494 research outputs found
Gamma-ray bursts and X-ray melting of material as a potential source of chondrules and planets
The intense radiation from a gamma-ray burst (GRB) is shown to be capable of
melting stony material at distances up to 300 light years which subsequently
cool to form chondrules. These conditions were created in the laboratory for
the first time when millimeter sized pellets were placed in a vacuum chamber in
the white synchrotron beam at the European Synchrotron Radiation Facility
(ESRF). The pellets were rapidly heated in the X-ray and gamma-ray furnace to
above 1400 C melted and cooled. This process heats from the inside unlike
normal furnaces. The melted spherical samples were examined with a range of
techniques and found to have microstructural properties similar to the
chondrules that come from meteorites. This experiment demonstrates that GRBs
can melt precursor material to form chondrules that may subsequently influence
the formation of planets. This work extends the field of laboratory
astrophysics to include high power synchrotron sources.Comment: 8 pages, 10 figures. Proceedings of the 5th INTEGRAL Workshop, Munich
16-20 February 2004. High resolution figures available at
http://bermuda.ucd.ie/%7Esmcbreen/papers/duggan_01.pd
Analysis of Temporal Features of Gamma Ray Bursts in the Internal Shock Model
In a recent paper we have calculated the power density spectrum of Gamma-Ray
Bursts arising from multiple shocks in a relativistic wind. The wind optical
thickness is one of the factors to which the power spectrum is most sensitive,
therefore we have further developed our model by taking into account the photon
down-scattering on the cold electrons in the wind. For an almost optically
thick wind we identify a combination of ejection features and wind parameters
that yield bursts with an average power spectrum in agreement with the
observations, and with an efficiency of converting the wind kinetic energy in
50-300 keV emission of order 1%. For the same set of model features the
interval time between peaks and pulse fluences have distributions consistent
with the log-normal distribution observed in real bursts.Comment: ApJ in press, 2000; with slight revisions; 12 pag, 6 fi
Gamma-ray bursts and X-ray melting of material to form chondrules and planets
Chondrules are millimeter sized objects of spherical to irregular shape that
constitute the major component of chondritic meteorites that originate in the
region between Mars and Jupiter and which fall to Earth. They appear to have
solidified rapidly from molten or partially molten drops. The heat source that
melted the chondrules remains uncertain. The intense radiation from a gamma-ray
burst (GRB) is capable of melting material at distances up to 300 light years.
These conditions were created in the laboratory for the first time when
millimeter sized pellets were placed in a vacuum chamber in the white
synchrotron beam at the European Synchrotron Radiation Facility. The pellets
were rapidly heated in the X-ray and gamma-ray furnace to above 1400C melted
and cooled. This process heats from the inside unlike normal furnaces. The
melted spherical samples were examined with a range of techniques and found to
have microstructural properties similar to the chondrules that come from
meteorites. This experiment demonstrates that GRBs can melt precursor material
to form chondrules that may subsequently influence the formation of planets.
This work extends the field of laboratory astrophysics to include high power
synchrotron sources.Comment: 4 pages, 4 figures. Full resolution figures available from A&
Very High Energy gamma-rays from electron/positron Pair Halos
In this paper we study the formation of giant electrons-positron pair halos
around the powerful high energy extragalactic sources. We investigate the
dependence of radiation of pair halos, in particular the spectral and angular
distributions on the energy spectrum of the primary gamma-rays, the redshift of
the source, and the flux of the extragalactic background light.Comment: 17 pages, 17 figures, published in Volume No. 18, Issue No. 06 of
"International Journal Of Modern Physics D
The frontier of darkness: the cases of GRB 040223, GRB 040422, GRB 040624
Understanding the reasons for the faintness of the optical/near-infrared
afterglows of the so-called dark bursts is essential to assess whether they
form a subclass of GRBs, and hence for the use of GRBs in cosmology. With VLT
and other ground-based telescopes, we searched for the afterglows of the
INTEGRAL bursts GRB 040223, GRB 040422 and GRB 040624 in the first hours after
the triggers. A detection of a faint afterglow and of the host galaxy in the K
band was achieved for GRB 040422, while only upper limits were obtained for GRB
040223 and GRB 040624, although in the former case the X-ray afterglow was
observed. A comparison with the magnitudes of a sample of afterglows clearly
shows the faintness of these bursts, which are good examples of a population
that an increasing usage of large diameter telescopes is beginning to unveil.Comment: 4 pages, 2 figures. To appear in the proceedings of the 16th Annual
October Astrophysics Conference in Maryland "Gamma Ray Bursts in the Swift
Era", eds. S. Holt, N. Gehrels & J. Nouse
A Search for Ultra-High Energy Counterparts to Gamma-Ray Bursts
A small air shower array operating over many years has been used to search
for ultra-high energy (UHE) gamma radiation ( TeV) associated with
gamma-ray bursts (GRBs) detected by the BATSE instrument on the Compton
Gamma-Ray Observatory (CGRO). Upper limits for a one minute interval after each
burst are presented for seven GRBs located with zenith angles . A excess over background was observed between 10 and
20 minutes following the onset of a GRB on 11 May 1991. The confidence level
that this is due to a real effect and not a background fluctuation is 99.8\%.
If this effect is real then cosmological models are excluded for this burst
because of absorption of UHE gamma rays by the intergalactic radiation fields.Comment: 4 pages LaTeX with one postscript figure. This version does not use
kluwer.sty and will allow automatic postscript generatio
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