pith. sign in

arxiv: 2606.06922 · v1 · pith:PQUCUS7Cnew · submitted 2026-06-05 · 🌌 astro-ph.HE

Pulsar searches of Fermi-LAT gamma-ray sources with the MWA

C. P. Lee , N. D. R. Bhat , B. W. Meyers , W. van Straten , D. A. Smith This is my paper

Pith reviewed 2026-06-27 21:25 UTC · model grok-4.3

classification 🌌 astro-ph.HE
keywords pulsar searchesFermi-LAT unassociated sourcesMurchison Widefield Arraymillisecond pulsarslow-frequency radiodispersion removal
0
0 comments X

The pith

Survey of 308 Fermi-LAT sources at 154 MHz finds no new pulsars and sets flux limits of 30-220 mJy.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper describes a radio survey of 308 unassociated Fermi-LAT gamma-ray sources using archival MWA observations at 154 MHz. No new pulsars were detected across the sample. The authors attribute this null result to the survey's limited sensitivity and report corresponding flux density upper limits. They also describe a new semi-coherent dispersion removal pipeline that improves sensitivity to millisecond pulsars at low frequencies compared with standard incoherent methods. The work projects that the MWA Phase III upgrade would raise the number of detectable sources by roughly 30 percent under the same observing time.

Core claim

No new pulsars were identified in the survey, which the authors attribute to insufficient sensitivity. Flux density limits are estimated at approximately 30-220 mJy at 154 MHz (equivalent to 0.7-5.2 mJy at 1.4 GHz) for a 2 ms spin period and 28 percent duty cycle. The survey is the largest radio search of unassociated Fermi-LAT sources conducted below 300 MHz and employed a semi-coherent dispersion removal scheme that yields 2-3 times better sensitivity than fully incoherent removal for dispersion measures between 20 and 40 pc cm^{-3}.

What carries the argument

semi-coherent dispersion removal scheme applied to digitally beamformed MWA tile voltages, which improves sensitivity to millisecond pulsars over fully incoherent methods for moderate dispersion measures

If this is right

  • The MWA Phase III upgrade is projected to increase the number of detectable gamma-ray pulsars by about 30 percent for the same integration time.
  • The semi-coherent pipeline can be applied to pulsar searches in supernova remnants, globular clusters, and candidates from imaging surveys.
  • Results from this survey help calibrate expectations for the yield of future low-frequency surveys with SKA-Low.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Deeper or longer integrations at 154 MHz may still be needed to match the pulsar discovery rate achieved at higher radio frequencies.
  • Many unassociated Fermi-LAT sources could be either radio-quiet or require different search techniques such as targeted timing or multi-frequency follow-up.
  • The pipeline's utility extends to any low-frequency data set where dispersion smearing is the dominant sensitivity limiter.

Load-bearing premise

The semi-coherent dispersion removal scheme actually delivers the claimed 2-3 times sensitivity gain without substantial loss of real signals or introduction of false negatives that would explain the null result.

What would settle it

Detection of a pulsar in any of the 308 targets at a flux density below the stated 30-220 mJy limit at 154 MHz, or reprocessing of the same data with an independent pipeline that recovers a signal missed by the semi-coherent search.

Figures

Figures reproduced from arXiv: 2606.06922 by B. W. Meyers, C. P. Lee, D. A. Smith, N. D. R. Bhat, W. van Straten.

