Chandra X-Ray Observatory
	(CXC)
Skip to the navigation links
Last modified: 4 October 2013

Master Sources Table


Each distinct X-ray source identified on the sky is represented in the catalog by a single "master source" entry and one or more "source observation" entries, one for each observation in which the source has been detected. The master source entry records the best estimates of the properties of a source, based on the data extracted from the set of observations in which the source has been detected.

Note: Source properties in the catalog which have a value for each science energy band (type "double[6]" and "integer[6]" in the table below) have the corresponding letters appended to their names. For example, "flux_aper_b" and "flux_aper_h" represent the background-subtracted, aperture-corrected broad-band and hard-band energy fluxes, respectively.

Go to: Catalog Columns Index | Alphabetical List
Context Column Name Type Units Description
Source Name name string source name in the form "CXO Jhhmmss.s+ddmmss" [Chandra source names use the ICRS position to an accuracy of 0.1s in RA and 1.0s in Dec.]

Position and Position Errors ra double deg Source position, ICRS right ascension
dec double deg Source position, ICRS declination
err_ellipse_r0 double arcseconds major radius of the 95% confidence level error ellipse of the source position
err_ellipse_r1 double arcseconds minor radius of the 95% confidence level error ellipse of the source position
err_ellipse_ang double deg position angle of the major axis of the 95% confidence level error ellipse
gal_b double deg Source position, galactic latitude
gal_l double deg Source position, galactic longitude

Source Flags extent_flag Boolean Indicates an extended source. TRUE - deconvolved source extent is inconsistent with a point source at the 90% confidence level in any science energy band with a flux significance >= 3.0 in any contributing observation; otherwise, FALSE
conf_flag Boolean Indicates that source is in a confused region. FALSE - the source detection region is not confused [i.e. not found to contain multiple sources, does not overlap other source detection regions, and contains no overlapping source ellipses in all contributing observations]; otherwise, TRUE
pileup_flag Boolean Indicates that the source properties may be affected by ACIS pileup. FALSE - the pileup fraction does not exceed ~10% for all contributing ACIS observations and source detection energy bands; otherwise, TRUE
var_flag Boolean FALSE - variability is not detected within any single observation or between any pair of observations, in any science energy band; otherwise, TRUE
streak_src_flag Boolean Indicates that source lies on an ACIS readout streak. TRUE - all of the contributing observations are ACIS observations and contain source regions that overlap a defined region enclosing an identified readout streak; otherwise, FALSE
sat_src_flag Boolean Indicates a saturated source (strong ACIS pileup). TRUE - all of the contributing observations are ACIS observations that are significantly piled-up [to the extent that the source image may be flattened or have a central hole]; otherwise, FALSE.
man_inc_flag Boolean Indicates a source identified manually (automatic detection failed). TRUE - the source region was manually included in all of the contributing observations by human review; otherwise, FALSE
man_reg_flag Boolean Indicates that source parameters were manually adjusted due to pileup. TRUE - the source region parameters were manually modified in all of the contributing observations by human review [in the event of extreme pile-up]; otherwise, FALSE
man_match_flag Boolean Indicates that source observations were manually merged. TRUE - the set of individual source observations contributing to the current master source observation region was manually selected and modified by human review; otherwise, FALSE
var_inter_hard_flag Boolean Indicates that the source hardness ratios are variable. TRUE - the hardness ratios of at least one of the contributing individual source observations are statistically inconsistent with the corresponding hardness ratios of all of the other contributing individual source observations; otherwise, FALSE

Source Extent and Errors major_axis double arcseconds 1σ radius along the major axis of the ellipse defining the deconvolved source extent
major_axis_err double arcseconds Error on the deconvolved source extent major axis
minor_axis double arcseconds 1σ radius along the minor axis of the ellipse defining the deconvolved source extent
minor_exis_err double arcseconds Error on the deconvolved source extent minor axis
pos_angle double deg position angle of the major axis of the ellipse defining the deconvolved source extent
pos_angle_err double deg Error on the deconvolved source extent position angle

Source Fluxes For column names listed in this section, sources have at least one or as many as six filled (non-null) entries in the Master Source Catalog, corresponding to the six CSC energy bands (five ACIS bands, one HRC band).

