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Last modified: 21 February 2020

URL: https://cxc.cfa.harvard.edu/csc/download.html

How to access the Chandra Source Catalog Release 2.0


Release 2.0 of the Chandra Source Catalog (CSC) contains both tabular data—such as source name, position, and photometric properties, as well as related information linking a master source to the stack and obervation properties—as well as associated data products, including source spectra, images, exposure maps, and draws files from the MCMC error analysis stages.

There are a range of options for accessing the data—both columns and files—discussed below:


The CSCview application

The main interface to CSC 2.0 is the CSCview application. This is a Java program which allows you to search release 2.0 of the catalog, as well as previous releases (1.0 and 1.1). The application provides access to both the database columns—such as master-source name and aperture photometry—and the associated files, such as the per-stack limiting-sensitivity images and per-compact-source spectral products (PHA, ARF, and RMF). The CXCview help page provides help on how to use this application.

[NOTE]
Note

If you have an old version of CSCview you will be told to update when it starts, as it may not be capable of searching the CSC 2.0 release.


Quick Search: the CSC web interface

This is a new interface for CSC 2.0, and lets you perform a basic search (equivalent to the default master-search query in CSCview) around one or more locations. It returns a fixed set of columns and the limiting sensitivity for each location. The other services described on this page should be used for more complex queries, access to different columns, or downloading data products.

The interface is at: http://cda.cfa.harvard.edu/cscweb/

The Simple Cross-Match interface is a web application which provides direct access to a basic set of properties for master sources located within a user-specified radius around a given position or target name ("Single Cone") or multiple positions in the sky ("Crossmatch"). Limiting sensitivity values are also returned for the searched position(s) if located within the footprint of CSC 2.0.


Single Cone Search

Users can search for CSC 2.0 master sources located around a position specified by the values of "Right Ascension" and "Declination" expressed in decimal degrees or in sexagesimal convention. Right ascension can be passed as Hours Minutes Seconds (HMS) or Degrees Minutes Seconds (DMS) while Declination can only be expressed as DMS. Both accept single space and commas as separators between different units. Users can also provide a source name instead of coordinates by selecting the "by name" option on the left side of the panel and filling the "Name" field. Four options to select a specific name resolver used by the tool to associate coordinates to the source name can be found under the "Resolver" drop-down menu.

The value of the maximum angular separation ("Search Radius") can be set to any value between 0 and 1 degrees, 0 and 60 arcminutes or 0 and 3600 arcseconds. The unit of measure can be selected in the drop down menu in the "Search Radius" section. The drop-down menu in the "Display" section of the tab allows to choose whether only the number of returned sources will be displayed ("COUNT"), or a predefined number of sources (10, 100, 1000 or "ALL").

By clicking on the "Search" button, a new tab "Results" is created. In the "Results" tab, the upper panel "Source Properties" display the list of CSC 2.0 sources, sorted by increasing angular separation (shown in the first column "Separation" in arcseconds) from the searched position, with and a set of measured properties from the master source table for each master source returned:

name, ra, dec, err_ellipse_r0, err_ellipse_r1, err_ellipse_ang, significance, likelihood_class, conf_flag, sat_src_flag, streak_src_flag, flux_aper_b, flux_aper_lolib_b, flux_aper_hilim_b, flux_aper_w, flux_aper_lolim_w, flu_aper_hilim_w

The lower panel "Limiting Sensitivity" displays the limiting sensitivity values in the location specified by the searched coordinates or by the target name. The limiting sensitivity columns returned are:

usrid, ra, dec, sr, flux_sens_b, flux_sens_w, photflux_sens_b, photflux_sens_w, flux_sens_true_b, flux_sens_true_w, photflux_sens_true_b, photflux_sens_true_w

where usrid is a user identifier number and sr is the search radius expressed in degrees.

Both panels can be minimized by clicking on the arrow symbols in their upper right corners, and sorted according to the values contained in each of the columns by clicking on the column names (one time for ascending order and two times for ascending order).

The "Display Options" button allows users to choose between sexagesimal and decimal degrees representations of coordinates displayed in both panels. The "Save Source Properties" button can be selected to download the sources returned by the search in a table with one of the three formats (VOTable, TSV or CSV) available. "Save Limiting Sensitivity" offers the same capabilities for the table of limiting sensitivity value(s).


Crossmatch Search

By selecting the "Crossmatch" tab in the "Home" page, users will be able to upload a list of positions as a VOTable or TSV table. Clicking on "Choose file" will open a window that can be used to select the file containing the list of coordinates.

Once selected, a new tab named "User Table Definition" will open: here users will be asked to map properties used for the crossmatch to the names of the appropriate columns in the uploaded table: RA and DEC, source ID, Search Radius and Position Error. The last three parameters can also be set to predefined values (auto-indexing for the Object ID) or fixed values for the Search radius and Position error (search radius cannot be larger than 1 arcsecond). Units for the Search Radius and Position Error can be picked from the associated drop-down menus. As for the "Single Cone" case, the drop-down menu in the "Display" section of the tab allows to choose whether only the number of returned sources will be displayed ("COUNT"), or a predefined number of sources (10, 100, 1000 or "ALL").

The upper panel "Source Properties" will display the list of CSC 2.0 sources located within the search radius from the coordinates searched. The properties returned are the same as described for "Single Cone" search with the addition of the probability, which expresses the likelihood of each crossmatch.

