Chandra X-Ray Observatory

CXC response to CUC Recommendations following 2006 Apr CUC Meeting

> 1) Prioritizing the Chandra Source Catalog : The CSC is an important
> part of the scientific output of the Chandra observatory and we
> commend the work that has been performed to date. We believe that the
> Level-3 review panel was extremely useful and strongly endorse the
> recommendations of this panel. The CUC remains concerned, however,
> about the timetable/schedule for the first release of this catalog. It
> seems like this important project has been relegated to that of a
> "spare time project" for the SDS group resulting in large
> uncertainties about the release date.
> The CUC urges the CXC/SDS to take a serious look at the prioritization
> of the catalog in relation to the other on-going projects pursued by
> the SDS group. While the CUC fully acknowledges (and entirely
> supports) that spacecraft operations and basic data analysis needs
> must take priority, it is unclear that some of the other projects
> consuming the SDS group's time (e.g., the Sherpa/CHIPs update) demand
> a higher priority than the source catalog.
- We agree with the CUC that the Chandra Source Catalog (CSC) is an
important project, and we appreciate the suggestion to re-evaluate its
priority.  Now that we have a draft of the catalog characterization
plan, produced in response to the recommendations of the recent
external review of the CSC, we are identifying specific tasks to which
extra resources could reasonably be applied both immediately and on a
longer timescale. This analysis will be complete by mid-June.  In
addition to the existing work by 3 SDS and 3 DS scientists part-time
on the project, we anticipate that a larger fraction of SDS staff
time, probably around half of 2 extra scientists, will be devoted to
the CSC project.  This redirection will become easier as initial
Sherpa2 and Chips2 development and testing winds down later this year.
Both Sherpa2 and Chips2 will be used extensively in the catalog
project itself, and therefore their development complements that of
the CSC. 

- We are conducting a dialogue within SDS to help us better determine
what should be the appropriate balance among our current short term
goals and projects (e.g., Sherpa2 and Chips2), the CSC, and other user

> 2) Communication of basic technical information to the peer review
> panel : The concern has been raised that some members of the Chandra
> peer review committees may be applying incorrect preconceptions about
> the capabilities of Chandra, especially in comparison with XMM and
> Suzaku, and that this may affect the review of some proposals. It was
> felt that this is especially a concern for spectroscopic (grating)
> proposals. The CUC recommends that, starting in the Cycle-8 review,
> the CXC produces a simple one-page technical description showing, for
> example, plots of the effective area and spectral resolutions of the
> various instruments/modes of Chandra, XMM and Suzaku. This sheet
> should be distributed to the proposal reviewers along with the
> proposals, and should be widely available (in hard-copy format) at the
> time of the review. The CUC requests that a draft of this sheet be
> provided to the CUC at the time of the written CXC response.

- We will prepare a 1-page summary of Chandra capabilities based on 
information in the POG, post it to the review website, advertise it to the 
panelists and provide a hardcopy to each of them at the review. We will send 
the CUC a copy for their information and comment.

> 3) Announcement of future CUC meetings via the Chandra bulletin :
> Based on the small number of community complaints received by the CUC,
> we believe that the community is basically satisfied with all aspects
> of the Chandra program. However, the CUC would like to maximize the
> feedback received from the community. Thus, the CUC recommends that an
> announcement of future CUC meetings be made to the Chandra community
> (most likely through the Chandra Bulletin). The announcement should be
> at least 4-6 weeks prior to the meeting thereby allowing new agenda
> items to be added as necessary. The announcement should list the names
> and email addresses of the current CUC members as well as provide a
> link to the CUC website.

- We will advertise the CUC meetings via our usual bulletin email
address in advance of the meeting

> 4) Better definition of the cross calibration efforts : As stated
> above, the CUC is pleased to see continued and systematic
> cross-calibration activities with XMM. However, based on the concerns
> raised above, the CUC recommends that the calibration team and the
> cross-calibration team formulate a strategy for the (eventual)
> integration of their respective works and that this strategy be
> included in the Fall 2006 presentations to the CUC.
> Furthermore, it is unclear that the current cross-calibration efforts
> are being guided by a consideration of what is most useful for the
> "real" user. The work currently being performed is most relevant for
> those users who are performing a direct joint fit of XMM and
> Chandra-grating spectra. A more common occurence, however, will be a
> user who wishes to compare the flux and spectral fit parameters from
> XMM and Chandra observations taken at different epochs. It is
> important that the cross calibration efforts serve this type of user
> as well by quantifying the systematic errors on the flux and spectral
> parameters.

- To enable users to compare fluxes and spectral fit parameters from
Chandra and XMM-Newton observations taken at different epochs, we will
work with the XMM team to compare (absorbed) flux and spectral index
measurements in 4 bandpasses for all sources observed simultaneously.

These four bandpasses are: 0.54-0.85 keV, 0.85-1.5 keV, 1.5-4.0 keV,
and 4.0-10.0 keV.  The fluxes in the three low energy bands can be
measured directly to +/- 1% in almost all cases while the 4-10 keV
band can be measured directly to +/- 3% in all but a few cases.  The
spectral index uncertainties are estimated to be of order 0.2, 0.1,
0.03, and 0.1 in the four bands.  If the lowest two bands are
combined, then the spectral slope uncertainties can drop to about

The XMM calibration scientists are already at work fitting power law
spectra to various sources in these bandpasses and determining fluxes
for the various XMM instruments.  We will present all results on
publicly accessible web pages by September 1.  In addition, by
September 1, the CXC Calibration group will provide a long-term plan
for correcting any systematic differences between the fluxes and
spectral indices measured by Chandra and XMM.  This effort will be
relevant for those users who intend to perform joint fits of XMM and
Chandra spectra (with or without gratings).

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