Chandra X-Ray Observatory

CXC Response to CUC Recommendations following 2010 October CUC Meeting


> 1. Guaranteed Time Observations.
>  We find that the current GTO policy is very beneficial to efficient
> operations of the Chandra X-ray Observatory, and that maintaining the
> integrity of the GTO teams is important for the long term health of the
> Observatory. We emphatically concur with the recommendation of the
> Astrophysics Subcommittee that the current GTO policy be retained.
> In the event of future budget cuts, we suggest that the project itself
> should be allowed to decide where these cuts should fall so as to
> minimize the impact on Chandra science and operations. We note that in
> dollar amounts, the GO funding has not been cut since the beginning of
> the mission (obviously the buying power of those dollars has been
> eroded by inflation), and that so far all cuts have been absorbed by
> the instrument teams and other mission operations.
> While this recommendation and policy appears to make Chandra anomalous
> among comparable big observatories, we consider that astronomical
> instrumentation at this level of sophistication should not be handled
> with uniform policies. In particular, it appears that X-ray
> instrumentation is more robust and longer-lasting than optical or
> infra-red detectors, and that such considerations should inform the
> GTO data policies.
> RECOMMENDATION We also suggest that instrument teams collect important
> papers, engineering developments, etc from recent years in case the
> GTO policy comes under renewed pressure.  For instance, this time last
> year the CUC heard about the successful resolution of the MUPS
> pressure anomaly that occurred over the summer of 2009. This was due
> in no small part to having people who were familiar with the relevant
> spacecraft systems, including some of the instrument PIs, readily to
> hand, and so disaster was averted.

The CXC accepts the endorsement of the Users Committee for
a stable GTO program.

> 2. XVPs.  
> RECOMMENDATION We endorsed the draft announcement circulated to users
> in early November.  In particular, adhering to our recommendation, but
> changing the name VLP --> XVP emphasizes the novel and anticipated
> legacy aspects a little more.
> RECOMMENDATION In view of the relative decline in recent years of time
> proposed for VLPs and also in the time actually awarded, and the
> seemingly natural tendency for peer review panels to avoid long
> proposals (e.g. the article on The Hubble Multi-Cycle Treasury Science
> Program that was circulated to us before the meeting), we also
> recommend the CXC host a workshop dedicated to long projects, similar
> to those organized by HST.
> RECOMMENDATION We also recommend the XVPs be treated similarly to the
> VLPs in past years, being reviewed in the relevant topical panels
> first. It might also be beneficial to have the review pundits arrive
> at the review earlier than they have in the past, also to review the
> XVPs in parallel with the topical panels, so that as many people as
> possible have seen the proposals by the time the Big Project Panel
> meets at the end of the review. We also suggest that pundits be chosen
> with care, in the hope that people who would be willing to "champion"
> long proposals can be identified, in order to try and combat the
> natural bias of peer review panels towards short proposals.

The CXC is pleased to implement these recommendations for 
Cycle 13 Call and the subsequent peer review.  

The time between receipt of these recommendations and the Chandra
deadline was too short to schedule an XVP-related workshop that might
shape the response to the call for XVPs.  However, judging by the number
of Notices of Intent to propose XVPs, this new XVP initiative will
likely be oversubscribed at a healthy level, with a significant number
of unprecedentedly long programs (>2Msec) proposed.  We will re-assess
the feasibility and the need for a workshop, following the Cycle 13
review process and its results.  

> 3. Director's Discretionary Time. The CUC consider that the DDT time
> is awarded in a very fair and conscientious manner, and considering
> that a large amount of the original DDT allocation was contributed to
> the Chandra Deep Field South, we concur with the addition of an extra
> 300 ksec to DDT from the extra time becoming available due to the
> evolution of Chandra's orbit.
> RECOMMENDATION We endorse the transfer of 300 ksec to augment the DDT
> allocation for Cycle 12. Similar augmentations of the DDT time
> allocation for future cycles should be considered year by year at
> future CUC meetings.

The CXC accepts this recommendation, and will review DDT allocations
with the CUC as usual at future meetings.

> 4. Long term planning/next Senior Review? The CUC expressed a desire
> to help Chandra position itself to fare well in the next Senior
> Review.
> RECOMMENDATION We thought that Chandra should pursue a joint proposal
> arrangement with ALMA, as this would (a) broaden Chandra's user base
> and (b) strengthen Chandra's synergy with ground-based facilities.

The CXC is in communication with the NRAO about extending the
Chandra/NRAO Joint program to include ALMA.  ALMA is an international
partnership and the time assignment will be implemented under a single
process, meaning that the observing time will not be assigned by any
one of the partners' Executive Observatories (e.g. NRAO on behalf of
North America) independently.  While NRAO and the CXC are both
very positive about scientific synergies between ALMA and Chandra,
it is not yet clear at this early stage how the NRAO can make an
arrangement to set aside a fixed amount of ALMA observing time for
Chandra/ALMA joint time.  Both observatories will review the 
status in the coming year.  

In the meantime, Dan Schwartz will be attending the
the Mar 7-10 NRAO-hosted meeting "Building New Worlds, New
Horizons: New Science from SubMillimeter to Meter Wavelengths"
to describe the existing Chandra joint programs, and sketch just a few 
of the important X-ray/radio/mm/submm science opportunities unfolding
now and in the coming years. 

> 5. Sub-Pixel Event Reconstruction. The CUC discussed the tentative
> identification of a PSF anomaly. The anomaly is better defined in HRC
> images than in ACIS (due to the better resolving power of the former),
> and there was some evidence that the anomaly had only appeared
> post-launch.
> RECOMMENDATION We encourage the CXC to pursue the confirmation and
> characterization of the anomaly, since understanding the PSF at the
> sub-ACIS-pixel level will be critical to the CXC's ongoing efforts to
> implement subpixel event relocation (SER) -- as recommended by the
> most recent Senior Review -- and, even more, when trying to use SER in
> conjunction with deconvolution.  It is also very important to
> investigate the anomaly's energy dependence (via ACIS imaging).

We recently obtained a 20 ksec HRC-I observation of AR Lac to
better characterize the PSF anomaly.  The feature is clearly detected
in this observation and the good statistics will allow us to
better diagnose the origin of the feature.

A new tool "make_psf_asymmetry_region" has been released as part of
the CIAO contributed tar file. It creates a region file to
identify the area where the asymmetry may be affecting the analysis
(especially for a 2-D analysis looking for faint jets, shells, or
similar structures). 

A memo "Analysis of Chandra PSF feature using ACIS data"
( has been
posted about the PSF feature on the Chandra calibration web pages. 
A detailed data caveats "Probing higher resolution: an asymmetry in
the Chandra PSF"
( with
explanations and advice to users has been posted on the CIAO web page
and also linked from the Chart (Chandra Ray Tracer) web page.   

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