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

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Overview

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 D25 of NGC 1316 (LX in the range of 2 x 1037 to 8 x 1039 ergs s-1), 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 1037 ergs s-1.

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 10-6, 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 D25 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 D25 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 NH = 3 x 1020 cm-2; ECF = 6.037 x 10-12 erg cm-2 s-1 ergs per 1 count s-1 for the back-illuminated (BI) chips and 9.767 x 10-12 ergs per 1 count s-1 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 1037 to ~ 8 x 1039 erg s-1.


Catalog Bibcode

2003ApJ...586..826K

References

Chandra X-ray observations of NGC 1316 (Fornax A).
    Kim D.-W., Fabbiano G.
   <Astrophys. J. 586, 826 (2003)>
   =2003ApJ...586..826K

Provenance

This table was created by the HEASARC in July 2014 based on CDS Catalog J/ApJ/586/826 file table1.dat.

Parameters

Name
The standard Chandra X-ray source designation, viz., 'CXOU JHHMMSS.s+DDMMSS', where the prefix stands for Chandra X-ray Observatory, unregistered, and the numbers are the truncated J2000.0 coordinates of the source.

Source_Flag
This flag parameter indicates the localization of the Chandra source as follows:

        A = Within the D25 ellipse of NGC 1316
        B = Within the D25 ellipse of NGC 1317
        C = Beyond the D25 ellipses of NGC 1316 and NGC 1317
  

CCD_Number
The Chandra ACIS CCD number on which the source was detected. See http://cxc.harvard.edu/proposer/POG/html/chap6.html for more details.

Detection_Number
The source detection number on the specified ACIS CCD.

RA
The Right Ascension of the Chandra X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 0.1 seconds of time in the original table.

Dec
The Declination of the Chandra X-ray source in the selected equinox. This was given in J2000 equatorial coordinates to a precision of 0.1 arcseconds in the original table

LII
The Galactic Longitude of the Chandra X-ray source.

BII
The Galactic Latitude of the Chandra X-ray source.

Extraction_Radius
The extraction radius used for the Chandra X-ray source, i.e., 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 the PSF.

Counts
The net background-corrected counts of the Chandra X-ray source in the 0.3 - 8 keV energy range.

Counts_Error
The rms uncertainty in the net background-corrected counts of the Chandra X-ray source in the 0.3 - 8 keV energy range.

Count_Rate
The 0.3 - 8.0 keV band count rate of the Chandra X-ray source, in ct/s (converted by the HEASARC from the ct/ks units used in the original table).

Lx
The X-ray luminosity, in erg s-1, of the Chandra source, which is assumed to be at the distance of NGC 1316/NGC 1317 if within their D25 ellipses), and is calculated as described in the Overview (see above).

Note_Flags
This parameter contains flags indicating the following notes concerning the Chandra X-ray source:

        1 = Sources within 20" from the center of NGC 1316. The source count
            may be contaminated by the diffuse emission.
        2 = There is another source(s) within the source extraction radius.
        3 = Sources fall near the edge of the detector. The source count
            should be considered as a lower limit.
        4 = A potential ULX source.
        5 = Coincident with globular clusters listed in Shaya et al.
            (1996, AJ, 111, 2212) and Goudfooij et al. (2001, MNRAS, 322, 643).
        6 = At the center of NGC 1316.
        7 = Close to the center of NGC 1316. Its count may be overestimated.
        8 = At the center of NGC 1317.
        9 = A potential super soft X-ray source.
  

Contact Person

Questions regarding the FORNAXACXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 9-Jul-2014