1,313 research outputs found
PulsarSpectrum: simulating gamma-ray pulsars for the GLAST mission
We present here an overview of PulsarSpectrum, a program that simulates the
gamma ray emission from pulsars. This simulator reproduces not only the basic
features of the observed gamma ray pulsars, but it can also simulate more
detailed effects related to pulsar timing. It is a very useful tool to
understand the GLAST capabilities in the pulsar science.Comment: 6 pages, 3 figures, contribution for "Third Workshop on Science with
the New Generation of High Energy Gamma-ray Experiments", May 2005, Cividale
del Friuli (UD), Ital
New VLT observations of the Fermi pulsar PSR J1048-5832
PSR J1048-5832 is a Vela-like (P=123.6 ms; tau~20.3 kyr) gamma-ray pulsar
detected by Fermi, at a distance of ~2.7 kpc and with a rotational energy loss
rate dot{E}_{SD} ~2 x 10^{36} erg/s. The PSR J1048-5832 field has been observed
with the VLT in the V and R bands. We used these data to determine the colour
of the object detected closest to the Chandra position (Star D) and confirm
that it is not associated with the pulsar. For the estimated extinction along
the line of sight, inferred from a re-analysis of the Chandra and XMM-Newton
spectra, the fluxes of Star D (V~26.7; R~25.8) imply a -0.13 < (V-R)_0 < 0.6.
This means that the PSR J1048-5832 spectrum would be unusually red compared to
the Vela pulsar.Moreover, the ratio between the unabsorbed optical and X-ray
flux of PSR J1048-5832 would be much higher than for other young pulsars. Thus,
we conclude that Star D is not the PSR J1048-5832 counterpart. We compared the
derived R and V-band upper limits (R>26.4; V>27.6) with the extrapolation of
the X and gamma-ray spectra and constrained the pulsar spectrum at
low-energies. In particular, the VLT upper limits suggest that the pulsar
spectrum could be consistent with a single power-law, stretching from the
gamma-rays to the optical.Comment: 5 pages, 2 figures, accepted for publication on Monthly Notices of
the Royal Astronomical Society Main Journa
Local seismic response studies in the north-western portion of the August 24th, 2016 Mw 6.0 earthquake affected area. The case of Visso village (Central Apennines).
In this work, we investigate the possible causes of the differential damaging observed in Visso village (Central Apennines, about 28 km north from the August 24th, 2016 Mw 6.0 earthquake epicenter). Following insights from the available geological cartography at 1:10.000 scale, a preliminary geophysical survey has been performed in the damaged area in order to constrain geometries and extent of the subsoil lithotypes. Then, these results have been used to retrieve a Vs profile close to the most heavily damaged buildings. This latter has been used as input for a numerical analysis aimed at deriving the motion at the ground level in the study area. In particular, a linear equivalent simulation has been performed by means of EERA code and the waveform has been obtained convolving the time history recorded during the August 24th, 2016 mainshock at Spoleto Monteluco (SPM) site. Our preliminary results indicate a possible correlation of damaging to the thickness and shape of the geological units. Nevertheless, further analyses are necessary to highlight any 2D basin and / non- linear soil behaviour effects in order to compare them to the intrinsic buildings vulnerability, according to the EMS98 guidelines
A candidate optical counterpart to the middle-aged gamma-ray pulsar PSR J1741-2054
We carried out deep optical observations of the middle-aged -ray
pulsar PSR J1741-2054 with the Very Large Telescope (VLT). We identified two
objects, of magnitudes and , at positions
consistent with the very accurate Chandra coordinates of the pulsar, the
faintest of which is more likely to be its counterpart. From the VLT images we
also detected the known bow-shock nebula around PSR J1741-2054. The nebula is
displaced by \sim 0\farcs9 (at the confidence level) with respect
to its position measured in archival data, showing that the shock propagates in
the interstellar medium consistently with the pulsar proper motion. Finally, we
could not find evidence of large-scale extended optical emission associated
with the pulsar wind nebula detected by Chandra, down to a surface brightness
limit of magnitudes arcsec. Future observations are needed
to confirm the optical identification of PSR J1741-2054 and characterise the
spectrum of its counterpart.Comment: 8 pages, 3 figures, Astrophysical Journal, in pres
Reading a GEM with a VLSI pixel ASIC used as a direct charge collecting anode
In MicroPattern Gas Detectors (MPGD) when the pixel size is below 100 micron
and the number of pixels is large (above 1000) it is virtually impossible to
use the conventional PCB read-out approach to bring the signal charge from the
individual pixel to the external electronics chain. For this reason a custom
CMOS array of 2101 active pixels with 80 micron pitch, directly used as the
charge collecting anode of a GEM amplifying structure, has been developed and
built. Each charge collecting pad, hexagonally shaped, realized using the top
metal layer of a deep submicron VLSI technology is individually connected to a
full electronics chain (pre-amplifier, shaping-amplifier, sample and hold,
multiplexer) which is built immediately below it by using the remaining five
active layers. The GEM and the drift electrode window are assembled directly
over the chip so the ASIC itself becomes the pixelized anode of a MicroPattern
Gas Detector. With this approach, for the first time, gas detectors have
reached the level of integration and resolution typical of solid state pixel
detectors. Results from the first tests of this new read-out concept are
presented. An Astronomical X-Ray Polarimetry application is also discussed.Comment: 11 pages, 14 figures, presented at the Xth Vienna Conference on
Instrumentation (Vienna, February 16-21 2004). For a higher resolution paper
contact [email protected]
Evaluation of site effects by means of 3D numerical modeling of the Palatine Hill, Roman Forum, and Coliseum archaeological area
In this study we perform 3D nonlinear analyses of seismic site response of the
Central Archaeological Area of Rome, which includes the Palatine Hill, Roman Forum, Circus
Maximus, and Coliseum. The geological bedrock of the study area is constituted by a Pliocene
marine sandy-clayey unit (MonteVaticano Formation, MVA). At top of this unit a continental Quaternary succession is superimposed. Previous studies available for this area (Pagliaroli et al. 2014a; Mancini et al. 2014; Moscatelli et al. 2014) enabled to define a detailed three-dimensional reconstruction of the subsoil conditions, characterized by complex surficial and buried morphology, lateral heterogeneities and dynamic properties of involved material, natural as well as anthropogenic.
