arXiv subjects

Ka-Yui Au

Publications and source records attributed to Ka-Yui Au.

3 recordsLinked to original sources

arXiv2026

Sharpening the Mass Measurement of PSR J1048+2339 via High-Cadence Photometry

Neutron stars are among the densest objects in the universe, and the mass measurements are crucial to the understanding of their equation of state. Pulsars in tight binaries can be weighed dynamically, but accurate mass estimates are often hampered by uncertainties in orbital inclinations. In this paper, we report on multi-epoch optical monitoring of the pulsar binary, PSR J1048+2339, using the 0.5-m RIFT telescope at Lulin Observatory. Our observations reveal frequent optical flares with eclipses caused by the companion. Using the eclipse duration with archival photometric data and orbital ephemeris in the literature, we constrain the inclination to 78.0+/-1.0 degrees and the pulsar mass to 1.79 (+0.09, -0.08) solar masses. This measurement is among the most precise for any redback system to date, demonstrating a novel way to improve the pulsar mass measures with small aperture optical telescopes. Furthermore, the optical eclipse duration is significantly shorter than that measured in M/GeV gamma-rays, possibly suggesting that a fraction of the eclipsed gamma-ray emission originates from the apex of the intrabinary shock. Based on these constraints, we estimate the magnetic field strength of the companion to be 30-170 G. This is consistent with the high field strength implied by the X-ray orbital modulation observed.

astro-ph.HE↗

arXiv2025

Two Possible Optical--X-Ray Anti-Correlations of PSR J1023+0038

X-ray emission is generally believed to be one of the major heating sources for the optical modulation in redback pulsar binaries as we have seen similar phenomena in many low mass X-ray binaries (LMXBs). While, e.g., MeV/GeV gamma-rays from the neutron stars are also possible heating sources, X-ray observations are currently much more sensitive, and therefore, joint optical--X-ray data are observationally unique on the irradiation mechanism investigation. Using 18 X-ray/B-band simultaneous XMM-Newton observations (717 ks in total) of the redback system PSR J1023+0038 taken during the LMXB state, we find a general trend that the amplitude of the B-band orbital modulation was lower when the observed X-ray flux was higher. Depending on the analysis method adopted, the statistical significance of the anti-correlation can be from 1.7sigma to 3.1sigma. We also extended the analysis to the GeV gamma-ray band using the Fermi-LAT data, but the result is insignificant to claim any relations. Moreover, another X-ray/optical correlation regarding the low modes of the system was found in some of the \textit{XMM-Newton} observations, and the astrophysical reason behind is currently unclear yet. These anti-correlations likely suggest that the irradiation is generally stronger when the X-ray flux is in a fainter state, indicating that there is a more dominant irradiation source than the X-ray emission.

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arXiv2022

Multi-Wavelength Observations Of A New Redback Millisecond Pulsar 4FGL J1910.7-5320

We present the study of multi-wavelength observations of an unidentified Fermi Large Area Telescope (LAT) source, 4FGL J1910.7-5320, a new candidate redback millisecond pulsar binary. In the 4FGL 95% error region of 4FGL J1910.7-5320, we find a possible binary with a 8.36-hr orbital period from the Catalina Real-Time Transient Survey (CRTS), confirmed by optical spectroscopy using the SOAR telescope. This optical source was recently independently discovered as a redback pulsar by the TRAPUM project, confirming our prediction. We fit the optical spectral energy distributions of 4FGL J1910.7-5320 with a blackbody model, inferring a maximum distance of 4.1 kpc by assuming that the companion fills its Roche-lobe with a radius of R = 0.7R_sun. Using a 12.6 ks Chandra X-ray observation, we identified an X-ray counterpart for 4FGL J1910.7-5320, with a spectrum that can be described by an absorbed power-law with a photon index of 1.0+/-0.4. The spectrally hard X-ray emission shows tentative evidence for orbital variability. Using more than 12 years of Fermi-LAT data, we refined the position of the γ-ray source, and the optical candidate still lies within the 68% positional error circle. In addition to 4FGL J1910.7-5320, we find a variable optical source with a periodic signal of 4.28-hr inside the 4FGL catalog 95% error region of another unidentified Fermi source, 4FGL J2029.5-4237. However, the γ-ray source does not have a significant X-ray counterpart in a 11.7 ks Chandra observation, with a 3-σ flux upper limit of 2.4*10^-14 erg cm^-2 s^-1 (0.3-7 keV). Moreover, the optical source is outside our updated Fermi-LAT 95% error circle. These observational facts all suggest that this new redback millisecond pulsar powers the γ-ray source 4FGL J1910.7-5320 while 4FGL J2029.5-4237 is unlikely the γ-ray counterpart to the 4.28-hr variable.

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