36 research outputs found
ALMA high-frequency long-baseline campaign in 2017: an investigation of phase-referencing cycle times and effective baseline lengths using band-to-band and in-band phase calibration techniques
Interstellar matter and star formatio
Particle Dark Matter Constraints from the Draco Dwarf Galaxy
It is widely thought that neutralinos, the lightest supersymmetric particles,
could comprise most of the dark matter. If so, then dark halos will emit radio
and gamma ray signals initiated by neutralino annihilation. A particularly
promising place to look for these indicators is at the center of the local
group dwarf spheroidal galaxy Draco, and recent measurements of the motion of
its stars have revealed it to be an even better target for dark matter
detection than previously thought. We compute limits on WIMP properties for
various models of Draco's dark matter halo. We find that if the halo is nearly
isothermal, as the new measurements indicate, then current gamma ray flux
limits prohibit much of the neutralino parameter space. If Draco has a moderate
magnetic field, then current radio limits can rule out more of it. These
results are appreciably stronger than other current constraints, and so
acquiring more detailed data on Draco's density profile becomes one of the most
promising avenues for identifying dark matter.Comment: 13 pages, 6 figure
ALMA high-frequency long baseline campaign in 2021: highest angular resolution submillimeter wave images for the carbon-rich Star R Lep
Instrumentatio
ALMA high-frequency long baseline campaign in 2017: Band-to-band phase referencing in submillimeter waves
Instrumentatio
Spherically Symmetric Braneworld Solutions with R_{4} term in the Bulk
An analysis of a spherically symmetric braneworld configuration is performed
when the intrinsic curvature scalar is included in the bulk action; the
vanishing of the electric part of the Weyl tensor is used as the boundary
condition for the embedding of the brane in the bulk. All the solutions outside
a static localized matter distribution are found; some of them are of the
Schwarzschild-(A)dS_{4} form. Two modified Oppenheimer-Volkoff interior
solutions are also found; one is matched to a Schwarzschild-(A)dS_{4} exterior,
while the other does not. A non-universal gravitational constant arises,
depending on the density of the considered object; however, the conventional
limits of the Newton's constant are recovered. An upper bound of the order of
TeV for the energy string scale is extracted from the known solar system
measurements (experiments). On the contrary, in usual brane dynamics, this
string scale is calculated to be larger than TeV.Comment: 23 pages, 1 figure, one minor chang
Correlations between the peak flux density and the position angle of inner-jet in three blazars
We aim to investigate the relation between the long-term flux density and the
position angle (PA) evolution of inner-jet in blazars. We have carried out the
elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data,
and analyzed the variability properties of three blazars from the model-fit
results. Diverse correlations between the long-term peak flux density and the
PA evolution of the major axis of the `core' have been found in 20% of
the 50 sources. Of them, three typical blazars have been analyzed, which also
show quasi-periodic flux variations of a few years (T). The correlation between
the peak flux density and the PA of inner-jet is positive for S5~0716+714, and
negative for S4~1807+698. The two sources cannot be explained with the
ballistic jet models, the non-ballistic models have been analyzed to explain
the two sub-luminal blazars. A correlation between the peak flux density and
the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this
correlation can be explained with a ballistic precession jet model. All the
explanations are based mainly on the geometric beaming effect; physical flux
density variations from the jet base would be considered for more complicated
situations in future, which could account for the no or less significance of
the correlation between the peak flux density and the PA of inner-jet in the
majority blazars of our sample.Comment: 6 pages, 7 figures, accepted for publication in Astrophysics and
Space Scienc
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
First attempt at measuring the CMB cross-polarization
We compute upper limits on CMB cross-polarization by cross-correlating the
PIQUE and Saskatoon experiments. We also discuss theoretical and practical
issues relevant to measuring cross-polarization and illustrate them with
simulations of the upcoming BOOMERanG 2002 experiment. We present a method that
separates all six polarization power spectra (TT, EE, BB, TE, TB, EB) without
any other "leakage" than the familiar EE-BB mixing caused by incomplete sky
coverage. Since E and B get mixed, one might expect leakage between TE and TB,
between EE and EB and between BB and EB - our method eliminates this by
preserving the parity symmetry under which TB and EB are odd and the other four
power spectra are even.Comment: Polarization movies can be found at
http://www.hep.upenn.edu/~angelica/polarization.htm