Abstract
Long-period radio transients are a new class of astronomical objects characterized by prolonged periods ranging from 18 min to 54 min. They exhibit highly polarized, coherent, beamed radio emission lasting only 10–100 s. The intrinsic nature of these objects is subject to speculation, with highly magnetized white dwarfs and neutron stars being the prevailing candidates. Here we present ASKAP J183950.5−075635.0, boasting the longest known period of this class at 6.45 h. It exhibits emission characteristics of an ordered dipolar magnetic field, with pulsar-like bright main pulses and weaker interpulses offset by about half a period that are indicative of an oblique or orthogonal rotator. This phenomenon, observed in a long-period radio transient, confirms that the radio emission originates from both magnetic poles and that the observed period corresponds to the rotation period. The spectroscopic and polarimetric properties of ASKAP J183950.5−075635.0 are consistent with a neutron star origin, and this object is a crucial piece of evidence in our understanding of long-period radio sources and their links to neutron stars.
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Data availability
The data that support the findings of this study are available via Zenodo at https://doi.org/10.5281/zenodo.14043008 (ref. 91). All the ASKAP data are publicly available at CASDA (https://research.csiro.au/casda/). The MeerKAT data used in this study are available via the SARAO archive (https://archive.sarao.ac.za) under project ID DDT-20240209-JL-01. The ATCA data used in this study are available via the Australia Telescope Online Archive (https://atoa.atnf.csiro.au/) under project ID C3363.
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Acknowledgements
We acknowledge M. Bailes and L. Spitler as co-principal investigators (co-PIs) of the CRACO LIEF grant LE210100107. We thank M. Bailes for supporting the PTUSE backend machine used in the MeerKAT observation. We also thank Z. Arzoumanian and the NICER team for their assistance in conducting X-ray observations. We are grateful to the ASKAP engineering and operations team for their assistance in supporting the observations. This scientific work uses data obtained from Inyarrimanha Ilgari Bundara/the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamaji People as the Traditional Owners and native title holders of the Observatory site. CSIRO’s ASKAP radio telescope is part of the Australia Telescope National Facility (https://ror.org/05qajvd42). Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Research Centre. Establishment of ASKAP, Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Research Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund. This manuscript makes use of data from MeerKAT (Project ID: DDT-20240209-JL-01) and ATCA (Project ID: C3363). We thank SARAO for the approval of the MeerKAT DDT request and the science operations and CAM/CBF and operator teams for their time and effort invested in the observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation (DSI). This scientific work uses data obtained from telescopes within the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. PTUSE was developed with support from the Australian SKA Office and Swinburne University of Technology. This work made use of the NASA Astrophysics Data System. T.M., Y.W.J.L., J.N.J.S., A.D. and R.M.S. acknowledge funding from the Australian Research Council Discovery Project DP 220102305. M.C. acknowledges support of an Australian Research Council Discovery Early Career Research Award (project no. DE220100819) funded by the Australian Government. D.L.K. is supported by NSF grant no. AST-1816492. Z.W. acknowledges support by NASA under award no. 80GSFC21M0002. Parts of this research were conducted by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), project no. CE230100016. R.M.S. and N.H.W. acknowledge support through Australian Research Council Future Fellowships FT190100155 and FT190100231, respectively. M.G. and C.W.J. acknowledge support through the Australian Research Council’s Discovery Projects funding scheme (DP210102103). The development of the CRACO system has been supported through Australian Research Council Linkage Infrastructure Equipment and Facilities grant no. LE210100107.
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Y.W.J.L. and M.C. drafted the manuscript with suggestions from co-authors and were the PIs of the MeerKAT data. Y.W.J.L. reduced and analysed the MeerKAT imaging data and the ATCA data, analysed the ASKAP data and performed astrometry on the source. M.C. reduced the MeerKAT PTUSE data with Y.W.J.L. E.L. calibrated and reduced the ASKAP data. D.L.K. and S.M. conducted pulsar timing on the source. D.L.K. performed the Pan-STARRS and VPHAS+ archive search. T.M., L.F., Z.W. and N.H.W. contributed to discussions about the nature and emission mechanism of the source. A.A. performed the ASKAP and VLA archival searches and analyses. N.H.W. reduced the MWA data and analysed the spectral index. V.K. and M.M.K. performed the WIRC observation and calibrated the data. S.O. performed the FourStar camera observation and calibrated the data. H.Q. performed the Swift observation and analysed the data. K.M.R. and K.G. performed the NICER observation and analysed the data. A.Z. and M.E.L. analysed the rotation measure of the source. K.W.B., A.D., C.J. and R.M.S. were the PIs of CRACO. M.G., V.G., J.N.J.S., A.J., Y.W.J.L., P.U., Y.W. and Z.W. were the builders of CRACO. T.M. was the PI of the ATCA project no. C3363. T.M. and D.L.K. were the PIs of VAST, and D.D. and L.D. were the project scientists of VAST. The PIs and builders of VAST and CRACO coordinated the initial investigation of ASKAP J1839−0756.
