17 research outputs found
Wavelet Analysis and Lognormal Distributions in GRBs
A wavelet analysis has been performed on 80 intense gamma-ray bursts GRBs)
from the BATSE 3B catalog with durations longer than 2 seconds. The wavelet
analysis applied novel features developed for edge detection in image
processing and this filtering process was used to extract a fit to the
irregular GRB profile from the background. A straightforward algorithm was
subsequently used to identify statistically significant peaks in this profile.
The areas and FWHM of 270 peaks that were characterised as isolated were found
to be consistent with lognormal distributions. The distribution of time
intervals between peak maxima for all 963 identified peaks in the GRBs is also
presented.Comment: 5 pages, 4 figure
Localisation of gamma-ray interaction points in thick monolithic CeBr3 and LaBr3:Ce scintillators
Localisation of gamma-ray interaction points in monolithic scintillator
crystals can simplify the design and improve the performance of a future
Compton telescope for gamma-ray astronomy. In this paper we compare the
position resolution of three monolithic scintillators: a 28x28x20 mm3 (length x
breadth x thickness) LaBr3:Ce crystal, a 25x25x20 mm3 CeBr3 crystal and a
25x25x10 mm3 CeBr3 crystal. Each crystal was encapsulated and coupled to an
array of 4x4 silicon photomultipliers through an optical window. The
measurements were conducted using 81 keV and 356 keV gamma-rays from a
collimated 133Ba source. The 3D position reconstruction of interaction points
was performed using artificial neural networks trained with experimental data.
Although the position resolution was significantly better for the thinner
crystal, the 20 mm thick CeBr3 crystal showed an acceptable resolution of about
5.4 mm FWHM for the x and y coordinates, and 7.8 mm FWHM for the z-coordinate
(crystal depth) at 356 keV. These values were obtained from the full position
scans of the crystal sides. The position resolution of the LaBr3:Ce crystal was
found to be considerably worse, presumably due to the highly diffusive optical
in- terface between the crystal and the optical window of the enclosure. The
energy resolution (FWHM) measured for 662 keV gamma-rays was 4.0% for LaBr3:Ce
and 5.5% for CeBr3. The same crystals equipped with a PMT (Hamamatsu R6322-100)
gave an energy resolution of 3.0% and 4.7%, respectively
Experiences in firmware development for a CubeSat instrument payload
Recent advancements in gamma-ray detector technology have brought new opportunities to study gamma-ray bursts and other high-energy phenomena. However, there is a lack of dissemination on the development methods, tools and techniques used in the production of instrument flight firmware. This is understandable as firmware for spacecraft payloads may be proprietary or exceptionally hardware specific and so is not always published. However, this leaves a gap in the knowledge for CubeSat teams, especially those consisting of university students who may be building a custom spacecraft payload with limited initial experience. The Gamma-Ray Module (GMOD) on-board EIRSAT-1, a 2U CubeSat in the 2nd European Space Agency Fly Your Satellite! programme, is one such instrument. GMOD features a 25x25x40mm Scionix CeBr3 scintillator, coupled to an array of 16 (4x4) JSeries OnSemiconductor MicroFJ-60035-TSV silicon photomultipliers (SiPMs) with readout provided by the SIPHRA IDE3380 application specific integrated circuit. The instrument is supported by the Gamma-Ray Module motherboard which controls and configures the instrument, providing regulated voltage and current sources as well as generating time tagged event packets and a temporary on-board flash storage. At the core of this system is the Texas Instruments MSP430FR5994 microcontroller. A custom firmware was produced for the instrument by the EIRSAT-1 team over numerous cycles of testing and development to reliably perform the long duration tasks of readout, storage and transfer of time tagged event data to the EIRSAT-1 on-board computer. Recognising the value of sharing our experiences and pitfalls on firmware development with the wider CubeSat community, this paper will provide an introduction to GMOD, with focus primarily on the development approach of the firmware. The development, testing, version control, essential tools and an overview of how the resources provided by the device manufacturer were used will be examined, such that the lessons learned may be extended to other payloads from student-led mission
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
We propose to perform a continuously scanning all-sky survey from 200 keV to
80 MeV achieving a sensitivity which is better by a factor of 40 or more
compared to the previous missions in this energy range. The Gamma-Ray Imaging,
Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in
ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS
has its focus on the evolving, violent Universe, exploring a unique energy
window. We propose to investigate -ray bursts and blazars, the
mechanisms behind supernova explosions, nucleosynthesis and spallation, the
enigmatic origin of positrons in our Galaxy, and the nature of radiation
processes and particle acceleration in extreme cosmic sources including pulsars
and magnetars. The natural energy scale for these non-thermal processes is of
the order of MeV. Although they can be partially and indirectly studied using
other methods, only the proposed GRIPS measurements will provide direct access
to their primary photons. GRIPS will be a driver for the study of transient
sources in the era of neutrino and gravitational wave observatories such as
IceCUBE and LISA, establishing a new type of diagnostics in relativistic and
nuclear astrophysics. This will support extrapolations to investigate star
formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic
Vision 2010; 25 p., 25 figs; see also www.grips-mission.e
Localisation of gamma-ray interaction points in thick monolithic cebr3 and labr3:ce scintillators
Localisation of gamma-ray interaction points in monolithic scintillator crystals can simplify the design and improve the performance of a future Compton telescope for gamma-ray astronomy. In this paper we compare the position resolution of three monolithic scintillators: a 28x28x20 mm(3) (lengthxbreadth x thickness) LaBr3:Ce crystal, a 25x25x20 mm(3) CeBr3 crystal and a 25x25x10 mm(3) CeBr3 crystal. Each crystal was encapsulated and coupled to an array of 4x4 silicon photomultipliers through an optical window. The measurements were conducted using 81 keV and 356 keV gamma-rays from a collimated Ba-133 source. The 3D position reconstruction of interaction points was performed using artificial neural networks trained with experimental data. Although the position resolution was significantly better for the thinner crystal, the 20 mm thick CeBr3 crystal showed an acceptable resolution of about 5.4 mm FWHM for the x and y coordinates, and 7.8 mm FWHM for the z-coordinate (crystal depth) at 356 keV. These values were obtained from the full position scans of the crystal sides. The position resolution of the LaBr3: Ce crystal was found to be considerably worse, presumably due to the highly diffusive optical interface between the crystal and the optical window of the enclosure. The energy resolution (FWHM) measured for 662 keV gamma-rays was 4.0% for LaBr3: Ce and 5.5% for CeBr3. The same crystals equipped with a PMT (Hamamatsu R6322-100) gave an energy resolution of 3.0% and 4.7%, respectively