Decrease of Flux Density of the Radio Source Cassiopeia A at 81.5 MHz

Nature ◽  
1969 ◽  
Vol 223 (5211) ◽  
pp. 1139-1140 ◽  
Author(s):  
P. F. SCOTT ◽  
J. R. SHAKESHAFT ◽  
M. A. SMITH
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Cassiopeia A

Secular Variation of the Flux Density of the Radio Source Cassiopeia A

Nature ◽  
1961 ◽  
Vol 190 (4777) ◽  
pp. 705-706 ◽  
Author(s):  
D. S. HEESCHEN ◽  
B. L. MEREDITH
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Secular Variation ◽  
Cassiopeia A

Variation in the Flux Density of the Radio Source Cassiopeia-A During the Period 2007-2015

Astrophysics ◽  
2017 ◽  
Vol 60 (1) ◽  
pp. 83-89
Author(s):  
R. M. Martirosyan ◽  
A. G. Gulyan ◽  
G. A. Pirumyan ◽  
S. A. Sargsyan ◽  
G. S. Avetisyan
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Cassiopeia A

Secular Variation of the Flux Density of the Radio Source Cassiopeia A

Nature ◽  
1961 ◽  
Vol 189 (4764) ◽  
pp. 561-562 ◽  
Author(s):  
J. A. HÖGBOM ◽  
J. R. SHAKESHAFT
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Secular Variation ◽  
Cassiopeia A

Note on a periodic intensity variation of the radio source Cassiopeia-A

Astrophysics ◽  
2007 ◽  
Vol 50 (2) ◽  
pp. 203-206 ◽  
Author(s):  
R. M. Martirossyan ◽  
A. G. Goulyan ◽  
V. A. Sanamyan ◽  
H. A. Piroumyan
Keyword(s):  
Radio Source ◽  
Intensity Variation ◽  
Cassiopeia A ◽  
Periodic Intensity

The Radio Source Cassiopeia A

Nature ◽  
1966 ◽  
Vol 209 (5030) ◽  
pp. 1339-1340 ◽  
Author(s):  
R. MINKOWSKI
Keyword(s):  
Radio Source ◽  
Cassiopeia A

scholarly journals VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

2018 ◽  
Vol 616 ◽  
pp. A128 ◽  
Author(s):  
N. Herrera Ruiz ◽  
E. Middelberg ◽  
A. Deller ◽  
V. Smolčić ◽  
R. P. Norris ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Lower Limit ◽  
High Sensitivity ◽  
Host Galaxy ◽  
Radio Sources ◽  
Source Population ◽  
Star Forming ◽  
Brightness Temperatures ◽  
Long Baseline

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40−75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

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.

Optical Identification of the Strong Radio Source PKS 0511-48

1981 ◽  
Vol 4 (2) ◽  
pp. 187-189 ◽  
Author(s):  
J. G. Robertson ◽  
R. M. Smith
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Optical Identification ◽  
Low Frequencies ◽  
Complex Source ◽  
Optical Identifications

The radio source PKS 0511-48 is among the hundred strongest southern sources at low frequencies. It was catalogued in the Parkes survey (Ekers 1969) and mapped with the Molonglo Cross at 408 MHz by Schilizzi and McAdam (1975) with a resolution of 2′ .6 arc. It appeared in that work as a complex source, with an integrated flux density of 8.8 Jy. A search for optical identifications was made by Tritton and Schilizzi (1973), but none were found to a level of B ~ 19. We have inspected the field on the ESO B survey film, and find a group of ~ 20 faint galaxies (approximately 19-20 mag).

scholarly journals 24. The 400 Mc./s. flux from Cassiopeia A

1957 ◽  
Vol 4 ◽  
pp. 154-154
Author(s):  
Ch. L. Seeger
Keyword(s):  
Ambient Temperature ◽  
Flux Density ◽  
Boiling Point ◽  
Density Measurement ◽  
The Other ◽  
Noise Power ◽  
Pure Nitrogen ◽  
Cassiopeia A ◽  
Pyramidal Horn ◽  
Flux Density Measurement

The first trial of equipment designed for 400 Mc./s. absolute flux density measurement was completed just prior to this symposium. Using the midday sun, the gain of a 7·5 metre Würzburg (equipped with a TE°11 circular wave-guide feed) was found by comparison with an ‘optimum’ pyramidal horn of 20·2 square wave-lengths aperture. Cable losses and signal powers were measured against the available noise power from two co-axial resistors, one at ambient temperature and the other stabilized at the boiling-point of pure nitrogen.

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