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Strong and weak pulsar radio emission due to thunderstorms and raindrops of particles in the magnetosphere

Nature Astronomy volume 7, pages 1235–1244 (2023)Cite this article

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Abstract

Pulsars radiate radio signals when they rotate. However, some old pulsars often stop radiating for some periods. The underlying mechanism remains unknown, as the magnetosphere during nulling phases is hard to probe due to the absence of emission measurements. Here we report the detection and accurate polarization measurements of sporadic, weak, narrow dwarf pulses detected in the ordinary nulling state of pulsar B2111+46 via the Five-Hundred-Meter Aperture Spherical radio Telescope. Further analysis shows that their polarization angles follow the average polarization angle curve of normal pulses, suggesting no change of the magnetic-field structure in the emission region in the two emission states. Whereas radio emission of normal individual pulses is radiated by a ‘thunderstorm’ of particles produced by copious discharges in regularly formed gaps, dwarf pulses are produced by one or a few ‘raindrops’ of particles generated by pair production in a fragile gap of this near-death pulsar.

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Fig. 1: FAST detection of a dwarf pulse in a series pulses of PSR B2111+46.
Fig. 2: Dwarf pulses detected in the nulling periods with very low energy.
Fig. 3: Dwarf pulses of PSR B2111+46 as a distinct population from the partial nulling and normal pulses.
Fig. 4: PA distribution of dwarf pulses compared with the data of normal pulses.
Fig. 5: Phase-resolved spectral index for two individual pulses and two dwarf pulses observed on 8 March 2022 by FAST.

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Data availability

Original FAST observational data are open source after the one-year protection for the high-priority usage by observers, according to the FAST data policy. The processed data presented in this paper can be download from http://zmtt.bao.ac.cn/GPPS/B2111/.

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Acknowledgements

This work made use of data from FAST. FAST is a Chinese national mega-science facility, built and operated by the National Astronomical Observatories, Chinese Academy of Sciences. The authors of this work have been supported by the Natural Science Foundation of China: numbers 11988101 and 11833009 and National SKA Program of China 2020SKA0120100.

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Authors and Affiliations

  1. National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China

    X. Chen, Y. Yan, J. L. Han, C. Wang, P. F. Wang, W. C. Jing, T. Wang, Z. L. Yang, W. Q. Su, N. N. Cai, J. Xu & D. J. Zhou

  2. School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, Beijing, China

    X. Chen, Y. Yan, J. L. Han, C. Wang, P. F. Wang, W. C. Jing, T. Wang, Z. L. Yang, W. Q. Su, N. N. Cai, W. Y. Wang, G. J. Qiao & D. J. Zhou

  3. CAS Key laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China

    J. L. Han, C. Wang, P. F. Wang & J. Xu

  4. Department of Astronomy, Peking University, Beijing, China

    K. J. Lee, R. X. Xu, W. Y. Wang & G. J. Qiao

  5. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China

    K. J. Lee, R. X. Xu & W. Y. Wang

  6. Nevada Center for Astrophysics, University of Nevada, Las Vegas, NV, USA

    B. Zhang

  7. Department of Physics and Astronomy, University of Nevada, Las Vegas, NV, USA

    B. Zhang

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Contributions

X.C. and Y.Y. processed all related data and noticed the dwarf pulses, and they contributed to this paper equally. J.L.H. supervised and coordinated the team work, pursued the nature of the dwarf pulses and took the responsibility for paper writing. P.F.W., C.W., W.C.J. and D.J.Z. contributed to different aspects of data processing. T.W., W.Y.W., Z.L.Y., W.Q.S., N.N.C., J.X., R.X.X., K.J.L., G.J.Q. and B.Z. joined the discussions and contributed to some parts of paper writing or plot-making.

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Correspondence to J. L. Han.

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Extended data

Extended Data Fig. 1 The pulses of PSR B2111+46 observed by FAST in the session on 2020-08-24.

The left-most panel is the train of individual pulses for 886 periods, with the mean profile shown in the bottom and the intensity of which is normalized using the peak value. The total energy of every individual pulse is plotted in the immediately right, so that the energy fluctuations are seen very clearly which show the two predominate peaks for both nulling and emission states in the number distributions in the bottom. A segment of the pulse stack is shown in grey for high quality individual pulses, with significant fluctuations of profile amplitude, in which normal individual pulses can be seen in the period No. 702-700, 696 and 680, partial nulling in the period No. 679, and dwarf pulses of the period No. 699 and 682. The detailed polarization profiles for 4 pulses are presented in the right 4 panels, each with total intensity I, linear polarization L and circular polarization V in the bottom subpanel and P A in the upper subpanel. The polarization profiles of the mean pulse are shown in dashed line in these subpanels for comparison. The error bar for PA is ± 1σ.

