Discovery of a remarkable subpulse drift pattern in PSR B0818-41

We report the discovery of a remarkable subpulse drift pattern in the relatively less-studied wide profile pulsar B0818-41 using high-sensitivity Giant Metrewave Radio Telescope (GMRT) observations. We find simultaneous occurrences of three drift regions with two different drift rates: an inner region with steeper apparent drift rate flanked on each side by a region of slower apparent drift rate. Furthermore, these closely spaced drift bands always maintain a constant phase relationship. Though these drift regions have significantly different values for the measured P-2, the measured P-3 value is the same and equal to 18.3P(1). We interpret the unique drift pattern of this pulsar as being created by the intersection of our line of sight (LOS) with two conal rings on the polar cap of a fairly aligned rotator (inclination angle alpha similar to 11.), with an 'inner' LOS geometry (impact angle beta similar to -5 degrees.4). We argue that both rings have the same values for the carousel rotation periodicity P-4 and the number of sparks N-sp. We find that Nsp is 19-21 and show that it is very likely that P-4 is the same as the measured P-3, making it a truly unique pulsar. We present results from simulations of the radiation pattern using the inferred parameters, which support our interpretations and reproduce the average profile as well as the observed features in the drift pattern quite well.