Header Reducing GRB Data at Steward Observatory.

Important Links

Jochen Greiner's GRB Page

Steward Observatory Telescope Schedules

MMT Observatory Telescope Schedules

USNO Photometric Data

USNO Finder Charts

The STScI Digitized Sky Survey

GCN Circulars

GCN Bursts of Special Interest

Reduction Steps

  1. Make a data directory and include both raw and processed subdirectories.

    [ggwilli@grb ggwilli]$ mkdir /home/ggwilli/data/GRBYYMMDD
    [ggwilli@grb ggwilli]$ mkdir /home/ggwilli/data/GRBYYMMDD/90inch
    [ggwilli@grb ggwilli]$ mkdir /home/ggwilli/data/GRBYYMMDD/90inch/raw
    [ggwilli@grb ggwilli]$ mkdir /home/ggwilli/data/GRBYYMMDD/90inch/proc

  2. Get the GRB coordinates of the burst from the GCN Circulars or the GCN Bursts of Special Interest.

  3. Check the image quality with ds9.

  4. Download a finder chart from the STScI DSS.

  5. Download an 11x11 arcmin finder chart from the USNO Finder Charts.

  6. Calculate the scale between the DSS image and one of the science images. This can be done a number of ways:

    1. Use the science image first. Start the iraf task imexam.

      im> imexam

      Place the cursor over a reference star and type 'y'. This sets the coordinates of that star as a reference position. Put the cursor over a different star and type 'x'. The output values correspond to:

      col line pixval xorign yorigin dx dy r theta

      Origin: 357.50 494.00
      632.50 546.00 1945. 357.500 494.00 275.00 52.00 279.87 10.7

      Repeat the procedure for the second image.

      Origin: 439.50 494.50
      555.00 522.00 17492. 439.500 494.50 115.50 27.50 118.73 13.4

      Use the ratio of the radii to get the scale factor:

      scale = 118.73 / 279.87 = 0.4242

      Use the difference of the thetas to get the rotation:

      rot = 10.7 - 13.4 = -2.7 (NOTE: the order of the difference)

      Perform the transformation on the DSS image:

      im> imlintran test1.fits test10.fits -2.7 -2.7 0.4242 0.4242

      If the scales were different in x an y one could first rotate the image and then calculate xscale and yscale and then scale the image.

    2. Essentially the same as above but using the "Regions" capability in ds9. Click on "Region" in the task button bar. Choose "ruler" from the resulting shapes button bar. Click on the first star and drag the mouse until the cursor is over the second star. Select the region (or line) you just drew by clicking on it. From the "Region" menu at the top choose "Get Info...". The dx, dy and theta are given.

  7. Download the USNO field photometry data file.

  8. Plot a finder chart using the USNO field photometry data.


  9. Match the USNO stars with visible stars in data field.

  10. Make a revised USNO field photometry file containing only the stars that will be used with the data.

  11. Calculate the offsets.

  12. Plot the curve of growth. Adjust magnitudes accordingly.

  13. Determine the radius to use based on errors. Explain in greater detail.