Abstract : 

Confidence in spacecraft thermal models can be built by tuning their numerous parameters using the results of a thermal-balance test. In such a test, the flight article is placed in a thermal vacuum chamber configured to be as similar to the orbital environment as possible. High power-draw subsystems in the spacecraft are “pulsed” on for a few minutes so that the heat propagation through the system can be measured and conductive values in the model tuned. The thermal model can then be used to make more reliable predictions for the orbital temperatures. The ultimate validation of the model is a comparison of the predictions to the actual on-orbit measured temperatures. This paper describes the procedure, analysis, and results of all of the aforementioned as they apply to the first Miniature X-ray Solar Spectrometer 3U CubeSat. The first Miniature X-ray Solar Spectrometer was deployed from the International Space Station on 16 May 2016 and deorbited on 6 May 2017. Many of the tuned-model parameters are applicable to other CubeSats, and could provide a baseline for programs that do not have the resources to dedicate to detailed thermal modeling and testing. A generally good agreement was found to within a few degrees Celsius, between the thermal model and the actual orbital measurements.

Abstract : 

Typhoon is one of the major hazards in ocean coastal areas, but traditional techniques are inadequate to monitor typhoons due to limited or high-cost observations, like radio sounding and meteorological radar. Previous studies have found that typhoons can cause ionospheric disturbances, but the relationship and characteristics are still unclear. In this paper, about 400 stations observations of the Global Positioning System (GPS) network in Taiwan are used to extract ionospheric disturbances during multiple typhoons. The detailed characteristics of the ionospheric disturbances are investigated using a fourth-order Butterworth filter following the 2016 Nepartak, 2019 Lekima, 2019 Mitag, and 2020 Hagupit typhoons. The results show that significant ionospheric disturbances were observed during the typhoons, and the larger disturbances are mostly located 400–1200 km far from the typhoon eye. The estimated horizontal propagation velocity of the ionospheric disturbances is about 127–194 m/s. The locations of the ionospheric disturbances between the typhoon eye and the landfall site are related to the typhoon path. The azimuth distribution of the ionospheric disturbance around the typhoon eye is affected by the GPS elevation angles. At 500–700 km from the typhoon eye, the mean ionospheric disturbances are 0.17 TECU (TEC Unit) and 0.15 TECU for super typhoon Nepartak and Lekima, and 0.13 TECU and 0.18 TECU for typhoon Mitag and Hagupit. The higher the intensity of the typhoon is, the greater the magnitude of the ionospheric disturbance is.

Abstract : 

Measurements of the atmospheric carbon (C) and oxygen (O) relative to hydrogen (H) in hot Jupiters (relative to their host stars) provide insight into their formation location and subsequent orbital migration1,2. Hot Jupiters that form beyond the major volatile (H2O/CO/CO2) ice lines and subsequently migrate post disk-dissipation are predicted have atmospheric carbon-to-oxygen ratios (C/O) near 1 and subsolar metallicities2, whereas planets that migrate through the disk before dissipation are predicted to be heavily polluted by infalling O-rich icy planetesimals, resulting in C/O < 0.5 and super-solar metallicities1,2. Previous observations of hot Jupiters have been able to provide bounded constraints on either H2O (refs. 3,4,5) or CO (refs. 6,7), but not both for the same planet, leaving uncertain4 the true elemental C and O inventory and subsequent C/O and metallicity determinations. Here we report spectroscopic observations of a typical transiting hot Jupiter, WASP-77Ab. From these, we determine the atmospheric gas volume mixing ratio constraints on both H2O and CO (9.5 × 10−5–1.5 × 10−4 and 1.2 × 10−4–2.6 × 10−4, respectively). From these bounded constraints, we are able to derive the atmospheric C/H (0.35+0.17−0.10 × solar) and O/H (0.32+0.12−0.08 × solar) abundances and the corresponding atmospheric carbon-to-oxygen ratio (C/O = 0.59 ± 0.08; the solar value is 0.55). The sub-solar (C+O)/H (0.33+0.13−0.09 × solar) is suggestive of a metal-depleted atmosphere relative to what is expected for Jovian-like planets1 while the near solar value of C/O rules out the disk-free migration/C-rich2 atmosphere scenario.

