1,206 research outputs found
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
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
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]
Somatotropic gene response to recombinant growth hormone treatment in buffalo leucocytes
The use of recombinant bovine growth hormone (rbGH) to increase milk yield in cows is banned in some countries. In others, where it is authorised, it has triggered harsh debates on labelling of dairy products. If many studies have been performed on bovines, there is a lack of information on buffaloes, which are sometimes treated with rbGH and reÂpresent an important economical resource for dairy products in some countries. Analytical methods with legal value for surveillance of rbGH treatments do not yet exist. Research on gene expression biomarkers is one of the most promising approaches to this purpose. For this reason, we treated five buffaloes for 10 weeks with a sustained-release formulation of rbGH and analysed the response of 20 somatotropic axis genes in leucocytes by real-time polymerase chain reaction. Overall changes in gene expression levels were of low magnitude and sometimes affected by the ‘time’ factor. Only the IGFBP-1 gene showed a significant under-expression (about two-fold; p <0.001) in treated animals. Taken together, these results give evidence that expression analysis of the somatotropic axis genes in leucoÂcytes is little helpful for discrimination of rbGH-treated buffaloes, but do not exclude that another array of genes could provide useful patterns of variation
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
VLT Suzaku observations of the Fermi pulsar PSR J1028-5819
We used optical images taken with the Very Large Telescope (VLT) in the B and
V bands to search for the optical counterpart of PSR J1028-5819 or constrain
its optical brightness. At the same time, we used an archival Suzaku
observation to confirm the preliminary identification of the pulsar's X-ray
counterpart obtained by Swift. Due to the large uncertainty on the pulsar's
radio position and the presence of a bright (V = 13.2) early F-type star at <
4", we could not detect its counterpart down to flux limits of B~25.4 and V
~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku
observations, we found that the X-ray spectrum of the pulsar's candidate
counterpart is best-fit by a power-law with spectral index 1.7 +/- 0.2 and an
absorption column density NH < 10^21 cm-2, which would support the proposed
X-ray identification. Moreover, we found possible evidence for the presence of
diffuse emission around the pulsar. If real, and associated with a pulsar wind
nebula (PWN), its surface brightness and angular extent would be compatible
with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
Multiwavelength observations of PSR J2021+4026 across a mode change reveal a phase shift in its X-ray emission
Context. We have investigated the multiwavelength emission of PSR J2021+4026,
the only isolated gamma-ray pulsar known to be variable, which in October 2011
underwent a simultaneous change in gamma-ray flux and spin-down rate, followed
by a second mode change in February 2018. Multiwavelength monitoring is crucial
to understand the physics behind these events and how they may have affected
the structure of the magnetosphere. Aims.The monitoring of pulse profile
alignment is a powerful diagnostic tool for constraining magnetospheric
reconfiguration. We aim to investigate timing or flux changes related to the
variability of PSR J2021+4026 via multiwavelength observations, including
gamma-ray observations from Fermi-LAT, X-ray observations from XMM-Newton, and
a deep optical observation with the Gran Telescopio Canarias.Methods. We
performed a detailed comparison of the timing features of the pulsar in gamma
and X-rays and searched for any change in phase lag between the phaseogram
peaks in these two energy bands. Although previous observations did not detect
a counterpart in visible light, we also searched for optical emission that
might have increased due to the mode change, making this pulsar detectable in
the optical. Results.We have found a change in the gamma-to X-ray pulse profile
alignment by 0.210.02 in phase, which indicates that the first mode change
affected different regions of the pulsar magnetosphere. No optical counterpart
was detected down to g'=26.1 and r'=25.3. Conclusions.We suggest that the
observed phase shift could be related to a reconfiguration of the connection
between the quadrupole magnetic field near the stellar surface and the dipole
field that dominates at larger distances. This is consistent with the picture
of X-ray emission coming from the heated polar cap and with the simultaneous
flux and frequency derivative change observed during the mode changes.Comment: 9 pages, 7 figures, 1 Table. Accepted for publication in Astronomy
and Astrophysics (A&A
- …