how to extend the theory to include the effect of damping, which may be needed in order to have localized kinks.

Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced to $\lesssim 0.1$ pc by other mechanisms. Here, we explore a gravitational self-lensing binary SMBH model for the sharp (duration $\sim 1$ hr), quasi-regular X-ray flares -- dubbed quasi-periodic eruptions -- recently observed from two low mass active galactic nuclei: GSN 069 and RX J1301.9+2747. In our model, the binary is observed $\sim$edge-on, such that each SMBH gravitationally lenses light from the accretion disc surrounding the other SMBH twice per orbital period. The model can reproduce the flare spacings if the current eccentricity of RX J1301.9+2747 is $\epsilon_0 \gtrsim 0.16$, implying a merger within $\sim 1000$ yrs. However, we cannot reproduce the observed flare profiles with our current calculations. Model flares with the correct amplitude are $\sim 2/5$ the observed duration, and model flares with the correct duration are $\sim 2/5$ the observed amplitude. Our modelling yields three distinct behaviours of self-lensing binary systems that can be searched for in current and future X-ray and optical time-domain surveys: i) periodic lensing flares, ii) partial eclipses (caused by occultation of the background mini-disc by the foreground mini-disc), and iii) partial eclipses with a very sharp in-eclipse lensing flare. Discovery of such features would constitute very strong evidence for the presence of a supermassive binary, and monitoring of the flare spacings will provide a measurement of periastron precession.

We study the formation of over 6000 compact groups (CGs) of galaxies identified in mock redshift-space galaxy catalogues built from semi-analytical models of galaxy formation (SAMs) run on the Millennium Simulations. We select CGs of 4 members in our mock SDSS galaxy catalogues and, for each CG, we trace back in time the real-space positions of the most massive progenitors of their 4 galaxies. By analysing the evolution of the distance of the galaxy members to the centre of mass of the group, we identify 4 channels of CG formation. The classification of these assembly channels is performed with an automatic recipe inferred from a preliminary visual inspection and based on the orbit of the galaxy with the fewest number of orbits. Most CGs show late assembly, with the last galaxy arriving on its first or second passage, while only 10-20 per cent form by the gradual contraction of their orbits by dynamical friction, and only a few per cent forming early with little subsequent contraction. However, a SAM from a higher resolution simulation leads to earlier assembly. Assembly histories of CGs also depend on cosmological parameters. At similar resolution, CGs assemble later in SAMs built on parent cosmological simulations of high density parameter. Several observed properties of mock CGs correlate with their assembly history: early-assembling CGs are smaller, with shorter crossing times, and greater magnitude gaps between their brightest two members, and their brightest galaxies have smaller spatial offsets and are more passive.

HW Vir is a short-period binary that presents eclipse timing variations. Circumbinary planets have been proposed as a possible explanation, although the properties of the planets differ in each new study. Our aim is to perform robust model selection methods for eclipse timing variations (ETV) and error calculation techniques based on a frequentist approach for the case of the HW Vir system. We initially performed simultaneous light and radial velocity curve analysis to derive the masses of the binary. We then analyzed the eclipse timing variation of the system by fitting multiple models. To select the best model, we searched the confidence levels for the best model by creating an $\chi^2$ surface grid and bootstrap methods for each pair of parameters. We searched for stable orbital configurations for our adopted ETV model. The masses of the binary are found as 0.413 $\pm$ 0.008 $M_\odot$ and 0.128 $\pm$ 0.004 $M_\odot$. Under the assumption of two light time effects superimposed on a secular change, the minimum masses of the circumbinary objects are calculated as $25.0_{-2.2}^{+3.5} \ M_{Jup}$ and $13.9_{-0.45}^{+0.60}\ M_{Jup}$. The projected semi-major axes are found to be $7.8_{-1.0}^{+1.4}\ au$ and $4.56_{-0.22}^{+0.27}\ au$ in respective order. We find that this configuration is unstable within a 3$\sigma$ range on the semi-major axis and eccentricity of the outer circumbinary object.

Recently, GRAVITY onboard the Very Large Telescope Interferometer (VLTI) first spatially resolved the structure of the quasar 3C 273 with an unprecedented resolution of $\sim 10\mu$as. A new method of measuring parallax distances has been successfully applied to the quasar through joint analysis of spectroastrometry (SA) and reverberation mapping (RM) observation of its broad line region (BLR). The uncertainty of this SA and RM (SARM) measurement is about $16\%$ from real data, showing its great potential as a powerful tool for precision cosmology. In this paper, we carry out detailed analyses of mock data to study impacts of data qualities of SA observations on distance measurements and establish a quantitative relationship between statistical uncertainties of distances and relative errors of differential phases. We employ a circular disk model of BLR for the SARM analysis. We show that SARM analyses of observations generally generate reliable quasar distances, even for relatively poor SA measurements with error bars of $40\%$ at peaks of phases. Inclinations and opening angles of BLRs are the major parameters governing distance uncertainties. It is found that BLRs with inclinations $\gtrsim 10^{\circ}$ and opening angles $\lesssim 40^{\circ}$ are the most reliable regimes from SARM analysis for distance measurements. Through analysis of a mock sample of AGNs generated by quasar luminosity functions, we find that if the GRAVITY/GRAVITY+ can achieve a phase error of $0.1^{\circ}$ per baseline for targets with magnitudes $K \lesssim 11.5$, the SARM campaign can constrain $H_0$ to an uncertainty of $2\%$ by observing $60$ targets.

There are 88 stars which lack colours, but have measured parallaxes in \textit{Gaia} EDR3 that place them within 20\,pc from the sun. Among them we found two new common parallax and proper motion (CPPM) companions separated from their primaries by about 3\,arcsec. The CPPM companion of a nearby ($d=14.98$\,pc) F1 star, \object{HD 105452 B}, was already imaged with the \textit{Hubble Space Telescope} and is now confirmed with \textit{Gaia} data and photometrically classified by us as M4 dwarf. The other CPPM companion, \object{SCR J1214-2345 B} orbiting an M4.5 dwarf at $d=10.77$\,pc, represents the faintest brown dwarf discovery made by \textit{Gaia} so far. It was also imaged by the VISTA Hemisphere Survey and partly detected in the near-infrared. Our photometric classification led to an uncertain spectal type of T1$\pm$3 and needs to be confirmed by spectroscopic follow-up.

The Carina Nebula harbors a large population of high-mass stars, including at least 75 O-type and Wolf-Rayet stars, but the current census is not complete since further high-mass stars may be hidden in or behind the dense dark clouds that pervade the association. With the aim of identifying optically obscured O- and early B-type stars in the Carina Nebula, we performed the first infrared spectroscopic study of stars in the optically obscured stellar cluster Tr 16-SE, located behind a dark dust lane south of eta Car. We used the integral-field spectrograph KMOS at the ESO VLT to obtain H- and K-band spectra with a resolution of R sim 4000 (Delta lambda sim 5 A) for 45 out of the 47 possible OB candidate stars in Tr 16-SE, and we derived spectral types for these stars. We find 15 stars in Tr 16-SE with spectral types between O5 and B2 (i.e., high-mass stars with M >= 8 Msun, only two of which were known before. An additional nine stars are classified as (Ae)Be stars (i.e., intermediate-mass pre-main-sequence stars), and most of the remaining targets show clear signatures of being late-type stars and are thus most likely foreground stars or background giants unrelated to the Carina Nebula. Our estimates of the stellar luminosities suggest that nine of the 15 O- and early B-type stars are members of Tr 16-SE, whereas the other six seem to be background objects. Our study increases the number of spectroscopically identified high-mass stars (M >= 8 Msun) in Tr 16-SE from two to nine and shows that Tr 16-SE is one of the larger clusters in the Carina Nebula. Our identification of three new stars with spectral types between O5 and O7 and four new stars with spectral types O9 to B1 significantly increases the number of spectroscopically identified O-type stars in the Carina Nebula.

