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Blundell, Raymond

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Blundell

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Raymond

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Blundell, Raymond
Author's Publications: search.filters.isAuthorOfPublication.6c49a651-eb31-49dc-9a13-92737fc4d2a0

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Now showing 1 - 7 of 7
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    The High-Density Ionized Gas in the Central Parsec of the Galaxy
    (American Astronomical Society, 2010) Zhao, Jun-Hui; Blundell, Raymond; Moran, James; Downes, Dennis; Schuster, Karl F.; Marrone, Daniel P.
    We report a study of the \(H30\alpha\) line emission at 1.3 mm from the region around Sgr A* made with the Submillimeter Array at a resolution of 2'' over a field of 60'' (2 pc) and a velocity range of \(-360 to +345 km s^{–1}\). This field encompasses most of the Galactic center's "minispiral." With an isothermal homogeneous H II model, we determined the physical conditions of the ionized gas at specific locations in the Northern and Eastern Arms from the \(H30\alpha\) line data along with Very Large Array data from the \(H92\alpha\) line at 3.6 cm and from the radio continuum emission at 1.3 cm. The typical electron density and kinetic temperature in the minispiral arms are \(3-21×104 cm^{–3}\) and 5000-13,000 K, respectively. The \(H30\alpha\) and \(H92\alpha\) line profiles are broadened due to the large velocity shear within and along the beam produced by dynamical motions in the strong gravitational field near Sgr A*. We constructed a three-dimensional model of the minispiral using the orbital parameters derived under the assumptions that the gas flows are in Keplerian motion. The gas in the Eastern Arm appears to collide with the Northern Arm flow in the "Bar" region, which is located 0.1-0.2 pc south of and behind Sgr A*. Finally, a total Lyman continuum flux of \(3 × 10^{50}\) photons \(s^{–1}\) is inferred from the assumption that the gas is photoionized and the ionizing photons for the high-density gas in the minispiral arms are from external sources, which is equivalent to ~250 O9-type zero-age-main-sequence stars.
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    Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87
    (American Association for the Advancement of Science (AAAS), 2012) Doeleman, Sheperd; Fish, V. L.; Schenck, D. E.; Beaudoin, C.; Blundell, Raymond; Bower, G. C.; Broderick, Alithia Carol; Chamberlin, R.; Freund, R.; Friberg, P.; Gurwell, Mark; Ho, Po-Yi; Honma, M.; Inoue, M.; Krichbaum, T. P.; Lamb, Justin; Loeb, Abraham; Lonsdale, C.; Marrone, D. P.; Moran, James; Oyama, T.; Plambeck, R.; Primiani, Rurik; Rogers, A. E. E.; Smythe, D. L.; SooHoo, J.; Strittmatter, P.; Tilanus, R. P. J.; Titus, M.; Weintroub, Jonathan; Wright, Bennett Bennett; Young, K. H.; Ziurys, L. M.
    Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion of matter onto super massive black holes. While the measured width profiles of such jets on large scales agree with theories of magnetic collimation, predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.
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    Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
    (American Astronomical Society, 2016) Fish, Vincent; Johnson, Michael; Doeleman, Sheperd; Broderick, Avery; Psaltis, Dimitrios; Lu, Ru-Sen; Akiyama, Kazunori; Alef, Walter; Algaba, Juan; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, Lindy; Blundell, Raymond; Bower, Geoffrey; Brinkerink, Christiaan; Cappallo, Roger; Chael, Andrew; Chamberlin, Richard; Chan, Chi-Kwan; Crew, Geoffrey; Dexter, Jason; Dexter, Matt; Dzib, Sergio; Falcke, Heino; Freund, Robert; Friberg, Per; Greer, Christopher; Gurwell, Mark; Ho, Paul; Honma, Mareki; Inoue, Makoto; Johannsen, Tim; Kim, Junhan; Krichbaum, Thomas; Lamb, James; León-Tavares, Jonathan; Loeb, Abraham; Loinard, Laurent; MacMahon, David; Marrone, Daniel; Moran, James; Mościbrodzka, Monika; Ortiz-León, Gisela; Oyama, Tomoaki; Özel, Feryal
    The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3 mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over 4 years. Closure phases, the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180-degree rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.
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    230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy γ-ray state in 2012