ACIS source detection energy bands (keV): B (0.5-7.0), S (0.5-1.2), M (1.2-2.0), H (2.0-7.0)

ACIS science energy bands (keV): b (0.5-7.0), u (0.2-0.5), s (0.5-1.2), m (1.2-2.0), h (2.0-7.0)

HRC source detection and science energy band (keV): ~0.1-10.0

photflux_aper double[6] photons s-1 cm-2 background-subtracted, aperture-corrected photon fluxes for each science energy band, calculated from counts in the source region using the `direct' flux algorithm
photflux_aper90 double[6] photons s-1 cm-2 background-subtracted, aperture-corrected photon fluxes for each science energy band, calculated from counts in the elliptical aperture that includes the 90% Encircled Counts Fraction of the PSF at the source location using the `direct' flux algorithm
photflux_aper_hilim double[6] photons s-1 cm-2 upper confidence limits for "photflux_aper" values
photflux_aper_lolim double[6] photons s-1 cm-2 lower confidence limits for "photflux_aper" values
photflux_aper90_hilim double[6] photons s-1 cm-2 upper confidence limits for "photflux_aper90" values
photflux_aper90_lolim double[6] photons s-1 cm-2 lower confidence limits for "photflux_aper90" values
flux_aper double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in the source region using the `direct' flux algorithm
flux_aper90 double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in the elliptical aperture that includes the 90% Encircled Counts Fraction of the PSF at the source location, using the `direct' flux algorithm
flux_aper_hilim double[6] ergs s-1 cm-2 upper confidence limits for "flux_aper" values
flux_aper_lolim double[6] ergs s-1 cm-2 lower confidence limits for "flux_aper" values
flux_aper90_hilim double[6] ergs s-1 cm-2 upper confidence limits for "flux_aper90" values
flux_aper90_lolim double[6] ergs s-1 cm-2 lower confidence limits for "flux_aper90" values
flux_powlaw_aper double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in the source region by scaling a fixed power-law spectral model
flux_powlaw_aper90 double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in an elliptical aperture that includes the 90% Encircled Counts Fraction of the PSF at the source location by scaling a fixed power-law spectral model
flux_bb_aper double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in the source region by scaling a fixed blackbody spectral model
flux_bb_aper90 double[6] ergs s-1 cm-2 background-subtracted, aperture-corrected energy fluxes for each science energy band, calculated from counts in an elliptical aperture that includes the 90% Encircled Counts Fraction of the PSF at the source location, by scaling a fixed blackbody spectral model
flux_powlaw_aper_hilim double[6] ergs s-1 cm-2 upper confidence limits on "flux_powlaw_aper" values
flux_powlaw_aper_lolim double[6] ergs s-1 cm-2 lower confidence limits on "flux_powlaw_aper" values
flux_powlaw_aper90_hilim double[6] ergs s-1 cm-2 upper confidence limits on "flux_powlaw_aper90" values
flux_powlaw_aper90_lolim double[6] ergs s-1 cm-2 lower confidence limits on "flux_powlaw_aper90" values
flux_bb_aper_hilim double[6] ergs s-1 cm-2 upper confidence limits on "flux_bb_aper" values
flux_bb_aper_lolim double[6] ergs s-1 cm-2 lower confidence limits on "flux_bb_aper" values
flux_bb_aper90_hilim double[6] ergs s-1 cm-2 upper confidence limits on "flux_bb_aper90" values
flux_bb_aper90_lolim double[6] ergs s-1 cm-2 lower confidence limits on "flux_bb_aper90" values

Source Significance significance double highest value of source flux significance among all science energy bands and contributing observations to the merged source entry

Spectral Properties hard_xy double[3] hardness ratio for a pair of ACIS science energy bands, where x and y represent the higher (harder) and lower (softer) energy band designations, respectively.
hard_xy_hilim double[3] upper confidence limit on ''hard_xy'' value
hard_xy_lolim double[3] lower confidence limit on ''hard_xy'' value
alpha double photon index (α, defined as FE~E- α) for best-fit power-law model spectral fit to the PI event data extracted from the source region
alpha_hilim double upper confidence limit for alpha
alpha_lolim double lower confidence limit for alpha
flux_powlaw double ergs s-1 cm-2 integrated 0.5-7.0 keV energy flux for best fit power-law model spectral fit to the PI event data extracted from the source region
flux_powlaw_hilim double ergs s-1 cm-2 upper confidence limit on "flux_powlaw"
flux_powlaw_lolim double ergs s-1 cm-2 lower confidence limit on "flux_powlaw"
nh_powlaw double HI atoms 1020 cm-2 total neutral Hydrogen absorbing column density, NH, of the best fitting power-law model spectral fit to the PI event data extracted from the source region
nh_powlaw_hilim double HI atoms 1020 cm-2 upper confidence limit on "nh_powlaw"
nh_powlaw_lolim double HI atoms 1020 cm-2 lower confidence limit on "nh_powlaw"
kt double keV temperature of the best-fitting blackbody model spectral fit to the PI event data extracted from the source region
kt_hilim double keV upper confidence limit on kt
kt_lolim double keV lower confidence limit on kt
flux_bb double ergs s-1 cm-2 integrated 0.5-7.0 keV flux of the best-fitting blackbody model spectral fit
flux_bb_hilim double ergs s-1 cm-2 upper confidence limit on flux_bb
flux_bb_lolim double ergs s-1 cm-2 lower confidence limit on flux_bb
nh_bb double HI atoms 1020 cm-2 total neutral Hydrogen absorbing column density, NH, derived from the best-fitting thermal (black body) model spectral fits to the PI event data extracted from the source region
nh_bb_hilim double HI atoms 1020 cm-2 upper confidence limit on nh_bb
nh_bb_lolim double HI atoms 1020 cm-2 lower confidence limit on nh_bb
nh_gal double HI atoms 1020 cm-2 Galactic neutral Hydrogen column density, NH, in the direction of the source [determined from the interpolation data of Dickey and Lockman (1990; Ann. Rev. Astron. Astrophys., 28, 215)]

