SXT REPORT FOR WEEK 22;  23 MAY 1993 TO 29 MAY 1993

GENERAL STATUS

     Sxt continued to work well this week.  Highlights of the week's 
operations included a N-S off-point to check scattered light, a test 
of a sequence for making high time resolution de-saturated movies at 
the East limb, and CCD dark current calibrations observations.  
Results of last week's campaign have been reviewed, and discussions 
are underway for another campaign late in June, emphasizing high 
time-resolution observations.

PERSONNEL

     M. Bruner, H. Hudson are the U.S. SXT team scientists in 
residence, and M. Morrison is providing software support.  B. Labonte 
from the Univ. of Hawaii will be in residence for another month.     

SOLAR ACTIVITY

     A Bear Alert received late on Monday led us to try a 2 ROI 
program to observe both the E limb and an EFR described in the alert.  
The sequence was modestly successful, but the EFR did not produce the 
expected flare and filament activation.  Region 7514/15 appeared on 
the East limb early in the week and provided most of the flare 
activity.  Two M flares and over forty C class events were observed 
during the week.  The average GOES level was around B 5.

SCIENCE PROGRESS

     Labonte is making good progress in studying the temperature 
distribution in the loop system seen above the flare of 1992, 25 June.  
He has made a systematic comparison of the temperatures determined 
from the thick to thin aluminum ratio with that from the Be to thick 
aluminum ratio, finding a bi-modal distribtuion in the correlation 
plot.  The structure of the loop system is clearly visible in the 
temperature maps, and there is a high temperature region above the 
loop tops (where the emission measure is low) that appears to be 
statistically significant.  At intermediate altitudes, the temperature 
appears to be highest on the axes of the loops and to drop with 
distance from the axes, in accordance with Bruner's shell model 
concept.

SXT OPERATIONS

     On the evening on 22 May, the spacecraft pointing was altered to 
the south to place the north limb of the sun tangent to the top edge 
of the CCD.  The intent of the maneuver was to see whether the amount 
of stray light leaking through the pinhole in the thin aluminum filter 
could be significantly reduced, as it was during the E-W offpoints 
performed during the SPARTAN flight.  A modest reduction of about 30 % 
was observed; disappointing, but not too surprising.  

     On Tuesday, 25 May, a dual ROI sequence running under ARS2 was 
designed to alternate between observing the bright E limb region and 
the location of a considerably fainter EFR.  The sequence was 
moderately successful; it made a burst of two pairs of exposures in 
each ROI, completing a full sequence every 64 seconds.  In retrospect, 
it would have been preferable to interleave the exposures for the 
first ROI with those of the second to give a more even cadence.  
Interleaving would permit a cadence of 32 seconds for 2 x 1 ROI's.  
This type of sequence should be used with considerable caution if 
intense flaring activity is expected, since the AEC functions 
independently for each ROI.  The danger is that the fainter region 
will call for long exposures that could damage the CCD in the location 
covering the brighter region.

     Wednesday's operations included a CCD dark current calibration 
sequence, and a test of a sequence to observe coronal loop expansion 
and wave activity above the limb.  The strategy was to use a range of 
fixed exposures spanning a larger intensity range than is possible 
under AEC, which favors only the bright central portion.  The data set 
can be used to create a desaturated movie of a limited region with 
high time resolution.  This test was successful, and a good data set 
was obtained, including the development of a C flare.  There was a 
brief concern about over-exposure of the CCD, as an artifact was noted 
in the dark frames taken immediately following the flare.  However, it 
quickly annealed out and faded within less than 48 hours.  It would 
probably not have been discovered except for the CCD calibration that 
was in progress.  A second CCD calibration, run on Thursday, verified 
that the artifact was gone.  

     Normal ARS1 observations were resumed Friday, to run for the 
remainder of the weekend.  H. Hudson will assume the Chief Observer 
duties next week.  Operations for next week include high time 
resolution sequences under ARS1, and the proposed beginning of routine 
weekly E-W offpoint observations.  Comments on the latter are 
requested from SXT team members, and should be directed to Hudson.  
Hudson has prepared a proposal discussing the weekly offpoint program; 
copies are available by request via E-mail.


                                        Marilyn Bruner
                                        SXT Chief Observer