Towards 21-cm intensity mapping at z=2.28 with uGMRT using the tapered gridded estimator - IV. Wide-band analysis

We present a Wide-band tapered gridded estimator (TGE), which incorporates baseline migration and variation of the primary beam pattern for neutral hydrogen (H i) 21-cm intensity mapping (IM) with large frequency bandwidth radio-interferometric observations. Here we have analysed 394-494MHz (z = 1.9-2.6) uGMRT data to estimate the Multifrequency Angular Power Spectrum (MAPS) C-l(Delta nu) from which we have removed the foregrounds using the polynomial fitting (PF) and Gaussian Process Regression (GPR) methods developed in our earlier work. Using the residual C-l(Delta nu) to estimate the mean-squared 21-cm brightness temperature fluctuation Delta(2)(k), we find that this is consistent with 0 +/- 2 sigma in several k bins. The resulting 2 sigma upper limit Delta(2)(k)<(4.68)(2) mK(2) at k = 0.219 Mpc(-1) is nearly 15 times tighter than earlier limits obtained from a smaller bandwidth (24.4 MHz) of the same data. The 2 sigma upper limit [Omega(Hi) b(Hi)] <1.01 x 10(-2) is within an order of magnitude of the value expected from independent estimates of the H i mass density Omega(H i) and the H i bias b(H i). The techniques used here can be applied to other telescopes and frequencies, including similar to 150 MHz Epoch of Reionization observations.