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  • X-Ray and Radio Monitoring ...
    Ng, Mason; Hughes, Andrew K.; Homan, Jeroen; Miller, Jon M.; Pike, Sean N.; Altamirano, Diego; Bult, Peter; Chakrabarty, Deepto; Buisson, D. J. K.; Coughenour, Benjamin M.; Fender, Rob; Guillot, Sebastien; Güver, Tolga; Jaisawal, Gaurava K.; Jaodand, Amruta D.; Malacaria, Christian; Miller-Jones, James C. A.; Sanna, Andrea; Sivakoff, Gregory R.; Strohmayer, Tod E.; Tomsick, John A.; van den Eijnden, Jakob

    The Astrophysical journal, 05/2024, Letnik: 966, Številka: 2
    Journal Article

    Abstract We report on X-ray (NICER/NuSTAR/MAXI/Swift) and radio (MeerKAT) timing and spectroscopic analysis from a 3 month monitoring campaign in 2022 of a high-intensity outburst of the dipping neutron star low-mass X-ray binary 1A 1744−361. The 0.5–6.8 keV NICER X-ray hardness–intensity and color–color diagrams of the observations throughout the outburst suggest that 1A 1744−361 spent most of its outburst in an atoll-state, but we show that the source exhibited Z-state-like properties at the peak of the outburst, similar to a small sample of other atoll-state sources. A timing analysis with NICER data revealed several instances of an ≈8 Hz quasiperiodic oscillation (QPO; fractional rms amplitudes of ∼5%) around the peak of the outburst, the first from this source, which we connect to the normal branch QPOs seen in the Z-state. Our observations of 1A 1744−361 are fully consistent with the idea of the mass accretion rate being the main distinguishing parameter between atoll- and Z-states. Radio monitoring data by MeerKAT suggests that the source was at its radio-brightest during the outburst peak, and that the source transitioned from the “island” spectral state to the “banana” state within ∼3 days of the outburst onset, launching transient jet ejecta. The observations present the strongest evidence for radio flaring, including jet ejecta, during the island-to-banana spectral state transition at low accretion rates (atoll-state). The source also exhibited Fe xxv , Fe xxvi K α , and K β X-ray absorption lines, whose origins likely lie in an accretion disk atmosphere.