GMRT observations of a sample of

extragalactic radio sources at 618 MHz

Assoc. Prof Somanah R

University of Mauritius

Dr. Oozeer Nadeem

HartRAO

OutlineLow frequency survey

The Mauritius Radio Telescope

Our sample

GMRT observations

Preliminary Analysis & Results

Conclusion

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.

AGN

Analytical model of FRII source

Q - energy supplied per unit timeU - energy densityr - distance frome coreAssume density IGM = k r - α

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.

Elements – Helical antenna

MRT layout

DATA processing steps at MRT

Data Selection

Calibration

Fourier Transform

Deconvolution

Source extraction

Dirty Image

CLEANed image

Galactic centre at 151.5 MHz

SNRs in the galactic plane

VELA SNR

Extragalactic radio sources from MRT survey

Spectra

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

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

Sample Region

MRC 1404-209 MRC 1947-284

MRC 1410-298 MRC 1421-272

Spectra of some sources

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.

Morphology

41% - singles or unresolved, 49% - apparent double structures 5% - triple sources 5% - complex structures.

MRC 1925-296