scholarly journals Occultation Observations of the Galactic Center Region at 327 MHz

1974 ◽  
Vol 60 ◽  
pp. 499-509 ◽  
Author(s):  
G. Swarup ◽  
Gopal-Krishna ◽  
N. V. G. Sarma
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
The South ◽  
Electron Densities ◽  
Lunar Occultation ◽  
Contour Diagram ◽  
Center Region ◽  
Sgr A ◽  
Thermal Sources

Lunar occultation observations of the thermal sources Sgr B2, G0.9 + 0.1 and G1.1-0.1 at 327 MHz have been used to estimate their electron densities and temperatures. A new nonthermal source of size ∼ 10 × 5′ has been found about 7′ to the south of G1.1 − 0.1. A brightness contour diagram with a resolution of approximately 25 × 6′ is presented for the background radio emission near the sources Sgr A and Sgr B2.

scholarly journals The Radio Spectrum of Sgr A∗

1996 ◽  
Vol 169 ◽  
pp. 199-204
Author(s):  
Wolfgang J. Duschl ◽  
Harald Lesch
Keyword(s):  
Synchrotron Radiation ◽  
Radio Emission ◽  
Galactic Center ◽  
Radio Spectrum ◽  
Relativistic Electrons ◽  
Frequency Range ◽  
Center Region ◽  
Sgr A

We discuss the radio spectrum of Sgr A∗ in the frequency range between ≈ 1 GHz and ≈ 1 000 GHz, show that it can be explained by optically thin synchrotron radiation of relativistic electrons, and point toward a possible correlation between the spectrum of Sgr A∗ and larger-scale (≲ 50 pc) radio emission from the Galactic Center region.

scholarly journals Radio Continuum Emission from the Nuclei of Normal Galaxies

1980 ◽  
Vol 5 ◽  
pp. 177-184 ◽  
Author(s):  
J. M. van der Hulst
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Thermal Source ◽  
Very Large Array ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.

scholarly journals A Survey of Radio Recombination Line Emission From the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 159-166 ◽  
Author(s):  
K. R. Anantharamaiah ◽  
Farhad Yusef-Zadeh
Keyword(s):  
Galactic Center ◽  
Line Emission ◽  
Radio Continuum ◽  
Strong Line ◽  
Line Profiles ◽  
Ionized Gas ◽  
Center Region ◽  
Radio Recombination Line ◽  
Nonthermal Emission ◽  
Sgr A

Preliminary results of a systematic survey of H78α, H91α and H98β emission from the inner 40′ of the Galactic center region are presented. This region consists of two prominent continuum features, the Sgr A complex and the radio continuum Arc. In spite of much nonthermal emission arising from these two features, we detected strong line emission with large line widths in more than half of the observed 130 positions. Many of the detections are new, in particular −50 km s−1 ionized gas linking the Sgr A complex and the Arc, β line emission from GO.1+0.08 (the arched filaments), and α line emission from the loop-like structures which surround the non-thermal filaments near G0.2−0.05. We find that much of the detected lines are probably associated with the −50 km s−1 and the 20 km s−1 molecular clouds, known to lie near the Galactic center. We present line profiles of a number of Galactic center sources including Sgr B1, Sgr C and Sgr D.

scholarly journals OH in the Environment of Sgr A

1989 ◽  
Vol 136 ◽  
pp. 421-422
Author(s):  
Aa. Sandqvist ◽  
R. Karlsson ◽  
J. B. Whiteoak
Keyword(s):  
Radial Velocity ◽  
Shell Structure ◽  
Spiral Structure ◽  
Angular Resolution ◽  
Galactic Center ◽  
Absorption Lines ◽  
Molecular Gas ◽  
Center Region ◽  
Circumnuclear Disk ◽  
Sgr A

The 18-cm distribution of OH in the Galactic Center region near Sgr A has been mapped in all four of the 1612, 1665, 1667 and 1720 MHz OH absorption lines using the VLA with 4 arcsec angular resolution and 9 kms-1 velocity resolution. The OH gas at +50 and +20 kms-l is seen clearly in absorption against the shell structure of Sgr A East but not against the spiral structure of Sgr A West, possibly implying that this molecular gas lies between the two continuum components - behind Sgr A West and in front of Sgr A East. Inside the Circumnuclear Disk, there is a new neutral streamer which sweeps from the disk in towards Sgr A∗ as the observed radial velocity decreases from +78 to +16 kms-1. The streamer may have a negative-velocity counterpart on the opposite side of Sgr A∗.

scholarly journals Methanol masers in Galactic center region supernova remnants

2013 ◽  
Vol 9 (S303) ◽  
pp. 156-158
Author(s):  
Y. M. Pihlström ◽  
B. C. McEwen ◽  
L. O. Sjouwerman
Keyword(s):  
Molecular Clouds ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Cosmic Ray ◽  
Large Array ◽  
Very Large Array ◽  
Center Region ◽  
Cosmic Ray Acceleration ◽  
Methanol Masers ◽  
Sgr A

AbstractMethanol masers can be used to constrain densities and estimate kinematical distances to supernova remnants (SNRs), important parameters in cosmic ray acceleration models. With the goal of testing those models both for SNRs inside and outside the Galactic center (GC) region, we have used the Very Large Array to search for 36 GHz and 44 GHz methanol lines in Galactic SNRs. We report on the overall results of the maser search, and in particular the results of the GC SNR G1.4–0.1 in which more than 40 masers were found. They may be due to interactions between the SNR and at least two separate molecular clouds. Methanol masers were also detected in W28 and in Sgr A East.

scholarly journals NH3 Observations of the Sgr A Complex Region with the Nobeyama Millimeter Array

1989 ◽  
Vol 136 ◽  
pp. 371-377 ◽  
Author(s):  
S. K. Okumura ◽  
M. Ishiguro ◽  
E. B. Fomalont ◽  
Y. Chikada ◽  
T. Kasuga ◽  
...  
Keyword(s):  
Strong Interaction ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Molecular Gas ◽  
Kinetic Temperature ◽  
Complex Region ◽  
Physical Conditions ◽  
Center Region ◽  
Sgr A ◽  
The Continuum

We report NH3 observations of the Sgr A complex region including Sgr A West and the 20 km/s and 50 km/s molecular clouds (M–0.13–0.08 and M–0.02–0.07) using the Nobeyama Millimeter Array and the 45m telescope. NH3(1,1) and (2,2) lines were simultaneously observed to estimate the kinetic temperature. Our results suggest strong interaction between the molecular clouds and the continuum sources in the Sgr A complex. The interaction with continuum sources might be an important factor in determining the physical conditions of molecular gas in the galactic center region.

scholarly journals X-RAY DIAGNOSTICS OF GIANT MOLECULAR CLOUDS IN THE GALACTIC CENTER REGION AND PAST ACTIVITY OF Sgr A*

2011 ◽  
Vol 740 (2) ◽  
pp. 103 ◽  
Author(s):  
Hirokazu Odaka ◽  
Felix Aharonian ◽  
Shin Watanabe ◽  
Yasuyuki Tanaka ◽  
Dmitry Khangulyan ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
Giant Molecular Clouds ◽  
X Ray ◽  
Center Region ◽  
Sgr A ◽  
Past Activity

scholarly journals Molecular Fan of 360-pc Radius in the Galactic Center Region

1980 ◽  
Vol 87 ◽  
pp. 209-211
Author(s):  
Yasuo Fukui
Keyword(s):  
Molecular Complex ◽  
Galactic Center ◽  
Carbon Isotope Ratio ◽  
Central Line ◽  
Line Profiles ◽  
Center Region ◽  
On Line ◽  
Sgr A ◽  
Inner Region ◽  
Large Velocity Gradient

Molecular hydrogen of ≳108M⊙ exists in the galactic center region, as has been revealed by recent observations of molecular emission lines (see e.g. Oort 1977). In the inner region of most of the dominant emission features concentrate at and 0 km s-1 ≲v ≲100 km s-1 extremely unevenly with respect to the galactic center (see Fig. 1). As a model of the molecular complex we propose a fan of 360-pc radius whose pivot is at the center. The vertical angle of the fan is about 50° and the central line of the fan makes an angle of about 60° to the line of sight. Molecules in the fan are flowing out radially from the center with a velocity of 110-140 km s-1. The ℓ-v pattern of the fan model is superposed on the CO map in Fig. 1. The model can explain the whole structure of the molecular complex as well as several fine details such as asymmetry in emission line profiles (Fukui et al. 1979). As for Sgr A and Sgr B2, numerical calculations of molecular line profiles have been made by using the large velocity gradient approximation. The calculations show that the broad and asymmetric line profiles in the complex are well reproduced by the fan model. Further, an isotope effect on line shape is predicted, which will be useful as an observational check of the fan model. Additionally, the carbon isotope ratio 12C/13C in HCN and CO was estimated to be 10-20 in the Sgr A +50-km s-1 cloud.

First results from the NuSTAR “mini-survey” of the Galactic center region

2013 ◽  
Vol 9 (S303) ◽  
pp. 439-443
Author(s):  
Charles J. Hailey ◽  
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Pulsar Wind Nebulae ◽  
Telescope Array ◽  
X Ray ◽  
Center Region ◽  
First Results ◽  
Pulsar Wind ◽  
Sgr A

AbstractOne of the major science objectives of the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory is to perform the first sub-arcminute, hard X-ray survey of several square degrees of the Galactic plane, centered on a region near the Galactic center. As a prelude to the full survey, which began in July 2013, NuSTAR conducted a ∼500 ks, 0.3 × 0.4° “mini-survey” focused on Sgr A* and its environs. We present analysis of several candidate pulsar wind nebulae and filaments, which are revealed to be intense sources of X-ray emission at >10 keV.

scholarly journals Gamma-Ray Imaging of the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 581-585
Author(s):  
W. R. Cook ◽  
D. M. Palmer ◽  
T. A. Prince ◽  
S. M. Schindler ◽  
C. H. Starr ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Galactic Center ◽  
Coded Aperture ◽  
Center Region ◽  
Gamma Ray Imaging ◽  
The Galaxy ◽  
Γ Ray ◽  
Luminous Objects

The Caltech imaging γ-ray telescope was launched by balloon from Alice Springs, NT, Australia and performed observations of the galactic center during the period 12.62 to 13.00 April 1988 UT. The first coded-aperture images of the galactic center region at energies above 30 keV show a single strong γ-ray source which is located 0.7±0.1° from the galactic nucleus and is tentatively identified as 1E1740.7-2942. If the source is at the distance of the galactic center, it is one of the most luminous objects in the galaxy at energies from 35 to 200 keV.

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