A5051426108- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Neutrino Physics Research
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Particle Accelerators and Free-Electron Lasers
- Dark Matter and Cosmic Phenomena
- Astronomy and Astrophysical Research
- GNSS positioning and interference
- Solar and Space Plasma Dynamics
- Superconducting and THz Device Technology
- Astronomical Observations and Instrumentation
- Particle accelerators and beam dynamics
- Ionosphere and magnetosphere dynamics
- Geophysics and Gravity Measurements
- Gyrotron and Vacuum Electronics Research
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Planetary Science and Exploration
- Computational Physics and Python Applications
- Precipitation Measurement and Analysis
- Calibration and Measurement Techniques
Max Planck Institute for Radio Astronomy
2016-2025
King Abdulaziz University
2022
Leiden University
2022
Sorbonne Université
2022
Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères
2022
Centre National de la Recherche Scientifique
2022
Collège de France
2022
Turku Centre for Computer Science
2021
University of Turku
2021
Commonwealth Scientific and Industrial Research Organisation
2021
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A$^*$), Galactic center source associated with a supermassive black hole. These were conducted in 2017 using global interferometric array eight telescopes operating at wavelength $\lambda=1.3\,{\rm mm}$. The EHT data resolve compact emission region intrahour variability. A variety imaging and modeling analyses all support an image that is dominated by bright, thick ring diameter $51.8 \pm 2.3$\,\uas (68\%...
(Abridged) We have conducted a detailed investigation of the broad-band spectral properties \gamma-ray selected blazars Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated gamma-ray spectra with Swift, radio, infra-red, optical and other hard X-ray/gamma-ray data, collected within three months LBAS data taking period, we were able to assemble high-quality quasi-simultaneous Spectral Energy Distributions (SED) for 48 blazars.The SED these sources is similar that...
Astrophysical black holes are expected to be described by the Kerr metric. This is only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside of event horizon. We present new constraints on potential deviations from prediction based 2017 EHT observations Sagittarius A* (Sgr A*). calibrate relationship between geometrically defined hole shadow observed size ring-like images using a library includes...
Abstract In this paper we provide a first physical interpretation for the Event Horizon Telescope's (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT from radio X-ray wavelengths predictions library models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, stellar-wind-fed simulations; radiative transfer performed assuming both thermal nonthermal electron distribution...
Abstract We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with Event Horizon Telescope in 2017 April at a wavelength 1.3 mm. Imaging has been conducted through surveys over wide range imaging assumptions using classical CLEAN algorithm, regularized maximum likelihood methods, Bayesian posterior sampling method. Different prescriptions have used to account for scattering effects by interstellar medium toward Galactic center. Mitigation rapid intraday...
We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at position supermassive black hole Sagittarius A* (Sgr A*), collected during 2017 April 5--11 campaign. The observations were carried out with eight facilities six locations across globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. majority emission arises from horizon scales, where intrinsic structural variability is detected on timescales minutes hours. effects...
In this paper we quantify the temporal variability and image morphology of horizon-scale emission from Sgr A*, as observed by EHT in 2017 April at a wavelength 1.3 mm. We find that A* data exhibit exceeds what can be explained uncertainties or effects interstellar scattering. The magnitude substantial fraction correlated flux density, reaching $\sim$100\% on some baselines. Through an exploration simple geometric source models, demonstrate ring-like morphologies provide better fits to than...
M87 is one of the nearest radio galaxies with a prominent jet extending from sub-pc to kpc-scales. Because its proximity and large mass central black hole, it best sources study formation. We aim at studying physical conditions near base projected separations BH $\sim7-100$ Schwarzschild radii ($R_{\rm sch}$). Global mm-VLBI Array (GMVA) observations 86 GHz ($\lambda=3.5\,$mm) provide an angular resolution $\sim50\mu$as, which corresponds spatial only $7~R_{\rm sch}$ reach small scale. use...
The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of in 2017, at wavelength 1.3 mm, revealed ring-like structure, which was interpreted as gravitationally lensed emission around central hole3. Here we report images obtained 2018, 3.5 showing that the compact core spatially resolved. High-resolution imaging shows structure [Formula: see text] Schwarzschild radii diameter, approximately 50% larger than...
The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in Galactic Center on 2017 April 5-11 1.3 millimeter wavelength band. At same time, interferometric array data from Atacama Large Millimeter/submillimeter Array and Submillimeter were collected, providing Sgr light curves simultaneous with EHT observations. These sets, complementing very-long-baseline interferometry, are characterized by a cadence signal-to-noise ratio previously unattainable for at...
Abstract Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at center M87 galaxy. EHT images in linear polarization further identified coherent spiral pattern hole, produced from ordered magnetic fields threading emitting plasma. Here we present first analysis circular using data, acquired 2017, which can potentially provide additional insights into and plasma composition near hole. Interferometric closure quantities...
