SXT Status Report 6 November - 3 December 1995 (Weeks 45, 46, 47, and 48) --------- Serge Savy 3-Dec-95 SXT operations during the last four weeks have been relatively simple and nearly error-free, as we are between campaigns. The low level of solar activity drew our attention towards the quiet corona, with special observations directed towards exploring its structure. SOLAR ACTIVITY Activity has been low during the last four weeks with few active regions observed. There has been only one C class flare (C2 on 10 November) in the last four weeks. Interesting activity, however, was observed in a small active region (AR7929) that emerged on 28 November and produced two tiny jets on its western edge that were observed in the PFI images at 10:10 and 10:30 UT on 30 November. SXT INSTRUMENT STATUS The SXT instrument has continued to work well. There were no significant SXT errors during the last four weeks. A CCD bake-out was carried out for one day on Wednesday 22 November to reduce image artifacts caused by in-situ contamination of the CCD surface. The CCD was cooled to normal operating temperature the next day. The bake-out was successful, and SXT continues to function normally. SXT CALIBRATION ACTIVITIES During his visit to ISAS in the month of November, L. Acton worked on several items to improve the ability to correct SXT images for observational artifacts. Since the additional entrance filter rupture in August '95 the stronger visible stray-light changed the pattern of stray-light in the thin aluminium images. This "grill" pattern was characterized and a method devised for including it in our routine stray-light correction images. (Acton noted that the filter ruptures have appreciably increased the SXT sensitivity at longer wavelengths, which is appropriate for the lower temperatures of solar minimum). These correction images are obtained by acquiring pictures when the X-ray sun has set but the visible sun is unaffected by atmospheric absorption. This interval is about 10 seconds long each orbit sunset. Software to improve ability of the SXT Chief Observer to obtain these images at the precise pointing needed for the stray-light correction data base was written and tested. For study of very faint coronal features such as coronal holes it is necessary to correct for X-rays scattered from other features on the disc. With the help of Carl Foley at MSSL and David Weston of MSU Acton was able to improve our understanding of the azimuthal variation of X-ray scattering and to observes changes in the scattering intensity associated with the entrance filter failures. Ultimately this information may be incorporated into an improved scattering algorithm as well as improvements in knowledge of the sensitivity function of SXT. PASS CONFLICTS Week 45: 6 passes lost to ASCA. Week 46: 10 passes lost to ASCA. Week 47: 10 passes lost to ASCA. Week 48: 6 passes lost to ASCA. CAMPAIGNS There have been no official SXT campaigns during the past four weeks but a number of special observations were carried out. In week 46 we started an unofficial campaign (with L.Acton) to obtain PFI exposures of the quiet corona near disc centre away from any active regions. We made these observations on two days that week, and plan to return to the campaign this week. In week 48 we made high time resolution (4 second) PFI observations of a single active region in a single filter. The unusual anemone shaped AR7929 was the target. These data will be used by David McKenzie of U. Delaware for investigation of wave heating of AR loops as part of his PhD thesis research. SCIENCE Before he left, Ron Moore found several good examples of eruptive events that appear to be consistent with his models (basically the sheared-core concept of Hirayama). One new wrinkle in this pattern is the common occurrence of "elbows" at either end of the eruption; Moore speculated that this might reflect the field expansions seen in the simulations of sheared static fields by Antiochos et al. Nariaki Nitta continued working on super-hot flares primarily from the imaging point of view and found more examples showing the super-hot emission even if the Fe XXVI Lyman alpha flux is not very high. Hudson has been working on HXT spectra of the superhot events in the Pike et al. list. Savy was busy finishing a paper on SXT observations of chromospheric evaporation and helping J.Khan and Hudson interpret the apparently simple 11 July '92 flare that had a distinctly strange spectral evolution. SEMINARS Week 45: E.E. DeLuca (CfA) told us "What we don't know about the solar cycle". Week 46: Ron Moore (NASA/MSFC) gave a fascinating seminar on "Coronal Magnetic Eruptions Observed by Yohkoh", in which seven unusual eruptive flares were presented. Week 47: No seminar. Week 48: K. Fujisaki and Y. Uchida from the Science University of Tokyo enlightened us about "Polar Arcade Formation and the Giant Cusp of Jan 25, 1992", and discussed a few other similar events. PERSONNEL Len Culhane (MSSL) arrived at ISAS at the start of week 47 and stayed for ten days working with H.Hara and Loren Acton on SXT observations of the quiet corona. During week 46 Nariaki Nitta arrived at ISAS. At the end of week 48 Ron Moore (NASA/MSFC) returned to the U.S. after a three month stay at ISAS and Loren Acton returned to the U.S. after a productive one month stay refining the calibration techniques for SXT data. Week 45 Tohban: SSOC: K.Ichimoto, T.Ishii KSC: M.Yamamoto, M.Mizutani SXT Chief Observer: S. Savy SXT Systems and Data Engineer: Week 46 Tohban: SSOC: S.Kubo, K.Suga KSC: Y.Hanaoka, M.Mizutani SXT Chief Observer: L. Acton, S. Savy SXT Systems and Data Engineer: Week 47 Tohban: SSOC: T.Magara, T.Sakao KSC: Y.Hanaoka, K.Shibata SXT Chief Observer: S. Savy SXT Systems and Data Engineer: Week 48 Tohban: SSOC: H.Miyazaki, K.Fujiki KSC: K.Shibata, S.Suematsu SXT Chief Observer: S. Savy, L. Acton SXT Systems and Data Engineer: