Chandra Users Committee
June 25-26, 2002
Members Attending: M. Arnaud, J.P. Henry, J.P. Hughes, W. Latter,
J. Krolik, J. Mohr (by telecon), and F. Paerels
Others: A. Tennant, H. Tananbaum, B. Wilkes
Manager's Report (Roger Brissenden):
Roger reported that the S/C is performing superbly and operations are
routine. His reports on status, operations, expendables usage,
observing efficiency, observations, data systems, data delivery, and
grant awards are all appreciated by the committee. Roger reported that
SAO and NASA have begun negotiations on the 5 year extension to the
CXC contract. It was decided that any action by the CUC on this issue
would be premature at this time.
Director's Report (Harvey Tananbaum):
Harvey reported on the use of the Director's Discretionary Time from
February through June 2002. About 585 ks of cycle 3 DDT have been used
already, making it unlikely that a significant chunk of time will be
available for a single large observation as happened in the past two
cycles (RXJ1856.5-3754 in cycle 2 and the CDSF in cycle 1). It was
noted that over the three month period from 3 March to 3 June there
were 8 load interrupt ToOs of which 4 were DDTs while the remainder
were ToOs awarded by the peer review. Nominally the peer review gives
out 9 ToOs, HST one, and the Director two.
 The committee briefly discussed this issue and noted that the
fast response time DDTs were in addition to the others and were
therefore a significant benefit to the user community. The CUC also
realizes the increased workload that these observations entail for
the mission operations staff and greatly appreciates their
Summary of issues from Chandra AO-4 proposal submission and peer
review (Fred Seward):
This round Fred avoided using reviewers from previous cycles. The
Large Projects in AO4 received 23% of the total available time which
is similar to the fraction awarded in previous cycles (AO2: 25%, AO3:
20%). Seventy percent of the GTO proposals submitted after the
deadline in reaction to a conflict with a GO target were successful.
Fred noted that he has not been able to figure out a way to disguise
the GTO proposals from the panels.
 The CUC discussed this issue briefly and recommends that the CXC
implement (for Cycle 5) some of the suggestions for disguising GTO
proposals that are offered in the minutes of the CUC meeting from
January 31, 2002. In particular the panels should not be told which
are GTO proposals and they should be instructed to treat any GTO and
GO conflicted proposals purely on the basis of scientific merit.
Finally the panels should not be aware of how much GTO time there is
in their panel.
TOO and time-constrained proposals turned out to be a problem, because
not all such proposals were properly indicated by the proposer. Fred
presented a few examples and suggested that the CXC staff put some
effort into a technical review of proposals beforehand.
 It was not immediately obvious to the CUC that the examples
presented demonstrated the need for a significant technical review
of proposals. We note that technical reviews are a considerable
amount of effort and that the technical reviewers would need to be
present at the peer review to support the panels. However, a
minimal technical review that verifies that what is proposed in the
scientific justification squares with the various constraints
indicated on the forms would be valuable. If this is what's being
considered, then it seems like a fine suggestion and we encourage
Fred to implement it for the next cycle.
Theory and archive proposals are not currently constrained by a
"budget" as observing proposals are constrained by the available time
for the entire cycle. Fred notes that ultimately it may be necessary
to go to a dollar budget for theory and archive proposals, but it's
not necessary yet.
 The CUC agrees that the current situation is not yet a concern
and so no action is necessary.
Plans for AO5 (Belinda Wilkes):
Regarding the Chandra/XMM deadline collision for next year, Belinda
reported that the two observatories have worked out a schedule that
has the Chandra deadline on 15 March and the XMM deadline in late
April. This seems to be the best that can be done for now. The XMM
AO3 cycle will be for 1.25 yr, leading ultimately to a 3-6 month
spread in schedules between the Chandra and XMM review cycles.
Belinda reported on two new joint time programs for AO5: with NRAO
(details to be worked) and RXTE (500 ks). Both of these will be
one-way like the NOAO joint time agreement. The CXC will investigate
a joint time program with SIRTF during their second review cycle.
Other changes for AO5 include requiring proposers to list previous
Chandra awards as well as relevant publications in the submitted
 The CUC applauds this addition and strongly encourages the CXC
to implement it for cycle 5.
For the Chandra AO5 review, the CXC will send out paper copies of
proposals as well as CD-ROMs.
Belinda explained the reasons behind the lack of advertising for the
Chandra theory program which premiered during the last cycle. She
indicated that the CXC will investigate wider distribution for any
future new initiatives.
 The CUC agrees and suggests, more generally, that the CXC
publicize important Chandra updates during open AO periods through
the HEAD newsletter, HEAD mailing list, the Astrophysics Theory
Program mailing list, and other broad community lists in the future.
Occasional complaints from astronomers about getting too much e-mail
should be ignored. Every day we all delete dozens of spam e-mail
with absolutely no value to anyone. Announcements from a major NASA
observatory are of value to many of us and should be distributed
The question of allowing for multi-year proposals was raised for
consideration by the CUC.
