185 research outputs found
Multiwavelength Observations of Relativistic Jets from General Relativistic Magnetohydrodynamic Simulations
This work summarizes a program intended to unify three burgeoning branches of
the high-energy astrophysics of relativistic jets: general relativistic
magnetohydrodynamic (GRMHD) simulations of ever-increasing dynamical range, the
microphysical theory of particle acceleration under relativistic conditions,
and multiwavelength observations resolving ever-decreasing spatiotemporal
scales. The process, which involves converting simulation output into time
series of images and polarization maps that can be directly compared to
observations, is performed by (1) self-consistently prescribing models for
emission, absorption, and particle acceleration and (2) performing
time-dependent polarized radiative transfer. M87 serves as an exemplary
prototype for this investigation due to its prominent and well-studied jet and
the imminent prospect of learning much more from Event Horizon Telescope (EHT)
observations this year. Synthetic observations can be directly compared with
real observations for observational signatures such as jet instabilities,
collimation, relativistic beaming, and polarization. The simplest models
described adopt the standard equipartition hypothesis; other models calculate
emission by relating it to current density or shear. These models are intended
for application to the radio jet instead of the higher frequency emission, the
disk and the wind, which will be subjects of future investigations.Comment: 10 pages, 7 figure
GUT-Scale Primordial Black Holes: Consequences and Constraints
A population of very light primordial black holes which evaporate before
nucleosynthesis begins is unconstrained unless the decaying black holes leave
stable relics. We show that gravitons Hawking radiated from these black holes
would source a substantial stochastic background of high frequency
gravititational waves ( Hz or more) in the present universe. These
black holes may lead to a transient period of matter dominated expansion. In
this case the primordial universe could be temporarily dominated by large
clusters of "Hawking stars" and the resulting gravitational wave spectrum is
independent of the initial number density of primordial black holes.Comment: 4 pages; grey body factors included in graviton emission
calculations, and a couple of references added, but the conclusions are
unchanged. v3 Minor changes to references and wording; final versio
Strongly Magnetized Tidal Disruption Event Disks via Stream Injection in GRMHD
Magnetically arrested accretion disks (MADs) around a rapidly rotating black
hole (BH) have been proposed as a model for jetted tidal disruption events
(TDEs). However, the dynamics of strongly magnetized disks in a more realistic
simulation which can mimic the chaotic dynamics during a TDE have previously
been unexplored. Here we employ global GRMHD simulations of a pre-existing MAD
disk interacting with an injected TDE stream with impact parameter to investigate how strongly magnetized TDEs differ from the
standard MAD picture. We demonstrate for the first time that a MAD or semi-MAD
state can be sustained and jets powered by the BH spin are produced in a TDE.
We also demonstrate that the strength of the self-intersection shock depends on
how dense the disk is relative to the stream, or the density contrast
. The jet or funnel can become significantly tilted (by
) due to the self-intersection outflow when . In
models with a powerful jet and , the tilted jet interacts with
and ultimately tilts the disk by as much as 23 degrees from the incoming
stream. We illustrate that as increases, the tilt of the jet and disk
is expected to realign with the BH spin once . We illustrate
how the tilt can rapidly realign if increases rapidly and apply this
to TDEs which have shown X-ray evolution on timescales of days-weeks.Comment: 21 pages, 22 figures, videos available at
https://www.youtube.com/playlist?list=PL6Na55ZD3RmoJl7Rjhn6gCeAE0HWYCI0
Jets from SANE Super-Eddington Accretion Disks: Morphology, Spectra, and Their Potential as Targets for ngEHT
We present general relativistic radiation magnetohydrodynamics (GRRMHD)
simulations of super-Eddington accretion flows around supermassive black holes
(SMBHs) which may apply to tidal disruption events (TDEs). We perform long
duration () simulations which achieve mass accretion
rates times the Eddington rate and produce thermal synchrotron
spectra and images of their jets. The jet reaches a maximum velocity of , but the density weighted outflow velocity is .
Gas flowing beyond the funnel wall expands conically and drives a strong shock
at the jet head while variable mass ejection along the jet axis results in
internal shocks and dissipation. For a model, the
radio/submillimeter spectra peak at GHz and the luminosity increases
with BH spin, exceeding in the brightest
models. The emission is extremely sensitive to as some models show an
order of magnitude decrease in the peak frequency and up to four orders of
magnitude decline in their radio/submillimeter luminosity as
approaches 20. Assuming a maximum VLBI baseline distance of $10 \
{\rm{G}}\lambdaT_i/T_e=1D\lesssim1105\sigmaD\lesssim45\lesssim10^{36} \
{\rm{erg\, s^{-1}}}>230$ GHz
radio/submillimeter followup of future TDEs
Generating Gravitational Waves After Inflation
I review two mechanisms by which gravitational waves can be generated at the
end of inflation: preheating, and gravitons Hawking radiated during the decay
of very small primordial black holes. These mechanisms are contrasted with the
gravitational waves during inflation, and may provide a window into the
physical processes that govern the end of the inflationary phase.Comment: Conference proceeding
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