Abstract:
We observed 4B/X17.2 flare in Hα from super-active region
NOAA 10486 at ARIES, Nainital. This is one of the largest flares of current solar cycle 23, which occurred near the Sun’s center and produced
extremely energetic emission almost at all wavelengths from γ -ray to radio-
waves. The flare is associated with a bright/fast full-halo earth directed
CME, strong type II, type III and type IV radio bursts, an intense proton
event and GLE. This flare is well observed by SOHO, RHESSI and TRACE.
Our Hα observations show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south–west direction of the
active region with bright shock front followed by rapid increase in intensity
and area of the gigantic flare. The flare shows almost similar evolution in
Hα, EUV and UV. We measure the speed of Hα ribbon separation and the
mean value is ∼ 70 km s− ¹ . This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at
the flare maximum. In this paper, we also discuss the energetics of active
region filament, flare and associated CME.
