Chandra Users Committee June 25-26, 2002

Members Attending: M. Arnaud, J.P. Henry, J.P. Hughes, W. Latter, J. Krolik, J. Mohr (by telecon), and F. Paerels
Others: A. Tennant, H. Tananbaum, B. Wilkes

Manager's Report (Roger Brissenden):

Roger reported that the S/C is performing superbly and operations are routine. His reports on status, operations, expendables usage, observing efficiency, observations, data systems, data delivery, and grant awards are all appreciated by the committee. Roger reported that SAO and NASA have begun negotiations on the 5 year extension to the CXC contract. It was decided that any action by the CUC on this issue would be premature at this time.

Director's Report (Harvey Tananbaum):

Harvey reported on the use of the Director's Discretionary Time from February through June 2002. About 585 ks of cycle 3 DDT have been used already, making it unlikely that a significant chunk of time will be available for a single large observation as happened in the past two cycles (RXJ1856.5-3754 in cycle 2 and the CDSF in cycle 1). It was noted that over the three month period from 3 March to 3 June there were 8 load interrupt ToOs of which 4 were DDTs while the remainder were ToOs awarded by the peer review. Nominally the peer review gives out 9 ToOs, HST one, and the Director two.

[1] The committee briefly discussed this issue and noted that the fast response time DDTs were in addition to the others and were therefore a significant benefit to the user community. The CUC also realizes the increased workload that these observations entail for the mission operations staff and greatly appreciates their tremendous efforts.

Summary of issues from Chandra AO-4 proposal submission and peer review (Fred Seward):

This round Fred avoided using reviewers from previous cycles. The Large Projects in AO4 received 23% of the total available time which is similar to the fraction awarded in previous cycles (AO2: 25%, AO3: 20%). Seventy percent of the GTO proposals submitted after the deadline in reaction to a conflict with a GO target were successful. Fred noted that he has not been able to figure out a way to disguise the GTO proposals from the panels.

[2] The CUC discussed this issue briefly and recommends that the CXC implement (for Cycle 5) some of the suggestions for disguising GTO proposals that are offered in the minutes of the CUC meeting from January 31, 2002. In particular the panels should not be told which are GTO proposals and they should be instructed to treat any GTO and GO conflicted proposals purely on the basis of scientific merit. Finally the panels should not be aware of how much GTO time there is in their panel.

[3] It was not immediately obvious to the CUC that the examples presented demonstrated the need for a significant technical review of proposals. We note that technical reviews are a considerable amount of effort and that the technical reviewers would need to be present at the peer review to support the panels. However, a minimal technical review that verifies that what is proposed in the scientific justification squares with the various constraints indicated on the forms would be valuable. If this is what's being considered, then it seems like a fine suggestion and we encourage Fred to implement it for the next cycle.

[4] The CUC agrees that the current situation is not yet a concern and so no action is necessary.

Plans for AO5 (Belinda Wilkes):

Regarding the Chandra/XMM deadline collision for next year, Belinda reported that the two observatories have worked out a schedule that has the Chandra deadline on 15 March and the XMM deadline in late April. This seems to be the best that can be done for now. The XMM AO3 cycle will be for 1.25 yr, leading ultimately to a 3-6 month spread in schedules between the Chandra and XMM review cycles.

Belinda reported on two new joint time programs for AO5: with NRAO (details to be worked) and RXTE (500 ks). Both of these will be one-way like the NOAO joint time agreement. The CXC will investigate a joint time program with SIRTF during their second review cycle. Other changes for AO5 include requiring proposers to list previous Chandra awards as well as relevant publications in the submitted forms.

[5] The CUC applauds this addition and strongly encourages the CXC to implement it for cycle 5.

Belinda explained the reasons behind the lack of advertising for the Chandra theory program which premiered during the last cycle. She indicated that the CXC will investigate wider distribution for any future new initiatives.

[6] The CUC agrees and suggests, more generally, that the CXC publicize important Chandra updates during open AO periods through the HEAD newsletter, HEAD mailing list, the Astrophysics Theory Program mailing list, and other broad community lists in the future. Occasional complaints from astronomers about getting too much e-mail should be ignored. Every day we all delete dozens of spam e-mail with absolutely no value to anyone. Announcements from a major NASA observatory are of value to many of us and should be distributed widely.

