SXT Status Report 23 November 1999 - 13 December 1999 (Weeks 48-50) H.S. Hudson, D.E. McKenzie, N.V. Nitta SUMMARY Activity began high during this three-week period (12 M flares and an X1.4), then plunged to a mini-minimum. We carried out a routine bakeout of the CCD. There were no major problems. SOLAR ACTIVITY Again the Sun is lopsided, no doubt producing beautiful rotational modulation of all of the global indices. The GOES time profile for the three-week interval provided a beautiful example of the decoupling between the background coronal luminosity and flare occurrence. The lopsidedness really just refers to flare occurrence, since the background level only changed by a factor of two or so. Ergo, there are two kinds of coronal structures: hot transient ones, and cool steady ones. OBSERVING CAMPAIGNS There were no formal joint observing campaigns, but we continued with high-rate whole-sun images, hoping to catch wave events from events below the flare trigger level (perhaps C6 at its present setting). We may have been rewarded with a detection, but it is only feebly significant and can't be believed until we confirm that EIT saw it too. If so, this will mean that we can start to build up statistics on how the soft X-ray and EUV views of the corona differ under global wave conditions. The upcoming Flare Genesis telescope observations will see a major joint observing campaign effort. We have been asked to offer opinions about target regions (two targets: flares and sigmoids) and have been practicing this while waiting for stratospheric wind patterns to permit the balloon launch. Please see our webpages for more details about campaigns past and future: http://isass1.solar.isas.ac.jp/sxt_co/sxt_catalog.html http://isass1.solar.isas.ac.jp/sxt_co/sxt_future.html SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES A normal pointing update was done Nov. 29, using the new software with no problem. A CCD bakeout, which we routinely try to do every few months, took place December 10/11 with no problem. We may review the policy about doing these bakeouts, we may have reached the level of diminishing returns here. If an eight-year vacuum soak won't outgas a spacecraft, it must be made of cream cheese - would be one theory. We have made no further efforts to improve the flare ARS function (see the last report) but now have many images of the patrol type and should analyze them. But there are so few flares! We continue to tweak the offset exposure settings in the flare low-resolution images (again, these modifications are to help us follow waves, SAD's, and ejecta, all of which are faint features on large scales). A SAD, for reference, is a "Super-Arcade Downflow", as opposed of course to a HAPPY, which would be a "Humdrum Arcade Process Prior to Yohkoh." The operations software now routinely saves version numbers for OPs and Wallops planning files. This should help us sort through the occasional confusions. Final data reformatting is complete through 13 November 1999. SXT OBSERVING SEQUENCE TABLES ------------------------------------------------------------- UT Date & Time Pass Table ID ============================================================= Monday 22-NOV-99 13:13 3 991122 P3 ARS1 DARK Tuesday 23-NOV-99 10:02 1 991123 P1 ARS1 DIFF Tuesday 23-NOV-99 15:09 4 991123 P4 ARS1 HI-FFI Wednesday 24-NOV-99 13:39 3 991124 P3 ARS1 HI-FFI Thursday 25-NOV-99 10:26 1 991125 P1 ARS1 HI-FFI Friday 26-NOV-99 14:10 "4" 991126 P1 ARS1 STD Monday PM 29-NOV-99 07:52 1 991129 P1 ARS1 DARK Tuesday PM 30-NOV-99 06:24 1 991130 P1 ARS1 DIFF Tuesday PM 30-NOV-99 11:29 4 991130 P4 ARS1 HI-FFI Wednesday PM 01-DEC-99 06:35 1 991201 P1 ARS1 HI-FFI Thursday PM 02-DEC-99 10:12 3 991202 P3 ARS1 HI-FFI Friday PM 03-DEC-99 07:00 2 991203 P2 ARS1 HI-FFI Saturday PM 04-DEC-99 08:55 3 991204 P3 ARS1 HI-FFI Sunday PM 05-DEC-99 09:07 3 991205 P3 ARS1 STD Tuesday PM 7-DEC-99 07:50 3 991207 P3 ARS1 DARKCAL Wednesday PM 8-DEC-99 04:38 1 991208 P1 ARS1 DIFF Thursday PM 9-DEC-99 06:33 3 991209 P3 ARS1 STD Friday PM 10-DEC-99 05:03 1 991210 P1 BAKE Saturday PM 11-DEC-99 05:15 3 991211 P3 ARS1 STD ============================================================= SCIENCE The weekly science nuggets: November 26: "Yohkoh observations of superhot flares" - these events are different qualitatively from other flare events, in that they produce have substantial emission measure above (say) 30 MK, resulting in strong FeXXVI emission in addition to the bremsstrahlung continuum. This nugget points out interesting morphological features - Yohkoh now has quite a collection of events. We don't have good theories yet, but that's not surprising. December 3: "Anticipating flares" - some bits of preparation for the target selection for the Flare Genesis telescope. We tried to see how well the brightest region (the usual Yohkoh observing mode) predicted where a flare would occur. This algorithm works pretty well, especially when applied on short time scales. Contrary to expectation, incidentally, the statistics failed to show that most flares occur at night. December 10: "A fifth kind of dimming? Or a second?" serves to introduce the interconnecting loop disappearances studied by Khan and Akiyama in the context of coronal X-ray dimming. It's after all an IL wind that blows nobody good. The full list of nuggets is kept on http://isass1.solar.isas.ac.jp/sxt_co/index.html , and the current week's nugget also normally resides on http://isass1.solar.isas.ac.jp/sxt_co/SXTweekly.html . SEMINARS None. There were many meetings. PERSONNEL Nariaki Nitta and David McKenzie returned to Palo Alto and Bozeman, respectively. Greg Slater arrived at ISAS. Many visitors showed up for the Solar-B and Yohkoh 8th anniversary meetings, including L.W. Acton. All were impressed by the tidiness legacy of the Crown Prince, whose visit may incidentally turn out to have led to a blessed event. TOHBANS (spacecraft operators) Tohbans for week 48 SSOC: H. Hara, M. Hata(-24) KSC: S. Masuda(-4), H. Sekiguchi SXT_CO: N. Nitta, H. Hudson SXT_SW: - Tohbans for week 49 SSOC: H. Hudson, K. Aoki KSC: S. Masuda, H. Sekiguchi SXT_CO: H. Hudson SXT_SW: G. Slater Tohbans for week 50 SSOC: (K. Shinoda), T. Yokoyama KSC: H. Sekiguchi, K. Kumagai SXT_CO: H. Hudson SXT_ST: G. Slater SXT chief observer for week 51: H. Hudson, N. Nitta