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Last modified: 4 October 2013

Source Observations Table


Each identified distinct X-ray source on the sky is represented in the catalog by one or more "source observation" entries - one for each observation in which the source has been detected - and a single "master source" entry. The individual source entries record all of the properties about a detection extracted from a single observation, as well as associated file-based data products, which are observation-specific.

Note: Source properties in the catalog which have a value for each science energy band (type "double[6]", "long[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
Observation Identification obsid integer Observation Id (ObsID)
obi integer Observation Interval (ObI)

Pointing Information targname string target name for the observation
ra_targ double deg ICRS right ascension of the target
dec_targ double deg ICRS declination of the target
ra_pnt double deg ICRS right ascension of the mean pointing
dec_pnt double deg ICRS declination of the mean pointing
roll_pnt double deg roll angle of the mean pointing
ra_nom double deg ICRS right ascension of the tangent point
dec_nom double deg ICRS declination of the tangent point
roll_nom double deg roll angle of the tangent point

Timing Information gti_start double s start time for the valid data in mission elapsed time
gti_stop double s stop time for the valid data in mission elapsed time
gti_elapse double s total elapsed time of the observation. The total elapsed time is not equal to the total exposure time of the observation because periods of bad time may have been filtered out.
gti_obs string start time for the valid data in FITS standard format (ISO 8601)
gti_end string stop time for the valid data in FITS standard format (ISO 8601)
gti_mjd_obs double modified Julian date for the start time of the valid data
mjd_ref double modified Julian date reference corresponding to zero seconds mission elapsed time

Instrument Information instrument string instrument used for the observation: ACIS or HRC
grating string grating used for the observation: NONE, HETG, or LETG
datamode string data mode used for the observation
readmode string readout mode used for the observation: TIMED or CONTINUOUS; ACIS only
cycle string cycle for alternating exposure (interleaved) mode observations: P (primary) or S (secondary); ACIS only. Value is P for full-frame observations.
exptime double CCD frame time; ACIS only
timing_mode boolean TRUE if the observation was done in precision timing mode, FALSE if not; HRC only

Processing Information ascdsver string software version used to create the Level 3 event file
caldbver string calibration database version used to create the Level 3 event file
crdate string creation date and time (UTC) of the Level 3 event file

Observing Cycle ao integer Announcement of Opportunity (AO) number for the Chandra observing cycle in which the observation was scheduled

Source Identification region_id integer source region within the observation
source_id integer source component within the source region. For the first catalog release, this is always "1".

Position and Position Errors ra double[6] deg ICRS right ascension of the source for each science energy band
dec double[6] deg ICRS declination of the source for each science energy band
err_ellipse_r0 double[6] arcsec major radius of the 95% confidence level error ellipse of the source position for each science energy band
err_ellipse_r1 double[6] arcsec minor radius of the 95% confidence level error ellipse of the source position for each science energy band
err_ellipse_ang double[6] deg position angle of the major axis of the 95% confidence level error ellipse of the source position for each science energy band
gal_l double[6] deg Galactic longitude of the source for each science energy band for equinox J2000.0 and epoch J2000.0
gal_b double[6] deg Galactic latitude of the source for each science energy band for equinox J2000.0 and epoch J2000.0
theta double arcmin off-axis angle, θ, of the source
phi double deg azimuthal angle, φ, of the source
chipx double pixel the chipx position corresponding to the off-axis angles (θ, φ) of the source
chipy double pixel the chipy position corresponding to the off-axis angles (θ, φ) of the source

Source Significance detect_significance double[6] source significance of the detection computed by wavdetect for each source detection energy band
flux_significance double[6] flux significance for each source detection energy band

Source Flags extent_code coded byte indicates whether the source is extended in all science energy bands
conf_code coded byte indicates whether the source is in a confused region in any source detection energy band
pileup_warning double indicates that the source properties may be affected by ACIS pileup
var_code coded byte indicates source variability in any science energy band
edge_code coded byte indicates that the position or region dithered off a chip boundary
multi_chip_code coded byte indicates that the position or region dithered over multiple chip boundaries
streak_src_flag boolean indicates that the source lies on an ACIS readout streak
sat_src_flag boolean indicates a saturated source (strong ACIS pileup)
man_inc_flag boolean indicates the source was identified manually (automatic detection failed)
man_reg_flag boolean indicates that source parameters were manually adjusted due to pileup

