SXT REPORT FOR WEEK 25; 13 JUNE 1993 TO 19 JUNE 1993 GENERAL STATUS Sxt continued to work well this week. With the exception of some minor problems, the operations could be described as routine. The sun has become very, very quiet, with the background level remaining below B-1 for most of the week. The largest flares were around the GOES B5 level in soft X-rays. An attempt to test the high time-resolution sequence for possible use on bright points did not yield the desired observations because a "feature" of the table uploading software failed to upload the desired pointing coordinates. The table ran correctly, but observed an active region instead of the bright point target region. The weekly dark current measuring sequence worked well, and produced an excellent set of dark frame images. This weeks attempt to observe the far corona and obtain scattered light measurements at spacecraft sunset succeeded with the aid of an improved SXT table and an OP procedure worked out by Hudson and the SSOC Tobans. There were some problems with missing data in the Sirius database, which prevented the updating of the SXT observing table database. Also, there was no data at all entered into the Sirius database from Saturday's passes. The SSOC Toban reported that the person who normally is responsible for transferring the data was on holiday. We received no prior notification of this condition. PERSONNEL H. Hudson departed on Wednesday to attend a meeting on solar irradiance variability, Boulder, Colo. He will present a paper on the radiometric analysis of the SXT data. Labonte served as SSOC Tohban this week. Bruner spend Friday in a visit to the Nobeyama Radio Observatory, and presented an informal seminar on early results from the high time-resolution studies. S. Enome and colleagues had hoped that they had co-temporal observations, but it turned out that there was no overlap on this occasion. Plans were made for future observing, and the first SXT sequences for this were run on Saturday morning. An LDE M flare observed by both Nobeyama and Owens Valley Radio Observatory on June 3,4 was identified as an event for which SXT data would be very helpful. Bruner found that this event was well observed by Yohkoh and that the SXT data are of excellent quality. SOLAR ACTIVITY Following the West limb passage of AR 7518, the sun became very quiet, the brightest region being AR 7522 during the first part of the week. The general corona was quite dark in X-rays, and many X-ray bright points were visible. New regions appeared on the East limb toward the end of the week, and the corona above the East limb suggested that the activity level may increase next week. This would be consistent with the expected return of several active regions observed during the previous rotation. The current state of the sun seems to be bi-modal; one hemisphere is very quiet and the other moderately active. SCIENCE PROGRESS The comparison of the SXT and C IV images continued this week, with the analysis moving to the comparison of the SXT full resolution PFI's with the full resolution C IV image. The comparisons were carried out with the aid of selection software completed by Morrison, and with the aid of a blink comparison program prepared earlier by Kashyap and Bruner. The data covered the active region that was the prime target of the campaign, and also a nearby emerging flux region (EFR). As with the full frame images, we find that most of the X-ray loops have bright C IV emission at their footpoints. The EFR was fairly active at the time of the rocket flight, and a considerable amount of evolution of the overlying X-ray structure was seen during the orbit covering the launch. In addition to the bright footpoints seen elsewhere in the C IV image, very thin loops could be seen that were more or less parallel to the X-ray arcade, but were not coincident with any of the X-ray loops. The most prominent C IV loop was at the East edge of the X-ray arcade. A second seemed to lie between two of the X-ray loops. The blink comparator analysis also revealed a loop in the active region that was common to both C IV and X-ray images over part of its length. The C IV image extended further in one direction, and the X-ray portion of the loop extended further in the other, suggesting the presence of an axial temperature gradient. Extended analysis of these structures should prove to be quite interesting. OPERATIONS The major effort of the week was the testing of an improved sequence for coronal-offpoint observations. The use of pre-programmed procedures for controlling the spacecraft pointing were successfully tested last week. This week's operation was based on a new version of the SXT FFI table, which contained the for the exposures for occultation part of the sequence at the beginning of the table. The exposures emphasizing the coronal observations followed. A command sequence in the DP executed the "control-manual" and "control-auto" functions at a time predicted to start the table at its beginning just before the expected time of the day night transition. This new sequence was tested on Thursday, and worked very well. The desired scattered light data were obtained on both terminator passages. Hudson has written and distributed a procedure for routine execution of these observations. The real test of the system will be made next week, when we attempt to perform the operation in Hudson's absence. The most troublesome aspect of the week's activities were difficulties with the reception of data, and the proper operation of the table generation software. Initial attempts by Bruner to prepare the tables for the Bright Point Sequence test were troubled by unexpectedly slow responses by the FACOM main frame computer that left the operator uncertain as to what state the program was in. The table was transmitted at least twice by Bruner, and was corrected by Hudson after the file was received at KSC with a blank header. In correcting the table, Hudson used the "create" option of the program rather than the "update" version. Normally this has no effect. However, when the "create" option is selected, the program specifically ignores the coordinate entries in the ROI table. These entries are properly modified when the "update" option is chosen. This unrecognized feature of the table management software left the final upload with its previous coordinates, which specified the location of the last region selected by the ARS. We live and learn. Future table managers should be sure to use the "update" option when preparing tables to observe pre-determined locations on the disk. Marilyn Bruner SXT Chief Observer