[7] It was suggested that a separate peer review panel for theory proposals might be worth considering at some point. The CUC discussed this and concluded that at least for AO5 the same procedure should be used as was followed previously, i.e., that theory proposals be reviewed in the appropriate science panel along with observing proposals. This puts a greater load on the CXC to select reviewers with broad backgrounds in theoretical astrophysics in order to properly cover the range of scientific studies that may be proposed in a given panel. It was also felt by most of the membership that it was good that observers reviewed theory proposals, since it would require theory proposals to connect their research to relevant Chandra observations.

[8] It was suggested that perhaps the page limit on theory proposals be relaxed, but the majority of the committee membership decided not to endorse this, opting instead to retain the current 4 page limit.

[9] The committee sees no compelling reason whatsoever to implement multi-year proposals for observing time. However there was support among the committee for multi-year funding requests. Large projects, theory projects, and archive proposals would all benefit from stable funding over two or three years. Theory projects in particular are considerably less credible when squeezed into a single year of investigation. Furthermore we point out that NASA's Astrophysics Data Program (ADP) which supports archive research for a number of high energy missions (including XMM, but excluding Chandra) allows for multi-year funding requests.

ACIS Modeling and Analysis (Dan Schwartz):

Dan described the research of a group of CXC scientists working under his supervision to address two important issues related to the performance of ACIS: the decrease in low energy quantum efficiency (LEQE) and CTI correction of the FI chips.

Dan presented an excellent summary of what is known about the change in LEQE, which appears to be a result of the build-up of an unknown contaminant on the ACIS filters and/or CCDs. As of the time of the meeting the chemical composition was not well-determined. There is evidence for a strong C absorption edge and the O edge is directly detected. N and F are also likely to be present. The LEQE appears to be decreasing at a rate of 10% per year at E=0.67 keV and the degradation appeared to commence within 2-3 months of on-orbit insertion. Dan outlined plans for further analysis, modeling, and the need for additional calibration observations.

[10] We note that this information was posted on the CXC web site soon after the CUC meeting along with off-line (non-CIAO) software tools to implement a first-order LEQE correction. We thank Dan and his group for making this available to the community so quickly. Some of us are already using it.

[11] The CUC acknowledges the great progress that this work represents and strongly encourages Dan and his team to continue carrying it forward. The committee offers its opinion that the 4 ACIS-I chips and S3 are the highest priority devices to correct.

Calibration (Larry David):

Larry gave the Chandra calibration status report covering new and improved calibration products (ACIS, HRC, LETG, and HETG), caveats associated with these, uncertainties and issues remaining, the AO4 calibration plan (totaling 911 ks of observing time), and Chandra/XMM-Newton cross calibration issues. Larry announced that the CXC was holding a Chandra Calibration Workshop in the fall, which would be open to the entire scientific community, and encouraged CUC members to attend.

[12] The AO4 calibration plan looks good and the team is making progress on several fronts. One suggestion that the CUC had is for the CXC to assess systematic errors in derived spectral parameters that arise from the uncertainties in the effective area difference between FI and BI chips.

GTO time beyond prime phase (Paul Hertz, by telecon):

Paul reported that NASA headquarters is transitioning to the extended phase mission for Chandra and is planning all activities, such as the budgets for GOs and public outreach. They wish to establish an appropriate policy for GTO during this phase. He claimed that the various documents related to this are ambiguous at best. The issue is not one of money, but rather the best way of allocating Chandra observing time. He notes that generally NASA policy is evolving toward less GTO time for new missions. Headquarters would like our input, including points they should consider, and they plan to make a decision by the end of the calendar year.

[13] There were a variety of opinions on this topic. The majority of the committee was in favor of continuing the GTO program for Chandra IPIs in the extended mission phase (vote 5 - 2). The main argument on the con side was that GTO time circumvents the peer review process which is the best system we currently have for allocating resources across all fields of science. The main argument for the pro side was that the expertise of the IPI teams is of great value to the Chandra project and that the availability of observing time will help to retain the pool of good scientists that provide this expertise. Thus, regardless of whether they retain guaranteed observing time, the integrity of the IPIs teams must be maintained (this is the unanimous opinion of the CUC). NASA headquarters should provide sufficient funding to maintain the viability of these groups, including supporting individuals for a fraction of their time to do their own scientific research.

