Astrophysical Observatory Research Articles

The Radio Fundamental Catalog. I. Astrometry

We present an all-sky catalog of absolute positions and estimates of correlated flux density of 21,942 compact radio sources determined from processing interferometric visibility data of virtually all very long baseline interferometry (VLBI) observing sessions at 2–23 GHz from 72 programs suitable for absolute astrometry collected for 30 yr. We used a novel technique of generation of a data set of fused observables that allowed us to incorporate all available data in our analysis. The catalog is the most complete and most precise to date. It forms the foundation and reference for positional astronomy, space geodesy, space navigation, and population analysis of active galactic nuclei (AGNs), and provides calibrators for phase referencing for differential astrometry and VLBI astrophysical observations. Its accuracy was evaluated through a detailed accounting of systematic errors, rigorous decimation tests, comparison of different data sets, and comparison with other catalogs. The catalog preferentially samples AGNs with strong contemporary parsec-scale synchrotron emission. Its milliarcsecond-level positional accuracy allows association of these AGNs with detections in a wide range of the electromagnetic spectrum from low-frequency radio to γ rays and high-energy neutrinos. We describe the innovative data processing and calibration technique in full detail, report the in depth analysis of random and systematic positional errors, and provide a list of associations with large surveys at different wavelengths.

Constraining Dark Matter Models with a Light Mediator from CDEX-10 Experiment at China Jinping Underground Laboratory

Abstract We search for nuclear recoil signals of dark matter models with a light mediator using data taken
from a p-type point-contact germanium detector of the CDEX-10 experiment at the China Jinping
Underground Laboratory. The 90% confidence level upper limits on the DM-nucleon interaction
cross section from 205.4 kg-day exposure data are derived, excluding new parameter space in 2∼3
GeV DM mass when the mediator mass is comparable to or lighter than the typical momentum
transfer. We further interpret our results to constrain a specific self-interacting dark matter model
with a light mediator coupling to the photon through kinetic mixing, and set experimental limits
on the model parameter region favored by astrophysical observations.

Resonant or asymmetric: the status of sub-GeV dark matter

Sub-GeV dark matter (DM) particles produced via thermal freeze-out evade many of the strong constraints on heavier DM candidates but at the same time face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In this work we combine all of these constraints in order to perform frequentist and Bayesian global analyses of fermionic and scalar sub-GeV DM coupled to a dark photon with kinetic mixing. For fermionic DM, we find viable parameter regions close to the dark photon resonance, which expand significantly when including a particle-antiparticle asymmetry. For scalar DM, the velocity-dependent annihilation cross section evades the strongest constraints even in the symmetric case. Using Bayesian model comparison, we show that both asymmetric fermionic DM and symmetric scalar DM are preferred over symmetric fermionic DM due to the reduced fine-tuning penalty. Finally, we explore the discovery prospects of near-future experiments both in the full parameter space and for specific benchmark points.We find that the most commonly used benchmark scenarios are already in tension with existing constraints and propose a new benchmark point that can be targeted with future searches.

IAU South-West and Central Asian Regional Office of Astronomy for Development

The International Astronomical Union (IAU) announced its Strategic Plan on Astronomy for Development in 2009, during the International Year of Astronomy (IYA) (for 2011-2020, extended to 2021-2030). One of its main components was the creation of the Office of Astronomy for Development (OAD) and corresponding Regional Offices (ROADs) for implementation and coordination of its aims. The OAD was created in Cape Town, South Africa and later on ROADs were created in 11 regions. Since 2015, Armenia has hosted one of them, IAU South West Asian (SWA) IAU ROAD, later renamed South West and Central Asian (SWCA) ROAD. At present, already six countries have officially joined (Armenia, Georgia, Iran, Kazakhstan, Tajikistan, and Turkey), but the Office serves for a rather broad region, from Eastern Europe to Central Asia. Armenia’s geographical location and its historical role in astronomy (both for well-known archaeoastronomical heritage and the presence of the famous Byurakan Astrophysical Observatory (BAO) founded by Viktor Ambartsumian in 1946) serve as a link between Europe and Eastern Partnership countries, Middle East and Asia in general. We run activities in 3 directions, Task Forces (TF): TF1 Universities and Research, TF2 Children and Schools and TF3 Public Outreach. In addition, we participate in the OAD Flagship Projects; Flagship 1: Astrotourism, Flagship 2: Astro for Mental Health, Flagship 3: Hack4Dev. We present our projects and all other accomplishments and discuss the role of our ROAD in maintaining contacts and development of astronomy in the region, as well as contacts between Europe and the Eastern Partnership countries. The most up-to-date information about the IAU SWCA ROAD is available on its webpage at http://iau-swa-road.aras.am/eng/index.php.