The area of Rome is affected by earthquakes from different seismogenic districts: i) the
central Apennine mountain chain (D = 90–130km and M = 6.7–7.0); ii) the Colli Albani volcanic
district (D = 20km and M=5.5); iii) Rome area itself, which is characterized by rare, shallow,
low-magnitude events (M < 5). Both natural and artificial signals have been considered to define the input motion for the numerical modeling of the site response of the whole archeological area.
This was accomplished by means of the finite differences code FLAC3D. To evaluate the seismic hazard and, consequently, to assess possible priorities for seismic retrofitting of the monuments, contour maps of Housner intensity amplification ratio FH (defined as the ratio between Housner intensity at the top of the model and the corresponding input at the bedrock outcrop), are carried out. To cover the entire range of natural periods pertaining to the monuments in the examined area, FH was evaluated over three ranges of period: 0.1–0.5s, 0.5–1.0s, and 1.0–2.0s. Numerical results shown that: 1) within the range of periods 0.1–0.5s, high values of FH = 2.2–2.6 occur both in
correspondence of narrow valleys filled with soft alluvial deposits and at top of Palatine Hill; 2)
within the range of periods 0.5–1.0s, high values of FH occur in correspondence of the deepest valleys; 3) within the range of periods 1.0–2.0s, low values of FH occur except in correspondence of the deepest valleys.Results show a good agreement with the previous 2D numerical modeling and with the microzonation maps (Pagliaroli et al 2014a, b), even if interesting differences show up highlighting the usefulness of 3D modeling in such complex settings. Such results are significantly relevant for the monumental and archaeological heritage of this area, as it is highly vulnerable due to its old age and state of conservation
Long term effectiveness of electrochemotherapy for the treatment of lower lip squamous cell carcinoma
Purpose: Electrochemotherapy (ECT) is a therapeutic approach based on the local application of electrical pulses that permeabilize cell membranes to enhance the uptake of low-permeant chemotherapeutic agents, thus increasing their cytotoxic effects. Materials and Methods: Twenty-one patients with SCC of the lower lip were treated according to the European Standard Operating Procedures of Electrochemotherapy. Bleomycin (15,000 IU/m2 body surface area) was administered intravenously over a 1-minute period. Eight electrical pulses (amplitude, 1000 V/cm; duration, 100 μs) were generated and delivered at a repetition frequency of 5 kHz. Changes in tumor volume were used to assess treatment response. Results: Objective response (OR), complete response (CR), and partial response (PR) rates of 100%, 71.4%, and 28.6% respectively were demonstrated following a single session of ECT. ECT was well tolerated, and no adverse events occurred. Conclusions: Intravenous bleomycin-based ECT is a safe and effective therapy for SCC of the lower lip. ECT improves the quality-of-life of patients by preserving the function and the aesthetic appearance of the affected area. ECT provides a therapeutic option for elderly and frail patients who, due to their state of health, are not suitable for, or refuse surgical interventions
A phase-resolved Fermi-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere
The goal of our work is to study the mode changes of the radio-quiet
gamma-ray pulsar PSR J2021+4026 with improved detail. By accurately
characterizing variations in the gamma-ray spectrum and pulse profile, we aim
to relate the Fermi-LAT observations to theoretical models and interpret the
mode changes in terms of variations in the structure of a multipolar
dissipative magnetosphere. We continually monitored the rotational evolution
and the gamma-ray flux of PSR J2021+4026 using more than 13 years of Fermi-LAT
data with a binned likelihood approach. We clearly detect the previous mode
changes and confirm a more recent mode change that occurred around June 2020.
We investigated the features of the phase-resolved spectrum and pulse profile,
and we inferred the macroscopic conductivity, the electric field parallel to
the magnetic field, and the curvature radiation cutoff energy. These physical
quantities are related to the spin-down rate and the gamma-ray flux and
therefore are relevant to the theoretical interpretation of the mode changes.
We computed the relative variations in the best-fit parameters, finding typical
flux changes between 13% and 20%. Correlations appear between the gamma-ray
flux and the spectral parameters, as the peak of the spectrum shifts by about
10% toward lower energies when the flux decreases. The analysis of the pulse
profile reveals that the pulsed fraction of the light curve is larger when the
flux is low. We introduced a simple magnetosphere model that combines a dipole
field with a strong quadrupole component. We simulated magnetic field
configurations to determine the positions of the polar caps for different sets
of parameters, and we conclude that some configurations could explain the
observed multiwavelength variability.Comment: 12 pages, 5 figures, to be publish in Astronomy & Astrophysics,
submitted December 12, 2023, accepted February 17, 202
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