SDS: CIAO 3 Plans and Status (Aneta Siemiginowska):

Aneta talked about the Slang scripting language in CIAO as well as plans for CIAO 3. She noted that CIAO has a lot of capabilities, which are not fully used by the users and that users have problems, but are unable to identify directly the reason. CIAO 3, the so-called Infrastructure Release, will help to solve these problems.

[14] The CUC members applaud the SDS group's effort to reach out to the community to provide software that is useful for Chandra analysis. Along these lines, the CUC suggests that the CXC poll current Chandra PIs to learn about their software usage patterns. Specifically questions like the following should be posed: (1) what CIAO analysis tools do you use; (2) what non-CIAO tools do you use; (3) are there Chandra specific tools that are missing; and (4) in what directions would you like to see CIAO develop.

SDS: Analysis Using CTI-corrected Products (Antonella Fruscione):

Antonella reported on the official Chandra software for CTI correcting ACIS-I data. The plan is to release all new ACIS-I FEFs for CTI-corrected data and software in the fall 2002. The software update will likely be a patch to CIAO2.2.2.

[15] This is an acceptable time frame.

SDS: CIAO Documentation Plans (Doug Burke):

Doug talked mainly about providing users with analysis threads. There are now almost 100 threads accessible from the Chandra web site. Keep up the good work.

SDS: Web_SAOSAC (Margarita Karovska):

Margarita presented information about ChaRT - Chandra Ray Tracer - which is a Web interface to SAOsac.

[16] This is a very nice new feature and the CUC is very happy to see it made available to the Chandra community. We would also like to see more canned image models in the next release, as well as a feature where a FITS image file could be used as the image model input.

SDS: ATOMDB (Randall Smith):

Randall described the ATOMDB which is an atomic database that includes the Astrophysical Plasma Emission database (APED) and Astrophysical Plasma Emission Code (APEC).

E&PO (Kathy Lestition):

Kathy reviewed the scope of the CXC Education and Public Outreach effort from Jan to June 2002. Chandra is getting good coverage in the national press. NASA headquarters wants to have more Chandra Space Science Updates (SSUs) and the E&PO group is hiring additional staff to support this, including a dedicated scientist, animator, image processor, and graphic illustrator.

[17] E&PO is an important part of NASA's mission and we compliment the CXC for expanding their effort in this direction. The committee is particularly pleased that a full-time active research scientist will be part of the team, since the scientific validity of press releases is of the greatest importance.

[18] The committee reviewed a request from a user that the CXC offer a special category for technical or instrumental proposals for Chandra. There was no support for this suggestion among the committee members.

Harvey noted that deep surveys were a unique science for Chandra. Considerable resources have been devoted to this already: 2 million seconds of time in the Chandra deep field north and 1 million seconds of time in the Chandra deep field south. However he expressed concerns that future increases in time on these fields might be difficult to obtain through the standard pool of time. He therefore suggested that a new category of proposals, presumably for very large allocations of time, be initiated for deep surveys. A group of people who do this type of science would be assembled and tasked to decide upon an optimal observing strategy and to put forth the best proposal argument. A separate panel of non-deep-survey scientists would then review this.

[19] The CUC carefully reviewed and discussed this suggestion. First, the committee questions the fundamental premise behind this suggestion, i.e., that deep surveys are unique science for Chandra. Chandra has made lasting impact on a number of fields any one of which could make a compelling argument for uniqueness. Furthermore, the science of deep surveys may be at a turning point. Increasing exposures are likely to result in comparatively few additional new sources, so that the main goal of going deeper will be to characterize source properties, measure spectra, and search for unusual sources types. Whether this will result in "breakthrough" or "incremental" science is not clear. Thus, the CUC does not support this suggestion, as proposed only for deep surveys.

But when considered more broadly, the idea has quite a bit of merit. It seems reasonable to surmise that a huge award (1 or 2 million seconds) of Chandra time could lead to a fundamental breakthrough in one or more subject areas across the entire field of X-ray astronomy. On the other hand this potential needs to balanced against Chandra's limitations, e.g., some observations may be limited by fundamental uncertainties in spectral calibration rather than random error from counting statistics. Nevertheless, the CUC recommends that a focused workshop be convened on the science breakthroughs that would be made possible over the next 5 years or so by large million-second class awards of Chandra time. The CUC would be willing to help with the scientific organization of such a workshop.