Astronomy in Georgia

We provide a brief history of Georgian astronomy and discuss its current state. The discussion also covers the scientific facilities of Georgia’s leading astrophysical institute, the Evgeni Kharadze Georgian National Astrophysical Observatory, as well as current scientific projects and specialists involved in them. It also includes educational activities on astronomy in Georgia.

Complex investigations of an active star-formation region in southern part of Mon R2

Abstract We continue to present the results of a Byurakan Narrow Band Imaging Survey (BNBIS). In this work we present the results of the search and further detailed investigation of the objects, found in the course of the BNBIS survey in the southern part of the Mon R2 association. For the search of HH objects the narrow band images, obtained with the 1-m Schmidt telescope of the Byurakan Observatory, were used. Newly found objects were imaged in optical and near-IR range with the Apache Point Observatory 3.5 meter telescope, and observed spectrally with long-slit spectrograph and scanning Fabry-Perot interferometer on 6 m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences using SCORPIO-2. We found three new HH groups: HH 1233, HH 1234 and HH 1235, two of them represent extended collimated flows. HH 1233 is the C-shape bipolar outflow system associated with the 2MASS 06084223−0657385 source star. HH 1234 is the helical chain of HH knots near the star V963 Mon. HH 1235 is a separate compact knot, connected with the visible only in mid- and far-IR source WISE J060856.57−070103.5. We found also several molecular hydrogen outflows, one of which coincides with HH 1233 and two other are associated with the deeply embedded IR sources in the same field. One more probable bipolar H2 outflow is related to WISE J060856.57−070103.5. The emission spectra and spectral energy distributions of the source stars were analyzed. According to them they should be under rather early evolutional stage.

Testing the Universality of Self-organized Criticality in Galactic, Extragalactic, and Black Hole Systems

In this study, we test whether the power law slopes (α F ) for fluxes (F), and (α E ) for energies (E) are universal in their size distributions, N(F)∝F−αF and N(E)∝E−αE , in astrophysical observations of galactic, extragalactic, and black hole systems. This is a test of fundamental importance for self-organized criticality (SOC) systems. The test decides whether (i) power laws are a natural consequence of the scale-freeness and inherent universality of SOC systems, or (ii) if they depend on more complex physical scaling laws. The former criterion allows quantitative predictions of the power-law-like size distributions, while the latter criterion requires individual physical modeling for each SOC variable and data set. Our statistical test, carried out with 61 published data sets, is consistent with the former option, which implies that observed power laws can simply be derived from the scale-freeness and do not require specific physical models to understand their statistical distributions. The observations show a mean and standard deviation of α F = 1.78 ± 0.29 for SOC fluxes and α E = 1.66 ± 0.22 for SOC fluences, and thus are consistent with the prediction of the fractal-diffusive SOC model, with α F = 1.80 and α E = 1.67.

Revisiting Radio Variability of the Blazar 3C 454.3

We examine lengthy radio light curves of the flat spectrum radio galaxy 3C 454.3 for possible quasiperiodic oscillations (QPOs). The data used in this work were collected at five radio frequencies, 4.8, 8.0, 14.5, 22.0, and 37.0 GHz between 1979 and 2013 as observed at the University of Michigan Radio Astronomical Observatory, Crimean Astrophysical Observatory, and Aalto University Metsähovi Radio Observatory. We employ generalized Lomb–Scargle periodogram and weighted wavelet transform analyses to search for periodicities in these light curves. We confirm a QPO period of ∼2000 days to be at least 4σ significant using both methods at all five radio frequencies between 1979 and 2007, after which a strong flare changed the character of the light curve. We also find a ∼600 day period, which is at least 4σ significant, but only in the 22.0 and 37.0 GHz light curves. We briefly discuss physical mechanisms capable of producing such variations.

