Explanipedia

Pinpointing the location of the <i>γ</i> -ray emitting region in the FSRQ 4C +01.28 Open

F. Rösch, M. Kadler, E. Ros, L. Ricci, Mark Gurwell , et al. · 2025

Aims. The flat-spectrum radio quasar (FSRQ) 4C +01.28 is a bright and highly variable radio and γ -ray emitter. We aim to pinpoint the location of the γ -ray emitting region within its jet in order to derive strong constraints on γ -ray em…

Synthetic spectra from particle-in-cell simulations of relativistic jets containing an initial toroidal magnetic field Open

I. Duţan, Ken‐Ichi Nishikawa, A. Meli, Oleh Kobzar, Christoph Köhn , et al. · 2025

The properties of relativistic jets, their interaction with the environment, and their emission of radiation can be self-consistently studied by using collisionless particle-in-cell (PIC) numerical simulations. Using three-dimensional rela…

A helical magnetic field in quasar NRAO 150 revealed by Faraday rotation Open

J. D. Livingston, A. S. Nikonov, Sergio A. Dzib, L. C. Debbrecht, Yu. A. Kovalev , et al. · 2025

Context. Active galactic nuclei (AGN) are some of the most luminous and extreme environments in the Universe. The central engines of AGN are believed to be super-massive black-holes (SMBHs) are fed by accretion discs threaded by magnetic f…

Multidisciplinary Science in the Multimessenger Era Open

Eric Burns, Chris L. Fryer, Ivan Agullo, Jennifer E. Andrews, E. Aydi , et al. · 2025

Astrophysical observations of the cosmos allow us to probe extreme physics and answer foundational questions on our universe. Modern astronomy is increasingly operating under a holistic approach, probing the same question with multiple dia…

Investigating launching of black hole jets with the combined power of the EVN and the EHT Open

Georgios Filippos Paraschos, L. C. Debbrecht, Joana A. Kramer, Efthalia Traianou, Ioannis Liodakis , et al. · 2025

AGN-launched jets are a crucial element in the study of supermassive black holes (SMBH) and their closest surroundings. The formation of such jets, whether they are launched by magnetic field lines anchored to the accretion disc or directl…

Demographics of black holes at $<$100 R$_{\rm g}$ scales: accretion flows, jets, and shadows Open

Dhanya G. Nair, Neil M. Nagar, Venkatessh Ramakrishnan, Maciek Wielgus, Vicente Arratia , et al. · 2024

Using the Event Horizon Telescope (EHT), the gravitationally lensed rings around the supermassive black holes (SMBHs) in Messier 87 (M87) and Sagittarius A* (Sgr A*) have now been successfully imaged at a resolution under 10 gravitational …

3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses Open

Joana A. Kramer, Nicholas R. MacDonald, Georgios Filippos Paraschos, L. Ricci · 2024

Context. Relativistic jets in active galactic nuclei are known for their exceptional energy output, and imaging the synthetic synchrotron emission of numerical jet simulations is essential for a comparison with observed jet polarization em…

3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses Open

Joana A. Kramer, Nicholas R. MacDonald, Georgios Filippos Paraschos, L. Ricci · 2024

Context. Relativistic jets in active galactic nuclei are known for their exceptional energy output, and imaging the synthetic synchrotron emission of numerical jet simulations is essential for a comparison with observed jet polarization em…

Innovations and advances in instrumentation at the W. M. Keck Observatory, vol. III Open

Marc Kassis, Carlos Álvarez, Ashley Baker, John I. Bailey, Ravinder K. Banyal , et al. · 2024

Evidence of a toroidal magnetic field in the core of 3C 84 Open

Georgios Filippos Paraschos, L. C. Debbrecht, Joana A. Kramer, Efthalia Traianou, Ioannis Liodakis , et al. · 2024

The spatial scales of relativistic radio jets, probed by relativistic magneto-hydrodynamic (RMHD) jet launching simulations and by most very long baseline interferometry (VLBI) observations differ by an order of magnitude. Bridging the gap…

Synthetic Spectra from Particle-in-cell Simulations of Relativistic Jets containing an initial Toroidal Magnetic Field Open

