SXT Status Report May 4 through May 24, 1999 (Weeks 19-21) D. McKenzie and H. Hudson SUMMARY Solar activity picked up a bit, with several M flares. SXT conducted many joint observations with SOHO, TRACE, and ground-based observatories (notably Tenerife). There were no technical problems. SOLAR ACTIVITY Solar activity went through two peaks during this three-week interval, reflecting the occurrence of major flare activity in multiple regions. The biggest event was M7.6 (May 9), which was on the NW limb. The prompt event reports variously had H-alpha flares at N19E29 (17:55 peak), N21E55 (18:00 peak), and N18W02 (18:06 peak), none of which seemed to be the correct location! This just confirms our preconception, as X-ray astronomers, that H-alpha doesn't tell you very much very directly. Where are the Air Force microwave locator data? The M7.6 flare, which was inexplicably _not_ the subject of a weekly science nugget, displays extremely interesting ejecta. The outward flow persisted for a considerable period along the same path, strongly inclined to the vertical. OBSERVING CAMPAIGNS This has been a busy season for observing campaigns. In the last few weeks we have taken part in JOPs 104 (X-ray jets, Davina Innes coord.), 100 (differential emission measures, Jeff Brosius coord.), 103 (TRACE moss, Tom Berger coord.), and 017 (arch filament systems, Lidia Van Driel Gesztelyi coord.), in addition to making images in support of the VAULT rocket mission. Now who's going to reduce all these data? SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES We resumed offpoint terminator acquisition in order to support the forthcoming SOHO/UVCS collaboration arranged by Jing Li (Hawaii). The offpoint position is to the SE limb. Normal terminator acquisition is almost complete for the epoch commencing April 18, 1999. A new straylight monitor image (WdBan/Open Dark DPE=4) is now replacing the old one (NaBan/Open + Dark) which was near saturation. We're running this on trial for a bit. A "streak artifact" was noted near the northwest limb, presumably due to excessive exposure of the CCD. This artifact has disappeared and reappeared at least twice in the last month; we are contemplating a slight (10") westward adjustment to the normal pointing, to reduce the amount of time that these troublesome pixels are illuminated. SXT OBSERVING SEQUENCE TABLES -------------------------------------------------------- JST Day UT Time Pass Table ID ======================================================== Mon 03-May-99 2 990503 P2 ARS2 ST+J104 Tue 04-May-99 2 990504 P2 ARS2 ST+J104 Tue 04-May-99 4 990504 P4 ARS2 DK+J104 Wed 05-May-99 2 990505 P2 ARS2 DF+J104 Wed 05-May-99 4 990505 P4 ARS2 ST+J104 Thu 06-May-99 2 990506 P2 ARS2 ST+J104 Fri 07-May-99 2 990507 P2 ARS2 ST+J104 Fri 07-May-99 4 990507 P4 ARS2 VAULT Sat 08-May-99 2 990508 P2 ARS2 ST+J100 Mon 10-May-99 2 990510 P2 ARS2 ST+J104 Tue 11-May-99 2 990511 P2 ARS1 DARKCAL Wed 12-May-99 2 990512 P2 ARS1 DIFF Thu 13-May-99 4 990513 P4 ARS2 ST+J100 Fri 14-May-99 2 990514 P2 ARS1 STD Tue 18-May-99 3 990518 P3 ARS2 DK+J017 Wed 19-May-99 4 990519 P4 ARS1 ST+J017 Thu 20-May-99 4 990520 P4 ARS2 DF+J103 Fri 21-May-99 2 990521 P2 ARS2 ST+J103 Sat 22-May-99 4 990522 P4 ARS2 ST+J100 ======================================================= SCIENCE Weekly science nuggets were: 21-May-99: "Plasma ejection and flow" 14-May-99: "Curious if not spectacular N-S loop phenomena" 7-May-99: "S-shaped active regions and the prediction of CMEs" The full list of nuggets is kept on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week's nugget is also normally known as http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. SEMINARS May 6 R. Canfield (Montana State U.): "What is the meaning of the cusp signature?" This was in the form of a round-table discussion including many participants, including key Yohkoh theorists Shibata and Yokoyama. Of course the cusp structure is itself one of Yohkoh's major discoveries, and the soft X-ray images see them much better than the EUV images of EIT or TRACE. The key immediate question was regarding their reliability as an indicator of CME-style eruption. But what do they mean, and when is a cusp really a cusp? This latter basic question seemed to baffle the pundits, and there was little concensus in explicit detail, although the "big picture" of large-scale reconnection following a massive eruption seems to find a concensus. YOHKOH OPERATIONS ISSUES HXT has terminated its "cal mode" of observation. In this mode HXT gets 64 energy channels at 8-sec binning, as opposed to 4 channels at 1/2-sec binning. There is user software (HXT_MULTIMG) that can handle these data, thanks to Jim McTiernan and Jun Sato, so users are encouraged to take a look - these data are a good predecessor of HESSI imaging spectroscopy, at low resolution, and thus far no papers have been written on the Yohkoh observations of this type. VISITORS AND PERSONNEL Visitor Dick Canfield departed; visitor Silja Pohjolainen arrived. TOHBANS (spacecraft operators) Tohbans for week 19 SSOC : T.Watanabe(3-5) K.Nakakubo(ex.6) Yashiro(6-11) KSC : M. Shimojo and M. Shinkawa SXT_CO: D. McKenzie SXT_SW: - Tohbans for week 20 SSOC : M. Miyashita and M. Ohyama KSC : M. Shinkawa and T. Sakao SXT_CO: D. McKenzie SXT_SW: - Tohbans for week 21 SSOC : Y.Suematsu, S.Yashiro/T.Watanabe KSC : T. Sakao, R.Haga SXT_CO: D. McKenzie SXT_SW: -