Source Extent and Errors ra_aper double deg ICRS right ascension of the center of the source and background regions
dec_aper double deg ICRS declination of the center of the source and background regions
mjr_axis_aper double arcsec semi-major axis of the source region ellipse
mnr_axis_aper double arcsec semi-minor axis of the source region ellipse
pos_angle_aper double deg position angle of the semi-major axis of the source region ellipse
mjr_axis1_aperbkg double arcsec semi-major axis of the inner background annulus ellipse
mnr_axis1_aperbkg double arcsec semi-minor axis of the inner background annulus ellipse
mjr_axis2_aperbkg double arcsec semi-major axis of the outer background annulus ellipse
mnr_axis2_aperbkg double arcsec semi-minor axis of the outer background annulus ellipse
pos_angle_aperbkg double deg position angle of the inner and outer semi-major axes of the background annulus ellipse
area_aper double sq. arcseconds area of the modified source region
area_aperbkg double sq. arcseconds area of the modified background region
mjr_axis_raw double[6] arcsec 1σ radius along the major axis of the rotated elliptical Gaussian parameterization of the raw extent of a source for each science energy band
mnr_axis_raw double[6] arcsec 1σ radius along the minor axis of the rotated elliptical Gaussian parameterization of the raw extent of a source for each science energy band
pos_angle_raw double[6] deg position angle of the rotated elliptical Gaussian parameterization of the raw extent of a source for each science energy band
mjr_axis_raw_err double[6] arcsec error on the "mjr_axis_raw" value for each science energy band
mnr_axis_raw_err double[6] arcsec error on the "mnr_axis_raw" value for each science energy band
pos_angle_raw_err double[6] deg error on the "pos_angle_raw" value for each science energy band
psf_mjr_axis_raw double[6] arcsec major axis of the rotated elliptical Gaussian parameterization of the raw extent of the PSF for each science energy band
psf_mnr_axis_raw double[6] arcsec minor axis of the rotated elliptical Gaussian parameterization of the raw extent of the PSF for each science energy band
psf_pos_angle_raw double[6] deg position angle of the rotated elliptical Gaussian parameterization of the raw extent of the PSF for each science energy band
psf_mjr_axis_raw_err double[6] arcsec error on the "psf_mjr_axis_raw" value for each science energy band
psf_mnr_axis_raw_err double[6] arcsec error on the "psf_mnr_axis_raw" value for each science energy band
psf_pos_angle_raw_err double[6] arcsec error on the "psf_pos_angle_raw" value for each science energy band
major_axis double[6] arcsec best estimate value for the 1σ radius along the major axis of the rotated elliptical Gaussian parameterization of the deconvolved source extent ellipse for each science energy band
minor_axis double[6] arcsec best estimate value for 1σ radius along the minor axis of the rotated elliptical Gaussian parameterization of the deconvolved source extent ellipse for each science energy band
pos_angle double[6] deg best estimate value for the position angle of the rotated elliptical Gaussian parameterization of the deconvolved source extent ellipse for each science energy band
major_axis_err double[6] arcsec error on the "major_axis" value for each science energy band
minor_axis_err double[6] arcsec error on the "minor_axis" value for each science energy band
pos_angle_err double[6] deg error on the "pos_angle" value for each science energy band

