Radio Observations of a Candidate Redback Millisecond Pulsar: 1FGL J0523.5-2529

TL;DR

This study targets 1FGL J0523.5-2529, a candidate redback millisecond pulsar, with a coordinated radio search using Parkes and the GBT across 0.7–4 GHz to probe for pulsar emission across most of its 16.5 hr orbit. Despite 34.5 hours of data and rigorous acceleration and single-pulse searches, no radio pulsations were detected, yielding stringent upper limits on radio flux and a pseudo-luminosity limit near 106 μJy kpc² at 2.2 kpc. The nondetection, consistent with eclipsing, faint, or highly scattered emission, underscores the elusiveness of pulsars in some redback systems and motivates higher-frequency follow-up and multi-wavelength timing to constrain the binary dynamics. The appendix’s serendipitous detection of PSR J0520-2553 validates the pipelines and demonstrates the value of cross-field checks in such searches, supporting the need for continued multi-wavelength observations to place J0523.5-2529 within the redback population framework.

Abstract

Redback pulsars are a subclass of millisecond pulsar system with a low-mass non-degenerate companion star being ablated by the pulsar. They are of interest due to the insights they can provide for late-stage pulsar evolution during the recycling process. J0523.5-2529 is one such candidate where redback-like emission has been seen at multiple wavelengths except radio. It is a system with a binary orbit of 16.5 hours and a low-mass non-degenerate companion of approximately 0.8 solar masses. The aim of this work was to conduct follow-up radio observations to search for any exhibited radio pulsar emission from J0523.5-2529. This work employs a periodicity and single burst search across 74 percent of the system's orbital phase using a total of 34.5 hours of observations. Observations were carried out using the Murriyang Telescope at Parkes and the Robert C. Byrd Green Bank Telescope (GBT). Despite extensive orbital phase coverage, no periodic or single-pulse radio emission was detected above a signal-to-noise threshold of 7. A comprehensive search for radio pulsations from J0523.5-2529 using Parkes and GBT yielded no significant emission, likely due to intrinsic faintness, scattering, or eclipses by the companion's outflow. The results demonstrate the elusiveness of the pulsar component in some redback systems and highlight the need for multi-wavelength follow-up and higher-frequency radio observations to constrain the source nature and binary dynamics.

Figures (5)

• Figure 1: Top: Phase convention used during this search, with superior conjunction at $\phi = 0.5$. Pulsar shown in blue, companion shown in orange (top down view). Bottom: Bar chart of epochs and corresponding phase coverage of the observation campaign from Parkes (Blue), MeerKAT (Pink) and GBT (Green).
• Figure 2: Z-parameter values for various J0523 trial spin periods. Here the max z-value corresponds to the value at the time from ascending node.
• Figure 3: Radial velocity measurements from strader_1fgl_2014 as a function of phase. This illustrates the need to separate observations into chunks of $\lesssim P_b/10$ in duration so as to maintain an approximately linear radial acceleration for periodicity searches.
• Figure 4: System temperatures across both Parkes (left) and GBT (right) bands. The plots show the contributions from the sky, Low-Noise Amplifier (LNA), spillover, and receiver temperatures, along with the total system temperature. Sky temperature values were obtained from zheng_improved_2017, Parkes values were referenced from hobbs_ultra-wide_2020, and GBT values from the proposer's guide.
• Figure 5: Flux limits in mJy for S-band observations of J0520-2553 from