A5101731618- Astrophysics and Star Formation Studies
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- High-pressure geophysics and materials
- Geophysics and Gravity Measurements
- Astro and Planetary Science
- Atmospheric Ozone and Climate
- Galaxies: Formation, Evolution, Phenomena
- Distributed and Parallel Computing Systems
- Scientific Research and Discoveries
- Molecular Spectroscopy and Structure
- Inertial Sensor and Navigation
- Geomagnetism and Paleomagnetism Studies
- Advanced Frequency and Time Standards
- Advanced Combustion Engine Technologies
- Radio Astronomy Observations and Technology
- Atomic and Molecular Physics
- Spectroscopy and Laser Applications
Fort Worth Museum of Science and History
2017-2019
Northwestern University
2007-2017
Adler Planetarium
2003-2011
University of Illinois Urbana-Champaign
1994-2000
National Center for Supercomputing Applications
1996-1998
National Center for Supercomputing Applications
1996
National Radio Astronomy Observatory
1992
University of Oklahoma
1990
Context.We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the Sgr A* counterpart associated with massive black hole at Galactic Center.
The high energy activity in the inner few degrees of Galactic center is traced by diffuse radio, X-ray and gamma-ray emission. physical relationship between different components gas emitting at multiple wavelengths a focus this work. We first present radio continuum observations using Green Bank Telescope model nonthermal spectrum terms broken power-law distribution GeV electrons synchrotron radiation. show that emission detected Fermi primarily due to bremsstrahlung produced population...
We have carried out Very Large Array (VLA) continuum observations to study the variability of Sgr A* at 43 GHz (λ = 7 mm) and 22 13 mm). A low level flare activity has been detected with a duration ~2 hr these frequencies, showing peak emission leading by ~20-40 minutes. The overall characteristics are interpreted in terms plasmon model van der Laan considering ejection adiabatic expansion uniform, spherical plasma blob due activity. observed spectral index, ν-α, α 1.6 is consistent...
(abridged) We describe highlights of the results two observing campaigns in 2004 to investigate correlation flare activity Sgr A* different wavelength regimes, using a total nine ground and space-based telescopes. report detection several new near-IR flares during campaign based on {\it HST} observations. The level can be as low $\sim0.15$ mJy at 1.6 $μ$m continuous up about 40% time. Using NICMOS instrument HST}, XMM-Newton} CSO observatories, we also detect simultaneous bright X-ray which...
view Abstract Citations (132) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiconfiguration VLA H92 alpha Observations of Sagittarius A West at 1 Arcsecond Resolution Roberts, D. A. ; Goss, W. M. H 92-alpha observations Sgr have been carried out with greater resolution and sensitivity than previous ones. Kinematic features the western arc, northern arm, extended bar are identified. The arc is modeled as half a ring in circular rotation...
We present radio images within 30'' of Sgr A* based on recent VLA observations at 34 GHz with 7.8 μJy sensitivity and resolution mas. report 44 partially resolved compact sources clustered in two regions the E arm ionized gas that orbits A*. These have size scales ranging between ∼50 200 mas (400–1600 AUs), a bow-shock appearance facing direction Unlike previously identified near-IR but associated massive stars, these do not appear to counterparts 3.8 μm. interpret as candidate population...
Radio observations of the Sgr A region have been carried out at 1720 MHz transition OH molecule, using Very Large Array and Australia Telescope Compact Array. OH(1720 MHz) maser emission is detected seven different positions within a few arcminutes Galactic center. Most masers are located to southeast A*, boundary East nonthermal source with M-0.02-0.07 molecular cloud. One circumnuclear disk (CND), another may arise as result an expansion into gas northwest A*. It likely that these features...
We report the detection of variable emission from Sgr A* in almost all wavelength bands (i.e. centimeter, millimeter, submillimeter, near-IR and X-rays) during a multi-wavelength observing campaign. Three new moderate flares are detected simultaneously both X-ray bands. The ratio to flux is consistent with inverse Compton scattering photons by submillimeter emitting relativistic particles which follow scaling relations obtained size measurements A*. also find that flare statistics...
Sgr A*, the massive black hole at center of Galaxy, varies in radio through X-ray emission on hourly timescales. The flare activity is thought to arise from innermost region an accretion flow onto A*. We present simultaneous light curves A* radio, submillimeter and X-rays that show a possible time delay 110 ± 17 minutes between 850 μm suggesting optically thick. At wavelengths, we detect lags 20.4 6.8, 30 12, 20 6 peaks observed 13 7 mm (22 43 GHz) three different epochs using VLA. Linear...
The compact radio source Sgr A* is coincident with a 4 million solar mass black hole at the dynamical center of Galaxy and surrounded by dense orbiting ionized molecular gas. We present high resolution continuum images central 3' report faint continuous linear structure centered on PA~60 degrees. extension this feature appears to be terminated symmetrically two linearly polarized structures 8.4 GHz, ~75" from A*. A number weak blobs emission X-ray counterparts are detected along axis...
We report on new modeling results based the mm- to X-ray emission of SgrA* counterpart associated with massive black hole at Galactic Center. Our is simultaneous observations carried out 07 July, 2004, using ESO NACO adaptive optics instrument and ACIS-I aboard Chandra Observatory as well SMA VLA. The revealed several flare events in all wavelength domains. Here we show that a combined synchrotron self-Compton (SSC) model followed by an adiabatic expansion source components can fully account...
