1,265 research outputs found
X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness
We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.Comment: 9 pages, AJ, in pres
Rapid recurrence and radiographic progression of sarcomatoid renal cell carcinoma
© 2017 Sarcomatoid renal cell carcinoma (sRCC) is an aggressive variant of renal cell carcinoma (RCC) that has a significantly lower overall survival. Even after prompt surgical extirpation, this histologic variant progresses rapidly. We present a case of an early recurrence and rapid progression of sRCC despite successful radical resection
XMM-NEWTON High Resolution Spectroscopy of NGC 5548
We analyze a 137 ks exposure X-ray spectrum of the Seyfert 1 galaxy NGC 5548
obtained with the XMM-Newton Reflection Grating Spectrometer. Due to the long
exposure time, the spectrum is of higher statistical quality than the previous
observations of this AGN. Therefore, we detect for the first time in NGC 5548
inner-shell transitions from O III to O VI ions, and the Unresolved Transition
Array of M-shell iron. The warm absorber found from this X-ray observation
spans three orders of magnitude in ionization parameter. We detect O III, which
is as lowly ionized as the warm absorber detected in the UV band, to Fe XXIV.
For O VI the column density determined from our X-ray data is an order of
magnitude larger than the column density measured in previous UV observations.
We conclude that there is substantially more low ionized material than
previously deduced from UV observations. However, only a few percent of the
warm absorber detected in the X-rays is lowly ionized. A 99.9 % significant
increase in the derived absorbing column density with higher ionization states
is observed. The outflow velocities determined from the X-ray absorption lines
are consistent with those deduced from the UV lines, evidence, together with
the detection of O VI, that the X-ray and UV warm absorber are different
manifestations of the same phenomenon. From a simple mass conservation
argument, we indicate that our data set is consistent with an outflow with
small opening angle formed due to instabilities in the accretion disk. Possible
due to uncertainties in the radiative transport mechanism, an apparent deviant
iron to oxygen abundance is detected. No strong relativistically broadened
emission lines of O VIII, N VII and C VI were detected.Comment: 10 pages, 10 figures, to be published in A&
Long-Term X-ray Spectral Variability in Seyfert 1 Galaxies
Direct time-resolved spectral fitting has been performed on continuous RXTE
monitoring of seven Seyfert 1 galaxies in order to study their broadband
spectral variability and Fe K alpha variability characteristics on time scales
of days to years. Variability in the Fe K alpha line is not detected in some
objects but is present in others, e.g., in NGC 3516, NGC 4151 and NGC 5548
there are systematic decreases in line flux by factors of ~2-5 over 3-4 years.
The Fe K alpha line varies less strongly than the broadband continuum, but,
like the continuum, exhibits stronger variability towards longer time scales.
Relatively less model-dependent broadband fractional variability amplitude
(Fvar) spectra also show weaker line variability compared to the continuum
variability. Comparable systematic long-term decreases in the line and
continuum are present in NGC 5548. Overall, however, there is no evidence for
correlated variability between the line and continuum, severely challenging
models in which the line tracks continuum variations modified only by a
light-travel time delay. Local effects such as the formation of an ionized skin
at the site of line emission may be relevant. The spectral fitting and Fvar
spectra both support spectral softening as continuum flux increases.Comment: Accepted for publication in ApJ. 29 page
Telecommunications systems design techniques handbook
Handbook presents design and analysis of tracking, telemetry, and command functions utilized in these systems with particular emphasis on deep-space telecommunications. Antenna requirements are also discussed. Handbook provides number of tables outlining various performance criteria. Block diagrams and performance charts are also presented
Multi-band optical micro-variability observations of BL Lacertae
We have observed BL Lacertae in the B, R and I bands for 2 nights in July,
1999, and 3 nights in July, 2001. The observations resulted in almost evenly
sampled light curves, with an average sampling interval of ~5 min. The source
is significantly variable in all bands. On average, the variability amplitude
increases from ~5% in the I band, to ~5.5% in the R and ~6.5% in the B band
light curves. The rising and decaying time scales are comparable within each
band, but they increase from the B, to R and I band light curves. The optical
power spectrum shows a red noise component with a slope of ~ -2.
Cross-correlation analysis shows that in most cases the delay between the
variations in the B and I band light curves is less than ~ 0.4 hrs. The
cross-correlation functions are asymmetric, implying complex delays of the I
band variations with respect to the B band variations. Furthermore, in one case
we find that the I band variations are significantly delayed (by ~0.2 hrs) with
respect to the B band variations. We also detect significant spectral
variations: the spectrum becomes steeper as the flux increases, and the
flattest spectral index corresponds to the maximum B band flux. Our results
imply that the fast, intra-night variations of the source correspond to
perturbations of different regions in the jet which cause localized injections
of relativistic particles on time scales much sorter that the average sampling
interval of the light curves. The variations are controlled by the cooling and
light crossing time scales, which are probably comparable.Comment: Accepted for publication in A&
Evidence for Rapid Iron K_alpha Line Flux Variability in MCG--6-30-15
This paper employs direct spectral fitting of individual orbital data in
order to measure rapid X-ray iron K_alpha line and continuum spectral slope
variations in Seyfert 1 galaxies with unprecedented temporal resolution.
Application of this technique to a long RXTE observation of MCG--6-30-15
indicates that the line flux does vary on short (~1d) timescales, but that
these variations are not correlated with changes in the continuum flux or
slope. These rapid variations indicate that the line does indeed originate
close to the black hole, confirming predictions based on its very broad
profile. However, the lack of a correlation with the continuum presents
problems for models in which the line variations are driven by those in the
continuum, modified only by light-travel time effects. Instead, it may be that
the line responds according to a physical process with a different time scale,
such as ionization instabilities in the disk, or perhaps that the geometry and
physical picture is more complex than implied by the simplest disk-corona
models.
These data also indicate that the slope of the underlying power-law continuum
(Gamma) shows strong variability and is tightly correlated with the continuum
flux in the sense that the spectrum steepens as the source brightens. All of
these results have been checked with extensive simulations, which also
indicated that a spurious correlation between Gamma and Compton reflection
fraction (R) will result if these quantities are measured from the same
spectra. This casts serious doubts on previous claims of such a Gamma-R
correlation.Comment: Accepted for publication in Ap
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