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.
| Column Name | Type | Units | Description |
|---|---|---|---|
| alpha | double | best-fit power law photon index (γ, defined as FE ∼ E-γ) | |
| 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 | |
| ao | integer | Announcement of Opportunity (AO) number for the Chandra observing cycle in which the observation was scheduled | |
| area_aper | double | sq. arcseconds | area of the modified source region |
| 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 |
| area_aperbkg | double | sq. arcseconds | area of the modified background region |
| ascdsver | string | software version used to create the Level 3 event file | |
| bb_stat | double | χ2 (data variance) statistic per degree of freedom for the best-fitting thermal (black body) spectral fit | |
| caldbver | string | calibration database version used to create the Level 3 event file | |
| 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 |
| cnts_aper | long[6] | counts | total counts measured in the modified source 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 |
| cnts_aperbkg | long[6] | counts | total counts measured in the modified background region for each science energy band |
| conf_code | coded byte | indicates whether the source is in a confused region in any source detection energy band | |
| crdate | string | creation date and time (UTC) of the Level 3 event file | |
| cycle | string | cycle for alternating exposure (interleaved) mode observations: P (primary) or S (secondary); ACIS only. Value is P for full-frame observations. | |
| datamode | string | data mode used for the observation | |
| dec | double[6] | deg | ICRS declination of the source for each science energy band |
| dec_aper | double | deg | ICRS declination of the center of the source and background regions |
| dec_nom | double | deg | ICRS declination of the tangent point |
| dec_pnt | double | deg | ICRS declination of the mean pointing |
| dec_targ | double | deg | ICRS declination of the target |
| detect_significance | double[6] | source significance of the detection computed by wavdetect for each source detection energy band | |
| 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. | |
| 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. | |
| edge_code | coded byte | indicates that the position or region dithered off a chip boundary | |
| 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 |
| 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 |
| exptime | double | CCD frame time; ACIS only | |
| extent_code | coded byte | indicates whether the source is extended in all science energy bands | |
| flux_aper | double[6] | ergs s-1 cm-2 | background-subtracted flux inferred from the modified source region 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_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_bb | double | ergs s-1 cm-2 | best-fit thermal (black body) spectral fit flux |
| 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_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 |
| 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_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 |
| 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_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_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_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_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 |
| flux_significance | double[6] | flux significance for each source detection energy band | |
| gal_b | double[6] | deg | Galactic latitude of the source for each science energy band for equinox J2000.0 and epoch J2000.0 |
| gal_l | double[6] | deg | Galactic longitude of the source for each science energy band for equinox J2000.0 and epoch J2000.0 |
| grating | string | grating used for the observation: NONE, HETG, or LETG | |
| 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_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 | |
| gti_obs | string | start time for the valid data in FITS standard format (ISO 8601) | |
| 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 |
| 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 | |
| instrument | string | instrument used for the observation: ACIS or HRC | |
| kp_prob | double[6] | Kuiper's test probability for each science energy band | |
| ks_prob | double[6] | Kolmogorov-Smirnov test probability for each science energy band | |
| 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 |
| livetime | double | s | effective exposure time for the observation after applying the good time intervals and deadtime correction factor |
| 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 |
| major_axis_err | double[6] | arcsec | error on the "major_axis" value for each science energy band |
| 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 | |
| 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 |
| minor_axis_err | double[6] | arcsec | error on the "minor_axis" value for each science energy band |
| mjd_ref | double | modified Julian date reference corresponding to zero seconds mission elapsed time | |
| mjr_axis1_aper90bkg | double | arcsec | major axis of the inner annulus of the co-located, scaled elliptical background aperture |
| mjr_axis1_aperbkg | double | arcsec | semi-major axis of the inner background annulus ellipse |
| mjr_axis2_aper90bkg | double | arcsec | major axis of the outer annulus of the co-located, scaled elliptical background aperture |
