SXT REPORT FOR WEEK 15: 5 APRIL 1993 - 11 APRIL 1993

GENERAL STATUS

     SXT continued to work well this week. Most of the week was taken up
     planning and re-planning for support of the Shuttle SPARTAN payload
     and NIXT. Solar activity has steadily increased over the week, giving
     us two M flares and at least 38 C flares. SXT has taken over
     1,026,300 images to date.

     The weather remains ideal, warm and sunny so the cherry blossoms have
     lasted much longer than expected.

PERSONNEL

     Dave Pike is visiting ISAS for a few weeks. This is the last week
     here for Gary Linford and Keith Strong. Jim Lemen will be coming out
     to join the team next week.

SOLAR ACTIVITY

     The steady increase in solar background has not been accompanied by a
     corresponding increase in flare activity. A large active region
     complex, given 4 numbers by NOAA (AR7465, 7469, 7470, and 7472), has
     been responsible for most of this activity. In particular it has been
     prone to produce Long-Duration Events. In particular, there was a C7
     flare on 8 April 93 starting at about 0200 UT that lasted for at
     least 9 hours. It was followed by similar (but shorter) C2 and C9
     events within the next 24 hours. The first flare had characteristic
     cusped structure develop late in the flare.  The PFIs have remained
     on this region all week and show the region to be highly dynamic with
     many small-scale brightenings.

     The southern coronal hole is large and well developed stretching
     nearly to S40. There is a coronal hole channel originating from this
     coronal hole across the equator, but it is less well defined than at
     the last rotation. The northern polar coronal hole is poorly seen at
     the present time, due to the tilt of the Sun. The leading edge of a
     trans-equatorial coronal hole that stretched from the northern hole
     about S30 on the last rotation is just reappearing on the east limb.

SCIENCE PROGRESS

     Gary Linford put another week of full-disk images on the video disk
     this week that has helped tremendously in planning the SPARTAN and
     NIXT observations. However it showed up a feature that had not been
     seen in the KSC data. An X-ray bright point at about 50S flared and
     filled a loop that stretched for between 8-10 arcmin in less than 500
     s. This give a propagation velocity of nearly 800 km/s. The event
     occurred at 08:41 UT on 26 March 93.

     Marilyn Bruner has continued to work on the SPDE rocket data and its
     comparison to the SXT images. Keith Strong and Hugh Hudson have made
     some progress on the Hard/ soft X-ray comparison in flares.

     Professor Hirayama gave a seminar describing the scientific rationale
     behind Solar B at ISAS on Wednesday. He spent the whole day here
     discussing the topic with Barry Labonte, Marilyn Bruner, Hugh Hudson,
     and Keith Strong.

SXT OPERATIONS

     The week has been dominated by preparations for the NIXT rocket and
     planning for support of the SPARTAN mission. Nariaki Nitta
     volunteered to be SSOC toban to help ensure the success of these
     programmes. The KSC tobans, Hara-san and Takeda-san have also been of
     tremendous help during these intense operations. The tobans should
     get a special vote of thanks this week for all the hard work they
     have put in under difficult circumstances.

     On Monday we discovered that there was new contamination "blotches"
     on the CCD so we did a two-day CCD bakeout which seems to have gotten
     the worst of the problem. We may consider doing the bakeouts more
     frequently that originally planned to keep the CCD clean. Although
     the Sun was relatively quiet the we mained PFI pointing on the active
     centers throughout his period by using a new combination of filters
     and exposures for the patrol images.

     OGs were prepared under the supervision of Kosugi-san and
     Watanabe-san to automatically achieve S/C offpoints. We did a
     successful test of the planned off points and SXT tables for SPARTAN
     after the CCD warm-up was complete. Although the test was prematurely
     halted we did obtain a spectacular series of images of the
     large-scale coronal structure. This has increased our hope that data
     on the large scale structure of he Sun can be taken regularly
     throughout solar minimum despite the pin-hole in the thin aluminium
     filter. The images were taken in quarter resolution. Professor Uchida
     is hoping to use such data to see how far and how fast the coronal
     dynamic coronal loops that he discovered move out.

     Hugh Hudson has been acting as communications director keeping the
     SPARTAN and NIXT teams informed by phone, fax and email of what we
     are doing and providing feed back for the Yohkoh team. Marilyn Bruner
     and Keith Strong have been preparing and evaluating the SXT tables in
     consultation with other experienced SXT team members. The complex OP
     plans have been made (several times due to slips in launch schedules)
     by Shimizu-san. We also completed a pre-launch calibration run,
     however we will have to wait until the DSN data is in to see whether
     we have a complete set of dark-frame images.

     This has been a good example of how the whole Yohkoh team has worked
     very hard together with minimal communication problems; all we have
     to do now is hope the Sun cooperates and we should get some unique
     joint data with these two missions.


                                            Keith Strong, 11-April-1993