Name: Magnetic Fields Around Compact Objects Workshop
Start: 2025-03-26T08:00:00-04:00
End: 2025-03-28T17:00:00-04:00
Location: Perimeter Institute for Theoretical Physics

Magnetic Fields Around Compact Objects Workshop

from Wednesday, March 26, 2025 (8:00 AM) to Friday, March 28, 2025 (5:00 PM)

Wednesday, March 26, 2025

8:30 AM Registration
Registration
8:30 AM - 9:00 AM

9:00 AM Opening Remarks
Opening Remarks
9:00 AM - 9:15 AM
Room: PI/4-405 - Bob Room
9:15 AM Snap, Crackle and Pop - Roger Blandford (Roger Blandford)
Snap, Crackle and Pop
- Roger Blandford (Roger Blandford)
9:15 AM - 9:45 AM
Room: PI/4-405 - Bob Room An alternative interpretation of the EHT observations of M87, involving a strongly magnetized ergomagnetosphere, that expels essentially of the gas supplied at large radius as a jet-collimating MHD wind is described. In this case, the emitting regions are approximated as rapidly evolving flares or sparks. Six generic consequences, that can be sought in existing data, are described.
9:45 AM Modeling Luminous Black Hole Accretion Flows with AthenaK - James Stone (IAS)
Modeling Luminous Black Hole Accretion Flows with AthenaK
- James Stone (IAS)
9:45 AM - 10:15 AM
Room: PI/4-405 - Bob Room A new version of the Athena++ AMR MHD code implemented using the Kokkos library for performance-portability will be described. The code is being used for a variety of problems related to accretion onto (and merger of) compact objects. This talk will focus on results from general relativistic radiation MHD models of accretion in luminous systems such as X-ray binaries and AGN. The models allow observationally important quantities such as the radiative efficiency, variability, and kinetic feedback in winds to be measured over a range of luminosities, from sub-Eddington to highly super-Eddington. A new “cyclic-zoom” approach for modeling such flows over very long time scales will also be briefly introduced.
10:15 AM Black Hole Jet Sheath as a Candidate for the Comptonizing Corona - Navin Sridhar (Stanford)
Black Hole Jet Sheath as a Candidate for the Comptonizing Corona
- Navin Sridhar (Stanford)
10:15 AM - 10:30 AM
Room: PI/4-405 - Bob Room What powers the hard, non-thermal X-rays from accreting compact objects has been a longstanding mystery. In my talk, I will address the underlying question of what energizes the particles of the Comptonizing “corona” against the strong inverse Compton (IC) cooling losses with first-principle particle-in-cell simulations of magnetic reconnection subject to IC cooling in magnetically dominated electron-positron plasmas, and in mildly-magnetized electron-ion plasmas. I will also show---using results of global resistive GRMHD simulations of accreting black holes---that the black hole jet sheath is a site of efficient electromagnetic dissipation through processes such as magnetic reconnection and turbulence. The distribution of bulk motions of the radially outflowing plasma along the jet sheath also resembles a Maxwellian distribution with an effective bulk temperature of a few 100 keV, and this could be a candidate for the Comptonizing corona.
10:30 AM Hot, Retrograde Tilted MADs: Misaligned, Precessing, and Shaped by Electromagnetic Torques - Sajal Gupta (University of Colorado Boulder)
Hot, Retrograde Tilted MADs: Misaligned, Precessing, and Shaped by Electromagnetic Torques
- Sajal Gupta (University of Colorado Boulder)
10:30 AM - 10:45 AM
Room: PI/4-405 - Bob Room Tilted magnetically arrested disks (MADs) around black holes—where strong magnetic fields regulate accretion and jets—exhibit striking alignment behavior dictated by black hole spin direction. Using 3D general-relativistic magnetohydrodynamic (GRMHD) simulations of tilted MADs, we find that prograde disks align via a two-stage process: an initial rapid alignment phase, ending at the flux saturation timescale, followed by a slower, spin-independent phase. In contrast, retrograde MADs remain persistently misaligned, with their inner disks precessing four times faster than weakly magnetized systems—a potential explanation for high-frequency quasi-periodic oscillations (QPOs). By analyzing magnetic and hydrodynamic torques within ideal GRMHD, we show that alignment in prograde disks is dominated by electromagnetic stresses from the magnetosphere. However, the same magnetic forces— which always act to align the disk with the black hole spin—are significantly weaker in retrograde disks, allowing opposing hydrodynamic torques to dominate. These results suggest that jets alone may not be sufficient to align MAD disks, instead highlighting the magnetosphere’s crucial role in mediating spin-disk coupling.
10:45 AM Break
Break
10:45 AM - 11:15 AM
Room: PI/4-405 - Bob Room
11:15 AM Workshop Talk - Luciano Combi (Perimeter Institute)
Workshop Talk
- Luciano Combi (Perimeter Institute)
11:15 AM - 11:45 AM
Room: PI/4-405 - Bob Room
11:45 AM Rethinking The Black Hole Corona as an Extended, Multizone Outflow - Lia Hankla (University of Maryland, College Park)
Rethinking The Black Hole Corona as an Extended, Multizone Outflow
- Lia Hankla (University of Maryland, College Park)
11:45 AM - 12:15 PM
Room: PI/4-405 - Bob Room Observations of luminous black holes in X-ray binaries and Seyfert galaxies show power-law emission, thought to originate from photons that inverse Compton scatter off a hot electron cloud. If the coronal electrons are heated by magnetic dissipation, i.e. reconnection or turbulence, then one might expect to observe direct synchrotron emission in the radio/mm from these electrons. However, because timing studies constrain the X-ray emission to be within ~10 rg of the central black hole, the direct synchrotron emission from this compact volume would be strongly self-absorbed until much further away from BH. In this talk, I will question the de facto definition of the corona as a compact, X-ray-emitting region and shift instead to a paradigm where the corona encompasses multiple layers with distinct spectral components. Motivated by highly-magnetized winds found in GRMHD simulations, I will present a model for such an extended, outflowing corona. I will discuss this model in the context of radio-quiet AGN, where recent observations have demonstrated the presence of compact mm emission.
12:15 PM Lightning Talk: Lightning Talks
Lightning Talks
12:15 PM - 12:30 PM
Room: PI/4-405 - Bob Room
Contributions

