Browsing by Author "Konar, C."

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Multifrequency study of giant radio sources I. Low-frequency Gaint Metrewave Radio Telescope observations of selected sources
(2007-09-27) Konar, C.; Jamrozy, M.; Saikia, D. J.; et al.
We present low-frequency observations with the Giant Metrewave Radio Telescope (GMRT) of a sample of giant radio sources (GRSs), and high-frequency observations of three of these sources with the Very Large Array (VLA). From multifrequency observations of the lobes we estimate the magnetic ﬁeld strengths using three diﬀerent approaches, and show that these diﬀer at most by a factor of ∼3. For these large radio sources the inverse-Compton losses usually dominate over synchrotron losses when estimates of the classical minimum energy magnetic ﬁeld are used, consistent with earlier studies. However, this is often not true if the magnetic ﬁelds are close to the values estimated using the formalism of Beck & Krause. We also examine the spectral indices of the cores and any evidence of recurrent activity in these sources. We probe the environment using the symmetry parameters of these sources and suggest that their environments are often asymmetric on scales of ∼1 Mpc, consistent with earlier studies.
Multifrequency study of giant radio sources II. Spectral ageing analysis of the lobes of selected sources
(2007-12-02) Jamrozy, M.; Konar, C.; Machalski, J.; et al.
Multifrequency observations with the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA) are used to determine the spectral breaks in consecutive strips along the lobes of a sample of selected giant radio sources (GRSs) in order to estimate their spectral ages. The maximum spectral ages estimated for the detected radio emission in the lobes of our sources range from ∼6 to 36 Myr with a median value of ∼20 Myr using the classical equipartition ﬁelds. Using the magnetic ﬁeld estimates from the Beck & Krause formalism the spectral ages range from ∼5 to 38 Myr with a median value of ∼22 Myr. These ages are signiﬁcantly older than smaller sources. In all but one source (J1313+6937) the spectral age gradually increases with distance from the hotspot regions, conﬁrming that acceleration of the particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero spectral ages in the hotspots, as is the case in earlier studies of smaller sources. This is likely to be largely due to contamination by more extended emission due to relatively modest resolutions. The injection spectral indices range from ∼0.55 to 0.88 with a median value of ∼0.6. We discuss these values in the light of theoretical expectations, and show that the injection spectral index appears to be correlated with luminosity and/or redshift as well as with linear size.