Project Scientist's Report

The highlight of this past year was a wonderful conference highlighting six years of observations with Chandra and honoring the memory of our Telescope Scientist, Leon Van Speybroeck. Project Science was especially pleased to be able to present the results of a collaborative study of the first Chandra field. Before the official first-light images, the Chandra X-Ray Observatory obtained an X-ray image of the field to which its focal plane was first exposed. Fifteen X-ray sources, the brightest being dubbed ``Leon X-1’’ were detected. Based upon the analysis of the X-ray data and spectroscopy at the European Southern Observatory, we found that Leon X-1 is a Type-1 (unobscured) active galactic nucleus at a redshift z=0.3207. Leon X-1 exhibits strong Fe II emission and a broad-line Balmer decrement that is unusually flat for an AGN. The study was performed by M. C. Weisskopf, T. L.
Aldcroft, R. A. Cameron, P. Gandhi, C. Foellmi, R. F. Elsner, S. K. Patel, K. Wu, and S. L. O’Dell and the results appeared in the Astrophysical Journal in February, 2006.

Project Science also continues to monitor and to support analyses of issues potentially impacting the performance of the Observatory. The following briefly summarizes the three main concerns:

1. 1. Radiation damage to ACIS CCDs. The Chandra team’s radiation-protection program has successfully reduced the rate of charge transfer inefficiency increase of the front-illuminated CCDs to only 2%/year. A 2005 paper (Proc. SPIE 5898, 212-223) describes the current status of radiation management.
2. 2. Molecular contamination of ACIS. The low-energy response of the ACIS CCDs continues to drop, due to accumulation of molecular contaminants. After detailed analyses of potential risks, the Chandra team has indefinitely postponed a bake-out of ACIS. A major concern is that contamination-migration simulations show only a small phase space for success and a possibility of increasing the contamination on the ACIS OBF. A 2005 paper (Proc. SPIE 5898, 301-312) describes the contamination-migration modeling.
3. 3. Thermal degradation of the spacecraft. The systematic rise in spacecraft temperatures has increasingly constrained observations. Thus, the Chandra team has relaxed limits on the temperature experienced by the EPHIN radiation monitor. So far, the EPHIN performance has not degraded due to higher temperatures. Nevertheless, the team has developed contingency radiation-protection plans (Proc. SPIE 5898, 212-223), should they be needed.