12:15 PM Quantifying flux rope characteristics in relativistic 3D reconnection simulations - Jesse Vos (KU Leuven)

12:20 PM Understanding Magnetic Dissipation in the Magnetar Magnetosphere Regime - Michael Grehan (University of Toronto)

12:25 PM Ion-synchrotron emission from reconnecting current sheets in M87 - Amir Levinson (Tel Aviv university)
12:30 PM Lunch
Lunch
12:30 PM - 2:00 PM
Room: PI/4-405 - Bob Room
2:00 PM Colloquium: Radiation of Extreme Plasmas near the Neutron Stars and Black holes - Alexander Philippov (University of Maryland)
Colloquium: Radiation of Extreme Plasmas near the Neutron Stars and Black holes
- Alexander Philippov (University of Maryland)
2:00 PM - 3:00 PM
Room: PI/4-405 - Bob Room Astrophysical compact objects, neutron stars, and black holes are powerful sources of non-thermal electromagnetic emission spanning many orders of magnitude in photon energy, from radio waves to multi-TeV gamma rays. Despite multiple groundbreaking observational discoveries done in recent years, our understanding of the dynamics of relativistic plasmas that produce these emission signatures remains limited. In this talk, I will describe a few successful examples of modeling the observed light coming from these remarkable astrophysical laboratories using various numerical approaches. I will focus on advances in understanding coherent radio emission of rotating neutron stars, pulsars, and multi-wavelength flares from accreting black holes.
3:00 PM Break
Break
3:00 PM - 3:30 PM
Room: PI/4-405 - Bob Room
3:30 PM The Impact of Plasma Angular Momentum on Magnetically Arrested Flows and Relativistic Jets in Hot Accretion Flows Around Black Holes - Leon Chan (Unviersity of Colorado, Boulder)
The Impact of Plasma Angular Momentum on Magnetically Arrested Flows and Relativistic Jets in Hot Accretion Flows Around Black Holes
- Leon Chan (Unviersity of Colorado, Boulder)
3:30 PM - 3:45 PM
Room: PI/4-405 - Bob Room In certain scenarios, the accreted angular momentum of plasma onto a black hole could be low; however, how the accretion dynamics depends on the angular momentum content of the plasma is still not fully understood. We present three-dimensional, general relativistic magnetohydrodynamic simulations of low angular momentum accretion flows around rapidly spinning black holes (with spin $a = +0.9$). The initial condition is a Fishbone-Moncrief (FM) torus threaded by a large amount of poloidal magnetic flux, where the angular velocity is a fraction $f$ of the standard value. For $f = 0$, the accretion flow becomes magnetically arrested and launches relativistic jets but only for a very short duration. After that, free-falling plasma breaks through the magnetic barrier, loading the jet with mass and destroying the jet-disk structure. Meanwhile, magnetic flux is lost via giant, asymmetrical magnetic bubbles that float away from the black hole. The accretion then exits the magnetically arrested state. For $f = 0.1$, the dimensionless magnetic flux threading the black hole oscillates quasi-periodically. The jet-disk structure shows concurrent revival and destruction while the gas efficiency at the event horizon changes accordingly. For $f \geq 0.3$, we find that the dynamical behavior of the system starts to approach that of a standard accreting FM torus. Our results thus suggest that the accreted angular momentum is an important parameter that governs the maintenance of a magnetically arrested flow and launching of relativistic jets around black holes.
3:45 PM AsterX: a new open-source GPU-accelerated GRMHD code for dynamical spacetimes - Liwei Ji (Rochester Institute of Technology)
AsterX: a new open-source GPU-accelerated GRMHD code for dynamical spacetimes
- Liwei Ji (Rochester Institute of Technology)
3:45 PM - 4:00 PM
Room: PI/4-405 - Bob Room With the ongoing transition toward exascale computing to tackle a range of open questions via numerical simulations, the development of GPU-optimized codes has become essential. In this talk, I will highlight the key features of AsterX, a novel open-source, modular, GPU-accelerated general relativistic magnetohydrodynamic (GRMHD) code for fully dynamical spacetimes in 3D Cartesian coordinates. Built for exascale applications, AsterX integrates with CarpetX, the new driver for the Einstein Toolkit, leveraging AMReX for block-structured adaptive mesh refinement (AMR). The code employs the flux-conservative Valencia formulation for GRMHD, and uses high-resolution shock capturing schemes to ensure accurate hydrodynamic modeling. Alongside discussions on the ongoing code development, I will also present the results of comprehensive 1D, 2D, and 3D GRMHD tests conducted on OLCF's Frontier supercomputer, highlighting AsterX's performance gains through subcycling in time and demonstrating its scaling efficiency across thousands of nodes.
4:00 PM Panel Discussion #1
Panel Discussion #1
4:00 PM - 4:45 PM
Room: PI/4-405 - Bob Room

