Hi,

I'm forwarding an e-mail from Peter Brown who is reporting about one
definite airwave detection from the impact at the Kenyian Infrasonic Array.
He send also an attached map which you can see here:
http://www.minorplanets.org/OLS/images/map-prelim.jpg

Thanks to Peter Brown!


Best regards,
Aleksanadar Cikota
J75 La Sagra Sky Survey

-----------------------------------------
Aleksandar Cikota
(University of Zurich)
e-mail: alexci@...
acikota@...
SkyPe: Aleksandar_Cikota
MSN: Aleksandar_Cikota@...


-------Original Message-------

From: Pbrown
Date: 10/07/08 19:42:17
To: 'Aleksandar Cikota'
Subject: RE: 2008 TC3

A very preliminary examination of several infrasound stations proximal to
the predicted impact point for the NEO 2008 TC3 has yielded one definite
airwave detection from the impact. The airwave was detected at the Kenyian
Infrasonic Array, (IMS station IS32), beginning near 05:10 UT on Oct 7, 2008
and lasting for several minutes. The signal correlation was highest at very
low frequencies – the dominant period of the waveform was 5-6 seconds. The
backazimuth of the signal over the entire 7 element array is shown in the
attached map – it clearly points to within a few degrees of the expected
arrival direction. Moreover, assuming a stratospheric mean signal speed of 0
28 km/s, the arrival time corresponds to an origin time near 02:43 UT, which
is consistent with the expected impact time near 02:45:40 UT given expected
variations in stratospheric arrival speeds. The dominant period of 5-6
seconds corresponds to an estimated energy (using the AFTAC period at
maximum amplitude relationship from ReVelle, 1997) of 1.1 – 2.1 kilotons of
TNT. The five other closest infrasound stations were briefly examined for
obvious signals and showed none – more detailed signal processing of these
additional data are ongoing in the search for additional signals.

------------------------
Dr. Peter Brown
Canada Research Chair in Meteor Science
Acting Director - Centre for Planetary Science and Exploration (CPSX)
Associate Professor
Department of Physics and Astronomy
University of Western Ontario
London, ON N6A 3K7
CANADA
519-661-2111 x86458
http://aquarid.physics.uwo.ca/~pbrown



From: Aleksandar Cikota [mailto:alexci@...]
Sent: Tuesday, October 07, 2008 1:41 PM
To: Wayne Edwards
Cc: pbrown@...
Subject: 2008 TC3

Hi Wayane and Peter,

I'm sure you heard about 2008 TC3 - the small 2-3m asteroid which was
discovered on 2008 Oct. 6 by the Mt. Lemmon Survey in Arizona. The
atmospheric impact over northern Sudan was expected today morning - 2008 Oct
07 0246 UTC, but there is no official report that it entered the atmosphere
yet.
The predicted time and location of the impact should be precise, we and many
other astronomers observed the asteroid until it entered the Earth's shadow.

I wanted to aks, did some of your infrasound stations detected somethig at
this time?

Here are the predicted informations for the entery:

Object: 2008 TC3 (discovered Oct. 6 at Mt. Lemmon by the Catalina Sky
Survey) H=31.2
Impact time: 2454746.61578 JD = 2008-10-07 02:46 UT = 19:46 PT = 22:46 EDT
Long., Lat. (deg) = 31.697 20.855 (Northern Sudan)
V_imp = 12.82 km/s Atmospheric impact velocity
Zenith Angle= 70.86 (Shallow, near-grazing impact)

Thank You!

Best regards,
Aleksandar Cikota
J75 La Sagra Sky Survey


P.S. A nice image of the asteorid entering the Earth's shadow:
http://www.minorplanets.org/OLS/2008_TC3/


-----------------------------------------
Aleksandar Cikota
(University of Zurich)
e-mail: alexci@...
acikota@...
SkyPe: Aleksandar_Cikota
MSN: Aleksandar_Cikota@...






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