Abstract : 

The density profiles of dark matter halos are typically modeled using empirical formulas fitted to the density profiles of relaxed halo populations. We present a neural network model that is trained to learn the mapping from the raw density field containing each halo to the dark matter density profile. We show that the model recovers the widely used Navarro-Frenk-White profile out to the virial radius and can additionally describe the variability in the outer profile of the halos. The neural network architecture consists of a supervised encoder-decoder framework, which first compresses the density inputs into a low-dimensional latent representation, and then outputs ρ(r) for any desired value of radius r. The latent representation contains all the information used by the model to predict the density profiles. This allows us to interpret the latent representation by quantifying the mutual information between the representation and the halos’ ground-truth density profiles. A two-dimensional representation is sufficient to accurately model the density profiles up to the virial radius; however, a three-dimensional representation is required to describe the outer profiles beyond the virial radius. The additional dimension in the representation contains information about the infalling material in the outer profiles of dark matter halos, thus discovering the splashback boundary of halos without prior knowledge of the halos’ dynamical history.

Abstract : 

Most of the light from blazars, active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight, is produced by high-energy particles, up to around 1 TeV. Although the jets are known to be ultimately powered by a supermassive black hole, how the particles are accelerated to such high energies has been an unanswered question. The process must be related to the magnetic field, which can be probed by observations of the polarization of light from the jets. Measurements of the radio to optical polarization—the only range available until now—probe extended regions of the jet containing particles that left the acceleration site days to years earlier, and hence do not directly explore the acceleration mechanism, as could X-ray measurements. Here we report the detection of X-ray polarization from the blazar Markarian 501 (Mrk 501). We measure an X-ray linear polarization degree ΠX of around 10%, which is a factor of around 2 higher than the value at optical wavelengths, with a polarization angle parallel to the radio jet. This points to a shock front as the source of particle acceleration and also implies that the plasma becomes increasingly turbulent with distance from the shock.

Abstract : 

Measuring time lags between time series or light curves at different wavelengths from a variable or transient source in astronomy is an essential probe of physical mechanisms causing multiwavelength variability. Time lags are typically quantified using discrete correlation functions (DCFs), which are appropriate for linear relationships. However, in variable sources such as X-ray binaries, active galactic nuclei (AGNs), and other accreting systems, the radiative processes and the resulting multiwavelength light curves often have nonlinear relationships. For such systems it is more appropriate to use nonlinear information-theoretic measures of causation such as mutual information, routinely used in other disciplines. We demonstrate with toy models the limitations of using the standard DCF and show improvements when using a discrete mutual information function (DMIF). For nonlinear correlations, the latter accurately and sharply identifies the lag components as opposed to the DCF, which can be erroneous. Following that, we apply the DMIF to the multiwavelength light curves of AGN NGC 4593. We find that X-ray fluxes are leading UVW2 fluxes by ∼0.2 days, closer to model predictions from reprocessing by the accretion disk than the DCF estimate. The uncertainties with the current light curves are too large, though, to rule out negative lags. Additionally, we find another delay component at approximately-1 day, i.e., UVW2 leading x rays, consistent with inward propagating fluctuations in the accretion disk scenario. This is not detected by the DCF. Keeping in mind the nonlinear relation between x ray and UVW2, this is worthy of further theoretical investigation. From both the toy models and real observations, it is clear that the mutual-information-based estimator is highly sensitive to complex nonlinear relations. With sufficiently high temporal resolution and signal-to-noise ratio, we will precisely detect each of the lag features corresponding to these relations.

