REPORT FROM ISAS  5-April-92

SXT Status Report for week ending 4 April 1992
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OPERATIONS
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Operations went quite smoothly this week.  Hudson and Takahashi were
SSOC duty scientists (tobans), Hara was toban at KSC and Ishido and Kato
were SXT tobans at ISAS.  Acton was SXT sequence table preparer.  This
sounds like a lot of people but, in fact, it takes about 4 people to
safely prepare, check, upload tables and monitor telemetry contacts. 
Finally, someone must check the downlink data in detail to make certain
that everything went well.  On a week like this one when there were no
SEUs or other crises it is manageable, even when the station contacts
are in the middle of the night, because of the willing and cooperative
attitude of team members.

Sequence tables have now been prepared and run for regular calibration
of the aspect sensor, CCD gain and CCD dark images.  Evaluation of the
results (except for CCD gain which must await DSN data and the return of
Mons Morrison) provided no surprises.  The optical diffuser image now
shows a limb x-ray ghost of 25% maximum.  No trace of this is detectable
in CCD dark current nor in x-ray response.  The CCD dark frame continues
to acquire dark spikes (single pixels of enhance dark current) at a rate
of about 100 per month.  I haven't done the statistics properly but
perhaps 10 of these are big ones.  With 1,048,576 pixels to work with
this does not represent a problem.  

Sam Freeland investigated why we were losing some image frames in flare
mode and discovered that the guard band of the optical image was too
wide to permit 2 sec cadence.  An experiment was done to establish
exposure parameters to permit narrowing the guard band enough to
maintain flare cadence--but we've had no flares!  Next week I hope to
conduct the CCD warm-up experiment to see if this makes any change in
the optical response of the instrument.  When the thermo-electric cooler
was switched off in January as part of an SEU recovery action we found
that some kind of condensation disappeared from the CCD and the optical
image improved.  We wish to do this again in a more controlled way.

SCIENCE PROGRESS
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A meeting was held this week to plan for the "initial results" papers to
be published in PASJ.  It is gratifying to see the excellent results
that will soon be forthcoming.  Over 20 papers are planned involving
primarily SXT data.  These papers will appear in October if all goes as
planned.  Following the submission of these papers the publication of
Yohkoh results will be free to follow the standard practices.   A goodly
number of papers are in preparation for the ASS meeting in Columbus, OH,
which will take place in June.  Greg Slater and Jim Lemen are hard at
work at Lockheed on preparation of the first SXT movie destined for
public release as a "show film".  This movie will comprise 2 or 3 weeks
in November 1991.

Our efforts to follow a single active region produced good results. 
This is not a completely trivial activity and it complicates the job of
the sequence table preparer somewhat.  On 29 March we captured an
amazing "jet into a loop" event that was very cleanly observed.  The
time sequence begins with a tiny flare at one end of a 2 arcmin long
thin loop.  A bright x-ray front is seen to move from the flare site up
and over the top of the loop at a velocity af about 500+ km/sec.  When
the front reaches the far side that leg of the loop rapidly brightens
from the bottom.  The sequence ends with the top of the loop expanding
and the whole thing gradually fading.  A truly remarkable sequence. 
This is not the only example of such behavior in our data set but
this one is beautifully observed at full resolution. 

Nariaki Nitta is leading the effort to coordinate with the MAX '91
campaign involving use of the Very Large Array radio telescope.  Several
changes of target were carried out based on a multiplicity of inputs
including near real time SXT images.  For a first attempt this has
worked out quite well.  The sun, however, has not rewarded the campaign
with very much activity.

PERSONNEL
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Nitta, Strong, Linford, Hudson and Acton are the SXT-U cadre at ISAS at
the present time.  We have had the pleasure of "Ohanami" or cherry
blossom viewing.  This is something that must be seen to be believed. 
At this moment the back grounds of the National Astronomical Observatory
at Mitaka is one of the lovliest places on the face of planet earth. 

			Loren Acton
			5 April 1992