CXOXASSIST - Chandra XAssist Source List

Overview

This database table contains the latest Chandra XAssist source list. XAssist is a NASA-funded project for the automation of X-ray astrophysics, with emphasis on galaxies. It is capable of data reprocessing, source detection, and preliminary spatial, temporal, and spectral analysis for all sources with sufficient counts. The bulk of the system is written in Python, which in turn drives underlying software, e.g., CIAO for Chandra data. Pipelines running on Chandra observations of galaxies have generated the source list which comprises this HEASARC table. The pipeline also includes fields requested by users for various projects, most notably observations of a sample of quasars and several deep field observations have been processed. Note that the pipline processing is completely automated; therefore, users should visually inspect the results of any queries.

Catalog Bibcode

2003ASPC..295..465P

Bulletin

The CXOXASSIST database table was last updated on 18 August 2013.

References

`XAssist: A System for the Automation of X-ray Astrophysics Analysis', Ptak, A. and Griffiths, R., in ADASS XII: ASP Conference Series, 2003, Vol. 295, p. 465.

Provenance

This table was first created by the HEASARC in May 2005 based on the Chandra source list available at the XAssist website. In September 2010, the HEASARC switched over to using the "pipeline4" Chandra source list. It is updated on a weekly basis when and if the XAssist source list file at https://asd.gsfc.nasa.gov/xassist/pipeline4/chandra/master_srclist.csv is updated.

Parameters

Field_Name
The Chandra field designation.

Initial_Exposure
The initial exposure in seconds, i.e., the exposure time prior to filtering out of flares.

Exposure
The net exposure in seconds, i.e., the exposure time after filtering out of flares.

Source_Number
The X-ray source number within the given field.

Name
An unofficial designation for the X-ray source using the prefix 'X' for X-ray source and the J2000 coordinates HHMMSS.ss+DDMMSS.s.

Detector
The name of the Chandra detector for the particular source; in the case of the individual CCDs for an ACIS observation, this is the CCD number.

X_Pixel
The x-pixel position of the X-ray source in image coordinates.

Y_Pixel
The y-pixel position of the X-ray source in image coordinates.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates in the original source list.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates in the original source list.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Counts
The net X-ray source counts.

Counts_Error
The error in the net X-ray source counts.

Count_Rate
The net X-ray source count rate (ct/s).

Count_Rate_Error
The error in the net X-ray source count rate (ct/s).

SNR
The signal-to-noise ratio (SNR) of the X-ray source in terms of the equivalent number of backround fluctuations, defined as the net counts in the source over the square root of the background counts (C/B^0.5). Note that this is not the traditional definition of the SNR of a source, which is net counts over the square root of the total counts (C/T^0.5) for Poisson statistics.

Probability
The Poisson probability of the X-ray source, which should be similar to the integral of a normal curve from -1 * SNR to +1 * SNR for sources with large numbers of counts.

Major_Axis
The major axis, in arcsecs, of the elliptical Gaussian fit to the stamp image.

Major_Axis_Neg_Err
The negative error bar of the major axis of the elliptical Gaussian fit, in arcsecs.

Major_Axis_Pos_Err
The positive error bar of the major axis of the elliptical Gaussian fit, in arcsecs.

Minor_Axis
The minor axis, in arcsecs, of the elliptical Gaussian fit to the stamp image.

Minor_Axis_Neg_Err
The negative error bar of the minor axis of the elliptical Gaussian fit, in arcsecs.

Minor_Axis_Pos_Err
The positive error bar of the minor axis of the elliptical Gaussian fit, in arcsecs.

Position_Angle
The position angle (PA), in degrees, of the major axis of the elliptical Gaussian fit.

Position_Angle_Neg_Err
The negative error bar of the PA of the major axis of the elliptical Gaussian fit, in degrees.

Position_Angle_Pos_Err
The positive error bar of the PA of the major axis of the elliptical Gaussian fit, in degrees.