Abstract : 

The Evolutionary Map of the Universe (EMU) large-area radio continuum survey will detect tens of millions of radio galaxies, giving an opportunity for the detection of previously unknown classes of objects. To maximise the scientific value and make new discoveries, the analysis of this data will need to go beyond simple visual inspection. We propose the coarse-grained complexity, a simple scalar quantity relating to the minimum description length of an image, that can be used to identify unusual structures. The complexity can be computed without reference to the broader sample or existing catalogue data, making the computation efficient on new surveys at very large scales (such as the full EMU survey). We apply our coarse-grained complexity measure to data from the EMU Pilot Survey to detect and confirm anomalous objects in this data set and produce an anomaly catalogue. Rather than work with existing catalogue data using a specific source detection algorithm, we perform a blind scan of the area, computing the complexity using a sliding square aperture. The effectiveness of the complexity measure for identifying anomalous objects is evaluated using crowd-sourced labels generated via the Zooniverse.org platform. We find that the complexity scan identifies unusual sources, such as odd radio circles, by partitioning on complexity. We achieve partitions where 5 per cent of the data is estimated to be 86 per cent complete, and 0.5 per cent is estimated to be 94 per cent pure, with respect to anomalies and use this to produce an anomaly catalogue.

Abstract : 

Binary formation is an important aspect of star formation. One possible route for close-in binary formation is disk fragmentation. Recent observations show that small-scale asymmetries (<300 au) around young protostars, although not always resolving the circumbinary disk, are linked to disk phenomena. In later stages, resolved circumbinary disk observations (<200 au) show similar asymmetries, suggesting that the asymmetries arise from binary-disk interactions. We observed one of the youngest systems to study the connection between disk and dense core. We find a bright and clear streamer in chemically fresh material (carbon-chain molecular species) that originates from outside the dense core (>10,500 au). This material connects the outer dense core with the region where asymmetries arise near disk scales. This new structure type, ten times larger than those seen near disk scales, suggests a different interpretation of previous observations: large-scale accretion flows funnel material down to disk scales. These results reveal the under-appreciated importance of the local environment on the formation and evolution of disks in early systems and a possible initial condition for the formation of annular features in young disks.

Binary formation is an important aspect of star formation One possible route for close-in binary formation is disk fragmentation . Recent observations show that small-scale asymmetries (<300 au) around young protostars. although not always resolving the circumbinary disk, are linked to disk phenomena In later stages. resolved circumbinary disk observations (<200 au) show similar asymmetries. suggesting that the asymmetries arise from binary-disk interactions We observed one of the youngest systems to study the connection between disk and dense core . We find a bright and clear streamer in chemically fresh material (carbon-chain molecular species) that originates from outside the dense core (> 10,500 au) . This material connects the outer dense core with the region where asymmetries arise near disk scales. This new structure type, ten times larger than those seen near disk scales, suggests a different interpretation of previous observations: large-scale accretion flows funnel material down to disk scales. These results reveal the under-appreciated importance of the local environment on the formation and evolution of disks in early systems and a possible initial condition for the formation of annular features in young disks.

Abstract:

The lunar polar regions contain permanently shadowed regions (PSRs) or local topographic depressions that never receive direct sunlight. These environments (<110 K) have the potential to cold-trap volatile materials in the form of ice, which are essential resources for exploration and industrialization of cislunar space and the Solar System. Orbital observations and those from the LCROSS impactor experiment provide evidence of the existence of water ice and other cold-trapped volatiles in PSRs; however, constraints on volatile abundance and distribution remain ambiguous as individual observations are not always in concord. Here we compile observations indicating the presence of volatiles from ten remotely sensed datasets in 65 PSRs to estimate the locations and mass of water ice deposits. Faustini, Cabeus, de Gerlache, Shoemaker, Haworth, Sverdrup, Slater, and Amundsen are likely the most resource-rich PSRs. Based on co-locations of observations indicative of surface frost and subsurface hydrogen abundance, we find that the craters with the highest potential mass in metric tons (t) of water ice include Cabeus (~11 × 106 t), Shoemaker (~5 × 106 t), Faustini (~4 × 106 t), de Gerlache (~3 × 106 t), and Haworth (~3 × 106 t). Future prospecting of lunar volatiles and water ice is contingent on filling knowledge gaps in resource potential, notably accurate measurements of grade and depth of volatiles. Our proposed ranking and estimates for resource tonnage are a tool to guide future orbital and landed missions that could accurately determine the resource potential of PSR deposits.

