A5004668135- Astrophysics and Cosmic Phenomena
- Neutrino Physics Research
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Astronomical Observations and Instrumentation
- Relativity and Gravitational Theory
- Atomic and Subatomic Physics Research
- Particle physics theoretical and experimental studies
- History and Developments in Astronomy
- Topic Modeling
- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Radiation Detection and Scintillator Technologies
- Atmospheric Ozone and Climate
- Magnetic confinement fusion research
- Geophysics and Gravity Measurements
- Astrophysics and Star Formation Studies
- Advanced Text Analysis Techniques
- Particle Detector Development and Performance
Woodwell Climate Research Center
2022-2025
Harvard University
2022-2025
Max Planck Institute for Radio Astronomy
2021-2025
P.N. Lebedev Physical Institute of the Russian Academy of Sciences
2019-2024
Astro Space Center
2017-2024
Harvard University Press
2024
Center for Astrophysics Harvard & Smithsonian
2024
National Radio Astronomy Observatory
2024
Moscow Institute of Physics and Technology
2015-2023
Parc Científic de la Universitat de València
2023
We present the Black Hole Explorer (BHEX), a mission that will produce sharpest images in history of astronomy by extending submillimeter Very-Long-Baseline Interferometry (VLBI) to space. BHEX discover and measure bright narrow "photon ring" is predicted exist black holes, produced from light has orbited hole before escaping. This discovery expose universal features hole's spacetime are distinct complex astrophysics emitting plasma, allowing first direct measurements supermassive spin. In...
ABSTRACT Observational studies of collimation in jets active galactic nuclei (AGN) are a key to understanding their formation and acceleration processes. We have performed an automated search for jet shape transitions sample 367 AGN using VLBA data at 15 1.4 GHz. This has found 10 out 29 nearby redshifts z < 0.07 with transition from parabolic conical shape, while the full analysed is dominated by distant typical ≈ 1. The ten UGC 00773, NGC 1052, 3C 111, 120, TXS 0815−094, Mrk 180,...
Context. The data release 1 (DR1) of milliarcsecond-scale accurate optical positions stars and galaxies was recently published by the space mission Gaia.
The apparent position of jet base (core) in radio-loud active galactic nuclei changes with frequency because synchrotron self-absorption. Studying this `core shift` effect enables us to reconstruct properties the regions close central engine. We report here results from core shift measurements AGNs observed global VLBI at 2 and 8 GHz epochs 1994 2016. Our sample contains 40 objects least 10 times during that period. is determined using a new automatic procedure introduced minimize possible...
ABSTRACT Evidence for bright-radio blazars being high-energy neutrino sources was found in recent years. However, specifics of how and where these particles get produced still need to be determined. In this paper, we add 14 new IceCube events from 2020–2022 update our analysis the neutrino-blazars connection. We test refine earlier findings by utilizing total 71 track-like 2009–2022. correlate them with complete sample 3412 extragalactic radio selected their compact emission. demonstrate...
ABSTRACT We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half (251° ≤l ≤ 358° and 2° 61° at |b| $1{_{.}^{\circ}}5$). SMGPS is largest, most sensitive, highest angular resolution 1 plane yet carried out, with an 8 arcsec broad-band root-mean-square sensitivity ∼10–20 μJy beam−1. Here, we describe first publicly available data release from which comprises cubes frequency-resolved images over 908–1656 MHz, power-law fits to images, zeroth moment...
ABSTRACT We have analysed the differences in positions of 9081 matched sources between Gaia Data Release 2 (DR2) and very long baseline interferometry (VLBI) catalogues. The median position uncertainty VLBI catalogue is a factor two larger than DR2. There are 9 per cent with statistically significant offsets both found that reported positional errors should be rescaled by 1.3 for 1.06 and, addition, multiplied square root chi squared degree freedom order to best fit normalized Rayleigh...
Abstract We analyze differences in positions of active galactic nuclei (AGNs) between Gaia data release 2 and very long baseline interferometry (VLBI) compare the significant VLBI-to- offsets more than 1000 objects with their jet directions. Remarkably at least three-fourths are confirmed to occur downstream or upstream representing a genuine astrophysical effect. Introducing redshift color into analysis can help distinguish contribution host galaxy, jet, accretion disk emission. find that...
Ultra-high angular resolution in astronomy has always been an important vehicle for making fundamental discoveries. Recent results direct imaging of the vicinity supermassive black hole nucleus radio galaxy M87 by millimeter VLBI system Event Horizon Telescope and various pioneering Space mission RadioAstron provided new momentum high astrophysics. In both mentioned cases, reached values about 10-20 microrcseconds. Further developments toward at least order magnitude "sharper" are dictated...
Abstract Astrophysical sources of neutrinos detected by large-scale neutrino telescopes remain uncertain. While there exist statistically significant observational indications that a part the flux is produced blazars, numerous theoretical studies suggest also presence potential Galactic point sources. Some them have been observed in gamma rays above 100 TeV. Moreover, cosmic-ray interactions disk guarantee diffuse flux. However, these not unambiguously so far. Here we examine whether such...