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

Extent_Flag
A source extent flag: F = point source, T = extended source, and A = asymmetric (the source may be extended or the point spread function (psf) may be asymmetric at that off-axis angle).

Variability_Flag
A variability flag: N = constant source, Y = source is variable.

NH_Gal
The Galactic Hydrogen column density, in H-atoms/cm².

Flux
The flux of the X-ray source, in erg/s/cm², in the 0.3 to 8 keV energy range, as estimated using a power-law model with a default slope of 1.8.

Fit_NH
The best-fit Galactic Hydrogen column density, in H-atoms/cm².

Fit_NH_Neg_Err
The negative error bar of the best-fit Galactic Hydrogen column density, in H-atoms/cm².

Fit_NH_Pos_Err
The positive error bar of the best-fit Galactic Hydrogen column density, in H-atoms/cm².

Fit_Photon_Index
The best-fit photon index to the spectrum of the X-ray source using an absorbed power-law model.

Fit_Photon_Index_Neg_Err
The negative error bar of the best-fit photon index.

Fit_Photon_Index_Pos_Err
The positive error bar of the best-fit photon index.

Fit_Chi_Squared
The Chi-squared of the best-fit absorbed power-law model.

Fit_DoF
The degrees of freedom (dof) of the best-fit spectral model.

Fit_Flux
The flux, in erg/s/cm², estimated from the best-fit spectral model.

Source_Flags
Source flags indicating the origin of the X-ray source parameters and whether the source is suspect, as follows:

          d (by itself): all parameters based on detection output
          s: counts, rate, and all spatial parameters derived from spatial fit
  	x: counts and rate determined from extracted source counts,
             flux determined using count rate and response specific to source
  	f: spectral fit performed
  	b: spatial fit was not successful (fitted source position deviated too
             much from detection position)
  	p: spatial fit model count rate is inconsistent with observed count
             rate, most likely indicating that the fit failed to converge
          c: source is confused (i.e., spatial extent of this source overlaps
             spatial extent of another source)

Html_File
This parameter is a link to the XAssist website and the file for the Chandra field in which the source was detected.

Version
The version number of XAssist which was used in the processing from which this X-ray source is taken.

Bckgrd_Counts
The current estimate of the number of background counts within the X-ray source region.

Aperture_Counts
The (net) number of counts for the X-ray source derived from aperture photometry.

Aperture_Counts_Error
The error in the net number of counts derived from aperture photometry.

Aperture_Bckgrd_Counts
The background counts in the X-ray source region derived from aperture photometry.

Simplespat_Counts
The counts in the X-ray source region derived from a simple (ie., not including PSF) spatial fit.

Simplespat_Bckgrd_Counts
The background counts in the X-ray source region derived from a simple spatial fit.

Soft_Counts
The (net) soft-band (0.5-2.0 keV) counts S in the X-ray source region from aperture photometry.

Hard_Counts
The (net) hard-band (2.0-8.0 keV) counts H in the X-ray source region from aperture photometry.

Soft_Bckgrd_Counts
The soft-band background counts in the source region.

Hard_Bckgrd_Counts
The hard-band background counts in the source region.

Hardness_Ratio
The X-ray source hardness ratio, defined as (H-S)/(H+S).

Hardness_Ratio_Error
The error in the X-ray source hardness ratio.

S_Scale
The source region size scale (from the bscale keyword in the source spectrum FITS file header). s_scale/b_scale gives the scale factor for subtracting the background from the source region.

B_Scale
The background region size scale (from the bscale keyword in the background spectrum FITS file header).

Aper_Count_Rate
The X-ray source count rate, in ct/s, based on aperture photometry.

Aper_Count_Rate_Error
The error in the aperture count rate, in ct/s.

Det_X
The x-position of the X-ray source in detector coordinates (tdetx for an ACIS source).

Det_Y
The y-position of the X-ray source in detector coordinates (tdety for an ACIS source).

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:26:30 EDT