Abstract:

The lunar polar regions contain permanently shadowed regions (PSRs) or local topographic depressions that never receive direct sunlight. These environments (<110 K) have the potential to cold-trap volatile materials in the form of ice, which are essential resources for exploration and industrialization of cislunar space and the Solar System. Orbital observations and those from the LCROSS impactor experiment provide evidence of the existence of water ice and other cold-trapped volatiles in PSRs; however, constraints on volatile abundance and distribution remain ambiguous as individual observations are not always in concord. Here we compile observations indicating the presence of volatiles from ten remotely sensed datasets in 65 PSRs to estimate the locations and mass of water ice deposits. Faustini, Cabeus, de Gerlache, Shoemaker, Haworth, Sverdrup, Slater, and Amundsen are likely the most resource-rich PSRs. Based on co-locations of observations indicative of surface frost and subsurface hydrogen abundance, we find that the craters with the highest potential mass in metric tons (t) of water ice include Cabeus (~11 × 106 t), Shoemaker (~5 × 106 t), Faustini (~4 × 106 t), de Gerlache (~3 × 106 t), and Haworth (~3 × 106 t). Future prospecting of lunar volatiles and water ice is contingent on filling knowledge gaps in resource potential, notably accurate measurements of grade and depth of volatiles. Our proposed ranking and estimates for resource tonnage are a tool to guide future orbital and landed missions that could accurately determine the resource potential of PSR deposits.

Abstract:

A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of non-migrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped far below the peak in ionospheric density. The observations can be explained by consideration of the dynamo interaction of the tides with the lower ionosphere (E-layer) in daytime. The influence of persistent tropical rainstorms is therefore an important new consideration for space weather.

Abstract:

In the present study, we explore the observational characteristics of Electromagnetic Ion Cyclotron (EMIC) wave propagation from the source region to the ground. We use magnetometers aboard Geostationary Operational Environment Satellite (GOES) 13, the geosynchronous orbit satellite at 75°W, and at Sanikiluaq ground station (SNK, 79.14°W and 56.32°N in geographic coordinates, and L ∼ 6.0 in a dipole magnetic field) which is located in northern Canada. Using these magnetically conjugate observatories, simultaneous EMIC wave observations are carried out. We found a total of 295 coincident and 248 non-coincident EMIC wave events between GOES 13 and the SNK station. Our statistical analysis reveals that the coincident events are predominantly observed on the dayside. The wave normal angles are slightly higher for the non-coincident events than for coincident events. However, the coincidence of the waves is mostly governed by the intensity and duration of the wave. This is confirmed by the geomagnetic environment which shows higher auroral electrojet (AE) and Kp indices for the coincident events. We also found that some events show high-frequency (f > 0.4 Hz) wave filtering. The statistics of the high-frequency filtered and non-filtered wave events show that there are clear magnetic local time (MLT) and F10.7 index differences between the two groups, as well as in ionospheric electron density measurements. In addition, we also found differences in the wave properties which possibly indicate that the propagation in the magnetosphere also plays an important role in the wave filtering.

Abstract:

Magnetic fields (B) are an important factor that controls the star formation process. The leading method to observe B is using polarized thermal emission from dust grains aligned with B. However, in dense environments such as protostellar cores, dust grains may have inefficient alignment due to strong gas randomizations, so that using dust polarization to trace B is uncertain. Hoang & Lazarian (2016) demonstrated that the grain alignment by RAdiative Torques is enhanced if dust grains contain embedded iron inclusions. Here we extend POLARIS code to study the effect of iron inclusions on grain alignment and thermal dust polarization toward a protostellar core, assuming uniform magnetic fields. We found that paramagnetic grains produce a low polarization degree of p∼1% in the envelope and negligible p≪1% in the central region due to the loss of grain alignment. In contrast, grains with a high level of iron inclusions can have perfect alignment and produce high p∼40% in the envelope and low p≤10% in the central region. Grains with a moderate level of iron inclusions induce the polarization flipping from P ∥ B at millimeter to P ⊥ B at submillimeter due to the change in the internal alignment caused by slow internal relaxation. The weak alignment of very large grains of a≥10μm reduces the polarization by dichroic extinction at submillimeter wavelengths. We found a positive correlation between p and the level of iron inclusions, which opens a new window to constrain the abundance of irons locked in dust through dust polarimetry.