6:00 PM Banquet
Banquet
6:00 PM - 8:00 PM
Room: PI/4-405 - Bob Room
Thursday, March 27, 2025
9:00 AM Neutron Star Mergers and AthenaK - David Radice (Pennsylvania State University)
Neutron Star Mergers and AthenaK
- David Radice (Pennsylvania State University)
9:00 AM - 9:30 AM
Room: PI/4-405 - Bob Room In this talk, I will explore key open questions in our understanding of neutron star mergers and their multi-messenger emission, highlighting recent progress made by our group. I will then introduce some of the first applications of AthenaK to compact binary mergers and outline our plans for its future development.
9:30 AM General Relativistic Magnetohydrodynamics Simulations of Accreting Supermassive Black Hole Binaries - Manuela Campanelli
General Relativistic Magnetohydrodynamics Simulations of Accreting Supermassive Black Hole Binaries
- Manuela Campanelli
9:30 AM - 10:00 AM
Room: PI/4-405 - Bob Room Supermassive black hole mergers represent a spectacular cosmic event with immense energy implications, emitting gravitational waves equivalent to the total light output of stars in the entire Universe within a brief timespan. These mergers play a crucial role in shaping the overall mass distribution of supermassive black holes across the cosmos. However, capturing visual evidence of these mergers remains elusive due to uncertainties surrounding the type of light emissions accompanying gravitational waves during these events. To address this challenge, novel General Relativistic Magnetohydrodynamics (GRMHD) simulations are being conducted to gain detailed insights into the astrophysical environments surrounding supermassive black hole binaries as they progress towards merger. By employing sophisticated computational techniques capable of accurately capturing the intricate dynamics of accretion within circumbinary disks and the relativistic flow of magnetized matter around each black hole, these simulations reveal the behavior of gas flows near binary systems, particularly when both black holes exhibit spin. These simulated scenarios provide critical data for predicting the electromagnetic and gravitational wave signatures produced by supermassive binary black holes, guiding future observational strategies utilizing advanced missions like LISA and other upcoming astronomical facilities. Ongoing initiatives are focused on refining computational tools to deepen our understanding of supermassive black hole behavior within binary systems and its interactions.
10:00 AM Long-term impact of the magnetic-field strength on the evolution and electromagnetic emission by neutron-star merger remnants - Michail Chabanov (Rochester Institute of Technology)
Long-term impact of the magnetic-field strength on the evolution and electromagnetic emission by neutron-star merger remnants
- Michail Chabanov (Rochester Institute of Technology)
10:00 AM - 10:15 AM
Room: PI/4-405 - Bob Room Numerical simulations are essential to understand the complex physics accompanying the merger of binary systems of neutron stars. However, these simulations become computationally challenging when they have to model the merger remnants on timescales over which secular phenomena, such as the launching of magneti- cally driven outflows, develop. To tackle these challenges, we have recently developed a hybrid approach that combines, via a hand-off transition, a fully general-relativistic code (FIL) with a more efficient code mak- ing use of the conformally flat approximation (BHAC+). We here report important additional developments of BHAC+ consisting of the inclusion of gravitational-wave radiation-reaction contributions and of higher-order formulations of the equations of