Short-Term Variability of Sagittarius A* at Millimeter Wavelengths

AbstractWe present preliminary results from the observations of the Galactic Center compact source, Sgr A* at 3 and 2 millimeter wavelengths using the Nobeyama Millimeter Array to monitor flux density variations on timescales shorter than a month. Such high spatial resolution observations at millimeter wavelengths are important to shed more light on the origin of the variability and the nature of this compact source. Our observations indicate the flux density varies at least by ~30% in one to two weeks at 3 mm.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308019078 ◽

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.

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A search for short-term variability of Sagittarius A∗ at Millimeter wavelengths

Advances in Space Research ◽

10.1016/s0273-1177(99)00251-3 ◽

1999 ◽

Vol 23 (5-6) ◽

pp. 977-980 ◽

Cited By ~ 10

Author(s):

A Miyazaki ◽

T Tsutsumi ◽

M Tsuboi

Keyword(s):

Short Term ◽

Sagittarius A ◽

Millimeter Wavelengths ◽

Short Term Variability

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Detection of relativistic effects on the S2 orbit with GRAVITY

Proceedings of the International Astronomical Union ◽

10.1017/s174392131601245x ◽

2016 ◽

Vol 11 (S322) ◽

pp. 25-30

Author(s):

Marion Grould ◽

Frédéric H. Vincent ◽

Thibaut Paumard ◽

Guy Perrin

Keyword(s):

Second Generation ◽

Galactic Center ◽

Relativistic Effects ◽

Compact Source ◽

Sagittarius A ◽

Sgr A

AbstractThe second generation instrument of the VLTI, GRAVITY, is expected to reach an astrometric accuracy of about 10 μas. It will thus possible to probe the spacetime close to the compact source Sagittarius A* (Sgr A*) at the Galactic Center by using accurate astrometric observations of the second closest star to the Galactic Center, S2. In particular, we show that combining GRAVITY and spectrograph instruments will allow us to detect several relativistic effects such as pericenter advance or the Lense-Thirring effect.

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Class I methanol masers in the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000416 ◽

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.

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How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa016 ◽

2020 ◽

Vol 72 (3) ◽

Author(s):

Masato Tsuboi ◽

Yoshimi Kitamura ◽

Takahiro Tsutsumi ◽

Ryosuke Miyawaki ◽

Makoto Miyoshi ◽

...

Keyword(s):

Galactic Center ◽

Three Dimensional ◽

Line Of Sight ◽

Recombination Line ◽

Intermediate Mass ◽

Ionized Gas ◽

Sagittarius A ◽

Projection Distance ◽

Spectroscopic Information ◽

Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

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Observations of the Quiet Sun with 6″ Resolution

Symposium - International Astronomical Union ◽

10.1017/s0074180900036627 ◽

1980 ◽

Vol 86 ◽

pp. 53-55

Author(s):

M. R. Kundu ◽

A. P. Rao ◽

F. T. Erskine ◽

J. D. Bregman

Keyword(s):

High Resolution ◽

Radio Emission ◽

Transition Region ◽

Spatial Resolution ◽

Radio Telescope ◽

Solar Radio ◽

High Spatial Resolution ◽

Solar Radio Emission ◽

Quiet Sun ◽

Millimeter Wavelengths

Solar radio emission at centimeter and millimeter wavelengths originates in the chromosphere and transition region and is a useful probe for the temperature and density in these regions. High spatial resolution observations of the quiet sun provide valuable information on the structure of the solar atmosphere. We have performed high resolution (~ 6″ (E-W) x 15″ (N-S)) observations at 6 cm with the Westerbork Synthesis Radio Telescope (WSRT) in June 1976 in order to search for the radio analog of the supergranulation network and to study the extent and symmetry of limb brightening. The use of the WSRT for high spatial resolution solar mapping has been described by Bregman and Felli (1976), Kundu et al. (1977), and others.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900187042 ◽

1989 ◽

Vol 136 ◽

pp. 535-541 ◽

Cited By ~ 3

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.

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Class I Methanol Masers in the Galactic Center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312007508 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 449-454

Author(s):

Loránt O. Sjouwerman ◽

Ylva M. Pihlström

Keyword(s):

Galactic Center ◽

Class I ◽

Large Array ◽

Maser Emission ◽

Very Large Array ◽

Sagittarius A ◽

Wave Radio ◽

Theoretical Predictions ◽

Methanol Masers ◽

Sgr A

AbstractWe report on 36 and 44 GHz Class I methanol (CH3OH) maser emission in the Sagittarius A (Sgr A) region with the Expanded Very Large Array (EVLA). At least three different maser transitions tracing shocked regions in the cm-wave radio regime can be found in Sgr A. 44 GHz masers correlate with the positions and velocities of 36 GHz CH3OH masers, but the methanol masers correlate less with 1720 MHz OH masers. Our results 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 cooler or denser conditions. We speculate that the geometry of the bright 36 GHz masers in Sgr A East outlines the location of a SNR shock front.

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