The lower panel "Limiting Sensitivity" will display the limiting sensitivity values for the positions located within the footprint of CSC 2.0. As for the "Single Cone" search, the "Display Options" button allows users to choose between sexagesimal and decimal degrees representations of coordinates displayed in both panels. The "Save Source Properties" button can be selected to download the sources returned in a table in one of the three formats available (VOTable, TSV or CSV) and "Save Limiting Sensitivity" provides the same capabilities for the table of limiting sensitivity value(s). Both panels can be minimized by clicking on the arrow symbols in their upper right corners and sorted according to the values contained in each of the columns by clicking on the column names (one time for ascending order and two times for ascending order).


CIAO scripts

The CIAO contributed-script package contains the search_csc and obsid_search_csc tools for searching the CSC. These scripts provide common "command-line" access services, but do not replicate all the functionality provided by CSCview.

The scripts default to search release 2.0, but can be changed to search release 1.1 with the catalog parameter.

[NOTE]
Note

You must update to at least version 4.11.5 of the contributed scripts package otherwise these scripts will fail with an error message similar to

# search_csc (06 March 2018): ERROR: Problem accessing CSC site.  Server responded with the following message:
Query error: master_obi_assoc not found. Specify owner.objectname or use sp_help to check whether the object
exists (sp_help may produce lots of output).

search_csc

Performs a cone search around a location—either given explicitly or as a name (which is converted to a location)—and returns the properties and associated data products for the matching sources. The exact set of columns and products returned can be changed.

The following example returns basic information—the master-source name, position, and observation id—for all sources within one arcminute of Polaris, with output to the screen and no download of associated data products:

unix% search_csc polaris 1 outfile=
search_csc
             pos = polaris
          radius = 1
         outfile = 
         radunit = arcmin
         columns = INDEF
     sensitivity = no
        download = none
            root = ./
           bands = broad,wide
       filetypes = regevt,pha,arf,rmf,lc,psf,regexp
         catalog = csc2
         verbose = 1
         clobber = no
            mode = ql


2 rows returned by query
2 Different Master Source(s).
1 Different Observation(s).

name                	ra          	dec         	sepn	obsid	
 2CXO J023149.6+891550	3.795698e+01	8.926411e+01	0.0085'	 6431	
 2CXO J023432.2+891529	3.863441e+01	8.925814e+01	0.64'	 6431	

obsid_search_csc

This script returns data—both columns and files—for one or more observation identifiers in the catalog.

Here we find all master sources in ObsId 6431, and save the results to the file sources.6431.tsv:

unix% obsid_search_csc 6431 sources.6431.tsv
obsid_search_csc
           obsid = 6431
         outfile = sources.6431.tsv
         columns = INDEF
        download = none
            root = ./
           bands = broad,wide
       filetypes = regevt,pha,arf,rmf,lc,psf,regexp
         catalog = csc2
         verbose = 1
         clobber = no
            mode = ql


34 rows returned by query
34 Different Master Source(s).
1 Different Observation(s).

name                	ra          	dec         	obsid	
 2CXO J014518.9+891732	2.632904e+01	8.929226e+01	 6431	
 2CXO J014614.3+891102	2.655971e+01	8.918411e+01	 6431	
...
 2CXO J033006.4+890752	5.252701e+01	8.913117e+01	 6431	
 2CXO J033910.1+892223	5.479212e+01	8.937325e+01	 6431	

The screen output shows name, location, and ObsId, whereas the fiel contains many-more columns. We can use the dmlist CIAO tool to view the contents (using the dmascii support for CSC TSV files):

unix% dmlist "sources.6431.tsv[opt kernel=text/tsv]" cols
 
--------------------------------------------------------------------------------
Columns for Table Block sources.6431.tsv
--------------------------------------------------------------------------------
 
ColNo  Name                 Unit        Type             Range
   1   name                              String[22]                          Source name in the format '2CXO Jhhmmss.s{+|-}ddmmss[X]'
   2   ra                   deg          Real4          -Inf:+Inf            Source position, ICRS right ascension
   3   dec                  deg          Real4          -Inf:+Inf            Source position, ICRS declination
   4   err_ellipse_r0       arcsec       Real4          -Inf:+Inf            Major radius of the 95% confidence level position error ellipse
   5   conf_flag                         String[5]                           Source may be confused (source and/or background regions overlap in one or more 
   6   sat_src_flag                      String[5]                           Source is saturated in all observations; source properties are unreliable
...
  61   var_index_b                       Int4           -                    Intra-observation Gregory-Loredo variability index in the range [0, 10]: indicat
  62   var_index_w                       Int4           -                    Intra-observation Gregory-Loredo variability index in the range [0, 10]: indicat
  63   detect_stack_id                   String[24]                          Detect stack identifier (designation of observation stack used for source detect

Using Virtual-Observatory interfaces

There are a number of interfaces provided to access release 2.0 of the CSC using International Virtual Observatory Alliance interfaces.

Astronomica Data Query Language

The ADQL interface can be used to query the catalog, but it does not provide access to the ancillary data products, such as spectral data files. Access is via a HTTP query, as described on the help page for the command-line interface.


Cone search

The VO cone-search service can be used to query version 2.0 of the CSC.

The interface is at: http://cda.cfa.harvard.edu/cscvo/

The cone search for version 1.1 of the CSC is available at http://cda.cfa.harvard.edu/csc1scs/


Table Access Protocol

The VO Table Access Protocol service can be used to query version 2.0 of the CSC.

The interface is at: http://cda.cfa.harvard.edu/csctap/

The TAP service for version 1.1 of the CSC is available at http://cda.cfa.harvard.edu/csc1tap/


Simple Image Access Protocal

The VO SIAP service can be used to identify images—in both FITS and JPEG formats—of sources and stacks in version 2.0 of the CSC.

The interface is at: http://cda.cfa.harvard.edu/cscsiap/

The SIA search for version 1.1 of the CSC is available at http://cda.cfa.harvard.edu/csc1siap/