Upper Limit of 3.3 Astronomical Units to the Diameter of the Galactic Center Radio Source Sgr A*

Science ◽  
1993 ◽  
Vol 262 (5138) ◽  
pp. 1414-1416 ◽  
Author(s):  
D. C. Backer ◽  
J. A. Zensus ◽  
K. I. Kellermann ◽  
M. Reid ◽  
J. M. Moran ◽  
...  
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Upper Limit ◽  
Sgr A

scholarly journals Long-Term Variations of the Compact Radio Source Sgr A∗ at the Galactic Center

1989 ◽  
Vol 136 ◽  
pp. 535-541 ◽  
Author(s):  
Jun-Hui Zhao ◽  
R. D. Ekers ◽  
W. M. Goss ◽  
K. Y. Lo ◽  
Ramesh Narayan
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Velocity ◽  
Galactic Center ◽  
Light Curves ◽  
Radio Flux ◽  
Compact Radio Source ◽  
Sgr A ◽  
Long Term Variations

We investigate the long-term flux density variations of the compact radio source Sgr A∗ at the galactic center by combining recent VLA observations with previous Green Bank interferometer data. We present radio flux density light-curves for Sgr A∗ at 20, 11, 6 and 3.7 cm from 1974 to 1987. Long-term variability with a timescale of at least 5 years is seen at 20 cm and there is evidence for more rapid variations at the shorter wavelengths. The variability timescales at 20, 11 and 6 cm fit the λ2 scaling predicted by the theory of refractive scintillation suggesting that the variability could be due to this cause. However, the timescales are relatively short, implying an unusually high velocity in the scattering screen. The modulation index of the variability is large and relatively independent of wavelength.

scholarly journals The Compact Nonthermal Radio Source at the Galactic Center: an Update

1989 ◽  
Vol 136 ◽  
pp. 527-534
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Central Star ◽  
Radio Sources ◽  
Stellar Objects ◽  
Nonthermal Radio ◽  
Compact Radio Source ◽  
The Galaxy ◽  
Observational Status ◽  
Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

The 3-mm flux density monitoring of Sagittarius A* with the ATCA

2007 ◽  
Vol 3 (S248) ◽  
pp. 204-205
Author(s):  
J. Li ◽  
Z. Q. Shen ◽  
A. Miyazaki ◽  
M. Miyoshi ◽  
T. Tsutsumi ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Galactic Center ◽  
Sagittarius A ◽  
Compact Radio Source ◽  
Sgr A

AbstractWe have performed monitoring observations of the 3-mm flux density toward the Galactic center compact radio source Sgr A* with the ATCA since 2005 October. It has been found that during several observing epochs Sgr A* was quite active, showing significant intraday variation. Here we report the detection of an IDV in Sgr A* on 2006 August 13, which exhibits a 27% fractional variation in about 2 hrs.

scholarly journals Understanding our Galaxy: from the center to outskirts

2007 ◽  
Vol 3 (S248) ◽  
pp. 470-473
Author(s):  
Z. Q. Shen ◽  
Y. Xu ◽  
J. L. Han ◽  
X. W. Zheng
Keyword(s):  
Magnetic Fields ◽  
Radio Source ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Disk ◽  
Spiral Arms ◽  
Compact Radio Source ◽  
Sgr A ◽  
Spiral Arm

AbstractWe describe the efforts to understand our Milky Way Galaxy, from its center to outskirts, including (1) the measurements of the intrinsic size of the galactic center compact radio source Sgr A*; (2) the determination of the distance from the Sun to the Perseus spiral arm; and (3) the revealing of large scale global magnetic fields of the Galaxy.With high-resolution millimeter-VLBI observations, Shen et al. (2005) have measured the intrinsic size of the radio-emitting region of the galactic center compact radio source Sgr A* to be only 1 AU in diameter at 3.5 mm. When combined with the lower limit on the mass of Sgr A*, this provides strong evidence for Sgr A* being a super-massive black hole. Comparison with the intrinsic size detection at 7 mm indicates a frequency-dependent source size, posing a tight constraint on various theoretical models.With VLBI phase referencing observations, Xu et al. (2006) have measured the trigonometric parallax of W3OH in the Perseus spiral arm with an accuracy of 10 μas and also its absolute velocity with an accuracy of 1 km s−1. This demonstrates the capability of probing the structure and kinematics of the Milky Way by determining distances to 12 GHz methanol (CH3OH) masers in star forming regions of distant spiral arms and Milky Way's outskirts.With pulsar dispersion measures and rotation measures, Han et al. (2006) can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the most inner Norma arm to the outer Perseus arm.

