PLEASE NOTE:


*

CCNet DIGEST, 7 May 1998
------------------------

(1) MOST POWERFUL EXPLOSION SINCE THE BIG BANG CHALLENGES GAMMA RAY
    BURST THEORIES
    NASA News

(2) THE TATAHOUINE METEORITE
    J.A. Barrat et al., UNIVERSITY OF ANGERS

(3) FIRST RESULTS OF IMPACT ANALYSIS FROM THE SPACE FLYER UNIT
    H. Yano et al., INSTITUTE OF SPACE & ASTRONAUTIC SCIENCE, JAPAN

(4) SIMULATING HYPERVELOCITY IMPACTS
    E.A. Taylor & J.A.M. McDonnell, UNIVERSITY OF KENT

(5) ASSESSING THE NATURE AND FREQUENCY OF ATMOSPHERIC IMPACTS
    I.V. Nemtchinov et al., RUSSIAN ACADEMY OF SCIENCE

(6) COMPARING THERMAL SPECTRA OF ASTEROIDS
    M. Cohen et al., UNIVERSITY OF CALIFORNIA


============================
(1) MOST POWERFUL EXPLOSION SINCE THE BIG BANG CHALLENGES GAMMA RAY
    BURST THEORIES

From NASA News <NASANews@hq.nasa.gov>

Donald Savage
Headquarters, Washington, DC                           May 6, 1998
(Phone:  202/358-1547) 

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5017)

Robert Tindol
California Institute of Technology, Pasadena, CA
(Phone:  626/395-3631)

RELEASE:  98-75

MOST POWERFUL EXPLOSION SINCE THE BIG BANG CHALLENGES GAMMA RAY BURST
THEORIES

       A recently detected cosmic gamma ray burst released a
hundred times more energy than previously theorized, making it the
most powerful explosion since the creation of the universe in the
Big Bang.

       "For about one or two seconds, this burst was as luminous
as all the rest of the entire universe," said Caltech professor
George Djorgovski, one of the two principal investigators on the
team from the California Institute of Technology, Pasadena, CA.

       The team measured the distance to a faint galaxy from which
the burst originated at about 12 billion light years from the
Earth. The observed brightness of the burst despite this great
distance implies an enormous energy release.  The team's findings
appear in the May 7 issue of the journal Nature.

       The burst was detected on Dec. 14, 1997, by the
Italian/Dutch BeppoSAX satellite and NASA's Compton Gamma Ray
Observatory satellite.  The Compton observatory provided detailed
measurements of the total brightness of the burst, designated GRB
971214, while BeppoSAX provided its precise location, enabling
follow-up observations with ground-based telescopes and NASA's Hubble
Space Telescope.

       "The energy released by this burst in its first few seconds
staggers the imagination," said Caltech professor Shrinivas
Kulkarni, the other principal investigator on the team. 

       The burst appears to have released several hundred times
more energy than an exploding star, called a supernova, until now
the most energetic known phenomenon in the universe.  Finding such
a large energy release over such a brief period of time is
unprecedented in astronomy, except for the Big Bang itself.

       "In a region about a hundred miles across, the burst
created conditions like those in the early universe, about one
millisecond (1/1,000 of a second) after the Big Bang," said Djorgovski.

       This large amount of energy was a surprise to astronomers. 
"Most of the theoretical models proposed to explain these bursts
cannot explain this much energy," said Kulkarni.  "However, there
are recent models, involving rotating black holes, which can work. 
On the other hand, this is such an extreme phenomenon that it is
possible we are dealing with something completely unanticipated
and even more exotic."

       Gamma-ray bursts are mysterious flashes of high-energy
radiation that appear from random directions in space and
typically last a few seconds.  They were first discovered by U.S.
Air Force Vela satellites in the 1960s.  Since then, numerous
theories of their origin have been proposed, but the causes of
gamma-ray bursts remain unknown.  The Compton observatory has
detected several thousand bursts so far.

