SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 62, Issue 5: 959504(2019) https://doi.org/10.1007/s11433-018-9358-8

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

Ye-Zhao Yu1,2,*, Bo Peng1,*, Kuo Liu1,3, Lin Wang1,2, Meng Yu1,
• AcceptedJan 19, 2019
• PublishedMar 13, 2019
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### 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 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 events 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.

### Acknowledgment

This work made use of the data from the FAST telescope (Five-hundred-meter Aperture Spherical radio Telescope). FAST is a Chinese national mega-science facility, built and operated by the National Astronomical Observatories, Chinese Academy of Sciences. This work was supported by the National Natural Science Foundation of China (Grant Nos. 11673031, 11703048, and U1731238), and the Open Project Program of the Key Laboratory of FAST, NAOC. Kuo Liu acknowledges the financial support by the European Research Council for the ERC Synergy Grant BlackHoleCam (Grant No. 610058), the FAST FELLOWSHIP from Special Funding for Advanced Users, budgeted and administrated by Center for Astronomical Mega-Science, Chinese Academy of Sciences (CAMS), and the MPG-CAS Joint Project “Low-Frequency Gravitational Wave Astronomy and Gravitational Physics in Space”.

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• Figure 1

(Color online) The three abnormal events identified in our observation. Panels in the same row show the same abnormal event in different frequency bands. Panels in the same column belong to the same frequency band, for which the centre frequency is marked at the top. Pulses between red dashed lines belong to the abnormal event, while the range constrained by the red solid lines are the regions with the “most-shifted” pulses.

• Figure 2

An example showing the definitions of $L_{\rm~50}$, $R_{\rm~50}$, and $W_{\rm~50}$. The black solid line shows a normalised integrated profile of PSR B0919$+$06.

• Figure 3

(Color online) Measurements of $L_{\rm~50}$, $R_{\rm~50}$, and $W_{\rm~50}$ from twenty-period sub-integrations are shown in the upper, middle and lower panels, respectively. The blue dashed lines represent the overall mean values. The red lines in the upper panel are linear fits to the $L_{\rm~50}$ values in three intervals: before the first event, between the first and third event, and after the third event. The obtained slopes are in order, $(-0.62\pm~2.28)\times10^{-4}$, $(2.96\pm~0.755)\times~10^{-4}$, and $(7.02\pm~1.74)\times~10^{-4}^\circ/P_{0}$, where $P_{\rm~0}$ is the pulse period.

• Figure 4

(Color online) Averaged profiles for normal, obvious pulse-phase shifted and dimmed pulses. The different panels display profiles in different frequency bands with the centre frequency and bandwidth (BW) marked at the top right. Black solid lines are the profiles averaged over individual pulses excluding those between the red dashed lines in Figure 1. The red solid lines are averaged profiles of the most-shifted pulses, which are in the range between the red solid lines in Figure 1. Averaged profiles of the dimmed pulses in the third abnormal pulses are plotted using blue solid lines. The zero intensity in each panel is indicated by a black dotted line. The de-composition results of the normal profile at each frequency band are shown in black dash-dotted lines for the profile components and as a black dashed line for the whole profile.

• Table 1   Pulse numbers of the abnormal events in our observation
 Event No. Entire event pulse No. Most-shifted pulse No. 1 930-1030 945-980 2 1490-1530 1500-1520 3 2885-2940 2900-2925

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