general-relativistic magnetohydrodynamics. Both improvements have allowed us to explore scenarios that would have been computationally prohibitive otherwise. More specifically, we have investigated the impact of the magnetic-field strength on the long-term (i.e., ∼ 200 ms) and high-resolution (i.e., 150 m) evolutions of the “magnetar” resulting from the merger of two neutron stars with a realistic equa- tion of state. In this way, and for sufficiently large magnetic fields, we observe the loss of differential rotation and the generation of magnetic flares in the outer layers of the remnant. These flares, driven mostly by the Parker instability, are responsible for intense and collimated Poynting flux outbursts and low-latitude emissions. This novel phenomenology offers the possibility of seeking corresponding signatures from the observations of short gamma-ray bursts and hence revealing the existence of a long-lived strongly magnetized remnant.
10:15 AM Magnetic field effects in binary neutron star mergers: insights from GRMHD simulations - Eduardo Gutierrez (The Pennsylvania State University)
Magnetic field effects in binary neutron star mergers: insights from GRMHD simulations
- Eduardo Gutierrez (The Pennsylvania State University)
10:15 AM - 10:30 AM
Room: PI/4-405 - Bob Room Magnetic fields play a key role in shaping the dynamics and observational phenomenology of binary neutron star (BNS) mergers. In this talk, I will present results from general relativistic magnetohydrodynamic (GRMHD) simulations performed with the code GR-Athena++, exploring how different initial magnetic field configurations affect the evolution of BNS mergers. We investigated magnetic field amplification, primarily driven by the Kelvin-Helmholtz instability, the post-merger remnant and disk structure, and the characteristics of the ejected material. I will discuss how these processes impact potential electromagnetic counterparts and their detectability. Finally, I will highlight recent advancements in our numerical methods that improve the modeling of magnetized neutron star mergers, paving the way for more accurate predictions of multimessenger signals from these extreme events.
10:30 AM Break
Break
10:30 AM - 11:00 AM
Room: PI/4-405 - Bob Room
11:00 AM Dark Photon Superradiance - Nils Peter Siemonsen
Dark Photon Superradiance
- Nils Peter Siemonsen
11:00 AM - 11:30 AM
Room: PI/4-405 - Bob Room Gravitational and electromagnetic signatures of black hole superradiance are a unique probe of ultralight particles that are weakly-coupled to ordinary matter. Through the kinetic mixing with the Standard Model photon, a dark photon superradiance cloud sources a rotating visible electromagnetic field. I will describe how this leads to the production of a turbulent pair plasma, characterized by efficient magnetic reconnection, which radiates large-luminosity high-energy electromagnetic emissions. This enables multi-messenger search strategies to probe unconstrained regions of parameter space.
11:30 AM Tayler instability in Protoneutron stars - Valentin Skoutnev
Tayler instability in Protoneutron stars
- Valentin Skoutnev
11:30 AM - 12:00 PM
Room: PI/4-405 - Bob Room Amplification of magnetic fields by differential rotation and feedback by magnetic instabilities is one of the main mechanisms for magnetizing a protoneutron star. I will discuss a recent revision of the Tayler instability of strong toroidal fields and its implications for the stably stratified interior of protoneutron stars. If time permits, I will briefly highlight new simulations quantifying the efficiency of the chiral dynamo instability.
12:00 PM Seminar
Seminar
12:00 PM - 1:00 PM
Room: PI/4-405 - Bob Room

