1,015 research outputs found
X-ray synchrotron emission from the oblique shock in the jet of the powerful radio galaxy 3C 346
We report the first detection, with Chandra, of X-ray emission from the jet
of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the
bright radio and optical knot at which the jet apparently bends by about 70
degrees. The Chandra observation also reveals a bright galaxy-scale atmosphere
within the previously-known cluster, and provides a good X-ray spectrum for the
bright core of 3C 346. The X-ray emission from the knot is synchrotron
radiation, as seen in lower-power sources. In common with these sources, there
is evidence of morphological differences between the radio/optical and X-ray
structures, and the spectrum is inconsistent with a one-component
continuous-injection model. We suggest that the X-ray-bright knot is associated
with a strong oblique shock in a moderately relativistic, light jet, at about
20 degrees to the line of sight, and that this shock is caused by the jet
interacting with the wake in the cluster medium behind 3C 346's companion
galaxy. The general jet curvature can result from pressure gradients in the
cluster atmosphere.Comment: Accepted for publication in the MNRAS. 9 page
The magnetic field and geometry of the oblique shock in the jet of 3C 346
We investigate the brightest regions of the kpc-scale jet in the powerful
radio galaxy 3C 346, using new optical HST ACS/F606W polarimetry together with
Chandra X-ray data and 14.9 GHz and 22.5 GHz VLA radio polarimetry. The jet
shows a close correspondence in optical and radio morphology, while the X-ray
emission shows an 0.80 +/- 0.17 kpc offset from the optical and radio peak
positions. Optical and radio polarimetry show the same apparent magnetic field
position angle and fractional polarization at the brightest knot, where the jet
undergoes a large kink of almost 70 degrees in the optical and radio images.
The apparent field direction here is well-aligned with the new jet direction,
as predicted by earlier work that suggested the kink was the result of an
oblique shock. We have explored models of the polarization from oblique shocks
to understand the geometry of the 3C 346 jet, and find that the upstream flow
is likely to be highly relativistic (0.91 +0.05 / -0.07 c), where the plane of
the shock front is inclined at an angle of 51 (+/- 11) degrees to the upstream
flow which is at an angle 14 (+8 / -7) degrees to our line of sight. The actual
deflection angle of the jet in this case is only 22 degrees.Comment: 11 pages, 5 figures. Accepted by MNRA
The inner jet of radio galaxy NGC 315 as observed with Chandra and the VLA
We present Chandra X-ray results for the jet, nucleus, and gaseous atmosphere
of NGC 315, a nearby radio galaxy whose jet kinematics are known through deep
radio mapping. Diffuse X-ray synchrotron emission is detected from the jet out
to 30 arcsec from the nucleus, through regions both of fast bulk flow and
deceleration. The X-ray to radio flux ratio drops considerably where the flow
decelerates, but the X-ray and radio emissions show similar transverse extents
throughout, requiring distributed particle acceleration to maintain the supply
of X-ray-emitting electrons. A remarkable knotty filament within the jet is
seen in both the radio and X-ray, contributing roughly 10 per cent of the
diffuse emission along its extent at both wavelengths. No completely
satisfactory explanation for the filament is found, though its oscillatory
appearance, roughly aligned magnetic field, and requirements for particle
acceleration, suggest that it is a magnetic strand within a shear layer between
fast inner and slower outer flow.Comment: Accepted for publication in the MNRAS. 13 pages,14 figures (some in
colour
The jet and counterjet of 3C 270 (NGC 4261) viewed in the X-ray with Chandra
The radio source 3C 270, hosted by NGC 4261, is the brightest known example
of counterjet X-ray emission from a low-power radio galaxy. We report on the
X-ray emission of the jet and counterjet from 130 ks of Chandra data. We argue
that the X-ray emission is synchrotron radiation and that the internal
properties of the jet and counterjet are remarkably similar. We find a smooth
connection in X-ray hardness and X-ray to radio ratio between the jet and one
of the X-ray components within the core spectrum. We observe wedge-like
depressions in diffuse X-ray surface brightness surrounding the jets, and
interpret them as regions where an aged population of electrons provides
pressure to balance the interstellar medium of NGC 4261. About 20% of the mass
of the interstellar medium has been displaced by the radio source. Treating 3C
270 as a twin-jet system, we find an interesting agreement between the ratio of
jet-to-counterjet length in X-rays and that expected if X-rays are observed
over the distance that an outflow from the core would have traveled in ~6x10^4
yr. X-ray synchrotron loss times are shorter than this, and we suggest that
most particle acceleration arises as a result of turbulence and dissipation in
a stratified flow. We speculate that an episode of activity in the central
engine beginning ~6x10^4 yr ago has led to an increased velocity shear. This
has enhanced the ability of the jet plasma to accelerate electrons to
X-ray-synchrotron-emitting energies, forming the X-ray jet and counterjet that
we see today.Comment: Accepted for publication in the MNRAS. 12 pages, 10 figs (some in
color).Some figures reduced in qualit
Virtual Adversarial Ladder Networks For Semi-supervised Learning
Semi-supervised learning (SSL) partially circumvents the high cost of labeling data by augmenting a small labeled dataset with a large and relatively cheap unlabeled dataset drawn from the same distribution. This paper offers a novel interpretation of two deep learning-based SSL approaches, ladder networks and virtual adversarial training (VAT), as applying distributional smoothing to their respective latent spaces. We propose a class of models that fuse these approaches. We achieve near-supervised accuracy with high consistency on the MNIST dataset using just 5 labels per class: our best model, ladder with layer-wise virtual adversarial noise (LVAN-LW), achieves 1.42%±0.12 average error rate on the MNIST test set, in comparison with 1.62%±0.65 reported for the ladder network. On adversarial examples generated with L2-normalized fast gradient method, LVAN-LW trained with 5 examples per class achieves average error rate 2.4%±0.3 compared to 68.6%±6.5 for the ladder network and 9.9%±7.5 for VAT
Multifrequency Study of The Radio Galaxy NGC326
We present the results of a multi-frequency study of the inversion symmetric
radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8,
8.5 and 14.9 GHz. The morphological, spectral and polarization properties of
this peculiar object are studied at different levels of spatial resolutions.
