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Detection of Cyclotron Absorption in the Radio Emission of GPM 1839-10

Yunpeng Men, Ewan Barr, Yuanhong Qu, Csanad Horvath, Jinchen Jiang, Gregory Desvignes, Natasha Hurley-Walker, Michael Kramer, Rui Luo, Samuel J. McSweeney, Jason Wu

Abstract

GPM 1839-10 is an intriguing long-period radio transient (LPT), distinguished by its activity spanning at least three decades and its highly unusual emission characteristics. These features include orthogonal polarization mode (OPM) switches, down-drifting sub-structures, and distinct linear-to-circular polarization conversion behaviors. In this work, we present follow-up observations utilizing the FAST telescope at L-band, yielding a total of seven detected radio pulses. We find a consistent association between OPM switches and a decrease in polarized intensity. This feature strongly supports the hypothesis that the OPM switches are generated by the incoherent summation of OPMs. Our measured Rotation Measures (RMs) are consistent with previous observations, indicating that the magneto-ionic environment is stable. If the source is in a binary system, such stability suggests it may host a weakly magnetized companion. Crucially, we firstly observe clear evidence of a cyclotron absorption feature in one radio pulse, a signature rarely observed in radio sources. This feature allows us to infer that the magnetic field strength at the absorption site has a lower limit of tens of Gauss, which is necessary for the phenomenon to occur. This characteristic can be explained in a scenario where GPM 1839-10 possesses a weakly magnetized companion star.

Detection of Cyclotron Absorption in the Radio Emission of GPM 1839-10

Abstract

GPM 1839-10 is an intriguing long-period radio transient (LPT), distinguished by its activity spanning at least three decades and its highly unusual emission characteristics. These features include orthogonal polarization mode (OPM) switches, down-drifting sub-structures, and distinct linear-to-circular polarization conversion behaviors. In this work, we present follow-up observations utilizing the FAST telescope at L-band, yielding a total of seven detected radio pulses. We find a consistent association between OPM switches and a decrease in polarized intensity. This feature strongly supports the hypothesis that the OPM switches are generated by the incoherent summation of OPMs. Our measured Rotation Measures (RMs) are consistent with previous observations, indicating that the magneto-ionic environment is stable. If the source is in a binary system, such stability suggests it may host a weakly magnetized companion. Crucially, we firstly observe clear evidence of a cyclotron absorption feature in one radio pulse, a signature rarely observed in radio sources. This feature allows us to infer that the magnetic field strength at the absorption site has a lower limit of tens of Gauss, which is necessary for the phenomenon to occur. This characteristic can be explained in a scenario where GPM 1839-10 possesses a weakly magnetized companion star.
Paper Structure (5 sections, 6 equations, 7 figures, 1 table)

This paper contains 5 sections, 6 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observation and data processing
  3. Results
  4. Discussions
  5. Conclusions

Figures (7)

  • Figure 1: Radio pulses from GPM 1839$-$10 detected with FAST. (a) PA variation, (b) total intensity (black), linearly polarized intensity (red), and circularly polarized intensity (blue), and (c) dynamic spectra of the radio pulses are shown.
  • Figure 2: RMs and DMs as measured at different epochs. The values are measured using the observations in this work and previous work Hurley-Walker2023NatMen2025SciA.
  • Figure 3: Correlation between OPM switches and decreases in polarized intensity. (a) PA variation, (b) total intensity (black), linearly polarized intensity (red), and circularly polarized intensity (blue) are shown. The gray dashed lines mark the times when OPM switches coincide with decreased polarized intensity.
  • Figure 4: Faraday de-rotated dynamic spectra for the Stokes parameters (I, Q, U, and V) showing signatures of cyclotron absorption. The data are from the FAST observation conducted on 2024 December 4. Frequency-dependent decreases in total intensity (I) and linear polarization intensity (Q and U), accompanied by an increase in circular polarization (V), are detected.
  • Figure 5: Results of fitting the variation of total intensity (black dots), linearly polarized intensity (red dots), and circularly polarized intensity (blue dots) as a function of radio frequency over multiple 100 ms time intervals. The time range for each panel is indicated at the top right, with the start time corresponding to 133.2 s in Fig. \ref{['fig:down_drifting']}.
  • ...and 2 more figures