68,547 research outputs found
Solar array subsystems study
The effects on life cycle costs of a number of technology areas are examined for a LEO, 500 kW solar array. A baseline system conceptual design is developed and the life cycle costs estimated in detail. The baseline system requirements and design technologies are then varied and their relationships to life cycle costs quantified. For example, the thermal characteristics of the baseline design are determined by the array materials and masses. The thermal characteristics in turn determine configuration, performance and hence life cycle cost
Ultraviolet/X-ray variability and the extended X-ray emission of the radio-loud broad absorption line quasar PG 1004+130
We present the results of recent Chandra, XMM-Newton, and Hubble Space
Telescope observations of the radio-loud (RL), broad absorption line (BAL)
quasar PG 1004+130. We compare our new observations to archival X-ray and UV
data, creating the most comprehensive, high signal-to-noise, multi-epoch,
spectral monitoring campaign of a RL BAL quasar to date. We probe for
variability of the X-ray absorption, the UV BAL, and the X-ray jet, on
month-year timescales. The X-ray absorber has a low column density of
cm when it is assumed to be fully
covering the X-ray emitting region, and its properties do not vary
significantly between the 4 observations. This suggests the observed absorption
is not related to the typical "shielding gas" commonly invoked in BAL quasar
models, but is likely due to material further from the central black hole. In
contrast, the CIV BAL shows strong variability. The equivalent width (EW) in
2014 is EW=11.240.56 \AA, showing a fractional increase of =1.160.11 from the 2003 observation, 3183 days earlier
in the rest-frame. This places PG 1004+130 among the most highly variable BAL
quasars. By combining Chandra observations we create an exposure 2.5 times
deeper than studied previously, with which to investigate the nature of the
X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a
synchrotron origin, is detected in the radio jet ~8 arcsec (30 kpc) from the
central X-ray source with a spatial extent of ~4 arcsec (15 kpc). No similar
X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal
diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic
Microwave Background photons, is also detected.Comment: 15 pages, 7 figures, 3 tables. Accepted for publication in Ap
A Chandra Survey of the X-ray Properties of Broad Absorption Line Radio-Loud Quasars
This work presents the results of a Chandra study of 21 broad absorption line
(BAL) radio-loud quasars (RLQs). We conducted a Chandra snapshot survey of 12
bright BAL RLQs selected from SDSS/FIRST data and possessing a wide range of
radio and CIV absorption properties. Optical spectra were obtained nearly
contemporaneously with the Hobby-Eberly Telescope; no strong flux or BAL
variability was seen between epochs. We also include in our sample 9 additional
BAL RLQs possessing archival Chandra coverage. We compare the properties of
(predominantly high-ionization) BAL RLQs to those of non-BAL RLQs as well as to
BAL radio-quiet quasars (RQQs) and non-BAL RQQs for context.
All 12 snapshot and 8/9 archival BAL RLQs are detected, with observed X-ray
luminosities less than those of non-BAL RLQs having comparable optical/UV
luminosities by typical factors of 4.1-8.5. (BAL RLQs are also X-ray weak by
typical factors of 2.0-4.5 relative to non-BAL RLQs having both comparable
optical/UV and radio luminosities.) However, BAL RLQs are not as X-ray weak
relative to non-BAL RLQs as are BAL RQQs relative to non-BAL RQQs. While some
BAL RLQs have harder X-ray spectra than typical non-BAL RLQs, some have
hardness ratios consistent with those of non-BAL RLQs, and there does not
appear to be a correlation between X-ray weakness and spectral hardness, in
contrast to the situation for BAL RQQs. RLQs are expected to have X-ray
continuum contributions from both disk-corona and small-scale jet emission.
While the entire X-ray continuum in BAL RLQs cannot be obscured to the same
degree as in BAL RQQs, we calculate that the jet is likely partially covered in
many BAL RLQs. We comment briefly on implications for geometries and source
ages in BAL RLQs.Comment: 48 pages, 5 tables, 14 figures, accepted by Ap
X-raying the Winds of Luminous Active Galaxies
We briefly describe some recent observational results, mainly at X-ray
wavelengths, on the winds of luminous active galactic nuclei (AGNs). These
winds likely play a significant role in galaxy feedback. Topics covered include
(1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL)
and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3)
Evidence for relativistic iron K BALs in the X-ray spectra of a few bright
quasars. We also mention some key outstanding problems and prospects for future
advances; e.g., with the International X-ray Observatory (IXO).Comment: 7 pages, 3 figures, to appear in proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June
2009, Madison, Wisconsi
The Physics Case for the New Muon (g-2) Experiment
This White Paper briefly reviews the present status of the muon (g-2)
experiment and the physics motivation for a new effort. The present comparison
between experiment and theory indicates a tantalizing deviation.
An improvement in precision on this comparison by a factor of 2--with the
central value remaining unchanged--will exceed the ``discovery'' threshold,
with a sensitivity above . The 2.5-fold reduction improvement goal of
the new Brookhaven E969 experiment, along with continued steady reduction of
the standard model theory uncertainty, will achieve this more definitive test.
Already, the (g-2) result is arguably the most compelling indicator of
physics beyond the standard model and, at the very least, it represents a major
constraint for speculative new theories such as supersymmetry or extra
dimensions. In this report, we summarize the present experimental status and
provide an up-to-date accounting of the standard model theory, including the
expectations for improvement in the hadronic contributions, which dominate the
overall uncertainty. Our primary focus is on the physics case that motivates
improved experimental and theoretical efforts. Accordingly, we give examples of
specific new-physics implications in the context of direct searches at the LHC
as well as general arguments about the role of an improved (g-2) measurement. A
brief summary of the plans for an upgraded effort complete the report.Comment: 18 pages, 7 figure
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