MINUTES
                     Einstein Users Committee Meeting
                          January 10. 1983
                    Board Room. Park Plaza Hotel

Attending were:   M. Elvis. CFA     L. Kaluzinksi. NASA
                   R. Harnden. CFA   F. Marshall. GSFC
                   D. Helfand. CAL   F. Seward, CFA
                   D. Harris. CFA    H. Tananbaum. CFA
                   J. Hutchings. GO  F. Walter. GO

I. NASA "Dear Colleague" Letter

A "Dear Colleague" letter announcing the continuing opportunity to  
participate in the Einstein Guest Observer Program and including  
instructions for the use of the Data Bank was mailed January 3.  
Instruction for preparation of proposals are about the same as before.

There is a difference. however. if no funding is requested. In this  
case it is necessary only for a potential Data Bank user to submit a  
Data Request listing the data desired. the purpose for which it will  
be used. and enough information to enable the evaluation of SAO time  
and facilities required. It is expected that such Data Requests will  
be automatically granted. unless they represent an unreasonably large  
burden on SAO resources. These large-burden proposals will be  
forwarded to NASA for prioritization.

Proposals requiring funding will be reviewed using a procedure  
dependent on the number of proposals received. If many proposals are  
received. a quarterly review will be conducted as before; if only a  
few, they will be sent out for peer review as received. Foreign  
requests will be reviewed if substantial effort is required to meet  
them. The review threshold for such proposals will be determined by  
SAO and NASA. dependent on the particular proposals and the number of  
Data Bank users at the time.

II. Status of Data Processing

A. HRI

The HRI reprocessing is finished. Briefly, the improvements  
incorporated in the reprocessed data are:

a.  new bore-sights and magnetic corrections have reduced source/ 
position error radii from - 10 seconds to - 3 seconds (90% confidence).

b.  Map mode has been used throughout the data set, increasing  
exposures by more than 25% for 60% of the observations.

c.  The use of a definitive satellite ephemeris has resulted in  
better high background rejection.  Regions when spacecraft was close  
to the edge of the South Atlantic anomaly or when the experiment was  
pointed close to the sunlit horizon have been identified and excluded  
from the data.

d. The parameters characterizing sources during the automatic data  
processing have been better derived.

e. The presentation of results has been revised to be clearer and  
more easily understood by those not familiar with the details of the  
instrument or processing.

Ninety percent of the data are in the Data Bank, with the rest  
scheduled for release between now and June 1, 1983. A list of these  
observations and the release schedule is available from F. Seward. A  
few observations (approximately 10) are listed as being not processed  
or having problems. Some of these problems are minor (short stretches  
of bad aspect) and will be cleared up quickly. In a few cases the  
problems are severe, and a great deal of time will be necessary to  
extract the data. Examples are: a) a planet in the field of view of  
the star sensors causing the pointing direction to drift to track the  
planet during the measurement; and b) an observation for which the  
pointing direction is at present unknown, difficult because an  
approximate pointing direction is necessary to derive aspect from the  
map mode data.

Some of the processed data (5 to 10%) also have problems which the  
user should be aware of. These are:

a. Some guide stars are "contaminated." If stars are double or  
surrounded with bright nebulosity, the tracker became confused about  
the position of the guide star and locked on two or more different  
positions separated by perhaps 10 arc-seconds.

b. The aspect solution in map mode is not as good as that with the  
trackers locked on guide stars.

c. The gaps in some images have not been removed properly.  
Occasionally a bright source will appear bisected by a line of low  
counting rate. This is distortion caused by an imperfect gap map  
solution.

CFA will write a brief description of these difficulties, explaining  
how the computer output for the reprocessed data indicates the  
presence of remaining problems.

B.  IPC

The software for processing IPC data has been completely rewritten,  
incorporating several basic procedural changes and an improved  
presentation of the output. This has just been accomplished, and CFA  
has been reprocessing IPC data with the new system for a few days.  
Data will be reprocessed in chronological order because of the  
necessity of using calibration data to obtain instrument gain. It is  
anticipated that data will be processed in approximately real time,  
although there is not yet enough experience to accurately estimate  
this rate. Because it is necessary to look at calibration data  
obtained between observations, data must be processed MOP by MOP. It  
is easiest to process MOPs in chronological order; however, a small  
fraction can be done out of this order. Requests for processing data  
out of order will be honored providing not more than 10% of the data  
falls in this high priority category.

The IPC reprocessing incorporates improved data screening. Slew data  
are now used to get instrument calibrations, and an improved  
ephemeris and calculation of background rate are used to eliminate  
regions of high-particle background and bad viewing geometry. Gain  
changes (high voltage changes) are determined and taken into account  
in the calibration. and the instrument on time is determined  
accurately by eliminating correctly periods when, the high voltage is  
off and the telemetry dropouts.

Source detection algorithms have been greatly improved. Data are  
divided into three fixed energy bands. (The calibration is used to  
convert pulse height into energy, giving a consistent output for data  
taken with different instrument gains.) The search for sources is  
conducted using a local determination of the background rather than  
the global background determination used previously. This results in  
a great improvement in the detection of weak point sources in fields  
with diffuse emission or outside the counter ribs. The software  
produces an estimated flux from detected sources in the different  
energy bands.

Spectral fits are generated for strong on-axis sources. The  
microscopic detector calibration in the central 4 minutes is  
incorporated in these fits. A hardness ratio is listed for all  
sources detected in the field.