The low-mass low-surface brightness (LSB) disc galaxy Arakelian 18 (Ark 18) resides in the Eridanus void and because of its isolation represents an ideal case to study the formation and evolution mechanisms of such a galaxy type. Its complex structure consists of an extended blue LSB disc and a bright central elliptically-shaped part hosting a massive off-centered star-forming clump. We present the in-depth study of Ark 18 based on observations with the SCORPIO-2 long-slit spectrograph and a scanning Fabry-Perot interferometer at the Russian 6-m telescope complemented by archival multi-wavelength images and SDSS spectra. Ark 18 appears to be a dark matter dominated gas-rich galaxy without a radial metallicity gradient. The observed velocity field of the ionised gas is well described by two circularly rotating components moderately inclined with respect to each other and a possible warp in the outer disc. We estimated the age of young stellar population in the galaxy centre to be ~140 Myr, while the brightest star-forming clump appears to be much younger. We conclude that the LSB disc is likely the result of a dwarf-dwarf merger with a stellar mass ratio of the components at least ~5:1 that occurred earlier than 300 Myr ago. The brightest star forming clump was likely formed later by accretion of a gas cloud.

We present an analysis of the dispersed spectral data from 11 epochs (March 2011 to September 2018) of supernova remnant (SNR) 1987A observations performed with Chandra. These observations were performed with the High Energy Transmission Grating (HETG) as part of our ongoing Chandra monitoring campaign of SNR 1987A, whose 1st-order dispersed spectrum provides a significantly greater energy resolution than the previously-published 0th-order spectrum. Our data sets with moderate exposure times of ~50-70ks per epoch cover the time period between deep Chandra HETG observations (with individual exposures >200ks) taken in March 2011 and March 2018. These data have a much higher cadence than the widely-spaced deep high-resolution spectra, at the expense of total exposure time. While statistical uncertainties are large due to low photon count statistics in the observed 1st-order spectra, we find that spectral model parameters are generally in line with the shock wave propagating into the medium beyond the dense inner ring, as suggested by Frank et al. 2016. As the reverse shock begins ionizing the heavier elements of the supernova ejecta interior to the equatorial ring, spectral fit parameters are expected to change as the chemical makeup and physical properties of the shocked gas evolve. Based on our broadband spectral model fits, we find that abundance values appear to be constant in this time period. While our results are somewhat limited due to photon statistics, we demonstrate the utility of the dispersed HETG spectral analysis that can be performed with our regular Chandra monitoring observations of SNR 1987A.

To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalog are used in large part. The working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at a solar distance is $V_0=240\pm3$~km s$^{-1}$. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be $R_0=8.27\pm0.10$~kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at present time and in the past. So, the value of the wavelength $\lambda_{R,\theta}$ is in the range of [2.4--3.0] kpc, the pitch angle $i_{R,\theta}$ is in the range of [$-13^\circ$,$-10^\circ$] for a four-arm pattern model, the amplitudes of the radial and tangential perturbations are $f_R\sim12$~km s$^{-1}$ and $f_\theta\sim9$~km s$^{-1}$, respectively. Velocities of Cepheids older than 120 Myr are currently giving a wavelength $\lambda_{R,\theta}\sim5$~kpc. This value differs significantly from one that we obtained from the samples of young Cepheids. An analysis of positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength $\lambda_{R,\theta}=2.7$~kpc, amplitudes of radial and tangential perturbations are $f_R=7.9$~km s$^{-1}$ and $f_\theta=5$~km s$^{-1}$, respectively.

Magnetically arrested accretion flows are thought to fuel some of the supermassive black holes and to power their relativistic jets. We calculate and study a time sequence of linear and circular polarimetric images of numerical, high resolution and long duration simulations of magnetically dominated flows to investigate observational signatures of strong magnetic fields near the event horizon of a non-rotating black hole. We find that the magnitude of resolved linear and circular polarizations is very sensitive to the assumption of the coupling of electron and ions in the accretion flow. Models with cooler electrons have higher Faraday rotation and conversion depths which results in scrambled linear polarization and enhanced circular polarization. In those high Faraday thickness cases the circular polarization is particularly sensitive to dynamics of toroidal-radial magnetic fields in the accretion flows. We also find that the emission region produced by light which is lensed around the black hole shows inversion of circular polarization sign with respect to the sign of the circular polarization of the entire emission region. Such polarity inversions are unique to near horizon emission.

We have developed a method that maps large astronomical images onto a two-dimensional map and clusters them. A combination of various state-of-the-art machine learning (ML) algorithms is used to develop a fully unsupervised image quality assessment and clustering system. Our pipeline consists of a data pre-processing step where individual image objects are identified in a large astronomical image and converted to smaller pixel images. This data is then fed to a deep convolutional autoencoder jointly trained with a self-organizing map (SOM). This part can be used as a recommendation system. The resulting output is eventually mapped onto a two-dimensional grid using a second, deep, SOM. We use data taken from ground-based telescopes and, as a case study, compare the system's ability and performance with the results obtained by supervised methods presented by Teimoorinia et al. (2020). The availability of target labels in this data allowed a comprehensive performance comparison between our unsupervised and supervised methods. In addition to image-quality assessments performed in this project, our method can have various other applications. For example, it can help experts label images in a considerably shorter time with minimum human intervention. It can also be used as a content-based recommendation system capable of filtering images based on the desired content.

I discuss constraints on the power spectrum of primordial tensor perturbations from a combination of Cosmic Microwave Background (CMB) measurements and the gravitational wave direct detection experiments LIGO/Virgo and DECIGO. There are two main points: (1) Inflation predicts an approximately power-law form for the primordial tensor spectrum, but makes no prediction for its amplitude. Given that neither Planck nor LIGO/Virgo has actually detected primordial tensor modes, it is trivially true that no model-independent constraint on the slope of the tensor power spectrum is possible with current data. (2) CMB and LIGO/Virgo scales differ by more than 19 orders of magnitude, and 16 for DECIGO. I show that a power-law extrapolation from CMB to direct detection frequencies overestimates the amplitude of primordial tensor modes by as much as two orders of magnitude relative to an ensemble of realistic single-field inflation models. Moreover, the primordial tensor amplitude at direct detection scales is mostly uncorrelated with the tensor spectral index at CMB scales, and any constraint is strongly dependent on the specific form of the inflationary potential.

We present a study on the relationship between the ratio of the depth of a crater to its diameter and the diameter for lunar craters both on the maria and on the highlands. We consider craters younger than 1.1 billion years in age, i.e. of Copernican period. The aim of this work is to improve our understanding of such relationships based on our new estimates of the craters's depth and diameter. Previous studies considered similar relationships for much older craters (up to 3.2 billion years). We calculated the depths of craters with diameters from 10 to 100 km based on the altitude profiles derived from data obtained by the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO). The ratio h/D of the depth h of a crater to its diameter D can diverge by up to a factor of two for craters with almost the same diameters. The linear and power approximations (regressions) of the dependence of h/D on D were made for simple and complex Copernican craters selected from the data from Mazrouei et al. (2019) and Losiak et al. (2015). For the separation of highland craters into two groups based only on their dependences of h/D on D, at D<18 km these are mostly simple craters, although some complex craters can have diameters D>16 km. Depths of mare craters with D<14 km are greater than 0.15D. Following Pike's (1981) classification, we group mare craters of D<15 km as simple craters. Mare craters with 15<D<18 km fit both approximation curves for simple and complex craters. Depths of mare craters with D>18 km are in a better agreement with the approximation curve of h/D vs. D for complex craters than for simple craters. At the same diameter, mare craters are deeper than highland craters at a diameter smaller than 30-40 km. For greater diameters, highland craters are deeper.

On 2019/07/30.86853 UT, IceCube detected a high-energy astrophysical neutrino candidate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 percent uncertainty region of the event. Our analysis of 15 GHz Very Long Baseline Array (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after the IceCube event, reveals evidence for a radio ring structure which develops with time. Several arc-structures evolve perpendicular to the jet ridge line. We find evidence for precession of a curved jet based on kinematic modelling and a periodicity analysis. An outflowing broad line region (BLR) based on the C IV line emission (Sloan Digital Sky Survey, SDSS) is found. We attribute the atypical ring to an interaction of the precessing jet with the outflowing material. We discuss our findings in the context of a spine-sheath scenario where the ring reveals the sheath and its interaction with the surroundings (narrow line region, NLR, clouds). We find that the radio emission is correlated with the $\gamma$-ray emission, with radio lagging the $\gamma$-rays. Based on the $\gamma$-ray variability timescale, we constrain the $\gamma$-ray emission zone to the BLR (30-200 $r_{\rm g}$) and within the jet launching region. We discuss that the outflowing BLR provides the external radiation field for $\gamma$-ray production via external Compton scattering. The neutrino is most likely produced by proton-proton interaction in the blazar zone (beyond the BLR), enabled by episodic encounters of the jet with dense clouds, i.e. some molecular cloud in the NLR.

