Luisa Rebull (by phone)
Matthias Ehle
Elizabeth Blanton
Joel Kastner
Martin Laming
Jon Miller (by phone)
Steve Allen (by phone)
Massimo Stiavelli
Joan Wrobel (byphone)
Harvey Tananbaum opened the meeting and welcomed the committee on behalf of the CXC. Members of the CUC then introduced themselves.
Roger Brissenden gave the "CXC Manager's Status Report" for the period October 2009 - April 2010. The current budget is on track with the FY 10 operating plan. The CXC contract extension for up to 10 more years was signed 0n 12/31/09, providing for a base extension to 9/30/13, and two three year options to 9/30/16 and 9/30/19. There are no high level staffing changes, though some reduced staffing is to be expected during the contract extension. The proposed FY11 NASA budget calls for a $3M decrease in FY11 over the previous budget.
The spacecraft and instruments continue to operate very well, with no safe mode now for a decade! ACIS required an unexpected reboot of a back end processor on 1/25/10, presumably due to an SEU. The ground operations team has changed schedule to two 10.5hr shifts/day, as of 1/2/10, which now matches the flight operations team.
The observing efficiency remains very good, at around 72% for the whole October - April period, during which there were 6 load-interrupting TOOs. Mission metrics remain good, 51 lbs (out of 60) MUPS fuel are left, enough for 100 years of operations. Data delivery, and grant award effectiveness are as efficient as ever.
Harvey Tananbaum briefed the committee on the use of Director's Discretionary Time. In the period October 2009 - April 2010, a total of 132 ks was used, with 20 ks from Cycle 10 and the remaining 112 ks from Cycle 11. 500 ks from Cycle 11 will be/has been used on the Chandra Deep Field South, to go with 1Ms from Cycles 9 and 10, and another 500 ks to come in Cycle 12 to bring total exposure to 2 Ms.
Larry David gave an update on the Chandra calibration. The first item was a summary of the IACHEC meeting, attended by 45 scientists representing Chandra, XMM-Newton, Suzaku, IXO, Swift, Integral, RXTE, MAXI, Hinode, NuStar and GEMS. As a result of this meeting, 9 papers are in preparation for A&A, 4 to be submitted by the end of the summer.
The second item concerned the new LETG/HRC-S calibration, as a result of an update to the HRC quantum efficiency, and will be included in CALDB 4.2.1. The relative distribution of energy into higher orders of diffraction is now slightly higher.
The third item was the ongoing calibration of the ACIS CC mode. The Charge Transfer Inefficiency produces a different flight grade distribution in CC mode, compared to TE mode. This impacts the use of CC mode with telemetry modes that do not telemeter all flight grades, especially GRADED mode. ACIS-CC GRADED mode comprises about 5% of ACIS observations. The use of 3 column averaged trap maps improves the situation, with a better flight mode grade distribution. Single column trap maps are now also being generated to further improve the CTI corrections.
Further issues here surround the calibration of HETG/ACIS-S in observations of bright sources in CC Graded mode. Observations in MEG ±1, HEG ±1 show marked differences from each other, and from observations in CC Faint mode. This is particularly true at short wavelengths and near the Si K-edge. These discrepancies also increase with increasing source brightness.
Alexey Vikhlinin gave a very clear account of progress in understanding the ACIS filter contamination. The significant new developments are a resetting of the "zero" level, i.e. the contamination level at launch, and that when this is done the "ad hoc" opacity components that are added to the known absorption edges, "fluffium" or "gaussium" (for ACIS-I and ACIS-S respectively) have the same time dependence as the known components. The "gaussium" model refers to a gaussian opacity component added to the known edges in the ACIS-S, as an update to the "fluffium" model. ACIS-I still uses fluffium. The CUC is pleased with these developments, but still concerned that non physical interpretation exists for the gaussian opacity component.
Belinda Wilkes summarized the Cycle 12 peer review so far. A total of 678 GO proposals, requesting a total of 87855 ks, were received, representing an oversubscription factor of 5.2 in time. These include 70 LPs and 5 VLPs. Requests for grating observations are up a little from Cycle 11. The LP time requested was also up from Cycle 11, but VLPs were down. Some VLP pressure may have been relieved due to the Chandra Deep Field South (CDFS) observations using DDT. In other categories, there were 76 archive proposals and 43 theory. Of these 76 archive proposals, 14 are associated with the CDFS, with a significantly lower oversubscription of 2.53. We comment briefly on this below. Finally, 47 GTO proposals were also received.