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Extended data
Extended Data Fig. 1 Light curves and dynamic spectrum of a sub-pulse detected in the MeerKAT UHF-band PTUSE data.
The sub-pulse was observed on 2024-02-18 at 05:53:09 UTC, lasting approximately 500 ms. The left panels show the sub-pulse before de-dispersion, while the right panels show it after de-dispersion at a DM of 188.4 pc cm−3.
Extended Data Fig. 2 Timing residuals of ASKAP J1839-0756.
Data are shown for the main pulse (filled circles) and interpulse (open squares), where the later have been shifted by the best-fit interpulse interval of 11466 s (or 177. 8°) relative to the main pulse. Data from ASKAP are shown in pink, data from MeerKAT are shown in blue, and data from ATCA are shown in orange. The error bars represent the 1 − σ error of the time residuals.
Extended Data Fig. 3 Rotation Measure of the main pulses (MP) and inter-pulses (IP) of ASKAP J1839-0756 as a function of pulse phase.
Columns 1 and 3 show the main pulse, while columns 2 and 4 show the interpulse. Rows are arranged in order of date, with adjacent subplots in rows 1-2 and 3-4 corresponding to the same observing epoch. The error bars denote the 1 − σ uncertainty of the RM. Missing axes are where there was no coverage or detection of the relevant pulse component.
Extended Data Fig. 4 Variability in polarization properties of an example main pulse on 2024-03-15.
The first and second rows show the total and polarized intensity, and the PA of the pulse. The third row shows the RM, and the fourth row shows the first-order frequency-dependence of V/I over λ2, κ = ∂(V/I)/∂(λ2). The error bars denote the 1 − σ uncertainty of the PA and RM. To guide the eye, we have placed a vertical dashed line at the phase corresponding to the steepest variability in κ.
Extended Data Fig. 5 MeerKAT images at the coordinates of ASKAP J1839-0756.
The upper left image shows a main pulse, while the upper right shows an interpulse. Both images are snapshots lasting for 30 minutes around the pulse ToA. The bottom image is a 2.5-hour deep image between the main pulse and interpulse (that is, off-pulse period) with an RMS of ~ 90 μJy/beam. The red circle in each image indicates the position of the source and does not carry any physical meaning on the accuracy of the position.
Extended Data Fig. 6 Simultaneous broadband measurements of the pulse at 2024-08-02 14:30 observed with the MWA and ASKAP.
All data have been corrected for the primary beam. A curved power-law fit of the form \({S}_{\nu }\propto {\nu }^{\alpha }\exp [q{\left(\log \nu \right)}^{2}]\) has been fit to the data, finding α = − 2.11 ± 0.07, q = − 1.38 ± 0.06, and S1GHz = 90.1 ± 0.6 mJy. A 10% empirical uncertainty (indicated by the error bars) is applied to the ASKAP data points to represent the flux density error when fitting the spectral equation. Since the MWA point is only a limit, the fitted curvature q value is an upper limit.
Extended Data Fig. 7 Dynamic spectrum of the MeerKAT UHF-band backend data with a time resolution of 60.24 μs.
The panels show the Stokes I, Q, U, and V parameters from left to right, top to bottom. The horizontal bright stripes at 600 MHz and 700 MHz are radio frequency interference and baseline variation that we were unable to mitigate. These stripes were also seen during off-pulse period. The zebra-like horizontal patterns are likely to be baseline variations that were also seen at different frequency range during off-pulse period. We therefore conclude that these patterns are not intrinsic to the source.
Extended Data Fig. 8 Dynamic spectrum of the MeerKAT S-band backend data with a time resolution of 37.45 μs.
The panels show the Stokes I, Q, U, and V parameters from left to right, top to bottom. Horizontal strips similar to Extend Data Fig. 7 are also seen in the dynamic spectrum and we determine that they are not intrinsic to the source.
Extended Data Fig. 9 Optical and near-infrared images of the field of ASKAP J1839-0756.
Each panel is centered at the source and 15″ on a side with north up and east to the left. We show the same VPHAS gri composite, a Pan-STARRS rzy composite, and our WIRC J-band and FourStar Ks-band images from left to right. In those images we show the best-fit radio position as the cyan error ellipse.
Extended Data Fig. 10 A period-period derivative diagram showing the spin-period against the period derivative for different types of neutron stars and compact objects.
The points are colour-coded according to their surface dipolar magnetic field (\(B=3.2\times 1{0}^{19}\sqrt{P\dot{P}}\) G). ASKAP J1839-0756is denoted by a star on the plot. The arrows represent the 3 − σ upper limit on the period derivative. The dotted lines represent the characteristic age of the compact object (\(\tau =P/2\dot{P}\)). The dashed line indicates the theoretical death lines for a pure dipole and the solid line for a twisted multipole configuration36. Below these lines, no radio emission is expected.
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Lee, Y.W.J., Caleb, M., Murphy, T. et al. The emission of interpulses by a 6.45-h-period coherent radio transient. Nat Astron 9, 393–405 (2025). https://doi.org/10.1038/s41550-024-02452-z
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DOI: https://doi.org/10.1038/s41550-024-02452-z
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