Chandra X-Ray Observatory

CXC response to CUC Recommendations following 2009 October CUC Meeting

> 1. MUPS anomaly. The CUC strongly endorses all the actions taken to
> resolve this issue, and congratulates all personnel on the successful
> outcome. Having the necessary expertise available "on call" was
> clearly critical.
> 2. Chandra Deep Field South. The CUC endorses this use of Director's
> Discretionary Time, and the suggestion to have archive proposals
> compete for the fund available to analyze this dataset at the Cycle 12
> Peer Review. We recognize that a number of (good) proposals to do just
> this have been submitted in recent years, but have not made it through
> the peer review process. While peer review is the best selection
> mechanism we have for proposals, it is not perfect, and the use of DDT
> to remedy such imperfections is wholly appropriate.
> RECOMMENDATION. Tell the community as soon as possible that this is
> going ahead. It looks like this has already been done to some extent
> in Chandra bulletin #89, e-mailed in 11/5/2009, and in AAS Electronic
> Announcement #202, e-mailed on November 11.

The archival research funds made available from DDT funds for
analysis of the new Chandra Deep Field South DDT observations
was described in the Cycle 12 Call for Proposals, released Dec 15,

> 3. Proposal to restore separate time allocations for LPs and VLPs in
> Cycle 12. It was noted in Cycle 11 that several of the LPs approved
> asked for substantially more than the 300 ks LP threshold, some for
> 700 - 800 ks, and so we felt that there is no real bias against long
> observations in the big project panel. Notwithstanding our endorsement
> of the 2Ms DDT observation of the CDFS, the CUC is unanimously opposed
> to restoring separate allocations for LPs and VLPs in Cycle 12.
> RECOMMENDATION. We recommend for Cycle 12 at least, not to go ahead
> with separate LP and VLP time allocations. This is a difficult issue
> and should probably be revisited every year after the peer review. We
> are generally cautious about the unintended consequences of
> "over-engineering" the peer review, and prefer to leave this process
> alone to decide the relative merits of proposals. Of course in extreme
> cases, such as the Chandra Deep Field South, external intervention is
> necessary and desirable. We don't feel that the relative lack of
> approved VLP projects in Cycle 11 yet rises to this level of concern.

The time allocations for LP and VLP proposals have been retained as a
single pool in Cycle 12, with no limitations on how much of the time is
allocated to each category.  The Chandra Director's Office will
continue to monitor trends in oversubscription as a function of
proposal type and length, and present results at each CUC meeting.

> 4. Web site. Great progress has been made. We like the new instrument
> sites, and the way they are linked to the rest.
> RECOMMENDATION. The web site should be exercised externally before the
> Cycle 12 Call for Proposals. Some of the CUC members expressed a
> willingness to help in this. We also endorse better integration of the
> MIT sites with the Chandra web site, with e.g. lots of reciprocal
> links.

The new instrument pages for ACIS, HRC and LETG were made available to
the CUC and the CXC web science group in mid December.  A few comments
were received and incorporated and the pages were released on 25 Jan
2010.  We hope for more feedback as the pages are used over the
proposal period.   Work is underway to create a HETG instrument page
and improve integration with the MIT HETG pages. 

> 5. CIAO. We endorse the choice of Python over S-Lang for the scripting
> language. It seems that Python is going to be the more widely used,
> and this change lowers the threshold for new users. We also endorse
> dropping support for Mac PPCs.
> RECOMMENDATION. The CIAO survey seems to have been valuable, and we
> suggest doing this more often. Not every year, but maybe every 2- 3
> years. We also recommend looking into providing support for the Mac
> Snow Leopard platform, and like the idea of keeping CHIPS and SHERPA
> separate from CIAO in the distribution.
> In the area of long term planning, we encourage discussions between the
> different projects (XMM, Suzaku, etc) to coordinate approaches to issues
> such as platforms, operating systems, libraries, compilers etc.

The CXC appreciates the support of the CUC for the architectural changes
in CIAO. Support for Mac Snow Leopard is available in CIAO4.2 via a
very minor workaround, and will be seamless in future releases. We will
continue to monitor trends in community platform usage, and concur with
the CUC that a circa 3 year timescale for user surveys is appropriate.

Over the years we have had occasional discussions with the XMM and GSFC
teams on system issues, and of course as scientists we all use each
others' systems in our research. We agree that more frequent contacts across
missions would be fruitful and we will arrange this.

> 6. Senior Review. The CUC feels that the 2010 Senior Review is of
> paramount importance, especially because Chandra will be held to a
> high standard as the flagship high energy astrophysics mission. Both
> in terms of science, and science/dollar, the CUC feels that Chandra
> should strive to achieve the top ranking.
> RECOMMENDATIONS. The CUC urges Chandra to engage with its observing
> community to help develop the strongest possible proposal, and to do
> so on a timescale that permits revisions and reflection.

We very much appreciate the strong support of the CUC and our users
generally. In early January a red team consisting of experts in a
variety of relevant areas reviewed the draft proposal. Their
recommendations have been incorporated and Chandra staff continue to
work, in consultation with Chandra scientists worldwide, towards
producing the best and most robust representation of Chandra's current
and future scientific contributions. 
> 7. Calibration. We recognize the extensive calibration effort that has
> been applied to the Chandra telescope, and the dedication of the
> calibration team, and endorse the approach of the calibration group in
> trying to understand the instrumentation as thoroughly as
> possible. Having said this there are still some aspects of the
> calibration that cause concern, particularly the cross calibration. We
> are aware that problems here might not be Chandra problems, but
> associated with the other missions. While the reanalysis of the ground
> calibration data undertaken since January appears to have improved
> things and validated the recent CALDB release, we note that the cross
> calibration plot only showed data from ACIS, where O VII and O VIII
> lines are blended together, as are Ne IX and Ne X. Data from HETG-MEG
> for these lines would be much more compelling, especially in
> comparison with the XMM Newton RGS.