The supermassive black hole Sgr A* is located at the Milky Way center. We studied its flaring activity close to DSO/G2 pericenter passage constrain physical properties and origin of flares. Simultaneous/coordinated observations were made in 2014 Feb-Apr with XMM-Newton, HST/WFC3, VLT/SINFONI, VLA CARMA. detected 2 X-ray 3 NIR flares on Mar. 10 Apr. XMM-Newton HST 4 VLT. flare has a long rise rapid decay. Its counterpart peaked 4320s before peak implying variation X-ray-to-NIR flux ratio....
A search using the Very Large Array was performed for 1720-megahertz OH maser line emission from a number of nonthermal radio continuum sources in galactic center region. The transition has recently been noted its potential as tracer shock activity. most striking result detection extended emission, well compact features, along interface between large-scale shell (G359.1-0.5) and surrounding ring high-velocity molecular gas. morphological correlation among neutral gas, shell, features...
A ring of dense molecular gas extending 2-7 pc orbits the supermassive black hole Sgr A* at center our Galaxy. Using Green Bank Telescope, we detected water maser lines and both narrow (0.35 km/s) broad (30 - 50 methanol emission from ring. Two strongest 44 GHz are confirmed as masers by interferometric observations. These class I collisionally excited signatures early phases massive star formation in disk Galaxy, suggesting that is its phase. Close inspection kinematics associated clumps...
ALMA observations of the Galactic center with a spatial resolution 261 × 097 resulted in detection 11 SiO (5–4) clumps molecular gas within 0.6 pc (15'') Sgr A*, interior to 2 circumnuclear ring. The three closest A* show largest central velocities, ∼150 km s−1, and broadest asymmetric line widths full width zero intensity (FWZI) ∼110–147 s−1. remaining clumps, distributed mainly NE ionized mini-spiral, have narrow FWZI (∼18–56 s−1). Using CARMA (2–1) data, Large Velocity Gradient modeling...
We report the discovery of 11 bipolar outflows within a projected distance 1pc from Sgr A* based on deep ALMA observations $^{13}$CO, H30$α$ and SiO (5-4) lines with sub-arcsecond $\sim1.3$ km/s, resolutions. These unambiguous signatures young protostars manifest as approaching receding lobes dense gas swept up by jets created during formation early evolution stars. The lobe masses momentum transfer rates are consistent protostellar found throughout disk Galaxy. mean dynamical age outflow...
Recent broad-band 34 and 44 GHz radio continuum observations of the Galactic center have revealed 41 massive stars identified with near-IR counterparts, as well proplyd candidates within 30" Sgr A*. Radio obtained in 2011 2014 been used to derive proper motions eight young near The accuracy motion estimates based on by Lu et al. Paumard investigated using their predict epoch positions comparing predicted those counterparts observations. Predicted from show an rms scatter 6 mas relative...
ABSTRACT We present an analysis of physical conditions in the Orion Veil, atomic photon-dominated region (PDR) that lies just front (≈2 pc) Trapezium stars Orion. This offers unusual opportunity to study properties PDRs, including magnetic field. have obtained 21 cm H i and 18 (1665 1667 MHz) OH Zeeman effect data yield images line-of-sight field strength B los molecular regions Veil. find ≈ −50 −75 μ G gas across much Veil (25″ resolution) −350 at one position (40″ resolution). The has two...
We have measured the line-of-sight magnetic field toward Sgr B2 North and Main regions with VLA by Zeeman mapping of H I line; Blos ≈ -0.5 mG spatial variations about 50%. It is likely that absorption line produced mainly within massive molecular envelope surrounding dense cores; if so, we measure cloud complex. Maps plane-of-sky direction from polarized emission dust led others to suggest present north-south elongation was due infall along predominantly east-west oriented lines. Our...
We have carried out VLA Zeeman observations of HI absorption lines toward the HII region in M17 giant molecular cloud complex. The show between 5 and 8 distinct velocity components which vary spatially a complex manner across source. explore possible physical connections these based on calculations column densities, line sight magnetic field strengths, as well comparisons with wide array previous optical, infrared, radio observations. In particular, an component at same southwestern (M17 SW)...
In late December 1990, a new radio source appeared near the center of our galaxy rivaling intensity Sgr A(*) (the compact at galactic center). Following its first detection, flux density transient (GCT) increased rapidly to maximum 1 month later, and then declined gradually with time scale about 3 months. Surprisingly, GCT maintained steep spectrum during both rising decay phases. The neutral hydrogen (HI) absorption shows similar that in front A(*); this indicates lies center. Furthermore,...
We present VLA observations of the Zeeman effect in 22 GHz H2O masers several high-mass star-forming regions. These are believed to arise from collisional pumping postshock environments. Therefore, data provide most direct measurements magnetic field strengths high-density (n ≳ 108 cm-3) gas, where energy determines other physical conditions. Our yield significant detections W3 IRS 5, W3(OH), W49 N, and OH 43.8-0.1. In these sources, we detect line-of-sight ranging 13 49 mG. For some...
view Abstract Citations (51) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Anisotropy in the Angular Broadening of Sagittarius A * at Galactic Center Yusef-Zadeh, Farhad ; Cotton, William Wardle, Mark Melia, Fulvio Roberts, Douglas A. We present results a lambda = 20 cm (VLA) squared observation compact center radio source Sgr A(*). The scatter-broadened image is elongated east-west direction, with an axial ratio 0.56 +/- 0.22 and position...