3,771 research outputs found
State-of-the-art survey of dissimilar metal joining by solid state welding
State-of-the-art of dissimilar metal joining by solid state diffusion bonding and roll and press welding, emphasizing stainless steel and aluminum allo
A Chandra Survey of Quasar Jets: First Results
We present results from Chandra X-ray imaging and spectroscopy of a
flux-limited sample of flat spectrum radio-emitting quasars with jet-like
extended structure. Twelve of twenty quasar jets are detected in 5 ks ACIS-S
exposures. The quasars without X-ray jets are not significantly different from
those in the sample with detected jets except that the extended radio emission
is generally fainter. New radio maps are combined with the X-ray images in
order to elucidate the relation between radio and X-ray emission in spatially
resolved structures. We find a variety of morphologies, including long straight
jets and bends up to 90 degrees. All X-ray jets are one-sided although the
radio images used for source selection often show lobes opposite the X-ray
jets. The FR II X-ray jets can all be interpreted as inverse Compton scattering
of cosmic microwave background photons by electrons in large-scale relativistic
jets although deeper observations are required to test this interpretation in
detail. Applying this interpretation to the jets as a population, we find that
the jets would be aligned to within 30 degrees of the line of sight generally,
assuming that the bulk Lorentz factor of the jets is 10.Comment: 25 pages with 5 pages of color figures; accepted for publication in
the Astrophysical Journal Supplements; higher resolution jpeg images are
available at http://space.mit.edu/home/jonathan/jets
Continuing a Chandra Survey of Quasar Radio Jets
We are conducting an X-ray survey of flat spectrum radio quasars (FSRQs) with
extended radio structures. We summarize our results from the first stage of our
survey, then we present findings from its continuation.
We have discovered jet X-ray emission from 12 of our first 20 Chandra
targets, establishing that strong 0.5-7.0 keV emission is a common feature of
FSRQ jets. The X-ray morphology is varied, but in general closely matches the
radio structure until the first sharp radio bend. In the sources with optical
data as well as X-ray detections we rule out simple synchrotron models for
X-ray emission, suggesting these systems may instead be dominated by inverse
Compton (IC) scattering. Fitting models of IC scattering of cosmic microwave
background photons suggests that these jets are aligned within a few degrees of
our line of sight, with bulk Lorentz factors of a few to ten and magnetic
fields a bit stronger than G.
In the weeks prior to this meeting, we have discovered two new X-ray jets at
. One (PKS B1055+201) has a dramatic, -long jet. The other (PKS
B1421-490) appears unremarkable at radio frequencies, but at higher frequencies
the jet is uniquely powerful: its optically-dominated, with jet/core flux
ratios of 3.7 at 1 keV and 380 at 480 nm.Comment: 4 pages, 8 figures. To appear in `X-Ray and Radio Connections', ed.
L.O. Sjouwerman and K.K. Dyer (published electronicly at
http://www.aoc.nrao.edu/events/xraydio/). Additional material and higher
resolution figures may be found at http://space.mit.edu/home/jonathan/jets
A Compact Extreme Scattering Event Cloud Towards AO 0235+164
We present observations of a rare, rapid, high amplitude Extreme Scattering
Event toward the compact BL-Lac AO 0235+164 at 6.65 GHz. The ESE cloud is
compact; we estimate its diameter between 0.09 and 0.9 AU, and is at a distance
of less than 3.6 kpc. Limits on the angular extent of the ESE cloud imply a
minimum cloud electron density of ~ 4 x 10^3 cm^-3. Based on the amplitude and
timescale of the ESE observed here, we suggest that at least one of the
transients reported by Bower et al. (2007) may be attributed to ESEs.Comment: 11 pages, 2 figure
A Multi-Wavelength Study of the Jet, Lobes and Core of the Quasar PKS 2101-490
We present a detailed study of the X-ray, optical and radio emission from the
jet, lobes and core of the quasar PKS 2101-490 as revealed by new Chandra, HST
and ATCA images. We extract the radio to X-ray spectral energy distributions
from seven regions of the 13 arcsecond jet, and model the jet X-ray emission in
terms of Doppler beamed inverse Compton scattering of the cosmic microwave
background (IC/CMB) for a jet in a state of equipartition between particle and
magnetic field energy densities. This model implies that the jet remains highly
relativistic hundreds of kpc from the nucleus, with a bulk Lorentz factor Gamma
~ 6 and magnetic field of order 30 microGauss. We detect an apparent radiative
cooling break in the synchrotron spectrum of one of the jet knots, and are able
to interpret this in terms of a standard one-zone continuous injection model,
based on jet parameters derived from the IC/CMB model. However, we note
