Last modified: 13 May 2021

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Chandra Source Catalog 2.0

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Hide the control panel.
Display the control panel.
Register the WWT display with a SAMP Hub.
Zoom out slightly.
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Zoom the display to a level appropriate for individual CSC sources.
Zoom the display out as far as it will go!
Copy RA and Dec to the clipboard, as decimal degrees.
Create a URL for the current display (location, zoom level, and selected wavelength for the background data) and copy it to the clipboard.
A name can be given (e.g. Orion cluster or M31), which is passed to the LookUp service, or a location can be given using a comma to separate the Right Ascension from the Declination. In this latter case a limited variety of coordinate formats are supported, including 205.842, -14.8367; 13 43 22, -14 50 12; 13:43:22, -14:50:12; 13h 43m 22s, -14d 50m 12s; and 13h 43m 22s, -14d 50' 12".
Find and move to the given location.
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Please explore the Chandra Source Catalog

This page uses the American Astronomical Society's World Wide Telescope interface to let you explore the sky coverage and source properties of version 2.0 of the Chandra Source Catalog.

The "control panel" on the left of the screen provides information about the current view - the location and size of the area of sky being shown - and various options to control the appearance and behavior of the display. The display can be moved by dragging it, entering a location or place name in the search box, selecting one of the popular places, or with a single click when the Move to point option is selected. The background data covers a large range of wavelengths (from Microwave to Gamma ray), and defaults to the optical.

Polygons indicate areas observed by Chandra that are included in CSC 2.0 ("stacks"), and the default behavior - Select nearest stack - is that selecting an area of sky will highlight the nearest polygon and provide information on the observations that form the stack. The locations of sources in CSC 2.0 can be loaded (Load CSC2.0 Sources), after which the button will change to Show CSC2.0 Sources, which will show all sources close to the current location and create a window which can be used to display several plots and send their properties to Virtual Observatory applications - such as TOPCAT or SAOImageDS9 - if a SAMP hub is running on the same machine as the web browser. The positions of detections from release 1.1 of the CSC and the latest XMM-Newton source catalog can also be displayed.

More details can be found using the Help and Credits buttons.

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About this page

The Chandra Source Catalog (CSC) is intended to be the definitive catalog of X-ray sources detected by the Chandra X-ray Observatory, and is described in more detail on the About the CSC page.

The 'Please explore the Chandra Source Catalog' page shows the Chandra observations (stacks) included in version 2.0 of the CSC as polygons on the sky. The display - which is based on the American Astronomical Association's World Wide Telescope - can be panned and zoomed into (or out of) to explore the whole sky, and the background data can also be changed, showing the sky in a range of wavelengths from the Cosmic Microwave Background to Gamma Rays. Positions of sources from the CSC (2.0 and the previous release, 1.1) and from the latest XMM-Newton source catalog can be displayed, and summary plots of the CSC 2.0 source properties can be shown.

What do all the icons mean?

There are a number of icons that can appear throughout the display (most of them at the top of the control panel, above the "Chandra Source Catalog 2.0" title):

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These two icons control whether a "window" (a panel of information) is hidden (minimised) or displayed.

Zoom fully out Zoom In Zoom Out

The zoom level of the WWT display can be changed with these three buttons. The three buttons allow you to zoom fully out (or at least as far as the WWT allows), slightly in, or slightly out.

Scissors (cut to clipboard)

This icon will copy the location (the value to the left of it) to the clipboard, so that it can then be pasted into another application (such as CSCView). The default format is to use decimal degrees, but this can be changed using the "Settings panel". The options are (a space is always used to separate the Right Ascension value from the Declination): decimal degrees; decimal degrees labelled with a trailing 'd' (as used in NED); colons separating the sexagesimal components; or hms/°'" separating the sexagesimal components.

Bookmark this location (copy URL to clipboard)

Create a URL to describe the current WWT view, and copy it to the clipboard. This URL can then be saved or sent to a colleague. The URL for the current display is (will be filled in in a few seconds).

Note that the only things that are "saved" in the URL are the location, zoom level, and choice of image. Source displays or settings are not saved.

Register with a SAMP Hub

This icon will only appear if a SAMP hub (one that supports the SAMP Web Profile) is running on the same machine as the web browser, such as the TOPCAT Virtual-Observatory table viewer and SAOImageDS9. Selecting the icon will register the WWT/CSC2 display with the SAMP hub: this is an optional step, but selecting it will mean that the WWT interface will respond to messages.

Change Properties

This icon will appear once the source information has been loaded, and allows you to change the color and size of the circles used to mark the source locations. Selecting the icon a second time will hide the source-property controls:

  • Source color:

  • Source size:


The Show Settings button will display the settings panel, which is used to control the appearance and behavior of the World-Wide Telescope. The settings will be saved on your local machine - and so remembered next time you visit this site with the same browser and machine - but this option can be turned off. Note that this only saves information on your machine; it is not stored by the Chandra X-ray Center.