Figure 1
Figure 1. Figure 1: Diagram illustrating the basic workflow of the semi-coherent pulsar search pipeline. Red rounded boxes indicate GPU-based processing tasks and blue rounded boxes indicate CPU-based processing tasks. See Sections 2.1 and 2.2 for details. then exhibit a constant frequency derivative ˙ f , causing the signal to drift through z = ˙ f T 2 bins in each Fourier power spectrum (where z is the Fourier frequency der… view at source ↗
Figure 2
Figure 2. Figure 2: Comparison of dedispersion plans in the SMART frequency band (138.88–169.60 MHz). Top: The worst-case temporal smearing (i.e. τsmear assuming the maximum τδDM) as a function of DM. The estimated scattering time (τscatt) is shown with an order-of-magnitude error band (Bhat et al. 2004). The test pulsars are indicated at their respective spin periods and DMs, and labelled by their right ascension. Bottom: Th… view at source ↗
Figure 3
Figure 3. Figure 3: Candidate plots generated by PREPFOLD for the five test pulsars blindly detected with the search pipeline: PSR J1959+2048 (top left), PSR J2051−0827 (top right), PSR J2241−5236 (centre left), PSR J2256−1024 (centre right), and PSR J0125−5854 (bottom). Each candidate plot shows the folded pulse profile over two full periods integrated over time and frequency (top left) and as a function of time and frequenc… view at source ↗
Figure 4
Figure 4. Figure 4: Distribution of source elevations (left) and Galactic latitudes (right) for the 308 Fermi-LAT sources searched in this work (grey unhatched) and the 52 sources in the LOFAR gamma-ray survey (red hatched; Pleunis et al. 2017). the centre of the localisation ellipse. The beam power (relative to the beam centre) for localisation errors of 0.1°, 0.2°, and 0.3° is approximately 82 %, 43 %, and 11 %, respectivel… view at source ↗
Figure 5
Figure 5. Figure 5: Galactic skymap of the 308 gamma-ray sources targeted in this survey (circles) and the six test pulsars (stars). The marker colours for the gamma-ray sources indicate the minimum detectable flux density (Smin) for a spin period of 2 ms, a duty cycle of 28 %, and an integration time of 20 min in the beamformed SMART observations used in this work (assuming negligible scatter broadening). The grey shaded reg… view at source ↗
Figure 6
Figure 6. Figure 6: shows how the survey sensitivity scales with DM for spin periods of 1, 10, and 100 ms. Each subplot shows the sensitivity curves for all 308 targets in the survey. For compar￾ison, we also show the sensitivity of the LOFAR gamma-ray survey for the 52 targets listed in Pleunis et al. (2017). Fol￾lowing Pleunis et al. (2017), we assume G = 5.6 K Jy−1 for 21 LOFAR Core stations and Tsys = 400 K for all of the… view at source ↗
Figure 7
Figure 7. Figure 7: Distribution of independent pulsar candidates (i.e. after harmonic grouping per beam) identified across searches of 308 unidentified 4FGL sources. Candidates with σFFT > 10 are emphasised, with the marker size scaled by σFFT. The two known pulsars identified in the searches are annot￾ated at their spin period and DM, with a vertical line to show the harmonics associated with the pulsar. that J1752−2806, be… view at source ↗
Figure 8
Figure 8. Figure 8: Cumulative distribution function (CDF) of the mean flux density at 1.4 GHz for the radio-loud gamma-ray pulsars in the 3PC catalogue with a DM less than 100 cm−3 pc (Smith et al. 2023). The shaded bands show the range of Smin for the SMART (blue) and LOFAR (red) gamma-ray surveys (see Section 3.2), scaled to 1.4 GHz assuming a spectral index of −1.7. MSPs follow a steep power-law between 100–200 MHz (i.e. … view at source ↗
read the original abstract