1:00 PM Lunch
Lunch
1:00 PM - 2:30 PM
Room: PI/4-405 - Bob Room
2:45 PM Relativistic Gas Accretion onto Supermassive Black Hole Binaries from Inspiral through Merger - Lorenzo Ennoggi (Rochester Institute of Technology)
Relativistic Gas Accretion onto Supermassive Black Hole Binaries from Inspiral through Merger
- Lorenzo Ennoggi (Rochester Institute of Technology)
2:45 PM - 3:00 PM
Room: PI/4-405 - Bob Room Accreting supermassive black hole binaries are powerful multimessenger sources emitting both gravitational and electromagnetic (EM) radiation. Understanding the accretion dynamics of these systems and predicting their distinctive EM signals is crucial to informing and guiding upcoming efforts aimed at detecting gravitational waves produced by these binaries. To this end, accurate numerical modeling is required to describe both the spacetime and the magnetized gas around the black holes. In this talk, I will outline two key advancements in this field of research. On the one hand, I will present a novel 3D general relativistic magnetohydrodynamics (GRMHD) framework that combines multiple numerical codes to simulate the inspiral and merger of supermassive black hole binaries starting from realistic initial data and running all the way through merger. Throughout the evolution, we adopt a simple but functional prescription to account for gas cooling through the emission of photons. On the other hand, I will present the application of our new computational method to following the time evolution of a circular, equal-mass, non-spinning black hole binary of total mass ${M}$ for ${\sim\!200}$ orbits starting from a separation of ${20\,r_g\equiv 20\,M}$ and reaching the post-merger evolutionary stage of the system. Our simulation has confirmed the predictions of previous works about the early inspiral phase, but has also revealed phenomena specific to the late-inspiral and merger so far undocumented in the literature. Perhaps our most striking finding is that, although the accretion rate onto the black holes is approximately constant from ${\sim\!3000\,M}$ before merger onward, the EM luminosity undergoes a sharp increase around the time of merger. This effect is caused by the sudden lack of binary torque, which allows the gas in the immediate vicinity of the remnant to quickly fall in, thus compressing and heating up as it shocks. Secondly, the magnetic flux brought to the ${\sim\!0.68\text{-spinning}}$ merger remnant is able to drive a relativistic, Poynting-flux-dominated jet. These dynamics could lead to potentially observable EM signals, supporting upcoming multimessenger observational campaigns.
3:00 PM Magnetar Formation via Accretion-Induced Collapse of White Dwarfs - Siu Hei Cheung (The Chinese University of Hong Kong)
Magnetar Formation via Accretion-Induced Collapse of White Dwarfs
- Siu Hei Cheung (The Chinese University of Hong Kong)
3:00 PM - 3:15 PM
Room: PI/4-405 - Bob Room We present the first two-dimensional axisymmetric Newtonian magnetohydrodynamic simulations of accretion-induced collapse (AIC) of rotating white dwarfs (WDs) with self-consistent initial magnetic progenitors and neutrino leakage. Our findings show that with initial surface magnetic field strength constrained by isolated WD observations, the protoneutron star can reach field strength consistent with magnetar observations. Our results suggest that single degenerate WDs can form magnetars via AIC.
3:15 PM Break
Break
3:15 PM - 3:45 PM
Room: PI/4-405 - Bob Room
3:45 PM Lightning Talk: Lightning Talks
Lightning Talks
3:45 PM - 4:00 PM
Room: PI/4-405 - Bob Room
Contributions

3:45 PM Consequences of Low Resolution and High Initial Magnetic Fields in Binary Neutron Star Merger Simulations - Allen Wen (Rochester Institute of Technology)

