Report of the June 29, 2001 CUC meeting

The Chandra User's Committee (CUC) met at Harvard on June 29.

I. The Manager's Report:
We were pleased to hear from Roger Brissendon that the observing efficiency of 70% which is close to the maximum possible and learn that the time to deliver data to the users has dramatically decreased to a median of 7 days and the time lag between the initiation of observations and approval of contracts to the user is now a mere three days. These issues -- observing efficiency, data turnaround and funding -- are important concerns to the user community. We congratulate Roger and CXC staff for steady improvement in these three critical areas.

We were happy to learn that through cleverness on the part of CXC staff the fuel usage for momentum control (MUPS) has decreased to the point that the fuel consumption is not limiting the lifetime of the Observatory. Again, congratulations.

We understood that the evaluation of the ACIS squeege mode is now complete and the decision has been taken to abandon it, given the small gains. We applaud the cooperation between CXC and PSU on this effort.

[1] While pleased at the decrease in the delay between observation and data delivery we did notice a number of observations which were clear outliers with large delays. We would like to hear the cause for significant outliers at our next meeting.

II. Director's Discretionary (DD) Time:

It appears that the Chandra Observatory has a very active DD program with targets ranging from nearby brown dwarfs to distant GRBs. The CUC remains committed to the DD program for three reasons. First, is the usual unforeseen targets of opportunity (TOO). Second, is allocation for ambitious program with high scientific returns. Usually these tend to be high risk projects that the peer panels considered (including investment of large amount of time for a single target or field). The DD time thus serves a mix of programs. Third, we are enthusiastic about using DD time to promote observations which are not only scientifically useful but also bring publicity to the Observatory. Illustrative examples are Chandra observations of the most distant quasar etc.

We make the following recommendations:

As noted above, the DD program has served a mix of programs (unanticipated TOOs, ambitious programs that somehow did not fit the peer review process). Given this mix, it would be useful to keep track of the approved DD projects and measure the impact of DD approved projects.
Separately (see the above discussion) we suggest that a "High Risk/Innovative" category be considered as a possible new category for AO-4.
We also suggest that some thought be given to "Chandra Heritage" program either as a part of the normal peer review process or as potential allocation from the DD time. Illustrative examples include obtaining scientifically interesting and pleasing images of classes of objects (Planetary Nebulae, Star Forming Regions, SNRs etc).
[2b]
A single entry point to the DD program would be useful. Specifically, we request a single URL where all matters pertaining to DD programs can be found: the past DD programs (with their abstracts and links to their publications or reports of the outcome of the DD observations) as well as instructions for DD time would be helpful. Such a URL could serve as the basis for evaluating the impact of the DD program.

III. Peer Review:

By all accounts AO-3 appeared to have been success. With 750 proposals, the oversubscription on Chandra remains very high. Fred Seward and his crew deserve kudos for making the AO-3 review a smooth process. The CUC also thanks Fred for seriously considering all of our suggestions (made in previous meetings; no grade normalization, panel restructuring) and implementing them.

There is some concern about how a uniform standard of quality is enforced across the the panels. We realize that this is a very difficult task mainly because the problem is not well defined! Nonentheless, the concern is important and we make a recommendation; see below.

[3] The merging panel should use its discretion to set varying acceptance thresholds for individual topical panels according to the merging panel's evaluation of the proposal quality. We would like to hear Seward's opinions on this matter at the next meeting.

IV. Data Archive: Chaser

Chaser, the Java interface to the Chandra archive, works. However, it was not clear to the committee that the choice of Java, with the overhead of requiring a Java Virtual Machine download & installation, and the associated overhead of additional startup time, was worth it. Java applications are superior to web screens when there is a significant amount of interactivity required and when Java classes and utilities written by others are used (leveraged). However, Chaser shows no evidence for interactivity beyond that provided by a web interface, and furthermore, no evidence for Java-interactivity with any other Java tools. The prospect of CXC having to create custom web forms for the CXC engineers seems to further diminish the wisdom of choosing Java. If the Chandra interface is so rigid that the engineers cannot configure Chaser screens to look at their own databases, why bother with Chaser at all? Admittedly, Chaser does work, but we are mystified as to the choice of Java over a web interface when no obvious advantages to the user or to the science center and its support functions are apparent.

