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

Abstract

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 P₂, the measured P₃ value is the same and equal to 18.3P₁. 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 angleα ~ 11°), with an 'inner' LOS geometry (impact angle β~-5°4). We argue that both rings have the same values for the carousel rotation periodicity P₄ and the number of sparks N_sp. We find that N_sp is 19-21 and show that it is very likely that P₄ is the same as the measured P₃, 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.