Now showing items 1-20 of 358

    • Electron-positron jets associated with the quasar 3C279 

      Wardle, J.F.C.; Homan, D.C.; Ojha, R.; Roberts, D.H. (Brandeis University, 1998)
      A long outstanding problem in extragalactic astrophysics is the composition of the relativistic jets of plasma streaming from the nuclei of quasars and active galaxies - whether it is predominantly a "normal" (electron-proton) ...
    • Multi-Photon Entanglement and Quantum Teleportation 

      Shih, Yanhua (U. S. Army Research Office, 1999-07-31)
      The project "Multi-Photon Entanglement and Quantum Teleportation" concerns a series of experimental and theoretical investigations on multi-photon entangled states and the applications, for example, quantum teleportation. ...
    • The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) 

      Stark, Antony A.; Bally, John; Balm, Simon P.; Bania, T. M.; Bolatto, Alberto D.; Chamberlin, Richard A.; Engargiola, Gregory; Huang, Maohai; Ingalls, James G.; Jacobs, Karl; Jackson, James M.; Kooi, Jacob W.; Lane, Adair P.; Lo, K.-Y.; Marks, Rodney D.; Martin, Christopher L.; Mumma, Dennis; Ojha, Roopesh; Schieder, Rudolf; Staguhn, Johannes; Stutzki, Juergen; Walker, Christopher K.; Wilson, Robert W.; Wright, Gregory A.; Zhang, Xiaolei; Zimmermann, Peter; Zimmermann, Ruediger (IOP, 2000-12-15)
      AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at wavelengths between 200 and 2000 microns, was installed at the South Pole during the 1994-1995 Austral summer. The telescope operates continuously ...
    • AST/RO Observations of Atomic Carbon near the Galactic Center 

      Ojha, Roopesh; Stark, Antony A.; Hsieh, Henry H.; Lane, Adair P.; Chamberlin, Richard A.; Bania, Thomas M.; Bolatto, Alberto D.; Jackson, James M.; Wright, Gregory A. (IOP, 2001-02-10)
      We present a coarsely sampled map of the region |l| ≤ 2°, |b| ≤ 0°1 in the 492 GHz (³P₁ → ³P₀) fine-structure transition of neutral carbon, observed with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO). ...
    • Parsec-Scale Blazar Monitoring: Proper Motions 

      Homan, Daniel C.; Ojha, Roopesh; Wardle, John F. C.; Roberts, David H.; Aller, Margo F.; Aller, Hugh D.; Philip A. Hughes (IOP, 2001-03-10)
      We present proper motions obtained from a dual-frequency, six-epoch, VLBA polarization experiment monitoring a sample of 12 blazars. The observations were made at 15 and 22 GHz at bimonthly intervals over 1996. A total of ...
    • Parsec-Scale Blazar Monitoring: Flux and Polarization Variability 

      Homan, Daniel C.; Ojha, Roopesh; Wardle, John F. C.; Roberts, David H.; Aller, Margo F.; Aller, Hugh D.; Hughes, Philip A. (IOP, 2002-03-20)
      We present analysis of the flux density and polarization variability of parsec-scale radio jets from a dual-frequency, six-epoch, VLBA polarization experiment monitoring 12 blazars. The observations were made at 15 and 22 ...
    • Predictive Mining of Time Series Data in Astronomy 

      Perlman, Eric; Java, Akshay (2003-01-01)
      We discuss the development of a Java toolbox for astronomical time series data. Rather than using methods conventional in astronomy (e.g., power spectrum and cross-correlation analysis) we employ rule discovery techniques ...
    • Accurate Astrometry of 22 Southern Hemisphere Radio Sources 

      Fey, Alan L.; Ojha, Roopesh; Jauncey, David L.; Johnston, Kenneth J.; Reynolds, John E.; Lovell, James E. J.; Tzioumis, Anastasios K.; Quick, Jonathan F. H.; Nicolson, George D.; Ellingsen, Simon P.; McCulloch, Peter M.; Koyama, Yasuhiro (IOP, 2003-12-03)
      Milliarcsecond-accurate radio positions for 22 southern hemisphere extragalactic sources are reported. These positions are derived from Mark III very long baseline interferometry observations made between 2003 February and ...
    • The Impact of Interstellar Scintillation on Astrometric VLBI 

      Jauncey, David; Lovell, James; Ojha, Roopesh; Fey, Alan L.; Koyama, Yasuhiro; Bignall, Hayley E.; Kedziora-Chudczer, Lucyna; Macquart, Jean-Pierre; Rickett, Barney J.; Titov, Oleg; Tzioumis, Anastasios K. (2004)
      We review the evidence demonstrating the interstellar scintillation (ISS) is the principal mechanism responsible for the intra-day variability (IDV) seen at cm wavelengths in many compact, flat-spectrum extra-galactic radio ...
    • Parsec-Scale Blazar Monitoring: The Data 

      Ojha, Roopesh; Homan, Daniel C.; Roberts, David H.; Wardle, John F. C.; Aller, Margo F.; Aller, Hugh D.; Hughes, Philip A. (IOP, 2004-01-01)
      We present the images and modeling data obtained from a dual frequency, six-epoch, VLBA polarization experiment monitoring a sample of 12 blazars. The observations were made at 15 and 22 GHz at evenly spaced, bimonthly ...
    • VLBI Observations of the Gigahertz-Peaked Spectrum Galaxy PKS 1934−638 

      Ojha, Roopesh; Fey, Alan L.; Johnston, Kenneth J.; Tzioumis, Anastasios K.; Reynolds, John E. (IOP, 2004-04-01)
      We present 8.4 GHz VLBI observations of the gigahertz-peaked spectrum source PKS 1934-638 made with the Australian Long Baseline Array. Our observations confirm the compact double nature of the source and yield measured ...
    • VLBI Observations of Southern Hemisphere ICRF Sources. I. 

