10,448 research outputs found
Long Term Wind-Driven X-Ray Spectral Variability of NGC 1365 with Swift
We present long-term (months-years) X-ray spectral variability of the Seyfert
1.8 galaxy NGC 1365 as observed by Swift, which provides well sampled
observations over a much longer timescale (6 years) and a much larger flux
range than is afforded by other observatories. At very low luminosities the
spectrum is very soft, becoming rapidly harder as the luminosity increases and
then, above a particular luminosity, softening again. At a given flux level,
the scatter in hardness ratio is not very large, meaning that the spectral
shape is largely determined by the luminosity. The spectra were therefore
summed in luminosity bins and fitted with a variety of models. The best fitting
model consists of two power laws, one unabsorbed and another, more luminous,
which is absorbed. In this model, we find a range of intrinsic 0.5-10.0 keV
luminosities of approximately 1.1-3.5 ergs/s, and a very large range of
absorbing columns, of approximately 10^22 - 10^24 cm^-2. Interestingly, we find
that the absorbing column decreases with increasing luminosity, but that this
result is not due to changes in ionisation. We suggest that these observations
might be interpreted in terms of a wind model in which the launch radius varies
as a function of ionising flux and disc temperature and therefore moves out
with increasing accretion rate, i.e. increasing X-ray luminosity. Thus,
depending on the inclination angle of the disc relative to the observer, the
absorbing column may decrease as the accretion rate goes up. The weaker,
unabsorbed, component may be a scattered component from the wind.Comment: 9 pages, 7 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Long-Term X-ray Spectral Variability of Seyfert Galaxies with Swift
We present analysis of the long-term X-ray spectral variability of Seyfert
galaxies as observed by Swift, which provides well-sampled observations over a
much larger flux range and a much longer timescale than any other X-ray
observatory. We examine long-term variability of three AGN: NGC 1365 (see
Connolly et al. 2014), Mkn 335 and NGC 5548. At high fluxes, the 0.5-10 keV
spectra soften with increasing flux, as seen previously within the 2-10 keV
band. However, at very low fluxes the sources also become very soft. We have
fitted a number of models to the data and find that both intrinsic luminosity
variability and variable absorption are required to explain the observations.
In some systems, e.g. NGC 1365, the best explanation is a two-component wind
model in which one component represents direct emission absorbed by a disc wind
wind, with the absorbing column inversely proportional to the intrinsic
luminosity, and the second component represents unabsorbed emission reflected
from the wind. In other AGN the situation is more complex.Comment: 6 pages, 5 figues, to appear in "Swift: 10 years of discovery",
Proceedings of Scienc
Improving the Reliability and Modal Stability of High Power 870 nm AlGaAs CSP Laser Diodes for Applications to Free Space Communication Systems
The operating characteristics (power-current, beam divergence, etc.) and reliability assessment of high-power CSP lasers is discussed. The emission wavelength of these lasers was optimized at 860 to 880 nm. The operational characteristics of a new laser, the inverse channel substrate planar (ICSP) laser, grown by metalorganic chemical vapor deposition (MOCVD), is discussed and the reliability assessment of this laser is reported. The highlights of this study include a reduction in the threshold current value for the laser to 15 mA and a degradation rate of less than 2 kW/hr for the lasers operating at 60 mW of peak output power
The extraordinary mid-infrared spectral properties of FeLoBAL Quasars
We present mid-infrared spectra of six FeLoBAL QSOs at 1<z<1.8, taken with
the Spitzer space telescope. The spectra span a range of shapes, from hot dust
dominated AGN with silicate emission at 9.7 microns, to moderately obscured
starbursts with strong Polycyclic Aromatic Hydrocarbon (PAH) emission. The
spectrum of one object, SDSS 1214-0001, shows the most prominent PAHs yet seen
in any QSO at any redshift, implying that the starburst dominates the mid-IR
emission with an associated star formation rate of order 2700 solar masses per
year. With the caveats that our sample is small and not robustly selected, we
combine our mid-IR spectral diagnostics with previous observations to propose
that FeLoBAL QSOs are at least largely comprised of systems in which (a) a
merger driven starburst is ending, (b) a luminous AGN is in the last stages of
burning through its surrounding dust, and (c) which we may be viewing over a
restricted line of sight range.Comment: ApJ, accepte
Characterization of frequency drift of sampled-grating DBR laser module under direct modulation
The authors demonstrate the drift in frequency of a static sampled-grating distributed Bragg reflector (SG DBR) laser module when it is subjected to direct modulation. The magnitude of drift and its settling time is characterized as a function of the index of modulation. Results show that when the directly modulated SG DBR is optically filtered, as in a dense wavelength- division- multiplexed system, a power penalty of 6.7 dB is incurred in comparison to the unfiltered case
Titanium in phengite: a geobarometer for high temperature eclogites
Phengite chemistry has been investigated in experiments on a natural SiO2-TiO2-saturated greywacke and a natural SiO2-TiO2-Al2SiO5-saturated pelite, at 1.5-8.0GPa and 800-1,050°C. High Ti-contents (0.3-3.7 wt %), Ti-enrichment with temperature, and a strong inverse correlation of Ti-content with pressure are the important features of both experimental series. The changes in composition with pressure result from the Tschermak substitution (Si+R2+=AlIV+AlVI) coupled with the substitution: AlVI+Si=Ti+AlIV. The latter exchange is best described using the end-member Ti-phengite (KMgTi[Si3Al]O10(OH)2, TiP). In the rutile-quartz/coesite saturated experiments, the aluminoceladonite component increases with pressure while the muscovite, paragonite and Ti-phengite components decrease. A thermodynamic model combining data obtained in this and previous experimental studies are derived to use the equilibrium MgCel+Rt=TiP+Cs/Qz as a thermobarometer in felsic and basic rocks. Phengite, rutile and quartz/coesite are common phases in HT-(U)HP metamorphic rocks, and are often preserved from regression by entrapment in zircon or garnet, thus providing an opportunity to determine the T-P conditions of crystallization of these rocks. Two applications on natural examples (Sulu belt and Kokchetav massif) are presented and discussed. This study demonstrates that Ti is a significant constituent of phengites that could have significant effects on phase relationships and melting rates with decreasing P or increasing T in the continental crus
YF-12 cooperative airframe/propulsion control system program, volume 1
Several YF-12C airplane analog control systems were converted to a digital system. Included were the air data computer, autopilot, inlet control system, and autothrottle systems. This conversion was performed to allow assessment of digital technology applications to supersonic cruise aircraft. The digital system was composed of a digital computer and specialized interface unit. A large scale mathematical simulation of the airplane was used for integration testing and software checkout
Effects of crosstalk in WDM optical label switching networks due to wavelength switching of a tunable laser
rosstalk caused by switching events in fast tunable lasers in an optical label switching (OLS) system is investigated for the first time. A wavelength-division-multiplexed OLS system based on subcarrier multiplexed labels is presented which employs a 40-Gb/s duobinary payload and a 155-Mb/s label on a 40-GHz subcarrier. Degradation in system performance as the transmitters switch between different channels is then characterized in terms of the frequency drift of the tunable laser
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