SXT Status Report
                          11 - 31 August 1997
                            (Weeks 33 - 35)
                          N. Nitta, H. Hudson 


SUMMARY

Several new active regions appeared, but one of them was more flare active
than the others.  In AR 8076, we observed an M1.4 flare, which showed 
a short-lived (15 s) spike in the hard X-ray (~30 keV) light curves.  
SXT continued to be in fine working order.

SOLAR ACTIVITY

The GOES background level started at B2, going down to A2, and it is
now back at  B2-3 again.  Such a modulation is due essentially to bright 
regions rotating on to the east limb and disappearing from the west 
limb.  Some regions do grow or decay considerably during their disk
passages.  Active region NOAA 8076, which produced an M class flare
on 29 August at 23:30 UT, appeared to grow systematically, as reported 
by Bearalerts.  There was a beautiful eruptive event on the sourtheast
limb on 28 August, but the parent region was modest in brightness.  The
special flare sequence for eruptive flares worked well for the M 1.4
flare.


SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES

SXT continues to operate well.  We will avoid taking long-exposure images
as the activity level increases.

An ongoing calibration effort is to improve straylight corrections
especially for thin Al images.  With careful examination of the terminator
(sunset) images that are used for these corrections, we feel that the
straylight pattern may be more sensitive to pointing than expected
before.  We have also reviewed the pointing information, and found that
the one from the temporary reformatted database (on which the criterion
for the terminator image is based) agrees quite well with the one from
the permanent database, but for safety it may be a good idea to regenerate
the terminator database at the time of permanent reformatting.


PASS CONFLICTS AT KSC

Week 33:  2 passes were cancelled (both HALCA)
Week 34:  No passes were cancelled 
Week 35:  No passes were cancelled 

CAMPAIGNS

During 23-30 August, we participated in a campaign between SoHO/CDS
and NAOJ/Norikura to measure the nonthermal velocity along coronal 
loops.  The coordinated observations took place during passes 4-5.
Three regions were selected as the target, including AR 8076
when it was still near the east limb.  Fixed pointing was used. 
Requested by H. Hara (NAOJ), we used AlMg and thick Al filters, but
the regions other than AR 8076 were not bright enough to produce
significant signals in the latter filter.  Outside the campaign
periods, PFIs were taken in four filters for a better determination
of the plasma parameters.

For Yohkoh target planning, the SXT weekly observing plan is available
on the Web at
        http://www.space.lockheed.com/SXT/html2/First_Light.html
or with
        "finger campaign@isass0.solar.isas.ac.jp | more"        .

See http://sohowww.nascom.nasa.gov/operations/targets/today
for SoHO target planning.


VISITORS AND PERSONNEL

Hudson made a visit to the US, mainly to attend the STEREO meeting.
Lee McDonald (graduate student at MSSL) went back to England.
Following the solar sessions at the Kyoto IAU General Assembly, Yihua
Yan (Wuerzburg/Beijing) visited here for two days to transport his code
for magnetic field extrapolation (using the boundary element method) to
the workstations at ISAS.


SEMINARS

14 August 

M. R. Kundu (U. Md.):  "Radio observations of coronal X-ray jets"
N. Nitta (LMSAL):  "Some observational aspects of the loop-top flare
 kernels"

The former emphasized the importance of spatially resolved observations
to identify radio counterparts to X-ray jets.  It also touched on an
ongoing project to study polar regions in different wavelengths.  The
latter briefly reviewed the recent paper by Jakimiec et al., and
discussed the difficulty of interpreting the SXT, BCS and HXT measurements 
in a consistent way.


OTHER SCIENCE TOPICS

On 11 August, Hudson and Nitta went to NAOJ to attend a seminar by Jun Sato
immediately preceding the PhD defense.  The thesis title was "Improvement of
Yohkoh Hard X-ray Imaging and Analysis of Long Duration Solar Flares."   
Because of his major contributions of improving the HXT modulation pattern
and correcting for the DC offset, the images produced in the MEM algorithm
are now much better, and many in-depth analyses of flares are to be
expected with these images.  Nitta reanalyzed all the 36 flares listed in 
Jakimiec's controversial paper and found in several flares that the HXT L
band source (presumably representing "superhot" emission) are clearly not 
cospatial with the soft X-ray kernel.  Hudson continued to be excited by
the remarkable filament channel of June and July and its amazing contents.
For those not familiar with this, SXT sees a hot (or at least dense, at
coronal temperatures) region that appears to run down the core of the
hypothesized flux rope defining the cavity. In some ways this very stable
quiescent structure looks a great deal like the 21 Feb. 1992 "candle flame"
flare event.



TOHBANS

Tohbans for Week 33:

    SSOC :  Akita, Kozuka
    KSC  :  Saita, Nagata
    SXT_CO: Hudson/Nitta
    SXT_SW: -

Tohbans for Week 34:

    SSOC :  Shin, Nitta
    KSC  :  Nagata, Masuda
    SXT_CO: Nitta
    SXT_SW: -

Tohbans for Week 35:

    SSOC :  Khan, Kano
    KSC  :  Masuda, Ogura
    SXT_CO: Nitta
    SXT_SW: -