  We report detailed investigation of nulling and drifting behavior of two
pulsars PSRs J1741-0840 and J1840-0840 observed from the Giant Meterwave Radio
Telescope at 625 MHz. PSR J1741-840 was found to show nulling fraction (NF) of
around 30(5)% while PSR J1840-0840 was shown to have NF of around 50(6)%. We
measured drifting behavior from different profile components in PSR J1840-0840
for the first time with the leading component showing drifting with 13.5(0.7)
periods while the weak trailing component showed drifting of around 18(1)
periods. Large nulling do hamper accuracy of these quantities derived using
standard Fourier techniques. A more accurate comparison was drawn from
driftband slopes, measured after sub-pulse modeling. These measurements
revealed interesting sporadic and irregular drifting behavior in both pulsars.
We conclude that the previously reported different drifting periodicities in
the trailing component of PSR J1741-0840 is likely due to the spread in these
driftband slopes. We also find that both components of PSR J1840-0840 show
similar driftband slopes within the uncertainties. Unique nulling-drifting
interaction is identified in PSR J1840-0840 where, in most occasions, the
pulsar tends to start nulling after what appears to be an end of a driftband.
Similarly, when the pulsar switches back to an emission phase, in most
occasions it starts at the beginning of a new driftband in both components.
Such behaviors have not been detected in any other pulsars to our knowledge. We
also found that PSR J1741-0840 seems to have no memory of its previous burst
phase while PSR J1840-0840 clearly exhibits memory of its previous state even
after longer nulls for both components. We discuss possible explanations for
these intriguing nulling-drifting interactions seen in both pulsars based on
various pulsar nulling models.
