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Pulsar Discoveries from the TRAPUM UHF Survey of Fermi-LAT Sources

Tinn Thongmeearkom, Colin J. Clark, Rene P. Breton, Marta Burgay, Lars Nieder, Oliver G. Dodge, Brian McGloughlin, Ewan D. Barr, Sarah Buchner, Benjamin W. Stappers, Joanna Berteaud, Elizabeth C. Ferrara, Paulo C. C. Freire, Lina Levin, Scott M. Ransom, Laila Vleeschower, Sergio Belmonte Díaz, Francesca Calore, Ismaël Cognard, Vik S. Dhillon, Jean-Mathias Grießmeier, Ramesh Karuppusamy, Mark R. Kennedy, Michael Kramer, Prajwal V. Padmanabh, Maria A. Papa, Adipol Phosrisom, Benjamin Steltner

Abstract

The Fermi Large Area Telescope (LAT) provides advantages for radio pulsar searches by enabling efficient target selection. We can confidently point radio telescopes to the positions of Fermi unidentified gamma-ray sources that have a high probability of hosting a pulsar. As part of Transients and Pulsars with MeerKAT (TRAPUM), we conducted a survey of Fermi-LAT sources using the Ultra High Frequency (UHF; 544-1088 MHz) receiver of the MeerKAT radio telescope. We observed 79 sources that were identified as pulsar-like candidates using a random forest technique from the Fermi-LAT Fourth Source Catalogue. We observed each target for 10 minutes at two separate epochs. As a result, we discovered nine new millisecond pulsars (MSPs) and six slow pulsars. Based on the radio discoveries, we also searched for gamma-ray pulsations, confirming that seven of the newly discovered MSPs are associated with Fermi-LAT sources, and performed joint radio and gamma-ray pulsar timing. Companion mass estimates and evidence of radio eclipses indicate that among the nine MSPs there are three black widows and three redbacks. Lastly, we compared the discovered pulsars in the MeerKAT UHF survey against the previous Fermi sources TRAPUM survey at L band, concluding the superiority of UHF observations in sensitivity to fainter pulsars and in detection rate than L band for finding new gamma-ray MSPs.

Pulsar Discoveries from the TRAPUM UHF Survey of Fermi-LAT Sources

Abstract

The Fermi Large Area Telescope (LAT) provides advantages for radio pulsar searches by enabling efficient target selection. We can confidently point radio telescopes to the positions of Fermi unidentified gamma-ray sources that have a high probability of hosting a pulsar. As part of Transients and Pulsars with MeerKAT (TRAPUM), we conducted a survey of Fermi-LAT sources using the Ultra High Frequency (UHF; 544-1088 MHz) receiver of the MeerKAT radio telescope. We observed 79 sources that were identified as pulsar-like candidates using a random forest technique from the Fermi-LAT Fourth Source Catalogue. We observed each target for 10 minutes at two separate epochs. As a result, we discovered nine new millisecond pulsars (MSPs) and six slow pulsars. Based on the radio discoveries, we also searched for gamma-ray pulsations, confirming that seven of the newly discovered MSPs are associated with Fermi-LAT sources, and performed joint radio and gamma-ray pulsar timing. Companion mass estimates and evidence of radio eclipses indicate that among the nine MSPs there are three black widows and three redbacks. Lastly, we compared the discovered pulsars in the MeerKAT UHF survey against the previous Fermi sources TRAPUM survey at L band, concluding the superiority of UHF observations in sensitivity to fainter pulsars and in detection rate than L band for finding new gamma-ray MSPs.
Paper Structure (22 sections, 4 equations, 6 figures, 8 tables)

This paper contains 22 sections, 4 equations, 6 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Survey Properties
  3. MeerKAT and TRAPUM Processing Infrastructure
  4. Observing Strategy
  5. Search Pipeline
  6. Target Selection
  7. Results
  8. Localisation
  9. Radio Timing
  10. Spider Pulsars
  11. Other MSPs
  12. Gamma-ray Pulsations and Timing
  13. Slow Pulsars
  14. Distance to PSR J0657$-$4657
  15. Continuous Gravitational Wave Searches
  16. ...and 7 more sections

Figures (6)

  • Figure 1: Radio (red) pulse profiles for all nine MSPs with phase-aligned gamma-ray (black) profiles for seven of them, showing two identical rotations for clarity. The dashed line represents the gamma-ray background level, estimated from photon weights as $b=\sum_i w_i(1-w_i)/n_{\rm bins}$. The radio profiles are shown in arbitrary units, scaling the amplitude to match the highest gamma-ray peak and moving the baseline flux level to the gamma-ray background level.
  • Figure 2: Radio pulse profiles for the six slow pulsars, showing two identical rotations. The profiles display the radio flux density in arbitrary units. The dashed line represents the baseline, estimated as the median of the off-pulse region.
  • Figure 3: Optical light curves (points), Icarus model fits (solid lines) and resiudals (bottom panels) for PSR J1346$-$2610 from ULTRACAM data.
  • Figure 4: Histograms of discovered MSPs at L band Clark2023+Lband and UHF. The blue and red colours represent L band and UHF, respectively, while the red hatched histogram represents the pulsars that would have been discovered with UHF if the survey had begun at UHF instead of L band. This illustrates the advantage of using UHF in our setup for discovering pulsars.
  • Figure 5: The distribution of discovered MSPs from the L-band survey Clark2023+Lband and the UHF survey (circles) over pulse period and dispersion measure (DM). The color map represents the expected distance of each MSP according to the YMW16 electron density model YMW16, while the grey lines display the difference between DM of each MSP and the maximum DM along the line of sight. The red line is expected discoverable pulsar periods corresponding to the DM smearing effect at UHF, while the L-band smearing line lies beyond the plotted range.
  • ...and 1 more figures