55 research outputs found
Effective two-body scatterings around a massive object
Two-body scatterings under the potential of a massive object are very common
in astrophysics. If the massive body is far enough away that the two small
bodies are in their own gravitational sphere of influence, the gravity of the
massive body can be temporarily ignored. However, this requires the scattering
process to be fast enough that the small objects do not spend too much time at
distances near the surface of the sphere of influence. In this paper, we derive
the validation criteria for effective two-body scattering and establish a
simple analytical solution for this process, which we verify through numerical
scattering experiments. We use this solution to study star-black hole
scatterings in the disks of Active Galactic Nuclei and planet-planet
scatterings in planetary systems, and calculate their one-dimensional
cross-section analytically. Our solution will be valuable in reducing
computational time when treating two-body scatterings under the potential of a
much more massive third body, provided that the problem settings are in the
valid parameter space region identified by our study.Comment: Comments are Welcom
The first high-redshift changing-look quasars
We report on three redshift quasars with dramatic changes in their C IV
emission lines, the first sample of changing-look quasars (CLQs) at high
redshift. This is also the first time the changing-look behaviour has been seen
in a high-ionisation emission line. SDSS J1205+3422, J1638+2827, and J2228+2201
show interesting behaviour in their observed optical light curves, and
subsequent spectroscopy shows significant changes in the C IV broad emission
line, with both line collapse and emergence being displayed on rest-frame
timescales of 240-1640 days. These are rapid changes, especially when
considering virial black hole mass estimates of
for all three quasars. Continuum and emission line measurements from the three
quasars show changes in the continuum-equivalent width plane with the CLQs seen
to be on the edge of the full population distribution, and showing indications
of an intrinsic Baldwin effect. We put these observations in context with
recent state-change models, and note that even in their observed low-state, the
C IV CLQs are generally above 5\% in Eddington luminosity.Comment: 12 pages, 7 figures, 4 tables. All data, analysis code and text are
fully available at: github.com/d80b2t/CIV_CLQs. Comments, questions and
suggestions welcome and encourage
The first high-redshift changing-look quasars
We report on three redshift z > 2 quasars with dramatic changes in their C IV emission lines, the first sample of changing-look quasars (CLQs) at high redshift. This is also the first time the changing-look behaviour has been seen in a high-ionization emission line. SDSS J1205+3422, J1638+2827, and J2228 + 2201 show interesting behaviour in their observed optical light curves, and subsequent spectroscopy shows significant changes in the C IV broad emission line, with both line collapse and emergence being displayed on rest-frame time-scales of ∼240–1640 d. These are rapid changes, especially when considering virial black hole mass estimates of M_(BH) > 10⁹M⊙ for all three quasars. Continuum and emission line measurements from the three quasars show changes in the continuum-equivalent width plane with the CLQs seen to be on the edge of the full population distribution, and showing indications of an intrinsic Baldwin effect. We put these observations in context with recent state-change models, and note that even in their observed low-state, the C IV CLQs are generally above ∼5 per cent in Eddington luminosity
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