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ABSTRACT Spider pulsars are millisecond pulsars in short-period (≲12-h) orbits with low-mass (~0.01–0.4 _M_⊙) companion stars. The pulsars ablate plasma from the companion star, causing time

delays and eclipses of the radio emission from the pulsar. The magnetic field of the companion has been proposed to strongly influence both the evolution of the binary system1 and the

eclipse properties of the pulsar emission2. Changes in the rotation measure (RM) have been seen in a spider system, implying that there is an increase in the magnetic field near the

eclipse3. Here we report a diverse range of evidence for a highly magnetized environment in the spider system PSR B1744 – 24A4, located in the globular cluster Terzan 5. We observe

semi-regular profile changes to the circular polarization, _V_, when the pulsar emission passes close to the companion. This suggests that there is Faraday conversion where the radio wave

tracks a reversal in the parallel magnetic field and constrains the companion magnetic field, _B_  (> 10 G). We also see irregular, fast changes in the RM at random orbital phases,

implying that the magnetic strength of the stellar wind, _B_, is greater than 10 mG. There are similarities between the unusual polarization behaviour of PSR B1744 – 24A and some repeating

fast radio bursts (FRBs)5,6,7. Together with the possible binary-produced long-term periodicity of two active repeating FRBs8,9, and the discovery of a nearby FRB in a globular cluster10,

where pulsar binaries are common, these similarities suggest that a proportion of FRBs have binary companions. Access through your institution Buy or subscribe This is a preview of

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* Log in * Learn about institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS A BINARY PULSAR IN A 53-MINUTE ORBIT Article Open access

20 June 2023 RADIO PULSATIONS FROM A NEUTRON STAR WITHIN THE GAMMA-RAY BINARY LS I +61° 303 Article 17 March 2022 ENHANCED MAGNETIC ACTIVITY IN RAPIDLY ROTATING BINARY STARS Article 23 May

2025 DATA AVAILABILITY Data are available at https://doi.org/10.5281/zenodo.6983925. CODE AVAILABILITY DSPSR is available at http://dspsr.sourceforge.net and PSRCHIVE is available at

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Ravi, H. Vedantham, U.-L. Pen, S. Phinney, J. Fuller and C. Thompson. A.B. is supported by the European Research Council under the European Union’s Seventh Framework Programme

(FP/2007-2013)/ERC Grant Agreement No. 617199 (‘ALERT’) and by the Vici research programme ‘ARGO’ with project number 639.043.815, financed by the Dutch Research Council (NWO). Y.-P.Y. is

supported by the National Natural Science Foundation of China grant No.12003028, the National Key Research and Development Program of China (2022SKA0130101), and the China Manned Spaced

Project (CMS-CSST-2021-B11). S.R. is a CIFAR fellow and is supported by the NSF Physics Frontiers Center awards 1430284 and 2020265. The National Radio Astronomy Observatory is a facility of

the National Science Foundation operated under cooperative agreement by Associated Universities. The Green Bank Observatory is a facility of the National Science Foundation operated under

cooperative agreement by Associated Universities. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena,

CA, USA Dongzi Li * ASTRON, The Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands Anna Bilous * National Radio Astronomy Observatory, Charlottesville, VA, USA Scott

Ransom * Max-Planck-Institut für Radioastronomie, Bonn, Germany Robert Main * South-Western Institute For Astronomy Research, Yunnan University, Yunnan, China Yuan-Pei Yang * Purple Mountain

Observatory, Chinese Academy of Sciences, Nanjing, China Yuan-Pei Yang Authors * Dongzi Li View author publications You can also search for this author inPubMed Google Scholar * Anna Bilous

View author publications You can also search for this author inPubMed Google Scholar * Scott Ransom View author publications You can also search for this author inPubMed Google Scholar *

Robert Main View author publications You can also search for this author inPubMed Google Scholar * Yuan-Pei Yang View author publications You can also search for this author inPubMed Google

Scholar CONTRIBUTIONS D.Z.L. modelled and interpreted the data, and prepared the majority of the manuscript. A.B. performed data pre-processing, calibration and intermediate measurements.