       The principal limitation in understanding the bursts was
the difficulty in pinpointing their direction on the sky.  Unlike
visible light, gamma rays are exceedingly difficult to observe
with a telescope, and the bursts' short duration exacerbates the
problem.  With BeppoSAX, scientists now have a tool to localize
the bursts on the celestial sphere with sufficient precision to
permit follow-up observations with the world's most powerful
ground-based telescopes.

       This breakthrough led to the discovery of long-lived
"afterglows" of bursts in X-rays, visible and infrared light, and
radio waves.  While gamma-ray bursts last only a few seconds,
their afterglows can be studied for several months.  Study of the
afterglows indicated that the bursts do not originate within our
own galaxy, the Milky Way, but rather are associated with
extremely distant galaxies.

       Both BeppoSAX and NASA's Rossi X-ray Timing Explorer
spacecraft detected an X-ray afterglow.  BeppoSAX precision led to
the detection of a visible light afterglow, found by a team from
Columbia University, New York, NY, and Dartmouth College, Hanover,
NH, including Professors Jules Halpern, David Helfand, John
Torstensen, and their collaborators, using a 2.4-meter telescope
at Kitt Peak, AZ, but no distance could be measured from these
observations.

       As the visible light from the burst afterglow faded, the
Caltech team detected an extremely faint galaxy at its location,
using one of the world's largest telescopes, the 10-meter Keck II
telescope at Mauna Kea, Hawaii.  The galaxy is about as faint as
an ordinary 100 watt light bulb would be as seen from a distance
of a million miles. 

       Subsequent images taken with the Hubble Space Telescope
confirmed the association of the burst afterglow with this faint
galaxy and provided a more detailed image of the host galaxy.


       The Caltech team succeeded in measuring the distance to
this galaxy, using the light-gathering power of the Keck II
telescope. The galaxy is at a redshift of z=3.4, or about 12
billion light years distant (assuming the universe to be about 14
billion years old).

       From the distance and the observed brightness of the burst,
astronomers derived the amount of energy released in the flash. 
Although the burst lasted approximately 50 seconds, the energy
released was hundreds of times larger than the energy given out in
supernova explosions, and it is about equal to the amount of
energy radiated by our entire Galaxy over a period of a couple of
centuries. Scientists say it is possible that other forms of
radiation from the burst, such as neutrinos or gravity waves,
which are extremely difficult to detect, carried a hundred times
more energy than that.

       NASA is planning two missions to further investigate gamma-
ray bursts:  the High Energy Transient Experiment II (HETE II),
scheduled to launch in the fall of 1999, and the Gamma Ray Large
Area Space Telescope (GLAST), scheduled to launch in 2005.  HETE
II will be able to precisely locate gamma-ray bursts in near real-
time and quickly transmit their locations to ground-based
observatories, permitting rapid follow-up studies.  GLAST will
detect only those gamma-ray bursts that emit the highest energy
gamma rays, and will be able to locate them with sufficient
precision to permit coordinated observations from the ground. 
Because not much is known about the bursts at these high energies,
the observations may permit researchers to choose among competing
theories for the origin of gamma-ray bursts.

                           - end -

NOTE TO EDITORS: Images of the GRB 971214 field are available
at:
          FTP://PAO.GSFC.NASA.GOV/newsmedia/GRB/
Information on the BeppoSAX spacecraft is available at:
           http://www.sdc.asi.it/
Information on the Compton Gamma Ray Observatory is available at:
           http://cossc.gsfc.nasa.gov/cossc/descriptions/cgro.html
Information on Gamma Ray Bursts is available at:
http://cossc.gsfc.nasa.gov/cossc/nasm/VU/overview/bursts/bursts.html

============================
(2) THE TATAHOUINE METEORITE

J.A. Barrat*), P. Gillet, C. Lecuyer, S.M.F. Sheppard, M. Lesourd:
Formation of carbonates in the Tatahouine meteorite. SCIENCE, 1998,
Vol.280, No.5362, pp.412-414

