3,013 research outputs found
Ranking the importance of nuclear reactions for activation and transmutation events
Pathways-reduced analysis is one of the techniques used by the Fispact-II
nuclear activation and transmutation software to study the sensitivity of the
computed inventories to uncertainties in reaction cross-sections. Although
deciding which pathways are most important is very helpful in for example
determining which nuclear data would benefit from further refinement,
pathways-reduced analysis need not necessarily define the most critical
reaction, since one reaction may contribute to several different pathways. This
work examines three different techniques for ranking reactions in their order
of importance in determining the final inventory, comparing the pathways based
metric (PBM), the direct method and one based on the Pearson correlation
coefficient. Reasons why the PBM is to be preferred are presented.Comment: 30 pages, 10 figure
Microlensing of the Lensed Quasar SDSS0924+0219
We analyze V, I and H band HST images and two seasons of R-band monitoring
data for the gravitationally lensed quasar SDSS0924+0219. We clearly see that
image D is a point-source image of the quasar at the center of its host galaxy.
We can easily track the host galaxy of the quasar close to image D because
microlensing has provided a natural coronograph that suppresses the flux of the
quasar image by roughly an order of magnitude. We observe low amplitude,
uncorrelated variability between the four quasar images due to microlensing,
but no correlated variations that could be used to measure a time delay. Monte
Carlo models of the microlensing variability provide estimates of the mean
stellar mass in the lens galaxy (0.02 Msun < M < 1.0 Msun), the accretion disk
size (the disk temperature is 5 x 10^4 K at 3.0 x 10^14 cm < rs < 1.4 x 10^15
cm), and the black hole mass (2.0 x 10^7 Msun < MBH \eta_{0.1}^{-1/2}
(L/LE)^{1/2} < 3.3 x 10^8 Msun), all at 68% confidence. The black hole mass
estimate based on microlensing is consistent with an estimate of MBH = 7.3 +-
2.4 x 10^7 Msun from the MgII emission line width. If we extrapolate the
best-fitting light curve models into the future, we expect the the flux of
images A and B to remain relatively stable and images C and D to brighten. In
particular, we estimate that image D has a roughly 12% probability of
brightening by a factor of two during the next year and a 45% probability of
brightening by an order of magnitude over the next decade.Comment: v.2 incorporates referee's comments and corrects two errors in the
original manuscript. 28 pages, 10 figures, published in Ap
The Gravitational Lens Candidate FBQ 1633+3134
We present our ground-based optical imaging, spectral analysis, and high
resolution radio mapping of the gravitational lens candidate FBQ 1633+3134.
This z=1.52, B=17.7 quasar appears double on CCD images with an image
separation of 0.66 arcseconds and a flux ratio of ~3:1 across BVRI filters. A
single 0.27 mJy radio source is detected at 8.46 GHz, coincident to within an
arcsecond of both optical components, but no companion at radio wavelengths is
detected down to a flux level of 0.1 mJy (3 sigma). Spectral observations
reveal a rich metal-line absorption system consisting of a strong Mg II doublet
and associated Fe I and Fe II absorption features, all at an intervening
redshift of z=0.684, suggestive of a lensing galaxy. Point spread function
subtraction however shows no obvious signs of a third object between the two
quasar images, and places a detection limit of I > 23.0 if such an object
exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot
be ruled out, the evidence is consistent with it being a single quasar lensed
by a faint, metal-rich galaxy.Comment: 24 pages, 5 figures. Accepted by AJ. A calibration error affecting B
and V band apparent magnitudes has been corrected. The conclusions of the
paper are not change
Simultaneous Estimation of Time Delays and Quasar Structure
We expand our Bayesian Monte Carlo method for analyzing the light curves of
gravitationally lensed quasars to simultaneously estimate time delays and
quasar structure including their mutual uncertainties. We apply the method to
HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and
intrinsic variability on comparable time scales. For HE1104-1805 the resulting
time delay of (Delta t_AB) = t_A - t_B = 162.2 -5.9/+6.3 days and accretion
disk size estimate of log(r_s/cm) = 15.7 -0.5/+0.4 at 0.2 micron in the rest
frame are consistent with earlier estimates but suggest that existing methods
for estimating time delays in the presence of microlensing underestimate the
uncertainties. We are unable to measure a time delay for QJ0158-4325, but the
accretion disk size is log(r_s/cm) = 14.9 +/- 0.3 at 0.3 micron in the rest
frame.Comment: 21 pages, 6 figures, submitted to Ap
CTQ 414: A New Gravitational Lens
We report the discovery and ground based observations of the new
gravitational lens CTQ 414. The source quasar lies at a redshift of z = 1.29
with a B magnitude of 17.6. Ground based optical imaging reveals two point
sources separated by 1.2 arcsec with a magnitude difference of roughly 1 mag.
