SXT Status Report August 2 through August 15, 1999 (Weeks 32-33) H. Hudson SUMMARY Success at last - the Sun finally came through with an X-class flare, just at the beginning of this reporting period. It was the first in 1999. Following this the activity subsided rather completely, so that the eclipse of August 11 occurred during a rather quiet corona. SXT experienced no technical difficulties and we had minimal coordinated observing activity. SOLAR ACTIVITY During the first seven months of the year there had been many M flares, so many in fact that the standard flare/microflare distribution function would have predicted 13-26 X-class events (power-law index range 1.8-1.5). The fact that none occurred strongly suggests that this distribution has a time-variable "knee". The X-class flare was the product of an active region with a bright X-ray sigmoid structure, and not a delta spot configuration, incidentally. See the science nugget for August 6 for fuller details. It was a 1B optical flare, with 1300 SFU at 15,400 GHz and had a type II burst, but no type IV burst. Interestingly, it came from NOAA 8647, not NOAA 8651 which had a colossal sunspot area of 1,370 millionths at about the same time. OBSERVING CAMPAIGNS The eclipse of August 11 was the subject of much coordination, including a "quasi-real-time" display on the Internet on behalf of the 10:00 pm Tokyo news program "Night Station." We provided them with a movie of Q-resolution SFDs. All of the software, both on-board (thanks to Kano_san especially) and ground-based (thanks to software@isass0 especially, plus Soma_san of NAO for ephemeris work both for Yohkoh and for TRACE) worked fine, and Shimojo_san at ISAS arranged the actual data presentation. A good experience, given our frequent troubles in the past with getting eclipse data to work as predicted! One shortcoming of this eclipse was rather poor PFI coverage. We are distinctly interested in the use of H resolution PFI data to assess the SXT point-response function (correspondence with the Wroclaw group, Gburek and J. Sylwester). Luckily there is archive eclipse data for this purpose, and we can hope for a brighter corona on the next opportunity. In the following weeks, we will be supporting the Whole Sun Month campaign, along with its "bumping" program for sigmoid eruptions. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES The terminator acquisition program completed one full cycle since the re-pointing on July 2, and did so in world-record time. Because we are frequently getting Al.1 images (see the time plot of apparent solar diameter on the QUICK page, http://isass1.solar.isas.ac.jp/sxt_co.quick.html , I believe that the Al.1 SFD corrections are the best they've been in recent memory. Here are the current images in the SFD archive: ------- Summary ------- Al.1 AlMg Mg3 Al12 Be119 Open 18 3 2 2 2 NuDen 2 1 2 2 1 As planned, the Al.1/Open number is about half of the total. SXT OBSERVING SEQUENCE TABLES -------------------------------------------------------- JST Day/UT Day Pass Table ID ======================================================== 2-Aug-99 (Mon) 1 990802 P1 ARS1 DARK 2-Aug-99 (Mon) 5 990802 P4 ARS1 DIFF 3-Aug-99 (Tue) 3 990803 P3 ARS1 STD 4-Aug-99 (Wed) 2 990804 P1 ARS1 ECL_TEST 4-Aug-99 (Wed) 5 990804 P5 ARS1 STD 5-Aug-99 (Thu) 3 990805 P4 ARS1 STD 6-Aug-99 (Fri) 2 990806 P2 ARS1 STD 7-Aug-99 (Sat) 3 990807 P3 ARS1 STD 9-AUG-99 (Mon) 5 990809 P5 ARS1 DARK* 10-AUG-99 (Tue) 3 990810 P3 ARS1 ECL1* 11-AUG-99 (Wed) 1 990811 P1 ARS0 ECL2 11-AUG-99 (Wed) 2 990811 P2 ARS1 DIFF 12-AUG-99 (Thu) 1 990812 P1 ARS1 STD 13-AUG-99 (Fri) 4 990813 P4 ARS1 STD* 14-AUG-99 (Sat) 4 990814 P2 ARS1 STD ======================================================= Note: the 14-Aug table was uploaded on a later contact pass because of flare mode during the scheduled pass. SCIENCE Weekly science nuggets were: 13-Aug-99: Eclipse observations - a QRT success 6-Aug-99: One of the missing X flares appears 30-Jul-99: A Lyman-alpha "Rosetta Stone" 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 . The flare nugget discusses the odd distribution function (the "knee" mentioned above), and the eclipse nugget points to the quasi-real-time pages plus makes comments about the SXT point-response function. SEMINARS 12-Aug: T.Sakurai (NAO), "Fifty years of green-line observations from Norikura" Norikura may now be the best-equipped solar coronal station on the ground, with 2D CCD capability for line-profile observations as a function of position and time. There is an intriguing byproduct of the long-term coronal observations in the form of an apparent dependence of sky brightness upon phase in the solar cycle - but not peaked at maximum! YOHKOH OPERATIONS ISSUES We are considering a possible upward shift in Yohkoh flare mode threshold, perhaps by a factor of 2 (from about C2 to about C4). A decision on this will probably be made next week. VISITORS AND PERSONNEL No changes TOHBANS (spacecraft operators) Tohbans for week 32 SSOC: M. Akioka, T. Naito KSC: M. Otogawa, K. Yoshimura SXT_CO: H. Hudson SXT_SW: - Tohbans for week 33 SSOC: T.Sakurai (except 11), K.Marubashi (9,10,14), S.Watari (11-13) R.Kano (SXT eclipse operation) KSC: K.Hori, M.Otogawa SXT_CO: H. Hudson SXT_SW: -