AstroSat and NICER timing view of the Z-type neutron star X-ray binary GX 340 + 0
Abstract
The timing properties of the Z-type low-mass X-ray binaries provide insights into the emission components involved in producing the unique Z-shaped track in the hardness-intensity diagrams of these sources. In this work, we investigate the AstroSat and NICER observations of the GX 340 + 0 covering the complete 'Z'-track from the horizontal branch (HB) to the extended flaring branch (EFB). For the first time, we present the Z-track as seen in soft X-rays using the AstroSat/Soft X-ray Telescope and NICER (the soft colour is defined as a ratio of 3-6 to 0.5-3 keV). The shape of the track is distinctly different in soft X-rays, strongly suggesting the presence of additional components active in soft X-rays. The detailed timing analysis revealed significant quasi-periodic oscillation throughout the HB and the normal branch (NB) using large area X-ray proportional counter and the first NICER detection of 33.1 ± 1.1 Hz HB oscillation (HBO) in 3-6 keV. The oscillations at the HB/NB vertex are observed to have higher frequencies (41-52 Hz) than the HBOs (16-31 Hz) and NB oscillations (6.2-8 Hz) but significantly lower rms (~1.6 per cent). The HBO is also limited to the energy range 3-20 keV, indicating an association of HBO origin with the non-thermal component. It is also supported by earlier studies that found the strongest X-ray polarization during HB.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2024
- DOI:
- 10.1093/mnras/stae309
- arXiv:
- arXiv:2401.15367
- Bibcode:
- 2024MNRAS.528.4125P
- Keywords:
-
- accretion;
- accretion discs;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 15 pages, 12 figures, 4 tables, accepted for publication in the MNRAS