1,882 research outputs found
A Statistical Description of AGN Jet Evolution from the VLBA Imaging and Polarimetry Survey (VIPS)
A detailed analysis of the evolution of the properties of core-jet systems
within the VLBA Imaging and Polarimetry Survey (VIPS) is presented. We find a
power-law relationship between jet intensity and width that suggests for the
typical jet, little if any energy is lost as it moves away from its core. Using
VLA images at 1.5 GHz, we have found evidence that parsec-scale jets tend to be
aligned with the the direction of emission on kiloparsec scales. We also found
that this alignment improves as the jets move farther from their cores on
projected scales as small as ~50-100 pc. This suggests that realignment of jets
on these projected scales is relatively common. We typically find a modest
amount of bending (a change in jet position angle of ~5 deg.) on these scales,
suggesting that this realignment may typically occur relatively gradually.Comment: Accepted to ApJ, 20 pages, 8 figure
Characteristics of Gamma-Ray Loud Blazars in the VLBA Imaging and Polarimetry Survey
The radio properties of blazars detected by the Large Area Telescope (LAT) on
board the Fermi Gamma-ray Space Telescope have been observed as part of the
VLBA Imaging and Polarimetry Survey (VIPS). This large, flux-limited sample of
active galactic nuclei (AGN) provides insights into the mechanism that produces
strong gamma-ray emission. At lower flux levels, radio flux density does not
directly correlate with gamma-ray flux. We find that the LAT-detected BL Lacs
tend to be similar to the non-LAT BL Lacs, but that the LAT-detected FSRQs are
often significantly different from the non-LAT FSRQs. The differences between
the gamma-ray loud and quiet FSRQs can be explained by Doppler boosting; these
objects appear to require larger Doppler factors than those of the BL Lacs. It
is possible that the gamma-ray loud FSRQs are fundamentally different from the
gamma-ray quiet FSRQs. Strong polarization at the base of the jet appears to be
a signature for gamma-ray loud AGN.Comment: 32 pages, 9 figures, accepted by Ap
J16021+3326: New Multi-Frequency Observations of a Complex Source
We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly.Comment: 16 pages, 7 Figures, 2 Tables, accepted to Ap
Nonlocal appearance of a macroscopic angular momentum
We discuss a type of measurement in which a macroscopically large angular
momentum (spin) is "created" nonlocally by the measurement of just a few atoms
from a double Fock state. This procedure apparently leads to a blatant
nonconservation of a macroscopic variable - the local angular momentum. We
argue that while this gedankenexperiment provides a striking illustration of
several counter-intuitive features of quantum mechanics, it does not imply a
non-local violation of the conservation of angular momentum.Comment: 10 pages, 1 figur
Rotating strings
Analytical expressions are provided for the configurations of an
inextensible, flexible, twistable inertial string rotating rigidly about a
fixed axis. Solutions with trivial radial dependence are helices of arbitrary
radius and pitch. Non-helical solutions are governed by a cubic equation whose
roots delimit permissible values of the squared radial coordinate. Only curves
coplanar with the axis of rotation make contact with it.Comment: added to discussion and made small revisions to tex
Correlation of Fermi-LAT sources with the AT20GHz radio survey
We cross correlate the Fermi 11 months survey catalogue (1FGL) with the 20
GHz Australia Telescope Compact Array radio survey catalogue (AT20G) composed
by 5890 sources at declination <0 deg. Among the 738 Fermi sources distributed
in the southern sky we find 230 highly probable candidate counterparts in the
AT20G survey. Of these, 222 are already classified as blazars (176 of known
type and 46 of unknown optical class) in the Fermi 1-year LAT AGN Catalogue
(1LAC) and 8 are new associations. By studying the gamma-ray and radio
properties of these associations we find a strong correlation between the
