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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The Dependence of Gamma-Ray Burst Jet Collimation on Black Hole Spin

Gamma-ray bursts (GRBs) are the most luminous events in the Universe and are excellent laboratories to study extreme physical phenomena in the cosmos. Despite a long trajectory of progress in understanding these highly energetic events, there are still many observed features that are yet to be fully explained. Observations of the jet opening angle of long gamma-ray bursts (LGRBs) suggest that LGRB jets are narrower for those GRBs at higher redshift. This phenomenon has been explained in the context of collimation by the stellar envelope, with denser (lower metallicity) stars at higher redshifts able to collimate the jet more effectively. However, until now, the dependence of the jet opening angle on the properties of the central engine has not been explored. We investigate the effect of black hole spin on the jet collimation angle for a magnetically launched jet, using the general relativistic radiation magnetohydrodynamical code ν bhlight . We present 3D results for a range of spin values. The simulations show that higher-spinning black holes tend to create narrower jets. If indeed LGRB progenitors in the early Universe are able to produce black hole central engines with higher spin, this could account for at least some of the observed jet opening angle-redshift correlation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Fitting improved accretion disk models to the multiwavelength continua of quasars and active galactic nuclei

Fits to the ultraviolet-optical-infrared spectra of 60 quasars and active galactic nuclei (AGNs) are investigated, using black hole accretion disk models. The disk is assumed to be geometrically thin and optically thick. The observed spectrum from a black hole accretion disk, rotating (Kerr) or nonrotating (Schwarzschild), is transformed by the geometric inclination effect, Doppler shifts, gravitational redshifts, and gravitational focusing. These effects alter the locally emitted fluxes and produce harder spectra for an observer at higher inclination angles. The relativistic corrections are much more significant in the Kerr geometry since the inner edge of the disk is much closer to the rotating black hole. A simple inverse relation between the inferred black hole mass and the assumed inclination angle was found in the Kerr case, while the inferred accretion rate (solar masses/yr) remains independent of the angle. In the Schwarzschild case, the ratio of the inferred accretion rate to the black hole mass remains roughly constant when the viewing angle changes. In both geometries, low-redshift Seyfert galaxies have relatively low accretion rates, only a few percent of their Eddington luminosities, while the most luminous quasars are accreting near their Eddington limits.

Sun, Wei-Hsin↗
DOE OSTI2020

HIJING can describe the anisotropy-scaled charge-dependent correlations at the BNL Relativistic Heavy Ion Collider

The experimentally measured charge-dependent correlations in heavy-ion collisions have been suggested as a signature of the chiral magnetic effect (CME). Early model studies could not reproduce the measurement. For example, the HIJING model yielded far smaller magnitude for the charge-dependent correlation than observed in data. This led to the conclusion that the CME had to be invoked to explain the observed correlations in heavy-ion collisions. In this paper we show that this conclusion of the CME interpretation is premature. We show that the reason that HIJING predicts a far smaller correlation than data is because the elliptic anisotropy $(v_ 2)$ parameter in HIJING is too small. When properly scaled, the HIJING model can reproduce in entirety the measured correlations. Further, we also employ the AMPT model, which has a large enough $v_2$, to demonstrate that the measured data can be easily accommodated by models without invoking the CME.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Study of the deformed halo nucleus 31 Ne with Glauber model based on microscopic self-consistent structures

In this work, the exotic deformed nucleus 31 Ne is studied with an approach that combines self-consistent structure and reaction theories. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) is utilized to demonstrate that deformation and pairing correlations give rise to a halo structure with a large-amplitude p-wave configuration in 31 Ne. Then the valence nucleon wave functions and angle-averaged density distributions of 30 Ne from this theory are used as input for the Glauber reaction model to study the observables of neutron-rich neon isotopes to search halo signatures. With NL1 effective interaction, our predictions of the reaction cross sections for these exotic neon isotopes on a carbon target can better reproduce the experimental data than those from the relativistic mean field model for a spherical shape with resonances and pairing correlation contributions, and are roughly 3.3% (~ 50 mb) larger than those with Gaussian function-fitted densities of the core nuclei. The calculated one-neutron removal cross section at 240 MeV/nucleon, and the inclusive longitudinal momentum distribution of the 30 Ne residues from the 31Ne breakup reaction are largely improved over previous theoretical predictions and agree well with data. These reaction evaluations indicate a dilute density distribution in coordinate space and are a canonical signature of a halo structure. Moreover, our predictions with the NL3 and PK1 effective interactions give slightly better descriptions of reaction observables for exotic neon isotopes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Collective plasma effects of electron–positron pairs in beam-driven QED cascades

