ACCRETION STATE AND LOCAL ENVIRONMENT ANALYSIS OF ULTRALUMINOUS X-RAY SOURCE HOLMBERG II X-1 USING SWIFT DATA

• Main Author: Hafizah, Izatul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/49781
• Institution: Institut Teknologi Bandung

\textit{Ultraluminous X-ray sources (ULXs) are point-like X-ray sources located outside the nucleus of a galaxy, with luminosities in excess of $3\times10^{39}$ erg s$^{?1}$. If it is assumed that ULX radiation is emitted isotropically, the luminosity of ULX exceeds the Eddington luminosity limit for a $\sim10 M_\odot$ black hole. If the Eddington limit applies to these objects then ULXs is one of the best candidates for an intermediate-mass black hole (IMBH). Alternatively, ULXs may represent a class of super-Eddington emitters and probe a regime in which the accretion rate is much higher than that seen in Galactic black hole binaries. If ULX has a high accretion rate, it does not require a large black hole mass, it can be supported by a stellar-mass black hole. However, the mechanism in ULX currently remains debated. In addition, environmental studies of ULX are also important to support analytical studies of the nature of ULX. This work aims to study the physical mechanism and local environment of one of the ULXs, Holmberg II X-1.}\\ \textit{Holmberg II X-1 data used in this study were taken from Swift observation archives, consisted of UVOT for UV-optical data and XRT for X-ray data. There are a total of 174 UVOT observation IDs until September 2019. Only 82 observation IDs were selected for XRT data. Because the XRT data available have low exposure time, we co-added the spectra to improve spectrum quality. There are three scenarios in co-adding the spectra applied for current study. Comparisons of these scenarios indicate spectral dependence on both the count rate and hardness ratio. The light curves of UVOT and XRT data show that the emission source in the optical-UV band and X-rays is not directly related because the light curves in these two bands do not show a correlation trend. Intensity analysis and Optical-UV image yielding a source that is dominated by H\textsubscript{II} region. Spectral fitting of Holmberg II X-1 indicates the requirement of high accretion rate.}