apparent substructure in the bright optical knot in one of the HST bands. We
confront the IC/CMB model with independent estimates of the jet power, and find
that the IC/CMB model jet power is consistent with the independent estimates,
provided that the minimum electron Lorentz factor gamma_min > 50, and the knots
are significantly longer than the jet width, as implied by de-projection of the
observed knot lengths.Comment: 16 pages, 10 figures, 6 table
Small scale irrigation using collector wells pilot project - Zimbabwe. Final report October 1992 - January 1996
Discovery of an X-ray Jet and Extended Jet Structure in the Quasar PKS 1055+201
This letter reports rich X-ray jet structures found in the Chandra
observation of PKS 1055+201. In addition to an X-ray jet coincident with the
radio jet we detect a region of extended X-ray emission surrounding the jet as
far from the core as the radio hotspot to the North, and a similar extended
X-ray region along the presumed path of the unseen counterjet to the Southern
radio lobe. Both X-ray regions show a similar curvature to the west, relative
to the quasar. We interpret this as the first example where we separately
detect the X-ray emission from a narrow jet and extended, residual jet plasma
over the entire length of a powerful FRII jet.Comment: Accepted for publication in Ap. J. Letters. 4 pages, 3 figure
The Chandra X-ray Observatory Resolves the X-ray Morphology and Spectra of a Jet in PKS 0637-752
The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first
celestial object observed with the Chandra X-ray Observatory, offering the
early surprise of the detection of a remarkable X-ray jet. Several observations
with a variety of detector configurations contribute to a total exposure time
with the Chandra Advanced CCD Imaging Spectrometer (ACIS; Garmire et al. 2000,
in preparation) of about 100ks. A spatial analysis of all the available X-ray
data, making use of Chandra's spatial resolving power of about 0.4 arcsec,
reveals a jet that extends about 10 arcsec to the west of the nucleus. At least
four X-ray knots are resolved along the jet, which contains about 5% of the
overall X-ray luminosity of the source. Previous observations of PKS 0637-752
in the radio band (Tingay et al. 1998) had identified a kpc-scale radio jet
extending to the West of the quasar. The X-ray and radio jets are similar in
shape, intensity distribution, and angular structure out to about 9 arcsec,
after which the X-ray brightness decreases more rapidly and the radio jet turns
abruptly to the north. The X-ray luminosity of the total source is log Lx ~
45.8 erg/s (2 - 10keV), and appears not to have changed since it was observed
with ASCA in November 1996. We present the results of fitting a variety of
emission models to the observed spectral distribution, comment on the
non-existence of emission lines recently reported in the ASCA observations of
PKS 0637-752, and briefly discuss plausible X-ray emission mechanisms.Comment: 24 pages, includes 8 figures, Accepted for publication in Ap
Earth Radiation Budget Experiment (ERBE) scanner instrument anomaly investigation
The results of an ad-hoc committee investigation of in-Earth orbit operational anomalies noted on two identical Earth Radiation Budget Experiment (ERBE) Scanner instruments on two different spacecraft busses is presented. The anomalies are attributed to the bearings and the lubrication scheme for the bearings. A detailed discussion of the pertinent instrument operations, the approach of the investigation team and the current status of the instruments now in Earth orbit is included. The team considered operational changes for these instruments, rework possibilities for the one instrument which is waiting to be launched, and preferable lubrication considerations for specific space operational requirements similar to those for the ERBE scanner bearings
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Development of variable-width ribbon heating elements for liquid-metal and gas-cooled fast breeder reactor fuel-pin simulators
Variable-width ribbon heating elements that provide a chopped-cosine variable heat flux profile have been fabricated for fuel pin simulators used in test loops by the Breeder Reactor Program Thermal-Hydraulic Out-of-Reactor Safety test facility and the Gas-Cooled Fast Breeder Reactor-Core Flow Test Loop. Thermal, mechanical, and electrical design considerations are used to derive an analytical expression that precisely describes ribbon contour in terms of the major fabrication parameters. These parameters are used to generate numerical control tapes that control ribbon cutting and winding machines. Infrared scanning techniques are developed to determine the optimum transient thermal profile of the coils and relate this profile to that generated by the coils in completed fuel pin simulators
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