[DX] Lisää keliselityksiä

["Mauno Ritola" <Mauno.Ritola@xxxxxxxxxxxxxxx>]

Via A-DX-/MWC-/NDB-/QRP-listat:

"There have been some episodes over the past week of some very strange
Sudden Ionospheric Disturbances, or SIDs.  These have not been caused
by solar flares or the like, but rather from GRBs ... Gamma Ray Bursts,
from very distant objects, like several hundred light years away. 

The biggest recent event was on December 27, 2004 when a massive gamma
ray burst hit the earth about 2130 UTC from a Magnetar called
SGR-1806.  This GRB was so powerful that it was able to ionize our
ionosphere, just like a solar flare, and cause ionospheric absorption
down to the VLF frequencies.  This indicates a GLE, a Ground Level
Event,
meaning the ionizing radiation from the GRB penetrated our atmosphere,
all the way to ground level. 

There are amateur astronomers of sorts who monitor the signal strength
from high powered VLF transmitters, such as the Navy stations NAA, NPM,
NLK, etc.  At VLF, signal strengths are fairly constant, varying a bit
during day and night.  Some of these amateur stations show a sudden
absorption of signals at VLF due to the arrival of the GRB's.  Some of
their plots can be seen at:
http://aavso.org
Click on the "GCN #2932" button for the SID plots.  Very interesting. 

For the real neophytes out there,
http://gcn.gsfc.nasa.gov/gcn3_archive.html 

This is the clearinghouse for all observatories and satellites doing
GRB monitoring and/or observing.  A little on the heavy side, including
several reports about the observing we're doing at the Very Large Array
(VLA) radiotelescope on SGR-1806.  Our normal observing schedule has
been interupted to observe this strange phenomenon. 

The VLA has found SGR-1806 and is making images of it daily right now.
It's not clear yet what SGR-1806 is, or was, other than something that
possibly blew up big time, perhaps a collapsing pulsar, that has spewed
debris and electrons out into space, traveling from 0.3 to 0.7 times the
speed of light.  It was the initial explosion, on Dec. 27th, that
showered gamma rays into the earths ionosphere.  This is an explosion
that occured 200+ years ago, and the shockwave of gamma rays is so
powerful, it was able to ionize our E and F layers, and absorb VLF
propagation.  Pretty impressive."
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