Abstract:

Brown dwarfs with masses below 0.075 solar masses are thought to form like low-mass stars (e.g., the Sun).However, it is still unclear how the physical formation processes occur in brown dwarfs at the ealiest stages (i.e., proto-brown dwarfs) of their formation. Up to date, only a few proto-brown dwarfs have been detected. The detection of proto-brown dwarfs offers us excellent benchmarks to study the formation process of brown dwarfs, and thus understand their formation mechanism.In this paper, we present our identification of a proto-brown dwarf candidate in the star-forming region(\rho) Ophiuchus. The candidate shows a small-scale bipolar molecular outflow that is similar to the outflows observed inother young brown dwarfs. The detection of this candidate provides us with additional important implications for the formation mechanism of brown dwarfs.

Abstract:

We explore how information in images of nearby galaxies can be used to estimate their distance. We train a convolutional Neural Network (NN) to do this, using galaxy images from the Illustris simulation. We show that if the NN is trained on data with random errors added to the true distance (representing training using spectroscopic redshift instead of actual distance), then the NN can predict distances in a test dataset with greater accuracy than it was given in the training set. This is not unusual, as often NNs are trained on data with added noise, in order to increase robustness. In this case, however, it offers a route to estimating peculiar velocities of nearby galaxies. Given a galaxy with a known spectroscopic redshift one can use the NN-predicted distance to make an estimate of the peculiar velocity. Trying this using relatively low resolution (1.4 arcsec per pixel) simulated galaxy images we find fractional RMS distance errors of 7.7% for galaxies at a mean distance of 75 Mpc from the observer, leading to RMS peculiar velocity errors of 440 km/s. In a companion paper we apply the technique to 145,115 nearby galaxies from the NASA Sloan Atlas.

Abstract:

We have complemented existing observations of H i absorption with new observations of HCO+, C2H, HCN, and HNC absorption from the Atacama Large Millimeter/submillimeter Array and the Northern Extended Millimeter Array in the directions of 20 background radio continuum sources with 4° ≤ ?b? ≤ 81° to constrain the atomic gas conditions that are suitable for the formation of diffuse molecular gas. We find that these molecular species form along sightlines where AV ? 0.25, consistent with the threshold for the H i-to-H2 transition at solar metallicity. Moreover, we find that molecular gas is associated only with structures that have an H i optical depth >0.1, a spin temperature <80 K, and a turbulent Mach number ? 2. We also identify a broad, faint component to the HCO+ absorption in a majority of sightlines. Compared to the velocities where strong, narrow HCO+ absorption is observed, the H i at these velocities has a lower cold neutral medium fraction and negligible CO emission. The relative column densities and linewidths of the different molecular species observed here are similar to those observed in previous experiments over a range of Galactic latitudes, suggesting that gas in the solar neighborhood and gas in the Galactic plane are chemically similar. For a select sample of previously observed sightlines, we show that the absorption line profiles of HCO+, HCN, HNC, and C2H are stable over periods of ∼3 yr and ∼25 yr, likely indicating that molecular gas structures in these directions are at least ?100 au in size.

Abstract:

Transverse Pc1 waves propagating from magnetospheric source regions undergo mode conversion to the compressional mode in the ionosphere due to the induced Hall current. Mode converted Pc1 waves propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). PWDs have been observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal and longitudinal range. In this work, we present the statistical analysis results of PWD exploiting Swarm satellites from 2015 to 2019. Spatial distributions show that the PWDs are mainly observed over the South Atlantic Anomaly longitudes, possibly due to the high Hall conductivity and F region density, and at subauroral/auroral latitudes (±50°−70° MLAT). The occurrence rate of PWD increases with increasing AE and |SYM H| indices. Seasonal dependence shows that PWD exhibits a high occurrence rate during equinox and local summer while local winter hosts only a low occurrence. The asymmetry between summer and winter can be explained by the ionospheric plasma density. The high occurrence rate in equinox may result from intense geomagnetic activity during the equinox, probably due to the Russell McPherron effect. From our statistical analysis, we conclude that the occurrence of PWD is controlled by both ionospheric plasma conditions and geomagnetic activity, and that the mode conversion and PWD occur more efficiently as plasma density increases.

