Investigation of transient X-ray sources in NGC 4214 and NGC 4303

In this thesis study, X-ray binary (XRB) and transient XRB sources in the galaxies NGC 4214 and NGC 4303 have been identified using archival data from the Chandra satellite. Analysis of the Chandra datasets revealed 51 X-ray sources in NGC 4214 and 54 in NGC 4303. Among these sources, 19 XRBs were identified in NGC 4214 and 23 in NGC 4303 falling within the field of view of HST/WFC3 imaging. A total of 3 transient XRBs and 6 transient source candidates were identified in both galaxies. The presence of potential optical counterparts of XRBs was investigated in HST/WFC3 images through precise astrometric calculations. Based on the masses of the identified optical counterparts in color-magnitude diagrams, XRBs in both galaxies were classified as 14 HMXBs, 8 IMXBs, and 16 LMXBs in total. Additionally, 2/3 of the transient sources were classified as LMXBs, while half of the transient source candidates were identified as HMXBs.