• how to find available Chandra images of objects other than those on the "official" Chandra server list

 
• how to download them, uncompress them, load them into ds9, & use the Analysis Tools

 
• how to obtain the optical image of the same field showing in the x-ray image

• easy-to-follow instructions on downloading and installing the ds9 software for Windows
• several activities introducing the ds9 software as applied to a few interesting x-ray sources

(including the supernova remnant Cas A, the quasar 3C273, the galaxy M31 (Andromeda),
and the Coma cluster of galaxies)
• a summary of Chandra x-ray satellite mission
• a detailed guide to the ds9 software

• what other Chandra images are available
• how to acquire/download other Chandra images
• how to use the ds9 Analysis commands on these other images

• 1) If you know the ObsId number of the object,  there are 2 options:
  
  
  • the best option (although it doesn't always work) is to open Virtual Observatory under the Analysis menu;
    then click in the Chandra-Ed Archive Server box in the new pop-up window;
    in the new pop-up window (listing Chandra-Ed Images), page down to near the bottom and click on the Unofficial Chandra Public Archive link;
    type in the ObsId number in the box and then click on the Search button. 
    
    If the ObsId requested is returned with an active link under the column Title, this means that the image is available.
    Click on this link under Title and the image will open in the ds9 window.
    (Do NOT click on the ObsId link.)
    
    The advantages of retrieving the image with this method (when it works) are twofold:
    a) you bypass the tedious image uncompress routines that the method below requires
    b) in further Chandra Archive sessions, the image will appear on the list of link-accessible images,
         and you no longer have to search via the ObsId number
    
    However, if the ObsId requested is returned without an active link under the Title column,
    an image file has not been created.
    Point source objects, grating observations, & observations in CC (continuous capture mode) are not likely to have an associated image file.
    Furthermore, you will NOT be able to access the FTOOLS commands in the ds9 processor.
    
    
  • the second option involves downloading and uncompressing the image; see the download section below
    

 
• 2) If you know the object's name or sky coordinates

• 3) If you aren't interested in a specific object, but are interested in certain types of object (for example, quasars)

The images are located in the science directory, but not in a very user-friendly manner.  In the science directory, there is a subdirectory for each cycle (or calendar year) that Chandra has been operating.  The sub-directories are titled ao<nn> (where the number nn stands for the Chandra operating year, with 00 standing for the year beginning in mid-1999 when Chandra began observations).  Within each ao<nn> sub-directory are further sub-drectories (each named cat<i>) which contain objects of homogeneous type.  <i> types are

    0 Non-celestial (Engineering) Observation
    1 Solar System
    2 Normal Stars and White Dwarfs
    3 White Dwarf Binaries and Cataclysmic Variables
    4 Black Hole and Neutron Star Binaries
    5 Supernovae, Supernova Remnants, and Isolated Neutron Stars
    6 Normal Galaxies
    7 Active Galaxies and Quasars
    8 Clusters of Galaxies
    9 Extragalactic Diffuse Emission and Surveys and Galactic Diffuse Emission and Surveys

Therefore, the cat1 sub-directory contains observations of only Solar System objects.

Archived data and observations
Within each category sub-directory are the observations sorted by ObsId number.  So you still don't know the specific object associated with an observation unless you open the image and read the FITS header.
 

• 4) if you know the object name, an alternative to using the image archives at Harvard is to use HEASARC

Once you've filled in the Object Name and checked the appropriate mission/catalogs boxes, make sure that, under #3, the "Archived data and observations" box is checked (probably the only one you want checked), and then click on the 
"start search" button under #5.

If option 1 above did not work....
If you know the ObsId number, you can type it in directly in the box provided at the Chandra Data Archive Observation Search Page

A new Search Results page will be returned with the appropriate ObsId along with other information about the image;
in general, the primary and secondary products boxes will be checked for retrieval; it's likely that you will want only primary products;
click on the Retrieval List link at the upper right; the products that will be retrieved are listed;
click on the Browse Products link at the upper left to see what specific files will be retrieved;
click on the Retrieve Products link at the upper left to retrieve these files;
the Retrieval Results page will contain an ftp link will be returned for downloading the images

Most likely the file you want will end with ...evt2.fits (it's called an "events file" and essentially contains the most detailed information, including the arrival time and energy of each photon). 
Files ending in img.fits contain images, but cannot be analyzed to produce light curves or spectra.

Select the "Save to Disk" option.

Start DS9 and load one of the special images available on the Chandra-Ed or Rutgers servers (this will allow us to access the Analysis tools for any image):

    (1)   Load DS9
    (2)   Under Analysis, select Virtual Observatory
    (3)   Check one of the server options in the Dialog box that opens
            (Chandra Education, Chandra-ed Archive, Rutgers)
    (4)   The check box should turn green and color, and another web page should load
            which allows the user to choose an image
    (5)   Load any one of the images made available by the server

    The advantage of doing step 5 above is that once the Analysis Tools are loaded for one
    of the special images (Cas A, 3C273, M31, plus some others listed by either the Chandra-Ed
    server or the Basho Rutgers server) is that the Analysis Tools (except the FTOOLS
    commands at the bottom of the Analysis meny) will be subsequently available for ANY
    other Chandra image.

    Warning:  although any FITS image can be loaded into ds9 and many of the functions will
    work (e.g., scale, color, pixel table, etc.) don't expect the bulk of the Analysis tools
    (e.g., light curve, energy spectrum, etc.) to work

Chandra also has the capability to load the DSS (Palomar's Digital Sky Survey in the visible
part of the spectrum) image in a side frame, automatically change the two images to the
same scale, and match the cursor positions on the two images:

    (1) Under Frame, select Tile Frames
    (2) Under Analysis, select DSS
    (3) Click Retrieve in the Dialog Box that opens (which should have the right ascension
                and declination inserted)
     (4)  The optical DSS image should now open in a frame to the right of the Chandra x-ray image
     (5)  Under Frame, select Match Frames --> WCS
     (6)  Under Frame, select Lock Crosshairs --> WCS
     (7)  Under Edit, select Crosshair
     (8)  You should now be able to click & drag the cursor around in one image and have the cursor
                move correspondingly in the adjacent image