ABSTRACT The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report 60 bursts detected the Effelsberg telescope at 1.4 GHz. We observe large variations in rate, first ‘burst storm’, where suddenly became active 53 (fluence ≥0.04 Jy ms) occurred within only 40 min. find no strict periodicity arrival times, nor any evidence for source’s activity between observations. storm shows steep energy...
Abstract The Event Horizon Telescope observed the horizon-scale synchrotron emission region around Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with diameter of 51.8 ± 2.3 μ as and modest azimuthal brightness asymmetry, consistent expected appearance hole mass M ≈ 4 × 10 6 ⊙ . From these observations, we present first resolved linear circular polarimetric images Sgr A*. polarization demonstrate that is...
Abstract In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using Event Horizon Telescope, global very long baseline interferometric array operating at wavelength 1.3 mm. Here interpret this both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large linear polarization fraction (24%–28%, peaking ∼40%) is most stringent constraint parameter space, disfavoring...
In April 2019, the Event Horizon Telescope (EHT) Collaboration reported first-ever event-horizon-scale images of a black hole, resolving central compact radio source in giant elliptical galaxy M 87. These reveal ring with southerly brightness distribution and diameter ∼42 μas, consistent predicted size shape shadow produced by gravitationally lensed emission around supermassive hole. results were obtained as part 2017 EHT observation campaign, using global very long baseline interferometric...
Eight optical and four radio observatories have been intensively monitoring the BL Lac object 0716+714 in last years: 4854 data points collected UBVRI bands since 1994, while light curves extend back to 1978. Many of these are presented here for first time. The long-term trend shown by seems vary with a characteristic time scale about 3.3 years, longer period 5.5-6 years characterize variations. In general, colour indices only weakly correlated brightness. flux behaviour at different...
We present time-resolved broad-band observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during first two years Fermi Gamma-ray Space Telescope mission. While investigating previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that emission appears delayed with respect to gamma-ray about 10 days. X-ray reveal pair `isolated' flares separated ~90 days, only weak counterparts. The spectral structure measured...
We present the first polarimetric space VLBI imaging observations at 22 GHz. BL Lacertae was observed in 2013 November 10 with RadioAstron mission, including a ground array of 15 radio telescopes. The instrumental polarization telescope is found to be within 9%, demonstrating capabilities Ground-space fringes were obtained up projected baseline distance 7.9 Earth's diameters length, allowing us image jet maximum angular resolution 21 $\mu$as, highest achieved date. find evidence for emission...
Abstract The Galactic center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study dynamics accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), emission from Sgr resolvable Global Millimeter VLBI Array (GMVA). We present first observations phased Atacama Large Millimeter/submillimeter (ALMA) joining GMVA. Our achieve an angular resolution ∼87 μ as, improving upon previous experiments by a factor...
Inverse Compton cooling limits the brightness temperature of radiating plasma to a maximum $10^{11.5}$ K. Relativistic boosting can increase its observed value, but apparent temperatures much in excess $10^{13}$ K are inaccessible using ground-based very long baseline interferometry (VLBI) at any wavelength. We present observations quasar 3C273, made with space VLBI mission RadioAstron on baselines up 171,000 km, which directly reveal presence angular structure as small 26 $\mu$as (2.7 light...
Very long baseline interferometric (VLBI) localisations of repeating fast radio bursts (FRBs) have demonstrated a diversity local environments: from nearby star-forming regions to globular clusters. Here we report the VLBI localisation FRB 20201124A using an ad-hoc array dishes that also participate in European Network (EVN). In our campaign, detected 18 total at two separate epochs. By combining visibilities both observing epochs, were able localise with 1-$\sigma$ error 4.5 milliarcseconds...
3C84 is a nearby radio source with complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates use VLBI above hitherto available maximum frequency 86GHz. Using ultrahigh resolution observations at highest 228GHz, we aim to directly detect compact structures understand physical conditions in 3C84. We used EHT 228GHz and, given limited (u,v)-coverage, applied geometric model fitting data. also employed...
ABSTRACT We present very long-baseline interferometry (VLBI) observations of the hyperactive repeating FRB 20220912A using European VLBI Network (EVN) outside regular observing sessions (EVN-Lite). detected 150 bursts from over two epochs in 2022 October. Combining burst data allows us to localize a precision few milliarcseconds, corresponding transverse scale less than 10 pc at distance source. This precise localization shows that lies closer centre its host galaxy previously found,...
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. maximum brightness detected was R = 12.0, which represents the most luminous state thus far observed (M_B ~ -31.4). In order to follow emission behaviour of source detail, a large multiwavelength campaign organized by Whole Earth Blazar Telescope (WEBT). Continuous optical, near-IR monitoring performed several bands. ToO pointings Chandra INTEGRAL satellites provided...