Now showing items 1-20 of 59

    • 1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales 

      Fish, Vincent L.; Doeleman, Sheperd Samuel; Beaudoin, Christopher; Blundell, Raymond; Bolin, David E.; Bower, Geoffrey C.; Chamberlin, Richard; Freund, Robert; Friberg, Per; Gurwell, Mark Andrew; Honma, Mareki; Inoue, Makoto; Krichbaum, Thomas P.; Lamb, James; Marrone, Daniel P.; Moran, James M.; Oyama, Tomoaki; Plambeck, Richard; Primiani, Rurik A.; Rogers, Alan E. E.; Smythe, Daniel L.; SooHoo, Jason; Strittmatter, Peter; Tilanus, Remo P. J.; Titus, Michael; Weintroub, Jonathan; Wright, Melvyn; Woody, David; Young, Ken Harbour; Ziurys, Lucy M. (IOP Publishing, 2011)
      Sagittarius A*, the ~4 × 106 M ☉ black hole candidate at the Galactic center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm ...
    • 230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy γ-ray state in 2012 

      Akiyama, Kazunori; Lu, Ru-Sen; Fish, Vincent; Doeleman, Sheperd S.; Broderick, Avery; Dexter, Jason; Hada, Kazuhiro; Kino, Motoki; Nagai, Hiroshi; Honma, Mareki; Johnson, Michael D.; Algaba, Juan; Asada, Keiichi; Brinkerink, Christiaan; Blundell, Raymond; Bower, Geoffrey; Cappallo, Roger; Crew, Geoffrey; Dexter, Matt; Dzib, Sergio; Freund, Robert; Friberg, Per; Gurwell, Mark Andrew; Ho, Paul; Inoue, Makoto; Krichbaum, Thomas; Loinard, Laurent; MacMahon, David; Marrone, Daniel; Moran, James M.; Nakamura, Masanori; Nagar, Neil; Ortiz-Leon, Gisela; Plambeck, Richard; Pradel, Nicolas; Primiani, Rurik A.; Rogers, Alan; Roy, Alan; SooHoo, Jason; Tavares, Jonathan-León; Tilanus, Remo; Titus, Michael; Wagner, Jan; Weintroub, Jonathan; Yamaguchi, Paul Isami; Young, Ken Harbour; Zensus, Anton; Ziurys, Lucy (IOP Publishing, 2015)
      We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and Cedar Flat in California. For the first time, we have acquired 230 ...
    • A 4% Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk 

      Herrnstein, J.; Moran, James M.; Greenhill, Lincoln Jared; Diamond, P.; Inoue, M.; Nakai, N.; Miyoshi, M.; Henkel, C.; Riess, A. (Springer Nature, 1999)
      The accurate measurement of extragalactic distances is a central challenge of modern astronomy, being required for any realistic description of the age, geometry and fate of the Universe. The measurement of relative ...
    • Accelerations of Water Masers in NGC 4258 

      Bragg, Ann E.; Greenhill, Lincoln Jared; Moran, James M.; Henkel, Christian (IOP Publishing, 2000)
      The water masers in NGC4258 delineate the structure and dynamics of a sub-parsec-diameter accretion disk around a supermassive black hole. VLBA observations provide precise information about the positions in the plane of ...
    • ALMA reveals a candidate hot and compact disc around the O-type protostar IRAS 16547-4247 

      Zapata, L. A.; Palau, A.; Galvan-Madrid, R.; Rodriguez, L. F.; Garay, G.; Moran, James M.; Franco-Hernandez, R. (Oxford University Press (OUP), 2015)
      We present high angular resolution (∼ 0.3′′) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547−4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA). In the ...
    • Atmospheric Phase Correction Using Total Power Radiometry at the Submillimeter Array 

      Battat, James Benjamin Royston; Blundell, Raymond; Moran, James M.; Paine, Scott (IOP Publishing, 2004)
      Phase noise caused by an inhomogeneous, time-variable water vapor distribution in our atmosphere reduces the angular resolution, visibility amplitude and coherence time of millimeter and submillimeter wavelength interferometers. ...
    • The Black-Hole Accretion Disk in NGC 4258: One of Nature’s Most Beautiful Dynamical Systems 

      Moran, James M. (Astronomical Society of the Pacific, 2008)
      In this talk I will summarize some of the work that the CfA group has done to study the structure of the water masers in the accretion disk of NGC4258. A series of 18 epochs of VLBA data taken from 1997.3 to 2000.8 were ...
    • The Circular Polarization of Saggitarius A* at Submillimeter Wavelengths 

      Muñoz, D. J.; Marrone, D. P.; Moran, James M.; Rao, R. (American Astronomical Society, 2012)
      We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2\pm0.3% at 1.3 mm wavelength (230 ...
    • The circular polarization of Sagittarius A* at submillimeter wavelengths 

      Muñoz, D. J.; Marrone, D. P.; Moran, James M.; Rao, R. (IOP Publishing, 2012)
      We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2% ± 0.3% at 1.3 mm wavelength (230 ...
    • Coexisting conical bipolar and equatorial outflows from a high-mass protostar 