S.R. led the data acquisition and discovered the variability of circularly polarized emission. R.M. and Y.-P.Y. helped to revise the draft and provided valuable comments. CORRESPONDING

AUTHOR Correspondence to Dongzi Li. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. PEER REVIEW PEER REVIEW INFORMATION _Nature_ thanks the anonymous

reviewers for their contribution to the peer review of this work. Peer reviewer reports are available. ADDITIONAL INFORMATION PUBLISHER’S NOTE Springer Nature remains neutral with regard to

jurisdictional claims in published maps and institutional affiliations. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIG. 1 THE LARGE-SCALE _B_∥ REVERSAL WITH VARIOUS ORIENTATIONS OF THE

COMPANION MAGNETIC AXIS. We specify the direction of the north magnetic pole _P_ with the longitude and latitude (_α_, _δ_), with which the point at the equator facing the pulsar is defined

to be (0, 0). Panels A,B and C correspond to _P_ pointing towards (180°, 50°), (0°, 50°) and (90°, 20°), respectively. In all cases, _B_∥ experiences a large-scale reversal when the ∣_B_∣ is

around the maximum. With the same companion magnetic-field configuration as in Fig. 3, we calculate _ξ_ following equation (10), and show that they are greater than 1 at orbit phase 0.25 in

all three cases, which means that Faraday conversion will happen. EXTENDED DATA FIG. 2 THE INDIVIDUAL INFLUENCE OF THE TWO POLARIZED PROPAGATION EFFECTS ON THE PULSE PROFILE. We use the

best-fit parameter (equation (15)) near the superior conjunction, where the degree of conversion (_C_ ) = −1, _A_ = 1.1, _α_ = −3.5, _A__v_ = −0.21, _α__v_ = −3.7, the optical depth for _I_

(_τ_ ) =  _A_(_f_/_f_0)–α, the optical depth for _V_ (_τ__v_)  =  \({A}_{v}{(\int /{\int }_{0})}^{-{a}_{v}}\), and _f_0 = 2 GHz. (A) The unperturbed profile of _I_ (black) and _V_ (blue),

which are also shown in Fig. 2d. (B,C) The model _I_ (purple) and _V_ (green) when the unperturbed profiles in (A) have gone through only circularly polarized absorption or Faraday

conversion. (D) The joint effects of the absorption and conversion on the pulse profile. The resulting profiles are also shown in the purple and green curves in Fig. 2e, which matches the

observed profiles. EXTENDED DATA FIG. 3 CIRCULAR POLARIZATION VARIES WITH ORBITAL PHASE AND FREQUENCY. (A) The predicted change in circular polarization, _V_, at higher frequency with the

model in Fig. 3. The waterfall shows the _V_ behaviour for a single spin phase, with red and blue representing different signs. Around the superior conjunction, _ϕ_ = 0.25, _V_ will

experience Faraday conversion resulting in the change of sign. The window for Faraday conversion will become narrower at higher frequency. (B) The fitted optical depth near the superior

conjunction following equation (15). Both the total optical depth, _τ,_ and the circular polarization related _τ__V_ are decreasing fast with frequency. The modelling of circularly polarized

absorption against orbital phase has more uncertainty than with Faraday conversion, owing to the unknown distribution of mildly relativistic electrons as a function of orbital phase.

However, it is safe to ignore _τ__V_ and study the conversion against orbital phase at higher frequency, because _τ__V_ is already small at 2.4 GHz. SUPPLEMENTARY INFORMATION PEER REVIEW

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Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Li, D., Bilous, A., Ransom, S. _et al._ A highly magnetized environment in a pulsar binary system. _Nature_ 618, 484–488

(2023). https://doi.org/10.1038/s41586-023-05983-z Download citation * Received: 07 May 2022 * Accepted: 20 March 2023 * Published: 17 May 2023 * Issue Date: 15 June 2023 * DOI:

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