Understanding the Fe II emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as “Eigenvector 1” and tracing the chemical evolution of the cosmos. Recently, three large Fe II atomic data sets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code Cloudy and examined predictions using a new generation of AGN spectral energy distribution (SED), which indicates that the ultraviolet (UV) emission can be quite different depending on the data set utilized. The Smyth et al. data set better reproduces the observed Fe II template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of ≈100 km s−1 reproduces the observed shape and strength of the so-called Fe II “UV bump.” Comparing our predictions to the observed Fe II template, we derive a typical cloud density of 1011 cm−3 and photon flux of 1020 cm−2 s−1, and show that these largely reproduce the observed Fe II emission in the UV and optical. We calculate the I(Fe II)/I(Mg II) emission-line intensity ratio using our best-fitting model and obtain log(I(Fe II)/I(Mg II)) ∼ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.
Efficient clustering algorithms play a very important role in the fast connection establishment of ad hoc networks. In this paper, we describe a communication model that is derived directly from that of Bluetooth, an emerging technology for perva.~ive computing; this teclmology is expected to play a major role in future personal area network applications. We filrther propose two new distributed algorithms for clustermg in wireless ad hoc networks. The existing algorithms often become infeasible because they use models where the discovering devices broadcast their Ids and exchange substantial information in the initial stages of the algorithm.We propose a 2-stage distributed O(N) randomized algorithm for an N node complete network, that always finds the minimum number of star-shaped clusters, which have maximum size. We then present a completely deterministic O(N) distributed algorithm for the same model, which achieves the same purpose. ~,Ve describe in detail how these algorithms can be applied to Bluetooth for efficient scatternet formation. Finally, we evaluate both algorithms using simulation experiments based on the Bluetooth communication model, and compare their performance.
Coalescence of low mass compact binaries of neutron stars and black holes are primary burst sources for LIGO and VIRGO. Of importance in the early stages of observations will be the classification of candidate detections by source-type. The diversity in source parameters and serendipity in any new window of observations suggest to consider model-independent detection algorithms. Here a frequency dynamics algorithm is described which extracts a trajectory in thė f (f )-plane from the noisy signal. The algorithm is studied in simulated binary coalescence. Robust results are obtained with experimental noise data. Experiments show the method to be superior to matched filtering in the presence of model imperfections.
We report the first unambiguous detection of an axial merger shock in the early-stage merging cluster Abell 98 using deep (227 ks) Chandra observations. The shock is about 420 kpc south from the northern subcluster of Abell 98, in between the northern and central subclusters, with a Mach number of ≈ 2.3 ± 0.3. Our discovery of the axial merger shock front unveils a critical epoch in the formation of a massive galaxy cluster, when two subclusters are caught in the early phase of the merging process. We find that the electron temperature in the postshock region favors the instant collisionless model, where electrons are strongly heated at the shock front, by interactions with the magnetic field. We also report on the detection of an intercluster gas filament, with a temperature of kT = 1.07 ± 0.29 keV, along the merger axis of Abell 98. The measured properties of the gas in the filament are consistent with previous observations and numerical simulations of the hottest, densest parts of the warm–hot intergalactic medium (WHIM), where WHIM filaments interface with the virialization regions of galaxy clusters.
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