oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Survival analysis of the optical brightness of GRB host galaxies  [PDF]
I. I. Racz,L. G. Balazs,Z. Bagoly,L. V. Toth
Physics , 2015,
Abstract: We studied the unbiased optical brightness distribution which was calculated from the survival analysis of host galaxies and its relationship with the Swift GRB data of the host galaxies observed by the Keck telescopes. Based on the sample obtained from merging the Swift GRB table and the Keck optical data we also studied the dependence of this distribution on the data of the GRBs. Finally, we compared the HGs distribution with standard galaxies distribution which is in the DEEP2 galaxies catalog.
Population Synthesis of the GRB Progenitors and their Brightness and Redshift Distribution  [PDF]
I. Panchenko
Physics , 1999,
Abstract: We estimate the relativistic binaries merger rate and redshift distribution population synthesis of an ensemble of evolving close binaries. Results of such simulations definitely depend on the cosmic star formation rate history, which is different in galaxies of different types. This leads to a difference in merger rate in spiral and elliptical galaxies, which in principle can be an observational test for GRB models. Also a fit of BATSE long bursts \lns is performed, showing that only a wide (2-3 orders of magnitude) luminosity function provides a good fit.
Microlensing and the Surface Brightness Profile of the Afterglow Image of GRB 000301C  [PDF]
B. Scott Gaudi,Jonathan Granot,Abraham Loeb
Physics , 2001, DOI: 10.1086/323244
Abstract: The optical afterglow of Gamma-Ray Burst (GRB) 000301C exhibited a significant, short-timescale deviation from the power-law flux decline expected in the standard synchrotron shock model. Garnavich, Loeb & Stanek found that this deviation was well-fit by an ad hoc model in which a thin ring of emission is microlensed by an intervening star. We revisit the microlensing interpretation of this variability, first by testing whether microlensing of afterglow images with realistic surface brightness profiles (SBPs) can fit the data, and second by directly inverting the observed light curve to obtain a non-parametric measurement of the SBP. We find that microlensing of realistic SBPs can reproduce the observed deviation, provided that the optical emission arises from frequencies above the cooling break. Conversely, if the variability is indeed caused by microlensing, the SBP must be significantly limb-brightened. Specifically, greater than 60% of the flux must originate from the outer 25% of the area of the afterglow image. The latter requirement is satisfied by the best fit theoretical SBP. The underlying optical/infrared afterglow lightcurve is consistent with a model in which a jet is propagating into a uniform medium with the cooling break frequency below the optical band.
"No High Energy Emission" GRB Class Is Attributable to Brightness Bias  [PDF]
J. T. Bonnell,J. P. Norris
Physics , 1999,
Abstract: The inhomogeneous brightness distribution of BATSE detected gamma-ray bursts has been considered strong evidence for their cosmological origin. However, subclasses of gamma-ray bursts have been shown to have significantly more homogeneous brightness distributions. Pendleton et al. (1997) have found such a result for gamma-ray bursts with no detectable emission at energies >300 keV. Accordingly, it has been suggested that these no high energy (NHE) emission bursts represent an underluminous population of nearby sources. A distinct homogeneous NHE brightness distribution has also been considered as evidence for beaming of different spectral components of the prompt burst emission. We synthesize observed distributions of gamma-ray bursts based on a sample of typical bright BATSE bursts with intrinsic high energy emission and adopt a single cosmological distance scale for all sources. We find that the resulting synthetic NHE bursts do indeed have a more nearly homogeneous intensity distribution when an appropriate decrease in signal to noise and redshifted spectrum is incorporated. We argue that the definition of NHE bursts, and soft-spectrum bursts in general, naturally produces a steep distribution. The NHE class of gamma-ray bursts is therefore likely due to brightness bias.
