SXT REPORT FOR WEEK 7: 7-13 February 1993 ========================================= General Status -------------- SXT continued to function well. The Sun has become more active in the last week; producing at least 4 M-flares and about 50 C-flares. SXT has now taken over 912,000 images (151,000 full-frame and 761,000 partial-frame). Personnel --------- Gary Lindford and Hugh Hudson have returned to the U.S. for short visits. Keith Strong returned to ISAS from California on Monday. Karen Harvey has come to visit ISAS for several weeks to work on her bright point study and prepare for the Yohkoh Science meeting at the end of February. The Chief Observer duties were shared between Nariaki Niita and Keith Strong. The KSC tobans were Ichimoto-san and Akioka-san. The SSOC tobans were Watanabe-san and Alphonse Sterling. We had a seminar by T. Watanabe about the work he did at MSSL during his extended visit there. The main point of discussion was the superhot component seen in the flare plasma by the BCS and its relation to the plasma dynamics and other flare characteristics. There was also supposed to be a presentation of some of the latest results from the S XV data but there was so much lively discussion of the superhot results that we ran out of time. However, the S XV results will be presented at the science meeting. Solar Activitiy and Interesting Events -------------------------------------- SXT has mainly folloed AR7420 for most of the week as it has been the dominant region on the disk. It has produced a series of compact, impulsive C flares associated with a small area of (emerging?) magnetic flux in the moat that is near the leader spot. Larger flares seem to be associated with the gamma region in the trailing region of the spot group. It has produced some fascinating sequences of full-resolution flare and quiet mode partial-frame images while the full-frame images have shown the complex structure of the larger and fainter loops connecting the various parts of the active region. A new region is rotating over the southeast limb and has been visible for the last couple of days. The high loops have shown considerable development as the region has approached the limb, including continuous expansion phenomena that Uchida et al. reported in a recent PASJ publication. The southern polar coronal hole that extended to near the equator has rotated over the west limb and there is only a modest-sized hole at both poles. There are many X-ray bright points visible on the Sun at the moment, several of which have shown considerable dynamics. A couple of outstanding examples of XBPs joined by or at the foot of relatively bright loops (compared with the surrounding quiet-sun emission) have been observed recently. Science Progress ---------------- Greg Slater has been working with Dr. R. White at HAO on solar irradience problems and has supplied him with the X-ray flux as a function of time for the first 17 months of the mission. Karen Harvey and Keith Strong have been analyzing data from the special XBP observation run in December 1992. This comprised of a series of 128 x 128 partial frame images taken in two filters. Even at this preliminary stage several interesting results are evident. The obervation run was very successful (thanks to the efforts of Nariaki Nitta in planning the observations), but we have learned a great deal about how to make much better observations next time. It is apparent from even this small sample of observations that the 32-s time resolution is insuficient to follow some of the rapid changes that are occuring in XBPs. A surprising large number of XBPs were varying significantly during the observations. One, for which a light curve has been derived, doubled in intensity in 32 s. Also background subtraction is more critical than we initially believed. By casual inspection 3-4 XBPs are visible in this region but when the background is properly subtracted 14 XBPs are clearly visible in this 5-arcmin square area. By comparing the location of XBPs with the magnetic bipoles visible in the NSO/Kitt Peak data we have been surprised by some of the magnetic connections indicated by the X-ray images. Also the magnetic field does not seem to be evolving as rapidly as the change in the XBPs would indicate. SXT Operations -------------- There was a problem with the network links to three of our workstations at ISAS. Greg Slater made a temporary fix while the Centrecom multiport repeater is repaired. Gary linford made considerable progress in developing the software for tranferring reformatted data to the magneto-optical disks. A few changes were made to the SXT tables. They were all loaded up sucessfully. Astro D launch preparations have not disrupted the operations of SXT in any way this week. The launch has now been postponed until 16-Feb-1993. We supported the successful launch of the NRL rocket and obtained joint data. Unfortunately Yohkoh went into medium rate telemetry and we obtained images at a much lower rate than planned, however there should be ample data to make quantitative comparisons between the rocket-borne grazing-incidence X-ray telescope and SXT. Keith Strong, 14-Feb-1993