4 Evolution of the different structures due to the flare and jet

4.1 Detailed description of the chromospheric evolution

At 10:29:17 UT (during the flare maximum) a significant increase of B1 brightness as well as fainter increase of the B2 brightness was observed. In the spot's penumbra, very close to the northern part of the umbra, a small, point-like brightening, formed by two short comma-like structures was seen (see Fig. 2). In various fibrils of F2 system high redshifts and blueshifts were observed. Around the time of the flare maximum the region of high blueshifts (V1) situated to the west of the spot, started to enlarge its area (see Fig. 3, image at 10:29 UT). V1, being very likely a region of strong upflow of the matter, reached the biggest area and the highest velocities about 10:37 UT. Then V1 started to decrease and it disappeared about 10:45 UT (see Fig. 3, image at 10:58 UT). Above the northern end of filament P2 there were several small, elongated regions of redshifts. They were also signatures of the material flowing down to the chromosphere along the fibrils forming this end part of filament P2. At the north end of filament P2 small regions of fast downflows were present and were still observed at the southern leg of P2.

At 10:58:30 UT, after the flare which ended at 10:43 UT, the intensity of B1 was still very high, a local increase of the B2 brightness was remarkable and the emission of B3 was strongly increased in comparison with the emission at 09:08:54 UT. The velocities detected in fibrils F2 were much smaller than previously, a significant blueshifts were only present close to the southern part of that region. There were strong redshifts at both ends of filament P2 being evidence for efficient downflow of the matter. A new, quite big region of very strong redshifts (V2) appeared to the east of the southern end of filament P2 (see Fig. 3, image at 10:58 UT). That region was not related to any noteworthy structure visible in the H$\alpha$ line centre except for a small brightening spatially correlated with the area of the highest (larger than $\rm 20~km\,s^{-1}$) redshifts (see Fig. 3).

Later on, at 11:28:30 UT the east part of the filament P1 and northern part of P2 were hardly visible. A strong downflow (V3) was present in the northern part of P2. At the southern end of filament P2, near B3, high redshifts were still present. A small, ephemeral bright region appeared to the north of brightening B2. It was situated close to the west border of the strong redshifts region in the northern part of filament P2. The brightness of B4 was significantly enhanced. This region corresponded to the well visible western parts of the fibrils F3, displaying some redshifts. The small brightening in V2 region was more prominent than previously. The area of V2 region was smaller than at 10:58:30 UT while redshifts in the whole region were still very high. Some superpenumbral fibrils of F2 showed blueshifts related to the often observed inflow of material into the spot. On the basis of comparison of the H$\alpha$ line centre images and the corresponding velocity maps, taking into account the geometrical effect of active region location with respect to the line-of-sight, we came to a conclusion that fibrils forming F1 were inclined to the solar surface with their tops tilted towards the solar equator. From the careful investigation of the line of sight velocity maps, which show the velocities between $\rm -5 \;km\, s^{-1}$ and $\rm +5 \;km\, s^{-1}$, it is well seen, that the material flowed along the fibrils forming F1 from their north-west to their south-east legs. Moreover, the brightening B1 is spatially correlated with this downflow region.

At 12:41:26 UT the brightness of all the B-regions described previously was more or less the same as at 11:28:30 UT except for the disappearance of the ephemeral brightening seen at 11:28:30 UT and significant enhancement of B3 brilliance. The northern part of filament P2 was well visible again, while a region of redshift present at the same location was reduced to the narrow strip along the filament with much smaller velocities. Redshifts near the brightening B3, at the south end of filament P2 were still high, and, what is interesting, in the same region both, from and toward the observer velocities were present. Some fibrils of F2 still showed blueshifts in the parts located at the place of anchorage of the superpenumbral fibrils close to the penumbra outer border. Blueshifts were also visible in some F1 fibrils. The area of V2 region increased while its brightness became weaker.

At 13:14:08 UT almost all redshifts became smaller except of B3 brightening, where the velocities stayed the same. Once again, there were higher redshifts in the western part of fibrils F2 at the vicinity of the outer superpenumbral border of the spot. Then, owing to the larger area recorded, filament P3 was well visible again.

The filaments P2 and P3, previously clearly anchored in B3, form now a continuous rope seen quite well in projection above the brightening B3. The leg of the filament P2+P3 anchored in the area of B3 expanded to a long, arch-shaped filament running now above the brightening B3. V3 was almost not visible at that moment. It reached its maximum area, after long gradual increase, at about 11:25 UT. After that time V3 very quickly disappeared. In the velocity map from 12:41 UT stronger redshifts in the region of west legs of P1 anchorage were visible again. A new region of strong redshifts appeared in the vicinity of former V2. All the bright B-areas became smaller although their brightness stayed the same. It looks as if the overall activity of the NOAA 7912 active region was gradually going down.

4.2 Summary of the observed changes in H$\alpha$ and X-rays

The flare and jet in X-rays appeared above the P2 filament. Footpoints of the jet and related flare loops are close to B1 and B3 brightenings (Fig. 2, image at 09:08 UT). The brightness of both B1 and B3 increased after the flare.

The filament/fibril changed considerably after the flare. Strong velocities appeared all along it. There was a shift in its position between 09:08 UT and 10:29 UT, consistent with a temporary rise of its middle part. One hour after the flare, the filament appears broken in two in the vicinity of B1. Around that position, at 10:58 UT the line-of-sight velocities showed a double structure already (Fig. 3). In the red and blue wing images these two parts appear differently: upflow is stronger in the southern part and downflow is dominant along the northern part. The downflow was already present at the time of the flare maximum at 10:29 UT. Filament P3, which is the south continuation of P2, disappeared at the time of the flare and jet (compare images at 09:08 UT and 10:58 UT in Fig. 2), and needed almost three hours to re-form (see Fig. 2, image at 13:14 UT). Possibly it erupted during the event, providing material for the jet. Downflows in filament pointing to the sunspots have been previously observed by e.g. [7, Mouradian et al. (1988).]

Strong blueshift appeared along the fibril F2 at the time of the flare at the western part of the big spot. SXR loops rooted in F2 region appear to connect to the region around B1 brightening and also to the northern part of the positive polarity, where we observe a strong downflow (V2 in Fig. 3, image at 10:58 UT).