 It was suggested that a separate peer review panel for theory
proposals might be worth considering at some point. The CUC
discussed this and concluded that at least for AO5 the same
procedure should be used as was followed previously, i.e., that
theory proposals be reviewed in the appropriate science panel along
with observing proposals. This puts a greater load on the CXC to
select reviewers with broad backgrounds in theoretical astrophysics
in order to properly cover the range of scientific studies that may
be proposed in a given panel. It was also felt by most of the
membership that it was good that observers reviewed theory
proposals, since it would require theory proposals to connect their
research to relevant Chandra observations.
 It was suggested that perhaps the page limit on theory proposals
be relaxed, but the majority of the committee membership decided not
to endorse this, opting instead to retain the current 4 page limit.
 The committee sees no compelling reason whatsoever to implement
multi-year proposals for observing time. However there was support
among the committee for multi-year funding requests. Large
projects, theory projects, and archive proposals would all benefit
from stable funding over two or three years. Theory projects in
particular are considerably less credible when squeezed into a
single year of investigation. Furthermore we point out that NASA's
Astrophysics Data Program (ADP) which supports archive research for
a number of high energy missions (including XMM, but excluding
Chandra) allows for multi-year funding requests.
Harvey briefed the committee on his view of the "GTO beyond prime
phase" issue in preparation for Paul Hertz's call after lunch. He
mentioned that the AXAF Level 1 Policy Document (recently found by
M. Weisskopf, signed by Alan Bunner) stated that IPIs would be awarded
GTO time in the amount of 15% of the observing time for the duration
of the mission. More on this topic below
ACIS Modeling and Analysis (Dan Schwartz):
Dan described the research of a group of CXC scientists working under
his supervision to address two important issues related to the
performance of ACIS: the decrease in low energy quantum efficiency
(LEQE) and CTI correction of the FI chips.
Dan presented an excellent summary of what is known about the change
in LEQE, which appears to be a result of the build-up of an unknown
contaminant on the ACIS filters and/or CCDs. As of the time of the
meeting the chemical composition was not well-determined. There is
evidence for a strong C absorption edge and the O edge is directly
detected. N and F are also likely to be present. The LEQE appears to
be decreasing at a rate of 10% per year at E=0.67 keV and the
degradation appeared to commence within 2-3 months of on-orbit
insertion. Dan outlined plans for further analysis, modeling, and the
need for additional calibration observations.
 We note that this information was posted on the CXC web site
soon after the CUC meeting along with off-line (non-CIAO) software
tools to implement a first-order LEQE correction. We thank Dan and
his group for making this available to the community so quickly.
Some of us are already using it.
The other portion of Dan's presentation covered work on implementing a
CTI correction for FI chips. They are using an algorithm recommended
by the PSU/MIT IPI team. As of the time of the meeting a new version
of acis_process_events had been verified and shown to produce an
improvement in both the width of spectral features and their amplitude
(gain). Dan then went on to describe a new and improved method for
generating RMFs for ACIS. They have developed a technique (based on a
clever idea by Alexey Vikhlinin) that significantly reduces the labor
(i.e., Dick Edgar's) required to produce RMFs.
 The CUC acknowledges the great progress that this work
represents and strongly encourages Dan and his team to continue
carrying it forward. The committee offers its opinion that the 4
ACIS-I chips and S3 are the highest priority devices to correct.
Calibration (Larry David):
Larry gave the Chandra calibration status report covering new and
improved calibration products (ACIS, HRC, LETG, and HETG), caveats
associated with these, uncertainties and issues remaining, the AO4
calibration plan (totaling 911 ks of observing time), and
Chandra/XMM-Newton cross calibration issues. Larry announced that the
CXC was holding a Chandra Calibration Workshop in the fall, which
would be open to the entire scientific community, and encouraged CUC
members to attend.
 The AO4 calibration plan looks good and the team is making
progress on several fronts. One suggestion that the CUC had is for
the CXC to assess systematic errors in derived spectral parameters
that arise from the uncertainties in the effective area difference
between FI and BI chips.
GTO time beyond prime phase (Paul Hertz, by telecon):
Paul reported that NASA headquarters is transitioning to the extended
phase mission for Chandra and is planning all activities, such as the
budgets for GOs and public outreach. They wish to establish an
appropriate policy for GTO during this phase. He claimed that the
various documents related to this are ambiguous at best. The issue is
not one of money, but rather the best way of allocating Chandra
observing time. He notes that generally NASA policy is evolving
toward less GTO time for new missions. Headquarters would like our
input, including points they should consider, and they plan to make a
decision by the end of the calendar year.
 There were a variety of opinions on this topic. The majority
of the committee was in favor of continuing the GTO program for
Chandra IPIs in the extended mission phase (vote 5 - 2). The main
argument on the con side was that GTO time circumvents the peer
review process which is the best system we currently have for
allocating resources across all fields of science. The main argument
for the pro side was that the expertise of the IPI teams is of great
value to the Chandra project and that the availability of observing
time will help to retain the pool of good scientists that provide
this expertise. Thus, regardless of whether they retain guaranteed
observing time, the integrity of the IPIs teams must be maintained
(this is the unanimous opinion of the CUC). NASA headquarters
should provide sufficient funding to maintain the viability of these
groups, including supporting individuals for a fraction of their
time to do their own scientific research.