*) UNIVERSITY OF ANGERS, GEOLOGY LAB, 2 BLVD LAVOISIER, F-49045 ANGERS,
   FRANCE

The Tatahouine meteorite, in southern Tunisia, shows terrestrial
contamination that developed during 63 years of exposure on Earth's
surface. Samples collected on the day of the fall in 1931 contained
fractures, with no secondary minerals, whereas samples collected in
1994 contain calcite aggregates (70 to 150 micrometers) and rod-shaped
forms (100 to 600 nanometers in length and 70 to 80 nanometers in
diameter) on the fractures. Carbon isotope analysis of the carbonates
within the Tatahouine meteorite [delta(13)C = -2.0 per mil Pee Dee
belemnite standard (PDB)] and the underlying ground (delta(13)C = -3.2
per mil PDB) confirm their terrestrial origin. Copyright 1998,
Institute for Scientific Information Inc.

==========================
(3) FIRST RESULTS OF IMPACT ANALYSIS FROM THE SPACE FLYER UNIT

H. Yano*), S. Kibe, S.P. Deshpande, M.J. Neish: The first results of
meteoroid and debris impact analyses on space flyer unit. ADVANCES IN
SPACE RESEARCH, 1997, Vol.20, No.8, pp.1489-1494

*) INSTITUTE OF SPACE & ASTRONAUTIC SCIENCE, PLANETARY SCI DIV, 3-1-1
YOSHINODAI, KANAGAWA 229, JAPAN

The Space Flyer Unit (SFU) was retrieved from space after its 10-month
mission in January 1996. Here we report the first findings from the
post flight analysis of its Kapton MLI and Teflon radiators in terms of
impact flux, crater morphology and implications of impactors' origins.
The impact flux on the Sun face is also compared with the LDEF, EuReCa
and HST data. On the Kapton MLI, some directional information can be
deduced and its capture cell Structure promises a high survivability
of, residues for chemical analysis. The peripheral flux variation is
not inconsistent with the EuReCa data favouring for the Earth's apex.
The anti-sun face flux exceeded the Sun face by a factor of 1.7. The
size distribution index of the impact features on the Sun face Teflon
agreed with the certain size ranges of the previous spacecraft. Plans
of forthcoming studies such as detailed CCD/laser scanning, calibration
impact experiments and chemical analysis are also addressed. (C) 1997
COSPAR. Published by Elsevier Science Ltd.

====================
(4) SIMULATING HYPERVELOCITY IMPACTS

E.A. Taylor & J.A.M. McDonnell: Hypervelocity impact on soda lime
glass: Damage equations for impactors in the 400-2000m range. ADVANCES
IN SPACE RESEARCH, 1997, Vol.20, No.8, pp.1457-1460

UNIVERSITY OF KENT, PHYSICS LAB, UNIT SPACE SCIENCE & ASTROPHYSICS,
CANTERBURY CT2 7NR, KENT, ENGLAND

The results of a Light Gas Gun hypervelocity impact program on 25 mm
thick soda-lime (float) glass targets are compared to the values
predicted by an empirically determined power law spallation equation
(Paul and Berthoud, 1996). Impact velocities were in the vicinity of 5
km s(-1) projectile densities were between 1 and 8 g cm(-1) and the
projectile diameters, d(p) were 0.8 to 2 mm respectively, producing
spallation diameters between 10 mm and 50 mm. Previously published data
in the range d(p) = 7 - 1000 mu m are also used to assess the validity
of the equation. We conclude that D-spall is predicted by the
empirically determined power law spallation diameters for d(p) < 400 mu
m but only to within +/- 50%. An alternative equation to describe the
response of target material for d(p) > 400 mu m is presented. (C) 1997
COSPAR. Published by Elsevier Science Ltd.

