Now showing items 21-40 of 453

    • 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 ...
    • The Detailed Optical Light Curve of GRB 030329 

      Lipkin, Y. M.; Ofek, E. O.; Gal-Yam, A.; Leibowitz, E. M.; Poznanski, D.; Kaspi, S.; Polishook, D.; Kulkarni, S. R.; Fox, D. W.; Berger, E.; Mirabal, N.; Halpern, J.; Bureau, M.; Fathi, K.; Price, P. A.; Peterson, B. A.; Frebel, A.; Schmidt, B.; Orosz, J. A.; Fitzgerald, J. B.; Bloom, J. S.; Dokkum, P. G. van; Bailyn, C. D.; Buxton, M. M.; Barsony, M. (IOP, 2004-01-19)
      We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst (GRB) 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published ...
    • Can a simple instrument measure polarization in gamma-ray bursts? 

      Curioni, A.; Mirabal, N. (2004-02-25)
      The recent claim of a high degree of linear polarization in the prompt gamma-ray burst (GRB) emission of GRB 021206 might have important implications for the underlying mechanism ultimately responsible for the GRB radiation. ...
    • 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 ...
    • A Redshift Determination for XRF 020903: First Spectroscopic Observations of an X-Ray Flash 

      Soderberg, A. M.; Kulkarni, S. R.; Berger, E.; Fox, D. B.; Price, P. A.; Yost, S. A.; Hunt, M. P.; Frail, D. A.; Walker, R. C.; Hamuy, M.; Shectman, S. A.; Halpern, J. P.; Mirabal, N. (IOP, 2004-05-10)
      We report the discovery of optical and radio afterglow emission from the extremely soft X-ray flash XRF 020903. Our spectroscopic observations provide the first redshift for an X-ray flash, thereby setting the distance ...
    • 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 ...
    • Was the X-ray Afterglow of GRB 970815 Detected? 

      Mirabal, N.; Halpern, J. P.; Gotthelf, E. V.; Mukherjee, R. (AIP publishing, 2004-10-01)
      GRB 970815 was a well‐localized gamma‐ray burst (GRB) detected by the All‐Sky Monitor (ASM) on the Rossi X‐Ray Timing Explorer (RXTE) for which no afterglow was identified despite follow‐up ASCA and ROSAT pointings and ...
    • A Search for Short Time‐Scale Optical Variability in the GRB 030329 Afterglow 

      Mirabal, N.; Halpern, J. P.; Bureau, M.; Fathi, K. (AIP publishing, 2004-10-01)
      We present a densely sampled R‐band light curve of the optical afterglow of GRB 030329 obtained during the period 15.5–23 hours after the burst. This dataset allows us to search for short time‐scale fluctuations that must ...
    • 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 ...
    • The X-Ray Afterglow of Dark GRB 970815: A Common Origin for Gamma-Ray Bursts and X-Ray Flashes? 

      Mirabal, N.; Halpern, J. P.; Gotthelf, E. V.; Mukherjee, R. (IOP, 2004-10-25)
      GRB 970815 is a well-localized gamma-ray burst (GRB) detected by the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer (RXTE) for which no afterglow was identified despite follow-up ASCA and ROSAT pointings and ...
    • 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 ...
    • The Unique, Optically-Dominated Quasar Jet of PKS 1421-490 

      Gelbord, J.M.; Marshall, H.L.; Worrall, D.M.; Birkinshaw, M.; Lovell, J.E.J.; Ojha, R.; Godfrey, L.; Jauncey, D.L.; Schwartz, D.A.; Perlman, E.S.; Georganopoulos, M.; Murphy, D.W. (MIT School of Science, 2005-01-10)
    • Coordinated Multiwavelength Observation of 3C 66A during the WEBT Campaign of 2003-2004 

      Mirabal, N.; et al. (IOP, 2005-06-09)
      The BL Lac object 3C 66A was the target of an extensive multiwavelength monitoring campaign from 2003 July through 2004 April (with a core campaign from 2003 September to 2003 December) involving observations throughout ...
    • Optical Light Curve and Cooling Break of GRB 050502A 

      Yost, S. A.; Alatalo, K.; Rykoff, E. S.; Aharonian, F.; Akerlof, C. W.; Ashley, M. C. B.; Blake, C. H.; Bloom, J. S.; Boettcher, M.; Falco, E. E.; Göğüş, E.; Güver, T.; Halpern, J. P.; Horns, D.; Joshi, M.; Kızıloǧlu, Ü.; McKay, T. A.; Mirabal, N.; Özel, M.; Phillips, A.; Quimby, R. M.; Rujopakarn, W.; Schaefer, B. E.; Shields, J. C.; Skrutskie, M.; Smith, D. A.; Starr, D. L.; Swan, H. F.; Szentgyorgyi, A.; Vestrand, W. T.; Wheeler, J. C.; Wren, J. (IOP, 2005-09-16)
      We present light curves of the afterglow of GRB 050502A, including very early data at t - tGRB < 60 s. The light curve is composed of unfiltered ROTSE-IIIb optical observations from 44 s to 6 hr postburst, R-band MDM ...