Extensive X-ray variability studies of NGC 7314 using long XMM-Newton observations

We present a detailed X-ray variability study of the low mass Active Galactic Nuclei (AGN) NGC 7314 using the two newly obtained XMM-Newton observations ($140$ and $130$ ks), together with two archival data sets of shorter duration ($45$ and $84$ ks). The relationship between the X-ray variability characteristics and other physical source properties (such as the black hole mass) are still relatively poorly defined, especially for low-mass AGN. We perform a new, fully analytical, power spectral density (PSD) model analysis method, which will be described in detail in a forthcoming paper, that takes into consideration the spectral distortions, caused by red-noise leak. We find that the PSD in the $0.5-10$ keV energy range, can be represented by a bending power-law with a bend around $6.7\times10^{-5}$ Hz, having a slope of $0.51$ and $1.99$ below and above the bend, respectively. Adding our bend time-scale estimate, to an already published ensemble of estimates from several AGN, supports the idea that the bend time-scale depends linearly only on the black hole mass and not on the bolometric luminosity. Moreover, we find that as the energy range increases, the PSD normalization increases and there is a hint that simultaneously the high frequency slope becomes steeper. Finally, the X-ray time-lag spectrum of NGC 7314 shows some very weak signatures of relativistic reflection, and the energy resolved time-lag spectrum, for frequencies around $3\times10^{-4}$ Hz, shows no signatures of X-ray reverberation. We show that the previous claim about ks time-delays in this source, is simply an artefact induced by the minuscule number of points entering during the time-lag estimation in the low frequency part of the time-lag spectrum (i.e. below $10^{-4}$ Hz).Comment: Accepted for publication in MNRAS. The paper is 21 pages long and contains 15 figures and 3 table

No-vent fill pressurization tests using a cryogen simulant

The results are described of an experimental program which studied the performance of various no-vent fill techniques for tank-to-tank liquid transfer. The tests were performed using a cryogen simulant (Freon-114) and a test bed consisting of a multiple tank/plumbing network that enabled studies of a variety of different inlet flow and active mixing regimes. Several results and conclusions were drawn from the 26 transfer experiments comprising the program. Most notable was the significant improvement in fill performance (i.e., minimized fill time and maximized fill fraction) with increased agitation of the liquid surface. Another was the close correlation between measured condensation rates and those predicted by recent theories which express condensation as a function of turbulent eddy effects on the liquid surface. In most cases, test data exhibited strong agreement with an analytical model which accounts for tank heat transfer and thermodynamics in a 1 g environment

A modified Oster-Murray-Harris mechanical model of morphogenesis

There are two main modeling paradigms for biological pattern formation in developmental biology: chemical prepattern models and cell aggregation models. This paper focuses on an example of a cell aggregation model, the mechanical model developed by Oster, Murray, and Harris [Development, 78 (1983), pp. 83--125]. We revisit the Oster--Murray--Harris model and find that, due to the infinitesimal displacement assumption made in the original version of this model, there is a restriction on the types of boundary conditions that can be prescribed. We derive a modified form of the model which relaxes the infinitesimal displacement assumption. We analyze the dynamics of this model using linear and multiscale nonlinear analysis and show that it has the same linear behavior as the original Oster--Murray--Harris model. Nonlinear analysis, however, predicts that the modified model will allow for a wider range of parameters where the solution evolves to a bounded steady state. The results from both analyses are verified through numerical simulations of the full nonlinear model in one and two dimensions. The increased range of boundary conditions that are well-posed, as well as a wider range of parameters that yield bounded steady states, renders the modified model more applicable to, and more robust for, comparisons with experiments

Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model

We suggest that the energy source of the observed diffuse gamma-ray emission from the direction of the Galactic center is the Galactic black hole Sgr A*, which becomes active when a star is captured at a rate of $\sim 10^{-5}$ yr^{-1}. Subsequently the star is tidally disrupted and its matter is accreted into the black hole. During the active phase relativistic protons with a characteristic energy $\sim 6\times 10^{52}$ erg per capture are ejected. Over 90% of these relativistic protons disappear due to proton-proton collisions on a timescale $\tau_{pp} \sim 10^4$ years in the small central bulge region with radius $\sim 50$ pc within Sgr A*, where the density is $\ge 10^3$ cm^{-3}. The gamma-ray intensity, which results from the decay of neutral pions produced by proton-proton collisions, decreases according to $e^{-t/\tau_{pp}}$, where t is the time after last stellar capture. Less than 5% of relativistic protons escaped from the central bulge region can survive and maintain their energy for >10^7 years due to much lower gas density outside, where the gas density can drop to $\sim 1$ cm$^{-3}$. They can diffuse to a $\sim 500$ pc region before disappearing due to proton-proton collisions. The observed diffuse GeV gamma-rays resulting from the decay of neutral pions produced via collision between these escaped protons and the gas in this region is expected to be insensitive to time in the multi-injection model with the characteristic injection rate of 10^{-5} yr^{-1}. Our model calculated GeV and 511 keV gamma-ray intensities are consistent with the observed results of EGRET and INTEGRAL, however, our calculated inflight annihilation rate cannot produce sufficient intensity to explain the COMPTEL data.Comment: 8 pages, 3 figures, accepted by A&