Extended Data Fig. 2 The pulses of PSR B2111+46 observed by FAST in the session on 2020-08-26.

The left-most panel is the train of individual pulses for 886 periods, with the mean profile shown in the bottom and the intensity of which is normalized using the peak value. The total energy of every individual pulse is plotted in the immediately right. A segment of the pulse stack is shown in grey for high quality individual pulses, with a dwarf pulse in the period No. 377 and partial nulling in the period No. 365. The detailed polarization profiles for 4 pulses are presented in the right 4 panels, each with total intensity I, linear polarization L and circular polarization V in the bottom subpanel and P A in the upper subpanel. The polarization profiles of the mean pulse are shown in dashed line in these subpanels for comparison. The error bar for PA is ± 1σ.

Extended Data Fig. 3 The pulses of PSR B2111+46 observed by FAST in the session on 2020-09-17.

The left-most panel is the train of individual pulses for 885 periods, with the mean profile shown in the bottom and the intensity of which is normalized using the peak value. The total energy of every individual pulse is plotted in the immediately right. A segment of the pulse stack is shown in grey for high quality individual pulses, with a dwarf pulse in the period No. 136 and partial nulling in the period No. 137. The detailed polarization profiles for 4 pulses are presented in the right 4 panels, each with total intensity I, linear polarization L and circular polarization V in the bottom subpanel and P A in the upper subpanel. The polarization profiles of the mean pulse are shown in dashed line in these subpanels for comparison. The error bar for PA is ± 1σ.

Extended Data Fig. 4 The pulses of PSR B2111+46 observed by FAST in the session on on 2022-03-08.

The left-most panel is the train of individual pulses for 7098 periods, with the mean profile shown in the bottom and the intensity of which is normalized using the peak value. The total energy of every individual pulse is plotted in the immediately right. A segment of the pulse stack is shown in grey for high quality individual pulses, with a dwarf pulse in period of No.5895 and two partial nullings in the period No. 5891 and 5897. The detailed polarization profiles for 4 pulses are presented in the right 4 panels, each with total intensity I, linear polarization L and circularpolarization V in the bottom subpanel and P A in the upper subpanel. The polarization profiles of the mean pulse are shown in dashed line in these subpanels for comparison. The error bar for PA is ± 1σ.

Extended Data Fig. 5 Examples of polarization profiles for two dwarf pulses and two strong individual pulses in high time resolution.

All of them are observed on 2022-03-08 by FAST with time resolution of 49.152 μs. Polarization profiles for two strong individual pulses are shown for their elongated central part in the next panel. Each rip in the profiles is real, well-significant above the noise fluctuations. These unrepresented details indicate that the observed individual pulses are an incoherent collection of many elementary pulses generated separately in the magnetosphere. The error bar for PA is ± 1σ. The intensity is scaled with the off-pulse fluctuations expressed by σbin.

Extended Data Fig. 6 Longitude distribution of dwarf pulses.

Longitude distribution of dwarf pulse locations are compared to the mean pulse profile indicated by the dash line. The bar length stands for dwarf pulse width, and the dots mark the peak locations in the longitude.

Extended Data Fig. 7 Pulsar period and period derivative (\({{{\rm{P}}}}-\dot{{{{\rm{P}}}}}\)) diagram and the location of PSR B2111+46 in the death valley.

The death lines are given for the curvature radiation in a dipole field (upper one) and an extremely curved field (lower one) in the vacuum gap model (sold lines) and the space- charged-limited flow model (dashed lines) given in44. All pulsar data are taken from the ATNF pulsar Catalogue32 (version 1.70). The background gray dashed and dotted lines stand for constant surface magnetic field strengths and characteristic ages, respectively.

Extended Data Fig. 8 Distributions for spectral indexes of three kinds of individual pulses.

All these pulses, including 5175 normal pulses, 199 partial nulling pulses and 67 dwarf pulses, are observed by FAST on 2022-03-08. The indexes are calculated for each individual pulse by using the on-pulse integrated intensity, and have an uncertainty less than 0.5.

Extended Data Fig. 9 The number distribution of phase-resolved spectral indexes.

Data of spectral indexes of all phase bins have an uncertainty less than 0.5 for all individual pulses observed by FAST on 2022-03-08, as shown in the upper subpanel, together with the mean polarization profile for understanding in the lower subpanel scaled with the peak value.

Extended Data Fig. 10 The phase shift distribution of polarization angles of 62 dwarf pulses.

The shift values are obtained by comparison of their PA to the mean PA curve at the longitude of dwarf pulses.

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Chen, X., Yan, Y., Han, J.L. et al. Strong and weak pulsar radio emission due to thunderstorms and raindrops of particles in the magnetosphere. Nat Astron 7, 1235–1244 (2023). https://doi.org/10.1038/s41550-023-02056-z

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