  It has recently been shown that the persistent emission of a neutron star
low-mass X-ray binary (LMXB) evolves during a thermonuclear (type-I) X-ray
burst. The reason of this evolution, however, is not securely known. This
uncertainty can introduce significant systematics in the neutron star radius
measurement using burst spectra, particularly if an unknown but significant
fraction of the burst emission, which is reprocessed, contributes to the
changes in the persistent emission during the burst. Here, by analyzing
individual burst data of AstroSat/LAXPC from the neutron star LMXB 4U 1728--34
in the soft state, we show that the burst emission is not significantly
reprocessed by a corona covering the neutron star. Rather, our analysis
suggests that the burst emission enhances the accretion disk emission, possibly
by increasing the accretion rate via disk. This enhanced disk emission, which
is Comptonized by a corona covering the disk, can explain an increased
persistent emission observed during the burst. This finding provides an
understanding of persistent emission components, and their interaction with the
thermonuclear burst emission. Furthermore, since burst photons are not
significantly reprocessed, non-burst and burst emissions can be reliably
separated, which is required to reduce systematic uncertainties in the stellar
radius measurement.