3:50 PM General Relativistic Magnetohydrodynamic Simulations of Circumbinary Disk Accretion onto Unequal Mass Black Hole Binaries - Maria Chiara de Simone (Rochester Institute of Technology)
4:00 PM Panel Discussion #2
Panel Discussion #2
4:00 PM - 4:45 PM
Room: PI/4-405 - Bob Room
Friday, March 28, 2025
9:00 AM Numerical simulations of accreting neutron stars in a general relativistic framework. - Pushpita Das
Numerical simulations of accreting neutron stars in a general relativistic framework.
- Pushpita Das
9:00 AM - 9:30 AM
Room: PI/4-405 - Bob Room Numerical modeling of accreting millisecond X-ray pulsars (AMXPs) allows us to understand the physical origin of different observational signatures detected from these systems. Since the birth sites of these signals are strongly influenced by the gravitational potential of the star, magnetohydrodynamic (MHD) simulations in full GR (GRMHD) are essential to accurately capture space-time curvature effects and inherent variations in the X-ray spectra. In this talk, I will present results from 3D GRMHD simulations of accreting neutron stars with oblique magnetospheres. I will discuss the pulse profiles generated from the GRMHD simulations and their implications for mass-radius inference in the accreting sources. Apart from the surface features, AMXPs are also good candidates for studying neutron star jet formation mechanisms. Though there have been extensive investigations into black hole jets, neutron star jets remain highly unexplored. Our 2D axisymmetric study in the quiescent regime suggests that the thick disk collimates the initial open stellar flux, leading to jets like the Blandford-Znajek mechanism proposed for black holes. However, much remains to be done before we can draw a complete picture of jets launched from neutron stars. The global 3D GRMHD simulations of the accreting neutron stars allow us to explore the jet formation mechanisms in these systems in detail for the first time.
9:30 AM Transient Radio Emission of Quiescent Magnetars - Alexander Philippov (UMD)
Transient Radio Emission of Quiescent Magnetars
- Alexander Philippov (UMD)
9:30 AM - 10:00 AM
Room: PI/4-405 - Bob Room
10:00 AM Hybrid Forcefree-(GR)MHD simulations of Magnetar Giant Flares - Koushik Chatterjee (University of Maryland)
Hybrid Forcefree-(GR)MHD simulations of Magnetar Giant Flares
- Koushik Chatterjee (University of Maryland)
10:00 AM - 10:15 AM
Room: PI/4-405 - Bob Room Neutron stars (NSs) represent exceptional astrophysical laboratories, exhibiting extreme magnetic fields and dynamic magnetospheres that drive diverse high-energy phenomena such as giant flares in magnetars. In this talk, I will discuss my research on driving giant flares from non-spinning neutron stars via twisting of magnetic field footpoints, simulated with my new hybrid forcefree-(general relativistic) magnetohydrodynamics code H-AMR. I will focus on the production and evolution of a hot inner magnetosphere (called the 'fireball') and a magnetized bubble, which is one of the leading progenitors of Fast Radio Bursts.
10:15 AM Magnetic Field Evolution and Superconductivity of Pulsars - Ashley Bransgrove (Princeton University, PCTS)
Magnetic Field Evolution and Superconductivity of Pulsars
- Ashley Bransgrove (Princeton University, PCTS)
10:15 AM - 10:30 AM
Room: PI/4-405 - Bob Room Radio pulsars display a range of puzzling long-term variability in their magnetospheric emission and spin-down. In this talk I will discuss the mechanisms for internal magnetic field evolution of pulsars, how it differs from the MHD of classical conducting fluids, and how the neutron star interior couples to the magnetosphere and its radiation.
10:30 AM Break
Break
10:30 AM - 11:00 AM
Room: PI/4-405 - Bob Room
11:00 AM Radiation from fast magnetic dissipation around compact objects - Andrei Beloborodov (Columbia University)
Radiation from fast magnetic dissipation around compact objects
- Andrei Beloborodov (Columbia University)
11:00 AM - 11:30 AM
Room: PI/4-405 - Bob Room Fast magnetic dissipation powers the bursting activity of isolated neutron stars, merging neutron stars, and flares from black holes. Four mechanisms of fast dissipation can operate in the magnetospheres of compact objects: Alfvenic turbulent cascade, magnetic reconnection, collision of Alfvén waves, and monsters shocks. Radiation produced by these dissipation modes is controlled by the compactness parameter. The main radiative output is usually in X-rays; in some cases, radio bursts are produced.
11:30 AM GRMHD simulations of accretion disks: QPOs, truncated disks and QPOs from truncated disks - Gibwa Musoke (Canadian Institute for Theoretical Astrophysics)
GRMHD simulations of accretion disks: QPOs, truncated disks and QPOs from truncated disks
- Gibwa Musoke (Canadian Institute for Theoretical Astrophysics)
11:30 AM - 12:00 PM
