Fornax A (NGC 1316) Chandra X-Ray Source Catalog

This table contains some of the results from a Chandra ACIS sub-arcsecond resolution X-ray observation of the archetypal merger radio galaxy NGC 1316 (Fornax A). The authors detect 81 point sources within the 25th magnitude isophotal ellipse D&lt;sub&gt;25&lt;/sub&gt; of NGC 1316 (L&lt;sub&gt;X&lt;/sub&gt; in the range of 2 x 10&lt;sup&gt;37&lt;/sup&gt; to 8 x 10&lt;sup&gt;39&lt;/sup&gt; ergs s&lt;sup&gt;-1&lt;/sup&gt;), with hard (kT ~ 5 keV) X-ray spectra, typical of X-ray binaries, and a spatial radial distribution consistent with that of the optical (i.e., stellar) surface brightness. In the reference paper, they derive the X-ray luminosity function (XLF) of these sources, correcting for the incompleteness at the faint end caused by the presence of the diffuse emission from the hot ISM in the central regions of NGC 1316 and by the widening of the Chandra point-spread functions at increasing distance from the aim point. With these corrections, the XLF is well reproduced by a single unbroken power law with a slope of -1.3 down to their threshold luminosity of ~ 3 x 10&lt;sup&gt;37&lt;/sup&gt; ergs s&lt;sup&gt;-1&lt;/sup&gt;. NGC 1316 was observed for 30 ks on 2001 April 17 (ObsID 2022), with the Chandra Advanced CCD Imaging Spectrometer (ACIS). The authors used the back-illuminated (BI) CCD S3 (CCD ID 7) because of its sensitivity at low energies. To include NGC 1317 (6.3 arcminutes away from NGC 1316) in the same S3 chip, a small offset was applied to the SIM (Science Instrument Module) position. NGC 1316 was kept close to on-axis to achieve the best spatial resolution. To detect X-ray sources, the authors used WAVDETECT, a wavelet detection algorithm available in CIAO. They set the WAVDETECT significance threshold parameter to be 10&lt;sup&gt;-6&lt;/sup&gt;, which corresponds to 1 possibly spurious source, and the scale parameter to cover seven steps between 1 and 64 pixels. This made them sensitive to sources ranging from point-like to 32 arcseconds in size, and in particular accommodates the variation of the point-spread function (PSF) as a function of the off-axis angle of the sources. To extract source properties (such as count rates, spectra, etc.), the authors used the 95% encircled energy (at 1.5 keV) radius centered at the WAVDETECT centroid, with a minimum of 3 arcseconds to accommodate the radial variation of he PSF. Background counts were determined locally for each source from an annulus from 2 to 5 times the source radius, after excluding nearby sources. Extended sources were found at the locations of NGC 1316 and NGC 1317. In addition, the Chandra observations reveal 94 sources (the HEASARC notes that 95 are contained in this table), 83 of them in CCD S3. Of these, 81 sources (77 in S3 and 4 in S2) are within the D&lt;sub&gt;25&lt;/sub&gt; ellipse. The source density increases toward the center of NGC 1316, indicating that most of them are related to NGC 1316. Three sources are found within the D&lt;sub&gt;25&lt;/sub&gt; ellipse of NGC 1317, with the brightest, extended one at the center of NGC 1317. The list of detected sources also includes sources found on CCDs other than S3 (CCD number 7). After correcting for effective exposure and vignetting, the X-ray flux in the 0.3 - 8.0 keV band is calculated with an energy conversion factor (ECF) assuming a power-law source spectrum with a slope of 1.7 and N&lt;sub&gt;H&lt;/sub&gt; = 3 x 10&lt;sup&gt;20&lt;/sup&gt; cm&lt;sup&gt;-2&lt;/sup&gt;; ECF = 6.037 x 10&lt;sup&gt;-12&lt;/sup&gt; erg cm&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; ergs per 1 count s&lt;sup&gt;-1&lt;/sup&gt; for the back-illuminated (BI) chips and 9.767 x 10&lt;sup&gt;-12&lt;/sup&gt; ergs per 1 count s&lt;sup&gt;-1&lt;/sup&gt; for the front-illuminated (FI) CCD chips. With the adopted distance of 18.6 Mpc, the X-ray luminosities of the point sources range from ~ 2 x 10&lt;sup&gt;37&lt;/sup&gt; to ~ 8 x 10&lt;sup&gt;39&lt;/sup&gt; erg s&lt;sup&gt;-1&lt;/sup&gt;. This table was created by the HEASARC in July 2014 based on &lt;a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/586/826"&gt;CDS Catalog J/ApJ/586/826&lt;/a&gt; file table1.dat. This is a service provided by NASA HEASARC .

Tags: __
Organization: National Aeronautics and Space Administration