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We study the connection between the variations in the far ultra-violet (FUV),near ultra-violet (NUV) and X-ray band emission from NGC 4051 using 4-days longAstroSat observations performed during 5-9 June 2016. NGC 4051 showed rapidvariability in all three bands with the strongest variability amplitude in theX-ray band ($F_{var} \sim 37\%$) and much weaker variability in the UV bands($F_{var} \sim 3 - 5\%$). Cross-correlation analysis performed usingInterpolated cross-correlation Functions (ICCF) and Discrete cross-correlationFunctions (DCF) revealed a robust correlation ($\sim 0.75$) between the UV andX-ray light curves. The variations in the X-ray band are found to lead those inthe FUV and NUV bands by $\sim 7.4{\rm~ks}$ and $\sim 24.2{\rm~ks}$,respectively. The UV lags favour the thermal disc reprocessing model. The FUVand NUV bands are strongly correlated ($\sim 0.9$) and the variations in theFUV band lead those in the NUV band by $\sim 13{\rm~ks}$. Comparison of the UVlags found using the AstroSat observations with those reported earlier and thetheoretical model for thermal reverberation time-lag suggests a possible changein either the geometry of the accretion disc/corona or the height of thecorona.

Detection of X-ray/UV delay in NGC 4051 using AstroSat observations