Searches of unassociated gamma-ray sources in the Fermi-LAT catalogues have led to the discoveries of around a fifth of all known millisecond pulsars (MSPs). These searches have almost exclusively been performed at radio frequencies above 300 MHz, where dispersion and scattering in the interstellar medium are less significant. We report on a shallow survey for pulsars targeting 308 unassociated Fermi-LAT sources in archival Murchison Widefield Array (MWA) observations from the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey at 154 MHz. This is the largest radio survey of unassociated Fermi-LAT sources to date, and only the second to be conducted below 300 MHz after a survey with the Low Frequency Array (LOFAR) that discovered three MSPs. Each source was observed for 20 min by digitally beamforming the MWA tile voltages. Searches were then performed using a new pipeline that implements a semi-coherent dispersion removal scheme for MWA data, enabling greater sensitivities to MSPs than is possible with fully-incoherent dispersion removal (e.g. 2-3 times better sensitivity for dispersion measures between 20-40 pc/cm^3). No new pulsars were identified in the survey, which we attribute to insufficient sensitivity. We estimate flux density limits of approximately 30-220 mJy at 154 MHz (or 0.7-5.2 mJy at 1.4 GHz) for a spin period of 2 ms and a duty cycle of 28%. We discuss how the improved instantaneous sensitivity from the Phase III upgrade of the MWA will increase the number of detectable gamma-ray pulsars by ~30% for the same integration time. The semi-coherent search pipeline we have developed will also be useful for searches of supernova remnants, globular clusters, and pulsar candidates identified in imaging surveys, all of which will help to inform the significance of future surveys with SKA-Low.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript reports results from a shallow pulsar survey of 308 unassociated Fermi-LAT gamma-ray sources using 20-minute archival MWA observations at 154 MHz. A new semi-coherent dispersion removal pipeline is introduced that is stated to provide 2-3 times better sensitivity to MSPs than incoherent dedispersion for DMs of 20-40 pc cm^{-3}. No new pulsars are detected; the authors attribute this null result to insufficient sensitivity and quote flux density limits of approximately 30-220 mJy at 154 MHz (0.7-5.2 mJy at 1.4 GHz) for P=2 ms and 28% duty cycle. The paper also discusses gains expected from the MWA Phase III upgrade and the broader utility of the pipeline.

Significance. If the pipeline performance claims hold, this is the largest low-frequency survey of unassociated Fermi-LAT sources and supplies useful upper limits on MSP detectability below 300 MHz, complementing existing higher-frequency searches and informing SKA-Low strategies. The pipeline itself represents a methodological advance applicable to other targets such as supernova remnants and globular clusters.

major comments (1)
  1. [Abstract and pipeline description section] Abstract and pipeline description section: the stated 2-3 times sensitivity gain of the semi-coherent dispersion removal scheme for DM 20-40 pc cm^{-3} is presented without quantitative support such as injection-recovery fractions, false-negative rates, or side-by-side metrics versus incoherent dedispersion. This validation is required to support the central attribution of the null result to sensitivity alone rather than possible pipeline limitations.
minor comments (2)
  1. [Abstract] Abstract: the quoted flux-density limits lack uncertainties, explicit calculation details, or sensitivity to the chosen spin period and duty cycle assumptions.
  2. [Abstract] Abstract: no information is given on the fraction of sources with usable data or any exclusion criteria applied to the 308 targets.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and for highlighting the significance of the survey and pipeline. We address the single major comment below.

read point-by-point responses

  1. Referee: [Abstract and pipeline description section] Abstract and pipeline description section: the stated 2-3 times sensitivity gain of the semi-coherent dispersion removal scheme for DM 20-40 pc cm^{-3} is presented without quantitative support such as injection-recovery fractions, false-negative rates, or side-by-side metrics versus incoherent dedispersion. This validation is required to support the central attribution of the null result to sensitivity alone rather than possible pipeline limitations.

    Authors: We agree that the manuscript presents the 2-3 times sensitivity gain without the quantitative validation requested. The figure originates from the expected performance of the semi-coherent dedispersion algorithm relative to incoherent methods, but we will add an appendix containing injection-recovery tests on simulated MSP signals (including recovery fractions, false-negative rates, and direct comparisons to incoherent dedispersion) specifically for DMs of 20-40 pc cm^{-3}. This addition will directly support the attribution of the null result to sensitivity. revision: yes