The variability analysis has been incorporated into the program in a  
more understandable way.

A sample of the computer output generated by the new IPC reprocessing  
was distributed to the Committee and slides were shown illustrating  
results obtained with the old and new IPC processing. A great  
improvement in the image was seen when high-background times were  
eliminated. The detection of weak sources within diffuse emission or  
in a crowded field was also seen to be much improved.

As the IPC data are reprocessed, CFA plans to have the computer  
generate a list of reprocessed sequence numbers ordered by observers.  
These lists will be mailed approximately once a month to the "owners"  
of these data and will serve both as a notification that reprocessed  
data are available for inspection and that these data will be  
incorporated into the Data Bank in six months. The Committee felt  
that a monthly time scale was appropriate.

Thanks were given to Rick Harnden, who was responsible for the  
development and implementation of the new IPC software, and to CAL  
for providing services of a programmer at a critical time.

These data, as before, are considered to be in the Data Bank now and  
available for guest observers. Both GSFC and MIT stated that, since  
they did not get funding to support Data Bank users, any use of these  
data requiring their time and effort should be a collaboration  
between the host institution and the guest. Since the procedure for  
extracting useful spectral information from these data require the  
participation of someone familiar with the instrument and its  
peculiarities, a collaboration is probably not unreasonable.

III.

Status of Data Bank

Eight requests have been received for Einstein data. The short  
requests have been honored. One long request from the Soviet Union  
was deferred and the proposers asked to be more specific. NASA stated  
that they would like foreign requests to go through the appropriate  
NASA office. CFA and NASA will forward copies of requests received to  
one another, so each will keep a complete set of records of Data Bank  
users.

CFA will try to keep potential users informed of other plans to use  
the particular data requested. Hopefully, Data Bank users will  
contact the original data owners to learn of work that has already  
been done or in progress and to learn of any particular problems that  
might be encountered. The consortium organizations expressed a desire  
to know who was using their data and for what purpose. It was  
suggested that a newsletter should be distributed periodically,  
listing new users of the Data Bank and their projects.

CFA plans this month to distribute an up-to-date list of all HRI data  
and its Data Bank status (whether it is in the Data Bank or not, and  
if not, the date when it will be available). This will be sent to all  
on the Einstein observer mailing list. After the IPC reprocessing has  
run long enough to determine the rate at which observations can be  
processed, CFA will distribute a list of all IPC observations and an  
estimated schedule for release for general use.

A questionnaire was mailed to all Einstein observers, requesting  
identification of IPC data which: (a) could be released immediately  
upon reprocessing; or (b) for which high priority processing was  
desired. Seventy-eight sequence numbers were okayed for early  
release, and it was requested that 66 sequence numbers be reprocessed  
early. A high priority
reprocessing schedule has not been made yet but will be generated  
after the initial shakedown period for the IPC reprocessing.

IV. Reprocessing and Release of MPC Data

The MPC data and analysis system is now capable of giving accurate  
timing information for any source and accurate spectral information  
for only strong sources. If a source is weaker than 0.3 UFU. the  
background determination is not good enough to enable the derivation  
of accurate spectral information or source intensity. The MPC  
processing uses a background which is a function of position over the  
Earth's surface. The map presently available does not incorporate  
time variability. which is important for weaker sources.

CFA plans to reprocess MPC data, hopefully starting in February. It  
is necessary to reprocess data in chronological order to generate a  
good background map. This processing will be done on the M600  
computer at night, and. as a very rough guess. it will take  
approximately one year to reprocess all the data.

CFA proposed releasing MPC data to the Data Bank on the following  
schedule:

a. All the reprocessed data would be released six months after  
reprocessing, resulting in a flow of MPC data to the Data Bank  
starting in approximately Fall 1983 and finishing approximately Fall  
1984.

b. If anyone requesting imaging data from the Data Bank wishes  
accompanying non-reprocessed MPC data, this will be given to them  
with a warning concerning the technical limitations.

c. Any proposals to use MPC data as such and involving a large  
quantity of data. would be restricted to use only reprocessed data  
that was in the Bank.

CFA also noted that requests for MPC data were more time consuming  
than requests for IPC or HRI data. since any use of MPC information  
requires computer processing to extract this information. The  
preprocessing of MPC data on the computer has not been accomplished  
for all observations as has been done for the imaging instruments.

The Committee was not in agreement about this proposed policy.  
Proposals concerning the use of MPC data accompanying SSS or FPCS  
observations were not provided for. CFA stated that these were  
categories they had not considered and wanted to discuss the  
situation in more detail with the present "owners" of the MPC data  
before recommending a policy.

V. Other Business

At the request of Phil Charles the possibility of including reduced  
and wavelength calibrated data from spectrometers (SSS, OGS and FPCS)  
in the Data Bank was discussed. The Committee agreed that this  
information would be useful but the resources necessary for the  
additional data processing necessary were not available at this stage.

A memo from R. Harnden was distributed describing the absolute  
accuracy of Einstein timing measurements. The ephemeris used to  
generate corrections to timing data caused by Earth and satellite  
motion was found to be in error when processing data for two Einstein- 
discovered pulsars. These errors produced a false phase shift of the  
pulsar wave train. These ephemeris errors have been corrected and the  
entire Einstein Data Bank has been searched for corresponding errors  
and is now free of them.

The next Users Committee meeting will be in approximately six months,  
the exact date to be arranged.