Work

X-ray and radio view of the Be/X-ray binary pulsar 1A 1118−61 during the 2026 giant outburst

Year: 2026

Type: article

Abstract: ABSTRACT We present a detailed X-ray and radio study of the Be/X-ray binary pulsar 1A 1118–61 during its 2026 giant outburst using NuSTAR, Swift/XRT, and MeerKAT observations. Timing analysis reveals coherent pulsations with spin periods of $\sim$408.77 and $\sim$408.30 s at luminosities of $\sim$2.44 $\times$ 10$^{37}$ erg s$^{-1}$ and $\sim$9.7 $\times$ 10$^{35}$ erg s$^{-1}$, respectively. The pulse profiles show a clear dependence on both energy and luminosity. At higher luminosity, the profile is smooth and single-peaked, whereas at lower luminosity, an absorption-like feature appears, indicating changes in the accretion geometry. A quasi-periodic oscillation (QPO) at 0.106 Hz is detected during the NuSTAR observation at higher luminosity. Broadband spectral analysis using NuSTAR data reveals a cyclotron resonance scattering feature (CRSF) at $\sim$53.9 keV during the high-luminosity observation, corresponding to a neutron star magnetic field strength of $\sim$6.0 $\times$ 10$^{12}$ G. However, no CRSF is detected in the spectrum at the lower luminosity. An iron K$\alpha$ line at 6.4 keV is evident in both NuSTAR observations, while an additional weak higher-energy iron emission feature at $\sim$6.9 keV is detected in the high-luminosity NuSTAR observation. The Swift/XRT spectra in the 1–10 keV energy range are well described using an absorbed power law and a blackbody component. Radio observation with MeerKAT during the decay phase of the X-ray outburst results in a non-detection, providing a stringent upper limit on the radio luminosity. This indicates weak or absent radio emission from 1A 1118–61 at the time of observation.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag1452