New Radio Observations of the Supernova Remnant CTA 1

We present new radio images of the supernova remnant (SNR) CTA 1 at 1420 and 408 MHz, and in the 21 cm line of H i observed with the Dominion Radio Astrophysical Observatory Synthesis Telescope and at 1420 MHz observed with the Effelsberg 100 m telescope. We confirm previously described continuum features and elaborate further on filamentary features identified using the high-resolution (1′) maps from these new observations. We investigate the abrupt change in sign of rotation measure (RM) across the SNR, using the linear polarization observations in the four bands around 1420 MHz. Following X. H. Sun et al.’s (2011) investigation, we both confirm that the distribution of signs of the RMs for extragalactic sources in the area appears to match that of the shell, as well as combine the data from the four bands to estimate the relative depolarization and the intrinsic rotation measure of the SNR. We do not conclusively reject X. H. Sun et al.’s (2011) claim of a Faraday screen in the foreground causing the distribution of RMs that we observe; however, we do suggest an alternative explanation of a swept-up stellar wind from the progenitor star with a toroidal magnetic field. Finally, we expand on the analysis of the H i observations by applying the Rolling Hough Transform to isolate filamentary structure and better identify H i emission with the SNR. Further constraining the H i velocity channels associated with CTA 1, we use more recent Galactic rotation curves to calculate an updated kinematic distance of 1.09 ± 0.2 kpc.

Falsifying anthropics

We propose using fuzzy axion dark matter to test the anthropic principle.A very light axion can be directly detectable, at least by black hole superradiance effects.The idea then is that gravitational and astrophysical observations candiscover a light axion in the regime where it must be all of dark matter with abundancewhich must be set up by the anthropic principle, due to excessive primordial misalignment induced byinflation-induced Brownian drift of fluctuations.Yet it may turn out that dark matter is something else instead of this axion. Since the de Sitter-inducedaxion misalignment controlled only by the de Sitter curvature cannot be evaded,this would invalidate the anthropic prediction of the dark matter abundance.

First operation of LArTPC in the stratosphere as an engineering GRAMS balloon flight (eGRAMS)

Abstract GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation balloon/satellite experiment utilizing a LArTPC (Liquid Argon Time Projection Chamber), to simultaneously target astrophysical observations of cosmic MeV gamma-rays and conduct an indirect dark matter search using antimatter. While LArTPCs are widely used in particle physics experiments, they have never been operated at balloon altitudes. An engineering balloon flight with a small-scale LArTPC (eGRAMS) was conducted on July 27th, 2023, to establish a system for safely operating a LArTPC at balloon altitudes and to obtain cosmic-ray data from the LArTPC. The flight was launched from the Japan Aerospace Exploration Agency’s (JAXA) Taiki Aerospace Research Field in Hokkaido, Japan. The total flight duration was 3 hours and 12 minutes, including a level-flight of 44 minutes at a maximum altitude of 28.9 km. The flight system was landed on the sea and successfully recovered. The LArTPC was successfully operated throughout the flight, and about 0.5 million events of the cosmic-ray data including muons, protons, and Compton scattering gamma-ray candidates, were collected. This pioneering flight demonstrates the feasibility of operating a LArTPC in high-altitude environments, paving the way for future GRAMS missions and advancing our capabilities in MeV gamma-ray astronomy and dark matter research.

Designing New Ultra-Radiopure, High-Strength Electroformed CuCr Alloys, for Rare Event Searches

