Showing papers by "F. Frontera published in 2013"

Average power density spectrum of long GRBs detected with BeppoSAX/GRBM and with Fermi/GBM

Abstract: From past experiments the average power density spectrum (PDS) of gamma-ray bursts (GRBs) with unknown redshift was found to be modelled from 0.01 to 1 Hz with a power law, f −α , with α broadly consistent with 5/3. Recent analysis of the Swift/Burst Alert Telescope (BAT) catalogue showed analogous results in the 15–150 keV band. We carried out the same analysis on the bright GRBs detected by BeppoSAX/Gamma-ray Burst Monitor (GRBM) and Fermi/Gamma-ray Burst Monitor (GBM). The BeppoSAX/GRBM data, in the energy range 40–700 keV and with 7.8 and 0.5 ms time resolutions, allowed us to explore for the first time the average PDS at very high frequencies (up to 1 kHz) and reveal a break around 1–2 Hz, previously found in Compton Gamma Ray Observatory/Burst and Transient Source Experiment data. The Fermi/GBM data, in the energy band 8–1000 keV, allowed us to explore for the first time the average PDS within a broad energy range. Our results confirm and extend the energy dependence of the PDS slope, according to which harder photons have shallower PDS.

IPN localizations of Konus short gamma-ray bursts

Abstract: Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the IPN consisted of up to eleven spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, $\sim$18 per year, exceeds that of many individual experiments.

Spectral evolution of the X-ray nova XTE J1859+226 during its outburst observed by BeppoSAX and RXTE

Abstract: We report results of an extensive analysis of the X-ray nova XTE J1859+226 observed with BeppoSAX and RXTE during its 1999 outburst. We modelled the source spectrum with a multicolour blackbody-like feature plus the generic Comptonization model bmc which has the advantage of providing spectral description of the emitted– radiation properties without assumptions on the underlying physical process. The multicolour component is attributed to the geometrically thin accretion disk, while the Comptonization spectrum is claimed to originate in the innermost sub-Keplerian region of the system (transition layer). We find that XTE J1859+226 covers all the spectral states typical of black-hole sources during its evolution across the outburst, however during the very high state, when the disk contribution to the total luminosity is more than 70% and the root mean square variability . 5%, the high-energy photon index is closer to a hard state value ( � 1.8). The bmc normalization and photon index well correlate with the radio emission, and we also observed a p ossible saturation effect of at the brightest radio emission levels. A strong pos itive correlation was found between the fraction of Comptonized seed photons and the observed integrated root mean square variability, which strengthens the idea that most of the fast variability in these systems is provided by the innermost Compton cloud, which may be also identified as a jet.

Light from the Cosmic Frontier: Gamma-Ray Bursts

Abstract: White paper submitted to ESA as a contribution to the deliberations on the science themes for the L2 and L3 mission opportunities

LAUE LENSES FOR HARD X–/SOFT γ–RAYS: NEW PROTOTYPE RESULTS

Abstract: The results obtained with the new Laue lens prototype built in the LARIX facility in the Physics Department of University of Ferrara will be present. Thanks to the methods adopted for improving the first prototype (SPIE conference in San Diego, Ferrari et al. 2009) here we present the results of the new prototype with improved performances in terms of point spread function (PSF) and spectral response.

The ground support equipment for the LAUE project

Abstract: The development of wide band Laue lens imaging technology is challenging, but has important potential applications in hard X- and γ-ray space instrumentation for the coming decades. The Italian Space Agency has funded a project dedicated to the development of a reliable technology to assemble a wide band Laue lens for use in space. The ground support equipment (GSE) for this project was fundamental to its eventual success... The GSE was implemented in a hard X-ray beam line built at the University of Ferrara and had the main purpose of controlling the assembly of crystals onto the Laue lens petal and to verify its final performance. The GSE incorporates the management and control of all the movements of the beam line mechanical subsystems and of the precision positioner (based on a Hexapod tool) of crystals on the petal, as well as the acquisition, storing and analysis of data obtained from the focal plane detectors (an HPGe spectrometer and an X-ray flat panel imager). The GSE is based on two PC’s connected through a local network: one, placed inside the beam line, to which all the movement subsystems and the detector I/O interface and on which all the management and acquisition S/W runs, the other in the control room allows the remote control and implements the offline analysis S/W of the data obtained from the detectors. Herein we report on the GSE structure with its interface with the beam line mechanical system, with the fine crystal positioner and with the focal plane detector. Furthermore we describe the SW developed for the handling of the mechanical movement subsystems and for the analysis of the detector data with the procedure adopted for the correct orientation of the crystals before their bonding on the lens petal support.