Astrophysics and Space Science

, 362:223 | Cite as

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

  • Akram Chandrajit SinghaEmail author
  • A. Senorita Devi
Original Article


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 \({\ge} 100\) 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 (\(\varGamma \sim 1.42\mbox{--}1.86\)), which may be due to thermal comptonization. If explained by absorbed diskblackbody 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 \(4.4 \times 10^{40}~\mbox{ergs}\,\mbox{s}^{-1}\) to \(2.27 \times 10^{40}~\mbox{ergs}\,\mbox{s}^{-1} \) in the 0.3–10.0 keV energy range within a period of 11 years.


Galaxies: individual (NGC 5643, NGC 7547) X-rays: binaries 



The authors would like to thank CXC Archive for the resource of data used for the present work and also the anonymous referee for helpful comments, which have improved the quality of this paper.


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Copyright information

© Springer Science+Business Media B.V. 2017

Authors and Affiliations

  1. 1.Assam UniversitySilcharIndia

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