Immense progress has been achieved in understanding the Cosmos over more than 45 orders of magnitude in length. Alas, fundamental questions remain about the nature of; a) Dark Matter (DM); and b) neutrinos. DM’s existence, corresponding to 84.5% of the Universe’s matter, is established via astrophysical observations and precise measurements. Several search approaches have been employed, but “direct detection” is the most prominent: aiming to observe DM from the Milky Way halo via its coherent elastic scattering off a nucleus.Copper is the material of choice for rare event searches: it can be procured commercially at low cost and high purity, and it has no long lifetime isotopes. Alas, it may be contaminated during manufacturing and can be activated by fast neutrons from cosmic rays. In an effort to achieve even higher radiopurity, attention is focused on electroformed copper (EFCu), which has favorable radiochemical, thermal, and electrical properties. To fulfil the unique radiopurity requirements, experiments pioneer large-scale additive-free Cu electroformation, e.g. the on-going project ECUME. This novel technique [1] leads to extreme radiopurities with contamination below 10- 14 grams of 232Th and 238U per Cu gram. However, Copper is highly ductile and of low strength, limiting its use for moving mechanical, high-pressure, and load-bearing parts. This would improve the capability for experiments such as DarkSPHERE [2], a large-scale fully electroformed underground spherical proportional counter operating under high pressureto probe uncharted territory in the search for DM, and is vital for nEXO', a neutrinoless-double β-decay experiment aiming to clarify the nature of neutrinos.The most promising alloying element for improved strength of EFCu is Chromium (Cr). It has been experimentally demonstrated that small additions of Cr, combined with heat treatment and aging, improve strength by 70% [3]. However, Cr additions lead to impurities, and a compromise between strength and radiopurity is required by exploring a complex parameter space of compositions and strengthening mechanisms [4].Cr solubility in Cu is very limited and small additions of Ti can allow for improved mechanical strengthening due to reinforced precipitation. A critical evaluation of the ternary phase diagram of the Cr-Cu-Ti system is underway to inform the particular parameter space of compositions and strengthening mechanisms within the CALPHAD framework. This system has gained recently significant interest in the development of CuCrTi alloys for contact wires of high-speed, large-scale integrated circuit lead frames and electronic connectors [5].Our work addresses materials challenges by developing high radiopure CuCr and CuCrTi alloys with significantly higher strength compared to Cu. The project will deliver a novel approach based on the Integrated Computational Materials Engineering (ICME) framework enabling rapid design of new, application-specific alloys for fields where thermodynamic and kinetic description of the system are crucial. Electroformation in additive-free bath is the focus of the project, which will push the boundaries in many fields, from fundamental science to industrial applications.

Neutrino oscillation in the presence of background classical sources

Abstract The presence of background classical sources affects a quantum field theory significantly in different ways. Neutrino oscillation is a phenomenon that confirms that neutrinos are massive fermions in nature, a celebrated result in modern physics. Neutrino oscillation plays an important role in many astrophysical observations. However, the interactions between the background classical sources with neutrinos are not often considered. In the present article, we show the effect of some classical sources, namely matter currents, electromagnetic waves, torsion, and gravitational waves on neutrino oscillation. It is shown explicitly that the above sources can change the helicity state of neutrinos during neutrino oscillation.

Re-visiting the role of short-range correlations on neutron-star properties

The impact of short-range correlations (SRCs) on neutron star (NS) properties is re-examined across various classes of relativistic mean-field (RMF) models. The coupling strengths of the models are so adjusted that the low-density part of the equation of state (EoS), complemented with saturation properties such as binding energy of symmetric nuclear matter and nuclear symmetry energy responsible for the bulk properties of finite nuclei, remains practically unaffected with the inclusion of SRCs. The EoS for symmetric nuclear matter and the nuclear symmetry energy at supra-saturation densities which governs the EoS for NS matter become softer or stiffer in the presence of the SRCs, depending on the type of RMF model considered. These distinct effects of SRCs are observed to be more significant at higher densities, as expected, when behaviour of the EoS at low densities, which govern the finite nuclei physics, is not compromised. For most of the models with self-couplings of scalar and vector mesons, the EoS of symmetric nuclear matter stiffens, with a slight effect on nuclear symmetry energy with the inclusion of SRCs. Conversely, in the models incorporating cross-couplings between mesons, the addition of SRCs leads to softer symmetry energy, compensating the stiffening effect of the EoS of symmetric nuclear matter. With the inclusion of SRCs, the values of radius and tidal deformability of canonical mass star and maximum mass of NSs for realistic EoSs align well the present constraints on astrophysical observations.

