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 2.1 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 (2.1) and from the latest XMM-Newton source catalog can be displayed, and summary plots of the CSC 2.1 source properties can be shown.

A number of actions can be performed with the keyboard. Use the k key to view the options. This can be turned off in the settings area, if needed.

The Processing Status page provides more information on the current status of version 2.1 of the Chandra Source Catalog.

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 2.1" title):

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

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.

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.

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.

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 coord.pointAt.sky messages.

This icon will appear once the source information has been loaded, and allows you to change the color, size, and opacity 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:

• Source opacity:

Settings

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 or any other web site.

The settings which can be saved include:

• Can keys be used to control parts of the display (default is yes, use the k key to view the options)?
• 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

Unfortunately we are currently unable to search by name, such as M31, as the service we used for this had to be closed down because it was being misused. We hope to bring this feature soon.

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. 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".

An alternative is to use the name of a CSC 2.1 source, which begins 2CXO J. If the CSC 2.1 sources have been loaded then we search directly from this list, otherwise we use the name server to try and identify the location (which will be slower).

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 a name server 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 CSC 2.1 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 2.1.

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 2.1 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, XMM, and eROSITA sources

Since the data files can take some time to load, the source catalogs must be loaded - using the "Load CSC2.1 Sources", "Load 4XMM-DR13 Detections", or "Load eROSITA DR1 Sources", buttons - before they can be shown. Once the data has loaded the button will change its label. Selecting the "Show CSC2.1 Sources", "Show 4XMM-DR13 Detections", or "Show eROSITA DR1 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 2.1 sources).

By default, the CSC2.1 sources are drawn as cyan circles with a radius of 5 arcseconds, the XMM sources are green circles with a radius of 10 arcseconds, and the eROSITA sources are yellow circles with a radius of 30 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 DR13 list as described on the credits page.

When the CSC 2.1 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".

Thanks

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

The display is provided by the WorldWide Telescope, which is funded by the American Astronomical Society. The target search used to use the lookUP service, operated by Stuart R. Lowe, but unfortunately it had to be closed down due to misuse by the community, so an alternative solution has been created, but it does not provide all the features that lookUP did. The Milky Way outline is from the d3-celestial project - which converted the original Milky Way Outline Catalogs data (link appears to be dead) 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 4XMM-DR13 locations are taken from the RA and DEC columns of the 4XMM_DR13cat_v1.0.fits.gz downloaded from the 4XMM-DR13 catalog page, after applying the following filter: SUM_FLAG < 3.

Background images

The background imagery is provided by the following organisations:

Planck

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)

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

NASA/JPL-Caltech/UCLA

2MASS

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

Copyright DSS Consortium

Hα

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

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

NASA and the FERMI-LAT Team.