From: Greg Preston (gregpreston_at_bellsouth.net)
Date: Thu Jan 06 2005 - 15:32:36 PST
Hello,
Since most on this list are interested in astronomy and radio, I thought
you would enjoy this....
Quotation below.
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From: <na5n_at_zianet.com>
To: <qrp-l_at_mailman.qth.net>
Sent: Tuesday, January 04, 2005 9:49 PM
Subject: [QRP-L] Sudden Ionospheric Disturbances
Gang,
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:
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.
If you look at the above link, "signal strengths" of the radio energy is
measured by scientists by "flux density," using units of mJy ... milli
Jansky's. For example, current VLA detected flux density of this event
is about 100 mJy at L-band (1 GHz) and 30 mJy at C-band (8 GHz).
1 Jy (1 Jansky) = 1.7 x 10EE-23 mW.
1 mJy = 1.7 x 10EE-26 mW.
Figure out what the dBm is of that. Now THAT is QRP!
I noticed some complaining on qrp-l for several days after Dec. 27 about
weird propagation and how some couldn't hear a "peep" on 80M, 6M, etc.
Now you know why.
72, Paul NA5N
PS - I work at the NRAO Very Large Array (VLA), the world's largest
radio telescope, in Socorro, NM. However, I am posting this information
from observatory information as a private individual ham radio QRP
kind of guy. This is not an official observatory press release. It's not
an official anything. You don't even have to believe it. And, I'm not
using my work computer that tax payers bought me. So for those 3
individuals that have gotten a kick out of contacting my employer over
my past solar/propagation posts, save your breath. I am not representing
the NRAO in any way shape or form in this post or using tax payer stuff.
For the rest of you, I hope you enjoy and find the info interesting.
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