NGC55CXO - NGC 55 Chandra X-Ray Point Source Catalog

Overview

This table contains a comprehensive X-ray point source catalog of the SB(s)m galaxy NGC 55, a member of the nearby Sculptor group of galaxies, as part of the Chandra Local Volume Survey. The combined archival observations of this galaxy have an effective exposure time of 56.5 ks. When combined with the catalogs of sources in NGC 2403 and NGC 4214 given in this same reference paper, and the authors' previously published catalogs for NGC 300 (Binder et al. 2012, ApJ, 758, 15) and NGC 404 (Binder et al. 2013, ApJ, 763, 128), the CLVS contains 629 high-significance X-ray sources total down to a limiting unabsorbed luminosity of ~ 5 x 10³⁵ erg s^-1 in the 0.35-8.0 keV band in each of the five galaxies. In the reference paper, the authors present X-ray hardness ratios, spectral analysis, radial source distributions, and an analysis of the temporal variability for the X-ray sources detected at high significance. To constrain the nature of each X-ray source, they carried out cross-correlations with multi-wavelength data sets. They searched overlapping Hubble Space Telescope observations for optical counterparts to their X-ray detections to provide preliminary classifications for each X-ray source as a likely X-ray binary, background active galactic nucleus, supernova remnant, or foreground star.

The authors utilized archival X-ray observations: NGC 55 was observed by the Chandra X-Ray Observatory on 2001 September 11 for 47 ks using the ACIS-I array (Obs. ID 2255), and on 2004 June 29 for 9.5 ks using the ACIS-I array (Obs. ID 4744). The iterative source detection strategy that was used is described in Section 2.3 of Binder et al. (2012, ApJ, 758, 15). ACIS-Extract (AE) was run a final time on the source list that was produces after an initial run of wavdetect followed by several iterations of AE, and the Poisson probability of not being a source (pns) value was computed in each of the following nine energy bands: 0.5 - 8.0, 0.5 - 2.0, 2.0 - 8.0, 0.5 - 1.0, 1.0 - 2.0, 2.0 - 4.0, 4.0 - 8.0, 0.35 - 1.0 or 0.35 - 8.0 keV. To be included in the final NGC 55 catalog, a source was required to have a pns value less than 4 x 10^-6 in any of the nine energy bands. The final CLVS source catalog for NGC 55 contains 154 sources.

Catalog Bibcode

2015AJ....150...94B

References

The Chandra Local Volume Survey. I. The X-ray point-source populations of
NGC 55, NGC 2403, and NGC4214.
    Binder B., Williams B.F., Eracleous M., Plucinsky P.P., Gaetz T.J.,
    Anderson S.F., Skillman E.D., Dalcanton J.J., Kong A.K.H., Weisz D.R.
   <Astron. J., 150, 94 (2015)>
   =2015AJ....150...94B

Provenance

This table was created by the HEASARC in September 2015 based on machine-readable versions of those parts of Table 5 and 8 from the reference paper which pertained to the 154 high-significance (pns < 4 x 10^-6) X-ray sources which were detected in NGC 55. It does not include the 76 lower-significance sources in NGC 55 which had 4 x 10^-6 < pns < 1.0 x 10^-3, some of which are likely to be genuine X-ray sources.

Parameters

Source_Number
A running X-ray source number in order of increasing J2000.0 Right Ascension.

Name
The name of the X-ray source using the 'CXOLV' prefix (for Chandra X-ray Observatory Local Volume Survey source) and the J2000.0 coordinates of the source in the (higher precision than standard) HHMMSS.ss+DDMMSS.s format.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10^-6 degrees in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10^-6 degrees in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The positional uncertainty of the X-ray source, being the radius of a simple error circle around the source position, in arcseconds.

Off_Axis
The off-axis angle of the X-ray source, in arcminutes.

Counts
The total net counts in the X-ray source in the 0.35 - 8 keV band.

Counts_Pos_Err
The upper uncertainty in the total net counts in the X-ray source in the 0.35 - 8 keV band.

Counts_Neg_Err
The lower uncertainty in the total net counts in the X-ray source in the 0.35 - 8 keV band.

Log_Prob_NS_Limit
This limit parameter is set to '<' if the corresponding parameter value is an upper limit rather than an actual value.

Log_Prob_NS
The logarithm of the Poisson probability of not being a source (log prob_no_source or log pns) in the 0.35 - 8 keV band. Values smaller than -10 have been replaced by "<-10".

Flux
This parameter contains the unabsorbed X-ray flux in the 0.35-8 keV energy band, in erg cm^-2 s^-1.

Hardness_Ratio_1
The hardness ratio HR1 (the "soft" color), where HR1 = (M-S)/(H+M+S) and S, M and H are the net counts in the following bandpasses:

       S = 0.35-1.1 keV;
       M = 1.1-2.6 keV;
       H = 2.6-8 keV.

Hardness_Ratio_1_Error
The uncertainty in the "soft" hardness ratio HR1.

Hardness_Ratio_2
The hardness ratio HR2 (the "hard" color), where HR2 = (H-M)/(H+M+S) and S, M and H are the net counts in the following bandpasses:

       S = 0.35-1.1 keV;
       M = 1.1-2.6 keV;
       H = 2.6-8 keV.

Hardness_Ratio_2_Error
The uncertainty in the "hard" hardness ratio HR2.

Source_Type
The classification of the Chandra source based on the X-ray hardness ratios HR1 and HR2. In Section 5.1 and Table 7 of the reference paper, the authors define six categories of X-ray sources: "XRB/AGN"-like (which contains both XRBs and background AGNs, given their X-ray similarities), "ABS" for heavily absorbed sources, "SNR"-like (which also contains foreground stars and supersoft sources), indeterminate "HARD" and "SOFT" sources, and "INDET" for sources with an indeterminate spectral shape.

Contact Person

Questions regarding the NGC55CXO database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:32:06 EDT