Last modified: March 2024

AHELP for CIAO 4.16


Context: Tools::Download


Search the Chandra Source Catalog by OBS_ID


obsid_search_csc  obsid outfile [columns] [download] [root] [bands]
[filetype] [catalog] [verbose] [clobber]


'obsid_search_csc' uses the command line interface to the Chandra Source Catalog (CSC) to retrieve source properties and associated data products by Observation ID (obsid).

Users enter one or more OBS_ID values and the tool will query the CSC. The source properties results are written, one line per source, to a tab-separated-value (TSV) format output file, and when verbose is one or higher a subset of the data for each source is printed to the screen. The output file will contain a default set of catalog columns unless this is overridden with the 'columns' parameter. The data products associated with the sources may also be retrieved including the event files, response files (ARF, RMF, PSF, exposure map), and related histograms (spectra, lightcurves, images).

More complex queries including doing cross matches must be done using the CSCView application.


Example 1

unix% obsid_search_csc obsid=635 outfile=635.tsv download=none mode=h

Search for all sources that were detected in OBS_ID 635 in CSC 2:

           obsid = 635
         outfile = 635.tsv
         columns = INDEF
        download = none
            root = ./
           bands = broad,wide
       filetypes = regevt,pha,arf,rmf,lc,psf,regexp
         catalog = csc2
         verbose = 1
         clobber = no
            mode = h

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

name                	ra          	dec         	obsid	
 2CXO J162603.0-242336	2.465126e+02	-2.439342e+01	  635	
 2CXO J162605.7-242756	2.465241e+02	-2.446565e+01	  635	
 2CXO J162606.3-242132	2.465264e+02	-2.435916e+01	  635	
 2CXO J162607.0-242724	2.465293e+02	-2.445679e+01	  635	
 2CXO J162754.6-243715	2.469778e+02	-2.462110e+01	  635	
 2CXO J162755.1-242839	2.469800e+02	-2.447770e+01	  635	

Returns a TSV format file with source list. The default set of columns returned are not printed to the screen but are saved in the TSV file.

% dmlist "635.tsv[opt kernel=text/tsv]" cols
Columns for Table Block 635.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 regions overlap in one or more contributing stack
   6   sat_src_flag                      String[5]                           Source is saturated in all observations; source properties are unreliable
   7   significance                      Real4          -Inf:+Inf            Highest flux significance (S/N) across all stacked observations and energy bands
   8   flux_aper_b          erg/s/cm^2   Real4          -Inf:+Inf            Aperture-corrected net energy flux inferred from the source region aperture, bes
  63   detect_stack_id                   String[24]                          Detect stack identifier (designation of observation stack used for source detect

Example 2

unix% obsid_search_csc 635,637 outfile=none download=ask filetype=evt
columns=o.cnts_aper_b catalog=csc2

Search for two observations obsid=635 and 637 from CSC 2. We have asked that the full field evt file be return but will be prompted (download=ask). Additionally we require the broad-band source counts for each observation.

           obsid = 635,637
         outfile = none
         columns = o.cnts_aper_b
        download = ask
            root = ./
           bands = broad,wide
       filetypes = evt
         catalog = csc2
         verbose = 1
         clobber = no
            mode = ql

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

name                	ra          	dec         	obsid	cnts_aper_b	
 2CXO J162524.3-241543	2.463514e+02	-2.426214e+01	  637	        954	
 2CXO J162537.0-241759	2.464043e+02	-2.429996e+01	  637	        576	
 2CXO J162538.1-242235	2.464089e+02	-2.437658e+01	  637	       3064	
 2CXO J162541.2-242136	2.464219e+02	-2.436005e+01	  637	        354	
 2CXO J162552.4-241705	2.464686e+02	-2.428499e+01	  637	        175	
 2CXO J162754.6-243715	2.469778e+02	-2.462110e+01	  635	         39	
 2CXO J162755.1-242839	2.469800e+02	-2.447770e+01	  635	         65	
Download data for  2CXO J162524.3-241543 in 00637_001 [y,n,a,q]: y
Retrieving files for obsid_obi 00637_001
Retrieved file ./637/acisf00637_001N020_evt3.fits
Download data for  2CXO J162537.0-241759 in 00637_001 [y,n,a,q]: a

When prompted for downloads: 'y' will retrieve the file and continue onto the next. 'n' will skip the current file and continue. 'a' will retrieve the remaining files with further prompting, and 'q' will skip the current file and will not retrieve nor prompt for any remaining files.

Example 3

unix% obsid_search_csc @bootes.lis catalog=csc2

The list of observations can also be supplied using standard CIAO stacks.


name type def min max reqd stacks
obsid string       yes yes
outfile file       yes  
columns string INDEF     no yes
download string none        
root file          
bands string broad,wide        
filetype string regevt,pha,arf,rmf,lc,psf,regexp        
catalog string csc2.1        
verbose integer 1 0 5    
clobber boolean no        

Detailed Parameter Descriptions

Parameter=obsid (string required stacks=yes)

Observation Identification

The OBS_ID number. Multiple obsid's may be input via a comma separated list or any other stack.

