[論文レビュー] 50-250 MHz Pulsar Census with an SKA-Low prototype station: Spectra and Polarization

Pratik Kumar, Marcin Sokolowski+1 more|arXiv (Cornell University)|Mar 12, 2026

Pulsars and Gravitational Waves Research被引用数 0

ひとこと要約

The paper presents the largest southern low-frequency pulsar census (50–250 MHz) with the SKA-Low prototype EDA2, detecting 120 pulsars and delivering spectra, DMs, RMs, and full-polarimetric profiles across five sub-bands.

ABSTRACT

Low-frequency pulsar observations are crucial for understanding pulsar emission spectra and population physics, as well as for probing the interstellar medium (ISM) and Earth's ionosphere. We report the largest low-frequency pulsar census conducted in the southern hemisphere, covering 50-250 MHz, using the EDA2, an SKA-Low prototype station. In this survey, we detected 120 pulsars, including 23 first-time detections below 150 MHz and 5 below 100 MHz. For each source, we provide integrated pulse profiles and flux-density measurements across five sub-bands spanning 50-250 MHz. We also obtained improved dispersion measure (DM) values for 110 pulsars, with a median absolute DM correction of about 0.1 pc cm^-3. We measured significant Faraday rotation for 40 pulsars with improved rotation measure (RM) values for 4 pulsars, as well as phase-resolved RM variation in J1453-6413. Full-polarimetric pulse profiles are provided for all these pulsars, with multi-frequency polarimetric data for 20 of them. These results will enhance future SKA-Low science: refining pulsar population models, informing survey strategies, and advancing characterization of both the ISM and the ionosphere through low-frequency pulsar monitoring.

研究の動機と目的

• Characterize pulsar spectra and profiles across 50–250 MHz to constrain emission physics and spectral turnover.
• Improve dispersion measure (DM) and rotation measure (RM) estimates for a large southern-hemisphere pulsar sample.
• Provide full-polarimetric profiles to inform SKA-Low survey strategies and ISM/ionosphere studies.
• Assess how low-frequency observations impact pulsar population models and ISM/ionospheric characterization.

提案手法

• Use the EDA2 SKA-Low prototype station in beamformed mode to observe 240 targets across 50–250 MHz.
• Record raw voltage data across coarse channels and reduce to folded archives with 512 phase bins and 256 fine channels coherently de-dispersed.
• Detect pulsars via visual inspection, EPN catalog comparison, and PDMP S/N optimization for DM refinement.
• Measure flux densities using the radiometer equation with SEFD calibration and Gaussian-component pulse width modeling.
• Model spectra with five analytic forms (PL, BPL, PLL, PLH, DT) and select the best model via AIC and P_best.
• Apply RM-synthesis to derive RM and phase-resolved RM across pulse phase, with RMSF deconvolution (RM-CLEAN).
• Correct RM for ionospheric contribution using IonFR/IGS maps and compare with MeerKAT results.

Figure 1: Distribution of census targets in Galactic coordinates. Red and blue indicate the detected targets, with periods below and above 30 ms, respectively, and non-detected targets are shown in yellow. Contours show the line of equal declination, and the shaded region shows the region inaccessib

実験結果

リサーチクエスチョン

• RQ1 What is the prevalence and spectral behavior of pulsars in the 50–250 MHz range in the southern sky?
• RQ2 How do low-frequency DMs and RMs improve pulsar population models and ISM/ionospheric studies?
• RQ3 What is the incidence of low-frequency spectral turnover among detected pulsars, including MSPs?
• RQ4 How do phase-resolved RM measurements inform magnetospheric vs. interstellar Faraday effects?
• RQ5 How do EDA2-based polarimetric measurements compare with higher-frequency surveys and catalogs (e.g., EPN, MeerKAT)?

主な発見

• Detected 120 pulsars in 50–250 MHz with EDA2; 23 first-time detections below 150 MHz and 5 below 100 MHz.
• 110 pulsars exhibit significant DM corrections with a median absolute change ≈ 0.1 pc cm^-3.
• _significant_ RM detected for 40 pulsars; RM values updated for 4 pulsars; phase-resolved RM variations observed in J1453-6413.
• Turnover detected in 52 pulsars at low frequencies; mean turnover frequency 115 ± 10 MHz; simple power-law pulsars have mean spectral index -1.78 ± 0.17.
• Pulsar spectra for 120 sources largely described by standard models; several sources show updated or new spectral model classifications due to new low-frequency data.
• Full-polarimetric profiles provided; RM synthesis enables Faraday depth analysis and ionospheric RM subtraction to isolate ISM RM values.

Figure 2: (Top) RM ISM for pulsar J0630-2834 as a function of source elevation and observing time in UTC on MJD 60640. (Bottom) Variation of fractional linear polarization with elevation.