We present results of optical-UV observations of the 200 Myr old rotation-powered radio pulsar J0108$-$1431 with the Hubble Space Telescope. We found a putative candidate for the far-UV (FUV) pulsar counterpart, with the flux density $f_\nu = 9.0\pm 3.2$ nJy at $\lambda = 1528$ \AA. The pulsar was not detected, however, at longer wavelengths, with $3\sigma$ upper limits of 52, 37, and 87 nJy at $\lambda =$ 4326, 3355, and 2366 \AA, respectively. Assuming that the pulsar counterpart was indeed detected in FUV, and the previously reported marginal $U$ and $B$ detections with the Very Large Telescope were real, the optical-UV spectrum of the pulsar can be described by a power-law model with a nearly flat $f_\nu$ spectrum. Similar to younger pulsars detected in the optical, the slope of the nonthermal spectrum steepens in the X-ray range. The pulsar's luminosity in the 1500--6000 \AA wavelength range, $L \sim 1.2\times 10^{27} (d/210\,{\rm pc})^2$ erg s$^{-1}$, corresponds to a high efficiency of conversion of pulsar rotation energy loss rate $\dot {E}$ to the optical-UV radiation, $\eta = L/\dot{E} \sim (1$--$6)\times 10^{-4}$, depending on somewhat uncertain values of distance and spectral slope. The brightness temperature of the bulk neutron star surface does not exceed 59,000 K ($3\sigma$ upper bound), as seen by a distant observer. If we assume that the FUV flux is dominated by a thermal component, then the surface temperature can be in the range of 27,000--55,000 K, requiring a heating mechanism to operate in old neutron stars.

More than 10% of the barred galaxies with a direct measurement of the bar pattern speed host an ultrafast bar. These bars extend beyond the corotation radius and challenge our understanding of the orbital structure of barred galaxies. Most of them are found in spiral galaxies, rather than in lenticular ones. We analysed the properties of the ultrafast bars detected in the CALIFA Survey to investigate whether they are an artefact resulting from an overestimation of the bar radius and/or an underestimation of the corotation radius or a new class of bars, whose orbital structure has not yet been understood. We revised the available measurements of the bar radius based on ellipse fitting and Fourier analysis and of the bar pattern speed from the Tremaine-Weinberg method. In addition, we measured the bar radius from the analysis of the maps tracing the transverse-to-radial force ratio, which we obtained from the deprojected i-band images of the galaxies retrieved from the SDSS Survey. We found that nearly all the sample galaxies are spirals with an inner ring or pseudo-ring circling the bar and/or strong spiral arms, which hamper the measurement of the bar radius from the ellipse fitting and Fourier analysis. According to these methods, the bar ends overlap the ring or the spiral arms making the adopted bar radius unreliable. On the contrary, the bar radius from the ratio maps are shorter than the corotation radius. This is in agreement with the theoretical predictions and findings of numerical simulations about the extension and stability of the stellar orbits supporting the bars. We conclude that ultrafast bars are no longer observed when the correct measurement of the bar radius is adopted. Deriving the bar radius in galaxies with rings and strong spiral arms is not straightforward and a solid measurement method based on both photometric and kinematic data is still missing.

Parker Solar Probe (PSP) routinely observes magnetic field deflections in the solar wind at distances less than 0.3 au from the Sun. These deflections are related to structures commonly called 'switchbacks' (SBs), whose origins and characteristic properties are currently debated. Here, we use a database of visually selected SB intervals - and regions of solar wind plasma measured just before and after each SB - to examine plasma parameters, turbulent spectra from inertial to dissipation scales, and intermittency effects in these intervals. We find that many features, such as perpendicular stochastic heating rates and turbulence spectral slopes are fairly similar inside and outside of SBs. However, important kinetic properties, such as the characteristic break scale between the inertial to dissipation ranges differ inside and outside these intervals, as does the level of intermittency, which is notably enhanced inside SBs and in their close proximity, most likely due to magnetic field and velocity shears observed at the edges. We conclude that the plasma inside and outside of a SB, in most of the observed cases, belongs to the same stream, and that the evolution of these structures is most likely regulated by kinetic processes, which dominate small scale structures at the SB edges.

The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the beam model of the low-band (50-100~MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes of numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated driftscan observation from an early EDGES low-band instrument that had a 10~m~$\times$~10~m ground plane, we find residual levels after fitting and removing a five-term foreground model to data binned in Local Sidereal Time (LST) average about 250~mK with $\pm$40~mK variation between numerical solvers. A similar analysis of the primary 30~m~$\times$~30~m sawtooth ground plane reduced the LST-averaged residuals to about 90~mK with $\pm$10~mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power which is within 4$\%$ of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that soil conductivity of 0.02~Sm$^{-1}$ and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by \citet{Sutinjo_2015} for the Murchison Radio-astronomy Observatory, where EDGES is located.

We present an investigation of the magnetic activity and flare characteristics of the sub-giant stars mostly from F and G spectral types and compare the results with the main-sequence (MS) stars. The light curve of 352 stars on the sub-giant branch (SGB) from the Kepler mission is analyzed in order to infer stability, relative coverage and contrast of the magnetic structures and also flare properties using three flare indexes. The results show that: (i) Relative coverage and contrast of the magnetic features along with rate, power and magnitude of flares increase on the SGB due to the deepening of the convective zone and more vigorous magnetic field production (ii) Magnetic activity of the F and G-type stars on the SGB does not show dependency to the rotation rate and does not obey the saturation regime. This is the opposite of what we saw for the main sequence, in which the G-, K- and M-type stars show clear dependency to the Rossby number; (iii) The positive relationship between the magnetic features stability and their relative coverage and contrast remains true on the SGB, though it has lower dependency coefficient in comparison with the MS; (iv) Magnetic proxies and flare indexes of the SGB stars increase with increasing the relative mass of the convective zone.

Context: The analytical results of Chandrasekhar's semi-infinite diffuse reflection problem is crucial in the context of stellar or planetary atmosphere. However, the atmospheric emission effect was not taken into account in this model, and the solutions are applicable only for diffusely scattering atmosphere in absence of emission. Aim: We extend the model of semi-infinite diffuse reflection problem by including the effects of thermal emission B(T ), and present how this affects Chandrasekhar's analytical end results. Hence, we aim to generalize Chandrasekhar's model to provide a complete picture of this problem. Method: We use Invariance Principle Method to find the radiative transfer equation accurate for diffuse reflection in presence of B(T ). Then we derive the modified scattering function S(${\mu},{\phi}; {\mu}_0 , {\phi}_0$ ) for different kind of phase functions. Results: We find that, the scattering function S(${\mu}, {\phi}; {\mu}_0 , {\phi}_0$ ) as well as diffusely reflected specific intensity $I(0, {\mu}; {\mu}_0 )$ for different phase functions are modified due to the emission $B(T)$ from layer ${\tau} = 0$. In both cases, B(T) is added to the results of only scattering case derived by Chandrasekhar, with some multiplicative factors. Thus the diffusely reflected spectra will be enriched and carries the temperature information of ${\tau} = 0$ layer. As the effects are additive in nature, hence our model reduces to the sub-case of Chandrasekhar's scattering model in case of $B(T) = 0$. We conclude that our generalized model provides more accurate results due to the inclusion of the thermal emission effect in Chandrasekhar's semi-infinite atmosphere problem.

Most cosmic microwave background experiments observe the sky along circular or near-circular scans on the celestial sphere. For such experiments, we show that simple linear systems connect the Fourier spectra of temperature and polarization time-ordered data to the harmonic spectra of T, E and B on the sphere. We show how this can be used to estimate those spectra directly from data streams. In addition, the inversion of the linear system that connects Fourier spectra to angular power spectra offers a natural way to down-weight those modes of observation most contaminated by low-frequency noise, ground pickup, or fluctuations of atmospheric emission on large angular scale. This can be of interest for the analysis of future CMB data sets, as an alternative or in complement to other approaches that involve map-making as a first analysis step.