Understanding the interplay of strong-field QED and collective plasma effects is important for explaining extreme astrophysical environments like magnetars. It has been shown that QED pair plasma can be produced and observed by passing a relativistic electron beam through an intense laser field. This work presents in detail multiple sets of 3D QED-particle-in-cell simulations to show the creation of pair plasma in the QED cascade. The beam driven method enables a high pair particle density and also a low particle Lorentz factor, which both play equal roles on exhibiting large collective plasma effects. Finite laser frequency upshift is observed with both ideal parameters (24 PW laser colliding with a 300 GeV electron beam) and with existing technologies (3 PW laser colliding with a 30 GeV electron beam).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Absolute laser energy absorption measurement of relativistic 0.7 ps laser pulses in nanowire arrays

Laser absorption is one of the most important parameters governing laser–matter interactions. The laser energy absorption on nanowire array targets is measured for the first time in the relativistic regime at intensities of 10 19 W=cm 2 and compared to foil targets. The results show that the laser energy absorption of 0.7 ps frequency doubled (527 nm) pulses on Au nanowire targets varies widely with nanowire parameters, reaching laser energy absorption values up to 71% of the incident energy, significantly exceeding those of solid flat targets obtained in similar irradiation conditions. The analysis shows that the increase in absorption strongly correlates with larger effective target surface area over a broad range of nanowire parameters explored. These direct absorption measurements provide valuable data to benchmark simulations of the relativistic laser pulse interactions with nanostructures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Local spin polarizations in relativistic heavy-ion collisions

Here, based on a generalized side-jump formalism for massless chiral fermions, which naturally takes into account the spin-orbit coupling in the scattering of two chiral fermions and the chiral vortical effect in a rotating chiral fermion matter, we have developed a covariant and total-angular-momentum-conserved chiral transport model to study both the global and local polarizations of this matter. For a system of massless quarks of random spin orientations and finite vorticity in a box, we have demonstrated that the model can exactly conserve the total angular momentum of the system and dynamically generate the quark spin polarization expected from a thermally equilibrated quark matter. Using this model to study the spin polarization in relativistic heavy-ion collision, we have found that the local quark spin polarizations depend strongly on the reference frame where they are evaluated as a result of the nontrivial axial charge distribution caused by the chiral vortical effect. We have further shown that because of the anomalous orbital or side-jump contribution to the quark spin polarization, the local quark polarizations calculated in the medium rest frame are qualitatively consistent with the local polarizations of Lambda hyperons measured in experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1989

X ray emission from relativistic jets in AGNs and statistical implications

Calculations of the Compton scattering interaction between an ultrarelativistic jet and a thermal radiation field, in an Active Galactic Nuclei (AGN), are presented. This process can be effective in decelerating ultrarelativistic jets that are accelerated by electromagnetic or hydromagnetic forces closer in to the central black hole. A narrow distribution of terminal Lorentz factors gamma sub infinity, consistent with the values inferred in superluminal radio sources, arises naturally in this model. The hard X-ray component detected in the spectra of 3C273 and several BL Lac objects may be due to the inverse Compton radiation produced in the course of the initial deceleration of their relativistic jets. The requirement that the luminosity of the hard X-ray component must exceed the total power in the associated jet is considered.

Melia, Fulvio↗
DOE OSTI2022

Measuring differential flow angle fluctuations in relativistic nuclear collisions

Recently studies of the differential nature of the flow angle fluctuations, known as event plane angular decorrelation, indicated that measurements that assume a common symmetry plane may need to consider the flow angle fluctuations effect. Using the HIJING and AMPT models, it is shown that the flow angle fluctuations measurements, obtained with the two- and three-subevents correlation method, could have significant nonflow effects associated with long- and short-range nonflow correlations. The current study demonstrates the four-subevents cumulant methods' ability to reduce the nonflow effects. Finally, it is further argued that the measurements using the four-subevents correlation method can be used to provide accurate quantification of the differential flow angle fluctuations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Tearing-mediated Alfvénic Turbulence in a Relativistic Plasma