      Greenhill, Lincoln Jared; Gwinn, C. R.; Schwartz, C.; Moran, James M.; Diamond, P. J. (Springer Nature, 1998)
      The BN/KL region in the Orion molecular cloud1 is an archetype in the study of the formation of stars much more massive than the Sun2. This region contains luminous young stars and protostars, but it is difficult to study ...
    • The Collimated Jet Source in IRAS 16547-4247: Time Variation, Possible Precession, and Upper Limits to the Proper Motions along the Jet Axis 

      Rodríguez, Luis F.; Moran, James M.; Franco-Hernández, Ramiro; Garay, Guido; Brooks, Kate J.; Mardones, Diego (American Astronomical Society, 2008)
      The triple radio source detected in association with the luminous infrared source IRAS 16547-4247 has previously been studied with high angular resolution and high sensitivity with the Very Large Array at 3.6 cm wavelength. ...
    • Discovery of Candidate H2O Disk Masers in Active Galactic Nuclei and Estimations of Centripetal Accelerations 

      Greenhill, Lincoln Jared; Kondratko, Paul T.; Moran, James M.; Tilak, Avanti (IOP Publishing, 2009)
      Based on spectroscopic signatures, about one-third of known H2O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These “disk maser candidates” ...
    • The Discovery of H2O Maser Emission in Seven AGN and at High Velocities in the Circinus Galaxy 

      Greenhill, Lincoln Jared; Kondratko, P. T.; Lovell, J. E. J.; Kuiper, T. B. H.; Moran, James M.; Jauncey, D. L.; Baines, G. P. (IOP Publishing, 2002)
      We report the discovery of H2O maser emission at 1.35 cm wavelength in seven active galactic nuclei (at distances up to < 80 Mpc) during a survey conducted at the 70-m diameter antenna of the NASA Deep Space Network near ...
    • Discovery of Water Maser Emission in Eight AGNs with 70 m Antennas of NASA’s Deep Space Network 

      Kondratko, P. T.; Greenhill, Lincoln Jared; Moran, James M.; Lovell, J. E. J.; Kuiper, T. B. H.; Jauncey, D. L.; Cameron, L. B.; Gomez, J. F.; Garcia‐Miro, C.; Moll, E.; de Gregorio‐Monsalvo, I.; Jimenez‐Bailon, E. (IOP Publishing, 2006)
      We report the discovery of water maser emission in eight active galactic nuclei (AGN) with the 70-m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia and Robledo, Spain. The positions of the newly discovered ...
    • Discovery of Water Maser Emission in Five AGNs and a Possible Correlation Between Water Maser and Nuclear 2–10 keV Luminosities 

      Kondratko, Paul T.; Greenhill, Lincoln Jared; Moran, James M. (IOP Publishing, 2006)
      We report the discovery of water maser emission in five active galactic nuclei (AGN) with the 100-m Green Bank Telescope (GBT). The positions of the newly discovered masers, measured with the VLA, are consistent with the ...
    • A disk of dust and molecular gas around a high-mass protostar 

      Patel, Nimesh A.; Curiel, Salvador; Tirupati, Tirupati Kumaran; Zhang, Qizhou; Hunter, Todd R.; Ho, Paul T. P.; Torrelles, José M.; Moran, James M.; Gómez, José F.; Anglada, Guillem (Springer Nature, 2005)
      The processes leading to the birth of low-mass stars such as our Sun have been well studied1, but the formation of high-mass (over eight times the Sun's mass, Mcircle dot) stars remains poorly understood2. Recent studies ...
    • The Diversity and Versatility of Gamma-Ray Bursts 

      Laskar, Tanmoy (2015-05-17)
      Gamma-ray bursts (GRBs) are the most energetic explosions in the Universe, thus providing a unique laboratory for the study of extreme astrophysical processes. In parallel, their large luminosity makes GRBs a premier probe ...
    • Donald Charles Backer 

      Moran, James M. (American Institute of Physics, 2011)
    • Event-Horizon-Scale Structure in the Supermassive Black Hole Candidate at the Galactic Centre 

      Doeleman, Sheperd S.; Weintroub, Jonathan; Rogers, Alan E. E.; Plambeck, Richard; Freund, Robert; Tilanus, Remo P. J.; Friberg, Per; Ziurys, Lucy M.; Moran, James M.; Corey, Brian; Young, Ken Harbour; Smythe, Daniel L.; Titus, Michael; Marrone, Daniel P.; Cappallo, Roger J.; Bock, Douglas C.-J.; Bower, Geoffrey C.; Chamberlin, Richard; Davis, Gary R.; Krichbaum, Thomas P.; Lamb, James; Maness, Holly; Niell, Arthur E.; Roy, Alan; Strittmatter, Peter; Werthimer, Daniel; Whitney, Alan R.; Woody, David (Nature Publishing Group, 2008)
      The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source ...
    • Evidence for a Geometrically Thick Self‐Gravitating Accretion Disk in NGC 3079 

      Kondratko, Paul T.; Greenhill, Lincoln Jared; Moran, James M. (IOP Publishing, 2005)
      We have mapped, for the first time, the full velocity extent of the water maser emission in NGC 3079. The largely north-south distribution of emission, aligned with a kpc-scale molecular disk, and the segregation of blue- ...