Discovery of the Slowest Radio Pulsar in the Small Magellanic Cloud

The gist: A new radio pulsar, PSR J0103−72, was discovered in the Small Magellanic Cloud (SMC) through reanalysis of archival Parkes/Murriyang observations, making it the slowest known radio pulsar in the SMC with a dispersion measure of 272±13 pc cm−3

Discovery and Significance

The paper reports the discovery of a new radio pulsar PSR J0103−72 in the Small Magellanic Cloud (SMC) through a reanalysis of Parkes/Murriyang archival observations targeting supernova remnants and pulsar-wind nebulae in the SMC It has a spin period of 1.327 s and a dispersion measure (DM) of 272±13 pc cm−3, making it the slowest known radio pulsar in the SMC with the second-highest DM This discovery shows that candidates with weak Fourier-domain significance can reveal faint, narrow-duty-cycle pulsars missed in earlier extragalactic pulsar searches PSR J0103−72 is the 15th radio pulsar known in the SMC

Targeting and Methodology

The research involved reprocessing archival data obtained from the ATNF Data Access Portal (DAP) using a search pipeline optimized for discovering narrow duty cycle pulsars The observations were conducted using the 64-m Parkes radio telescope (Murriyang) as part of a targeted search for young radio pulsars in the SMC by N. Titus et al. Preprocessing steps included converting psrfits format files to filterbank format and downsampling to 512 channels and a temporal resolution of 128 µs using the digifil tool of dspsr To reduce radio frequency interference (RFI) impact, the filterbanks were cleaned using rfifind in the presto package, resulting in an average of 9.2% of the 512 channels being removed from analysis

Search Techniques and Candidate Selection

The search employed both FFT-based periodicity and acceleration searches to identify potential pulsars The periodicity search utilized the peasoup6 (E. Barr 2020) code, searching an average of 1093 DMs per pointing from 10 to 500 pc cm−3 with a DM tolerance of 1.03 In the second step, an acceleration search was performed by resampling observations over constant line-of-sight accelerations of up to ±10 m s−2 with 626 trial accelerations per trial DM To limit the number of candidates for folding, an adaptive S/NFFT threshold based on spin period and the number of harmonic sums (nh) was used This resulted in a total of ∼9 567 900 candidates for folding from all targeted observations in the acceleration search

Results and Interpretation

The inspection of non-accelerated candidates led to the discovery of PSR J0103−72, which was first detected in the 2017 August 28 pointing with a pdmp folded S/N of 14.2 after manually removing an RFI stripe The pulsar has a spin period of 1.327 s and is consistent with the known SMC pulsar DM range Its DM leaves approximately 230–242 pc cm−3 attributable to the SMC and material local to the pulsar The large DM of PSR J0103−72 could therefore arise from enhanced ionized gas along the sightline, a long path through the diffuse ionized medium of the SMC, or a combination of the two

Association and Context

The nearest known remnant is MCSNR J0103−7247, 14.9 arcmin away from PSR J0103−72 Given MCSNR J0103−7247’s age of 5.1 kyr, an association would require a projected velocity of ∼5×104 km s−1, which is beyond the known distribution of the birth velocities of radio pulsars The discovery shows that the detectable SMC population is not restricted to young, relatively faster pulsars, but also contains longer-period objects that are likely to have been under-represented in previous searches

Sensitivity Comparison

The flux density sensitivity limits were compared using the radiometer equation applied to pulsar observations The discovery observation of PSR J0103−72 had a 1400-MHz flux density of approximately 39 µJy and a pseudo-luminosity of 151 mJykpc2 This is a lower limit estimate because the pulsar position is uncertain by 7 arcmin The TRAPUM Small Magellanic Cloud pulsar survey could have detected PSR J0103−72, as its nominal detection threshold was comparable to the estimated discovery-epoch flux density

Conclusion

The discovery of PSR J0103−72 demonstrates how faint, long-period pulsars can remain unidentified in existing survey data sets Its detection with period and harmonic dependent FFT thresholds in noise floor candidates highlights the importance of candidate selection in discovering faint pulsars Therefore, reanalysis of archival observations remains immensely useful The only known SMC radio pulsar with a higher DM is PSR J0048−7317, with DM = 292.42 pc cm−3 Given the 13 pc cm−3 uncertainty for PSR J0103−72, the difference is only ∼ 1.6σ The discovery of PSR J0103−72 shows how faint, long-period pulsars can remain unidentified in existing survey data sets

Acknowledgments

This research was conducted during a three month undergraduate research training program at the Max Planck Institute for Gravitational physics, Hannover W.W and R.S. are thankful for support from the Max Planck Society We thank Lawrence Toomey for making the archival Parkes observations available through the Data Access Portal, without which this work would not have been possible This work made use of the large computing cluster Atlas operated by the Observational Relativity and Cosmology division of the Albert Einstein Institute The Parkes Murriyang radio telescope is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO (the Commonwealth Scientific and Industrial Research Organisation) We acknowledge the Wiradjuri people as the Traditional Owners of the Observatory site

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1. textbf Rewriting FFT-based search techniques for faint sources: The improved system can now reveal faint, narrow-duty-cycle pulsars missed in earlier extragalactic pulsar searches by utilizing FFT-based reprocessing found PSR J0103−72 through search techniques which have previously been highly effective in discovering a large number of pulsars in other surveys.

2. textbf Adaptive S/NFFT thresholding: The system can now employ an adaptive S/NFFT threshold for candidate sifting based on spin period and the number of harmonic sums (nh) corresponding to each candidate, which is crucial because a uniform threshold might cause narrow duty-cycle pulsars to be missed, especially so for faint slow pulsars.

3. textbf RFI stripe identification in the Period-DM plane: The system can now be enhanced by identifying RFI stripes in the period–DM plane and rejecting candidates belonging to these stripes, as this technique helps reduce spurious signals caused by persistent periodic RFI that remained present for 10–20 minutes.

4. textbf Flux density sensitivity modeling: The improved system can accurately calculate flux density sensitivities using Equation 3, accounting for complex factors like pulse broadening due to scattering from multipath propagation through the interstellar medium and the specific effects of SMC conditions, leading to more reliable detection limits.