SXT Status Report September 14 - September 28, 1998 (Weeks 37-38) H. Hudson, J.-P. Wuelser SUMMARY Activity was low-to-moderate. There were no technical problems for Yohkoh or for SXT, except for an erroneous sequence-table upload. SXT conducted some coordinated observations with TRACE and ground-based observatories. SOLAR ACTIVITY The GOES background level (see the plots, for example, on our weekly SXT Web pages at http://www.solar.isas.ac.jp/sxt_co/index.html) remained around the mid-B level. There were no X flares, but two M flares including one (Sep. 23) nicely predicted by McIntosh. His prediction techniques emphasize white light; is there a role for the sigmoid characteristic we see, in forecasting? The Sun showed off lots of interesting things this week - active regions at extreme latitudes; interconnecting transequatorial loops; a remarkably aloof "anemone" region almost totally surrounding by AR 8340 and its henchmen; a beautiful faint sigmoid... OBSERVING CAMPAIGNS Limited joint observations took place, as organized by Karin Muglach and by Louise Harra. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES Wuelser has put in considerable effort to refurbish the Yohkoh coalignment software system. As has been discussed, we have been having problems with the interpretation of HXA limb-address data. HXA, to remind you, is the limb sensor for HXT, but we use it to calibrate the gyro drifts for SXT as well as HXT. The software has not been working as well as it used to, and Wuelser has identified (and fixed) at least one problem. The situation still is not ideal, however, and we are considering the possibility of an alternative method - not to use the HXA limb addresses themselves, which are determined on-board and are subject to noise, but to use the full image scans. Adopting this approach would require major surgery on the software. In the meanwhile Wuelser has written a program, SHOW_HXAFID, which allows us to check quickly whether or not the Yohkoh pointing places the solar limb in one of the shadows of the HXA fiducial marks. This information is now routinely being put on the SXT "quick functionality" page, http://www.solar.isas.ac.jp/sxt_co/quick/quick.html. A special effort was made (three table uploads for visible passes) to obtain calibration information so that Acton can assess the CCD properties after its first seven years in fast cold storage. Operations mistakes and flares got in the way, hence three tries were needed. SXT OBSERVING SEQUENCE TABLES ----------------------------------------------------------------- JST Day UT Start Time Pass Table ID ================================================================= Monday 14-Sep-98 06:06 3 980914 P3 ARS1 DARKCAL Tuesday 15-Sep-98 01:17 1 980915 P1 ARS2 SPOT Tuesday 15-Sep-98 06:24 4 980915 P4 ARS1 STD Thursday 17-Sep-98 03:22 2 980917 P2 ARS2 SPOT Thursday 17-Sep-98 06:59 4 980917 P4 ARS2 DIF Friday 18-Sep-98 02:08 2 980918 P2 ARS2 SPOT Saturday 19-Sep-98 02:25 2 980919 P2 ARS1 STD Monday 21-Sep-98 02:59 3 980920 P3 ARS1 DARKCAL Tuesday 21-Sep-98 23:51 2 980921 P2 ARS1 SPECIAL Tuesday 22-Sep-98 03:17 4 980921 P4 ARS1 DIF Wednesday 22-Sep-98 22:57 1 980922 P1 ARS1 SPECIAL Wednesday 23-Sep-98 01:51 3 980922 P3 ARS1 STD Thursday 23-Sep-98 22:43 3 980923 P2 ARS1 SPECIAL #Postponed due to FLARE mode in Pass 2 Thursday 24-Sep-98 02:09 4 980923 P4 ARS1 STD Friday 24-Sep-98 23:18 2 980924 P2 ARS1 STD Saturday 25-Sep-98 23:18 2 980925 P2 ARS2 NORI #Not postponed in spite of FLARE mode Saturday 26-Sep-98 01:01 3 980926 P3 ARS1 STD ----------------------------------------------------------------- SCIENCE The Astronomical Society of Japan meets next week, so many people are scrambling to get their presentations ready. We will try to capture some of these as "science nuggets". Meanwhile, the recent nuggets consist of: 26-Sep-98: Emerging flux and coronal activity 19-Sep-98: An over-the-limb event 12-Sep-98: Geometry of flare loops The URL's for these and for the full list of science nuggets are on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week is also always kept on http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. OPERATIONS ISSUES We have prepared software to place "add" requests to Wallops, in cases where tohbans feel that more data would be desirable. VISITORS AND PERSONNEL Greg Slater arrived. Nariaki Nitta returned to Palo Alto. SEMINARS Sep. 24 - J.-P. Wuelser (LMSAL): "EIT and Yohkoh observations of solar flares" The EIT instrument notoriously has a poor cadence, but in spite of this there are flare observations as snapshots. These are extremely interesting in comparison with the broad-band SXT observations, especially during the impulsive phase. In one interesting case a distinct compact loop-top source was observed by EIT, and the comparison with SXT requires that it have a quite low temperature (compare with the Masuda source, now quoted at 100MK). Sep. 24 - H.S. Hudson (SPRC): "HESSI overview: why image at high energies?" HESSI is approaching more rapidly than we may want (programatically) but not fast enough (solar-physically). Launch is July 4, 2000. TOHBANS (spacecraft operators) Tohbans for Week 38 SSOC : Yoshida, Nakajima KSC : Nagata, Yamaguchi SXT_CO: Nitta SXT_SW: Slater Tohbans for Week 39 SSOC : Shimizu,Aoki KSC : Yamaguchi,Takahashi SXT_CO: Hudson SXT_SW: Slater