===================
(5) ASSESSING THE NATURE AND FREQUENCY OF ATMOSPHERIC IMPACTS

I.V. Nemtchinov*) , V.V. Svetsov, I.B. Kosarev, A.P. Golub, O.P.
Popova, V.V. Shuvalov, R.E. Spalding, C. Jacobs, E. Tagliaferri:
Assessment of kinetic energy of meteoroids detected by satellite-based
light sensors. ICARUS, 1997, Vol.130, No.2, pp.259-274

*) RUSSIAN ACADEMY OF SCIENCE, INSTITUTE OF DYNAMIC GEOSPHERES, 38
   LENINSKII PROSPECT, BLDG 6, MOSCOW 117979, RUSSIA

Radiation energies of bright flashes caused by disintegration of large
meteoroids in the atmosphere have been measured using optical sensors
on board geostationary satellites. Light curves versus time are
available for some of the events. We have worked out several numerical
techniques to derive the kinetic energy of the meteoroids that produced
the flashes. Spectral opacities of vapor of various types of meteoroids
were calculated for a wide range of possible temperatures and
densities. Coefficients of conversion of kinetic energy to radiation
energy were computed for chondritic and iron meteoroids 10 cm to 10 m
in size using radiation-hydrodynamics numerical simulations. Luminous
efficiency increases with body size and initial velocity, Some
analytical approximations are presented for average conversion
coefficients for irons and H-chondrites. A mean value of this
coefficient for large meteoroids (1-10 m in size) is about 5-10%. The
theory was tested by analyzing the light curves of several events in
detail. Kinetic energies of impactors and energy-frequency distribution
of 51 bolides, detected during 22 months of systematic observations in
1994-1996, are determined using theoretical values of luminous
efficiencies and heat-transfer coefficients, The number of impacts in
the energy range from 0.25 to 4 kt TNT is 25 per year and per total
surface of the Earth. The energy-frequency distribution is in a rather
good agreement with that derived from acoustic observations and the
lunar crater record. Acoustic systems have registered one 1 Mt event
in 12 years of observation. Optical systems have not detected such an
event as yet due to a shorter time of observation. The probability of a
1 Mt impact was estimated by extrapolation of the observational data.
(C) 1997 Academic Press.

====================
(6) COMPARING THERMAL SPECTRA OF ASTEROIDS

M. Cohen, F.C. Witteborn, T. Roush, J. Bregman, D. Wooden: Spectral
irradiance calibration in the infrared. VIII. 5-14 micron spectroscopy
of the asteroids Ceres, Vesta, and Pallas. ASTRONOMICAL JOURNAL, 1998,
Vol.115, No.4, pp.1671-1679

*) UNIVERSITY OF CALIFORNIA BERKELEY, RADIO ASTRONOMY LAB, 601 CAMPBELL
   HALL,BERKELEY,CA,94720

We describe our efforts to seek 'closure' in our infrared absolute
calibration scheme by comparing spectra of asteroids, absolutely
calibrated through reference stars, with 'standard thermal models' and
'thermophysical models' for these bodies. Our use of continuous 5-14 mu
m airborne spectra provides complete sampling of the rise to, and peak,
of the infrared spectral energy distribution and constrains these
models. Such models currently support the absolute calibration of the
Infrared Space Observatory Imaging Photopolarimeter (ISOPHOT) at
far-infrared wavelengths (as far as 300 mu m) and contribute to that of
the Mid-Infrared Spectrometer on the Infrared Telescope in Space in the
6-12 mu m region. The best match to our observed spectra of Ceres and
Vesta is a standard thermal model using a beaming factor of unity. We
also report the presence of three emissivity features in Ceres that may
complicate the traditional model extrapolation to the far-infrared from
contemporaneous ground-based N-band photometry that is used to support
calibration of, for example, ISOPHOT. While identification of specific
materials that cause these features is not made, we discuss families of
minerals that may be responsible. Copyright 1998, Institute for
Scientific Information Inc.

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