We study milliarcsecond-scale properties of the persistent radio counterpart to FRB 121102 and investigate spectro-polarimetric a bright burst. For former, we use European VLBI Network (EVN) observations in 2017 at 1.7 4.8 GHz. latter, re-analyse 1.7-GHz data from 100-m Effelseberg telescope taken 2016. These predate other polarimetric studies 121102, yield highest burst Faraday rotation measure (RM) date, RM = 1.27*10^5 rad m^-2, consistent with decreasing trend. The fractional polarization...
Abstract We analyze the variability of parsec-scale jet directions in active galactic nuclei (AGNs). Our analysis involves 317 AGNs at frequencies ranging from 2 to 43 GHz, and is made possible by developing an automatic direction measurement procedure. find strong significant variations a one quarter these AGNs; effect likely ubiquitous, not detected rest due limited sensitivity observations epoch coverage. Apparent rotation speeds range 0.21 deg yr−1 GHz 1.04 GHz. This frequency dependence...
Abstract Recent observations of the Galactic component high-energy neutrino flux, together with detection diffuse gamma-ray emission up to sub-PeV energies, open new possibilities study acceleration and propagation cosmic rays in Milky Way. At same time, both large nonastrophysical backgrounds at TeV energies scarcity events band currently limit these analyses. Here, we use sample cascade estimated above 200 TeV, detected by partially deployed Baikal Gigaton Volume Detector (GVD) 6 yr...
Baikal-GVD has recently published its first measurement of the diffuse astrophysical neutrino flux, performed using high-energy cascade-like events. We further explore cascade dataset collected in 2018-2022, with aim to identify possible associations between neutrinos and known sources. leverage relatively high angular resolution telescope (2-3 deg.), made by use liquid water as detection medium, enabling study point sources even estimate telescope's sensitivity channel for refine our...
Observational information on high-energy astrophysical neutrinos is being continuously collected by the IceCube observatory. However, sources of are still unknown. In this study, we use radio very-long-baseline interferometry (VLBI) data for a complete VLBI-flux-density limited sample active galactic nuclei (AGN). We address problem origin with energies above 200 TeV in statistical manner. It found that AGN positionally associated events have typically stronger parsec-scale cores than rest...
We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C84 (NGC1275) at centre Perseus cluster. The were carried out on September 21-22, 2013 and involved a global array 24 ground telescopes observing 5 GHz 22 GHz, together with Space Radio Telescope (SRT). Furthermore, Very Long Baseline Array (VLBA) phased Large (VLA) observed source quasi-simultaneously 15 43 GHz. Fringes between SRT detected lengths up to 8.1 times Earth's...
Recently we have shown that high-energy neutrinos above 200 TeV detected by IceCube are produced within several parsecs in the central regions of radio-bright blazars, is active galactic nuclei with jets pointing towards us. To independently test this result and extend analysis to a wider energy range, use public data for all neutrino energies from seven years observations. The point-source likelihood map analyzed against positions blazars statistically complete sample selected their compact...
The direction of parsec-scale jets in active galactic nuclei (AGNs) is essential information for many astrophysical and astrometric studies, including linear polarization magnetic field structure, frequency-dependent synchrotron opacity, proper motion, reference frame alignment. We developed a rigorous, simple, completely automated method to measure the directions from calibrated interferometric visibility data at frequencies ranging 1.4 GHz 86 GHz. publish results 9220 AGNs with typical...
Abstract Bright blazars were found to be prominent neutrino sources, and a number of IceCube events associated with them. Evaluating high-energy photon emission such is crucial for better understanding the processes regions where neutrinos are produced. Here, we focus on hard X-ray observed by SRG/ART-XC telescope, Swift/BAT imager, INTEGRAL/IBIS telescope. Their energy range ≳10 keV well-suited probing photons that potentially participate in production interacting ultrarelativistic protons....
We used archival very long baseline interferometry (VLBI) data of active galactic nuclei (AGN) observed from 1.4 GHz to 86 measure the angular size VLBI radio cores in 8959 AGNs. analysed their sky distributions, frequency dependencies and created most densely sampled complete date distribution map large-scale scattering properties interstellar medium our Galaxy. Significant broadening measured AGN core sizes is detected for sources seen through Galactic plane, this effect especially strong...
The existence of high-energy astrophysical neutrinos has been unambiguously demonstrated, but their sources remain elusive. IceCube reported an association a 290-TeV neutrino with gamma-ray flare TXS 0506+056, active galactic nucleus compact radio jet pointing to us. Later, radio-bright blazars were shown be associated events high statistical significance. These associations remained unconfirmed the data independent experiments. Here we report on detection rare event estimated energy 224+-75...
Significant positional offsets of the value from 1 mas to more than 10 were found previously between radio (VLBI) and optical (Gaia) positions active galactic nuclei (AGN). They happen preferentially parallel parsec-scale jet direction. AGN with VLBI-to-Gaia pointed downstream are have favourably higher polarization, as expected if extended jets dominate in emission shift Gaia centroid away physical nucleus source. Upstream suggested domination accretion disks manifest themselves through...
The existence of high-energy astrophysical neutrinos has been unambiguously demonstrated, but their sources remain elusive. IceCube reported an association a 290-TeV neutrino with gamma-ray flare TXS 0506+056, active galactic nucleus compact radio jet pointing to us. Later, radio-bright blazars were shown be associated events high statistical significance. These associations remained unconfirmed the data independent experiments. Here we report on detection rare event estimated energy 224+-75...