[PPRAANet] SID's

[W0rw at aol.com]

a new message from Paul NA5N
-----------------

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. 


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  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 ham radio qrp individual.

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. 
----------------
via w0rw at aol.com
ps: You can monitor my LF Beacon on 480KHz  CW,
Paul   w0rw