    (IOP Publishing, 2015) Akiyama, Kazunori; Lu, Ru-Sen; Fish, Vincent; Doeleman, Sheperd; Broderick, Avery; Dexter, Jason; Hada, Kazuhiro; Kino, Motoki; Nagai, Hiroshi; Honma, Mareki; Johnson, Michael; Algaba, Juan; Asada, Keiichi; Brinkerink, Christiaan; Blundell, Raymond; Bower, Geoffrey; Cappallo, Roger; Crew, Geoffrey; Dexter, Matt; Dzib, Sergio; Freund, Robert; Friberg, Per; Gurwell, Mark; Ho, Paul; Inoue, Makoto; Krichbaum, Thomas; Loinard, Laurent; MacMahon, David; Marrone, Daniel; Moran, James; Nakamura, Masanori; Nagar, Neil; Ortiz-Leon, Gisela; Plambeck, Richard; Pradel, Nicolas; Primiani, Rurik; Rogers, Alan; Roy, Alan; SooHoo, Jason; Tavares, Jonathan-León; Tilanus, Remo; Titus, Michael; Wagner, Jan; Weintroub, Jonathan; Yamaguchi, Paul; Young, Ken; Zensus, Anton; Ziurys, Lucy
    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 GHz VLBI interferometric phase information on M87 through measurement of closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0◦ as expected by physically-motivated models for 230 GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ∼ 1 × 1010 K derived from the compact flux density of ∼ 1 Jy and the angular size of ∼ 40 µas ∼ 5.5 Rs, which is broadly consistent with the peak brightness of the radio cores at 1-86 GHz located within ∼ 102 Rs. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) γ-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ∼20-60 Rs.
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    1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales
    (IOP Publishing, 2011) Fish, Vincent L.; Doeleman, Sheperd; Beaudoin, Christopher; Blundell, Raymond; Bolin, David E.; Bower, Geoffrey C.; Chamberlin, Richard; Freund, Robert; Friberg, Per; Gurwell, Mark; Honma, Mareki; Inoue, Makoto; Krichbaum, Thomas P.; Lamb, James; Marrone, Daniel P.; Moran, James; Oyama, Tomoaki; Plambeck, Richard; Primiani, Rurik; 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; Ziurys, Lucy M.
    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 wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio Observatory's Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924–292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*.
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    Atmospheric Phase Correction Using Total Power Radiometry at the Submillimeter Array
    (IOP Publishing, 2004) Battat, James; Blundell, Raymond; Moran, James; Paine, Scott
    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. We present early results from our total power radiometry phase correction experiment carried out with the Submillimeter Array on Mauna Kea. From accurate measurements of the atmospheric emission along the lines of sight of two elements of the array, we estimated the differential atmospheric electrical path between them. In one test, presented here, the phase correction technique reduced the rms phase noise at 230 GHz from 72◦ to 27◦ over a 20 minute period with a 2.5 second integration time. This corresponds to a residual differential electrical path of 98 µm, or 15 µm of precipitable water vapor, and raises the coherence in the 20 minute period from 0.45 to 0.9.
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    Resolved magnetic-field structure and variability near the event horizon of Sagittarius A
    (American Association for the Advancement of Science (AAAS), 2015) Johnson, Michael; Fish, V. L.; Doeleman, Sheperd; Marrone, D. P.; Plambeck, R. L.; Wardle, J. F. C.; Akiyama, K.; Asada, K.; Beaudoin, C.; Blackburn, Lindy; Blundell, Raymond; Bower, G. C.; Brinkerink, C.; Broderick, A. E.; Cappallo, R.; Chael, Andrew; Crew, G. B.; Dexter, J.; Dexter, M.; Freund, R.; Friberg, P.; Gold, R.; Gurwell, M. A.; Ho, P. T. P.; Honma, M.; Inoue, M.; Kosowsky, Michael; Krichbaum, T. P.; Lamb, J.; Loeb, Abraham; Lu, R.-S.; MacMahon, D.; McKinney, J. C.; Moran, James; Narayan, Ramesh; Primiani, Rurik; Psaltis, D.; Rogers, A. E. E.; Rosenfeld, Katherine; SooHoo, J.; Tilanus, R. P. J.; Titus, M.; Vertatschitsch, L.; Weintroub, Jonathan; Wright, M.; Young, Ken; Zensus, J. A.; Ziurys, L. M.
    Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizonscale magnetic-field structure. We report interferometric observations at 1.3- millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered fields near the event horizon, on scales of ∼6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.