15,142 research outputs found
A method of detecting radio transients
Radio transients are sporadic signals and their detection requires that the
backends of radio telescopes be equipped with the appropriate hardware and
software to undertake this. Observational programs to detect transients can be
dedicated or they can piggy-back on observations made by other programs. It is
the single-dish single-transient (non-periodical) mode which is considered in
this paper. Because neither the width of a transient nor the time of its
arrival is known, a sequential analysis in the form of a cumulative sum (cusum)
algorithm is proposed here. Computer simulations and real observation data
processing are included to demonstrate the performance of the cusum. The use of
the Hough transform is here proposed for the purpose of non-coherent
de-dispersion. It is possible that the detected transients could be radio
frequency interferences (RFI) and a procedure is proposed here which can
distinguish between celestial signals and man-made RFI. This procedure is based
on an analysis of the statistical properties of the signals
Optimizing momentum resolution with a new fitting method for silicon-strip detectors
A new fitting method is explored for momentum reconstruction of tracks in a
constant magnetic field for a silicon-strip tracker. Substantial increases of
momentum resolution respect to standard fit is obtained. The key point is the
use of a realistic probability distribution for each hit (heteroscedasticity).
Two different methods are used for the fits, the first method introduces an
effective variance for each hit, the second method implements the maximum
likelihood search. The tracker model is similar to the PAMELA tracker. Each
side, of the two sided of the PAMELA detectors, is simulated as momentum
reconstruction device. One of the two is similar to silicon micro-strip
detectors of large use in running experiments. Two different position
reconstructions are used for the standard fits, the -algorithm (the best
one) and the two-strip center of gravity. The gain obtained in momentum
resolution is measured as the virtual magnetic field and the virtual
signal-to-noise ratio required by the two standard fits to reach an overlap
with the best of two new methods. For the best side, the virtual magnetic field
must be increased 1.5 times respect to the real field to reach the overlap and
1.8 for the other. For the high noise side, the increases must be 1.8 and 2.0.
The signal-to-noise ratio has similar increases but only for the
-algorithm. The signal-to-noise ratio has no effect on the fits with the
center of gravity. Very important results are obtained if the number N of
detecting layers is increased, our methods provide a momentum resolution
growing linearly with N, much higher than standard fits that grow as the
.Comment: This article supersedes arXiv:1606.03051, 22 pages and 10 figure
An approach for the detection of point-sources in very high resolution microwave maps
This paper deals with the detection problem of extragalactic point-sources in
multi-frequency, microwave sky maps that will be obtainable in future cosmic
microwave background radiation (CMB) experiments with instruments capable of
very high spatial resolution. With spatial resolutions that can be of order of
0.1-1.0 arcsec or better, the extragalactic point-sources will appear isolated.
The same holds also for the compact structures due to the Sunyaev-Zeldovich
(SZ) effect (both thermal and kinetic). This situation is different from the
maps obtainable with instruments as WMAP or PLANCK where, because of the
smaller spatial resolution (approximately 5-30 arcmin), the point-sources and
the compact structures due to the SZ effect form a uniform noisy background
(the "confusion noise"). Hence, the point-source detection techniques developed
in the past are based on the assumption that all the emissions that contribute
to the microwave background can be modeled with homogeneous and isotropic
(often Gaussian) random fields and make use of the corresponding spatial
power-spectra. In the case of very high resolution observations such an
assumption cannot be adopted since it still holds only for the CMB. Here, we
propose an approach based on the assumption that the diffuse emissions that
contribute to the microwave background can be locally approximated by
two-dimensional low order polynomials. In particular, two sets of numerical
techniques are presented containing two different algorithms each. The
performance of the algorithms is tested with numerical experiments that mimic
the physical scenario expected for high Galactic latitude observations with the
Atacama Large Millimeter/Submillimeter Array (ALMA).Comment: Accepted for publication on "Astronomy & Astrophysics". arXiv admin
note: substantial text overlap with arXiv:1206.4536 Replaced version is the
accepted one and published in A&
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