Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey

We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by co-adding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [OIII] luminosity, emission line ratios, and the strength of the 4000A break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the ~10^28 ergs/s/Hz level found for sources without any discernible star-formation. Furthermore, this additional radio emission correlates well with the strength of the 4000A break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star-formation vs. AGN). For both cases we find a strong, almost identical, correlation between [OIII] and radio luminosity, with the AGN sample extending toward lower, and the star-formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion of the host galaxy. For systems with similar redshifts and velocity dispersions, the star-formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.Comment: Accepted for publication in Astronomical Journal; 15 pages, 8 color figure

The Distance of the SNR Kes 75 and PWN PSR J1846-0258 System

The supernova remnant (SNR) Kes 75/PSR J1846-0258 association can be regarded as certain due to the accurate location of young PSR J1846-0258 at the center of Kes 75 and the detected bright radio/X-ray synchrotron nebula surrounding the pulsar. We provide a new distance estimate to the SNR/pulsar system by analyzing the HI and $^{13}$CO maps, the HI emission and absorption spectra, and the $^{13}$CO emission spectrum of Kes 75. No absorption features at negative velocities strongly argue against the widely-used large distance of 19 to 21 kpc for Kes 75, and show that Kes 75 is within the Solar circle, i.e. a distance $d<$13.2 kpc. Kes 75 is likely at distance of 5.1 to 7.5 kpc because the highest HI absorption velocity is at 95 km/s and no absorption is associated with a nearby HI emission peak at 102 km/s in the direction of Kes 75. This distance to Kes 75 gives a reasonable luminosity of PSR J1846-0258 and its PWN, and also leads to a much smaller radius for Kes 75. So the age of the SNR is consistent with the spin-down age of PSR J1846-0258, confirming this pulsar as the second-youngest in the Galaxy.Comment: 5 pages, two pictures, A&A letter

Accurate sampling using Langevin dynamics

We show how to derive a simple integrator for the Langevin equation and illustrate how it is possible to check the accuracy of the obtained distribution on the fly, using the concept of effective energy introduced in a recent paper [J. Chem. Phys. 126, 014101 (2007)]. Our integrator leads to correct sampling also in the difficult high-friction limit. We also show how these ideas can be applied in practical simulations, using a Lennard-Jones crystal as a paradigmatic case

VLBA measurement of the transverse velocity of the magnetar XTE J1810-197

We have obtained observations of the magnetar XTE J1810-197 with the Very Long Baseline Array at two epochs separated by 106 days, at wavelengths of 6 cm and 3.6 cm. Comparison of the positions yields a proper motion value of 13.5+-1.0 mas/yr at an equatorial position angle of 209.4+-2.4 deg (east of north). This value is consistent with a lower-significance proper motion value derived from infrared observations of the source over the past three years, also reported here. Given its distance of 3.5+-0.5 kpc, the implied transverse velocity corrected to the local standard of rest is 212+-35 km/s (1 sigma). The measured velocity is slightly below the average for normal young neutron stars, indicating that the mechanism(s) of magnetar birth need not lead to high neutron star velocities. We also use Australia Telescope Compact Array, Very Large Array, and these VLBA observations to set limits on any diffuse emission associated with the source on a variety of spatial scales, concluding that the radio emission from XTE J1810-197 is >96% pulsed.Comment: Accepted for publication in The Astrophysical Journal. Six pages, 2 figure

Computing and data processing

The applications of computers and data processing to astronomy are discussed. Among the topics covered are the emerging national information infrastructure, workstations and supercomputers, supertelescopes, digital astronomy, astrophysics in a numerical laboratory, community software, archiving of ground-based observations, dynamical simulations of complex systems, plasma astrophysics, and the remote control of fourth dimension supercomputers

The non-centrosymmetric lamellar phase in blends of ABC triblock and ac diblock copolymers

