SXT Status Report January 18, 1999 through February 7, 1999 (Weeks 4-6) D. McKenzie, H. Hudson SUMMARY This 3-week interval included a moderate level of activity for about the first half, but then the GOES level dropped to as low a level as it's been since mid-July, 1998. This coincided, of course, with a flare-oriented Sac Peak run organized by Gianna Cauzzi and Roberto Falciani. SXT continued to work well but suffered from its fifth entrance-filter rupture. SOLAR ACTIVITY There were three M-class flares during the interval, and the largest spot area was 480 millionths on 23-Jan-99, AR 8439. There may have been a higher level of activity on the invisible hemisphere, judging from the occurrence of an over-the-limb C5 long-duration event on Feb. 4. Once again, the NS interconnecting loops have shown interesting behavior. OBSERVING CAMPAIGNS A flare-oriented observing campaign, led by Gianna Cauzzi and Roberto Falciani, is running Feb. 1 through Feb. 12. By the time of this report it has been something of a wipeout, apparently, via a pernicious conjunction of bad weather and low activity. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES Another piece of the aperture filter of SXT ruptured on Feb. 1, resulting in another change in the stray-light brightness level and configuration. Somewhat surprisingly, the "pinhole" pattern of the thin Al filter changed rather radically. In the meanwhile we have obtained a terminator exposure for this filter and can now make adequate corrections, so there will be no long-term effects. Loren Acton is visiting ISAS this month and will be studying this phenomenon in greater detail. SXT OBSERVING SEQUENCE TABLES ----------------------------------------------------------------- JST Day UT Time Pass Table ID ================================================================= 18-JAN-99 16:26 2 990118 P2 ARS1 STD 19-JAN-99 14:59 2 990119 P2 ARS1 DARKCAL 20-JAN-99 15:15 2 990120 P2 ARS1 STD 21-JAN-99 17:15 4 990121 P1 ARS1 DIFF 22-JAN-99 14:05 2 990122 P2 ARS1 STD 23-JAN-99 12:38 2 990123 P2 ARS1 STD 25-JAN-99 16:26 2 990125 P2 ARS1 TRACE 26-JAN-99 14:59 3 990126 P3 ARS1 DARKCAL 27-JAN-99 15:15 2 990127 P2 ARS1 STD 28-JAN-99 17:15 3 990128 P3 ARS1 DIFF 29-JAN-99 14:05 2 990129 P2 ARS1 STD 30-JAN-99 12:38 3 990130 P3 ARS1 STD 02-FEB-99 11:53 4 990202 P4 ARS2 DARKCAL 03-FEB-99 08:43 2 990203 P2 ARS2 STD 04-FEB-99 07:17 2 990204 P3 ARS2 STD 05-FEB-99 07:33 2 990205 P2 ARS2 STD 06-FEB-99 07:49 3 990206 P3 ARS2 STD ===================================================== Here the "ARS2" tables show the Sac Peak support activity. SCIENCE The real excitement during this period concerns the remarkable "fan arcade" event of Jan. 20; in this type of event we see an array of spikes extending above the arcade. A prototype event in this class has been the 28-Feb-92 flare, the subject of several papers (see most recently Svestka et al., Solar Phys. 182, 179, 1998). The new event confuses earlier pictures rather completely, as described by McKenzie in the seminar Feb. 4 (also see the 22-Jan science nugget). 22-Jan-99 Motion and footpoint brightening in an M flare, 20-jan-99 29-Jan-99 Motion in flare loops 5-Feb-99 What holds an arcade up? The URL's for these and for the full list of science nuggets can be found on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week's nugget is also always kept on http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. SEMINARS Jan. 21, 1999 H. Hudson (SPRC/UCSD): "An SXT Global Wave at last?" Feb. 4, 1999 D. McKenzie (Montana State U.) "Arcade Formation During the 20-Jan-99 Slow LDE Flare" H. Hudson (SPRC/UCSD): "Reconnection at Streamer Cusps? (Journal review)" The Jan. 21 talk dealt with the wave-like eruption seen on May 6, 1998; it seems extremely plausible to interpret this as the first X-ray manifestation of a Moreton wave/Type II wave; see http://www.solar.isas.ac.jp/sxt_co/981225.html for much more detail, including the actual graphic material of the seminar presentation. The speculations about radiation pressure there can be discounted, but interested readers will find some useful ideas about SXT response issues, and at least a partial explanation of why we had to wait more than 7 years to see a wave so clearly! OPERATIONS ISSUES It has been decided to re-enable the HXT "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. Recently J. Sato (Nobeyama) and H. Hara (NAO) have found interesting properties from our first experimental use of this mode, and of course this kind of observation is a precursor to the HESSI observations due to start next year. VISITORS AND PERSONNEL G. Slater and L. Acton arrived. H. Hudson spent 5 days in the U.S. TOHBANS (spacecraft operators) Tohbans for week 04 SSOC : H. Hudson, M. Takahashi KSC : K.Kumagai, H. Ishizaki SXT_CO: D. McKenzie SXT_SW: - Tohbans for week 05 SSOC : A.Sterling, N.Shinohara KSC : K.Kumagai, K.Hori SXT_CO: D. McKenzie SXT_SW: G. Slater Tohbans for week 06 SSOC : M.Shimojo, Y.Suematsu KSC : K.Hori, S.Akiyama SXT_CO: D. McKenzie => H. Hudson SXT_SW: G. Slater