Weekly Notes from the Yohkoh Soft X-Ray Telescope

(Week 22, 1998)

Instrument Status

SXT continues in good health. After remaining mostly quiet for several days, the Sun's activity increased sharply at the end of the week. The GOES X-ray background went from low-B to low-C level in only about six hours.

See the weekly operations report for details. The GOES time series for the week of this "nugget" is shown below.

In the display above (click to enlarge), the colored lines show the times of SXT images that currently are on-line at ISAS. The purple lines are flare mode. The gaps will be considerably reduced when the NASA telemetry arrives and gets reformatted. For a summary index listing of the weekly science reports, click here.

Science nugget: Connecting Structure Between Distant Active Regions

This week's nugget is similar to that of 27-Dec-97, but this time we'll show some more images and further discuss the argument set forth in that Nugget.

A glance at an SXT image from today (29-may-98, see below) reveals a long coronal structure connecting two very distant active regions. As beautiful as this feature is, it raises a couple of questions. For one, how long has it been there? Secondly, did it form from a collection of smaller structures or was the connection always there and only chose to brighten up now?

Today's image (click to enlarge):


29-May-98

To answer these questions, we must look at earlier images. The link below is a movie, beginning on 21-may and continuing to today. The first indication of a connection between these two active regions is seen on 22-may (second frame in the movie), while these regions were still on the east limb of the Sun. Over the next few days, we see the connecting structure brighten and fade repeatedly. Notable appearances are at: 

	22-may-98   12:28:10
	23-may-98   07:43:50
	25-may-98   09:58:38 to 10:34:00
	29-may-98   06:09:45 (very faint)
	29-may-98   11:06:53 to 13:17:11

At some times, we can also see a faint channel running between these regions. This has the appearance of a filament channel similar to that described in last week's Nugget. Two examples are at:
	25-may-98   10:07:06
	28-may-98   05:50:57 to 06:16:59

Here is the link to the movie:

ftp://isass0.solar.isas.ac.jp/pub/http/movies/nugget_980529.html

Thus we cannot say precisely when this feature was created, but certainly it existed before today. If it were built up "piecewise from smaller structures" (quoting the 12-dec-97 Nugget), then that development must have taken place prior to 22-may-98. It appears that this magnetic connection persisted for several days, brightening from time to time, rather than forming spontaneously today.

David McKenzie, 29-May-98 (email mckenzie@isass0.solar.isas.ac.jp). For a summary index listing of the weekly science reports, click here.