A temporal scale to track the spectral transitions in low-mass X-ray binaries
Abstract
The results of a temporal analysis of observations for a sample of nine low-mass X-ray binaries (LMXBs) are presented. Of these sources, five host a neutron star (NS) primary (4U1608-52, Aql X-1, 4U1705-44, GX17+2-, and Cyg X-2), and four host a black hole (BH) (GX339-4, XTE J1859+226, H1743-322, and MAXI J1659-152). The NS group includes three Atolls and two Z-type sources. We utilized archival Proportional Counter Array (PCA)/RXTE data to construct high-resolution light-curves. A wavelet transform of the light curves is deployed to extract a minimal time-scale (MTS) associated with the spectral state of the sources. The MTS, together with the fractional root-mean-square (rms) and hardness ratios, is used to construct RMS-MTS and hardness-MTS diagrams that enable a direct comparison of the evolution of spectral transitions in the target sources. Observations with high fractional rms and high hardness cluster in a broad region occupied jointly by BH and NS sources. For low fractional rms observations, the Atolls exhibit large MTS whereas Z-type sources exhibit small MTS. This new feature raises the possibility of discriminating between these two types of sources. Moreover, in the hardness-MTS plane, BH sources are the sole occupiers of the low-hardness and small-MTS domain thus potentially signalling a unique property for distinguishing BH and NS hosts in LMXBs.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2022
- DOI:
- 10.1093/mnras/stab3352
- arXiv:
- arXiv:2111.01772
- Bibcode:
- 2022MNRAS.511.2535S
- Keywords:
-
- methods: data analysis;
- stars: black holes;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- accepted for publication in MNRAS