Room: PI/4-405 - Bob Room Black hole X-ray binaries (BHXRBs) and Active Galactic Nuclei (AGN) transition through a series of accretion states in a well-defined order. The accretion states, each associated with different luminosities, spectral and variability characteristics, quasi periodic oscillations (QPOs) and outflow properties, are thought to be triggered by physical changes in the accretion disk around the central black hole.The mechanisms behind state transitions, the geometry of transitional disks and the physical mechanisms driving the emission characteristics we observe remain highly debated. General relativistic magneto-hydrodynamic simulations (GRMHD) are increasingly providing crucial insights into the accretion process, the launch of outflows and the physical processes driving state transitions in BHXRBs and AGN. Using GRMHD simulations conducted with the H-AMR code I: 1) Discuss how high and low-frequency QPOs can be produced by a highly tilted, geometrically thin accretion disk. 2) Present the first GRMHD simulation showing the self-consistent formation of a truncated accretion disk– a proposed disk model for the hard intermediate accretion state, in which the accretion flow is thick and hot close to the black hole, while the outer regions of the flow are thin and cool. 3) Describe how QPOs can be generated at the truncation radius (the radius at which the disk transitions from thick to thin) in a truncated accretion disk.
12:00 PM Modeling X-ray emission in radiation-rich magnetar magnetospheres - Jens Mahlmann (Dartmouth College)
Modeling X-ray emission in radiation-rich magnetar magnetospheres
- Jens Mahlmann (Dartmouth College)
12:00 PM - 12:30 PM
Room: PI/4-405 - Bob Room Neutron star magnetospheres are a source of abundant X-ray activity. They have transients observed in different bands, like the fast radio burst (FRB) and associated hard X-ray flare from the Galactic magnetar SGR 1935+2154. We present global models for magnetar X-ray emission, including a landmark first-principle radiative particle-in-cell simulation of the twisted magnetar magnetosphere with the GPU-PIC code Entity. In one scenario, plasma particles accelerated by surface-motion-induced discharges interact resonantly with thermal background photons. Our GPU-accelerated particle-in-cell simulations track up-scattered high-energy photons that drive secondary pair production and ignite a magnetospheric circuit that persistently generates X-rays. We divulge the plasma properties of such a magnetospheric circuit, including densities and velocities, and give an outlook on alternative ignition scenarios for persistent magnetar X-ray emission.
12:30 PM Lunch
Lunch
12:30 PM - 2:00 PM
Room: PI/4-405 - Bob Room
2:00 PM Fast radio bursts as precursor radio emission from monster shocks - Amir Levinson (Tel Aviv university)
Fast radio bursts as precursor radio emission from monster shocks
- Amir Levinson (Tel Aviv university)
2:00 PM - 2:30 PM
Room: PI/4-405 - Bob Room It has been proposed recently that the breaking of MHD waves in the inner magnetosphere of strongly magnetized neutron stars can power different types of high-energy transients. We have studied the steepening and dissipation of a strongly magnetized fast magnetosonic wave propagating in a declining background magnetic field, by means of particle-in-cell simulations that encompass MHD scales. Our analysis confirms the formation of a monster shock as $B^2-E^2$ approaches zero, that dissipates about half of the fast magnetosonic wave energy, and reveals, for the first time, the generation of a high-frequency precursor wave at the monster shock, carrying a fraction of 0.001 of the total energy dissipated at the shock. The spectrum of the precursor wave exhibits several sharp harmonic peaks, with frequencies in the GHz band under conditions anticipated in magnetars. Such signals may appear as fast radio bursts.
2:30 PM Particle Acceleration in Magnetically-Dominated Turbulence - Rostom Mbarek
Particle Acceleration in Magnetically-Dominated Turbulence
- Rostom Mbarek
2:30 PM - 2:45 PM
Room: PI/4-405 - Bob Room Building on recent advancements in understanding particle transport in magnetized media, we present a first-principles scaling law for the formation of non-thermal tails in particle spectra within mildly and strongly magnetized turbulent plasmas. This scaling is validated using results from kinetic Particle-In-Cell simulations, which show excellent agreement with our theoretical predictions. Finally, we discuss the astrophysical implications of these findings, particularly for the proton spectra in the coronae of supermassive black holes.
2:45 PM Break
Break
2:45 PM - 3:15 PM
Room: PI/4-405 - Bob Room

3:15 PM Panel Discussion #3
Panel Discussion #3
3:15 PM - 4:15 PM
Room: PI/4-405 - Bob Room

4:15 PM Closing Remarks
Closing Remarks
4:15 PM - 4:30 PM
Room: PI/4-405 - Bob Room

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