43 research outputs found
Volcanoes muon imaging using Cherenkov telescopes
A detailed understanding of a volcano inner structure is one of the
key-points for the volcanic hazards evaluation. To this aim, in the last
decade, geophysical radiography techniques using cosmic muon particles have
been proposed. By measuring the differential attenuation of the muon flux as a
function of the amount of rock crossed along different directions, it is
possible to determine the density distribution of the interior of a volcano. Up
to now, a number of experiments have been based on the detection of the muon
tracks crossing hodoscopes, made up of scintillators or nuclear emulsion
planes. Using telescopes based on the atmospheric Cherenkov imaging technique,
we propose a new approach to study the interior of volcanoes detecting the
Cherenkov light produced by relativistic cosmic-ray muons that survive after
crossing the volcano. The Cherenkov light produced along the muon path is
imaged as a typical annular pattern containing all the essential information to
reconstruct particle direction and energy. Our new approach offers the
advantage of a negligible background and an improved spatial resolution. To
test the feasibility of our new method, we have carried out simulations with a
toy-model based on the geometrical parameters of ASTRI SST-2M, i.e. the imaging
atmospheric Cherenkov telescope currently under installation onto the Etna
volcano. Comparing the results of our simulations with previous experiments
based on particle detectors, we gain at least a factor of 10 in sensitivity.
The result of this study shows that we resolve an empty cylinder with a radius
of about 100 m located inside a volcano in less than 4 days, which implies a
limit on the magma velocity of 5 m/h.Comment: 21 pages, 21 figures, in press on Nuclear Inst. and Methods in
Physics Research, A. Final version published online: 3-NOV-201
The puzzling source IGR J17361-4441 in NGC 6388: a possible planetary tidal disruption event
On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361-4441
near the centre of the globular cluster NGC 6388. Follow up observations with
Chandra showed the position of the transient was inconsistent with the cluster
dynamical centre, and thus not related to its possible intermediate mass black
hole. The source showed a peculiar hard spectrum (Gamma \approx 0.8) and no
evidence of QPOs, pulsations, type-I bursts, or radio emission. Based on its
peak luminosity, IGR J17361-4441 was classified as a very faint X-ray
transient, and most likely a low-mass X-ray binary. We re-analysed 200 days of
Swift/XRT observations, covering the whole outburst of IGR J17361-4441 and find
a t^{-5/3} trend evident in the light curve, and a thermal emission component
that does not evolve significantly with time. We investigate whether this
source could be a tidal disruption event, and for certain assumptions find an
accretion efficiency epsilon \approx 3.5E-04 (M_{Ch}/M) consistent with a
massive white dwarf, and a disrupted minor body mass M_{mb}=1.9E+27(M/M_{Ch}) g
in the terrestrial-icy planet regime. These numbers yield an inner disc
temperature of the order kT_{in} \approx 0.04 keV, consistent with the
blackbody temperature of kT_{in} \approx 0.08 keV estimated by spectral
fitting. Although the density of white dwarfs and the number of free-floating
planets are uncertain, we estimate the rate of planetary tidal disruptions in
NGC 6388 to be in the range 3E-06 to 3E-04 yr^{-1}. Averaged over the Milky Way
globular clusters, the upper limit value corresponds to 0.05 yr^{-1},
consistent with the observation of a single event by INTEGRAL and Swift.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Main Journal on 2014 July 16; 9 pages, 5 figures. Added references;
corrected typo
Sub-luminous X-ray Bursters Unveiled with INTEGRAL
In 2005 March 22nd, the INTEGRAL satellite caught a type-I X-ray burst from
the unidentified source XMMU J174716.1-281048, serendipitously discovered with
XMM-Newton in 2003. Based on the type-I X-ray burst properties, we derived the
distance of the object and suggested that the system is undergoing a prolonged
accretion episode of many years. We present new data from a Swift/XRT campaign
which strengthen this suggestion. AX J1754.2-2754 was an unclassified source
reported in the ASCA catalogue of the Galactic Centre survey. INTEGRAL observed
a type-I burst from it in 2005, April 16th. Recently, a Swift ToO allowed us to
refine the source position and establish its persistent nature.Comment: To be published in AIP Proceedings - Conference 'A Population
Explosion: The Nature and Evolution of X-ray Binaries in Diverse
Environments', 28 Oct - 2 Nov, St. Petersburg Beach, F
Apparatus and method for non-invasive inspection of solid bodies by muon imaging
The present invention has application in the technical field of measuring instruments and it relates to an apparatus for non-invasive inspection of solid bodies by muon imaging usable in civil engineering, archeology, volcanology, tectonics and everywhere a radiographic and/or tomographic non-destructive inspection of geological and/or engineering structures, even of large dimensions, is necessary The invention further relates to a method for non-invasive inspection by muon imaging implementable by said apparatus
Spectral and timing evolution of the bright failed outburst of the transient black hole Swift J174510.8-262411
We studied time variability and spectral evolution of the Galactic black hole transient Swift J174510.8-262411 during the first phase of its outburst. INTEGRAL and Swift observations collected from 2012 September 16 until October 30 have been used. The total squared fractional rms values did not drop below 5% and QPOs, when present, were type-C, indicating that the source never made the transition to the soft-intermediate state. Even though the source was very bright (up to 1 Crab in hard X-rays), it showed a so called failed outburst as it never reached the soft state. XRT and IBIS broad band spectra, well represented by a hybrid thermal/non-thermalComptonisationmodel, showed physical parameters characteristic of the hard and intermediate states. In particular, the derived temperature of the geometrically thin disc black body was about 0.6 keV at maximum.We found a clear decline of the optical depth of the corona electrons (close to values of 0.1), as well as of the total compactness ratio lh/ls. The hard-to-hard/intermediate state spectral transition is mainly driven by the increase in the soft photon flux in the corona, rather than small variations of the electron heating. This, associated with the increasing of the disc temperature, is consistent with a disc moving towards the compact object scenario, i.e. the truncated-disc model. Moreover, this scenario is consistent with the decreasing fractional squared rms and increasing of the noise and QPO frequency. In our final group of observations, we found that the contribution from the non-thermal Comptonisation to the total power supplied to the plasma is 0.59+0.02/-0.05 and that the thermal electrons cool to kTe<26 keV