Cosmic-ray observatories necessarily rely on Monte Carlo simulations for their design, calibration and analysis of their data. Detailed simulations are very demanding computationally. We present a python-based package called ShowerModel to model cosmic-ray showers, their light production and their detection by an array of telescopes. It is based on parameterizations of both Cherenkov and fluorescence emission in cosmic-ray induced air showers. The package permits the modelling of fluorescence telescopes, imaging air Cherenkov telescopes, wide-angle Cherenkov detectors or any hybrid design. ShowerModel was conceived as a tool to speed up calculations that do not require a full simulation or that may serve to complement complex Monte Carlo studies and data analyses (e.g., as a cross-check). It can also be used for educational purposes.

We summarize the results of temporal and spectral analysis of the X-ray pulsar 2S 1553-542 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift during the outburst in January-February 2021. During the outburst, the spin period of the neutron star was $P = 9.2822\pm 0.0001$ s based on NuSTAR data. The temporal evolution of the spin period, pulse profile, and pulse fraction is studied during the outburst. The spectra of the source are studied for different days of the outburst and can be well described by a model consisting of -- a black body emission or a power law. We have investigated the inter-day evolution of different timing and spectral parameters during the outburst. The energy dependence of the pulse profile was studied to investigate the evolution of the individual peaks and emission geometry of the pulsar with a different energy. The pulse profile of the source shows strong single peak nature with a hump-like feature of relatively lower intensity and it evolves significantly with different energy ranges. The evolution of the pulse profile is studied during different phases of the outburst and the pulse fraction shows a positive correlation with energy.

The lunar South pole likely contains significant amounts of water in the permanently shadowed craters there. Extracting this water for life support at a lunar base or to make rocket fuel would take large amounts of power, of order Gigawatts. A natural place to obtain this power are the "Peaks of Eternal Light", that lie a few kilometers away on the crater rims and ridges above the permanently shadowed craters. The amount of solar power that could be captured depends on how tall a tower can be built to support the photovoltaic panels. The low gravity, lack of atmosphere, and quiet seismic environment of the Moon suggests that towers could be built much taller than on Earth. Here we look at the limits to building tall concrete towers on the Moon. We choose concrete as the capital cost of transporting large masses of iron or carbon fiber to the Moon is presently so expensive that profitable operation of a power plant is unlikely. Concrete instead can be manufactured in situ from the lunar regolith. We find that, with minimum wall thicknesses (20 cm), towers up to several kilometers tall are stable. The mass of concrete needed, however, grows rapidly with height, from $\sim$ 760 mt at 1 km to $\sim$ 4,100 mt at 2 km to $\sim 10^5$ mt at 7 km and $\sim 10^6$ mt at 17 km.

The nonlinear response associated with the current dependence of the superconducting kinetic inductance was studied in capacitively shunted NbTiN microstrip transmission lines. It was found that the inductance per unit length of one microstrip line could be changed by up to 20% by applying a DC current, corresponding to a single pass time delay of 0.7 ns. To investigate nonlinear dissipation, Bragg reflectors were placed on either end of a section of this type of transmission line, creating resonances over a range of frequencies. From the change in the resonance linewidth and amplitude with DC current, the ratio of the reactive to the dissipative response of the line was found to be 788. The low dissipation makes these transmission lines suitable for a number of applications that are microwave and millimeter-wave band analogues of nonlinear optical processes. As an example, by applying a millimeter-wave pump tone, very wide band parametric amplification was observed between about 3 and 34 GHz. Use as a current variable delay line for an on-chip millimeter-wave Fourier transform spectrometer is also considered.

We investigate the dust attenuation in both stellar populations and ionized gas in kpc-scale regions in nearby galaxies, using integral field spectroscopy data from MaNGA MPL-9. We identify star-forming (HII) and diffuse ionized gas (DIG) regions from MaNGA datacubes. From the stacked spectrum of each region, we measure the stellar attenuation, $E(B-V)_{\rm star}$, using the technique developed by Li et al.(2020), as well as the gas attenuation, $E(B-V)_{\rm gas}$, from the Balmer decrement. We then examine the correlation of $E(B-V)_{\rm star}$, $E(B-V)_{\rm gas}$, $E(B-V)_{\rm gas}-E(B-V)_{\rm star}$ and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ with 16 regional/global properties, and for regions with different $\rm H{\alpha}$ surface brightnesses ($\Sigma_{\rm H\alpha}$). We find a stronger correlation between $E(B-V)_{\rm star}$ and $E(B-V)_{\rm gas}$ in regions of higher $\Sigma_{\rm H\alpha}$. Luminosity-weighted age ($t_L$) is found to be the property that is the most strongly correlated with $E(B-V)_{\rm star}$, and consequently with $E(B-V)_{\rm gas}-E(B-V)_{\rm star}$ and $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$. At fixed $\Sigma_{\rm H\alpha}$, $\log_{10}t_L$ is linearly and negatively correlated with $E(B-V)_{\rm star}/E(B-V)_{\rm gas}$ at all ages. Gas-phase metallicity and ionization level are important for the attenuation in the gas. Our results indicate that the ionizing source for DIG regions is likely distributed in the outer-skirt of galaxies, while for HII regions our results can be well explained by the two-component dust model of Charlot & Fall (2000).

Extreme space weather events including $\ge$X5.0 flares, ground level enhancement (GLE) events and super geomagnetic storms (Dst $\le$ -250 nT) caused by super active regions (SARs) during solar cycles 21-24 were studied. The total number of $\ge$X5.0 solar flares was 62, 41 of them were X5.0-X9.9 flares and 21 of them were $\ge$X10.0 flares. We found that 83.9\% of the $\ge$X5.0 flares were produced by SARs. 78.05\% of the X5.0-X9.9 and 95.24\% of the $\ge$X10.0 solar flares were produced by SARs. 46 GLEs registered during solar cycles 21-24, and 25 GLEs were caused by SARs, indicating that 54.3\% of the GLEs were caused by SARs. 24 super geomagnetic storms were recorded during solar cycles 21-24, and 12 of them were caused by SARs, namely 50\% of the super geomagnetic storms are caused by SARs. It is found that only 29 SARs can produce $\ge$X5.0 flares, 15 SARs can produce GLEs and 10 SARs can produce super geomagnetic storms. Of the 51 SARs, only 33 SARs can produce at least one extreme space weather event, while none of the rest 18 SARs can produce an extreme space weather event. There were only 4 SARs, each of them can produce not only a $\ge$X5.0 flare, but also a GLE event and a super geomagnetic storm. Most of the extreme space weather events caused by the SARs appeared during solar cycles 22 and 23, especially for GLE events and super geomagnetic storms. The longitudinal distributions of source locations for the extreme space weather events caused by SARs were also studied.

We study the radio and optical properties of the brightest group galaxies (BGGs) in a sample of galaxy groups from the SDSS DR7. The luminosity difference between the BGG and the second ranked galaxy in the group (known as the luminosity, or magnitude, gap) has been used as a probe for the level of galaxy interaction for the BGG within the group. We study the properties of BGGs with magnitude gaps in the range 0-2.7 magnitudes, in order to investigate any relation between luminosity gap and the radio properties of the BGG. In order to eliminate selection biases, we ensure that all variations in stellar mass are accounted for. We then confirm that, at fixed stellar mass, there are no significant variations in the optical properties of the BGGs over the full range of luminosity gaps studied. We compare these optical results with the EAGLE hydrodynamical simulations and find broad consistency with the observational data. Using EAGLE we also confirm that no trends begin to arise in the simulated data at luminosity gaps beyond our observational limits. Finally, we find that, at fixed stellar mass, the fraction of BGGs that are radio-loud also shows no trends as a function of luminosity gap. We examine how the BGG offset from the center of group may affect the radio results and find no significant trend for the fraction of radio-loud BGGs with magnitude gap in either the BGG samples with greater or less than 100kpc offset from the center of group.

