The bright spiky emission of pulsar B0656+14

Abstract

We present a detailed study of the single radio pulses of PSR B0656+14, a pulsar also known to be a strong pulsed source of high-energy emission. Despite the extensive studies at high-energy wavelengths, there is little or no published work on its single-pulse behaviour in the radio band. In this report we rectify this omission. We have found that the shape of the pulse profile of PSR B0656+14 requires an unusually long timescale to achieve stability (over 25,000 pulses at 327 MHz). This instability is caused by very bright and narrow pulses with widths and luminosities comparable to those observed for the RRATs. Many pulses are bright enough to qualify as "giant pulses", but are broader than those usually meant by this term. At 327 MHz the brightest pulse was about 116 times brighter than the average pulse. Although the most powerful pulses peak near the centre of the profile, occasional sudden strong pulses are also found on the extreme leading edge of the profile. One of them has a peak flux of about 2000 times the average flux at that pulse longitude. No "break" in the pulse-energy distributions is observed, but nevertheless there is evidence of two separate populations of pulses: bright pulses have a narrow "spiky" appearance consisting of short quasi-periodic bursts of emission with microstructure, in contrast to the underlying weaker broad pulses. Furthermore, the spiky pulses tend to appear in clusters which arise and dissipate over about 10 periods. We demonstrate that the spiky emission builds a narrow and peaked profile, whereas the weak emission produces a broad hump, which is largely responsible for the shoulders in the total emission profiles at both high and low frequencies.