The settings which can be saved include:

  • Is the Milky Way outline shown (default is no)?
  • Is a cross-hair shown at the center of the field (default is yes)?
  • Is a coordinate grid (Right Ascension and Declination) shown (default is yes)?
  • Are the constellations shown (default is yes)?
  • Is the boundary of the current constellation (that is, the constellation which covers the aim point) shown (default is no)?
  • Should the page connect to Virtual Observatory applications such as TOPCAT and SAOImageDS9 using the SAMP standard (turning this on causes the page to poll for a SAMP hub every 5 seconds)?
  • What format is used when copying a location to the clipboard (default is decimal degrees)?

There are two settings which are not saved:

  • Are the header and footer banners displayed (default is yes)?
  • Should full-screen mode be used (default is no; this option is only displayed if the web-browser supports this option)?

Searching for a name or position

The Enter a Name or Position box lets you quickly move around the sky. Positions are in Right Ascension and Declination (ICRS) and must be separated by a comma, otherwise the text is sent to the LookUP service to try and identify a location. The support for positions is limited to the following formats: 205.842, -14.8367; 13 43 22, -14 50 12; 13:43:22, -14:50:12; 13h 43m 22s, -14d 50m 12s; or 13h 43m 22s, -14d 50' 12".

Selecting a stack

The default behavior is for the nearest stack to the selected position to be highlighted (the outline changes to cyan), and a window is displayed containing basic information about the stack: the target names used for the observations that form the stacks, and links to observation details at the Chandra Data Archive.

The Export ... button lets you send the stack event file or sensitivity image to a Virtual-Observatory application if a SAMP hub is running on your machine and SAOImageDS9 is connected to it (or any other client that responds to the SAMP image.load.fits message type). If there is no SAMP hub then the URL of the stack event file can be copied to the clipboard.

Selecting a source

When the "Show CSC2.0 Sources" button has been selected, the selction mode - which is displayed in the second row of the menu bar on the left of the page - changes to "Select nearest source" - and the nearest displayed source from CSC2 will be selected. A different window is created, this time containing summary details about the source from CSC 2.0.

The exact set of properties shown depend on the source, but the basics are the positional error, Galactic column Hydrogen density, the best estimate of the model-independent flux using an aperture correction, hardness-ratios, and several details about the data used for the source.

Above the properties are links to copy the search name to the clipboard, search in the NASA/IPAC Extragalactic Database or the SIMBAD Astronomical Database within 5 arcseconds of the source location, and to center-and-zoom the WWT display on the source.

If a SAMP hub is running on your machine then you will be able to send all the master properties for the source to a table viewer by clicking on the Export ... button. If no SAMP hub is running then the URL of the query can be copied to the clipboard. More-detailed access to the CSC 2.0 source and data properties - as well as to previous releases - is available either via the CSCView application or with direct ADQL queries, as described on the How to access the Chandra Source Catalog page.

Chandra and XMM sources

Since the data files can take some time to load, the source catalogs must be loaded - using the "Load CSC2.0 Sources", "Load CSC1.1 Sources", or "Load 3XMM-DR8 Sources" buttons - before they can be shown. Once the data has loaded the button will change its label. Selecting the "Show CSC2.0 Sources", "Show CSC1.1 Sources" or "Show 3XMM-DR8 Sources" button will add circles, indicating the sources, close to the location on the screen (the full catalogs are not drawn as this would result in the display being unusable!). An orange circle is drawn to show the maximum radius used for sources (only for the CSC 2.0 sources).

By default, the CSC2.0 sources are drawn as cyan circles with a radius of 5 arcseconds, the CSC1.1 sources are drawn as orange circles with a radius of 7 arcseconds, and the XMM sources are green circles with a radius of 10 arcseconds. These radii are generally significantly larger than the positional error on the location, as they were chosen to make sure that the sources are visible! The XMM source locations are taken from the DR8 list as described on the credits page.

When the CSC 2.0 sources are displayed, a panel will appear which lets you display summary plots of the displayed sources or send the source properties for the selected sources to Virtual Observatory applications - such as TOPCAT or SAOImageDS9 - if a SAMP hub is running on the same machine as the web browser.

Using the World Wide Telescope

The display - provided by the WorldWide Telescope - can be panned, zoomed into (or out of), and the background image changed to show one of a range of wavelengths (from Gamma Ray to Microwave) using the selection in the "control panel".


Many thanks to the software and data providers mentioned on the credits page. Without them, this interface to the CSC would not be possible!

