Multi wavelength analysis of selected ultraluminous X-ray sources
Abstract
Ultraluminous X-ray Sources (ULX) are point-like sources in external galaxies with an X-ray luminosity (πΏπ β₯1039 πππ π β1 ) exceeding the Eddington limit for a stellar-mass black hole. In this study, X-ray spectral, temporal and optical properties of transient M51 ULX-4 and NGC 1672 ULX X-7 extensively investigated using archival Chandra, XMMNewton, Swift and HST. In this study, for the first time X-7 was determined as ULX source using 2019 Chandra observations. Another important part of this study is ULX-4 which showed highly long-term X-ray flux variability (factor of ~200) over the 20-year. In this long-term, ULX-4 showed bi-modal X-ray flux distributions the same most pulsar ULXs. In this study focused on using the precise source positions obtained via improved astrometry based on Chandra and HST observations to search for and identify potential optical counterparts for ULXs. The astrometric error radius was calculated as 0,22" and 0,20" for X-7 and ULX-4, with 95% confidence, respectively. Within this error, one and two optical counterparts were determined for X-7 and ULX-4, respectively. The spectral energy distributions (SED) generated by the different wavelengths of the HST data provided important clues about the nature of optical emission. The SED of the optical counterpart of the X-7 well-fitted with power-law, while the two counterparts of the ULX-4 conformed to the blackbody model. One of ULX-4 counterparts exhibited a low-amplitude optical periodicity of 264 days. For this periodicity, two important scenarios are presented the nature of the compact object. These scenarios have been interpreted in terms of the orbital motion of the donor and possible interactions of the compact object with an accretion disk.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- September 2022
- DOI:
- 10.5281/zenodo.10004745
- Bibcode:
- 2022PhDT........15A
- Keywords:
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- X-ray binary;
- ULXs;
- NGC 1316;
- M51;
- optical counterparts