Development of a high-altitude airborne dial system: The Lidar Atmospheric Sensing Experiment (LASE)

The ability of a Differential Absorption Lidar (DIAL) system to measure vertical profiles of H2O in the lower atmosphere was demonstrated both in ground-based and airborne experiments. In these experiments, tunable lasers were used that required real-time experimenter control to locate and lock onto the atmospheric H2O absorption line for the DIAL measurements. The Lidar Atmospheric Sensing Experiment (LASE) is the first step in a long-range effort to develop and demonstrate an autonomous DIAL system for airborne and spaceborne flight experiments. The LASE instrument is being developed to measure H2O, aerosol, and cloud profiles from a high-altitude ER-2 (extended range U-2) aircraft. The science of the LASE program, the LASE system design, and the expected measurement capability of the system are discussed

Radio Observations of the Supernova Remnant Candidate G312.5-3.0

The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850 MHz have revealed a number of previously unknown radio sources. One such source, G312.5-3.0 (PMN J1421-6415), has been observed using the multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at frequencies of 1380 MHz and 2378 MHz. Further observations of the source were made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency of 843 MHz. The source has an angular size of 18 arcmin and has a distinct shell structure. We present the reduced multi-frequency observations of this source and provide a brief argument for its possible identification as a supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA

Discovery of KiloHertz Quasi-Periodic Oscillations in the Z source Cygnus X-2

During observations with RXTE we discovered two simultaneous kHz QPOs near 500 Hz and 860 Hz in the Z source Cyg X-2. In the X-ray color-color diagram and hardness-intensity diagram (HID) a clear Z track was traced out. A single kHz QPO peak was detected at the left end of the horizontal branch (HB) of the Z track, with a frequency of 731+/-20 Hz and an amplitude of 4.7+0.8-0.6 % rms in the energy band 5.0-60 keV. Further to the right on the HB, at somewhat higher count rates, an additional peak at 532+/-43 Hz was detected with an rms amplitude of 3.0+1.0-0.7 %. When the source moved down the HB, thus when the inferred mass accretion rate increased, the frequency of the higher-frequency QPO increased to 839+/-13 Hz, and its amplitude decreased to 3.5+0.4-0.3 % rms. The higher-frequency QPO was also detected on the upper normal branch (NB) with an rms amplitude of 1.8+0.6-0.4 % and a frequency of 1007+/-15 Hz; its peak width did not show a clear correlation with inferred mass accretion rate. The lower-frequency QPO was most of the time undetectable, with typical upper limits of 2 % rms, no conclusion on how this QPO behaved with mass accretion rate can be drawn. If the peak separation between the QPOs is the neutron star spin frequency (as required in some beat-frequency models) then the neutron star spin period is 2.9+/-0.2 ms (346+/-29 Hz).Comment: 10 pages, including 3 figures. Accepted for publication in ApJ Letter

Thermophysical and chemical characterization of charring ablative materials Final report

Thermophysical and chemical properties of charring ablative material

Nonlinear coherent transport of waves in disordered media

We present a diagrammatic theory for coherent backscattering from disordered dilute media in the nonlinear regime. The approach is non-perturbative in the strength of the nonlinearity. We show that the coherent backscattering enhancement factor is strongly affected by the nonlinearity, and corroborate these results by numerical simulations. Our theory can be applied to several physical scenarios like scattering of light in nonlinear Kerr media, or propagation of matter waves in disordered potentials.Comment: 4 pages, 3 figure

An XMM-Newton view of the `bare' nucleus of Fairall 9

We present the spectral results from a 130 ks observation, obtained from the X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves, reveals a `softer-when-brighter' behaviour which is typical for radio-quiet type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data of the reflection grating spectrometer and we did not find any significant evidence supporting the presence of warm-absorber in the low X-ray energy part of the source's spectrum. This means that the central nucleus of Fairall 9 is `clean' and thus its X-ray spectral properties probe directly the physical conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV energy-range, derived from the EPIC data, can be modelled by a relativistically blurred disc-reflection model. This spectral model yields for Fairall 9 an intermediate black-hole best-fit spin parameter of $\alpha=0.39^{+0.48}_{-0.30}$.Comment: Accepted for publication in MNRAS. The paper contains 11 figures and 1 tabl