X-Ray and Radio Monitoring of the Neutron Star Low-mass X-Ray Binary 1A 1744-361: Quasiperiodic Oscillations, Transient Ejections, and a Disk Atmosphere
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 Kα, and Kβ X-ray absorption lines, whose origins likely lie in an accretion disk atmosphere.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2024
- DOI:
- 10.3847/1538-4357/ad35bd
- arXiv:
- arXiv:2310.01511
- Bibcode:
- 2024ApJ...966..232N
- Keywords:
-
- High energy astrophysics;
- Transient sources;
- Low-mass x-ray binary stars;
- Neutron stars;
- Pulsars;
- Accretion;
- 739;
- 1851;
- 939;
- 1108;
- 1306;
- 14;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 30 pages, 13 figures, and 8 tables. Accepted by ApJ (before proofs)