| mjr_axis2_aperbkg | double | arcsec | semi-major axis of the outer background annulus ellipse |
| mjr_axis_aper | double | arcsec | semi-major axis of the source region ellipse |
| 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 |
| 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 |
| mjr_axis_raw_err | double[6] | arcsec | error on the "mjr_axis_raw" value for each science energy band |
| mnr_axis1_aper90bkg | double | arcsec | minor axis of the inner annulus of the co-located, scaled elliptical background aperture |
| mnr_axis1_aperbkg | double | arcsec | semi-minor axis of the inner background annulus ellipse |
| mnr_axis2_aper90bkg | double | arcsec | minor axis of the outer annulus of the co-located, scaled elliptical background aperture |
| mnr_axis2_aperbkg | double | arcsec | semi-minor axis of the outer background annulus ellipse |
| mnr_axis_aper | double | arcsec | semi-minor axis of the source region ellipse |
| 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 |
| 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 |
| mnr_axis_raw_err | double[6] | arcsec | error on the "mnr_axis_raw" value for each science energy band |
| multi_chip_code | coded byte | indicates that the position or region dithered over multiple chip boundaries | |
| 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 | |
| nh_powlaw | double | N HI atoms 1020 cm-2 | best-fit power law NH value |
| nh_powlaw_hilim | double | N HI atoms 1020 cm-2 | upper limit on the confidence interval of the "nh_powlaw" value |
| nh_powlaw_lolim | double | N HI atoms 1020 cm-2 | lower limit on the confidence interval of the "nh_powlaw" value |
| obi | integer | Observation Interval (ObI) | |
| obsid | integer | Observation Id (ObsID) | |
| phi | double | deg | azimuthal angle, φ, of the source |
| photflux_aper | double[6] | photons s-1 cm-2 | background-subtracted flux inferred from the modified source region 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 |
| 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 |
| pileup_warning | double | indicates that the source properties may be affected by ACIS pileup | |
| 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 |
| pos_angle_aper | double | deg | position angle of the semi-major axis of the source region ellipse |
| 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 |
| pos_angle_aper90bkg | double | deg | position angle of the co-located, scaled elliptical background aperture |
| pos_angle_aperbkg | double | deg | position angle of the inner and outer semi-major axes of the background annulus ellipse |
| pos_angle_err | double[6] | deg | error on the "pos_angle" value 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 |
| pos_angle_raw_err | double[6] | deg | error on the "pos_angle_raw" value for each science energy band |
| powlaw_stat | double | χ2 (data variance) statistic per degree of freedom for the best-fitting power law spectral fit | |
| psf_frac_aper | double[6] | fraction of the PSF included in the modified source 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 | |
| psf_frac_aperbkg | double[6] | fraction of the PSF included in the modified background region 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_mjr_axis_raw_err | double[6] | arcsec | error on the "psf_mjr_axis_raw" value 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_mnr_axis_raw_err | double[6] | arcsec | error on the "psf_mnr_axis_raw" value 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_pos_angle_raw_err | double[6] | arcsec | error on the "psf_pos_angle_raw" value for each science energy band |
| ra | double[6] | deg | ICRS right ascension of the source for each science energy band |
| ra_aper | double | deg | ICRS right ascension of the center of the source and background regions |
| ra_nom | double | deg | ICRS right ascension of the tangent point |
| ra_pnt | double | deg | ICRS right ascension of the mean pointing |
| ra_targ | double | deg | ICRS right ascension of the target |
| readmode | string | readout mode used for the observation: TIMED or CONTINUOUS; ACIS only | |
| region_id | integer | source region within the observation | |
| roll_nom | double | deg | roll angle of the tangent point |
| roll_pnt | double | deg | roll angle of the mean pointing |
| sat_src_flag | boolean | indicates a saturated source (strong ACIS pileup) | |
| source_id | integer | source component within the source region. For the first catalog release, this is always "1". | |
| 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 |
| src_rate_aper | double[6] | Hz | background-subtracted source count rate inferred from the modified source region 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 |
| 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 |
| streak_src_flag | boolean | indicates that the source lies on an ACIS readout streak | |
| targname | string | target name for the observation | |
| theta | double | arcmin | off-axis angle, θ, of the source |
| timing_mode | boolean | TRUE if the observation was done in precision timing mode, FALSE if not; HRC only | |
| var_code | coded byte | indicates source variability in any 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_max | double[6] | counts s-1 | maximum value of the source region count rate for each science energy band |
| var_mean | double[6] | counts s-1 | time-averaged value 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_prob | double[6] | Gregory-Loredo variability probability 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 |