2020ApJ...889..133B

Periodic modulations are seen in normal pulsars (P > 0.1 s) over timescales ranging from a few seconds to several minutes. Such modulations have usually been associated with the phenomenon of subpulse drifting. A number of recent studies have shown subpulse drifting to exhibit very specific physical characteristics: (i) drifting is seen only in conal components of the pulse profile and is absent in central core emission; (ii) drifting pulsars are distributed over a narrow range of spin-down energy loss ({dot}E), where pulsars with {dot}E< 2 x 10³² erg s^–1 show this behavior; and (iii) drifting periodicity (P₃) is anti-correlated with {dot}E, such that pulsars with lower values of {dot}E tend to have longer P₃. These detailed characterizations of drifting behavior, on the other hand, also revealed the presence of other distinct periodic modulations, which can be broadly categorized into two types, periodic nulling, and periodic amplitude modulation. In contrast to drifting, these periodic phenomena are seen across the entire profile in both the core and conal components simultaneously and are not restricted to any specific {dot}E range. In this work we have assembled an exhaustive list of around 70 pulsars that show such periodic modulations, 22 of which were newly detected using observations from the Giant Meterwave Radio Telescope and the remaining compiled from past publications. The presence of such a significant group in the pulsar population suggests periodic modulations to be newly emergent phenomena in pulsars, with a physical origin that is distinct from that of subpulse drifting.