The calibration team agrees that it needs to re-analyze the HETG-MEG
spectrum of E0102 with the new ACIS contamination model and compare
our results with the XMM-Newton RGS.  We will do this before the next
CUC meeting.  In addition to the E0102 cross-calibration results, the
calibration team also presented cross-calibration results for a set of
simultaneous AGN observations with XMM-Newton. These plots compare
HEG, MEG, LEG, PN, MOS and RGS derived fluxes and show that there is
now fairly good agreement between the Chandra and XMM-Newton flux
calibration above about 0.5 keV.

> Progress on the filter contamination looks good. We appreciate that
> this problem is exceedingly complex, given its temporal, spatial and
> spectral dimensions. However ideally the CUC would really like some
> more insight into what the calibration team knows and how they are
> dealing with it.

A new memo that gives a somewhat in-depth discussion of the history of
the calibration team's effort to calibrate the contamination on the
ACIS filter was posted on the calibration home page in early Jan.,
2010.  At present, the greatest uncertainties regard the composition
and spectral properties of the contaminant on the ACIS-I filter due to
the lack of deep gratings observations.  This will be remedied in
early Feb., 2010 with a set of 5 LETG/ACIS- I observations of Mkn 421
with the appropriate off-sets to place the O and F-K edges at 5
different locations on the ACIS-I3 chip.  The results of this
experiment will be discussed at the next CUC meeting.
> Concerning the Calibration website: We were told in response to our
> 4/09 report (see notes 1.2 and 1.3 from that report) that the
> Calibration team would add "new sections regarding hot topics" (like
> contamination and cross-calibration, we presume) and that "some
> prototypes for these new sections" would be presented at the 10/09
> meeting. Most of these issues were discussed, but not in the context
> of the CXC Calibration web page, which still poses difficulties for
> some users.

A new set of calibration web pages are scheduled to go public
by the end of Jan., 2010. 
> RECOMMENDATIONS. The cross calibration between the HETG-MEG and the
> RGS should be completed as soon as possible. With the change of
> effective area in January 2009, this comparison worsened (see
> e.g. slides 13 and 14 of
> and it would be interesting to see whether the application of the new
> contamination model improves this, as it appears to do for ACIS-S3.
> As has been mentioned before, our main concern is not so much with the
> technical aspects of the work, which we really cannot fault, but with
> communication with the user community who need advice that is as clear
> and well justified as possible. One possibility might be a
> comprehensive "Status of ACIS Calibration" memo describing the
> issue. Such a memo should address (a) what is known about the problem
> (i.e., collect and explain all the relevant data in a coherent
> fashion), (b) the various models proposed, and their strengths and
> weaknesses, (c) the near-term implementation of a contamination
> model(s) in the CALDB, and the rationale behind the implementation (as
> we understand the informal discussions during our 10/09 meeting, some
> sort of hybrid model was just put in place, consisting of one piece
> for ACIS-I and one piece for ACIS-S), and (d) the calibration team's
> longer-term plans for contamination monitoring and modeling.

These issues are addressed substantially in a new memo posted on the
calibration webpage
and linked as "latest calibration memos".

> 8. Catalogs. Significant progress has been made since the last CUC
> meeting in terms of accessibility. The Google Earth interface is a
> very nice thing to have, and will probably prove to be of more use in
> getting non-experts involved in X-ray astronomy than for professional
> astronomers.
> RECOMMENDATIONS. The 500,000 hits on the Google Earth interface, even
> if only from a few thousand distinct IP addresses, is impressive. We
> are prompted to suggest tracking scientific use of the catalog in this
> way, maybe for the Senior Review in two years time, and to encourage
> authors to acknowledge use of the catalog in publications. We also
> encourage the importation of extended sources to the catalog as soon
> as possible.

From the start, all accesses to the CSC have been logged.  For user
interfaces that access the catalog directly (e.g., CSCview, the
Command-line interface, the IVOA Simple Cone Search interface)
information is logged that both identifies the source of the query and
traces some details of the user's interaction.  For other interfaces
(e.g., CSC Sky in Google Earth, CSC-SDSS Cross-match, CSC Sensitivity
Map) the logging is restricted to recording accesses and source IP
addresses.  Usage statistics are extracted from all of these logs.  We
still have to complete work to better automate production of
statistics from the logs.

The CSC web site home page includes a request for acknowledgment of
use of the catalog, and also reminds catalog users to include the
appropriate catalog Dataset Identifier in their manuscripts.  If
the CUC has other ideas in this area, we welcome the input.

We agree with the desire to include extended sources in the CSC as
soon as possible, with the caveat that robust automated detection of
highly extended sources and extraction of meaningful source properties
is a complex problem in the general case.  In Release 1, extended
emission is either resolved into multiple overlapping detections or
results in the observation (or single chip in the case of ACIS) being
excluded from consideration.  We anticipate making some improvements
for Release 2 of the CSC, with emphasis on better handling of the
extended emission that is often detected in galaxy cores.   

However, the primary focus of Release 2 is to significantly improve
the catalog depth by stacking (combining) split observations prior to
source detection, and by lowering the source inclusion threshold to ~5
counts (on-axis).  We expect to achieve this through a combination of
improving the model backgrounds used for source detection and
significantly lowering the source detection threshold.  Each candidate
source will be graded using a maximum-likelihood estimator with a
source model that is convolved with the local PSF for each observation
in the stack.  These enhancements will more than double the number of
sources included in Release 2 of the catalog.

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