I. Duţan, Ken‐Ichi Nishikawa, A. Meli, Oleh Kobzar, C. Koehn , et al. · 2024

The properties of relativistic jets, their interaction with the environment, and their emission of radiation can be self-consistently studied by using collisionless particle-in-cell (PIC) numerical simulations. Using three-dimensional (3D)…

Lost in the curve: Investigating the disappearing knots in the blazar 3C 454.3 Open

Efthalia Traianou, T. P. Krichbaum, José L. Gómez, Rocco Lico, Georgios Filippos Paraschos , et al. · 2023

One of the most well-known extragalactic sources in the sky, quasar 3C 454.3, shows a curved parsec-scale jet that has been exhaustively monitored with very-long-baseline interferometry (VLBI) over the recent years. In this work, we presen…

First GMVA observations with the upgraded NOEMA facility: VLBI imaging of BL Lacertae in a flaring state Open

Dae-Won Kim, Michaël Janssen, T. P. Krichbaum, B. Boccardi, Nicholas R. MacDonald , et al. · 2023

We analyze a single-epoch Global mm-VLBI Array (GMVA) observation of the blazar BL Lacertae (BL Lac) at 86 GHz from April 2021. The participation of the upgraded, phased Northern Extended Millimetre Array (NOEMA) adds additional sensitivit…

Lost in the curve: Investigating the disappearing knots in blazar 3C 454.3 Open

Efthalia Traianou, T. P. Krichbaum, José L. Gómez, Rocco Lico, Georgios Filippos Paraschos , et al. · 2023

One of the most well-known extragalactic sources in the sky, quasar 3C 454.3 , shows a curved parsec-scale jet that has been exhaustively monitored with very-long-baseline interferometry (VLBI) over the recent years. In this work, we prese…

First GMVA observations with the upgraded NOEMA facility: VLBI imaging of BL Lacertae in a flaring state Open

Dae-Won Kim, Michaël Janssen, T. P. Krichbaum, B. Boccardi, Nicholas R. MacDonald , et al. · 2023

We analyze a single-epoch Global mm-VLBI Array (GMVA) observation of the blazar BL Lacertae (BL Lac) at 86 GHz from April 2021. The participation of the upgraded, phased Northern Extended Millimetre Array (NOEMA) adds additional sensitivit…

A Critical Review of Current States of Practice in Direct Shear Testing of Unfilled Rock Fractures Focused on Multi-Stage and Boundary Conditions Open

Nicholas R. MacDonald, Timothy R. M. Packulak, Jennifer J. Day · 2023

Direct shear (DS) is a common geotechnical laboratory test used to determine strength and deformation properties of rock discontinuities, such as normal and shear stiffness, peak and residual shear strength, and dilation. These are used as…

A ring-like accretion structure in M87 connecting its black hole and jet Open

Ru-Sen Lu, Keiichi Asada, T. P. Krichbaum, Jongho Park, Fumie Tazaki , et al. · 2023

The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation 1,2 . Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted a…

3D PIC Simulations for relativistic jets with a toroidal magnetic field Open

A. Meli, Ken‐Ichi Nishikawa, Christoph Köhn, I. Duţan, Yosuke Mizuno , et al. · 2022

We have investigated how kinetic instabilities such as the Weibel instability (WI), the mushroom instability (MI), and the kinetic Kelvin–Helmholtz instability (kKHI) are excited in jets without and with a toroidal magnetic field, and how …

Fabrication of Pupil Masks for a New Infrared Exoplanet Imager at Keck Observatory Open

Jialin Li, Andrew Skemer, Maaike van Kooten, Renate Kupke, Nicholas R. MacDonald · 2022

The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an instrument being designed to perform direct imaging of exoplanets in the mid-infrared (2-5 μm) with the Adaptive Optics System of W.M. Keck Observatory. T…

Design of SCALES: A 2-5 Micron Coronagraphic Integral Field Spectrograph for Keck Observatory Open

Andrew Skemer, R. Deno Stelter, Stephanie Sallum, Nicholas R. MacDonald, Renate Kupke , et al. · 2022