Parameter=outfile (file required)

Name of output table.

The output file name. If left blank or set to "none", the the table of source properties is not saved.

The output is the same Tab Separated Value (tsv) format as returned by CSCView. To use the file with DM tools users must explicitly specify the kernel:

unix% dmlist "mysrc.tsv[opt kernel=text/tsv]" cols
Columns for Table Block mysrc.tsv
ColNo  Name                 Unit        Type             Range
   1   name                              String[20]                          Source name in the format '2CXO Jhhmmss.s +/- ddmmss'
   2   ra                                String[12]                          Source position, ICRS right ascension
   3   dec                               String[11]                          Source position, ICRS declination
   4   err_ellipse_r0       arcsec       Real4          -Inf:+Inf            Major radius of the 95% confidence level error ellipse
   5   conf_flag                         String[5]                           Source regions overlap (source is confused)
   6   sat_src_flag                      String[5]                           Source is saturated; source properties are unreliable
   7   significance                      Real4          -Inf:+Inf            Highest source flux significance across all observations
   8   flux_aper_b          erg/s/cm^2   Real4          -Inf:+Inf            Aperture-corrected net energy flux inferred from the source region aper

Parameter=columns (string not required default=INDEF stacks=yes)

The list of catalog columns to return.

The list of catalog columns to return. The default (INDEF) returns the list of columns returned by the combination of CSCView Master Summary and Obsid Summary defaults.

Several columns will be added to the query if they are not explicitly provided. These inlcude:, m.ra, m.dec, o.instrument, o.obsid,, o.region_id, and a.match_type.

The prefix "m." or "o." should be used to specify the if the property is a Master Source property (ie a value derived from all individual observations) or an Obi Source property (computed from a single observation). The list of columns can also be input via a stack, eg columns=@my_favorite_cols.lis

The following special values may be used to return the standard set of columns defined by CSCView:

The values are case-sensitive, and can be used with other values such as

unix% search_csc ... columns="SOS,a.match_type,o.livetime" ...

Parameter=download (string default=none)

Retrieve the associated data products?

Determine if data products should be retrieved. The valid options are

When asked, users have 4 choices

Parameter=root (file default=)

Output root directory for data products.

Parameter=bands (string default=broad,wide)

A comma separated list of energy bands

Various data products are stored in different energy bands.

This parameter is the list of energy bands for those products.

If bands is blank, all bands are retrieved.

Parameter=filetype (string default=regevt,pha,arf,rmf,lc,psf,regexp)

Comma separated list of file types to retrieve.

For catalog=csc2, csc2.1 and current the list of filetype values is

The valid options for catalog=csc1 are

It is possible that the same file may be queued for retrieve more than once. The script will recognize this and will instead make a copy of the file instead of re-retrieving it from the archive.

The script will check if the file it is about to retrieve already exists. If so it will skip the and inform the user.

Files are place in subdirectories of the current directory. They are organized by OBS_ID, source name ("2CXOJ..." or "CXOJ..."), and then by region id. This hierarchy ensures that the large per-obi files are only retrieved/stored once per master source.

If filetype is left blank, all available file types are retrieved.

Parameter=catalog (string default=csc2.1)

Select which version of CSC catalog: csc1|csc2|csc2.1|current

Parameter=verbose (integer default=1 min=0 max=5)

Tool chatter level.

Parameter=clobber (boolean default=no)

Remove outfile if it already exists?

This only applies to outfile. Products are never overwritten.

Changes in the script 4.16.1 (April 2024) release

Updated for CSC 2.1 release; csc2.1 is now the default catalog.

Changes in the scripts 4.15.3 (August 2023) release

Added the master 'srcpoly' file type to retrieve the Per-Master extended source polygon regions.

Changes in the scripts 4.14.3 (September 2022) release

The script has been updated to support searching the "current" Chandra Source Catalog. The "current" CSC catalog is, as of September 2022, the in-production version of CSC 2.1. Please see the Chandra Source Catalog Release 2.1 page for details and important caveats.

Changes in the scripts 4.12.1 (December 2019) release

Change URLs to use the secure CXC web server.

Changes in the script 4.11.5 (October 2019) release

Version 2 of the Chandra Source Catalog has been officially released. The script has been updated to access csc2 by default. Users can access the previous version using catalog=csc1.

Changes in the scripts 4.11.2 (April 2019) release

Corrects logic introduced to fall back to using curl if CXC websites redirect to secure sites. User errors such as incorrect column names would not have been reported correctly.

Changes in the scripts 4.6.6 (September 2014) release

Corrects the "MSBS" (master source basic summary) macro.

Provide more information when CSC servers are down and the catalog is not available.

About Contributed Software

This script is not an official part of the CIAO release but is made available as "contributed" software via the CIAO scripts page. Please see this page for installation instructions.


There are no known bugs for this tool.

See Also

cda_data, cda_search
download_chandra_obsid, download_obsid_caldb, find_chandra_obsid, search_csc