4,223 research outputs found
Gamma Ray Burst Host Galaxies Have `Normal' Luminosities
The galactic environment of Gamma Ray Bursts can provide good evidence about
the nature of the progenitor system, with two old arguments implying that the
burst host galaxies are significantly subluminous. New data and new analysis
have now reversed this picture: (A) Even though the first two known host
galaxies are indeed greatly subluminous, the next eight hosts have absolute
magnitudes typical for a population of field galaxies. A detailed analysis of
the 16 known hosts (ten with red shifts) shows them to be consistent with a
Schechter luminosity function with as expected for
normal galaxies. (B) Bright bursts from the Interplanetary Network are
typically 18 times brighter than the faint bursts with red shifts, however the
bright bursts do not have galaxies inside their error boxes to limits deeper
than expected based on the luminosities for the two samples being identical. A
new solution to this dilemma is that a broad burst luminosity function along
with a burst number density varying as the star formation rate will require the
average luminosity of the bright sample (
or ) to be much greater than the
average luminosity of the faint sample ( or ). This places the bright bursts at distances
for which host galaxies with a normal luminosity will not violate the observed
limits. In conclusion, all current evidence points to GRB host galaxies being
normal in luminosity.Comment: 18 pages, 3 figures, Submitted to ApJLet
Information content of the weak-charge form factor
Parity-violating electron scattering provides a model-independent
determination of the nuclear weak-charge form factor that has widespread
implications across such diverse areas as fundamental symmetries, nuclear
structure, heavy-ion collisions, and neutron-star structure. We assess the
impact of precise measurements of the weak-charge form factor of Ca
and Pb on a variety of nuclear observables, such as the neutron skin
and the electric-dipole polarizability. We use the nuclear Density Functional
Theory with several accurately calibrated non-relativistic and relativistic
energy density functionals. To assess the degree of correlation between nuclear
observables and to explore systematic and statistical uncertainties on
theoretical predictions, we employ the chi-square statistical covariance
technique. We find a strong correlation between the weak-charge form factor and
the neutron radius, that allows for an accurate determination of the neutron
skin of neutron-rich nuclei. We determine the optimal range of the momentum
transfer that maximizes the information content of the measured weak-charge
form factor and quantify the uncertainties associated with the strange quark
contribution. Moreover, we confirm the role of the electric-dipole
polarizability as a strong isovector indicator. Accurate measurements of the
weak-charge form factor of Ca and Pb will have a profound
impact on many aspects of nuclear theory and hadronic measurements of neutron
skins of exotic nuclei at radioactive-beam facilities.Comment: 10 pages, 4 figure
Severe New Limits on the Host Galaxies of Gamma Ray Bursts
The nature of Gamma Ray Bursts (GRBs) remains a complete mystery, despite the
recent breakthrough discovery of low energy counterparts, although it is now
generally believed that at least most GRBs are at cosmological distances.
Virtually all proposed cosmological models require bursters to reside in
ordinary galaxies. This can be tested by looking inside the smallest GRB error
boxes to see if ordinary galaxies appear at the expected brightness levels.
This letter reports on an analysis of the contents of 26 of the smallest
regions, many from the brightest bursts. These events will have and
small uncertainties about luminosity functions, K corrections and galaxy
evolutions; whereas the recent events with optical transients are much fainter
and hence have high redshifts and grave difficulties in interpretation. This
analysis strongly rejects the many models with peak luminosities of as deduced from the curve with no evolution.
Indeed, the lower limit on acceptable luminosities is . The only possible solution is to either place GRBs at
unexpectedly large distances (with for the faint BATSE bursts) or to
require bursters to be far outside any normal host galaxy.Comment: 17 pages, to be published by ApJ
Gravitational Lensing Bound On The Average Redshift Of Gamma Ray Bursts In Models With Evolving Lenses
Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE
4B catalog can be used to constrain the average redshift of the GRBs.
In this paper we investigate the effect of evolving lenses on the of
GRBs in different cosmological models of universe. The cosmological parameters
$\Omega$ and $\Lambda$ have an effect on the of GRBs. The other factor
which can change the of GRBs is higher in evolving model of galaxies as compared to
non-evolving models of galaxies.Comment: 23 pages,one plain LaTeX file with three postscript figures This is
modified version with recent BATSE efficiency parameter and with the latest F
paramete
A Deep Multicolor Survey. VI. Near-Infrared Observations, Selection Effects, and Number Counts
I present near-infrared J (1.25um), H (1.65um), and K (2.2um) imaging
observations of 185 square arcminutes in 21 high galactic latitude fields.
