Chandra X-Ray Observatory

Announcement Regarding Chandra Extremely Large Projects

In November 2006, the Chandra X-ray Center announced that we were considering the implementation of a new category for Chandra proposals and observations - Extremely Large Projects (ELP). The announcement described parameters of a possible ELP program, under which one such program ranging from 3 to 5Ms exposure time could be selected once every 3 years if the ELP program were established. The announcement called for brief white papers from interested individuals and teams to assess the potential scientific merit of a Chandra ELP program, with a February 1, 2007 deadline. In response to this call, we received 10 White Papers.

To assess the White Papers we established 3 criteria:

  1. Demonstrated need to go beyond the current Very Large Project bound of 3 Ms to accomplish the key science objective(s)
  2. Intrinsic science merit of the suggested program
  3. Technical and scientific feasibility of program.

We determined that a program described in a White Paper should meet all 3 of these criteria in order to support the case for establishing Chandra ELPs.

We formed a small review team comprised of:
Harvey Tananbaum (SAO - Chandra X-ray Center Director)
Martin Weisskopf (MSFC - Chandra Project Scientist)
Belinda Wilkes (SAO - Chandra X-ray Center Assistant Director)
David Helfand (Columbia University - at-large representative).

We scored the White Papers on a scale of 1-3 for each of the 3 criteria above (effectively weighting all of the criteria equally). We selected a subset of the White Papers which scored highest using this procedure in order to further assess the arguments in favor of having Chandra ELPs based on what appeared to us to be the strongest projects. We also generated a list of VLPs and lower scoring 2/3 of the selected LPs for Chandra Cycles 6-8 in order to form 3 separate reference sets of science opportunities adding to ~5Ms each, which would be representative of what would be displaced once every 3 years were we to proceed with Chandra ELPs.

We met on April 13 to further discuss the White Papers and assess the merits of establishing Chandra ELPs. We dropped the mix of Cycle 8 VLPs and LPs from the comparison set since some of these observations are still in progress. We arrived at the consensus summarized next.

We believe that most, and in some cases all, of the proposed science described in the White Papers can be accomplished within the current Chandra framework utilizing the category of VLPs for which individual proposals can range from 1-3Ms. We note that only 4 proposals requesting 2Ms and none requesting more time have been submitted in the 4 Cycles since the category of VLPs was instituted in Cycle 5. We do not include Cycle 9 which is currently entering the review process. We can speculate about possible explanations for this situation, centering on strategies which proposers believe are most likely to succeed. We also note that none of the 4 proposals requesting 2Ms were selected, but that Cycle 8 did see the approval of a 1.8Ms project.

It is our intent to implement a few specific steps to encourage members of the community to consider submitting proposals for the full 3Ms currently available under VLPs when they believe the science objectives require and merit this amount of observing time. This message to Chandra users is a step along those lines, and we anticipate similar words of encouragement in the next Chandra Call for Proposals. We will also review the guidelines provided to the Peer Review Panels, particularly the Big Projects Panel, to ensure that they give fair and open consideration to proposals requesting times up to the 3Ms limit of the VLP category. We discussed all of this in some detail at the April 25-26 meeting of the Chandra Users Committee, and will fold relevant recommendations from the Users Committee into our future plans.

We appreciate the time invested by the teams submitting White Papers and anticipate achieving many of the science objectives they laid out in the coming years.

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