Since 2005, we have carried out a series of observations with the GMRT/uGMRT (Giant Metrewave Radio Telescope) in the frequency range between 150 -610 MHz frequency. The ultimate goal is to detect the cosmological HI 21-cm signal from the epoch of reionization, and post reionization. Currently our major focus is to characterise the foreground signal emitted from our galaxy (diffuse synchrotron radiation) and extragalactic radio point/extended sources and understand various systematics in the context of the cosmological 21-cm signal detection. Recently, we have successfully carried out observations of the ELAIS-N1 field with the uGMRT. Below are the details:

1. Detailed study of the ELAIS N1 field with the uGMRT - I. Characterizing the 325 MHz foreground for redshifted 21 cm observations [Chakraborty et al, 2019];

We, for the first time, have statistically quantified the Galactic and extragalactic foreground sources in the ELAIS-N1 field in the form of the angular power spectrum using the newly developed Tapered Gridded Estimator (TGE) (Choudhuri et al, 2016, 2017). We have calibrated the data with and without direction-dependent calibration techniques. The statistical fluctuations in the diffuse Galactic synchrotron emission has been quantified as a power law of the form C_l =A l^-b. The best-fitting values of (A, b) are (62 ± 6 mK^2, 2.55 ± 0.3) and (48 ± 4 mK^2, 2.28 ± 0.4) for the direction-dependent and -independent calibration.

More results using the wide band (300-500 MHz) to be updated very soon. Plz visit again. 

2. Foreground measurements at 150 MHZ using TGSS observations [Choudhuri et al 2018]

We quantify the fluctuations of the diffuse Galactic synchrotron emission using visibility data for two of the fields observed by the TIFR GMRT Sky Survey (TGSS) using the Tapered Gridded Estimator (TGE) (Choudhuri et al, 2016, 2017). We find that the sky signal, after subtracting the point sources, is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 240≤ℓ≲500. More details can be found in the above link.

The table below summaries our earlier observations :

• The details of the above observations, data reduction and relevant statistics for the FIELD IV are discussed in Ali,Bharadwaj & Chengalur (2008).
• Details for the FIELD I, II, III can be found in Ghosh, Bharadwah, Ali & Chengalur (2012)

1. Multi-frequency Angular Power Spectrum (MAPS): We have measured the multi-frequency angular power spectrum (MAPS) Cℓ(∆ν) from the initial data from the FIELD IV. We have found that the MAPS for the total signal varies in the range between 5 × 10^3 mK^2 to 2 × 10^4 mK^2 across 700 ≤ ℓ ≤ 2 × 10^4 and ∆ν ≤ 2.5 MHz, which is consistent with model predictions where point sources are the most dominant foreground component. We find that the measured Cℓ(∆ν) from the initial and residual visibility data do not show a smooth ∆ν dependence, which poses a severe difficulty for continuum foreground removal using polynomial fitting. The estimated Cℓ(∆ν) seems to be much more sensitive to calibration errors (Ali,Bharadwaj & Chengalur (2008)).

2. Differential Source counts: We have used FIELD I, which has a rms noise of 1.3 mJy/Beam, to study the properties of the radio source population to a limiting flux of 9 mJy. The differential source count is well fitted with a single power law of slope −1.6. We find that there is no evidence for flattening of the source counts towards lower flux densities which suggests that source population is dominated by the classical radio-loud Active Galactic Nucleus (AGN) (Ghosh, Bharadwah, Ali & Chengalur (2012)).

3. Measurements of Diffuse Galactic emission: The diffuse Galactic emission is revealed after the point sources with ≥ 9 mJy are subtracted out from FIELD I . We find Cℓ ∝ ℓ ^−2.34 for 253 ≤ ℓ ≤ 800 which is characteristic of the Galactic synchrotron radiation measured at higher frequencies and larger angular scales. We estimate the fluctuations in the Galactic synchrotron emission to be q ℓ(ℓ + 1)Cℓ/2π ≃ 10 K at ℓ = 800 (θ > 10′ ). The measured Cℓ is dominated by the residual point sources and artifacts at smaller angular scales where Cℓ ∼ 103 mK2 for ℓ > 800 (Ghosh, Bharadwah, Ali & Chengalur (2012)).