118 research outputs found
Spectral analysis of 50 GRBs detected by HETE-2
FREGATE, the gamma-ray detector of HETE-2 is entirely dedicated to the study
of GRBs. Its main characteristic is its broad energy range, from 7 keV to 400
keV. This energy range can be further extended down to 2 keV using the data
from the WXM, the X-ray detector of HETE-2. Such a large energy range allows to
study in details the prompt emission of GRBs, determining with a high precision
their spectral parameters. Moreover, because this energy range extends at low
energies, the sample of GRBs detected by both FREGATE and WXM contains a
significant fraction of X-Ray Rich GRBs and X-Ray Flashes.
We present here the distributions of the spectral parameters mesured for the
time integrated spectra of 50 GRBs. We put emphasis on the distribution of the
low energy spectral index alpha. Because FREGATE and WXM detected all classes
of GRBs, we also discuss the connection between GRBs, X-Ray Rich GRBs and X-Ray
Flashes.Comment: 4 pages aipTEX, contribution to the 2003 GRB Conference, held at
Santa Fe,N
Search for neutrinos from transient sources with the ANTARES telescope and optical follow-up observations
The ANTARES telescope has the opportunity to detect transient neutrino
sources, such as gamma-ray bursts, core-collapse supernovae, flares of active
nuclei... To enhance the sensitivity to these sources, we have developed a new
detection method based on the optical follow-up of "golden" neutrino events
such as neutrino doublets coincident in time and space or single neutrinos of
very high energy. The ANTARES Collaboration has therefore implemented a very
fast on-line reconstruction with a good angular resolution. These
characteristics allow to trigger an optical telescope network; since February
2009. ANTARES is sending alert trigger one or two times per month to the two 25
cm robotic telescope of TAROT. This follow-up of such special events would not
only give access to the nature of the sources but also improves the sensitivity
for transient neutrino sources.Comment: 3 pages, 3 figures, Proceedings of the 31st ICRC, Lodz, Polan, July
200
Global solutions of approximation problems in Krein spaces
Three approximation problems in Krein spaces are studied, namely the
indefinite weighted least squares problem and the related problems of
indefinite abstract splines and smoothing. In every case, we analyze if the
problem has a solution for every point of the Krein space, the existence of a
linear and continuous operator that maps each data point to its solution and
when the associated operator problem considering the J-trace has a solution
A Search for Early Optical Emission from Short and Long Duration Gamma-ray Bursts
Gamma-ray bursts of short duration may harbor vital clues to the range of
phenomena producing bursts. However, recent progress from the observation of
optical counterparts has not benefitted the study of short bursts. We have
searched for early optical emission from six gamma-ray bursts using the ROTSE-I
telephoto array. Three of these events were of short duration, including GRB
980527 which is among the brightest short bursts yet observed. The data consist
of unfiltered CCD optical images taken in response to BATSE triggers delivered
via the GCN. For the first time, we have analyzed the entire 16 degree by 16
degree field covered for five of these bursts. In addition, we discuss a search
for the optical counterpart to GRB 000201, a well-localized long burst. Single
image sensitivities range from 13th to 14th magnitude around 10 s after the
initial burst detection, and 14 - 15.8 one hour later. No new optical
counterparts were discovered in this analysis suggesting short burst optical
and gamma-ray fluxes are uncorrelated.Comment: 8 pages, 2 figures, subm. to ApJ Let
The Chinese-French SVOM mission for GRBs studies
We present the SVOM (Space-based multi-band astronomical Variable Objects
Monitor) mission that the Chinese National Space Agency and the French Space
Agency have decided to jointly implement. SVOM has been designed to detect all
known types of gamma-ray bursts (GRBs), to provide fast and reliable GRB
positions, to measure the broadband spectral shape and temporal properties of
the GRB prompt emission, and to quickly identify the optical/near-infrared
afterglows of detected GRBs, including high-redshift ones. Scheduled to be in
orbit in the second half of the present decade, the SVOM satellite will carry a
very innovative scientific payload combining for the first time a wide field X-
and gamma-ray coded mask imager for GRB real-time localizations to few arcmin,
a non-imaging gamma-ray monitor, and two narrow-field instruments for the study
of the GRB early afterglow emission in the X-ray and visible bands. The SVOM
payload is complemented by ground-based instruments including a wide-field
camera to catch the GRB prompt emission in the visible band and two robotic
telescopes to measure the photometric properties of the early afterglow. A
