SXT Status Report 4 January 1997 - 25 January 1997 (Weeks 2-4) H. Hudson, S. Savy, N. Nitta Success has always been a great liar. --Nietzsche SUMMARY Yohkoh has entered its seventh calendar year, and both spacecraft and SXT are operating smoothly. This is the first SXT status report of 1997. Solar activity remained at a low level but something quite phenomenal happened in terms of space weather. SOLAR ACTIVITY The highlight of this period was undoubtedly the remarkable "halo CME" seen by LASCO on Jan. 6, which led to a geomagnetic storm and apparently to the termination of an ATT communications satellite under circumstances somewhat reminiscent of the Anik failures of 1994, perhaps. This status report will not be definitive on this topic, which is of prime interest to ISTP and to SOHO as well as to Yohkoh and to many other people as well (including the lawyers, given the major financial impact - the cost of the satellite was quoted as $200M). To summarize what Yohkoh saw, the answer is "not much". There was an extremely weak LDE event in an active region on the central meridian, in the southern hemisphere as expected from the off-center bias of the halo CME seen by LASCO. SXT did not see "dimming", loop expansion, nor arcade formation, but a filament disappearance at the right time and place was apparently noted at Ramey and Nobeyama, so there can be little doubt that the weak LDE in the active region did the dirty work. The fact that the soft X-ray signatures were so weak is itself quite interesting scientifically, we believe. SXT INSTRUMENT STATUS SXT continues to perform well and to return excellent observations. There had been some rumors to the contrary because of the week-long bakeout that we did in Week 2-3, luckily starting up after the CME launch rather than before. SXT CALIBRATION ACTIVITIES As mentioned above, we baked the SXT CCD for about a week (from ~09:00 on 7 January to ~08:00 on 14 January), the first such long bakeout since launch. The effects are still being analyzed and will be reported later. Incidentally to the "space weather" story, EIT (SOHO) was also doing a long bakeout but theirs started before the CME, not after. It might be wise for us in the future not to have simultaneous bakeouts, as unintentionally happened this time, in order to keep the coverage as continuous as possible. The terminator program continued to keep up to date. As a result of the campaign activities, we accumulated quite a bit more data at E 5' and W 5' offpoint locations, so the current program is to re-visit those locations with the standard filters. PASS CONFLICTS There is presently little overlap between Yohkoh and ASCA KSC-Pass times. Akebono continues to take infrequent KSC passes from Yohkoh. Preparations for the launch of VSOP (nominally February 8) took many passes and will take more around the time of the launch itself. We don't have good knowledge yet of how VSOP operations might affect the routine work of Yohkoh after the launch, but will be able to comment on that in the next report. Week 2: 3 passes were lost due to conflicts with Asuka and Akebono. Week 3: 14 passes were cancelled due to preparations for the launch of MUSES-B Week 4: 10 passes were lost due to preparations for the launch of MUSES-B. CAMPAIGNS Joint observations with SOHO and Sac Peak around the time of the Galileo conjuction - maybe this is an opportunity to learn something about nature of the scintillation sources? - took place 17 - 22 January Yohkoh observed streamers at the east and west limbs in collaboration with SoHO. The campaign was coordinated by Shadia Habbal (CFA). Yohkoh was offpointed 5 arcmins east 17-19 January, and then 5 arcmins west 19-22 January. The bases of streamers were clearly observed in the special long exposure FFI tables we used. 23 January Yohkoh coordinated with SoHO CDS and LASCO observations of a small set of active loops on the East limb. 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 R.C. Canfield visited from Montana, doing yeoman service as tohban and as an investigator of network problems. SEMINARS There were no seminars during the reporting period due to travel and intense competition for time by other activities in Japan. A new series of seminars will commence on Feb. 6 (5th anniversary of a nice superhot flare in 1992, studied by Kosugi, by Sterling, and by others). SCIENCE In the last edition of the SXT Status Report we had neglected to mention the role of E. Hiei and French colleagues (Z. Mouradian) in the study of the "Shrimp Tempura" filament/arcade event. This well-observed event of 7 May 1992 seems to be a Rosetta Stone pointing to the interesting relationships among the H-alpha filament, related soft X-ray structures, the eruption, flare, and arcade, and cusp structures. We hope to see the finished works soon (two papers are in preparation). The science spectacular of the month, other than the CME, reflects glory on HXT rather than SXT. An extremely successful data-analysis workshop was held in Palo Alto, with participation by virtually all of the most active HXT data workers. M. Sato presented his new modulation parameters, derived from the orbital data, and they made a spectacular improvement in the quality of both MEM and Pixon reconstructions. Another breakthrough was the discovery and repair of a bug in both codes related to the DC level in the images. The HXT group now feels confident about routine image construction and we hope that this will lead to a comprehensive catalog with much-improved images. A. Sterling continued in his campaign to use BCS as an imager - via the technique of limb occultation during quiet conditions - and we have been learning a lot about the background counting rates of BCS, as well as seeing some interesting spectroscopy, as a result of this. PERSONNEL Nariaki Nitta arrived. Hugh Hudson spent 10 days away, participating slightly in the wonderful CDAW on hard X-ray imaging in Palo Alto (see above). SUMO Wakanohana toppled Akebono to take the winter title. He should probably move to New England and become a linebacker. Week 2 Tohbans SSOC: Y. Kato and S. Akiyama KSC: T. Watanabe and J. Koyama SXT CO: H. Hudson, S. Savy Software: --- Week 3 Tohbans SSOC: M. Shimojo and R. Canfield KSC: J. Koyama and K. Yoshimura SXT CO: S. Savy Software: --- Week 4 Tohbans SSOC: M. Akioka and N. Shinoda / S. Tsutsuki KSC: K. Yoshimura and T. Yokoyama SXT CO: S. Savy Software: ---