1,189 research outputs found
Hadronic model for radio-to-TeV gamma-ray emission from PSR B1259-63
We discuss the implications of the recent X-ray and TeV gamma-ray
observations of the PSR B1259-63 system (a young rotation powered pulsar
orbiting a Be star) for the theoretical models of interaction of pulsar and
stellar winds. We show that previously considered models in which the pulsar
wind is purely electron loaded have problems to account for the observed
behaviour of the system in the TeV and X-ray bands. We develop a model in which
the broad band (radio, X-ray and high energy gamma-ray) emission from the
binary system is produced in result of collisions of GeV-TeV energy protons
accelerated by the pulsar wind and interacting with the stellar disk. In this
model the high energy gamma-rays are produced in the decays of secondary
neutral pions, while radio and X-ray emission are synchrotron and inverse
Compton emission produced by low-energy (< 100 MeV) electrons from the decays
of secondary charged pi mesons. This model can explain not only the observed
energy spectra, but also the correlations between TeV, X-ray and radio emission
components.Comment: Proceeding of "The multi messenger approach to high energy gamma ray
sources", Barcelona, June 200
Evaluating the Maximum Likelihood Method for Detecting Short-Term Variability of AGILE gamma-ray Sources
The AGILE space mission (whose instrument is sensitive in the energy ranges
18-60 keV, and 30 MeV - 50 GeV) has been operating since 2007. Assessing the
statistical significance of time variability of gamma-ray sources above 100 MeV
is a primary task of the AGILE data analysis. In particular, it is important to
check the instrument sensitivity in terms of Poisson modeling of the data
background, and to determine the post-trial confidence of detections. The goals
of this work are: (i) evaluating the distributions of the likelihood ratio test
for "empty" fields, and for regions of the Galactic plane; (ii) calculating the
probability of false detection over multiple time intervals. In this paper we
describe in detail the techniques used to search for short-term variability in
the AGILE gamma-ray source database. We describe the binned maximum likelihood
method used for the analysis of AGILE data, and the numerical simulations that
support the characterization of the statistical analysis. We apply our method
to both Galactic and extra-galactic transients, and provide a few examples.
After having checked the reliability of the statistical description tested with
the real AGILE data, we obtain the distribution of p-values for blind and
specific source searches. We apply our results to the determination of the
post-trial statistical significance of detections of transient gamma-ray
sources in terms of pre-trial values. The results of our analysis allow a
precise determination of the post-trial significance of {\gamma}-ray sources
detected by AGILE.Comment: 12 pages, 13 figures, 8 tables, accepted to A&
A variability analysis of low-latitude unidentified gamma-ray sources
We present a study of 40 low-latitude unidentified 3EG gamma-ray sources
which were found to be not positionally coincident with any known class of
potential gamma-ray emitters in the Galaxy (Romero, Benaglia & Torres, 1999).
We have performed a variability analysis which reveals that many of these 40
sources are variable. These sources have, in addition, a steep mean value of
the gamma-ray spectral index, , which, combined with
the high level of variability seems to rule out a pulsar origin. The positional
coincidences with uncatalogued candidates to supernova remnants were also
studied. Only 7 sources in the sample are spatially coincident with these
candidates, a result that is shown to be consistent with the expected level of
pure chance association. A complementary search for weak radio counterparts was
also conducted and the results are presented as an extensive table containing
all significant point-like radio sources within the 40 EGRET fields. We argue
that in order to produce the high variability, steep gamma-ray spectra, and
absence of strong radio counterparts observed in some of the gamma-ray sources
of our sample a new class of objects should be postulated, and we analyze a
viable candidate.Comment: Paper updated to match the accepted version to appear in Astronomy
and Astrophysics, 2001. Tables 5,6,7 and 8 are in ascii format and need to be
printed separately. they can also be obtained from
http://www.iar.unlp.edu.ar/garra Table 5 is 62 pages long. Download the
source to obtain the table
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