In astrophysical relativistic plasmas, Alfvénic turbulence exists across a wide range of scales. Similar to a nonrelativistic case, this turbulence can be influenced by the tearing instability. We argue that in an ultrarelativistic pair plasma the tearing effects become significant at the critical scale given by ${a}_{t}\sim {d}_{\mathrm{rel}}{\left({L}_{\perp }/{d}_{\mathrm{rel}}\right)}^{n/(4+5n)}$, where L ⊥ represents the outer scale of the turbulence and d rel the relativistic electron inertial scale. Here n = 1 corresponds to the Harris magnetic configurations, while n = 2 applies to localized (non-Harris) magnetic profiles of turbulence-generated current sheets. Below the critical scale, the energy spectrum of magnetic fluctuations steepens to W(k)dk ∝ k -(7n+2)/3n dk. However, this happens only when $\tilde{\sigma }\ll {\left({L}_{\perp }/{d}_{\mathrm{rel}}\right)}^{(2+4n)/(4+5n)}$, where $\tilde{\sigma }$ is the magnetization parameter based on the magnetic fluctuations. If the opposite inequality holds, the Alfvénic cascade is instead affected by charge starvation at scales below ${a}_{\mathrm{ch}}\sim {d}_{\mathrm{rel}}{\left({d}_{\mathrm{rel}}/{L}_{\perp }\right)}^{1/3}{\tilde{\sigma }}^{2/3}$, and the energy spectrum becomes steeper than W(k)dk ∝ k -3 dk. When d rel is replaced by its nonrelativistic equivalent, our results agree with the nonrelativistic analysis of N. F. Loureiro & S. Boldyrev (2018). In the Harris case n = 1, they agree with the recent relativistic studies by I. Demidov & Y. Lyubarsky.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Comptonization by reconnection plasmoids in black hole coronae I: Magnetically dominated pair plasma

We perform 2D particle-in-cell simulations of reconnection in magnetically dominated electron–positron plasmas subject to strong Compton cooling. We vary the magnetization σ $\gg$ 1, defined as the ratio of magnetic tension to plasma inertia, and the strength of cooling losses. Magnetic reconnection under such conditions can operate in magnetically dominated coronae around accreting black holes, which produce hard X-rays through Comptonization of seed soft photons. We find that the particle energy spectrum is dominated by a peak at mildly relativistic energies, which results from bulk motions of cooled plasmoids. The peak has a quasi-Maxwellian shape with an effective temperature of ~100 keV, which depends only weakly on the flow magnetization and the strength of radiative cooling. The mean bulk energy of the reconnected plasma is roughly independent of σ, whereas the variance is larger for higher magnetizations. The spectra also display a high-energy tail, which receives ~25 percent of the dissipated reconnection power for σ = 10 and ~40 percent for σ = 40. We complement our particle-in-cell studies with a Monte Carlo simulation of the transfer of seed soft photons through the reconnection layer, and find the escaping X-ray spectrum. The simulation demonstrates that Comptonization is dominated by the bulk motions in the chain of Compton-cooled plasmoids and, for σ ~ 10, yields a spectrum consistent with the typical hard state of accreting black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Apparently superluminal superfluids

We consider the superfluid phase of a specific renormalizable relativistic quantum field theory. We prove that, within the regime of validity of perturbation theory and of the superfluid effective theory, there are consistent and regular vortex solutions where the superfluid’s velocity field as traditionally defined smoothly interpolates between zero and arbitrarily large superluminal values. We show that this solution is free of instabilities and of superluminal excitations. We show that, in contrast, a generic vortex solution for an ordinary fluid does develop an instability if the velocity field becomes superluminal. All this questions the characterization of a superfluid velocity field as the actual velocity of “something”.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Probing Strong-Field QED with Doppler-Boosted Petawatt-Class Lasers

In this work, we propose a scheme to explore regimes of strong-field quantum electrodynamics (SF QED) otherwise unattainable with the currently available laser technology. The scheme relies on relativistic plasma mirrors curved by radiation pressure to boost the intensity of petawatt-class laser pulses by Doppler effect and focus them to extreme field intensities. We show that very clear SF QED signatures could be observed by placing a secondary target where the boosted beam is focused.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Observation of Skewed Electromagnetic Wakefields in an Asymmetric Structure Driven by Flat Electron Bunches