particular attention is paid to the GRB follow-up in facilitating the
observation of the SVOM detected GRB by the largest ground based telescopes.Comment: 13 pages, 3 figures. To appear in a special issue of Comptes Rendus
Physique "GRB studies in the SVOM era", Eds. F. Daigne, G. Dubu
Reconciliation of the Disparate Gamma-Ray Burst Catalogs in the Context of a Cosmological Source Distribution
It is well known that Gamma-ray Burst spectra often display a break at
energies \simless 400 keV, with some exceptions extending to several MeV.\ \
Modeling of a cosmological source population is thus non-trivial when comparing
the catalogs from instruments with different energy windows since this spectral
structure is redshifted across the trigger channels at varying levels of
sensitivity. We here include this important effect in an attempt to reconcile
all the available data sets and show that a model in which bursts have a
``standard'' spectral break at keV and occur in a population uniformly
distributed in a \qo universe with no evolution can account very well
for the combined set of observations. We show that the source population cannot
be truncated at a minimum redshift beyond , and suggest
that a simple follow-on instrument to BATSE, with the same trigger window, no
directionality and 18 times better sensitivity might be able to distinguish
between a \qo and a \qo universe in years of full sky coverage,
provided the source population has no luminosity evolution.Comment: 12pages + 3 figures (available from [email protected]),
plainTeX, SO-93-112
Search for GRB counterparts
A state-of-the-art review is given on the search for counterparts of
-ray bursts. Particular emphasis is put on the search for flaring
counterparts, i.e. emission during or shortly after the gamma-ray emission.
With BACODINE working now for nearly one year, some of the highlights of the
herewith triggered follow-up studies will be summarized.Comment: 5 pages plain LATEX, no figures to appear in Proc. 17th Texas Symp.,
Munich, 12/199
Impact of Administrative Empowerment on Organizational Commitment (Field Study in Secondary Governmental Schools in Kingdom of Bahrain)
The study aims at exploring the impact of administrative empowerment on organizational commitment in secondary governmental schools in Kingdom of Bahrain, and recognizing the actual administrative empowerment in secondary governmental schools in Bahrain as well as the actual organizational commitment in the educational and administrative authority of secondary governmental schoolsâ teacher in Kingdom of Bahrain. The research has based on the descriptive analytical approach using questionnaire to stand on the opinion of educational and administrative panel in secondary governmental schools in Al Ganwbia and Al Mahraq provinces , representing 100% of the research sample. The total number was 108 educators from both educational and administrative panels, distributed on thirteen managers, thirty assistant managers and sixty five senior teachers. The research results indicated that there is static relation between administrative empowerment and organizational commitment in secondary governmental schools in Kingdom of Bahrain. Besides, the results showed that there are no static differences in administrative empowerment in secondary governmental schools in Bahrain due to demographic variables such as (sex, age and qualification). However, there are static differences in administrative empowerment in secondary governmental schools in Bahrain due to the variables of (experience and job title). Moreover, there are no static differences in organizational commitment in secondary governmental schools in Bahrain due to demographic variables such as (sex, age, and qualification), while there are static differences in organizational commitment in secondary governmental schools in Bahrain due to (experience and job title)variables. Keywords: Administrative empowerment â organizational commitmen
Thinplate Splines on the Sphere
In this paper we give explicit closed forms for the semi-reproducing kernels
associated with thinplate spline interpolation on the sphere. Polyharmonic or
thinplate splines for were introduced by Duchon and have become
a widely used tool in myriad applications. The analogues for are the thin plate splines for the sphere. The topic was first
discussed by Wahba in the early 1980's, for the case. Wahba
presented the associated semi-reproducing kernels as infinite series. These
semi-reproducing kernels play a central role in expressions for the solution of
the associated spline interpolation and smoothing problems. The main aims of
the current paper are to give a recurrence for the semi-reproducing kernels,
and also to use the recurrence to obtain explicit closed form expressions for
many of these kernels. The closed form expressions will in many cases be
significantly faster to evaluate than the series expansions. This will enhance
the practicality of using these thinplate splines for the sphere in
computations
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