The phase behaviour of blends of ABC triblock and ac diblock copolymers is examined using self-consistent field theory. Several equilibrium lamellar structures are observed, depending on the volume fraction of the diblocks, phi_2, the monomer interactions, and the degrees of polymerization of the copolymers. For segregations just above the order-disorder transition the triblocks and diblocks mix together to form centrosymmetric lamellae. As the segregation is increased the triblocks and diblocks spatially separate either by macrophase-separating, or by forming a non-centrosymmetric (NCS) phase of alternating layers of triblock and diblock (...ABCcaABCca...). The NCS phase is stable over a narrow region near phi_2=0.4. This region is widest near the critical point on the phase coexistence curve and narrows to terminate at a triple point at higher segregation. Above the triple point there is two-phase coexistence between almost pure triblock and diblock phases. The theoretical phase diagram is consistent with experiments.Comment: 9 pages, 8 figures, submitted to Macromolecule

Intrinsic profiles and capillary waves at homopolymer interfaces: a Monte Carlo study

A popular concept which describes the structure of polymer interfaces by ``intrinsic profiles'' centered around a two dimensional surface, the ``local interface position'', is tested by extensive Monte Carlo simulations of interfaces between demixed homopolymer phases in symmetric binary (AB) homopolymer blends, using the bond fluctuation model. The simulations are done in an LxLxD geometry. The interface is forced to run parallel to the LxL planes by imposing periodic boundary conditions in these directions and fixed boundary conditions in the D direction, with one side favoring A and the other side favoring B. Intrinsic profiles are calculated as a function of the ``coarse graining length'' B by splitting the system into columns of size BxBxD and averaging in each column over profiles relative to the local interface position. The results are compared to predictions of the self-consistent field theory. It is shown that the coarse graining length can be chosen such that the interfacial width matches that of the self-consistent field profiles, and that for this choice of B the ``intrinsic'' profiles compare well with the theoretical predictions.Comment: to appear in Phys. Rev.

High energy from space

The following subject areas are covered: (1) important scientific problems for high energy astrophysics (stellar activity, the interstellar medium in galaxies, supernovae and endpoints of stellar evolution, nucleosynthesis, relativistic plasmas and matter under extreme conditions, nature of gamma-bursts, identification of black holes, active nuclei, accretion physics, large-scale structures, intracluster medium, nature of dark matter, and the X- and gamma-ray background); (2) the existing experimental programs (Advanced X-Ray Astrophysics Facility (AXAF), Gamma Ray Observatory (GRO), X-Ray Timing Explorer (XTE), High Energy Transient Experiment (HETE), U.S. participation in foreign missions, and attached Shuttle and Space Station Freedom payloads); (3) major missions for the 1990's; (4) a new program of moderate missions; (5) new opportunities for small missions; (6) technology development issues; and (7) policy issues

Discovery of New Interacting Supernova Remnants in the Inner Galaxy

OH(1720 MHz) masers are excellent signposts of interaction between supernova remnants(SNRs) and molecular clouds. Using the GBT and VLA we have surveyed 75 SNRs and six candidates for maser emission. Four new interacting SNRs are detected with OH masers: G5.4-1.2, G5.7-0.0, G8.7-0.1 and G9.7-0.0. The newly detected interacting SNRs G5.7-0.0 and G8.7-0.1 have TeV gamma-ray counterparts which may indicate a local cosmic ray enhancement. It has been noted that maser-emitting SNRs are preferentially distributed in the Molecular Ring and Nuclear Disk. We use the present and existing surveys to demonstrate that masers are strongly confined to within 50 degrees Galactic longitude at a rate of 15 percent of the total SNR population. All new detections are within 10 degrees Galactic longitude emphasizing this trend. Additionally, a substantial number of SNR masers have peak fluxes at or below the detection threshold of existing surveys. This calls into question whether maser surveys of Galactic SNRs can be considered complete and how many maser-emitting remnants remain to be detected in the Galaxy.Comment: Accepted to ApJ Letters, with 2 figures and 2 table