Simulating Vertical Profiles of Optical Turbulence at the Special Astrophysical Observatory Site

In this paper, we used meteorological data to simulate vertical profiles of optical turbulence at the Special Astrophysical Observatory (SAO) (Russia, 43°40′19″ N 41°26′23″ E, 2100 m a.s.l.), site of the 6 m Big Telescope Alt-azimuthal. For the first time, the vertical profiles of optical turbulence are calculated for the SAO using ERA-5 reanalysis data. These profiles are corrected using DIMM measurements as well as estimations of atmospheric boundary layer heights. We may note that the method basically reconstructs the most important features of the shape of the measured profile under clear sky. Atmospheric turbulent layers were identified, and the strength of optical turbulence in these layers was estimated. The model hourly values of seeing corresponding to the obtained vertical profiles range from 0.40 to 3.40 arc sec; the values of the isoplanatic angle vary in the range from 1.00 to 3.00 arc sec (at λ = 500 nm). The calculated median of seeing is close to 1.21 arc sec. These estimations are close to the measured median of seeing (1.21 arc sec).

Shadows and quasinormal modes of rotating black holes in Horndeski theory: Parameter constraints using EHT observations of M87* and Sgr A*

One way to test the presence of scalar & vector fields in the spacetime of black holes is to get constraints on the fields and black hole parameters using astrophysical observations such as black hole shadow, quasiperiodic oscillations, etc. In this work, we aimed to investigate spacetime properties around black holes in Horndeski gravity. First, we obtain a rotating black hole solution using the Newman–Janis Algorithm (NJA), and we study the event horizon, statistic limits, and ergoregion of the black hole spacetime. In addition, we calculate the effective gravitational mass of the black hole. We derive equations for null geodesics and show the combined effects of the black hole spin and Horndeski gravity parameter on the shadow shape of the black hole and its radius distortion. We find that black hole spin and Horndeski parameters cause an increase in the values of shadow radius and its deformation. Next, we obtain constraints for the upper and lower values for black hole spin and Horndeski parameters using event horizon telescope (EHT) data from Sgr A* and M87*shadow sizes. Finally, we investigated the shadow radius, equatorial, and polar quasinormal modes using the geometric-optic relationship between the parameters of the quasinormal mode and the conserved values along the geodesics in the spacetime of the rotating Horndeski black hole.

KISS: Instrument Description and Performance

Kinetic inductance detectors (KIDs) have been proven as reliable systems for astrophysical observations, especially in the millimeter range. Their compact size enables them to optimally fill the focal plane, thus boosting sensitivity. The KIDs Interferometric Spectral Surveyor (KISS) instrument is a millimeter camera that consists of two KID arrays of 316 pixels each coupled to a Martin–Puplett interferometer (MPI). The addition of the MPI grants the KID camera the ability to provide spectral information in the 100 and 300 GHz range. In this paper, we report the main properties of the KISS instrument and its observations. We also describe the calibration and data analysis procedures used. We present a complete model of the observed data including the sky signal and several identified systematics. We have developed a full photometric and spectroscopic data analysis pipeline that translates our observations into science-ready products. We show examples of the results of this pipeline on selected sources: the Moon, Jupiter, and Venus. We note the presence of a deficit of response with respect to expectations and laboratory measurements. The detector's noise level is consistent with values obtained during laboratory measurements, pointing to a suboptimal coupling between the instrument and the telescope as the most probable origin for the problem. This deficit is large enough to prevent the detection of galaxy clusters, which were KISS's main scientific objective. Nevertheless, we have demonstrated the feasibility of this kind of instrument in the prospect of other KID interferometers (such as the CONCERTO instrument). In this regard, we have developed key instrumental technologies such as optical conception, readout electronics, and raw calibration procedures, as well as adapted data analysis procedures.

