Discovery of a radio emitting neutron star with an ultra-long spin period of 76 seconds

Abstract

The radio-emitting neutron star population encompasses objects with spin periods ranging from milliseconds to tens of seconds. As they age and spin more slowly, their radio emission is expected to cease. We present the discovery of an ultra-long period radio-emitting neutron star, PSR J0901-4046, with spin properties distinct from the known spin and magnetic-decay powered neutron stars. With a spin-period of 75.88 s, a characteristic age of 5.3 Myr, and a narrow pulse duty-cycle, it is uncertain how radio emission is generated and challenges our current understanding of how these systems evolve. The radio emission has unique spectro-temporal properties such as quasi-periodicity and partial nulling that provide important clues to the emission mechanism. Detecting similar sources is observationally challenging, which implies a larger undetected population. Our discovery establishes the existence of ultra-long period neutron stars, suggesting a possible connection to the evolution of highly magnetized neutron stars, ultra-long period magnetars, and fast radio bursts.

Extended Data Figure 1

Timing residuals of PSR J0901–4046. The residuals from the best fit timing model given in Table 1. The orange data points are determined from the original MeerTRAP detection images, the first red diamond corresponds to a single pulse and the remaining red diamonds are determined from each of the half hour long follow-up observations with MeerKAT. The error bars are 1-σ. We used the L-band MeerKAT data for the timing analysis. The light coloured data points are from the Parkes UWL observations.

Extended Data Figure 2

Examples of quasi-periodic pulses. The top two rows show pulse profiles and their corresponding ACFs at 306.24μs resolution, respectively. The value the of quasi-period is indicated by the black vertical lines. The bottom two rows show the off-pulse regions and their corresponding ACFs.

Extended Data Figure 3

Example of a pulse exhibiting more than one quasi-period. Some quasi-periodic pulses as shown here, exhibit multiple quasi-periods within a single rotation.

Extended Data Figure 4

Estimates of the quasi-period across all epochs. The (orange) circles are the measured quasi-periods for each single pulse. The most commonly observed average quasi-period is 75.82 ms with the minimum period being 9.57 ms. The lags are arranged in lag length and not in time order.

Extended Data Figure 5

Radio light-curves of PSR J0901–4046. A regular series of pulsed emission detected in the L-band snapshot imaging for six observing epochs. Please refer to Section 5 for details.

Extended Data Figure 6

Polarization profiles of PSR J0901–4046 at 1.3 GHz and 700 MHz. Top Panel: Time series of two single pulses of PSR J0901–4046 at 1284 MHz. Bottom Panel: Two different single pulse time series at 737 MHz. For both panels, the total intensity is represented by the black solid line, the red solid line denotes the linear polarization while the blue solid line denotes circular polarization. The polarization position angle is not absolutely calibrated at 737 MHz.

Extended Data Figure 7

MeerKAT image of the PSR J0901–4046 region at 1.28 GHz. The left hand panel shows the image with the pulsed emission included, and the right hand panel shows the same field following the removal of the integration times containing pulses. No persistent radio source is associated with PSR J0901–4046 to a 3σ limit of 18 μJy beam⁻¹. The diffuse shell-like structure that surrounds PSR J0901–4046 is partially visible, possibly the supernova remnant from the event that formed the neutron star.

Fig. 1

P – Ṗ diagram based on the ATNF pulsar catalog. The various sub-classes of pulsars are represented by the markers in the legend. The longest spin period radio pulsars and the white dwarf binary system AR Sco are highlighted in red. Lines of constant age and magnetic field are shown as dotted and dashed lines respectively. The lower right corner of the figure represents the ‘death valley’ with various death lines from the literature, where sources below these lines are not expected to emit in the radio. The solid death line represents Equation 9 in CR93 [22]. In dot-dashed and dashed are the death lines modeled on curvature radiation from the vacuum gap and SCLF models as shown by Equations 4 and 9 respectively in [52]. Sources above the low-twist death line are potential ultra-long period magnetars.

Fig. 2

Gallery of the pulse morphology types of PSR J0901–4046. The morphological type is given in the title for each panel. The top panels are pulses observed in the UHF-band while the bottom panels are pulses observed at L-Band.