We present the design of SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. SCALES enables low-resolution (R~50) sp…

Resolving the Inner Parsec of the Blazar J1924–2914 with the Event Horizon Telescope Open

Sara Issaoun, Maciek Wielgus, Svetlana G. Jorstad, T. P. Krichbaum, Lindy Blackburn , et al. · 2022

The blazar J1924–2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center’s black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unpre…

Exploring the disk-jet connection in NGC 315 Open

L. Ricci, B. Boccardi, E. E. Nokhrina, M. Perucho, Nicholas R. MacDonald , et al. · 2022

Aims. Hot accretion flows are thought to be able to power the relativistic jets observed in active galactic nuclei. They can be presented as standard and normal evolution (SANE) disks or magnetically arrested disks (MAD) – two states that …

Ray-Tracing in Relativistic Magnetohydrodynamic Jet Simulations: A Polarimetric Study Open

Joana A. Kramer, Nicholas R. MacDonald · 2022

The jets emanating from the centers of active galactic nuclei (AGNs) are among the most energetic objects in the universe. Investigations on how the morphology of the jet’s synchrotron emission depends on the magnetic nature of the jet’s r…

Principles of Hypotensive Shock: A Video Introduction to Pathophysiology and Treatment Strategies Open

Brittany MacDonald, Nicholas R. MacDonald, Jacob Garcia, Xiao Chi Zhang, Dimitrios Papanagnou · 2022

Audience: Emergency medicine interns, medical students, and mid-level providers (physician assistants, nurse practitioners).Introduction: Shock is defined as a state of global tissue hypoxia and is typically the result of hypotension and c…

Principles of Hypotensive Shock: A Video Introduction to Pathophysiology and Treatment Strategies Open

Brittany MacDonald, Nicholas R. MacDonald, Jacob Garcia, Xiao Chi Zhang, Dimitrios Papanagnou · 2022

Shock, hypotension, cardiovascular physiology, pulmonary artery catheterization, flipped classroom, asynchronous learning, emergency medicine.

3D PIC Simulations for Relativistic Jets with a Toroidal Magnetic Field Open

Ken‐Ichi Nishikawa, A. Meli, Christoph Köhn, I. Duţan, Yosuke Mizuno , et al. · 2021

Particle-in-Cell simulations can provide a possible answer to an important key issue for astrophysical plasma jets; namely on how a toroidal magnetic field affects the evolution of pair and electron-ion jets. We show that Weibel, mushroom,…

Ray-tracing in relativistic jet simulations: A polarimetric study of magnetic field morphology and electron scaling relations Open

Joana A. Kramer, Nicholas R. MacDonald · 2021

Context. The jets emanating from the centers of active galactic nuclei are among the most energetic objects in the Universe. Investigating how the morphology of the jet’s synchrotron emission depends on the magnetic nature of the jet’s rel…

From electrons to Janskys: Full stokes polarized radiative transfer in 3D relativistic particle-in-cell jet simulations Open

Nicholas R. MacDonald, Ken‐Ichi Nishikawa · 2021

Context. Despite decades of dedicated observation and study, the underlying plasma composition of relativistic extragalactic jets remains largely unknown. Aims. Relativistic magnetohydrodynamic (RMHD) models are able to reproduce many of t…

From electrons to Janskys: Full stokes polarized radiative transfer in\n 3D relativistic particle-in-cell jet simulations Open

Nicholas R. MacDonald, Ken‐Ichi Nishikawa · 2021

The underlying plasma composition of relativistic extragalactic jets remains\nlargely unknown. Relativistic magnetohydrodynamic (RMHD) models are able to\nreproduce many of the observed macroscopic features of these outflows. The\nnontherm…

Repeated pattern of gamma-ray flares in the light curve of the blazar 3C 279 Open

D. Blinov, Svetlana G. Jorstad, V. M. Larionov, Nicholas R. MacDonald, T. S. Grishina , et al. · 2021

The optical polarization plane of some blazars occasionally exhibits smooth hundred degree long rotations. Multiple theoretical models have been proposed to explain the nature of such events. A deterministic origin of these rotations, howe…

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