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Tytuł:
Analysis of Fermi gamma-ray burst duration distribution
Autorzy:
Tarnopolski, Mariusz
Opis:
Context. Two classes of gamma-ray bursts (GRBs), short and long, have been determined without any doubts, and are usually prescribed to different physical scenarios. A third class, intermediate in T_{90} durations has been reported in the datasets of BATSE, Swift, RHESSI, and possibly BeppoSAX. The latest release of >1500 GRBs observed by Fermi gives an opportunity to further investigate the duration distribution. Aims. The aim of this paper is to investigate whether a third class is present in the log T_{90} distribution, or whether it is described by a bimodal distribution. Methods. A standard x^{2} fitting of a mixture of Gaussians was applied to 25 histograms with different binnings. Results. Different binnings give various values of the fitting parameters, as well as the shape of the fitted curve. Among five statistically significant fits, none is trimodal. Conclusions. Locations of the Gaussian components are in agreement with previous works. However, a trimodal distribution, understood in the sense of having three distinct peaks, is not found for any binning. It is concluded that the duration distribution in the Fermi data is well described by a mixture of three log-normal distributions, but it is intrinsically bimodal, hence no third class is present in the T_{90} data of Fermi. It is suggested that the log-normal fit may not be an adequate model.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Analysis of the observed and intrinsic durations of Swift/BAT gamma-ray bursts
Autorzy:
Tarnopolski, Mariusz
Opis:
The duration distribution of 947 GRBs observed by Swift/BAT, as well as its subsample of 347 events with measured redshift, allowing to examine the durations in both the observer and rest frames, are examined. Using a maximum log-likelihood method, mixtures of two and three standard Gaussians are fitted to each sample, and the adequate model is chosen based on the value of the difference in the log-likelihoods, Akaike information criterion and Bayesian information criterion. It is found that a two-Gaussian is a better description than a three-Gaussian, and that the presumed intermediate-duration class is unlikely to be present in the Swift duration data.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Analysis of gamma-ray burst duration distribution using mixtures of skewed distributions
Autorzy:
Tarnopolski, Mariusz
Opis:
Two classes of GRBs have been confidently identified thus far and are prescribed to different physical scenarios – NS-NS or NS-BH mergers, and collapse of massive stars, for short and long GRBs, respectively. A third, intermediate in duration class, was suggested to be present in previous catalogs, such as BATSE and Swift, based on statistical tests regarding a mixture of two or three log-normal distributions of T_{90}. However, this might possibly not be an adequate model. This paper investigates whether the distributions of log T_{90} from BATSE, Swift, and Fermi are described better by a mixture of skewed distributions rather than standard Gaussians. Mixtures of standard normal, skew-normal, sinh-arcsinh and alpha-skew-normal distributions are fitted using a maximum likelihood method. The preferred model is chosen based on the Akaike information criterion. It is found that mixtures of two skew-normal or two sinh-arcsinh distributions are more likely to describe the observed duration distribution of Fermi than a mixture of three standard Gaussians, and that mixtures of two sinh-arcsinh or two skew-normal distributions are models competing with the conventional three-Gaussian in the case of BATSE and Swift. Based on statistical reasoning, and it is shown that other phenomenological models may describe the observed Fermi, BATSE, and Swift duration distributions at least as well as a mixture of standard normal distributions, and the existence of a third (intermediate) class of GRBs in Fermi data is rejected.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
The radio and optical luminosity evolution of quasars. II. the SDSS sample
Autorzy:
Stawarz, Łukasz
Lawrence, A.
Singal, J.
Petrosian, V.
Opis:
We determine the radio and optical luminosity evolutions and the true distribution of the radio-loudness parameter $\mathit{R}$, defined as the ratio of the radio to optical luminosity, for a set of more than 5000 quasars combining Sloan Digital Sky Survey optical and Faint Images of the Radio Sky at Twenty cm (FIRST) radio data. We apply the method of Efron and Petrosian to access the intrinsic distribution parameters, taking into account the truncations and correlations inherent in the data. We find that the population exhibits strong positive evolution with redshift in both wavebands, with somewhat greater radio evolution than optical. With the luminosity evolutions accounted for, we determine the density evolutions and local radio and optical luminosity functions. The intrinsic distribution of the radio-loudness parameter $\mathit{R}$ is found to be quite different from the observed one and is smooth with no evidence of a bimodality in radio loudness for log $\mathit{R} \geqslant -1$. The results we find are in general agreement with the previous analysis of Singal et al., which used POSS-I optical and FIRST radio data.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Wyświetlanie 1-10 z 14

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