SXT Status Report
                February 23 through March 8, 1999
                           (Weeks 9-10)

                        H. Hudson, L. Acton


SUMMARY

Solar activity remained moderate during these two weeks.  There were no
technical difficulties with SXT, and we conducted some joint
observations with TRACE and SOHO.

SOLAR ACTIVITY

There were twenty or more C-class events, but only one M-class at the
time of writing (see nugget http://www.solar.isas.ac.jp/sxt_co/990305.html
for some commentary). The NS interconnecting loops that had been so
remarkable in the previous two weeks were behind the limb, and at the
time of writing of this report had not reappeared - will they?

OBSERVING CAMPAIGNS

SXT co-observed briefly with TRACE and SOHO in an attempt to find clean
loops, not confused with foreground/background features, for modeling
by Jim Klimchuk. We also tried to follow VLA targets, but were hampered
by poor communication. We need better mechanisms for sharing target
information in Max Millenium.  

SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES

There is no particular technical news from this epoch. The accumulation 
of terminator images for the stray-light database continues slowly.
Normal pointing was redefined on Feb. 26. Acton proposes that we move
the normal pointing further north, in order to spread out the pinhole
stray-light corrections more evenly. This won't be implemented until
it is discussed at the next operations meeting, which will be March 15.

An early look at a Wallops telemetry pass showed many image gaps. Because
we don't often see pre-final data from the NASA sites, we looked into this
in some detail, obtaining a re-transmission of two dumps. These showed the
same image gaps (data problems at the major-frame level), so the link
between Wallops and D-toh via Sirius was not the problem. We will keep
our eye out for similar problems in the future.

The scheduling of telemetry dumps to the Santiago station resumed. This
is an important one for Yohkoh because its location fits in well with
the weekly KSC holiday schedule, so that our sometimes huge gaps can 
be filled in.

On March 5, the A400 minicomputer at KSC again caused a problem, and
we could not see real-time data on that day. The problem was fixed
and the system is again functional.

SXT OBSERVING SEQUENCE TABLES

     -----------------------------------------------------------------
        JST Day   UT Time  Pass   Table ID
      =================================================================

        22-FEB-99          4      990221 P4 ARS1 TRA
        22-FEB-99          2      990222 P2 ARS1 DAR
        24-FEB-99          4      990223 P4 ARS2 LOO
        24-FEB-99          3      990224 P3 ARS1 DIF
        26-FEB-99          4      990225 P4 ARS1 STD

         1-MAR-99          4      990301 P4 ARS1 DAR (*)
         2-MAR-99          2      990302 P2 ARS1 DIF (*)
         3-MAR-99          2      990303 P2 ARS1 STD (*)
         4-MAR-99          2      990304 P2 ARS1 STD (*)
         5-MAR-99          2      990305 P2 ARS1 STD (*)

        =====================================================

SCIENCE

Science focus at ISAS returned to sigmoids, CMEs, flares, and the like.
Science nuggets were:

             5-Mar-99: A compact beginning for a coronal mass ejection? 
            26-Feb-99: A mild case of "Ron Moore's Elbows"
            19-Feb-99: Transequatorial loops, the movie 

The March 5 nugget has a quite nice image of twisted structure in hot
(Be) SXT images of an active region. The reference to Ron Moore's elbows,
with permission of their owner, deals with the expansion of the outer
lobes of the sigmoid structure during an eruptive flare.

The full list of nuggets is kept on
http://www.solar.isas.ac.jp/sxt_co/index.html, 
and the current week's nugget is also always known as 
http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html.

SEMINARS

Feb. 25, 1999:
  L.W. Acton (MSU) "Conversion of SXT fluxes to irradiances"
  L.W. Acton (MSU) "Analysis of SXT entrance filter failures"

...Acton tergiversates re the micrometeorite impact model...

March 4, 1999
  J. Sato (NRO) "Spatially resolved hard X-ray spectra"
  T. Naito (NAO) "Particle acceleration in a shock wave at the 
    impulsive phase of a solar flare"

YOHKOH OPERATIONS ISSUES

HXT continues in the "cal mode" of observation. In this mode HXT gets 64
energy channels at 8-sec binning, as opposed to 4 channels at 1/2-sec binning.
The effect on SXT is to eliminate the quiet-mode PFI's following a given flare,
for the duration of that orbit. The hoped-for great flares at the limb have
not yet occurred.

VISITORS AND PERSONNEL

L. Acton returned to Montana.

TOHBANS (spacecraft operators)

Tohbans for week 9

  SSOC : K. Akita, H. Imai
  KSC  : S. Kawashima, T. Yamasaki
  SXT_CO: H. Hudson
  SXT_SW:  

Tohbans for week 10

  SSOC : Ichimoto, Naito
  KSC  : Shiosawa, Yamasaki
  SXT_CO: H. Hudson
  SXT_SW: -