MINUTES
Einstein Observatory Users' Committee Meeting
August 10, 1981
I. Statistics Concerning Observatory Usage Averaged Over Entire Mission
A. Division of Observing Time Among User Groups
CFA 34%
GO 25% (largest GO group 2.7%)
MIT 15%
GSFC 13%
CAL 12%
B. Division of Observing Time Between Instruments
IPC 50% 13.6 months
HRI 26% 6.9 "
OGS 2% 0.6 "
SSS 12% 3.1 "
FPCS 10% 2.7 "
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27.0 months
Since data processing proceeds at approximately the same rate as data
acquisition, the second column in the above table is an estimate of
the time required to process all data from a given instrument.
The attached figure shows final results concerning proposals reviewed
and accepted, fraction of observing time used by Guest Observers, and
number of Guest Observers each month using CFA computer facilities to
analyze data.
II. Status of Data Processing
All Einstein data have been processed once with the following
exceptions:
1. There is a I-week gap caused by a missing ephemeris tape.
2. The GSFC North Ecliptic Pole Survey data have not been processed
because at this time the Observatory was operating in a special mode.
This survey consists of 2 days of short observations, and processing
is awaiting manual entry of DOPs.
3. About one week's FPCS data have not been processed.
4. An exact aspect solution is needed for the SSS observations.
These aspect solutions will require about one month full time
computer use to generate. If this work is done only at night, about
four months are necessary to complete the project.
As a matter of interest, 31 months were required to process 27 months of
Observatory data. On the average, data processing has proceeded at a
rate ~15% slower than data acquisition.
III. Plans for Reprocessing Data
A. Benefits from Reprocessing
The format of the computer-generated results from all detectors will
be revised so that results will be more easily understood by people
not familiar with the system.
The timing files will be revised to incorporate barycenter
corrections. These new files will replace the timing bit maps
currently used.
1. HRI
Reprocessing will result in improved accuracy of source locations in
most HRI data. Star tracker signals can now be corrected for
distortion caused by the Earth's magnetic field. This has produced
smearing and occasional double images in the past with, at worst,
errors of 10 arcsec. Magnetic field corrections have been worked out
and have been used in processing HRI data since April 1980. The
calibration of star tracker C has been incorporated in the
processing. Fiducial light data will also be automatically included.
This has not been done before and will correct for mechanical motions
of the HRI/telescope/star trackers which can produce errors of 1-2
arcsec. The sky catalog will be replaced with the SAO catalog when
used as a reference for the star trackers. The sky catalog has been
found to have round-off errors up to 1 arcsec in some stars. The net
effect of all these improvements will be to improve the absolute
accuracy of source locations to ~2 arcsec.
2. IPC
Distortion in the IPC field has been calibrated and corrections
incorporated in the processing system since February 1981. Sources
close to the axis can be located with an accuracy of ~20 arcsec. In
the reprocessing, this distortion correction will be applied to all
data. Some processed data now has high backgrounds because the sunlit
Earth (a strong diffuse X-ray source) has been included in the
images. An improved algorithm for Earth blocking will be used to
remove times when the telescope is looking at the Earth from the
images. Spectral data will be derived for strong sources on-axis.
Stable aspect intervals will be identified, the gain calculated, and
results presented in fixed energy bands, not as pulse height.
Temporal changes in gain will be handled automatically and pulse
height information will be fit with spectral models in a more
accurate fashion than now. An improved background algorithm will be
used in the source detection routine with consequent improvement in
the automatic detection of weak sources close to the edge of the
field, and elimination of false sources in the center of the field.
Desirable improvements to be incorporated as time permits are
inclusion of diffuse gain map and automatic derivation of the spectra
of diffuse X-ray sources.
3. MPC
All MPC data will be reprocessed and background information recorded
to get a more accurate determination of background as a function of
time. This will result in useful MPC information from weak sources
that have not yet been reliably detected. The background of the MPC
is time dependent with contrbutions from charged particles and a
calibration source which decays with time.
B. Schedule for Reprocessing
The HRI software is almost ready. We anticipate reprocessing can
start approximately October 1 and that it will take ~7-8 months to
reprocess all HRI/OGS data. This HRI reprocessing will be done first
because the IPC software will take at least another six months to
develop. We anticipate starting IPC reprocessing in the spring of
1982. The MPC reprocessing will be started when software is ready,
probably sometime during the HRI reprocessing. Reprocessing of SSS or
FPCS data is not anticipated except for work done at GSFC or MIT.
C. Order of Reprocessing Data for Given Detector
1. Scientifically, it is desirable to reprocess the data ordered
target by target, thus all data for a given object or a given program
could be processed at about the same time. It would be necessary to
generate a detailed schedule. Time would be divided among the
different organizations, as was the observing time. Each organization
would set priorities for their own targets. The disadvantages of this
are: 1) considerable effort is required to generate a schedule and
priorities; 2) bookkeeping is difficult; 3) it would take ~20% longer
to process data because of inefficiencies in the interface between
data aides and the computer system; 4) magnetic tapes could be
handled as much as six times rather than once. We are concerned
because some data tapes have apparently deteriorated after being read
by our tape recorders. Excessive tape handling will increase the
probability of losing original data tapes.
