A confined flare with an interesting eruption

Science Nugget: October 06, 2000


This week's nugget details the happenings of an X1.2 flare that occurred on September 30 around 23:00 UT in NOAA Active Region #9177. This event had an interesting eruption that starts in typical fashion, but never gets anywhere -- i.e., it is "confined". The location of this flare event and the light curves from the GOES satellite are shown below (click the thumbnails to get the big picture). The image below (left) is from some 11 hours prior to the flare, but gives some context as to what we're looking at -- a bright active region near the Sun's West limb. The two bright knots in the center of this active region are the approximate locations of the footpoints of the flare's magnetic loops, seen below.

The GOES plot, above right, shows the time variation of the soft X-ray flux. The purple band near the top shows when SXT was in flare mode, the sparse set of orange lines just below that show the times of the full-frame images, and the blue lines that are packed tightly together show the times of the partial frame images. Yohkoh got great data coverage during the later impulsive phase of the flare, but for reasons not yet apparent to the author we have a gap in the data right before flare mode kicked in. It is possible, but unlikely, we'll be able to fill in this gap.

A CME denied?

The following movie is a series of Full-resolution (Open+NuDen)/AlMg images, with dark current and other artifacts removed. A blob of material being ejected to the west, away from the limb, is evident in several frames, but this ejection is not visible in the half-resolution or quarter-resolution images. This is curious because these lower resolutions have the advantage of having (a) larger field of view and (b) better signal to noise, but to no avail. Furthermore, a glance at the on-line LASCO data shows no obvious CME eruption from this event. A CME isn't necessarily required, per se, but CME signatures in X-rays have been thought about before at some length and are common for energetic flares.

So, we have an event that spurred the GOES X-ray flux to X1.2 and a ghostly ejection to the southwest. Did the Yohkoh hard X-ray telescope see anything?

The answer is yes: HXT has lots of counts in all channels:

Efforts to make quality movies of the HXT data have proven difficult for reasons not yet clear to this novice HXT user. However, we did succeed in collecting nice images near the beginning of the flare. This three figures below show soft X-ray images (SXT thick Al) with contours of the HXT imagery from the beginning of the flare. From left to right, this shows the HXT LO, M1, and M2 channels (thermal, intermediate, and highly nonthermal X-rays). The SXT image used here clearly shows the blob of material that is ejected to the southwest.

The bright blob of material ejected during the impulsive phase near the beginning of this event is sufficiently active as to appear in several of the HXT channels (though this is probably not well-demonstrated by the figures shown here). The questions raised by this nugget might include: what happened to the ejecta? How did this event manage an X1.2 rating? Why don't we see it in the quarter-resolution images? What happens between the end of our FOV, and the beginning of the LASCO C2 coronagraph, where it never (according to our untrained eyes) appears?

October 6, 2000

Brian Handy <handy@isass0.solar.isas.ac.jp>