Multi-wavelength Studies on X-ray Sources in Globular Clusters

• Main Authors: Lu, Ting-Ni, 盧亭霓
• Other Authors: Kong, Albert K. H.
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/95175941518318713011

博士 === 國立清華大學 === 天文研究所 === 101 === This research is composed of two parts: (I) Studying the X-ray sources populations in globular clusters (GCs), and (II) Searching for the intermediate-mass black holes (IMBHs) in GCs. They are summarized as below. Part I: The binary content in GCs is crucial for the dynamical evolution of GCs. Studying the X-ray sources population would be an efficient method to explore the binary content since most of the X-ray sources in GCs are close binaries. The X-ray sources population contains various exotic binaries: low mass X-ray binaries, cataclysmic variables, millisecond pulsars, or chromospherically active binaries. By using Chandra and HST data, we would be able to observe and identify the X-ray sources in GCs. In order to study the possible formation origins of the X-ray sources in GCs, we construct the correlation for the X-ray source number and the physical parameters (core radius, core density, and metallicity) from 18 GCs. With the correlation, we would be able to predict the X-ray source number in GCs and to constrain their formation mechanisms – if they are formed through dynamical interactions or from primordial binaries. Part II: We make use of the fundamental plane of black hole activities to predict the possible radio emissions from IMBHs in GCs. If GCs contain some amount of ionzied gas, the IMBH at the center will accrete the gas and emit radio emission. With the assumed ratio of X-ray to radio flux and the assumed accretion state of black holes, we could predict the radio emission from the central IMBH, which is observable with current radio facilities. In our study, we use Australis Telescope Compact Array (ATCA) to search for the possible radio emissions from IMBHs in the two most massive GCs – 47 Tucane and Omega Centauri. Although we did not detect any central radio source in both GCs, we set an upper limit for the black hole masses and the existence of IMBHs in GCs is still possible. Either a tighter upper limit for the black hole masses or a detection of central radio source in GCs will be the direct and solid evidence against or for the existence of IMBHs in GCs.