595 research outputs found
Constraining the range of Yukawa gravity interaction from S2 star orbits
We consider possible signatures for Yukawa gravity within the Galactic
Central Parsec, based on our analysis of the S2 star orbital precession around
the massive compact dark object at the Galactic Centre, and on the comparisons
between the simulated orbits in Yukawa gravity and two independent sets of
observations. Our simulations resulted in strong constraints on the range of
Yukawa interaction and showed that its most probable value in the
case of S2 star is around 5000 - 7000 AU. At the same time, we were not able to
obtain reliable constrains on the universal constant of Yukawa
gravity, because the current observations of S2 star indicated that it may be
highly correlated with parameter in the range . For
they are not correlated. However, the same universal constant
which was successfully applied to clusters of galaxies and rotation curves of
spiral galaxies () also gives a satisfactory agreement with the
observed orbital precession of the S2 star, and in that case the most probable
value for the scale parameter is AU. Also, the
Yukawa gravity potential induces precession of S2 star orbit in the same
direction as General Relativity for and for , and in
the opposite direction for . The future observations with
advanced facilities, such as GRAVITY or/and European Extremely Large Telescope,
are needed in order to verify these claims.Comment: 16 pages, 8 figures, accepted for publication in JCA
Constraints on gravity from precession of orbits of S2-like stars
We study some possible observational signatures of gravity at Galactic
scales and how these signatures could be used for constraining this type of
gravity. For that purpose, we performed two-body simulations in
gravity potential and analyzed the obtained trajectories of S2-like stars
around Galactic center, as well as resulting parameter space of gravity
potential. Here, we discuss the constraints on the gravity which can be
obtained from the observations of orbits of S2-like stars with the present and
next generations of large telescopes. We make comparison between the
theoretical results and observations. Our results show that the most probable
value for the parameter in gravity potential in the case of S2-like
stars is 100 AU, while the universal parameter is close to 0.01.
Also, the gravity potential induces the precession of S2-like stars orbit
in opposite direction with respect to General Relativity, therefore, such a
behavior of orbits qualitatively is similar to a behavior of Newtonian orbits
with a bulk distribution of matter (including a stellar cluster and dark matter
distributions).Comment: 12 pages, 12 figures, accepted in Phys. Rev.
The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole
One of the most intriguing scenarios proposed to explain how active galactic
nuclei are triggered involves the existence of a supermassive binary black hole
system in their cores. Here we present an observational evidence for the first
spectroscopically resolved sub-parsec orbit of a such system in the core of
Seyfert galaxy NGC 4151. Using a method similar to those typically applied for
spectroscopic binary stars we obtained radial velocity curves of the
supermassive binary system, from which we calculated orbital elements and made
estimates about the masses of components. Our analysis shows that periodic
variations in the light and radial velocity curves can be accounted for an
eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum
in the lightcurve correspond to the approaching phase of a secondary component
towards the observer. According to the obtained results we speculate that the
periodic variations in the observed H{\alpha} line shape and flux are due to
shock waves generated by the supersonic motion of the components through the
surrounding medium. Given the large observational effort needed to reveal this
spectroscopically resolved binary orbital motion we suggest that many such
systems may exist in similar objects even if they are hard to find. Detecting
more of them will provide us with insight into black hole mass growth process.Comment: 29 pages, 10 figures, published in ApJ, 759, 11
Winged DRAGN Source From Leahy’s Atlas: 3C 315
The goal of this paper is to inspect the flux density as well as the spectral index distribution of 3C 315, an X-shaped radio source with a steep spectrum core. To this end we used publicly available data and images of the source at different frequencies (specifically 1646 MHz and 2695 MHz, as well as Leahy’s atlas of double radio-sources). We found that synchrotron radiation is the dominant radiation mechanism over most of the area of 3C 315 with an average spectral index α of 0.956.SPIG 2022 : 31st Summer School and International Symposium on the Physics of Ionized Gases : Contributed papers and abstracts of invited lectures, topical invited lectures and progress reports; September 5-9,2022, Belgrad
Design and simulation of InGaAs/AlAsSb quantum-cascade lasers for short wavelength emission
The design and simulation of an In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade laser emitting in the near infrared is presented. Designed using a self-consistent rate equation solver coupled with an energy balance rate equation, the proposed laser has a calculated population inversion of ~20% at 77 K and sufficient gain to achieve room-temperature laser emission at λ ~2.8 µm. Threshold currents in the range 4–8 kA/cm2 are estimated as the temperature increases from 77 K to 300 K. The output characteristics of the proposed laser are compared to an existing λ ~3.1 µm In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade structure presented in the literature
Variability of the H-beta line profiles as an indicator of orbiting bright spots in accretion disks of quasars: a case study of 3C 390.3
Here we show that in the case when double peaked emission lines originate
from outer parts of accretion disk, their variability could be caused by
perturbations in the disk emissivity. In order to test this hypothesis, we
introduced a model of disk perturbing region in the form of a single bright
spot (or flare) by a modification of the power law disk emissivity in
appropriate way. The disk emission was then analyzed using numerical
simulations based on ray-tracing method in Kerr metric and the corresponding
simulated line profiles were obtained. We applied this model to the observed
H-beta line profiles of 3C 390.3 (observed in the period 1995-1999), and
estimated the parameters of both, accretion disk and perturbing region. Our
results show that two large amplitude outbursts of the H-beta line observed in
3C 390.3 could be explained by successive occurrences of two bright spots on
approaching side of the disk. These bright spots are either moving, originating
in the inner regions of the disk and spiralling outwards by crossing small
distances during the period of several years, or stationary. In both cases,
their widths increase with time, indicating that they most likely decay.Comment: 14 pages, 5 figures, 1 table. Accepted for publication in Ap
RXJ 0921+4529: a binary quasar or gravitational lens?
We report the new spectroscopic observations of the gravitational lens RXJ
021+4529 with the multi-mode focal reducer SCORPIO of the SAO RAS 6-m
telescope. The new spectral observations were compared with the previously
observed spectra of components A and B of RXJ 0921+4529, i.e. the same
components observed in different epochs. We found a significant difference in
the spectrum between the components that cannot be explained with microlensing
and/or spectral variation. We conclude that RXJ 0921+4529 is a binary quasar
system, where redshifts of quasars A and B are 1.6535 +/- 0.0005 and 1.6625 +/-
0.0015, respectively.Comment: 6 pages, 5 figures, accepted for publication in The Astrophysical
Journal Letter
LR and L+R Systems
We consider coupled nonholonomic LR systems on the product of Lie groups. As
examples, we study -dimensional variants of the spherical support system and
the rubber Chaplygin sphere. For a special choice of the inertia operator, it
is proved that the rubber Chaplygin sphere, after reduction and a time
reparametrization becomes an integrable Hamiltonian system on the
--dimensional sphere. Also, we showed that an arbitrary L+R system
introduced by Fedorov can be seen as a reduced system of an appropriate coupled
LR system.Comment: 18 pages, 1 figur
Applying machine learning to the problem of choosing a heuristic to select the variable ordering for cylindrical algebraic decomposition
Cylindrical algebraic decomposition(CAD) is a key tool in computational
algebraic geometry, particularly for quantifier elimination over real-closed
fields. When using CAD, there is often a choice for the ordering placed on the
variables. This can be important, with some problems infeasible with one
variable ordering but easy with another. Machine learning is the process of
fitting a computer model to a complex function based on properties learned from
measured data. In this paper we use machine learning (specifically a support
vector machine) to select between heuristics for choosing a variable ordering,
outperforming each of the separate heuristics.Comment: 16 page
- …