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The residual gain errors add to the systematics of the radio interferometricobservations. In case of the high dynamic range observations, these systematiceffects dominates over the thermal noise of the observation. In this work, weinvestigate the effect of time-correlated residual gain errors in theestimation of the power spectrum of the sky brightness distribution in highdynamic range observations. Particularly, we discuss a methodology to estimatethe bias in the power spectrum estimator of the redshifted 21-cm signal fromneutral hydrogen in the presence of bright extragalactic compact sources. Wefind, that for the visibility based power spectrum estimators, particularlythose use nearby baseline correlations to avoid noise bias, the bias in thepower spectrum arises mainly from the time correlation in the residual gainerror. The bias also depends on the baseline distribution for a particularobservation. Analytical calculations show that the bias is dominant for certaintypes of baseline pairs used for the visibility correlation. We performsimulated observation of extragalactic compact sources in the presence ofresidual gain errors with the GMRT like array and estimate the bias in thepower spectrum. Our results indicate that in order to estimate the redshifted21-cm power spectrum, better calibration techniques and estimator developmentare required.

Calibration Requirements for Epoch of Reionization 21-cm signal observations -- I. Effect of time-correlated gains