39 research outputs found
Fragmentation studies of high energy ions using CR39 nuclear track detectors
We report on the measurements of the total charge changing fragmentation
cross sections in high-energy nucleus-nucleus collisions using Fe, Si and Pb
incident ions. Several stacks of CR39 nuclear track detectors with different
target combinations were exposed at normal incidence to high energy accelerator
beams to integrated densities of about 2000 ions/cm^2. The nuclear track
detector foils were chemically etched, and ion tracks were measured using an
automatic image analyzer system. The cross section determination is based on
the charge identification of beam ions and their fragments and on the
reconstruction of their path through the stacks.Comment: 5 pages, 4 EPS figures. Corrected Eq. 3 and Table 1. Presented at the
10th Inter. Symp. Radiat. Phys., Coimbra, Portugal, 17-22 Sept. 200
Low energy polarization sensitivity of the Gas Pixel Detector
An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been
proposed to be included in many upcoming space missions to fill the gap of
about 30 years from the first (and to date only) positive measurement of
polarized X-ray emission from an astrophysical source. The estimated
sensitivity of the current prototype peaks at an energy of about 3 keV, but the
lack of readily available polarized sources in this energy range has prevented
the measurement of detector polarimetric performances.
In this paper we present the measurement of the Gas Pixel Detector
polarimetric sensitivity at energies of a few keV and the new, light, compact
and transportable polarized source that was devised and built to this aim.
Polarized photons are produced, from unpolarized radiation generated with an
X-ray tube, by means of Bragg diffraction at nearly 45 degrees.
The employment of mosaic graphite and flat aluminum crystals allow the
production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from
the diffraction of unpolarized continuum or line emission. The measured
modulation factor of the Gas Pixel Detector at these energies is in good
agreement with the estimates derived from a Monte Carlo software, which was up
to now employed for driving the development of the instrument and for
estimating its low energy sensitivity. In this paper we present the excellent
polarimetric performance of the Gas Pixel Detector at energies where the peak
sensitivity is expected. These measurements not only support our previous
claims of high sensitivity but confirm the feasibility of astrophysical X-ray
photoelectric polarimetry.Comment: 15 pages, 12 figures. Accepted for publication in NIM
Search for Intermediate Mass Magnetic Monopoles and Nuclearites with the SLIM experiment
SLIM is a large area experiment (440 m2) installed at the Chacaltaya cosmic
ray laboratory since 2001, and about 100 m2 at Koksil, Himalaya, since 2003. It
is devoted to the search for intermediate mass magnetic monopoles (107-1013
GeV/c2) and nuclearites in the cosmic radiation using stacks of CR39 and
Makrofol nuclear track detectors. In four years of operation it will reach a
sensitivity to a flux of about 10-15 cm-2 s-1 sr-1. We present the results of
the calibration of CR39 and Makrofol and the analysis of a first sample of the
exposed detector.Comment: Presented at the 22nd ICNTS, Barcelona 200
Design of a CZT Gamma-Camera for GRB and Fast Transient Follow-up: a Wide-Field-Monitor for the EDGE Mission
The success of the SWIFT/BAT and INTEGRAL missions has definitely opened a
new window for follow-up and deep study of the transient gamma-ray sky. This
now appears as the access key to important progresses in the area of
cosmological research and deep understanding of the physics of compact objects.
To detect in near real-time explosive events like Gamma-Ray bursts,
thermonuclear flashes from Neutron Stars and other types of X-ray outbursts we
have developed a concept for a wide-field gamma-ray coded mask instrument
working in the range 8-200 keV, having a sensitivity of 0.4 ph cm-2 s-1 in 1s
(15-150 keV) and arcmin location accuracy over a sky region as wide as 3sr.
