Gamma Ray Bursts as cosmological tools

The use of Gamma Ray Bursts as ``standard candles'' has been made possible by the recent discovery of a very tight correlation between their rest frame intrinsic properties. This correlation relates the GRB prompt emission peak spectral energy E_peak to the energy E_gamma corrected for the collimation angle theta_jet of these sources. The possibility to use GRBs to constrain the cosmological parameters and to study the nature of Dark Energy are very promising.Comment: 6 pages, 3 figures, Proceedings of the workshop 'Astrophysical sources of high energy particles and radiation', Torun - Poland 20-24 June 2005, Ed. T. Bulik, B. Rudak, G. Madejsk

Prone position: Does it help with acute respiratory distress syndrome (ARDS) requiring extracorporeal membrane oxygenation (ECMO)?

Introduction: Lung protective ventilation therapy with low tidal volume-high PEEP is the standard treatment for the patients with acute respiratory distress syndrome (ARDS). Oscillators are occasionally used for salvage ventilation in cases where poor compliance restricts the use of traditional ventilation with ARDS. In addition to ventilator therapy, prone positioning has been used to improve oxygenation. We presented a challenging case of ARDS, which failed medical management extracorporeal membrane oxygenation (ECMO) support and oscillatory ventilation. Prone positioning was initiated which improved oxygenation, respiratory compliance and posterior atelectasis. Case presentation: A 41-year-old morbid obese female developed ARDS due to influenza pneumonia. The patient remained hypoxic despite optimum medical and ventilator management and required veno-venous extracorporeal membrane oxygenation (VV ECMO). CT scan of the chest showed ARDS with posterior consolidation. Despite ARDSnet ventilation support, antiviral therapy and ECMO support, there was no clinical improvement. High frequency oscillatory ventilation was initiated on ECMO day #13, which resulted in no respiratory improvement over the next 5 days. On ECMO day #18, the patient was placed on a Rotaprone? bed Therapy, utilizing a proning strategy of 16 hours a day. The clinical improvements observed were resolving of the consolidation on CXR, improvements in ventilatory parameters and decreased oxygen requirements. The patient was successfully weaned off ECMO on POD#25 (8 days post prone bed). Conclusions: Prone position improved oxygen saturation and pulmonary compliance in severe ARDS requiring ECMO and it might facilitate early weaning

The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects

We study the distribution of long Gamma Ray Bursts in the Ep-Eiso and in the Ep,obs-Fluence planes through an updated sample of 76 bursts, with measured redshift and spectral parameters, detected up to September 2007. We confirm the existence of a strong rest frame correlation Ep ~ Eiso^0.54+-0.01. Contrary to previous studies, no sign of evolution with redshift of the Ep-Eiso correlation (either its slope and normalisation) is found. The 76 bursts define a strong Ep,obs-Fluence correlation in the observer frame (Ep,obs ~ F^0.32+-0.05) with redshifts evenly distributed along this correlation. We study possible instrumental selection effects in the observer frame Ep,obs-Fluence plane. In particular, we concentrate on the minimum peak flux necessary to trigger a given GRB detector (trigger threshold) and the minimum fluence a burst must have to determine the value of Ep,obs (spectral analysis threshold). We find that the latter dominates in the Ep,obs-Fluence plane over the former. Our analysis shows, however, that these instrumental selection effects do not dominate for bursts detected before the launch of the Swift satellite, while the spectral analysis threshold is the dominant truncation effect of the Swift GRB sample (27 out of 76 events). This suggests that the Ep,obs-Fluence correlation defined by the pre--Swift sample could be affected by other, still not understood, selection effects. Besides we caution about the conclusions on the existence of the Ep,obs-Fluence correlation based on our Swift sample alone.Comment: To appear in MNRA

Cosmological constraints with GRBs: homogeneous medium vs wind density profile

We present the constraints on the cosmological parameters obtained with the $E_{\rm peak}$--$E_{\gamma}$ correlation found with the most recent sample of 19 GRBs with spectroscopically measured redshift and well determined prompt emission spectral and afterglow parameters. We compare our results obtained in the two possible uniform jet scenarios, i.e. assuming a homogeneous density profile (HM) or a wind density profile (WM) for the circumburst medium. Better constraints on $\Omega_{M}$ and $\Omega_{\Lambda}$ are obtained with the (tighter) $E_{\rm peak}$--$E_{\gamma}$ correlation derived in the wind density scenario. We explore the improvements to the constraints of the cosmological parameters that could be reached with a large sample, $\sim$ 150 GRBs, in the future. We study the possibility to calibrate the slope of these correlations. Our optimization analysis suggests that $\sim 12$ GRBs with redshift $z\in(0.9,1.1)$ can be used to calibrate the $E_{\rm peak}$--$E_{\gamma}$ with a precision better than 1%. The same precision is expected for the same number of bursts with $z\in(0.45,0.75)$. This result suggests that we do not necessarily need a large sample of low z GRBs for calibrating the slope of these correlations.Comment: 7 pages, 7 figures, submitted to A&

Long Gamma-Ray Bursts as standard candles

As soon as it was realized that long GRBs lie at cosmological distances, attempts have been made to use them as cosmological probes. Besides their use as lighthouses, a task that presents mainly the technological challenge of a rapid deep high resolution follow-up, researchers attempted to find the Holy Grail: a way to create a standard candle from GRB observables. We discuss here the attempts and the discovery of the Ghirlanda correlation, to date the best method to standardize the GRB candle. Together with discussing the promises of this method, we will underline the open issues, the required calibrations and how to understand them and keep them under control. Even though GRB cosmology is a field in its infancy, ongoing work and studies will clarify soon if and how GRBs will be able to keep up to the promises.Comment: 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

Como escolhem as cagarras o seu par?

A secção Biologia é coordenada pelo Professor Universitário Armindo Rodrigues.[…]. No caso da Cagarra Calonectris borealis, os critérios envolvidos na escolha do parceiro começam agora a ser conhecidos como resultado do trabalho desenvolvido pelo Grupo de Aves Marinhas do Departamento de Oceanografia e Pescas (GAM-DOP) da Universidade dos Açores, em colaboração com a Universidade de Vigo (UV). As cagarras são consideradas espécies modelo para estudos de escolha de parceiro pois têm uma elevada fidelidade ao parceiro (aprox. 81.8 a 96.4%), vivem várias décadas e possuem baixa fecundidade. […].info:eu-repo/semantics/publishedVersio

Spectral analysis of Swift long GRBs with known redshift

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the spectral fitting is reliable only for fitting models with 2 or 3 parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, 2 parameters) and cut--off power law (CPL, 3 parameters) models to the time-integrated spectra of the 47 bursts, and present the corresponding parameters, their uncertainties, and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu peak energy Epk. For these GRBs, we calculate the energy fluence and the rest- frame isotropic-equivalent radiated energy, Eiso, as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a significant correlation between these two quantities (the "Amati" relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high energy power law index frozen to -2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift GRBs.Comment: 16 pages. To appear in MNRAS. Minor changes were introduced in this last versio

Recent results on GaAs detectors - 137

The present understanding of the charge collection in GaAs detectors with respect to the materials used and its processing are discussed. The radiation induced degradation of the charge collection efficiency and the leakage current of the detectors are summarised. The status of strip and pixel detectors for the ATLAS experiment are reported along with the latest results from GaAs X-ray detectors for non-high energy physics applications.Comment: 7 pages. 4 postscript figures + 1 postscript preprint logo + 1 LaTeX file + 1 style file. Also available at http://ppewww.ph.gla.ac.uk/preprints/97/05