Settings: Close icon (circle with times symbol in it) Hide

These settings control the appearance and behavior of the World Wide Telescope interface to the Chandra Source Catalog.

If the "Remember position and settings" checkbox is set below, then these settings will be used when you next view this page with the same browser (this information is only saved on your machine).

The following settings are not saved:

Move to: Close icon (circle with times symbol in it)
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The display is provided by the WorldWide Telescope, which is funded by the American Astronomical Society. The target search uses the LookUP service, operated by Stuart R. Lowe, which provides a simple way to search Astronomical targets by name. The Milky Way outline is from the d3-celestial project - which converted the original Milky Way Outline Catalogs data by Jose R. Vieira. The configuration, broadcast, close, resize, scissors, search, and zoom icons are from the free version of Font Awesome (released under the CC BY 4.0 License). The animated "spinner" - seen when loading the source catalogs or looking up a name - is taken from the SpinKit package by Tobias Ahlin, which is released under the MIT License. The color picker widget is provided by jscolor.js, plotting by plotly.js, and the Web-SAMP functionality by sampjs.

The display code is based on work originally done for the Chandra Observation Viewer and was enhanced based on the code used to create the NASA ADS All Sky Survey. The interface is also based on the excellent work done by the ESA Sky team.

Source catalogs

The 3XMM DR8 source locations are taken from the RA and DEC columns of the 3XMM_DR8cat_v1.0.fits.gz downloaded from the 3XMM DR8 catalog page, after applying the following filter: SUM_FLAG < 3.

Background images

The background imagery is provided by the following organisations:

Planck logo

Planck is a European Space Agency mission, with significant participation from NASA. NASAs Planck Project Office is based at JPL. JPL contributed mission-enabling technology for both of Plancks science instruments. European, Canadian and U.S. Planck scientists work together to analyze the Planck data.

VLA Low-frequency Sky Survey (VLSS)
VLA logo

VLSS Cohen, A. S.; Lane, W. M.; Cotton, W. D.; Kassim, N. E.; Lazio, T. J. W.; Perley, R. A.; Condon, J. J.; Erickson, W. C.; Served From NASA Skyview

WISE logo


2MASS logo

This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

DSS logo

Copyright DSS Consortium

Halpha survey logo

Image Courtesy Douglas Finkbeiner. The full-sky H-alpha map (6' FWHM resolution) is a composite of the Virginia Tech Spectral line Survey (VTSS) in the north and the Southern H-Alpha Sky Survey Atlas (SHASSA) in the south. The Wisconsin H-Alpha Mapper (WHAM) survey provides a stable zero-point over 3/4 of the sky on a one degree scale.

RASS logo

This is a composite of three RASS3 surveys from the ROSAT Data Archive of the Max-Planck-Institut fur extraterrestrische Physik (MPE) at Garching, Germany. TOAST-formatted data was obtained from NASA's SkyView Virtual Telescope. Red is soft band (RASS3sb), Green is broad band (RASS3bb), Blue is hard band (RASS3hb)

Fermi logo

NASA and the FERMI-LAT Team.

Overview of the selected CSC 2.0 sources Close icon (circle with times symbol in it) Hide

Note that no error ranges are included in these visualizations. For a more-detailed analysis try sending the data to TOPCAT, SAOImageDS9, or other Virtual Observatory application, since this provides more columns from the catalog, or use CSCView to search the CSC 2.0 database.

Select plot type:

This plot shows the aperture-corrected fluxes for the sources as a function of source significance. The fluxes are model independent - that is they do not assume a specfic input spectrum - and are for either the broad or wide bands. The fluxes are taken from the "longest block" of data using a flux-ordered Bayesian Block analysis, and the significance is the highest value measured across all the observations and source bands used in the catalog.

The plots use the following master-source columns: significance, flux_aper_b, and flux_aper_w.

This plot shows the semi-major axis and eccentricity of the 95% error ellipse on the source location (the eccentricity is calculated from the tabulated semi-major and semi-minor axis values).

The plots use the following master-source columns: err_ellipse_r0 and err_ellipse_r1 (err_ellipse_ang is available, but not used here).

The hardness ratio can be estimated for sources which are observed by ACIS. The Hard-Medium and Medium-Soft values are used here, although it excludes sources with a hardness-ratio close to ±1 as they tend to dominate the plot, obscuring the detail for those sources with lie towards the center of the plot.

The plots use the following master-source columns: hard_hm and hard_ms.

Some areas of the sky are observed multiple times, which provides the opportunity for measuring faint sources and to look for long-term (inter-observation) variability (not just short-term, intra-observation variability). The histogram shows the number of ACIS and HRC observations for each selected source.

The plots use the following master-source columns: acis_num and hrc_num.