Source Fluxes cnts_aper long[6] counts total counts measured in the modified source region for each science energy band
cnts_aperbkg long[6] counts total counts measured in the modified background region for each science energy band
cnts_aper90 long[6] counts total counts measured in the modified elliptical aperture for each science energy band
cnts_aper90bkg long[6] counts total counts measured in the modified elliptical background aperture for each science energy band
src_cnts_aper double[6] counts net background-subtracted source counts inferred from the modified source region for each science energy band
src_cnts_aper90 double[6] counts net background-subtracted source counts inferred from the modified elliptical aperture for each science energy band
mjr_axis_aper90 double arcsec major axis of the elliptical aperture that contains the 90% Encircled Counts Fraction of the PSF at the source location
mnr_axis_aper90 double arcsec minor axis of the elliptical aperture that contains the 90% Encircled Counts Fraction of the PSF at the source location
pos_angle_aper90 double deg position angle of the elliptical aperture that contains the 90% Encircled Counts Fraction of the PSF at the source location
mjr_axis1_aper90bkg double arcsec major axis of the inner annulus of the co-located, scaled elliptical background aperture
mnr_axis1_aper90bkg double arcsec minor axis of the inner annulus of the co-located, scaled elliptical background aperture
mjr_axis2_aper90bkg double arcsec major axis of the outer annulus of the co-located, scaled elliptical background aperture
mnr_axis2_aper90bkg double arcsec minor axis of the outer annulus of the co-located, scaled elliptical background aperture
pos_angle_aper90bkg double deg position angle of the co-located, scaled elliptical background aperture
area_aper90 double[6] sq. arcseconds area of the modified elliptical aperture
area_aper90bkg double[6] sq. arcseconds area of the modified elliptical background aperture
src_rate_aper double[6] Hz background-subtracted source count rate inferred from the modified source region for each science energy band
src_rate_aper_hilim double[6] Hz upper limit on the confidence interval of the "src_rate_aper" value for each science energy band
src_rate_aper_lolim double[6] Hz lower limit on the confidence interval of the "src_rate_aper" value for each science energy band
src_rate_aper90 double[6] Hz background-subtracted source count rate inferred from the modified elliptical aperture for each science energy band
src_rate_aper90_hilim double[6] Hz upper limit on the confidence interval of the "src_rate_aper90" value for each science energy band
src_rate_aper90_lolim double[6] Hz lower limit on the confidence interval of the "src_rate_aper90" value for each science energy band
photflux_aper double[6] photons s-1 cm-2 background-subtracted flux inferred from the modified source region for each science energy band
photflux_aper_hilim double[6] photons s-1 cm-2 upper limit on the confidence interval of the "photflux_aper" value for each science energy band
photflux_aper_lolim double[6] photons s-1 cm-2 lower limit on the confidence interval of the "photflux_aper" value for each science energy band
photflux_aper90 double[6] photons s-1 cm-2 background-subtracted flux inferred from the modified elliptical aperture for each science energy band
photflux_aper90_hilim double[6] photons s-1 cm-2 upper limit on the confidence interval of the "photflux_aper90" value for each science energy band
photflux_aper90_lolim double[6] photons s-1 cm-2 lower limit on the confidence interval of the "photflux_aper90" value for each science energy band
flux_aper double[6] ergs s-1 cm-2 background-subtracted flux inferred from the modified source region for each science energy band
flux_aper_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_aper" value for each science energy band
flux_aper_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_aper" value for each science energy band
flux_aper90 double[6] ergs s-1 cm-2 background-subtracted flux inferred from the modified elliptical aperture for each science energy band
flux_aper90_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_aper90" value for each science energy band
flux_aper90_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_aper90" value for each science energy band
flux_powlaw_aper double[6] ergs s-1 cm-2 power law model energy flux inferred from the modified source region for each science energy band
flux_powlaw_aper_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_powlaw_aper" value for each science energy band
flux_powlaw_aper_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_powlaw_aper" value for each science energy band
flux_powlaw_aper90 double[6] ergs s-1 cm-2 power law model energy flux inferred from the modified elliptical aperture for each science energy band
flux_powlaw_aper90_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_powlaw_aper90" value for each science energy band
flux_powlaw_aper90_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_powlaw_aper90" value for each science energy band
flux_bb_aper double[6] ergs s-1 cm-2 black body model energy flux inferred from the modified source region for each science energy band
flux_bb_aper_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_bb_aper" value for each science energy band
flux_bb_aper_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_bb_aper" value for each science energy band
flux_bb_aper90 double[6] ergs s-1 cm-2 black body model energy flux inferred from the modified elliptical aperture for each science energy band
flux_bb_aper90_hilim double[6] ergs s-1 cm-2 upper limit on the confidence interval of the "flux_bb_aper90" value for each science energy band
flux_bb_aper90_lolim double[6] ergs s-1 cm-2 lower limit on the confidence interval of the "flux_bb_aper90" value for each science energy band
psf_frac_aper double[6] fraction of the PSF included in the modified source region for each science energy band
psf_frac_aperbkg double[6] fraction of the PSF included in the modified background region for each science energy band
psf_frac_aper90 double[6] fraction of the PSF included in the modified elliptical aperture for each science energy band
psf_frac_aper90bkg double[6] fraction of the PSF included in the modified elliptical background aperture for each science energy band

