GMRT observations of a sample of extragalactic radio sources at 618 MHz
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GMRT observations of a sample of
extragalactic radio sources at 618 MHz
Assoc. Prof Somanah R
University of Mauritius
Dr. Oozeer Nadeem
HartRAO
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OutlineLow frequency survey
The Mauritius Radio Telescope
Our sample
GMRT observations
Preliminary Analysis & Results
Conclusion
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Low frequency survey
utility in identifying classes of objects that can be observed at other wavelengths
less affected by optical depth and beaming provides samples with an isotropic source distribution.
particular interest for finding radio galaxies, especially those at large redshifts.
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AGN
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Analytical model of FRII source
Q - energy supplied per unit timeU - energy densityr - distance frome coreAssume density IGM = k r - α
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The Mauritius Radio Telescope(MRT)
T-shaped Fourier synthesis non-coplanar array
2048 m long East-West (EW) arm
880 m long North-South (NS) arm
operating at 151.5 Mhz.
EW - 1024 fixed helices arranged in 32 groups at the same height but the different groups are at not co-planar.
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Elements – Helical antenna
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MRT layout
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DATA processing steps at MRT
Data Selection
Calibration
Fourier Transform
Deconvolution
Source extraction
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Dirty Image
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CLEANed image
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Galactic centre at 151.5 MHz
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SNRs in the galactic plane
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VELA SNR
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Extragalactic radio sources from MRT survey
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Spectra
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Giant Metre wave radio Telescope
Pune India 30 parabolic mesh grid
dish of 45m diameter each
Y-shaped Shortest spacing 60m
(central square) Longest spacing 25 km
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GMRT follow upSample
selected from the MRC using similar criteria as the MRC/1Jy sample 14h04m < RA < 20h20m
-30o < dec < -20o
No of sources 117 sources Frequency 618 Mhz Snapshots 3 x 15 min each
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Sample Region
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MRC 1404-209 MRC 1947-284
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MRC 1410-298 MRC 1421-272
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Spectra of some sources
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Results
By considering the spectral index a of the sources in the MRC/1Jy-B sample (107 sources), between 1400 MHz and the 408 MHz: 27.3% of the sources show ultra steep spectrum 67.3% show steep spectrum features and remaining, 4.6% were flat spectrum sources.
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Morphology
41% - singles or unresolved, 49% - apparent double structures 5% - triple sources 5% - complex structures.
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MRC 1925-296