As a basic characteristic of cosmic ray (CR) propagation, the diffusive halo can advance our understanding of many CR-related studies and indirect dark matter. The method to derive the halo size usually has degeneracy problems thus affected by large uncertainties. The diffusion gamma ray from high-latitude clouds might shed light on the halo size independently. Since the spatially dependent propagation (SDP) model has a better agreement with the observed CRs, compared with conventional propagation model, in this work, we investigate the halo thickness based on SDP model with Fermi-LAT $\rm\gamma$-ray observation on the high- and intermediate-velocity clouds. As a result, in order not to exceed the relative $\gamma$-ray emissivity in the high-latitude clouds, halo thickness should be in the range of $\rm ~3.3\sim9~ kpc$. Moreover, the spatial morphology of $\rm\gamma$-rays estimated based on SDP model under different values of halo thickness are distinctive, which provides us a tool to determine the halo size. We hope that our model could be tested and tuned by multi-wavelength observations in the future.

We present an analytic model for the splashback mass function of dark matter halos, which is parameterized by a single coefficient and constructed in the framework of the generalized excursion set theory and the self-similar spherical infall model. The value of the single coefficient that quantifies the diffusive nature of the splashback boundary is determined at various redshifts by comparing the model with the numerical results from the Erebos N-body simulations for the Planck and the WMAP7 cosmologies. Showing that the analytic model with the best-fit coefficient provides excellent matches to the numerical results in a wide mass range at all redshifts, we employ the Bayesian Information Criterion test to confirm that our model is most preferred by the numerical results to the previous models at almost all redshifts for both of the cosmologies. It is also found that the diffusion coefficient decreases almost linearly with redshifts, converging to zero at a certain threshold redshift, $z_{c}$, whose value significantly differs between the Planck and WMAP7 cosmologies. Our result implies that the splashback mass function of dark matter halos at $z\ge z_{c}$ is well described by an universal parameter-free analytic formula and that $z_{c}$ may have a potential to independently constrain the initial conditions of the universe.

Both long-duration gamma-ray bursts (LGRBs) from core collapse of massive stars and short-duration GRBs (SGRBs) from mergers of binary neutron star (BNS) or neutron star--black hole (NSBH) are expected to occur in the accretion disk of active galactic nuclei (AGNs). We show that GRB jets embedded in the migration traps of AGN disks are promised to be choked by the dense disk material. Efficient shock acceleration of cosmic rays at the reverse shock is expected, and high-energy neutrinos would be produced. We find that these sources can effectively produce detectable TeV--PeV neutrinos through $p\gamma$ interactions. From a choked LGRB jet with isotropic equivalent energy of $10^{53}\,{\rm erg}$ at $100\,{\rm Mpc}$, one expects $\sim2\,(7)$ neutrino events detectable by IceCube (IceCube-Gen2). The contribution from choked LGRBs to the observed diffuse neutrino background depends on the unknown local event rate density of these GRBs in AGN disks. For example, if the local event rate density of choked LGRBs in AGN disk is similar to that of classical LGRBs $(\sim1\,{\rm Gpc}^{-3}\,{\rm yr}^{-1})$, the neutrinos from these events would contribute to $\sim1\%$ of the observed diffuse neutrino background.

The probability number distribution function of binary black hole mergers observed by LIGO/Virgo O3a has double peaks as a function of chirp mass $M_c$, total mass $M_t$, primary black hole mass $M_1$ and secondary one $M_2$, respectively. The larger chirp mass peak is at $M_c \cong 30 M_{\odot}$. The distribution of $M_2$ vs. $M_1$ follows the relation of $M_2\cong 0.7M_1$. For initial mass functions of Population III stars in the form of $f(M) \propto M^{-\alpha}$, population synthesis numerical simulations with $0\leq \alpha \leq 1.5$ are consistent with O3a data for $M_c \gtrsim 20M_{\odot}$. The distribution of $M_2$ vs. $M_1$ for simulation data also agrees with $M_2\cong 0.7M_1$ relation of O3a data.

Within the framework of the theory of strongly-interacting quantum Bose liquids, we consider a general relativistic model of self-interacting complex scalar fields with logarithmic nonlinearity taken from dense superfluid models. We demonstrate the existence of gravitational equilibria in this model, described by spherically symmetric nonsingular finite-mass asymptotically-flat solutions. These equilibrium configurations can describe both massive astronomical objects, such as bosonized superfluid stars or cores of neutron stars, and finite-size particles and non-topological solitons, such as Q-balls. We give an estimate for masses and sizes of such objects.

The millihertz gravitational-wave frequency band is expected to contain a rich symphony of signals with sources ranging from galactic white dwarf binaries to extreme mass ratio inspirals. Many of these gravitational-wave signals will not be individually resolvable. Instead, they will incoherently add to produce stochastic gravitational-wave confusion noise whose frequency content will be governed by the dynamics of the sources. The angular structure of the power of the confusion noise will be modulated by the distribution of the sources across the sky. Measurement of this structure can yield important information about the distribution of sources on galactic and extra-galactic scales, their astrophysics and their evolution over cosmic timescales. Moreover, since the confusion noise is part of the noise budget of LISA, mapping it will also be essential for studying resolvable signals. In this paper, we present a Bayesian algorithm to probe the angular distribution of the stochastic gravitational-wave confusion noise with LISA using a spherical harmonic basis. We develop a technique based on Clebsch-Gordan coefficients to mathematically constrain the spherical harmonics to yield a non-negative distribution, making them optimal for expanding the gravitational-wave power and amenable to Bayesian inference. We demonstrate these techniques using a series of simulations and analyses, including recovery of simulated distributed and localized sources of gravitational-wave power. We also apply this method to map the gravitational-wave foreground from galactic white-dwarfs using a simplified model of the galactic white dwarf distribution.

Periodic outbursts are observed in several changing-look (CL) active galactic nuclei (AGNs). \citet{sniegowska_possible_2020} suggested a model to explain the repeating CL in these AGNs, where the periodic outbursts are triggered in a narrow unstable zone between an inner ADAF and outer thin disk. In this work, we intend to investigate the effects of large-scale magnetic fields on the limit cycle behaviors of CL AGNs. The winds driven by magnetic fields can significantly change the structure of thin disk by taking away the angular momentum and energy of the disk. It is found that the period of outburst in repeating CL AGNs can be substantially reduced by the magnetic fields. Conversely, if we keep the period unchanged, the outburst intensity can be raised for several times. These results can help to explain the observational properties of multiple CL AGNs. Besides the magnetic fields, the effects of transition radius $R_{\rm tr}$, the width of transition zone $\Delta R$ and Shakura-Sunyaev parameter $\alpha$ are also explored in this work.

BG Ind is a well studied, bright, nearby binary consisting of a pair of F stars in a 1.46-day orbit. We have discovered in the TESS lightcurve for TIC 229804573 (aka BG Ind) a second eclipsing binary in the system with a 0.53-day. Our subsequent analyses of the recent TESS and archival ground-based photometric and radial velocity data, reveal that the two binaries are gravitationally bound in a 721-day period, moderately eccentric orbit. We present the results of a joint spectro-photodynamical analysis of the eclipse timing variation curves of both binaries based on TESS and ground-based archival data, the TESS lightcurve, archival radial velocity data and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We confirm prior studies of BG Ind which found that the brighter binary A consists of slightly evolved F-type stars with refined masses of 1.32 and 1.43 $M_\odot$, and radii of 1.59 and 2.34 $R_\odot$. The previously unknown binary B has two less massive stars of 0.69 and 0.64 $M_\odot$ and radii of 0.64 and 0.61 $R_\odot$. Based on a number of different arguments which we discuss, we conclude that the three orbital planes are likely aligned to within 17$^\circ$.

The binary neutron star merger gravitational-wave signal GW170817 was followed by three electromagnetic counter-parts, of which a kilonova arising from the radioactivity of freshly synthesized r-process elements in ejecta from the merger. Finding kilonovae after gravitational-wave triggers is crucial (i) to the search for further counterparts such as the afterglow, (ii) to probe the diversity of kilonovae and their dependence on the system's inclination angle (iii) to build a sample for multimessenger cosmology. During the third observing run of the gravitational-wave interferometer network, no kilonova counterpart was found. We aim to predict the expected population of detectable kilonova signals for the upcoming O4 and O5 observing runs of the LIGO-Virgo-Kagra instruments. Using a a simplified criterion for gravitational-wave detection and a simple GW170817-calibrated model for the kilonova peak magnitude, we determine the rate of kilonovae in reach of follow-up campaigns and their distributions in magnitude for various bands. We briefly consider the case of GW190425, the only confirmed binary neutron star merger since GW170817, and obtain constraints on its inclination angle from the non-detection of its kilonova, assuming the source was below the follow-up thresholds. We also show that non gravitational-wave-triggered kilonovae can be a numerous class of sources in the future surveys and briefly discuss associations with short bright gamma-ray bursts. We finally discuss the detection of the jetted outflow afterglow in addition to the kilonova, and confirm former conclusions on the rareness of such counterparts in future observations.