[CXC Note: Since the meeting NASA HQ
announced an official extension of the GTO time at 15% for the full,
SDS: CIAO 3 Plans and Status (Aneta Siemiginowska):
Aneta talked about the Slang scripting language in CIAO as well as
plans for CIAO 3. She noted that CIAO has a lot of capabilities,
which are not fully used by the users and that users have problems,
but are unable to identify directly the reason. CIAO 3, the so-called
Infrastructure Release, will help to solve these problems.
 The CUC members applaud the SDS group's effort to reach out to
the community to provide software that is useful for Chandra
analysis. Along these lines, the CUC suggests that the CXC poll
current Chandra PIs to learn about their software usage patterns.
Specifically questions like the following should be posed: (1) what
CIAO analysis tools do you use; (2) what non-CIAO tools do you use;
(3) are there Chandra specific tools that are missing; and (4) in
what directions would you like to see CIAO develop.
SDS: Analysis Using CTI-corrected Products (Antonella Fruscione):
Antonella reported on the official Chandra software for CTI correcting
ACIS-I data. The plan is to release all new ACIS-I FEFs for
CTI-corrected data and software in the fall 2002. The software update
will likely be a patch to CIAO2.2.2.
 This is an acceptable time frame.
SDS: CIAO Documentation Plans (Doug Burke):
Doug talked mainly about providing users with analysis threads. There
are now almost 100 threads accessible from the Chandra web site. Keep
up the good work.
SDS: Web_SAOSAC (Margarita Karovska):
Margarita presented information about ChaRT - Chandra Ray Tracer -
which is a Web interface to SAOsac.
 This is a very nice new feature and the CUC is very happy to
see it made available to the Chandra community. We would also like
to see more canned image models in the next release, as well as a
feature where a FITS image file could be used as the image model
SDS: ATOMDB (Randall Smith):
Randall described the ATOMDB which is an atomic database that includes
the Astrophysical Plasma Emission database (APED) and Astrophysical
Plasma Emission Code (APEC).
E&PO (Kathy Lestition):
Kathy reviewed the scope of the CXC Education and Public Outreach
effort from Jan to June 2002. Chandra is getting good coverage in the
national press. NASA headquarters wants to have more Chandra Space
Science Updates (SSUs) and the E&PO group is hiring additional staff to
support this, including a dedicated scientist, animator, image
processor, and graphic illustrator.
 E&PO is an important part of NASA's mission and we compliment
the CXC for expanding their effort in this direction. The committee
is particularly pleased that a full-time active research scientist
will be part of the team, since the scientific validity of press
releases is of the greatest importance.
Before adjourning, Harvey Tananbaum raised the following issue that he
wanted the CUC to consider.
 The committee reviewed a request from a user that the CXC offer
a special category for technical or instrumental proposals for
Chandra. There was no support for this suggestion among the
Harvey noted that deep surveys were a unique science for Chandra.
Considerable resources have been devoted to this already: 2 million
seconds of time in the Chandra deep field north and 1 million seconds
of time in the Chandra deep field south. However he expressed concerns
that future increases in time on these fields might be difficult to
obtain through the standard pool of time. He therefore suggested that
a new category of proposals, presumably for very large allocations of
time, be initiated for deep surveys. A group of people who do this
type of science would be assembled and tasked to decide upon an
optimal observing strategy and to put forth the best proposal
argument. A separate panel of non-deep-survey scientists would then
 The CUC carefully reviewed and discussed this suggestion.
First, the committee questions the fundamental premise behind this
suggestion, i.e., that deep surveys are unique science for Chandra.
Chandra has made lasting impact on a number of fields any one of
which could make a compelling argument for uniqueness. Furthermore,
the science of deep surveys may be at a turning point. Increasing
exposures are likely to result in comparatively few additional new
sources, so that the main goal of going deeper will be to
characterize source properties, measure spectra, and search for
unusual sources types. Whether this will result in "breakthrough"
or "incremental" science is not clear. Thus, the CUC does not
support this suggestion, as proposed only for deep surveys.
But when considered more broadly, the idea has quite a bit of merit.
It seems reasonable to surmise that a huge award (1 or 2 million
seconds) of Chandra time could lead to a fundamental breakthrough in
one or more subject areas across the entire field of X-ray
astronomy. On the other hand this potential needs to balanced
against Chandra's limitations, e.g., some observations may be
limited by fundamental uncertainties in spectral calibration rather
than random error from counting statistics. Nevertheless, the CUC
recommends that a focused workshop be convened on the science
breakthroughs that would be made possible over the next 5 years or
so by large million-second class awards of Chandra time. The CUC
would be willing to help with the scientific organization of such a