Spectral Properties alpha double best-fit power law photon index (γ, defined as FE ∼ E)
alpha_hilim double upper limit on the confidence interval of the "alpha" value
alpha_lolim double lower limit on the confidence interval of the "alpha" value
flux_powlaw double ergs s-1 cm-2 integrated 0.5-7.0 keV flux derived from the best-fitting power law spectral fit
flux_powlaw_hilim double ergs s-1 cm-2 upper limit on the confidence interval of the "flux_powlaw" value
flux_powlaw_lolim double ergs s-1 cm-2 lower limit on the confidence interval of the "flux_powlaw" value
nh_powlaw double HI atoms 1020 cm-2 best-fit power law NH value
nh_powlaw_hilim double HI atoms 1020 cm-2 upper limit on the confidence interval of the "nh_powlaw" value
nh_powlaw_lolim double HI atoms 1020 cm-2 lower limit on the confidence interval of the "nh_powlaw" value
powlaw_stat double χ2 (data variance) statistic per degree of freedom for the best-fitting power law spectral fit
kt double keV best-fit thermal (black body) temperature (kT)
kt_hilim double keV upper limit on the confidence interval of the "kt" value
kt_lolim double keV lower limit on the confidence interval of the "kt" value
flux_bb double ergs s-1 cm-2 best-fit thermal (black body) spectral fit flux
flux_bb_hilim double ergs s-1 cm-2 upper limit on the confidence interval of the "flux_bb" value
flux_bb_lolim double ergs s-1 cm-2 lower limit on the confidence interval of the "flux_bb" value
nh_bb double best-fit thermal (black body) NH value
nh_bb_hilim double upper limit on the confidence interval of the "nh_bb" value
nh_bb_lolim double lower limit on the confidence interval of the "nh_bb" value
bb_stat double χ2 (data variance) statistic per degree of freedom for the best-fitting thermal (black body) spectral fit
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

Source Variability ks_prob double[6] Kolmogorov-Smirnov test probability for each science energy band
kp_prob double[6] Kuiper's test probability for each science energy band
var_prob double[6] Gregory-Loredo variability probability for each science energy band
var_index integer[6] variability index in the range [0,10] for each science energy band that combines the var_prob value with the fractions of the multi-resolution light curve output by the Gregory-Loredo analysis that are within 3 σ and 5 σ of the average count rate, to evaluate whether the source region flux is uniform throughout the observation
var_mean double[6] counts s-1 time-averaged value of the source region count rate for each science energy band
var_sigma double[6] counts s-1 time-averaged 1 σ statistical variability of the source region count rate for each science energy band
var_min double[6] counts s-1 minimum value of the source region count rate for each science energy band
var_max double[6] counts s-1 maximum value of the source region count rate for each science energy band
dither_warning_flag boolean TRUE if the highest statistically significant peak in the power spectrum of the source region count rate for each science energy band occurs either at the dither frequency of the observation or at a beat frequency of the dither frequency. Otherwise, the value is FALSE.

Source Timing Information livetime double s effective exposure time for the observation after applying the good time intervals and deadtime correction factor

Source Instrument Information detector string detector elements over which the background region bounding box dithers during the observation: HRC-I, HRC-S, or ACIS-<n>, where <n> is string of the CCD Ids (e.g. "ACIS-78"); see the ACIS focal plane figure in the POG.


Last modified: 4 October 2013
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