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: -