Belinda also reported on the Chandra Senior Review proposal and presentation. At the time of writing of this report, the Senior Review report has just been released, with Chandra being placed second behind Planck. This represents a very positive outcome for Chandra.
Andrea Prestwich updated us on the CXC Website overhaul. Phase 1, including the redesign of the top page and the identification of obsolete material (obsolete in the opinion of the authors) is complete. Phase 2, to create new instrument pages with clearer links between the calibration results and data analysis/observation is now also complete. Phase 3 will start after the peer-review, and will remove all obsolete material that does not show up via existing searches, determine a maintenance schedule and procedure for all pages, and provide a better interface between the MIT HETG pages and main CXC pages.
Jonathan McDowell gave a detailed account of the activities of the Science Data Systems Group. The CIAO 4.2 update was released in late 2009, and the CIAO 4.3 release is planned for late 2010. There have been no staff changes since the last CUC meeting. The helpdesk has received 150 new tickets, of which 10 are still open. Initial response times and times to ticket resolution remain, as ever, entirely satisfactory.
"Outreach" activities have included catalog GUI and CIAO demonstrations at the January 2010 AAS in Washington DC and at the March 2010 HEAD meeting in Hawaii. the 7th CIAO workshop was held at the CfA in February 2010.
A survey of downloads of CIAO 4.2 reveals that Linux and Mac (Intel) are the most widely used platforms. Support for the Mac PPC CIAO build is due to be retired. CIAO 4.2 is the first modular release, and is therefore easier to patch.
Progress on a number of R&D topics was discussed, related to calibration developments described above, the point spread function, and the rewriting of scripts to automate some of the Chandra analysis threads. Work is also ongoing in the conversion from S-Lang to Python, and in TGCat, which now has over 1000 observations from 326 distinct sources. A more detailed report was given on the Sherpa 4.2 release.
Belinda Wilkes gave a report on the early ingestion of targets for Cycle 12. Due to the MUPS anomaly in July/August of 2009, many of the "cold" targets due to be observed at that time of year in 2010 were brought forward a year. Now in 2010 we face a deficit of targets, and some from 2011, once approved by the peer review in June, will have to brought forward to fill out the schedule. An announcement is planned for May so that GOs may be prepared to respond quickly in July/August should that be necessary.
Ian Evans presented an update on the Chandra Source Catalog (CSC). Catalog Release 1.1 is nearing completion, release is expected in the next few weeks. It will include public HRC-I observations as well as newly public ACIS data, but otherwise to have the same limitations as release 1. In the longer term catalog release 2 will co-add multiple observations of the same source that use the same instrument, and improve background modeling. It will also include moderately extended sources and include numerous algorithm enhancements identified over the past couple of years. The simultaneous source detection across overlapping detectors and pointings, and the detection and classification of very extended sources will be deferred to future releases.
Finally, the use of the catalog as an interface to CIAO and data analysis was demonstrated in a movie.
A number of CUC members and their colleagues have expressed some concern about the RPS system, specifically the e-mail interface for handling proposals with more than five targets. It appears that the RPS system, and this aspect of it in particular, has not been updated since Chandra's launch. The e-mail interface seems to be vulnerable to hidden special characters that are inserted by modern e-mail handling applications, but that RPS cannot strip out. Given the fact that the vast majority of Chandra proposers appear to be happy and familiar with RPS (including some users of the e-mail interface) we are reluctant to recommend any big changes.
Perhaps the best compromise would be to offer users a simplified front end to RPS that can fill in all fields required in the e-mail version. We are thinking of proposals with target lists where the only change from one target to the next will be in the coordinates and the count rate, with all other instrument parameters the same, where the user would be asked to upload a target list to clone RPS forms. It might also be worth looking at whether it is reasonable to reduce the number of supported ACIS modes in such circumstances to ease implementation.
