Speaker
Description
Gamma-ray binaries are a rare subclass of high-mass systems in which a neutron star or black hole orbits an O- or B-type companion, producing broadband non-thermal emission that peaks in the γ-ray regime. This study investigates the particle populations responsible for the observed emission in the γ-ray binaries 1FGL J1018.6−5856 and LMC P3. Using phase-resolved 2019 MeerKAT L-band observations together with archival Swift-XRT data, we (i) perform a detailed radio analysis of each system and (ii) conduct a radio/X-ray cross-correlation study to probe the physical connection between these wavebands and constrain the dominant emission mechanisms.
Both systems appear as compact, unresolved radio sources in MeerKAT continuum images and show sinusoidal modulation consistent with their orbital periods. Their in-band spectral indices indicates a non-thermal synchrotron origin, and both binaries exhibit a clear “flatter-when-brighter" trend, with the spectral index α flattening near radio maxima and steepening toward minima, a behavior that can be interpreted as the result of phase-dependent absorption in the surrounding stellar material.
Discrete correlation functions reveal significant coherence between the radio and X-ray light curves. The best-fit lag values indicate that X-ray variations lead the radio by approximately one day in 1FGL J1018.6−5856 and by about four days in LMC P3, along their respective 16.5507-day and 10.301-day orbits. Although the lag estimates remain statistically consistent with zero within their uncertainties, the systematic tendency toward negative lags supports a synchrotron-cooling interpretation: high-energy electrons initially emit X-rays near the wind-wind shock interface before cooling and radiating at radio frequencies downstream.
Overall, the timing, spectral, and cross-correlation results favor a colliding-wind scenario in which particles are accelerated at the interaction boundary between the stellar and compact-object outflows. These findings therefore provide further indirect evidence that the compact companions in both systems are neutron stars.
| Stream | Science or Engineering |
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