Study of X-ray point sources in NGC 5643 and NGC 7457 with Chandra

In the present study we have analysed Chandra Observational data of 2 galaxies: NGC 5643 and NGC 7457. Four point sources from NGC 5643 and two point sources from NGC 7457 with net counts >= 100 were considered for the present study. The spectra of these sources were fitted using two spectral models-an absorbed powerlaw and an absorbed disk blackbody. The spectrum of all the sources can be explained almost equally by both the models. We report here the discovery of 3 Ultraluminous X-ray sources (ULXs), X-1, X-2 and X-3 in the galaxy NGC 5643 and one ULX, X-5 in the galaxy NGC 7457. The spectral parameters suggest that all the above four ULX sources are in hard state (Gamma similar to 1.42-1.86), which may be due to thermal comptonization. If explained by absorbed diskblack-body model, the Black Hole (BH) mass of these sources are estimated to be stellar mass BHs with X-2, & X-5 accreting at super-Eddington rate while X-1 and X-3 at sub-Eddington rate. Another ULX, X-4 in NGC 5643 which is also accreting at super-Eddington rate is found to be a variable ULX with its luminosity reducing from 4.4 x 10(40) ergs s(-1) to 2.27x10(40) ergs s(-1) in the 0.3-10.0 keV energy range within a period of 11 years.