Terry Gaetz's Home Page

Terry Gaetz, Astrophysicist Smithsonian Astrophysical Observatory 60 Garden Sreet, Mail Stop 70 Cambridge, MA, 02138 (617) 496-7584, (617) 495-7356 [FAX] tgaetz@head.cfa.harvard.edu gaetz@cfa.harvard.edu

Chandra X-Ray Observatory

As part of the SAO/MST AXAF Mission Support Team, I contributed to reviews of the design and manufacture of the High Resolution Mirror Assembly (HRMA) and Optical Bench portions of the Chandra X-Ray Observatory (CXO), and also to the alignment of the X-Ray mirrors. The HMRA consists of a nest of four pairs of Wolter Type-I paraboloid-hyperboloid X-Ray mirrors; it was designed and built by Eastman Kodak Company at Rochester, NY.

The MST was also responsible for the ground calibration of the HRMA at the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville, Alabama.

Currently I work on the calibration of the Chandra X-ray Observatory (CXO) as part of the CXC Calibration group. Here is a schematic of the observatory. Some of our work on CXO mirror calibration is described here and here.

The ground calibration and the on-orbit calibration are being used to refine a high-fidelity raytrace model of the CXO performance.

After two scrubbed launch attempts, Chandra was successfully launched 1999 July 23, 12:31AM EDT, as part of space shuttle mission STS-93.

Here are some pictures of the CXO at various phases of assembly. (More pictures can be seen at the Chandra photo gallery.

Further information on Chandra can be found at the Chandra website

Chandra Calibration

Her X-1 calibration observation

The faint dark lines spaced at 30 degrees are shadows of the struts in the support structure for the mirrors.

The narrow, bright line extending across the image is the ACIS transfer streak. The detector is exposed for 3.1 seconds at a time, and the image is then rapidly moved out for processing. In the course of reading out the image, the bright source spends a short time in each pixel along the column, producing a "transfer streak", a bright line of emission in the same columns as the source.

The hole in the middle of the bright image is the result of "pileup". Near the direct image of the very bright source, the count rate is so high that the X-ray events are not recognized as valid by the event recognition algorithm.

Because of the heavy pileup, the direct image cannot be used to get the source count rate and spectrum. However, because the effective exposure time in the transfer streak is very much shorter, the events in the transfer streak can be used to provide information on the source spectrum and count rate.

Figure 1: Image of Her X-1 (0.3 to 6.0 keV) from the recent calibration observation. Binned by a factor of 2, and filtered on energy; a logarithmic intensity stretch was used.

JPG (150kB) PNG (125kB) PS (1.2MB)

Research Interests

• Supernova Remnants
• Computational Fluid Dynamics (including Adaptive Mesh Refinement)
• Interstellar Medium

Please email gaetz@cfa.harvard.edu with comments and corrections.

last modified 20040329