Weekly Notes from the Yohkoh Soft X-Ray Telescope

(Week 19, 1998)

Instrument Status

SXT continues in good health. This week was exciting, because of the high level of solar activity: two X flares and nine M flares. Several were associated with CMEs, and some of these CMEs were Earth-directed. The GOES background level remained above 'C' for three days.

SXT took part in two Joint Observing Programs (JOPs) this week. We made images to support JOP 082 ("Magnetic Flux Disappearance in Cancelling Bipoles", Karen Harvey coordinating) and JOP 059 ("High Cadence Activity Studies and the Heating of Coronal Loops", Robert Walsh coordinating).

See weekly operations report for details (not frozen; this page shows the current week's information). 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: M flare ejecta and loop filling

At approximately 21:17 UT on 3-may-98, active region NOAA 8210 produced an M-class flare. Yohkoh was able to observe the event successfully, and for this week's Nugget we present some pictures.

A quick way to survey the hard X-rays produced in the event is provided by a set of light curves from HXT (below). The result here is interesting, because the spectrum is extremely hard and the event has a long duration. (Click on the graphs to see a larger version.)

When Flare Mode is triggered, SXT begins making images in a somewhat different manner than in Quiet Mode. The flare images are typically at a higher cadence (i.e., more images per minute), and also include some lower-resolution images to show a somewhat wider field of view. The links below will show you movies made from the half-resolution and quarter-resolution images, which give us a chance to look for material ejected from the flare site. The M flare of 3-may-98, the subject of these movies, threw off some visible, "clumpy" ejecta.

Quarter-resolution movie
Half-resolution movie

Note that there is quite a lot of pixel saturation in these images. But that won't keep you from seeing the ejecta.

Finally, a look at the Half-resolution images with a different color palette allows us to emphasize the filling of coronal loops near the flare site. Keep your eyes on the region just to the southwest (lower-right) of the central portion of the flare. Loop that are initially invisible fill in and brighten to the point where the image begins to saturate.

Loop-filling movie

David McKenzie and Hugh Hudson, 08-May-98 (email mckenzie@isass0.solar.isas.ac.jp). For a summary index listing of the weekly science reports, click here.