Source Variability ks_intra_prob double[6] Intra-observation Kolmogorov-Smirnov variability probability, i.e. probability that the source is variable within an observation, in each of the science energy bands, using the K-S test. (Highest value among contributing observations used).
kp_intra_prob double[6] Intra-observation Kuiper's test variability probability, i.e. probability that the source is variable within an observation, in each of the science energy bands, using Kuiper's test. (Highest value among contributing observations used).
var_intra_prob double[6] Intra-observation Gregory-Loredo variability probability, i.e. probability that the source is variable within an observation, in each of the science energy bands, using a Gregory-Loredo analysis. (Highest value among contributing observations used).
var_intra_index integer[6] Intra-observation variability index in the range [0,10] that indicates if the source region flux is uniform throughout an observation, in each of the science energy bands, using a Gregory-Loredo analysis. (Highest value among contributing observations used).
var_intra_sigma double[6] counts s-1 Intra-observation flux variability, i.e. the appropriately scaled count rate variability ("var_sigma"), in each of the science energy bands, using a Gregory-Loredo analysis. (Highest value among contributing observations used).
var_inter_prob double[6] Inter-observation source variability probability, i.e. the probability that the source region photon flux varied between the contributing observations, in each of the science energy bands, using the χ2 distribution of the photon fluxes and the standard deviations of the individual observations.
var_inter_index integer[6] Inter-observation variability index in the range [0,10] that indicates if the source region photon flux is constant between the contributing observations, in each of the science energy bands.
var_inter_sigma double[6] photons s-1 cm-2 Inter-observation flux variability, i.e. the spread of the source region photon flux densities of the individual observations about the error weighted mean source region photon flux density, in each of the science energy bands. (Highest value of flux variability among contributing observations used).

Observation Summary acis_num integer total number of ACIS imaging observations contributing to the Master Source Catalog record of the source
acis_hetg_num integer total number of ACIS/HETG observations contributing to the Master Source Catalog record of the source
acis_letg_num integer total number of ACIS/LETG observations contributing to the Master Source Catalog record of the source
acis_time double total ACIS imaging exposure time (seconds of good time) for all ACIS imaging observations contributing to the Master Source Catalog record of the source
acis_hetg_time double total ACIS/HETG observation exposure time (seconds of good time) for all ACIS/HETG observations contributing to the Master Source Catalog record of the source
acis_letg_time double total ACIS/LETG observation exposure time (seconds of good time) for all ACIS/LETG observations contributing to the Master Source Catalog record of the source
hrc_num integer total number of HRC imaging observations contributing to the Master Source Catalog record of the source
hrc_hetg_num integer total number of HRC/HETG observations contributing to the Master Source Catalog record of the source
hrc_letg_num integer total number of HRC/LETG observations contributing to the Master Source Catalog record of the source
hrc_time double total HRC imaging exposure time (seconds of good time) for all HRC imaging observations contributing to the Master Source Catalog record of the source
hrc_hetg_time double total HRC/HETG observation exposure time (seconds of good time) for all HRC/HETG observations contributing to the Master Source Catalog record of the source
hrc_letg_time double total HRC/LETG observation exposure time (seconds of good time) for all HRC/LETG observations contributing to the Master Source Catalog record of the source


Last modified: 4 October 2013
Smithsonian Institute Smithsonian Institute

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email:   cxcweb@head.cfa.harvard.edu Smithsonian Institution, Copyright © 1998-2016. All rights reserved.