2. The most efficient way of reprocessing data is to order
chronologically, and process MOP by MOP. A variation on this is to
retain the MOP by MOP processing but to order the MOPS by section of
the sky or according to right ascension so that all data from a given
region are reprocessed at about the same time. Or, some MOPs
containing high priority sources could be removed from strict
chronological order and processed first. Because of the fiducial
lights, the HRI data must be reprocessed MOP by MOP. The MPC data
must be reprocessed chronologically to generate the background map
necessary for the analysis of weak sources. The IPC also has a
calibration source activated once or twice a day and either must be
processed MOP by MOP or all calibration data must be extracted first
before proceeding with the rest of the IPC analysis.
3. Reprocessing could proceed using a combination of MOP by MOP and
target by target processing. Most data would be handled MOP by MOP
with a fraction of priority targets done first or upon request.
The Committee could come to no decision regarding the best order of
data reprocessing. After discussion, a vote was taken and first
choice of the various committee members was evenly distributed among
the various processing schemes.
The Committee did agree that the HRI data should be reprocessed MOP
by MOP since this order is necessary for the fiducial light
calibrations. Requests for rapid processing of HRI data will be
solicited and data will be handled chronologically or by right
ascension except for a small fraction of priority requests.
CFA \ViII generate a schedule for HPC reprocessing when more details
are known about the software status.
IV. Data Bank
Over 400 Guests have participated in the Einstein observations with
consequent great enrichment of science results. The Committee
stressed the importance of making Einstein data available to all
members of the astronomical community in a useful way. All Einstein
data will eventually go into a Data Bank, which, while it is being
set up, will be a library comprising all reprocessed Einstein data
which has no "owner". CFA will support Data Bank users with computer
time and staff assistance in the same manner that Guest Observers are
now supported.
A. Reservation of Data Rights
All Einstein data now have an "owner". After reprocessing, these data
will be reserved for exclusive use of the owner if he so desires for
a certain time interval. traveling The Committee discussed at length
the appropriate duration of the interval. NASA emphasized their
desire to release data rapidly. Even with a zero length interval it
will be five years from initial acquisition until some Einstein data
are reprocessed and in the bank. At the other extreme, an interval of
one year was suggested as appropriate for observers with programs
involving many objects. If processing is done chronologically, the
first objects will be released before the observer has seen
reprocessed data from the last. Thus, if one waits for all the data
to do the final analysis and publish the results, one runs the risk
of having Data Bank users publish results from the first objects to
be reprocessed. Target by target processing would eliminate this
concern. The problem is most acute for Guest Observers traveling long
distances to use the Einstein computer facilities and the Guest
Observer representatives argued for a time interval of six to twelve
months.
It was decided that a time delay of six months was appropriate for
the HRI. No decision was made about the IPC because the question of
order of processing was not decided. CFA will generate a plan for
reprocessing IPC data, taking into account the comments of the Users'
Committee.
Much of the data have already been published and, in some cases,
reprocessing will yield no interesting new results. Fred Seward will
mail an appropriate questionnaire to all users so that data can be
identified which can be released with zero time delay. As soon as
reprocessed, these data will go into the Data Bank. We will try to
put as much data in the Bank as soon as possible.
B. Use of Data Bank
The Data Bank should be as open as possible and use of data should be
essentially unrestricted. Rules developed here are for the purpose of
enabling users to obtain funding, to avoid unnecessary burdens on the
support staff, and to avoid unknowing duplication of effort.
1. The fact that a given observation has been placed in the Bank
will not restrict use of this observation by the original owner in
any way.
2. Potential users (new Guest Observers) will apply to use the
Bank by proposal, which will be evaluated by a NASA committee much as
Guest Observer requests were handled. This way, the users can apply
for funding to support travel and other expenses and the support
people at CPA will be protected against unreasonable requests.
3. Use of the Data Bank by the current Einstein observers is not
as clear. The observers felt it would be unreasonable to be required
to write the same proposals as new users, but agreed that completely
unrestricted Data Bank use was undesirable. It was pointed out that,
the original owner of data is free to use it as he wishes and can
give it to colleagues with no restrictions. Thus, requests through
the original owner would be one workable way of disseminating data
from the Bank.
The Consortium institutions agreed to allow unrestricted use of
Consortium data by each other after the agreed upon waiting period
and that the original owner would be informed of plans to use the
Bank. On the other hand, Consortium use of Guest Observer data would
be passed through the NASA review committee.
4. Records will be kept of Data Bank users so that potential users
will be aware of ongoing projects.
C. Communication to Potential Data Bank Users
A list of Einstein targets, a revised Yellow Book, has already been
sent to Einstein Observers. As soon as the order of reprocessing has
been decided upon, a schedule will be made generally available so
that potential users
will know when a given observation is expected to be available in the
Bank. An Announcement of Opportunity concerning the Einstein Data
Bank is being generated by NASA, and the earliest distributing date
is December 1981.
v. Other Business
The next Users Committee meeting will be scheduled approximately
April 1982, close to the Washington APS meeting. As usual, the
meeting will be constrained by travel requirements of the Guest
Observer representatives.
Attendees:
C. Canizares, P. Charles, M. Elvis, G.Fabbiano,
R. Harnden, D. Harris, D. Helfand, S. Holt,
J. Hutchings, L. Kaluzienski, F. Marshall,
J. Schwarz, F. Seward, H. Tananbaum