We present a method for automatised detection and analysis of quasi-periodic lineament structures from images at pixel-precision. The method exploits properties of the images' frequency domain found by using the Fourier transform. We developed this method with the goal of detecting lineament structures in an image of the Hathor cliff of comet 67P/Churyumov-Gerasimenko, which are caused by layerings and furrows in the nucleus material. Using our method, we determined the orientation and wavelength-range of these structures. The detected layering edges have similar orientations, spatial separations of 9-20 m, and are ubiquitous throughout the image. We suggest that the layerings are a global feature of the comet nucleus that provide information about formation and evolution of comet 67P. The furrows are non-uniformly distributed throughout the image. Their orientation is broadly parallel to the direction of the local gravity vector at the Hathor cliff, with spacings similar to that of the layering structures. The furrows are interpreted as signatures of local down-slope movement of cliff material. We demonstrate that the developed method is broadly applicable to the detection and analysis of various kinds of quasi-periodic structures like geological layering, folding and faulting, and texture analysis in general. In order to facilitate the application of our method, this paper is accompanied by a demo program written in Matlab.

Context. We have presented a numerical model for the non-thermal emission of gamma-ray binaries in a pulsar-wind driven scenario. Aims. We apply this model to one of the best-observed gamma-ray binaries, the LS 5039 system. Methods. The model involves a joint simulation of the pulsar- and stellar-wind interaction and the transport of electronic pairs from the pulsar wind accelerated at the emerging shock structure. We compute the synchrotron and inverse Compton emission in a post-processing step, while consistently accounting for relativistic beaming and $\gamma \gamma$-absorption in the stellar radiation field. Results. The stellar- and pulsar-wind interaction leads to the formation of an extended, asymmetric wind collision region developing strong shocks, turbulent mixing, and secondary shocks in the turbulent flow. Both the structure of the collision region and the resulting particle distributions show significant orbital variation. Next to the acceleration of particles at the bow-like pulsar wind and Coriolis shock the model naturally accounts for the reacceleration of particles at secondary shocks contributing to the emission at very-high-energy (VHE) gamma-rays. The model successfully reproduces the main spectral features of LS 5039. While the predicted lightcurves in the high-energy and VHE gamma-ray band are in good agreement with observations, our model still does not reproduce the X-ray to low-energy gamma-ray modulation, which we attribute to the employed magnetic field model. Conclusions. We successfully model the main spectral features of the observed multiband, non-thermal emission of LS 5039 and thus further substantiates a wind-driven interpretation of gamma-ray binaries. Open issues relate to the synchrotron modulation, which might be addressed through a magnetohydrodynamic extension of our model.

Giant radio galaxies (GRGs), with extended structures reaching hundreds of kpc, are among the most spectacular examples of ejection of relativistic plasma from super-massive black holes. In this work, third of a series, we present LOw Frequency ARray (LOFAR) images at 144 MHz, collected in the framework of the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources extracted from our sample of hard X-ray selected GRGs (HXGRG, i.e. from INTEGRAL/IBIS and Swift/BAT catalogues at >20 keV). Thanks to the resolution and sensitivity of LoTSS, we could probe the complex morphology of these GRGs, unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint off-axis wings, or a misaligned inner jet. In particular, for one source (B21144+35B), we could clearly detect a $\sim$300 kpc wide off-axis emission, in addition to an inner jet which orientation is not aligned with the lobes axis. For another source (J1153.9+5848) a structure consistent with jet precession was revealed, appearing as an X-shaped morphology with relic lobes having an extension larger than the present ones, and with a different axis orientation. From an environment analysis, we found 2 sources showing an overdensity of cosmological neighbours, and a correspondent association with a galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs from LoTSS DR1 suggested that, on average, HXGRG can grow to larger extents. These results highlight the importance of deep low-frequency observations to probe the evolution of radio galaxies, and ultimately estimate the duty cycle of their jets.

Aims: To investigate properties of [CII]158 $\mu$m emission of RCW36 in a dense filamentary cloud. Methods: [CII] observations of RCW36 covering an area of ~30 arcmin$\times$30 arcmin were carried out with a Fabry-P\'{e}rot spectrometer aboard a 100-cm balloon-borne far-infrared (IR) telescope with an angular resolution of 90 arcsec. By using AKARI and Herschel images, the spatial distribution of the [CII] intensity was compared with those of emission from the large grains and PAH. Results: The [CII] emission is spatially in good agreement with shell-like structures of a bipolar lobe observed in IR images, which extend along the direction perpendicular to the direction of a cold dense filament. We found that the [CII]--160 $\mu$m relation for RCW36 shows higher brightness ratio of [CII]/160 $\mu$m than that for RCW 38, while the [CII]--9 $\mu$m relation for RCW36 is in good agreement with that for RCW38. Conclusions: The [CII] emission spatially well correlates with PAH and cold dust emissions. This means that the observed [CII] emission dominantly comes from PDRs. Moreover, the L_[CII]/L_FIR ratio shows large variation compared with the L_[CII]/L_PAH ratio. In view of the observed tight correlation between L_[CII]/L_FIR and the optical depth at $\lambda$=160 $\mu$m, the large variation in L_[CII]/L_FIR can be simply explained by the geometrical effect, viz., L_FIR has contributions from the entire dust-cloud column along the line of sight, while L_[CII] has contributions from far-UV illuminated cloud surfaces. Based on the picture of the geometry effect, the enhanced brightness ratio of [CII]/160 $\mu$m is attributed to the difference in gas structures where massive stars are formed: filamentary (RCW36) and clumpy (RCW38) molecular clouds and thus suggests that RCW36 is dominated by far-UV illuminated cloud surfaces compared with RCW38.

We investigate in detail the spectrum of gravitational waves induced by a peaked primordial curvature power spectrum generated in single field inflationary models. We argue that the $f_{\rm NL}$ parameter can be inferred by measuring the high frequency spectral tilt of the induced gravitational waves. We also show that the intrinsically non-Gaussian impact of $f_{\rm NL}$ in $\Omega_{\rm GW}$ is to broaden its peak, although at a negligible level in order not to overproduce primordial black holes. We discuss possible degeneracies in the high frequency spectral tilt between $f_{\rm NL}$ and a general equation of state of the universe $w$. Finally, we discuss the constraints on the amplitude, peak and slope (or equivalently, $f_{\rm NL}$) of the primordial power spectrum by combining current and future gravitational wave experiments with limits on $\mu$ distortions from the cosmic microwave background.

We implement a sample-efficient method for rapid and accurate emulation of semi-analytical galaxy formation models over a wide range of model outputs. We use ensembled deep learning algorithms to produce a fast emulator of an updated version of the GALFORM model from a small number of training examples. We use the emulator to explore the model's parameter space, and apply sensitivity analysis techniques to better understand the relative importance of the model parameters. We uncover key tensions between observational datasets by applying a heuristic weighting scheme in a Markov chain Monte Carlo framework and exploring the effects of requiring improved fits to certain datasets relative to others. Furthermore, we demonstrate that this method can be used to successfully calibrate the model parameters to a comprehensive list of observational constraints. In doing so, we re-discover previous GALFORM fits in an automatic and transparent way, and discover an improved fit by applying a heavier weighting to the fit to the metallicities of early-type galaxies. The deep learning emulator requires a fraction of the model evaluations needed in similar emulation approaches, achieving an out-of-sample mean absolute error at the knee of the K-band luminosity function of 0.06 dex with less than 1000 model evaluations. We demonstrate that this is an extremely efficient, inexpensive and transparent way to explore multi-dimensional parameter spaces, and can be applied more widely beyond semi-analytical galaxy formation models.

Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in the Northern Hemisphere. It explores the origin of UHECRs by measuring their energy spectrum, arrival-direction distribution, and mass composition using a surface detector (SD) array covering approximately 700 km$^2$ and fluorescence detector (FD) stations. TA has found evidence for a cluster of cosmic rays with energies greater than 57 EeV. In order to confirm this evidence with more data, it is necessary to increase the data collection rate.We have begun building an expansion of TA that we call TAx4. In this paper, we explain the motivation, design, technical features, and expected performance of the TAx4 SD. We also present TAx4's current status and examples of the data that have already been collected.

A 54-km diameter Noachian-aged crater in the southern highlands of Mars contains unusually well-preserved inverted fluvial channel networks and lacustrine deposits, all of which formed completely inside the crater. This closed-source drainage basin (CSDB) crater is distinct from previously documented fluvially breached or groundwater-fed crater basin lakes on Mars. We compare our observations to previously established models of crater degradation, fluvial incision, and topographic inversion on Mars to assess the most likely origins of the water that formed the fluvial and lacustrine features. We favor top-down melting of a cold-based glacier as the source of water in the CSDB crater, which would represent the first examples of proglacial fluvial channels and lakes found on Noachian Mars.

We present the discovery in TMC-1 of allenyl acetylene, H2CCCHCCH, through the observation of nineteen lines with a signal-to-noise ratio ~4-15. For this species, we derived a rotational temperature of 7 +/- 1 K and a column density of (1.2 +/- 0.2)e13 cm-2. The other well known isomer of this molecule, methyl diacetylene (CH3C4H), has also been observed and we derived a similar rotational temperature, Trot = 7.0 +/- 0.3 K, and a column density for its two states (A and E) of (6.5 +/- 0.3)e12 cm-2. Hence, allenyl acetylene and methyl diacetylene have a similar abundance. Remarkably, their abundances are close to that of vinyl acetylene (CH2CHCCH). We also searched for the other isomer of C5H4, HCCCH2CCH (1.4-pentadiyne), but only a 3sigma upper limit of 2.5e12 cm-2 to the column density can be established. These results have been compared to state-of-the-art chemical models for TMC-1, indicating the important role of these hydrocarbons in its chemistry. The rotational parameters of allenyl acetylene have been improved by fitting the existing laboratory data together with the frequencies of the transitions observed in TMC-1.

Astronomers use to derive MOdified Newtonian Dynamics (MOND) rotation curves using the simple algebraic rule of calculating the acceleration as equal to the Newtonian acceleration ($a$) divided by some factor $\mu (a)$. However, there are velocity differences between this simple rule and the calculation derived from more sophisticated MOND versions such as AQUAL or QMOND, created to expand MOND heuristic law and preserve the conservation of momentum, angular momentum, and energy, and follow the weak equivalence principle. Here we provide recipes based on Milgrom's proposal to calculate semianalytically (without numerical simulations) MOND rotation curves for any density distribution based on AQUAL, applying it to different models of thin disks. The application of this formalism is equivalent to the creation of a fictitious phantom mass whose field may be used in a Newtonian way to calculate iteratively the MOND accelerations. In most cases, the differences between the application of the simple algebraic rule and the AQUAL-MOND calculations are small, $\lesssim 5$%. However, the error of the algebraic solution is larger than 5% when more than half of the mass is in the MONDian regime (where Newtonian and MOND rotation speeds differ by more than 10%), reaching in some cases $>70$% discrepance, such as in Maclaurin disks, representative of galaxies for which the rotational velocity rises to the edge of the disk as is seen in irregular galaxies. The slope of the rotation speed in the dependence with the radius or the vertical distance of the plane is also significantly changed.

The $\Lambda$CDM model provides a good fit to a large span of cosmological data but harbors areas of phenomenology. With the improvement of the number and the accuracy of observations, discrepancies among key cosmological parameters of the model have emerged. The most statistically significant tension is the $4-6\sigma$ disagreement between predictions of the Hubble constant $H_0$ by early time probes with $\Lambda$CDM model, and a number of late time, model-independent determinations of $H_0$ from local measurements of distances and redshifts. The high precision and consistency of the data at both ends present strong challenges to the possible solution space and demand a hypothesis with enough rigor to explain multiple observations--whether these invoke new physics, unexpected large-scale structures or multiple, unrelated errors. We present a thorough review of the problem, including a discussion of recent Hubble constant estimates and a summary of the proposed theoretical solutions. Some of the models presented are formally successful, improving the fit to the data in light of their additional degrees of freedom, restoring agreement within $1-2\sigma$ between {\it Planck} 2018, using CMB power spectra data, BAO, Pantheon SN data, and R20, the latest SH0ES Team measurement of the Hubble constant ($H_0 = 73.2 \pm 1.3{\rm\,km\,s^{-1}\,Mpc^{-1}}$ at 68\% confidence level). Reduced tension might not simply come from a change in $H_0$ but also from an increase in its uncertainty due to degeneracy with additional physics, pointing to the need for additional probes. While no specific proposal makes a strong case for being highly likely or far better than all others, solutions involving early or dynamical dark energy, neutrino interactions, interacting cosmologies, primordial magnetic fields, and modified gravity provide the best options until a better alternative comes along.[Abridged]

Young neutron stars (NSs) have exterior magnetic fields ranging over three or more orders of magnitude, up to around $10^{15}$ G. These fields are believed to be amplified to such high strengths by dynamo action, but neither the details of this, nor the resulting range of field strengths, is satisfactorily understood. Here we consider three possible eras in which a dynamo may operate. For the first, proto-NS, phase, we argue that generation of large-scale field is inefficient, inhibited by the relatively high fluid viscosity. Understanding dynamo action under these conditions calls for a revised theory of mean-field electrodynamics, potentially analogous to the equations for magnetic-field evolution in a type-II superconductor. In the second phase we propose a new dynamo mechanism, driven by precession. Such a dynamo would be effective even at relatively low rotation rates, and can produce the observed variation of exterior-field strengths from small differences in birth physics. It could also be a viable mechanism for long-term field generation in main-sequence stars. Finally, dynamo action in a cold NS is disfavoured, due to both a lack of suitable fluid motions and inhibition of magnetic reconnection by superconductivity.

We study dynamical systems which admit action-angle variables at leading order which are subject to nearly resonant perturbations. If the frequencies characterizing the unperturbed system are not in resonance, the long-term dynamical evolution may be integrated by orbit-averaging over the high-frequency angles, thereby evolving the orbit-averaged effect of the perturbations. It is well known that such integrators may be constructed via a canonical transformation, which eliminates the high frequency variables from the orbit-averaged quantities. An example of this algorithm in celestial mechanics is the von Zeipel transformation. However if the perturbations are inside or close to a resonance, i.e. the frequencies of the unperturbed system are commensurate, these canonical transformations are subject to divergences. We introduce a canonical transformation which eliminates the high frequency phase variables in the Hamiltonian without encountering divergences. This leads to a well-behaved symplectic integrator. We demonstrate the algorithm through two examples: a resonantly perturbed harmonic oscillator and the gravitational three-body problem in mean motion resonance.

Laser inter-satellite links (LISLs) are envisioned between satellites in upcoming satellite constellations, such as Phase I of SpaceX's Starlink. Within a constellation, satellites can establish LISLs with other satellites in the same orbital plane or in different orbital planes. We present a classification of LISLs based on the location of satellites within a constellation and the duration of LISLs. Then, using satellite constellation for Phase I of Starlink, we study the effect of varying a satellite's LISL range on the number of different types of LISLs it can establish with other satellites. In addition to permanent LISLs, we observe a significant number of temporary LISLs between satellites in crossing orbital planes. Such LISLs can play a vital role in achieving low-latency paths within next-generation optical wireless satellite networks.

We analyze the causal structure of McVittie spacetime for a classical bouncing cosmological model. In particular, we compute the trapping horizons of the metric and integrate the trajectories of radial null geodesics before, during, and after the bounce takes place. In the contracting phase up to the occurrence of the bounce, a dynamical black hole is present. When the universe reaches a certain minimum scale, the trapping horizons disappear and the black hole ceases to exist. After the bounce, the central weak singularity becomes naked. In the expanding phase, for large positive values of the cosmic time, the behaviour of null geodesics indicates that the solution contains a black hole. These results suggest that neither a contracting nor an expanding universe can accommodate a black hole at all times.

