Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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STUDY OF ULTRALUMINOUS X-RAY SOURCES IN SOME NEARBY GALAXIES

  • Received : 2018.09.19
  • Accepted : 2019.01.02
  • Published : 2019.02.28
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Abstract

We present the results of the spectral and temporal analysis of eight X-ray point sources in five nearby (distance < 20 Mpc) galaxies observed with Chandra. For spectral analysis, an absorbed powerlaw and an absorbed diskblackbody were used as empirical models. Six sources were found to be equally fitted by both the models while two sources were better fitted by the powerlaw model. Based on model parameters, we estimate the X-ray luminosity of these sources in the energy range 0.3 - 10.0 keV, to be of the order of ${\sim}10^{39}ergs\;s^{-1}$ except for one source (X-8) with $L_X>10^{40}ergs\;s^{-1}$. Five of these maybe classified as Ultraluminous X-ray sources (ULXs) with powerlaw photon index within the range, ${\Gamma}{\sim}1.63-2.63$ while the inner disk temperature, kT ~ 0.68 - 1.93 keV, when fitted with the disk blackbody model. The black hole masses harboured by the X-ray point sources were estimated using the disk blackbody model to be in the stellar mass range, however, the black hole mass of one source (X-6) lies within the range $68.37M_{\odot}{\leq}M_{BH}{\leq}176.32M_{\odot}$, which at the upper limit comes under the Intermediate mass black hole range. But if the emission is considered to be beamed by a factor ~ 5, the black hole mass reduces to ${\sim}75M_{\odot}$. The timing analysis of these sources does not show the presence of any short term variations in the kiloseconds timescales.

Keywords

CMHHBA_2019_v52n1_1_f0001.tif 이미지

Figure 1. Absorbed powerlaw spectra of the X-ray sources

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Figure 2. Absorbed diskblackbody spectra of the X-ray sources

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Figure 3. Lightcurves Of The X-ray point sources

Table 1 Observation log of the sample galaxies

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Table 2 Characteristics of the point sources

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