Abstract:

A sudden stratospheric waring occurred in the southern hemisphere during September 2019, accompanied by an exceptionally strong quasi 6 day wave (Q6DW). We examine the ionospheric response using global total electron content (TEC) maps, with a focus on the short period variability (5-48 h). A Fourier analysis of the TEC data reveals ionospheric variations associated with the secondary waves due to the non linear interaction between the Q6DW and atmospheric tides. The largest signatures among them are related to the ∼29 h standing oscillation, which is attributable to the Q6DW interaction with the migrating diurnal tide, with the maximum amplitude ∼8% of the zonal mean. Also detected are the signatures associated with the westward propagating ∼13 h oscillation with the zonal wavenumber 1 (∼4%) and westward propagating ∼11 h oscillation with the zonal wavenumber 3 (∼3%), both of which can be attributed to the Q6DW interaction with the migrating semidiurnal tide. The signatures related to the Q6DW interaction with the migrating terdiurnal tide and some non migrating tides are also observed. This is the first time that secondary wave signatures of the Q6DW tidal interaction are identified in ionospheric observations with predicted zonal wavenumbers and periods. The oscillations are symmetric about the magnetic equator with amplitude peaks at ±20° magnetic latitudes, suggesting that the oscillations are generated by the modulation of the equatorial plasma fountain.

Abstract:

The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf–Rayet stars emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars, leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion. Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients. Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf–Rayet stars may be the progenitors of some rapidly evolving transients.

Abstract:

We describe a method for the in-orbit calibration of body-mounted magnetometers based on the CHAOS-7 geomagnetic field model. The code is designed to find the true calibration parameters autonomously by using only the onboard magnetometer data and the corresponding CHAOS outputs. As the model output and satellite data have different coordinate systems, they are first transformed to a Star Tracker Coordinate (STC). Then, non-linear optimization processes are run to minimize the differences between the CHAOS-7 model and satellite data in the STC. The process finally searches out a suite of calibration parameters that can maximize the model-data agreement. These parameters include the instrument gain, offset, axis orthogonality, and Euler rotation matrices between the magnetometer frame and the STC. To validate the performance of the Python code, we first produce pseudo satellite data by convoluting CHAOS-7 model outputs with a prescribed set of the 'true' calibration parameters. Then, we let the code autonomously undistort the pseudo satellite data through optimization processes, which ultimately track down the initially prescribed calibration parameters. The reconstructed parameters are in good agreement with the prescribed (true) ones, which demonstrates that the code can be used for actual instrument data calibration. This study is performed using Python 3.8.5, NumPy 1.19.2, SciPy 1.6, AstroPy 4.2, SpacePy 0.2.1, and ChaosmagPy 0.5 including the CHAOS-7.6 geomagnetic field model. This code will be utilized for processing NextSat-1 and Small scale magNetospheric and Ionospheric Plasma Experiment (SNIPE) data in the future.

Abstract:

The mismatch between the locally measured expansion rate of the universe and the one inferred from the cosmic microwave background measurements by Planck in the context of the standard ΛCDM, known as the Hubble tension, has become one of the most pressing problems in cosmology. A large number of amendments to the ΛCDM model have been proposed in order to solve this tension. Many of them introduce new physics, such as early dark energy, modifications of the standard model neutrino sector, extra radiation, primordial magnetic fields or varying fundamental constants, with the aim of reducing the sound horizon at recombination r?. We demonstrate here that any model which only reduces r? can never fully resolve the Hubble tension while remaining consistent with other cosmological datasets. We show explicitly that models which achieve a higher Hubble constant with lower values of matter density Ωmh2 run into tension with the observations of baryon acoustic oscillations, while models with larger Ωmh2 develop tension with galaxy weak lensing data

Abstract:

The hitherto unprecedented angular resolution of the Event Horizon Telescope has created exciting opportunities in the search for new physics. Recently, the linear polarization of radiation emitted near the supermassive black hole M87? was measured on four separate days, precisely enabling tests of the existence of a dense axion cloud produced by a spinning black hole. The presence of an axion cloud leads to a frequency-independent oscillation in the electric vector position angle of this linear polarization. For the nearly face-on M87?, this oscillation in the electric vector position angle appears as a propagating wave along the photon ring. In this paper, we leverage the azimuthal distribution of electric vector position angle measured by the Event Horizon Telescope to study the axion-photon coupling. We propose a novel differential analysis procedure to reduce the astrophysical background, and derive stringent constraints on the existence of axions in the previously unexplored mass window of ~(10⁻²¹-10⁻²⁰) eV.