The CUC remains a little confused about the precise status of the Chandra calibration, especially in comparison to other missions like XMM. We attempt to summarize as follows:
The comparison between ACIS, PN and MOS gives ACIS fluxes higher than those for PN by ~10%, and MOS fluxes higher than PN by ~4-7%. Above 2 keV, these three instruments give the same plasma temperatures. Below 2 keV, ACIS can still be fit with a single temperature, although the 0.5-2 and 2-7 keV temperatures are inconsistent by about 10%. PN and MOS however both need 2 temperature component to give acceptable fits to spectra from what are presumed to be isothermal sources (outer regions of galaxy clusters). The soft band in XMM generally gives a lower temperature than Chandra, indicating a soft excess, or a hard deficit, in XMM relative to Chandra.
The comparison of spectral line fluxes (O VII, O VIII, Ne IX, Ne X) indicates higher fluxes at 1 keV and below with Chandra. A series of plots of blazar grating observations during the XMM and Chandra missions indicated the improved calibration in a series of energy bands, with the Chandra flux relative to XMM increasing slightly with energy.
Is this accurate? Ideally we would have liked to see the temperature and flux for both the ACIS/pn hard band and the ACIS/pn soft band.
The CXC's ongoing efforts to 'scrub' its web pages to remove obsolete and/or confusing documentation (which the CUC applauds!) should focus on the Cal group's areas. These are in particular need of updating and reorganization. Such update/reorganization should be aimed at clearly identifying areas that are well-understood and stable (e.g., CTI correction for all modes except CC graded) vs. areas that are 'under study' and in flux (mission cross-calibration work; ACIS filter contamination; CC graded mode), and should clarify the status of the latter. For example, the various memos concerning ACIS contamination could be 'bundled together,' and the obsolete documents among them should be clearly labeled as such.
We are pleased to hear of cross calibration papers nearing readiness for submission. We also support the ongoing efforts in calibration of the ACIS CC mode.
Calibration of ACIS-HETG (including CC mode) should aim for a goal of 5% between the various orders in MEG and HEG. This is driven by the need to accurately measure continua in a variety of applications from spectra of accreting binaries (black holes, neutron stars, white dwarfs) and AGN. In particular the measurement of absorption edges, existence/contribution of thermal bremsstrahlung components, and fitting the red wing of the Fe K alpha line from accreting black holes all depend critically on fixing the continuum level. To a lesser extent, the interpretation of emission line spectra from neutron star and black hole binaries also place demands on the calibration, since the dominant lines come from H-like ions for which the atomic data are accurate at this level. Other coronal sources which depend more on a wider selection of spectral line and less on the continuum do not stress the calibration so much, because atomic data used in interpretation is less accurate.
The CUC are mildly concerned about the reduced oversubscription in archive proposals to study the CDFS, compared with other archive and theory proposals. Of course there is no way to know a priori what will happen in response to the AO.
For the time being we just comment that in the peer review, we hope that CDFS archive proposals will be held to the same standard for funding as other archive proposals.
As the Chandra mission matures, the necessity to have CUC meetings twice a year has been questioned.
The CUC agrees that the meeting schedule could reasonably go to once a year, preferably in October after the peer review. We also agree that at each meeting, a time in April for a telecon should be set aside in case any issues arise that need discussion. Note that the telecon need not happen, but the CUC should be prepared in case it does become desirable.
We are impressed with the ongoing progress. Our discussions prompted a few further questions: What is likely to happen to the source catalog when the Chandra mission ends? Is CIAO envisaged to be an interface to the catalog?
Although solid progress is being made on the CSC, we remain concerned about the CSC's visibility in the wider astronomical community. We recommend that (1) CSC releases be announced via the AAS; and (2) when the manuscript defining the CSC is accepted, it be posted to astro-ph (we note with satisfaction that the accepted version of the Evans et al paper on the Chandra Source Catalog has been posted at http://arxiv.org/abs/1005.4665). We would also like to see a batch search engine.
The CUC is pleased with the progress that has been made.
It would be desirable to have a physical model for the "gaussium" component, not just for the intellectual satisfaction, but to be able to predict how the contamination might behave in the future. We recognize that this is asking a lot of the resources of the CXC, and that the main aim of providing a calibration that observers can use has basically been met.
Second place to Planck in a review with the metric science/NASA$ is a very satisfactory outcome, and we commend Harvey and the team on a job well done.
