Status report from ISAS
28-Apr-92  1750 JST
L. Acton

Intense work continues here on three fronts.  (1) Yohkoh operations. 
(2) Preparation of papers for the ASJ meeting at Osaka next month.  (3)
Preparation of manuscripts for the "first papers".  In addition, I have
continued to struggle with analysis of the 15 November flare preparatory
to completion of the SCIENCE paper.  J-P.  Wuesler prepared a data cube
of my "favorite flare" with pointing jitter removed.  Careful analysis
of this sequence promises to be much more revealing than similar
analysis of the raw data for which analysis be image differencing was
limited.  Thanks, J-P.  It is clear that production software for
sub-pixel alignment of flare data should have a high priority.

Operations continue to be quite smooth.  N.  Nitta and K.  Strong worked
on joint observing with the VLA and this appears to have been quite
successful even though the solar activity was not what we had hoped. 
The sun has been quite quiet.  Even though we have re-entered the SEU
prone phase of the orbit we have only experienced 2 SEU related errors
and these were recovered quite smoothly.  Good work, Sam Freeland, on
the software and operational improvements to get this troublesome monkey
off our backs. 

We experienced two low-M flares that were exceptionally fast rising and
with very hard spectra.  The first one was not picked up by the SXT
flare patrol image because it was fainter than the detector dark spikes.
Thus we centered on an off-sun pixel and the only image of the flare we
have is the one burned into the CCD because of the resulting long
exposures!  After carefully analyzing this failure we doubled the
exposure on the flare patrol and caught the subsequent flare perfectly. 
Furthermore, the revised flare table, designed to keep up with the
telemetery and not lose exposures, seemed to work just fine.

I continue to rejoice at the amazing discoveries in the Yohkoh
observations and the SXT images.  This week we observed a clearly
defined expanding x-ray loop that appeared to bump into a higher
neighbor and at the point of intersection--BANG!!  A beautiful ball of
bright x-ray emission appeared.  Later the whole distorted set of loops
evolved into lovely organized arches.  You have to believe in magnetic
reconnection with energy release when a clear case like this appears!

At any given time around here, especially at night, there will be 9 or
10 people work on Yohkoh data analysis.  Increasingly useful software
continues to appear.  For example, Alan McAllister has written a code to
take a Big Bear H-alpha image, scale and align it to an SXT image, take
out the limb darkening and put the 2 on the workstation screen with
separate color tables for the 2 images.  The relationships between
global chromospheric and prominence structure and x-ray emission become
powerfully and immediately obvious.  This same software can be applied to
any full disk ground based images.

A MAJOR milestone was achieved last week with the completion of the
first SXT video for public release.  It takes an inordinate amount of
work to go from "almost good enough" to a product one is willing to give
to the TV networks.  Thanks to G.  Slater and J.  Lemen for fighting this
one through to completion.  I shudder to think of the "science" time
that has gone into this project. 

With a super team effort by M.  Morrison, G.  Linford and our Japanese
colleagues a large number of impediments to progress on the reformatting
effort have been removed and 4 or 5 weeks of data were shipped out this
week.  The impact of the reformatting and Exabyte tape making on
scientific analysis will be relieved somewhat when the new disks being
generously provided by NRL arrive and are put on line.  Yea, BCS, yea,
NRL, yea Doschek!!!

Optical and dark frame calibrations are now being done weekly.  We have
reviewed the full-well saturation level from the 15 November 1992 flare
discovered a discrepancy of about 6% as compared to pre-launch
calibrations.  It is possible that this is due to a gain shift in the
CCD camera so we are putting a high priority on getting a CCD gain
calibration this week.  The technique we had planned pre-launch is no
longer feasible because of the decrease in optical sensitivity.

The last couple of days I've been sweating over what I thought was a
shutter problem.  After exhaustive analysis and release of a memo
describing the effect, I discovered it was all attributable to the fact
that the shutter calibration data was not included in the analysis
software.  I've eaten my crow and breathed a sigh of relief.  One of the
marvels of SXT is Dave Akins' amazing rotating shutter.

Keith Strong has departed, Hugh Hudson has returned and Tom Metcalf has
arrived.  Tomorrow Gary Linford goes home for R&R and Mons does the same
next week.  Tomorrow is the big press conference uptown so I'll have to
break out the dress-up duds.