At What Distance Can the Human Eye Detect a Candle Flame?  [PDF]
Kevin Krisciunas,Don Carona
Physics , 2015,
Abstract: Using CCD observations of a candle flame situated at a distance of 338 m and calibrated with observations of Vega, we show that a candle flame situated at ~2.6 km (1.6 miles) is comparable in brightness to a 6th magnitude star with the spectral energy distribution of Vega. The human eye cannot detect a candle flame at 10 miles or further, as some statements on the web suggest.
Probing the Cosmic Star Formation History by Brightness Distribution of Gamma-Ray Bursts  [PDF]
Tomonori Totani
Physics , 1998, DOI: 10.1086/306664
Abstract: Brightness distribution of Gamma-Ray Bursts (GRBs) is studied in detail under the assumption that GRB rate is related to cosmic star formation rate. The two populations of the long- and short-duration bursts in the 4B BATSE catalog are analyzed separately. Taking account of current uncertainties in the observational estimate of star formation rate (SFR), we have tried various models of the cosmic star formation history and we find that the SFR evolution in $z$ = 0--1 is strongly constrained by the GRB distribution if the standard candle approximation is valid. The strong SFR evolution by a factor of $\sim$ 15 from $z$ = 0 to 1 inferred from UV observations is too steep to be consistent with the GRB distribution for any distance scale of GRBs. Some possibilities to reconcile this discrepancy are discussed, including the intrinsic luminosity dispersion of GRBs and/or modification of star formation history estimated by UV observations. We argue that SFR increase factor from $z$ = 0 to 1 may be as low as about 4 if we choose different sets of cosmological parameters and/or take account of the evolution of metallicity and dust extinction in the UV data, and this would significantly remedy the discrepancy.
Gamma-ray bursts: towards a standard candle luminosity  [PDF]
J-L. Atteia
Physics , 1997,
Abstract: It is usual, in gamma-ray burst (GRB) studies, to compare the average properties of bright and faint GRBs, with the assumption that brightness classes reflect distance classes. When brightness is intented to reflect the distance to the sources, it is nevertheless important to use a quantity with a small intrinsic dispersion. We propose here a method to compare the intrinsic dispersion of various measures of GRB brightness. This method assumes that nearby bursters are homogeneously distributed in an Euclidean space with no density or luminosity evolution. We then use it to compare 5 measures of GRB brightness in the BATSE Catalog. Our analysis reveals that better (i.e. less dispersed) measures of brightness are obtained at low energy and that GRBs are much closer to standard candles below 100 keV than above. We suggest that a beaming of the emission above 100 keV could explain this behaviour.
Low emittance upgrade for CANDLE project  [PDF]
G. S. Zanyan
Physics , 2015,
Abstract: To improve the performance of CANDLE synchrotron light source and stay competitive with recently proposed low emittance upgrade programs in the world we have developed new low emittance lattices for CANDLE booster and storage ring. These lattices have been designed taking into account the new developments in magnet fabrication technology and the multi-bend achromat concept. The main design considerations, the linear and non-linear beam dynamics aspects of the modified lattices are presented.
Backtest of Trading Systems on Candle Charts  [PDF]
Stanislaus Maier-Paape,Andreas Platen
Quantitative Finance , 2014,
Abstract: In this paper we try to design the necessary calculation needed for backtesting trading systems when only candle chart data are available. We lay particular emphasis on situations which are not or not uniquely decidable and give possible strategies to handle such situations.
An independent estimate of the cosmological distance to GRB970228 and GRB970508  [PDF]
V. M. Lipunov,K. A. Postnov,M. E. Prokhorov
Physics , 1997,
Abstract: Assuming binary neutron star mergings as a standard-candle model for GRBs, an independent estimate is obtained for the redshift of GRB970228 and GRB970508 with optical counterparts, using mean statistical properties of GRBs observed by BATSE. We derive z=0.7\pm 0.1 and z=1.9\pm 0.1 for GRB970228 and GRB970508 respectively, depending on the power-law index of the GRB spectrum s=-1.1\pm 0.3 and the value of the redshift of the initial star formation z_*=3-10 in a flat \Omega=1 Universe with a cosmological term \Lambda=0.7.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.