Subtraction of two stellar point spread functions from images obtained in
subarcsecond seeing consistently leaves behind a faint, residual object. Fits
for two point sources plus an extended object places the fainter object
collinear with the two brighter components. Subsequent HST/NICMOS observations
have confirmed the identification of the fainter object as the lensing galaxy.
VLA observations at 8.46 GHz reveal that all components of the lensing system
are radio quiet down to the 0.2 mJy flux level.Comment: Latex, 18 pages including 2 ps figures; accepted for publication in
A
CTQ 839: Candidate for the Smallest Projected Separation Binary Quasar
We report the discovery of the new double quasar CTQ 839. This B = 18.3,
radio quiet quasar pair is separated by 2.1" in BRIH filters with magnitude
differences of delta m_B = 2.5, delta m_R = delta m_I = 1.9, and delta m_H =
2.3. Spectral observations reveal both components to be z = 2.24 quasars, with
relative redshifts that agree at the 100 km/s level, but exhibit pronounced
differences in the equivalent widths of related emission features, as well as
an enhancement of blue continuum flux in the brighter component longward of the
Ly alpha emission feature. In general, similar redshift double quasars can be
the result of a physical binary pair, or a single quasar multiply imaged by
gravitational lensing. Empirical PSF subtraction of R and H band images of CTQ
839 reveal no indication of a lensing galaxy, and place a detection limit of R
= 22.5 and H = 17.4 for a third component in the system. For an Einstein-de
Sitter cosmology and SIS model, the R band detection limit constrains the
characteristics of any lensing galaxy to z_lens >= 1 with a corresponding
luminosity of L >~ 5 L_*, while an analysis based on the redshift probability
distribution for the lensing galaxy argues against the existence of a z_lens >~
1 lens at the 2 sigma level. A similar analysis for a Lambda dominated
cosmology, however, does not significantly constrain the existence of any
lensing galaxy. The broadband flux differences, spectral dissimilarities, and
failure to detect a lensing galaxy make the lensing hypothesis for CTQ 839
unlikely. The similar redshifts of the two components would then argue for a
physical quasar binary. At a projected separation of 8.3/h kpc (Omega_matter =
1), CTQ 839 would be the smallest projected separation binary quasar currently
known.Comment: Latex, 23 pages including 5 ps figures; accepted for publication in
A
The Quasar Accretion Disk Size - Black Hole Mass Relation
We use the microlensing variability observed for nine gravitationally lensed
quasars to show that the accretion disk size at 2500 Angstroms is related to
the black hole mass by log(R_2500/cm) = (15.6+-0.2) +
(0.54+-0.28)log(M_BH/10^9M_sun). This scaling is consistent with the
expectation from thin disk theory (R ~ M_BH^(2/3)), but it implies that black
holes radiate with relatively low efficiency, log(eta) = -1.29+-0.44 +
log(L/L_E) where eta=L/(Mdot c^2). These sizes are also larger, by a factor of
~3, than the size needed to produce the observed 0.8 micron quasar flux by
thermal radiation from a thin disk with the same T ~ R^(-3/4) temperature
profile. More sophisticated disk models are clearly required, particularly as
our continuing observations improve the precision of the measurements and yield
estimates of the scaling with wavelength and accretion rate.Comment: 5 pages, 3 figures, submitted to ApJ
First Lensed Quasar Systems from the VST-ATLAS Survey: One Quad, Two Doubles, and Two Pairs of Lensless Twins
We have analyzed images from the VST-ATLAS survey to identify candidate gravitationally lensed quasar systems in a sample of WISE sources with W1 - W2 ≥ 0.7.. Results from follow-up spectroscopy with the Baade 6.5 m telescope are presented for eight systems. One of them is a quadruply lensed quasar, and two are doubly lensed systems. Two are projected superpositions of two quasars at different redshifts. In one system, two quasars, although at the same redshift, have very different emission line profiles and constitute a physical binary. In two systems, the component spectra are consistent with the lensing hypothesis, after allowing for microlensing. However, as no lensing galaxy is detected in these two systems, we classify them as lensless twins. More extensive observations are needed to establish whether they are in fact lensed quasars or physical binaries
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