Chandra Users Committee Meeting (6-7 April 2009)

Report issued on 12 May 2009


Harry Ferguson
Randall Smith
Luisa Rebull
Matthias Ehle
Elizabeth Blanton
Ken Ebisawa
Joel Kastner
Martin Laming
Jon Miller (by phone)
Steve Allen (by phone)



  1. Calibration. As mentioned above, while the agreement in cluster temperatures between Chandra, and XMM and Suzaku appears to have improved with the latest updates, the 0.5 - 2 keV Chandra flux now appears to be in disagreement not just with XMM and Suzaku, but many other x-ray astronomy missions as well. While the CUC do not consider that agreement with other missions should be the ultimate goal of calibration, and endorse the approach of the Chandra calibration team of trying to understand the instrumentation in as much detail as possible, we remain concerned at the continuing problems surrounding the Chandra HRMA calibration. We cannot really find fault with the technical approach, but wonder if better communication with the user community could be facilitated.


    1.1 Giving the changes in fit parameters for e.g. cluster source and AGN with power laws (extreme thermal and nonthermal sources) for each change in the CALDB. This would allow users a clearer idea of by how much their fit parameters could be in error due to the calibration uncertainties.

    1.2 A significant update to the instruments and calibration section on the Chandra website is needed. The initial table describing all calibration topics and their current status is useful, but there is no way for a user to know which topics are under active investigation; some bolding or use of color would help. At the next level down, however, we note that old archived powerpoint presentations are not adequate. We suggest written memos, possibly short, that describe the issues being worked by the calibration team. These can be then categorized as "Open Issues", "Best Working Guess" and "Obsolete Items" (or similar). Short reports on the HRMA A_eff (re)calibration and ACIS contamination represent especially important and timely items to include in the revamped Cal section of the (newly reworked) CXC website.

    1.3 Working with the CIAO team to annotate the CIAO analysis threads with warnings regarding the calibration at the appropriate places. Many users may just skim the real documentation (we know they should read it properly, but this is human nature!) and warnings in the threads would force them to take notice.

    1.4 The HRMA discrepancies were found and certainly addressed as an on-going effort of the IACHEC group that looks into the cross-calibration of several X-ray missions. We strongly recommend that CXC continues its involvement in this consortium.

  2. Software. As with the calibration, we have no real complaints about the technical quality of the work of this group, but similarly do have some concerns about their relationship to the user community. We now have two versions of CIAO, 3.4 and 4.1 that are currently widely used, and suspect that despite the 731 downloads of CIAO 4.1, the vast majority of users are still working with CIAO 3.4, largely due to the overheads associated with learning the new interface. We make the following recommendations:


    2.1 Survey current CIAO users to determine which version they are using and why, along with what they would like to see included in the next versions. A selected sample of recent authors of Chandra data based papers would work, or some other criteria to avoid self selection bias -- follow up may be needed to get a complete, or near-complete survey. As one example, the CUC believes that the software industry is going to go with Python and recommend that the Chandra software do the same, but this would be a good question for the survey.

    2.2 Make more example files available for the new interface. The service available to translate users' scripts is valuable, but the Chandra SDS group should understand that many people will be nervous about revealing their programming techniques (or lack thereof) to software professionals. [Some authors of this report would certainly be in this category!] In addition, even if the translation were perfect, the user would still have to explain the purpose of the code to the team, then test the results, and finally understand how it works -- a significant effort, even if less than rewriting it themselves. Making (many!) more example scripts available would allow users to make their own substitutions or translations as needed.

    2.3 The SDS need to market their software more effectively to the Chandra community. Something like an EPO effort (although of course this is not really public outreach, but outreach to professional astronomers) to motivate users to upgrade to CIAO 4.1 and Sherpa seems to be required. We are really suggesting that more effort be put into making better use of the existing functionality of the software, rather than developing more.

    2.4 It would also be good to hear (for example at the next CUC meeting) about CXC medium and long term plans for CIAO: which platforms will be maintained for how long, what is the planning for the time after the operational phase (i.e. post-existence-of-CXC, will the number of builds have to be decreased, are there any plans to go for virtual machines, grid solutions, etc)?

    2.5 Put mean/median helpdesk response times on the Chandra website so that people know they are fast.

  3. Catalogs: As mentioned before, the presentation of graphical interfaces for accessing source catalogs generated much interest and discussion among the CUC. So far, these interfaces all seem to be isolated efforts (the Chandra Source Catalog, TGCat, the JUDO and UDON interfaces developed for Suzaku) so:


    3.1 At a minimum we recommend that the various catalogs and interfaces have links to each other. In particular a link to SIMBAD would be desirable. Since most astronomers use this to search for sources, it would be a shame if Chandra sources did not show up in a SIMBAD search. It is also particularly important for a user to be informed that just because a position returns no 'hits' in the (evolving) Chandra source catalog does NOT mean that that position has not yet been observed by Chandra. In the longer term the CUC would be very excited to see a uniform graphical interface that allows access to all of the data of interest of a particular source from the various missions.

    3.2 The user interface to the catalog should be reconsidered, perhaps with advice from the ds9 developers -- who themselves have a goal of immediately-usable software. The current interface, tool tips and help, and error messages need quite a bit of attention in the very near term. Most of the CUC members who have tried the interface have found things confusing or gotten unexpected results. It is important to address the new-user experience now, since the first impression may drive away many potential users. The HEASARC Browse interface will provide a base level that most users are familiar with, so the goal for the CSC should be that an astronomer be able to immediately use the Chandra catalog (without reading any documentation) to get more useful information than will ever be available in Browse.

  4. Website. Finally, we just add a 'kudos' on the new website design. We encourage the CXC to go public with the new design ASAP, and to view its release as an opportunity to make major facelifts to individual team pages (the Calibration portion being a problem area, as noted above).