Relativistic charged -particle beams that generate intense longitudinal fields in accelerating structures also inherently couple to transverse modes. The effects of this coupling may lead to beam breakup instability and thus must be countered to preserve beam quality in applications such as linear colliders. Beams with highly asymmetric transverse sizes (flat beams) have been shown to suppress the initial instability in slab -symmetric structures. However, as the coupling to transverse modes remains, this solution serves only to delay instability. In order to understand the hazards of transverse coupling in such a case, we describe here an experiment characterizing the transverse effects on a flat beam, traversing near a planar dielectric lined structure. Further, the measurements reveal the emergence of a previously unobserved skew-quadrupolelike interaction when the beam is canted transversely, which is not present when the flat beam travels parallel to the dielectric surface. We deploy a multipole field fitting algorithm to reconstruct the projected transverse wakefields from the data. We generate the effective kick vector map using a simple two -particle theoretical model, with particle -in -cell simulations used to provide further insight for realistic particle distributions.

43 PARTICLE ACCELERATORS↗
NASA NTRS1972

A resonant instability of model proton radiation belts in the Jovian magnetosphere

The ion cyclotron instability and characteristics of the ion cyclotron wave are discussed. A mathematical perturbation technique is applied to the dispersion relations, and the results are applied to the case of propagation parallel to the magnetic field. The ion cyclotron wave is determined in its damping and growth characteristics by resonant protons and electrons, found in momentum space on resonant surfaces. In the relativistic case the resonant surfaces are hyperbolas of revolution around the magnetic field, and protons can have a stabilizing effect. Instability rates are calculated for the region in the equatorial plane with the Ioannidis and Brice density model. The upper limit of proton flux which gives an energy density of the same order of magnitude as the magnetic field energy density is obtained. The upper limit is plotted with respect to distance from Jupiter and the minimum resonant energy contributing to the instability is also plotted.

Neubauer, F. M.↗
NASA NTRS2003

The XMM-Newton Iron Line Profile of NGC 3783

We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (approx. 240 ks) XMM-Newton observation. The line profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV, with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV emission is the K(alpha) line from near neutral Fe, whilst the 7.0 keV feature probably originates from a blend of the neutral Fe K(beta) line and the Hydrogen-like line of Fe at 6.97 keV. The relatively narrow velocity width of the K(alpha) line (approx. less than 5000 km/s), its lack of response to the continuum emission on short timescales and the detection of a neutral Compton reflection component are all consistent with a distant origin in Compton-thick matter such as the putative molecular torus. A strong absorption line from highly ionized iron (at 6.67 keV) is detected in the time-averaged iron line profile, whilst the depth of the feature appears to vary with time, being strongest when the continuum flux is higher. The iron absorption line probably arises from the highest ionization component of the known warm absorber in NGC 3783, with an ionization of log xi approx 3 and column density of N(sub H) approx. 5 x 10(exp 22)/sq cm and may originate from within 0.1 pc of the nucleus. A weak red-wing to the iron K line profile is also detected below 6.4 keV. However when the effect of the highly ionized warm absorber on the underlying continuum is taken into account, the requirement for a relativistic iron line component from the inner disk is reduced.

Reeves, J. N.↗
DOE OSTI2024

Effectiveness of denoising diffusion probabilistic models for fast and high-fidelity whole-event simulation in high-energy heavy-ion experiments

Artificial intelligence (AI) generative models, such as generative adversarial networks (GANs), variational autoencoders, and normalizing flows, have been widely used and studied as efficient alternatives for traditional scientific simulations. However, they have several drawbacks, including training instability and inability to cover the entire data distribution, especially for regions where data are rare. This is particularly challenging for whole-event, full-detector simulations in high-energy heavy-ion experiments, such as sPHENIX at the Relativistic Heavy Ion Collider and Large Hadron Collider experiments, where thousands of particles are produced per event and interact with the detector. This work investigates the effectiveness of denoising diffusion probabilistic models (DDPMs) as an AI-based generative surrogate model for the sPHENIX experiment that includes the heavy-ion event generation and response of the entire calorimeter stack. DDPM performance in sPHENIX simulation data is compared with a popular rival, GANs. Results show that both DDPMs and GANs can reproduce the data distribution where the examples are abundant (low-to-medium calorimeter energies). Nonetheless, DDPMs significantly outperform GANs, especially in high-energy regions where data are rare. Additionally, DDPMs exhibit superior stability compared to GANs. The results are consistent between both central and peripheral centrality heavy-ion collision events. Moreover, DDPMs offer a substantial speedup of approximately a factor of 100 compared to the traditional Geant4 simulation method.

42 ENGINEERING↗