Circularity Check

0 steps flagged

No circularity: observational survey with direct empirical results

full rationale

This is an observational radio survey paper reporting a null detection from archival MWA data on 308 Fermi-LAT sources. The central claims (no new pulsars found; flux density limits of 30-220 mJy at 154 MHz) are direct outputs of applying the search pipeline to the observations, with no mathematical derivations, parameter fits presented as predictions, or self-referential steps. The semi-coherent dispersion removal scheme is described as new and enabling 2-3x sensitivity gain, but this performance statement is not derived from or equivalent to the survey results themselves; it is an input assumption whose validation is external to any derivation chain in the paper. No load-bearing self-citations, ansatzes, or renamings of known results appear. The paper is self-contained against external benchmarks of prior surveys and sensitivity estimates.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard radio-astronomy assumptions about interstellar medium effects and typical millisecond-pulsar properties; no new entities are postulated and no parameters are fitted to the survey data itself.

free parameters (2)
  • duty cycle = 28%
    Assumed value of 28% used to compute the quoted flux density limits for a 2 ms spin period.
  • spin period = 2 ms
    Assumed value of 2 ms used to compute the quoted flux density limits.
axioms (1)
  • domain assumption Dispersion and scattering in the interstellar medium can be mitigated by the semi-coherent removal scheme to achieve the stated sensitivity gain.
    Invoked when describing the new pipeline and its advantage over fully incoherent methods.

pith-pipeline@v0.9.1-grok · 5915 in / 1494 out tokens · 35938 ms · 2026-06-27T21:25:59.867186+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

11 extracted references · 10 canonical work pages · 5 internal anchors

  1. [1]

    Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4)

    Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4).arXiv e-prints(July): arXiv:2307.12546. https://doi.org/ 10.48550/arXiv.2307.12546. arXiv: 2307.12546[astro-ph.HE]. Bangale, P., B. Bhattacharyya, F. Camilo, C. J. Clark, I. Cognard, M. E. DeCesar, E. C. Ferrara et al. 2024. A 350 MHz Green Bank Telescope Survey of Unassociated Fer...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.2307.12546 2024

  2. [2]

    A&A 657 (January): A46

    Fourier-domain dedispersion. A&A 657 (January): A46. https : / / doi . org / 10 . 1051 / 0004 - 6361 / 202142099. arXiv: 2110 . 03482 [astro-ph.IM]. Bhat, N. D. R., N. A. Swainston, S. J. McSweeney, M. Xue, B. W. Meyers, S. Kudale, S. Dai et al. 2023a. The Southern-sky MW A Rapid Two- metre (SMART) pulsar survey—I. Survey design and processing pipeline. P...

    work page doi:10.1017/pasa.2023.17 2023

  3. [3]

    Parkes radio searches of Fermi gamma-ray sources and millisecond pulsar discoveries

    https://doi.org/10.1088/0004-637X/810/2/85. arXiv: 1507.04451 [astro-ph.HE]. Clark, C. J., R. P. Breton, E. D. Barr, M. Burgay, T. Thongmeearkom, L. Nieder, S. Buchner et al. 2023. The TRAPUM L-band survey for pulsars in Fermi-LA T gamma-ray sources. MNRAS 519, no. 4 (March): 5590–

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/810/2/85 2023

  4. [4]

    arXiv: 2212.08528 [astro-ph.HE]

    https://doi.org/10.1093/mnras/stac3742. arXiv: 2212.08528 [astro-ph.HE]. Cognard, I., L. Guillemot, T. J. Johnson, D. A. Smith, C. Venter, A. K. Hard- ing, M. T. W olff et al. 2011. Discovery of Two Millisecond Pulsars in Fermi Sources with the Nançay Radio Telescope. ApJ 732, no. 1 (May):

    work page doi:10.1093/mnras/stac3742 2011

  5. [5]

    Discovery of two millisecond pulsars in Fermi sources with the Nancay Radio Telescope

    https://doi.org/10.1088/0004-637X/732/1/47. arXiv: 1102.4192 [astro-ph.HE]. Cromartie, H. T., F. Camilo, M. Kerr, J. S. Deneva, S. M. Ransom, P. S. Ray, E. C. Ferrara, P. F. Michelson and K. S. W ood. 2016. Six New Milli- second Pulsars from Arecibo Searches of Fermi Gamma-Ray Sources. ApJ 819, no. 1 (March): 34. https://doi.org/10.3847/0004-637X/819/1/

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/732/1/47 2016

  6. [6]

    Six New Millisecond Pulsars from Arecibo Searches of Fermi Gamma-Ray Sources

    arXiv: 1601.05343[astro-ph.HE]. Das, Jyotirmoy, Jayanta Roy, Paulo C. C. Freire, Scott M. Ransom, Bhaswati Bhattacharyya, Karel Adámek, Wes Armour, Sanjay Kudale and Mekhala V. Muley. 2025. Globular Clusters GMRT Pulsar Search (GCGPS). I. Survey Description, Discovery and Timing of the First Pulsar in NGC6093 (M80). ApJ 988, no. 2 (August): 161. https://d...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1038/nbt.3820 2025

  7. [7]

    org / 10

    https : / / doi . org / 10 . 1093 / mnras / stv1604. arXiv: 1507 . 03732 [astro-ph.GA]. Kuzmin, A. D. and B. Ya. Losovsky. 2001. No low-frequency turn-over in the spectra of millisecond pulsars. A&A 368 (March): 230–238. https: //doi.org/10.1051/0004-6361:20000507. Lee, C. P., N. D. R. Bhat, B. W. Meyers, S. J. McSweeney, W. van Straten, C. M. Tan, M. Xue...

    work page doi:10.1051/0004-6361:20000507 2001

  8. [8]

    arXiv: 2401.05475 [astro-ph.GA]

    https://doi.org/10.3847/2515-5172/ad1bf 1. arXiv: 2401.05475 [astro-ph.GA]. . 2026. NE2025: An Updated Electron Density Model for the Galactic Interstellar Medium. ApJ 1002, no. 1 (May): 3. https://doi.org/10.3847/ 1538-4357/ae5825. arXiv: 2602.11838[astro-ph.GA]. Ord, S. M., S. E. Tremblay, S. J. McSweeney, N. D. R. Bhat, C. Sobey, D. A. Mitchell, P. J. ...

    work page doi:10.3847/2515-5172/ad1bf 2026

  9. [9]

    arXiv: 2003.02335 [astro-ph.HE]

    https://doi.org/10.1093/mnras/staa596. arXiv: 2003.02335 [astro-ph.HE]. Ransom, S. M., P. S. Ray, F. Camilo, M. S. E. Roberts, Ö. Çelik, M. T. W olff, C. C. Cheung et al. 2011. Three Millisecond Pulsars in Fermi LA T Unassociated Bright Sources. ApJ 727, no. 1 (January): L16. https://doi. org/10.1088/2041-8205/727/1/L16. arXiv: 1012.2862 [astro-ph.HE]. Ra...

    work page doi:10.1093/mnras/staa596 2003

  10. [10]

    Remazeilles, M., C

    arXiv: 1205.3089[astro-ph.HE]. Remazeilles, M., C. Dickinson, A. J. Banday, M. -A. Bigot-Sazy and T. Ghosh

    Pith/arXiv arXiv

  11. [11]

    An improved source-subtracted and destriped 408 MHz all-sky map

    An improved source-subtracted and destriped 408-MHz all-sky map. MNRAS 451, no. 4 (August): 4311–4327. https://doi.org/10.1093/ mnras/stv1274. arXiv: 1411.3628[astro-ph.IM]. Ridolfi, A., T. Gautam, P. C. C. Freire, S. M. Ransom, S. J. Buchner, A. Possenti, V. Venkatraman Krishnan et al. 2021. Eight new millisecond pulsars from the first MeerKA T globular ...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stab790 2021