This scientific requirement can be achieved by means of two large area, high
spatial resolution CZT detection planes made of arrays of relatively large
(~1cm2) crystals, which are in turn read out as matrices of smaller pixels. To
achieve such a wide Field-Of-View the two units can be placed at the sides of a
S/C platform serving a payload with a complex of powerful X-ray instruments, as
designed for the EDGE mission. The two units will be equipped with powerful
signal read out system and data handling electronics, providing accurate
on-board reconstruction of the source positions for fast, autonomous target
acquisition by the X-ray telescopes.Comment: 9 pages, 7 figures, SPIE Conference on UV, X-ray, and Gamma-Ray
Instrumentation for Astronomy, San Diego 26-30 August 200
Multiwavelength observations of 3C 454.3 II. The AGILE 2007 December campaign
We report on the second AGILE multiwavelength campaign of the blazar 3C 454.3
during the first half of December 2007. This campaign involved AGILE, Spitzer,
Swift,Suzaku,the WEBT consortium,the REM and MITSuME telescopes,offering a
broad band coverage that allowed for a simultaneous sampling of the synchrotron
and inverse Compton (IC) emissions.The 2-week AGILE monitoring was accompanied
by radio to optical monitoring by WEBT and REM and by sparse observations in
mid-Infrared and soft/hard X-ray energy bands performed by means of Target of
Opportunity observations by Spitzer, Swift and Suzaku, respectively.The source
was detected with an average flux of~250x10^{-8}ph cm^-2s^-1 above 100
MeV,typical of its flaring states.The simultaneous optical and gamma-ray
monitoring allowed us to study the time-lag associated with the variability in
the two energy bands, resulting in a possible ~1-day delay of the gamma-ray
emission with respect to the optical one. From the simultaneous optical and
gamma-ray fast flare detected on December 12, we can constrain the delay
between the gamma-ray and optical emissions within 12 hours. Moreover, we
obtain three Spectral Energy Distributions (SEDs) with simultaneous data for
2007 December 5, 13, 15, characterized by the widest multifrequency coverage.
We found that a model with an external Compton on seed photons by a standard
disk and reprocessed by the Broad Line Regions does not describe in a
satisfactory way the SEDs of 2007 December 5, 13 and 15. An additional
contribution, possibly from the hot corona with T=10^6 K surrounding the jet,
is required to account simultaneously for the softness of the synchrotron and
the hardness of the inverse Compton emissions during those epochs.Comment: 13 pages, 8 figures, 2 tables, Accepted for publication in Ap
First AGILE Catalog of High Confidence Gamma-Ray Sources
We present the first catalog of high-confidence gamma-ray sources detected by
the AGILE satellite during observations performed from July 9, 2007 to June 30,
2008. Catalogued sources are detected by merging all the available data over
the entire time period. AGILE, launched in April 2007, is an ASI mission
devoted to gamma-ray observations in the 30 MeV - 50 GeV energy range, with
simultaneous X-ray imaging capability in the 18-60 keV band. This catalog is
based on Gamma-Ray Imaging Detector (GRID) data for energies greater than 100
MeV. For the first AGILE catalog we adopted a conservative analysis, with a
high-quality event filter optimized to select gamma-ray events within the
central zone of the instrument Field of View (radius of 40 degrees). This is a
significance-limited (4 sigma) catalog, and it is not a complete flux-limited
sample due to the non-uniform first year AGILE sky coverage. The catalog
includes 47 sources, 21 of which are associated with confirmed or candidate
pulsars, 13 with Blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2
with SNRs, 1 with a colliding-wind binary system, 8 with unidentified sources.Comment: Revised version, 15 pages, 3 figures, 3 tables. To be published in
Astronomy and Astrophysics. Text improved and clarified. Refined analysis of
complex regions of the Galactic plane yields a new list of high-confidence
sources including 47 sources (compared with the 40 sources appearing in the
first version
AGILE detection of extreme gamma-ray activity from the blazar PKS 1510-089 during March 2009. Multifrequency analysis
We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089
observed by AGILE in March 2009. In the same period a radio-to-optical
monitoring of the source was provided by the GASP-WEBT and REM. Moreover,
several Swift ToO observations were triggered, adding important information on
the source behaviour from optical/UV to hard X-rays. We paid particular
attention to the calibration of the Swift/UVOT data to make it suitable to the
blazars spectra. Simultaneous observations from radio to gamma rays allowed us
to study in detail the correlation among the emission variability at different
frequencies and to investigate the mechanisms at work. In the period 9-30 March
2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2
s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on
daily integration. The gamma-ray activity occurred during a period of
increasing activity from near-IR to UV, with a flaring episode detected on
26-27 March 2009, suggesting that a single mechanism is responsible for the
flux enhancement observed from near-IR to UV. By contrast, Swift/XRT
observations seem to show no clear correlation of the X-ray fluxes with the
optical and gamma-ray ones. However, the X-ray observations show a harder
photon index (1.3-1.6) with respect to most FSRQs and a hint of
harder-when-brighter behaviour, indicating the possible presence of a second
emission component at soft X-ray energies. Moreover, the broad band spectrum
from radio-to-UV confirmed the evidence of thermal features in the optical/UV
spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand,
during 25-26 March 2009 a flat spectrum in the optical/UV energy band was
observed, suggesting an important contribution of the synchrotron emission in
this part of the spectrum during the brightest gamma-ray flare, therefore a
significant shift of the synchrotron peak.Comment: 13 pages, 7 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic