scholarly journals The Galactic Centre at 408 MHz

1974 ◽  
Vol 60 ◽  
pp. 491-497 ◽  
Author(s):  
A. G. Little
Keyword(s):  
Brightness Temperature ◽  
Radio Telescope ◽  
The Other ◽  
Galactic Centre ◽  
Thermal Spectrum ◽  
Centre Region ◽  
Background Emission ◽  
The Cross ◽  
Sgr A ◽  
Galactic Background

The Molonglo radio telescope has been used to map the galactic centre region with a resolution of 2.9′. Although similar to microwave maps of comparable resolution, there are differences. In particular, the source G1.05-0.1 is not visible at microwaves, and the source G0.1-0.0 is not visible at 408 MHz. The flux values of all the other sources around Sgr A confirm that they are thermal and that the sources G0.7−0.0, G0.5 − 0.0, and G0.2−0.0 are optically thick.A more extensive galactic background survey with the cross shows the existence of a peak in the background emission with a brightness temperature of about 500 K at the galactic centre. This is probably the nonthermal source observed at 85 MHz. The higher-resolution observations of this map show the narrower, hotter region which appears on the microwave map and which surrounds Sgr A. This has a brightness temperature of 2100 K, which cannot be accounted for by a simple thermal spectrum extrapolated from microwaves.

scholarly journals Can we see pulsars around Sgr A⋆? The latest searches with the Effelsberg telescope.

2012 ◽  
Vol 8 (S291) ◽  
pp. 382-384
Author(s):  
R. P. Eatough ◽  
M. Kramer ◽  
B. Klein ◽  
R. Karuppusamy ◽  
D. J. Champion ◽  
...  
Keyword(s):  
Binary Systems ◽  
Compact Objects ◽  
Galactic Centre ◽  
Radio Waves ◽  
Test Bed ◽  
Radio Pulsars ◽  
Massive Black Hole ◽  
Centre Region ◽  
Sgr A ◽  
Temporal Broadening

AbstractRadio pulsars in relativistic binary systems are unique tools to study the curved space-time around massive compact objects. The discovery of a pulsar closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr A⋆, would provide a superb test-bed for gravitational physics. To date, the absence of any radio pulsar discoveries within a few arc minutes of Sgr A⋆ has been explained by one principal factor: extreme scattering of radio waves caused by inhomogeneities in the ionized component of the interstellar medium in the central 100 pc around Sgr A⋆. Scattering, which causes temporal broadening of pulses, can only be mitigated by observing at higher frequencies. Here we describe recent searches of the Galactic centre region performed at a frequency of 18.95 GHz with the Effelsberg radio telescope.

scholarly journals Low radio frequency spectrum of Sgr-A*

2016 ◽  
Vol 11 (S322) ◽  
pp. 54-55
Author(s):  
Subhashis Roy
Keyword(s):  
Radio Frequency ◽  
Flux Density ◽  
Frequency Spectrum ◽  
Spectral Index ◽  
Radio Telescope ◽  
Major Axis ◽  
Galactic Centre ◽  
Preliminary Results ◽  
Radio Frequency Spectrum ◽  
Sgr A

AbstractWe observed the Galactic centre (GC) region with the partially upgraded Giant Metrewave Radio Telescope (GMRT) using a wideband system in frequency ranges of 300– 500 MHz with 16 antennas. Preliminary results are presented here. Sgr-A* is clearly detected down to 450 MHz. Sgr-A West slowly disappears at lower frequencies across the band. By taking cross-cuts across the known major-axis of Sgr-A*, we measure its total flux density across the band to be 0.4 Jy consistent with what is expected from earlier results. It clearly indicates lack of absorption from Sgr-A West. Its spectral index is consistent with its higher frequency value of +0.3.

scholarly journals Acceleration of particles up to PeV energies at the galactic centre

2016 ◽  
Vol 12 (S324) ◽  
pp. 317-321
Author(s):  
Stefano Gabici ◽  
Felix A. Aharonian ◽  
Emmanuel Moulin ◽  
Aion Viana
Keyword(s):  
Black Hole ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Galactic Centre ◽  
Acceleration Of Particles ◽  
Supermassive Black Hole ◽  
Centre Region ◽  
Very High Energy ◽  
Sgr A ◽  
Very High

AbstractRecent very high energy observations of the galactic centre region performed by H.E.S.S. revealed the presence of a powerful PeVatron. This is the first of such objects detected, and its most plausible counterpart seems to be associated to Sgr A*, the supermassive black hole in the centre of our galaxy. The implications of this discovery will be discussed, in particular in the context of the problem of the origin of galactic cosmic rays.

scholarly journals X-Ray Observations of the Galactic Centre

1989 ◽  
Vol 136 ◽  
pp. 567-580 ◽  
Author(s):  
G. K. Skinner
Keyword(s):  
Energy Range ◽  
High Energy ◽  
Point Sources ◽  
Galactic Centre ◽  
X Rays ◽  
Diffuse Emission ◽  
Variable Source ◽  
X Ray ◽  
Centre Region ◽  
Sgr A

Observations of the galactic centre region in the photon energy range 2–500 keV are reviewed. Point sources, transients, bursts and a patch of apparently diffuse emission ~1° in extent have all been observed. The relatively detailed information obtained with the Einstein observatory just above the bottom edge of the x-ray window is starting to be supplemented by observations at higher photon energies. Although there is known to be a strong, variable, source of high energy x-rays somewhere in the region there is little reason to associate it with Sgr A West, which is detectable, but relatively weak, in the energy range below 30 keV where detailed measurements have been possible.

The Velocities of 6cm Recombination Line Emission originating near the Galactic Nucleus

1977 ◽  
Vol 3 (2) ◽  
pp. 150-152 ◽  
Author(s):  
F. F. Gardner ◽  
J. B. Whiteoak
Keyword(s):  
Radio Source ◽  
Strong Evidence ◽  
Line Emission ◽  
Hii Regions ◽  
Galactic Centre ◽  
Recombination Line ◽  
The Galaxy ◽  
Centre Region ◽  
Sgr A

Although it is well known that HII regions are present in the innermost regions of the Galaxy their kinematics are still not fully understood. In one study Pauls et al. (1976) surveyed with a beamwidth of 3′ arc the 10 GHz recombination line emission in directions within 15′ arc of the nuclear radio source Sgr A. They found that the emission velocities varied from position to position within the range -50 to + 50 km s-1but appeared to lack any overall pattern. In contrast, we have recently observed the recombination line emission from the galactic centre region with a beamwidth of 4′.5 arc, and find strong evidence of ordered motions near the galactic nucleus.

scholarly journals URAN, A Decameter Band VLBI System

1988 ◽  
Vol 129 ◽  
pp. 481-481
Author(s):  
S. J. Braude ◽  
L. N. Litvinenko ◽  
A. V. Megn
Keyword(s):  
Radio Telescope ◽  
Radio Astronomy ◽  
Phased Array ◽  
Phased Arrays ◽  
Broad Band ◽  
The Other ◽  
Interplanetary Plasma ◽  
High Level ◽  
Academy Of Sciences ◽  
Galactic Background

Until recently, regular interferometric measurements were not performed at decameter wavelengths. The reasons are well known, i.e., effects of the ionosphere and the interplanetary plasma, the inherently high level of interference and of the galactic background, and the necessity to have very large antennas. Yet, because of the considerable interest in such observations, the Ukrainian SSR Academy of Sciences has started a project aimed at the development and construction of a system of decameter band interferometers (project URAN, from the “Ukrainian Radio Interferometers of Academy of Sciences (Nauk)”). By 1989, the system will involve four interferometers with baseline lengths between 40 and 900 km. The basic instrument of all these is the N–S arm of the large UTR-2 radio telescope operated by the Institute of Radio Astronomy in Kharkov. The antenna is an electrically controlled phased array of broad band dipoles (total length about 1800 m). At the other sites, the antennas are smaller phased arrays (maximum length about 230 m) consisting of crossed dipoles.

scholarly journals Filaments in the Galactic Centre—with Special Reference to the ‘Snake’

2001 ◽  
Vol 18 (4) ◽  
pp. 431-442 ◽  
Author(s):  
Geoffrey V. Bicknell ◽  
Jianke Li
Keyword(s):  
Special Reference ◽  
Observational Data ◽  
Resonant Scattering ◽  
Alfven Waves ◽  
The Other ◽  
Alfvén Waves ◽  
Galactic Centre ◽  
Relativistic Electrons ◽  
The Galaxy ◽  
Centre Region

AbstractThe non-thermal filaments in the Galactic centre constitute one of the great mysteries of this region of the Galaxy. We summarise the observational data on these filaments and critically review the various theories which currently outnumber the observed filaments. We summarise our theory for the longest of these filaments, the Snake, and discuss the relevance of this model for the other filaments in the Galactic centre region. The physics involved in our model for the Snake involves much of the physics that has dominated the career of Professor Don Melrose. In particular, the diffusion of relativistic electrons in the Snake is determined from the theory of resonant scattering by Alfvén waves.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

Progress report on 21-cm observations at low latitude between longitudes (l 11) 0° and 66°

1967 ◽  
Vol 31 ◽  
pp. 177-179
Author(s):  
W. W. Shane
Keyword(s):  
Preliminary Report ◽  
Progress Report ◽  
Galactic Centre ◽  
Low Latitude ◽  
The Third ◽  
Introductory Lecture ◽  
Centre Region

In the course of several 21-cm observing programmes being carried out by the Leiden Observatory with the 25-meter telescope at Dwingeloo, a fairly complete, though inhomogeneous, survey of the regionl11= 0° to 66° at low galactic latitudes is becoming available. The essential data on this survey are presented in Table 1. Oort (1967) has given a preliminary report on the first and third investigations. The third is discussed briefly by Kerr in his introductory lecture on the galactic centre region (Paper 42). Burton (1966) has published provisional results of the fifth investigation, and I have discussed the sixth in Paper 19. All of the observations listed in the table have been completed, but we plan to extend investigation 3 to a much finer grid of positions.

Observations of the continuum near the galactic centre

1967 ◽  
Vol 31 ◽  
pp. 405
Author(s):  
F. J. Kerr
Keyword(s):  
Galactic Centre ◽  
The Past ◽  
Centre Region ◽  
The Continuum

A continuum survey of the galactic-centre region has been carried out at Parkes at 20 cm wavelength over the areal11= 355° to 5°,b11= -3° to +3° (Kerr and Sinclair 1966, 1967). This is a larger region than has been covered in such surveys in the past. The observations were done as declination scans.

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