We analyze the propagation of high-frequency gravitational waves (GW) in scalar-tensor theories of gravity, with the aim of examining properties of cosmological distances as inferred from GW measurements. By using symmetry principles, we first determine the most general structure of the GW linearized equations and of the GW energy momentum tensor, assuming that GW move with the speed of light. Modified gravity effects are encoded in a small number of parameters, and we study the conditions for ensuring graviton number conservation in our covariant set-up. We then apply our general findings to the case of GW propagating through a perturbed cosmological space-time, deriving the expressions for the GW luminosity distance $d_L^{({\rm GW})}$ and the GW angular distance $d_A^{({\rm GW})}$. We prove for the first time the validity of Etherington reciprocity law $d_L^{({\rm GW})}\,=\,(1+z)^2\,d_A^{({\rm GW})}$ for a perturbed universe within a scalar-tensor framework. We find that besides the GW luminosity distance, also the GW angular distance can be modified with respect to General Relativity. We discuss implications of this result for gravitational lensing, focussing on time-delays of lensed GW and lensed photons emitted simultaneously during a multimessenger event. We explicitly show how modified gravity effects compensate between different coefficients in the GW time-delay formula: lensed GW arrive at the same time as their lensed electromagnetic counterparts, in agreement with causality constraints.

We review the recent progress in Higgs inflation focusing on Higgs-$R^2$ inflation, primordial black hole production and the $R^3$ term.

We propose a vector dark matter model with an exotic dark SU(2) gauge group. Two Higgs triplets are introduced to spontaneously break the symmetry. All of the dark gauge bosons become massive, and the lightest one is a viable vector DM candidate. Its stability is guaranteed by a remaining Z_2 symmetry. We study the parameter space constrained by the Higgs measurement data, the dark matter relic density, and direct and indirect detection experiments. We find numerous parameter points satisfying all the constraints, and they could be further tested in future experiments. Similar methodology can be used to construct vector dark matter models from an arbitrary SO(N) gauge group.

The recent launches of Parker Solar Probe (PSP), Solar Orbiter (SO) and BepiColombo, along with several older spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously. We take advantage of this unique spacecraft constellation, along with low solar activity across two solar rotations between May and July 2020, to investigate how the Heliospheric Current Sheet (HCS) structure varies with latitude. We visualise the sector structure of the inner heliosphere by ballistically mapping the polarity and solar wind speed from several spacecraft onto the Sun's source surface. We compare this observed sector structure, and the local orientations of the boundaries, to a predicted HCS. We show that fine scale ripples in the HCS can be resolved down to several degrees in longitude, with solar wind speed being a useful indicator of when a spacecraft is near the HCS without changing magnetic polarity. We found that the local orientation of sector boundaries were broadly consistent with the shape of the HCS but were steepened due to compression from stream interaction regions. We identified several transient magnetic clouds associated with HCS crossings, and have shown that these could disrupt the local HCS orientation up to five days after their passage, but did not significantly affect the position of the HCS. This spacecraft constellation, along with ballistic mapping, can reveal the structure of the HCS on scales of a few degrees in longitude and latitude, while discerning between co-rotating and transient structures. This also provides an accurate representation of the solar wind within $\pm 10^{\circ}$ latitude, which could be used as a more rigorous constraint on solar wind models and future space weather predictions. In the future, this range of latitudes will increase as SO's orbit becomes more inclined.

Single-stage or single-step high-order temporal discretizations of partial differential equations (PDEs) have shown great promise in delivering high-order accuracy in time with efficient use of computational resources. There has been much success in developing such methods for finite volume method (FVM) discretizations of PDEs. The Picard Integral formulation (PIF) has recently made such single-stage temporal methods accessible for finite difference method (FDM) discretizations. PIF methods rely on the so-called Lax-Wendroff procedures to tightly couple spatial and temporal derivatives through the governing PDE system to construct high-order Taylor series expansions in time. Going to higher than third order in time requires the calculation of Jacobian-like derivative tensor-vector contractions of an increasingly larger degree, greatly adding to the complexity of such schemes. To that end, we present in this paper a method for calculating these tensor contractions through a recursive application of a discrete Jacobian operator that readily and efficiently computes the needed contractions entirely agnostic of the system of partial differential equations (PDEs) being solved.

The AGILE (Advanced enerGetic Ion eLectron tElescope) project focuses on the development of a compact low-cost space-based instrument to measure the intensities of charged particles and ions in space. Using multiple layers of fast silicon sensors and custom front-end electronics, the instrument is designed for real-time particle identification of a large variety of elements from H to Fe and spanning energies from 1 to 100 MeV per nucleon. The robust method proposed in this work uses key defining features of electronic signals generated by charged particles (ions) traveling through silicon layers to reliably identify and characterize particles in situ. AGILE will use this real-time pulse shape discrimination technique for the first time in space based instrumentation.

Topology effects have being extensively studied and confirmed in strongly correlated condensed matter physics. In the large color number limit of QCD, baryons can be regarded as topological objects -- skyrmions -- and the baryonic matter can be regarded as a skyrmion matter. We review in this paper the generalized effective field theory for dense compact-star matter constructed with the robust inputs obtained from the skyrmion approach to dense nuclear matter, relying to possible ``emergent" scale and local flavor symmetries at high density. All nuclear matter properties from the saturation density $n_0$ up to several times $n_0$ can be fairly well described. A uniquely novel -- and unorthdox -- feature of this theory is the precocious appearance of the pseudo-conformal sound velocity $v^2_{s}/c^2 \approx 1/3$, with the non-vanishing trace of the energy momentum tensor of the system. The topology change encoded in the density scaling of low energy constants is interpreted as the quark-hadron continuity in the sense of Cheshire Cat Principle (CCP) at density $\gsim 2n_0$ in accessing massive compact stars. We confront the approach with the data from GW170817 and GW190425.

A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH$^+$-He and CH$^+$-He$_4$ complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C-H stretching vibrations are recorded in the range of 2720-2800 cm$^{-1}$. The spectrum of CH$^+$-He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm$^{-1}$, and thus confirms it to have a T-shaped structure. For CH$^+$-He$_4$, the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.

Rotational-vibrational transitions of the fundamental vibrational modes of the $^{12}$C$^{14}$N$^+$ and $^{12}$C$^{15}$N$^+$ cations have been observed for the first time using a cryogenic ion trap apparatus with an action spectroscopy scheme. The lines P(3) to R(3) of $^{12}$C$^{14}$N$^+$ and R(1) to R(3) of $^{12}$C$^{15}$N$^+$ have been measured, limited by the trap temperature of approximately 4 K and the restricted tuning range of the infrared laser. Spectroscopic parameters are presented for both isotopologues, with band origins at 2000.7587(1) and 1970.321(1) cm$^{-1}$, respectively, as well as an isotope independent fit combining the new and the literature data.

We study the gravitational wave (GW) signal sourced by primordial turbulence that is assumed to be present at cosmological phase transitions like the electroweak and quantum chromodynamics phase transitions. We consider various models of primordial turbulence, such as those with and without helicity, purely hydrodynamical turbulence induced by fluid motions, and magnetohydrodynamic turbulence whose energy can be dominated either by kinetic or magnetic energy, depending on the nature of the turbulence. We also study circularly polarized GWs generated by parity violating sources such as helical turbulence. Our ultimate goal is to determine the efficiency of GW production through different classes of turbulence. We find that the GW energy and strain tend to be large for acoustic or irrotational turbulence, even though its tensor mode amplitude is relatively small at most wave numbers. Only at very small wave numbers is the spectral tensor mode significant, which might explain the efficient GW production in that case.

Attractor inflation is a particularly robust framework for developing inflationary models that are insensitive to the details of the potential. Such models are most often considered in the metric formulation of gravity. However, non-minimal models may not necessarily maintain their attractor nature in the Palatini formalism where the connection is independent of the metric. In this work, we employ the $\beta$-function formalism to classify the strong coupling limit of inflationary models in both the metric and the Palatini approaches. Furthermore, we determine the range of values for the non-minimal coupling that lead to theories being observationally indistinguishable in metric and Palatini within current accuracy. Finally, we reconstruct the Jordan frame potential for $\xi$-attractors by imposing an explicit form for the $\beta$-function, demonstrating the effect that the choice of metric or Palatini has on the inflationary observables of the theory.