Long-Term Variations of the Compact Radio Source Sgr A* at the Galactic Center

1989 ◽  
pp. 535-541 ◽  
Author(s):  
Jun-Hui Zhao ◽  
R. D. Ekers ◽  
W. M. Goss ◽  
K. Y. Lo ◽  
Ramesh Narayan
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Compact Radio Source ◽  
Sgr A ◽  
Long Term Variations

scholarly journals ASCA Observations of the SgrA Region

1998 ◽  
Vol 188 ◽  
pp. 352-353 ◽  
Author(s):  
Y. Maeda ◽  
K. Koyama ◽  
H. Murakami ◽  
M. Sakano ◽  
K. Ebisawa ◽  
...  
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Dynamical Mass ◽  
Thermal Radio ◽  
Sgr A

The complex radio source Sgr A is embedded in a region near our Galactic Center. The dynamical center of our Galaxy is considered to be Sgr A*, the compact non-thermal radio source. Dynamical mass within ~0.1 pc from Sgr A* has been estimated to be ~ 3×106 M⊙. This places Sgr A* to be a candidate of a massive blackhole (Eckart and Genzel, 1997 and reference therein).

scholarly journals Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz

2016 ◽  
Vol 587 ◽  
pp. A37 ◽  
Author(s):  
C. Rauch ◽  
E. Ros ◽  
T. P. Krichbaum ◽  
A. Eckart ◽  
J. A. Zensus ◽  
...  
Keyword(s):  
Radio Source ◽  
Near Infrared ◽  
Galactic Center ◽  
Sgr A

scholarly journals Class I methanol masers in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 147-149
Author(s):  
L. O. Sjouwerman ◽  
Y. M. Pihlström
Keyword(s):  
Galactic Center ◽  
Class I ◽  
Large Array ◽  
Maser Emission ◽  
Very Large Array ◽  
Sagittarius A ◽  
Current Location ◽  
Theoretical Predictions ◽  
Methanol Masers ◽  
Sgr A

AbstractWe report on the detection of 36 and 44 GHz Class I methanol (CH3OH) maser emission in the Sagittarius A (Sgr A) complex with the Karl G. Jansky Very Large Array (VLA). These VLA observations show that the Sgr A complex harbors at least three different maser tracers of shocked regions in the radio regime. The 44 GHz masers correlate with the positions and velocities of previously detected 36 GHz CH3OH masers, but less with 1720 MHz OH masers. Our detections agree with theoretical predictions that the densities and temperatures conducive for 1720 MHz OH masers may also produce 36 and 44 GHz CH3OH maser emission. However, many 44 GHz masers do not overlap with 36 GHz methanol masers, suggesting that 44 GHz masers also arise in regions too hot and too dense for 36 GHz masers to form. This agrees with the non-detection of 1720 MHz OH masers in the same area, which are thought to be excited under even cooler and less dense conditions. We speculate that the geometry of the 36 GHz masers outlines the current location of a shock front.

scholarly journals THE UNUSUAL GALACTIC CENTER RADIO SOURCE N3

2016 ◽  
Vol 826 (2) ◽  
pp. 218 ◽  
Author(s):  
D. A. Ludovici ◽  
C. C. Lang ◽  
M. R. Morris ◽  
R. Mutel ◽  
E. A. C. Mills ◽  
...  
Keyword(s):  
Radio Source ◽  
Galactic Center

scholarly journals 3D moving mesh simulations of Galactic center cloud G2

2013 ◽  
Vol 9 (S303) ◽  
pp. 318-319 ◽  
Author(s):  
P. C. Fragile ◽  
P. Anninos ◽  
S. D. Murray
Keyword(s):  
Feeding Rate ◽  
Galactic Center ◽  
Equations Of State ◽  
Accretion Rate ◽  
Three Dimensional ◽  
Light Curves ◽  
Moving Mesh ◽  
Future Evolution ◽  
Sgr A ◽  
Gas Cloud

AbstractUsing three-dimensional, moving-mesh simulations, we investigate the future evolution of the recently discovered gas cloud G2 traveling through the galactic center. From our simulations we expect an average feeding rate onto Sgr A* in the range of (5−19) × 10−8M⊙ yr−1 beginning in 2014. This accretion varies by less than a factor of three on timescales ∼ 1 month, and shows no more than a factor of 10 difference between the maximum and minimum observed rates within any given model. These rates are comparable to the current estimated accretion rate in the immediate vicinity of Sgr A*, although they represent only a small (< 10%) increase over the current expected feeding rate at the effective inner boundary of our simulations (racc = 750 RS ∼ 1015 cm). We also explore multiple possible equations of state to describe the gas. In examining the Br-γ light curves produced from our simulations, we find that all of our isothermal models predict significant (factor of 10) enhancements in the luminosity of G2 as it approaches pericenter, in conflict with observations. Models that instead allow the cloud to heat as it is compressed do better at matching observations.

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