gamma-ray flux (above 100 MeV) and the 20 GHz flux density. This correlation is
more than 3 sigma statistically significant both for the population of BL Lacs
and of FSRQ considered separately. We also find that the radio counterparts
associated to the Fermi sources have on average flat radio spectra between 5
and 20 GHz and that Fermi gamma-ray sources are not preferentially associated
with "ultra inverted spectrum" radio sources. For 2 of the 8 new associations
we build the broad band spectral energy distribution combining Fermi, Swift and
radio observations. One of these two sources is identified with the high
redshift FSRQ Swift J1656.3-3302 (z=2.4) and we classify the other source as a
candidate new FSRQ. We also study the brightest radio source of the 46
associations without an optical classification and classify it as a new BL Lac
candidate "twin" of the prototypical BL Lac OJ 287 if its redshift is somewhat
larger, z~0.4.Comment: 12 pages, 10 figures, 3 tables. Submitted to MNRAS on the 22nd March
2010
ΠΠΈΠΊΠΎΠ»Π°ΠΉ ΠΠ»Π΅ΠΊΡΠ΅Π΅Π²ΠΈΡ ΠΠ·Π°ΡΠ΅Π½ΠΊΠΎΠ² (ΠΊ 60-Π»Π΅ΡΠΈΡ ΡΠΎ Π΄Π½Ρ ΡΠΎΠΆΠ΄Π΅Π½ΠΈΡ)
ΠΡΠΏΠΎΠ»Π½ΠΈΠ»ΠΎΡΡ 60 Π»Π΅Ρ ΠΈΠ·Π²Π΅ΡΡΠ½ΠΎΠΌΡ ΡΡΠ΅Π½ΠΎΠΌΡ Π² ΠΎΠ±Π»Π°ΡΡΠΈ ΡΠΈΠ·ΠΈΠΊΠΈ ΠΏΠ»Π°Π·ΠΌΡ, ΡΠ»Π΅Π½Ρ-ΠΊΠΎΡΡΠ΅ΡΠΏΠΎΠ½Π΄Π΅Π½ΡΡ ΠΠΠ Π£ΠΊΡΠ°ΠΈΠ½Ρ, Π΄ΠΎΠΊΡΠΎΡΡ ΡΠΈΠ·ΠΈΠΊΠΎ-ΠΌΠ°ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΡ
Π½Π°ΡΠΊ, Π·Π°ΡΠ»ΡΠΆΠ΅Π½Π½ΠΎΠΌΡ Π΄Π΅ΡΡΠ΅Π»Ρ Π½Π°ΡΠΊΠΈ ΠΈ ΡΠ΅Ρ
Π½ΠΈΠΊΠΈ Π£ΠΊΡΠ°ΠΈΠ½Ρ, ΠΎΡΠ»ΠΈΡΠ½ΠΈΠΊΡ ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ Π£ΠΊΡΠ°ΠΈΠ½Ρ, Π·Π°ΡΠ»ΡΠΆΠ΅Π½Π½ΠΎΠΌΡ ΠΏΡΠΎΡΠ΅ΡΡΠΎΡΡ Π₯Π°ΡΡΠΊΠΎΠ²ΡΠΊΠΎΠ³ΠΎ ΡΠ½ΠΈΠ²Π΅ΡΡΠΈΡΠ΅ΡΠ° ΠΠΈΠΊΠΎΠ»Π°Ρ ΠΠ»Π΅ΠΊΡΠ΅Π΅Π²ΠΈΡΡ ΠΠ·Π°ΡΠ΅Π½ΠΊΠΎΠ²Ρ
Spectroscopy of Broad Line Blazars from 1LAC
We report on optical spectroscopy of 165 Flat Spectrum Radio Quasars (FSRQs)
in the Fermi 1LAC sample, which have helped allow a nearly complete study of
this population. Fermi FSRQ show significant evidence for non-thermal emission
even in the optical; the degree depends on the gamma-ray hardness. They also
have smaller virial estimates of hole mass than the optical quasar sample. This
appears to be largely due to a preferred (axial) view of the gamma-ray FSRQ and
non-isotropic (H/R ~ 0.4) distribution of broad-line velocities. Even after
correction for this bias, the Fermi FSRQ show higher mean Eddington ratios than
the optical population. A comparison of optical spectral properties with Owens
Valley Radio Observatory radio flare activity shows no strong correlation.Comment: Accepted for publication in Ap
Static avalanches and Giant stress fluctuations in Silos
We propose a simple model for arch formation in silos. We show that small
pertubations (such as the thermal expansion of the beads) may lead to giant
stress fluctuations on the bottom plate of the silo. The relative amplitude
of these fluctuations are found to be power-law distributed, as
, . These fluctuations are related to large
scale `static avalanches', which correspond to long-range redistributions of
stress paths within the silo.Comment: 10 pages, 4 figures.p
Characteristics of EGRET Blazars in the VLBA Imaging and Polarimetry Survey (VIPS)
We examine the radio properties of EGRET-detected blazars observed as part of
the VLBA Imaging and Polarimetry Survey (VIPS). VIPS has a flux limit roughly
an order of magnitude below the MOJAVE survey and most other samples that have
been used to study the properties of EGRET blazars. At lower flux levels, radio
flux density does not directly correlate with gamma-ray flux density. We do
find that the EGRET-detected blazars tend to have higher brightness
temperatures, greater core fractions, and possibly larger than average jet
opening angles. A weak correlation is also found with jet length and with
polarization. All of the well-established trends can be explained by
systematically larger Doppler factors in the gamma-ray loud blazars, consistent
with the measurements of higher apparent velocities found in monitoring
programs carried out at radio frequencies above 10 GHz.Comment: 20 pages, 7 figures, accepted to Ap
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