These observations reach limiting magnitudes of J ~ 21 mag, H ~ 20 mag and K ~
18.5 mag. The detection efficiency, photometric accuracy and selection biases
as a function of integrated object brightness, size, and profile shape are
quantified in detail. I evaluate several popular methods for measuring the
integrated light of faint galaxies and show that only aperture magnitudes
provide an unbiased measure of the integrated light that is independent of
apparent magnitude. These J, H, and K counts and near-infrared colors are in
best agreement with passive galaxy formation models with at most a small amount
of merging (for Omega_M = 0.3, Omega_Lambda = 0.7).Comment: AJ Accepted (Feb 2001). 28 pages, 7 embedded ps figures, AASTEX5.
Minor changes to submitted version. Also available at
http://www.astronomy.ohio-state.edu/~martini/pubs
Generation of millijoule-level soft-x-ray laser pulses at a 4-Hz repetition rate in a highly saturated tabletop capillary discharge amplifier
Includes bibliographical references (page 1117).Laser pulses with energies of as much as 1 mJ were generated at a wavelength of 46.9 nm by single-pass amplification in a 34.5 cm-long Ne-like Ar capillary discharge plasma. The large gain-length product of this plasma column allows for soft-x-ray amplification in a highly saturated regime, resulting inefficient energy extraction. Average laser output pulse energy of 0.88 mJ and peak power of 0.6 MW were obtained at a repetition rate of 4 Hz. With an estimated peak spectral brightness of â1 Ă 1023 photons/s mm2 mrad2 0.01% bandwidth) this tabletop laser is one of the brightest soft-x-ray sources to date
CW laser action in atomic fluorine
Includes bibliographical references (pages 627-628).We have obtained CW laser action on four transitions in the doublet system of atomic fluorine for the first time. All previously reported laser action was on a pulsed basis only. CW laser radiation was obtained when F2 or AgF was used as a fluorine donor in an electron beam pumped helium plasma. A multiline output power of 200 mW was obtained
Femtosecond laser triggering of a sub-100 picosecond jitter high-voltage spark gap
Includes bibliographical references (page 3250).We have demonstrated sub-100 ps jitter operation of a pressurized high-voltage air spark gap triggered by a femtosecond Ti:Sapphire laser. Time delay statistical fluctuations with a standard deviation as low as +-Ï=0.037 ns were obtained
Generation of highly ionized cadmium plasma columns for a discharge-pumped Nickel-like Cd laser
Includes bibliographical references (page 574).We report the observation of strong line emission from Ni-like Cd ions in a capillary discharge plasma. Spectroscopically pure Cd vapor was produced in a room temperature environment utilizing a capacitive discharge. The metal vapor was injected into a capillary channel where it was subsequently excited with fast current pulses of up to 200 kA These results open the possibility of observing laser amplification in the 3d94d-394p line of Ni-like Cd at 13.2 nm and in laser lines of other Nickel-like ions in a discharge-created plasma
Relevance of terpenoids on flammability of Mediterranean species: an experimental approach at a low radiant heat flux
One of the major factors influencing forest fuel combustion are terpenoids, a fraction of flammable Biogenic Volatile Organic Compounds (BVOCs) produced and stored by most Mediterranean species. The qualitative and quantitative effect of terpenoids on flammability has been only partially explained. In this study several major terpenoid-storing Mediterranean species (common cypress and three pines) were considered and compared to Holm oak as a reference non-storing species. The terpenoids were quantified via gas chromatography (GC-MS) analysis from both live fine fuel (LFF) and litter samples, and the relations between flammability and the terpenoids content were investigated by categories (Monoterpenoids, oxygenated Monoterpenoids, Sesquiterpenoids). The effect of fuel moisture content and species on ignition probability of LFF was also explored. A very different ignition probability was observed at the same fuel moisture content for the different species (Pinus spp. > C. sempervirens > Q. ilex). The stored terpenoids explained 19% to 50% of the whole flammability of both LFF and litter. Fuel moisture content (FMC) did not substantially change the relative effect of terpenoids on flammability, except in C. sempervirens. Monoterpenoids do not seem to significantly affect flammability, while sesquiterpenoids greatly influenced most flammability components, though their relative effect varied among species. A relation between storing structure of terpenoids and flammability was suggested. The results of this study indicate that isoprenoids should be included in physical models of the prediction and propagation of wildfire in Mediterranean vegetation as significant factors in driving flammability. © SISEF
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