We strongly encourage the CXC to maintain some basic (generic) web-based retrieval, since that allows the largest number of users to search for and retrieve data. We encourage the CXC to review Chaser development plans and user comments on its installation and use on a variety of systems.

[4] The committee also recommended that the data retrieval options for the choices of files be grouped together in a sensible fashion. The user should not be expected to know file extensions in advance of retrieval. Perhaps a simple solution is to offer the most common grouping[s] as standard choice[s].

V. ACIS-Calibration:

The committee appreciated the comprehensive presentation on calibration progress. We strongly encourage the end of July release of the new BI FEFs and look forward to seeing new FI FEFs as soon as possible. The CXC must not let the perfect be enemy of the good.

Several members of the committee expressed serious concern over the illustrated difference between the current and new responses. Clearly, the shortcomings in the current responses have not been adequately advertised. We were all unaware that there was an error in the response width. Information on deficiencies and uncertainties must be released promptly and be prominently displayed. We recommend that the data caveats page be linked directly from the top page as well as appearing in the CIAO tree. We also recommend that graphical illustrations be included - the E0102 plots the committee were shown provide an excellent example. The committee noted that while there were many people involved on the ACIS calibration effort there seemed to be far fewer working on the grating calibration.

The committee applauds the continuing excellent work on the background and were happy with the new clean55 algorithm developed to remove more cosmic ray events. We recommend that the CXC consider whether an additional S3 background observation would be useful.

On a related matter, the CUC was impressed with the presentation on the CC mode by Glen Allen. We applaud the hardwork that has gone into making this unique mode more easily usable and even more powerful.

VI.Mirror PSF and Diffraction Grating Calibrations

The CUC is pleased with the general progress made on the calibration of the telescope PSF and grating spectrometer properties.

[5] The Committee has the following comments:

LETGS calibration: the persistent rumor is that the PI institution has an efficiency calibration that is slightly more advanced than the one currently in use at the CXC. Can CXC straighten this out? (i.e. is this true, if so- what are the differences, and if those represent an improvement, can CXC incorporate those in the standard distribution?)
HETGS calibration: the committee is worried about the discrepancies between the diffraction efficiencies as calibrated on the BI, and on the FI chips, and recommends that this issue be sorted out. It holds important information on the relative behavior of the two types of chips. The committee is concerned that not enough manpower is available for rapid progress on the HETGS calibration (which currently appears to rest primarily on the shoulders of a single individual).
Telescope PSF calibration: we note that significant progress has been made. However, we still find it difficult to judge how close the agreement between PSF models, and flight data really is, over the full dynamic range between the core and the far wings of the PSF. We would like to see a fairly comprehensive presentation on this issue at the next meeting.

General comments:

flight calibration program: there appears to be no single answer to the question as to whether or not the exposure time set aside for calibration is adequate; instead, the program makes somewhat of an 'ad hoc' impression. The best way to answer the question is to produce a structured calibration program, and to compare its requirements against the available time (like was done before launch). The CUC would like to see the plan if it exists, or strongly recommends that a plan be made and presented at the next meeting.
It makes sense to test the calibration by making a systematic cross-comparison of all suitable observations with both Chandra and XMM. The committee strongly recommends that a coherent plan to accomplish this be worked out, and would be interested in seeing such a plan (and the results of cross-calibration, of course).

VII. Calibration with XMM:

Cross-calibration with XMM provides an independent check of Chandra calibration. Furthermore, as both XMM and Chandra datasets grow the cross-calibration issue will attain even more importance.

[6] We wondered whether the calibration team is getting adequate amount of telescope time and also would like a presentation of the calibration plan.

VIII. Press Releases.

[7] The CUC is acutely aware of the importance of publicizing discoveries and findings from Chandra. We request that a summary of the Press Releases and Outreach program be a standard item in the presentation of the state of the Observatory at each CUC meeting.

The report was unfortunately not submitted in due time (the Chairman apologizes). A telecon was organized on December 11 to review the progress of three important issues to users: Chaser, ACIS Calibration and Chandra-XMM calibration. The CUC thanks the staff at CXC for making good progress on all fronts. Specifically, we are pleased to see a web version of Chaser already up and running. We were happy to hear of the extensive work on ACIS calibration. We reiterate the lack of understanding of the response response of ACIS at low energies is an important issue for many users.