Study of anisotropic quark stars with interacting quark matter in f(R,T) gravity

We explore the structural properties of quark stars (QSs) in a modified gravity theory known as f(R,T) gravity, which introduces a coupling between matter and spacetime geometry, through a basic linear functional form f(R,T)=R+2βT. Our study focuses on QSs made of interacting quark matter (IQM) as an equation of state. We first derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations for anisotropic matter in a spherically symmetric context and solve them numerically to obtain the structural properties of QSs. Stability is analyzed through static stability analysis, critical adiabatic indices, and sound speed profiles. Using astrophysical constraints from the “black widow” pulsar PSR J0952-0607 and the GW190814 event, we calibrate our model parameters. Our results indicate that with higher λ¯, both the maximum mass and radius of QSs increase, achieving a maximum mass of over 2M⊙, peaking at 3.15M⊙ for a radius of 14.90km at λ¯=0.9. The maximum compactness also rises to M/R=0.313 while adhering to the Buchdahl limit. Additionally, varying β in the range [−0.2,0.2] with fixed parameters shows that lower β values enhance the maximum mass of QSs, reaching 2.65M⊙ at β=−0.2, with the compactness remaining around M/R≈0.3. Furthermore, changes in μ from [−1.0,1.0] significantly affect maximum mass; at μ=1.0, the mass peaks at 3.15M⊙ and decrease to 2.68M⊙ at μ=0. The compactness increases with μ, indicating that anisotropic pressure influences the M−R relations. In summary, our findings reveal that the parameters λ¯, β, and μ play crucial roles in shaping the physical properties of QSs in the f(R,T) gravity framework, consistent with astrophysical observations from pulsars and gravitational wave events.

Toward UV models of kinetic mixing and portal matter. VI. A more complex dark matter sector?

Portal matter (PM), having both Standard Model (SM) and dark sector charges, can induce kinetic mixing between the U(1)D dark photon and the SM gauge fields at the 1-loop level offering an attractive mechanism by which light (≲1 GeV) thermal dark matter (DM) can interact with visible matter and obtain its observed relic density. In doing so, if the DM is fermionic, the CMB and other astrophysical observations inform us that it must be Majorana/pseudo-Dirac in nature to avoid velocity/temperature-independent s-wave annihilation to SM final states. How does this idea fit into a more UV-complete picture also including the SM interactions? There are some reasons to believe that at least a first step along this path may not lie too far away in energy due to the renormalization group equations running of the dark gauge coupling, which for a significant range of parameters, becomes nonperturbative at/before the ∼10’s of TeV energy range. This implies that U(1)D must become embedded in an asymptotically free, non-Abelian group, GD, before this can occur. The breaking of this larger group then produces the masses for the PM and the additional gauge fields associated with GD then can lead to new interactions between the SM and the dark sector. Following several bottom-up approaches, we have examined a set of distinctive and testable phenomenological features associated with this general setup, based upon a number of simplifying assumptions. Clearly, it behooves us to explore the impact of these specific assumptions on these predictions for the array of possible experimental tests of this class of models. In most past analyses it has been assumed that DM is a vectorlike, complex singlet under the group GD. If this assumption is relaxed, the dark sector must be augmented by additional fermion(s) and the associated scalar fields needed to break the gauge symmetries while generating the needed Majorana-like mass terms for the DM. In this paper, we analyze the simplest extension of this kind wherein the DM lies in a vectorlike doublet of GD, which we take to have the structure SU(2)I×U(1)YI as in earlier work, leading to new phenomenological implications. We find, for example, that given the current LHC search constraints on the masses of heavy gauge bosons, the production of these new dark states with large rates is unlikely to occur at colliders unless they are produced singly in gg fusion or their pair production cross sections are resonantly enhanced. We also find that an additional mechanism arises to generate hierarchal neutrino masses in such a setup. Published by the American Physical Society 2024

Changes in the longitude polarization dependence of Jupiter's moon Io as evidence of the long-term variability of its volcanic activity

The aim of the work was to investigate the longitude (orbital) dependence of the polarization of Jupiter's moon Io and compare results of our study with what is reported in the literature. We used our published observations and supplemented them with new measurements carried out with the polarimeters mounted on the 2.6 m Shajn telescope of the Crimean Astrophysical Observatory and the 2 m telescope of the Peak Terskol Observatory in the UBVRI bands at phase angles between 10° and 12° in August 2023 – February 2024. We have determined that amplitude of the orbital polarization in the V band does not exceed ≈0.1 %. It is the deepest −0.17 ± 0.03 % at L ≈ 270° and the shallowest −0.07 ± 0.03 % near L ≈ 130°. These parameters differ markedly from that obtained by Zellner and Gradie (1975), which found that the orbital polarization variations from 0.4 to 0.5 % for α > 10°, and the negative branch is the deepest near L = 160° and the shallowest near L = 300°. These differences may be a consequence of changes in the reflective properties of the local areas of Io's surface due to long-term changes in Io's local or global volcanic activity.