  We performed a detailed broadband spectral and timing analysis of a small
flaring event of ~120 ks in a narrow-line Seyfert 1 galaxy NGC 4051 using
simultaneous XMM-Newton and NuSTAR observations. The ~300 ks long NuSTAR
observation and the overlapping XMM-Newton exposure were segregated into
pre-flare, flare, and post-flare segments. During the flare, the NuSTAR count
rate peaked at 2.5 times the mean count rate before the flare. Using various
physical and phenomenological models, we examined the 0.3-50 keV X-ray
spectrum, which consists of a primary continuum, reprocessed emission, warm
absorber and ultra-fast outflows in different timescales. The mass of the
central black hole is estimated to be >1.32*10^5 solar mass from the spectral
analysis. The absence of correlation between flux in 6-7 keV and 10-50 keV
bands suggests different origins of the iron emission line and the Compton
hump. From the spectral analysis, we found that the reflection fraction drops
significantly during the flare, accompanied by an increase in the coronal
height above the disc. The spectrum became soft during the flare supporting the
"softer when brighter" nature of the source. After the alleviation of the
flare, the coronal height drops and the corona heats up. This indicates that
there could be inflation of the corona during the flare. We found no
significant change in the inner accretion disc or the seed photon temperature.
These results suggest that the flaring event occurred due to the change in the
coronal properties rather than any notable change in the accretion disc.
