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Description
This table contains some of the results from a study of the compact X-ray source population in the Seyfert 2 galaxy NGC 1068, imaged with a 50-ks Chandra observation. The authors find a total of 84 compact sources on the ACIS-S3 chip, of which 66 are located within the 25.0 B-mag/arcsec<sup>2</sup> isophote of the galactic disk of NGC 1068. In the reference paper, the spectra of the 21 X-ray sources with at least 50 counts were modeled with both multicolor disk blackbody and power-law models. The power-law model provides the better description of the spectrum for 18 of these sources. For fainter sources, the spectral index was estimated from the hardness ratio. Five sources have 0.4-8 keV intrinsic luminosities greater than 10<sup>39</sup> ergs s<sup>-1</sup>, assuming that their emission is isotropic and that they are associated with NGC 1068. The authors refer to these sources as intermediate-luminosity X-ray objects (IXOs). If these five sources are X-ray binaries accreting with luminosities that are both sub-Eddington and isotropic, then the implied source masses are >~7 solar masses, and so they are inferred to be black holes. Most of the spectrally modeled sources have spectral shapes similar to Galactic black hole candidates. However, the brightest compact source in NGC 1068 has a spectrum that is much harder than that found in Galactic black hole candidates and other IXOs. The brightest source also shows large amplitude variability on both short-term and long-term timescales, with the count rate possibly decreasing by a factor of 2 in ~2 ks during this Chandra observation, and the source flux decreasing by a factor of 5 between this observation and the grating observations taken just over 9 months later. The ratio of the number of sources with luminosities greater than 2.1 x 10<sup>38</sup> ergs s<sup>-1</sup> in the 0.4-8 keV band to the rate of massive (>5 solar masses) star formation is the same, to within a factor of 2, for NGC 1068, the Antennae, NGC 5194 (the main galaxy in M51), and the Circinus galaxy. This suggests that the rate of production of X-ray binaries per massive star is approximately the same for galaxies with currently active star formation, including "starbursts." The authors were concerned with the study of the discrete X-ray source population in NGC 1068, imaged within the 8.4 arcmin x 8.4 arcmin (35.3 kpc x 35.3 kpc) field of view of the ACIS S3 chip. Images were extracted from the reprocessed level 2 events file in soft (0.4-1.5 keV), hard (1.5-5.0 keV) and full (0.4-5.0 keV) energy bands. The authors used the CIAO program wavdetect to search the images in the three energy bands for discrete sources of X-ray emission. They analyzed the images using wavelet scales in the range from 1 pixel (0.492 arcsec) to 16 pixels (7.87 arcsec), separated by a factor of sqrt(2). The wavelet source detection threshold was set to 10<sup>-6</sup>, which gives approximately one false source for the whole S3 chip. The total number of sources detected by wavdetect in the soft, hard, and full energy band images was 115, 67, and 138, respectively. Each of these sources was examined carefully by eye, and only those 84 sources that appear compact to the eye are included in this source list. This table was created by the HEASARC in August 2015 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/591/138">CDS Catalog J/ApJ/591/138</a> file table1.dat. This is a service provided by NASA HEASARC .
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