The interpretation of the data will be discussed in forthcoming papers.Comment: 15 pages, 15 ps figures, accepted by A&
Harmonic Networks: Deep Translation and Rotation Equivariance
Translating or rotating an input image should not affect the results of many computer vision tasks. Convolutional neural networks (CNNs) are already translation equivariant: input image translations produce proportionate feature map translations. This is not the case for rotations. Global rotation equivariance is typically sought through data augmentation, but patch-wise equivariance is more difficult. We present Harmonic Networks or H-Nets, a CNN exhibiting equivariance to patch-wise translation and 360-rotation. We achieve this by replacing regular CNN filters with circular harmonics, returning a maximal response and orientation for every receptive field patch. H-Nets use a rich, parameter-efficient and low computational complexity representation, and we show that deep feature maps within the network encode complicated rotational invariants. We demonstrate that our layers are general enough to be used in conjunction with the latest architectures and techniques, such as deep supervision and batch normalization. We also achieve state-of-the-art classification on rotated-MNIST, and competitive results on other benchmark challenges
Ordered magnetic fields around radio galaxies: evidence for interaction with the environment
We present detailed imaging of Faraday rotation and depolarization for the
radio galaxies 0206+35, 3C 270, 3C 353 and M 84, based on Very Large Array
observations at multiple frequencies in the range 1365 to 8440 MHz. This work
suggests a more complex picture of the magneto-ionic environments of radio
galaxies than was apparent from earlier work. All of the sources show
spectacular banded rotation measure (RM) structures with contours of constant
RM perpendicular to the major axes of their radio lobes. We give a
comprehensive description of the banded RM phenomenon and present an initial
attempt to interpret it as a consequence of interactions between the sources
and their surroundings. We show that the material responsible for the Faraday
rotation is in front of the radio emission and that the bands are likely to be
caused by magnetized plasma which has been compressed by the expanding radio
lobes. A two-dimensional magnetic structure in which the field lines are a
family of ellipses draped around the leading edge of the lobe can produce RM
bands in the correct orientation for any source orientation. We also report the
first detections of rims of high depolarization at the edges of the inner radio
lobes of M 84 and 3C 270. These are spatially coincident with shells of
enhanced X-ray surface brightness, in which both the field strength and the
thermal gas density are likely to be increased by compression.Comment: 21 pages, 15 figures, accepted for publication in MNRAS. Full
resolution paper available at http://www.ira.inaf.it/~guidetti/bands/
Subjects: Astrophysics (astro-ph
A spectroscopic study of NGC 6251 and its companion galaxies
Measurements of the velocities of galaxies thought to be associated with the
giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a
systemic redshift of z= 0.0244 +/- 0.0004 and a line-of-sight velocity
dispersion of sigma_{z}= 283 (+109, -52) km/s. This suggests a cluster
atmosphere temperature of T = 0.7 (+0.6, -0.2) keV, which is not enough to
confine the radio jet by gas pressure. The core of NGC 6251 shows strong
emission lines of [O III] and H alpha + [N II], but there is no evidence for
line emission from the jet (detected in optical continuum by Keel (1988)).Comment: 7 pages, 2 figures, to be published in MNRA
Chandra Observations of the X-ray Environment of BL Lacs
We present Chandra observations of the X-ray environment of a sample of 6 BL
Lacertae objects. The improved sensitivity of the ACIS experiment allows us to
separate the core X-ray emission from the contribution of diffuse emission from
the host galaxy/cluster scales. Within the short (2-6 ks) ACIS exposures, we
find evidence for diffuse X-ray emission in 3 sources (BL Lac, PKS 0548-322,
and PKS 2005-489). The diffuse emission can be modeled with a King profile with
beta~0.3-0.6, core radii rc~15-28 kpc, and 0.4-5 keV luminosities in the range
10^{41}-10^{42} erg/s. In the remaining 3 sources, one (3C 371) has a radial
profile entirely consistent with an unresolved source, while two (1ES 2344+514
and 1ES 2321+419) show evidence for weak diffuse emission on kpc scales. These
results support current models for radio-loud AGN unifying BL Lacs and FRI
radio galaxies through the orientation of their jets. In PKS 0548-322 and PKS
2005-489, we also find evidence for diffuse emission on cluster scales,
although the spatial properties of this emission are not constrained. The
temperature and luminosity of the cluster gas are typical of normal clusters.
Interestingly, these are the two brightest sources of the sample, suggesting a
link between environment and nuclear activity.Comment: 12 pages, 5 figures, accepted for publication in A&
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