# FAST ultra-wideband observation of abnormal emission-shift events of PSR B0919+06

## TL;DR

This study uses FAST ultra-wideband observations to analyze abnormal emission-shift events in PSR B0919+06, revealing frequency-dependent behaviors, profile variations, and potential underlying mechanisms of the phenomenon.

## Contribution

First ultra-wideband simultaneous observations of PSR B0919+06's abnormal events, providing new insights into their frequency dependence and profile variations.

## Key findings

- Abnormal events become less apparent at lower frequencies.
- Profile shifts correlate with abnormal events, indicating a possible relationship.
- A slow-drifting mode exists between major abnormal events.

## Abstract

PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still under investigation. In this paper, we present our ultra-wideband observation of this pulsar using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), with simultaneous measurements in the frequency ranges 280-780 MHz and 1250-1550 MHz. We have identified three abnormal events, each of which becomes less apparent as the frequency decreases. At 1400 MHz, the averaged profile slightly shifted after the first and third abnormal events, implying a relationship between abnormal event and profile variation. We also found a linear trend in the left-edge position of the averaged profiles between the first and third event as well as after the third event, suggesting the existence of a slow-drifting mode between the two major events. The second event has a comparatively small shift in phase and is thus categorized as a `small flare state'. During the third event, a sequence of approximately nine pulses was seen to significantly weaken in all frequency bands, likely associated with the pseudo-nulling observed at 150 MHz. A three-component de-composition analysis of the normal averaged profiles shows that the trailing component is dominant at our observing frequencies, while the centre component has a comparatively steeper spectrum. We found the overall flux density in an abnormal event to slightly differ from that in an ordinary state, and the difference shows a frequency dependence. A comparison of the normal, abnormal and dimmed averaged profile indicates that the leading component is likely to be stable in all states.