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| FIGURE 3: (Left to right) Harvey Tananbaum, Riccardo Giacconi, Martin Weisskopf and Claude Canizares. |
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| FIGURE 3: (Left to right) Harvey Tananbaum, Riccardo Giacconi, Martin Weisskopf and Claude Canizares. |
More recently, the High Energy Astrophysics Division of the American Astronomical Society awarded Harvey Tananbaum and me the Rossi Prize, for our efforts in developing the Observatory. Both Harvey and I are flattered and honored. All participants in development, operation, and use of the Observatory can take pride in their own contributions which have led to such an honor.
Project Science is supporting efforts related to potential bake-out of the ACIS filters, in order to remove a molecular contaminant that has accumulated on this cold (-50 C) surface. Deciding whether to bake out and, if so, how to minimize risk to the ACIS instrument is a complex problem requiring due deliberation. Currently, Project Science is performing detailed molecular-transport computations to estimate the time required to remove the contaminating film. We are also performing detailed simulations to estimate proton irradiation of the ACIS at energies below 100 keV. These lower energy suprathermal protons cannot affect the charge-transfer inefficiency (CTI), but might (along with ultraviolet radiation) affect cross-linking of molecules in the contaminating film. See "Update on the ACIS Contamination Issue and Possible Bakeout" (p. 6).
Project Science continues to work with the CXC Science and Flight Operations Teams to control proton damage to the ACIS CCDs. Since identification of the CTI degradation early in the mission, our collective efforts have successfully limited the fractional CTI increase to 2.5% per year, for the (more proton sensitive) front-illuminated CCDs. We had expected our work (including middle-of-the-night telecons that Steve O'Dell supports) to get easier now that Solar Maximum has passed. However, the Sun surprised us and the space environment community as well. In what NOAA's Space Environment Center calls the "Halloween Storms of 2003" , three different active regions produced 17 major x-ray flares (including the largest flux ever measured an estimated X28!) between October 19 and November 5. These flares were associated with 6 energetic-proton events (including the fourth largest flux ever measured). Between autonomous and commanded radiation safings, the Observatory spent most of this period with the ACIS out of the focal plane. However, we were concerned that strongly penetrating protons might damage the CCDs. Indeed, MIT/Catherine Grant's preliminary analysis shows that these proton events did noticeably increase the CTI of the front-illuminated CCDs by about 2% - i.e., nearly equivalent to one-year exposure under average conditions. A large effect, but not fatal by any means. (See " Stormy Weather" , p. 22.)
We look forward to another year of successful operation, new exciting proposals submitted for Cycle 6, and numerous discoveries.
Martin Weisskopf