      Ojha, Roopesh; Fey, Alan L.; Johnston, Kenneth J.; Jauncey, David L.; Reynolds, John E.; Tzioumis, Anastasios K.; Quick, Jonathan F. H.; Nicolson, George D.; Ellingsen, Simon P.; Dodson, Richard G.; McCulloch, Peter M. (IOP, 2004-06-01)
      We present 8.4 GHz very long baseline interferometry (VLBI) observations of 69 southern hemisphere extragalactic sources in the International Celestial Reference Frame. These are the first in a series of observations ...
    • High-resolution observations of 6.7-GHz methanol masers with the Long Baseline Array 

      Dodson, R.; Ojha, R.; Ellingsen, S. P. (Oxford University Press, 2004-07-01)
      We have used the Australian Long Baseline Array (LBA) to produce milliarcsecond images of five sites of methanol (CH3OH) maser emission at 6.7 GHz. These are all sites that have linear morphologies at arcsecond resolutions, ...
    • VLBA Snapshot Imaging Survey of Scintillating Sources 

      Ojha, Roopesh; Fey, Alan L.; Lovell, James E. J.; Jauncey, David L.; Johnston, Kenneth J. (IOP, 2004-10-01)
      We present 8.4 GHz Very Long Baseline Array (VLBA) observations of 75 extragalactic radio sources drawn from the scintillating sources discovered in the Microarcsecond Scintillation-induced Variability survey. This survey ...
    • Milliarcsecond Structure of Microarcsecond Sources: Comparison of Scintillating and Nonscintillating Extragalactic Radio Sources 

      Ojha, Roopesh; Fey, Alan L.; Jauncey, David L.; Lovell, James E. J.; Johnston, Kenneth J. (IOP, 2004-10-20)
      We compare the milliarcsecond-scale morphology of scintillating and nonscintillating sources. The scintillating sources are drawn from those flat-spectrum extragalactic radio sources discovered, by the Micro-Arcsecond ...
    • Astrometry of 25 Southern Hemisphere Radio Sources from a VLBI Short-Baseline Survey 

      Fey, Alan L.; Ojha, Roopesh; Reynolds, John E.; Ellingsen, Simon P.; McCulloch, Peter M.; Jauncey, David L.; Johnston, Kenneth J. (IOP, 2004-11)
      Milliarcsecond-accurate radio positions for 25 southern hemisphere extragalactic sources are reported. These positions are derived from Mark III Very Long Baseline Interferometry observations made between 2003 September ...
    • The Radio Variability of the Gravitational Lens PMN J1838−3427 

      Winn, Joshua N.; Lovell, James E. J.; Bignall, Hayley; Gaensler, Bryan M.; Getts, Tracy J.; Kedziora-Chudczer, Lucyna; Ojha, Roopesh; Reynolds, John E.; Tingay, Steven J.; Tzioumis, Tasso (IOP, 2004-12-01)
      We present the results of a radio variability study of the gravitational lens PMN J1838-3427. Our motivation was to determine the Hubble constant by measuring the time delay between variations of the two quasar images. We ...
    • Interstellar scintillation as a probe of microarcsecond scale structure in quasars 

      Bignall, H.E.; Jauncey, D.L.; Lovell, J.E.J.; Kedziora-Chudczer, L.; Macquar, J-P.; Tzioumis, A.K.; Rickett, B.J.; Ojha, R.; Carte, S.; Cimo, G.; Ellingsen, S.; McCulloch, P.M. (2004-12-29)
      Observations over the last two decades have shown that a significant fraction of all flat-spectrum, extragalactic radio sources exhibit flux density variations on timescales of a day or less at frequencies of several GHz. ...
    • VLBA Polarimetry: A Faraday Screen in 3C 273 

      Ojha, Roopesh; Homan, Daniel C.; Wardle, John F. C.; Roberts, David H.; Aller, Hugh D.; Aller, Margo F.; Hughes, Philip A. (Astronomical Society of the Pacific Conference Series, 2005)
      The polarization of superluminal radio components moving at the base of the VLBI jet in 3C273 are tracked as part of a six epoch monitoring campaign at 15 and 22 GHz. The components rise sharply in fractional polarization ...
    • VLBA Snap-Shot Imaging of Scintillating Sources 

      Ojha, Roopesh; Lovell, James E.; Jauncey, David L.; Kedziora-Chudczer, Lucyna; Bignall, Hayley E.; Reynolds, John E.; Tzioumis, Anastasios K.; Macquart, Jean-Pierre; Fey, Alan L.; Johnston, Kenneth J. (Astronomical Society of the Pacific Conference Series, 2005)
      We present VLBA snap-shot images of weak scintillating sources and compare their morphologies with those of strong scintillating sources imaged by the USNO astrometry program. It is now clear that interstellar scintillation ...