Abstract:

It is well known that electromagnetic ion cyclotron (EMIC) waves play an important role in controlling particle dynamics inside the Earth’s magnetosphere, especially in the outer radiation belt. In order to understand the results of wave-particle interactions due to EMIC waves, it is important to know how the waves are distributed and what features they have. In this paper, we present some statistical analyses on the spatial distribution of EMIC waves in the low Earth orbit by using Swarm satellites from December 2013 to June 2017 (~3.5 years) as a function of magnetic local time, magnetic latitude, and magnetic longitude. We also study the wave characteristics such as ellipticity, wave normal angle, peak frequency, and wave power using our automatic wave detection algorithm based on the method of Bortnik et al. (2007, https://doi.org/10.1029/2006JA011900). We also investigate the geomagnetic control of the EMIC waves by comparing with geomagnetic activity represented by Kp and Dst indices. We find that EMIC waves are detected with a peak occurrence rate at midlatitude including subauroral region, dawn sector (3–7 magnetic local time), and linear polarization dominated with an oblique propagating direction to the background magnetic field. In addition, our result shows that the waves have some relation with geomagnetic activity; that is, they occur preferably during the geomagnetic storm’s late recovery phase at low Earth orbit.

Abstract:

The most stringent local measurement of the Hubble constant from Cepheid-calibrated Type Ia supernovae (SNe~Ia) differs from the value inferred via the cosmic microwave background radiation ({\it Planck}+ΛCDM) by more than 5σ. This so-called "Hubble tension" has been confirmed by other independent methods, and thus does not appear to be a possible consequence of systematic errors. Here, we continue upon our prior work of using Type II supernovae to provide another, largely-independent method to measure the Hubble constant. From 13 SNe~II with geometric, Cepheid, or tip of the red giant branch (TRGB) host-galaxy distance measurements, we derive H0=75.4+3.8−3.7 km s−1 Mpc−1 (statistical errors only), consistent with the local measurement but in disagreement by ∼2.0σ with the Planck +ΛCDM value. Using only Cepheids (N=7), we find H0=77.6+5.2−4.8 km s−1 Mpc−1, while using only TRGB (N=5), we derive H0=73.1+5.7−5.3 km s−1 Mpc−1. Via 13 variants of our dataset, we derive a systematic uncertainty estimate of 1.5 km s−1 Mpc−1. The median value derived from these variants differs by just 0.3 km s−1 Mpc−1 from that produced by our fiducial model. Because we only replace SNe~Ia with SNe~II -- and we do not find tension between the Cepheid and TRGB H0 measurements -- our work reveals no indication that SNe~Ia or Cepheids could be the sources of the "H0 tension." We caution, however, that our conclusions rest upon a modest calibrator sample; as this sample grows in the future, our results should be verified.

Abstract:

The local interstellar medium (ISM) is suffused with "dark" gas, identified by excess infrared and gamma-ray emission, yet undetected by standard ISM tracers such as neutral hydrogen (H i) or carbon monoxide emission. Based on observed dust properties from Planck, recent studies have argued that H i mixed with dust is strongly saturated and that dark gas is dominated by optically thick H i. We test this hypothesis by reproducing this model using data from Planck and new 21 cm emission maps from GALFA-H i—the first large-area 21 cm emission survey with comparable angular resolution to Planck. We compare the results with those from a large sample of H i column densities based on direct observations of H i optical depth, and find that the inferred column density corrections are significantly lower than those inferred by the Planck-based model. Further, we rule out the hypothesis that the pencil-beam H i absorption sight lines preferentially miss opaque "blobs" with small covering fraction, as these structures require densities and pressures that are incompatible with ISM conditions. Our results support the picture that excess dust emission in the local ISM is not dominated by optically thick H i, but is rather a combination of intrinsic changes in dust grain emissivities and H₂ missed by CO observations.