237 research outputs found
Energy spectra of X-ray quasi-periodic oscillations in accreting black hole binaries
We investigate the energy dependencies of X-ray quasi-periodic oscillations
in black hole X-ray binaries. We analyze RXTE data on both the low- and
high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate
that they do not contain the thermal disk component, even though the latter is
present in the time averaged spectra. The disk thus does not seem to
participate in the oscillations. Moreover the QPO spectra are harder than the
time averaged spectra when the latter are soft, which can be modeled as a
result of modulations occurring in the hot plasma. The QPO spectra are softer
than the time averaged spectra when the latter are hard. The absence of the
disk component in the QPO spectra is true also for the high-frequency
(hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra
expected from the model of disk resonances.Comment: 4 pages, Proc. of IAU Symposium 238, "Black Holes from Stars to
Galaxies - across the range of masses", Prague, Aug 200
Geomagnetic field and altitude effects on the performance of future IACT arrays
The performance of IACT's arrays is sensitive to the altitude and geomagnetic
field (GF) of the observatory site. Both effects play important role in the
region of the sub-TeV gamma-ray measurements. We investigate the influence of
GF on detection rates and the energy thresholds for five possible locations of
the future CTA observatory using the Monte Carlo simulations. We conclude that
the detection rates of gamma rays and the energy thresholds of the arrays can
be fitted with linear functions of the altitude and the component of the GF
perpendicular to the shower axis core. These results can be directly
extrapolated for any possible localization of the CTA. In this paper we also
show the influence of both geophysical effects on the images of shower and
gamma/hadron separation.Comment: 4 pages, 6 figures, two-column. Contribution to ICRC 2013 proceeding
Underwater detection of dangerous substances: status the SABAT project
The Neutron Activation Analysis (NAA) plays an exceptional role in the modern
nuclear engineering, especially in detection of hazardous substances. However,
in the aquatic environment, there are still many problems to be solved for
effective usage of this technique. We present status of SABAT (Stoichiometry
Analysis By Activation Techniques), one of the projects aiming at construction
of an underwater device for non-invasive threat detection based on the NAA
On variability and spectral distortion of the fluorescent iron lines from black-hole accretion discs
We investigate properties of iron fluorescent line arising as a result of
illumination of a black hole accretion disc by an X-ray source located above
the disc surface. We study in details the light-bending model of variability of
the line, extending previous work on the subject.
We indicate bending of photon trajectories to the equatorial plane, which is
a distinct property of the Kerr metric, as the most feasible effect underlying
reduced variability of the line observed in several objects. A model involving
an X-ray source with a varying radial distance, located within a few central
gravitational radii around a rapidly rotating black hole, close to the disc
surface, may explain both the elongated red wing of the line profile and the
complex variability pattern observed in MCG--6-30-15 by XMM-Newton.
We point out also that illumination by radiation which returns to the disc
(following the previous reflection) contributes significantly to formation of
the line profile in some cases. As a result of this effect, the line profile
always has a pronounced blue peak (which is not observed in the deep minimum
state in MCG--6-30-15), unless the reflecting material is absent within the
innermost 2--3 gravitational radii.Comment: 24 pages, 22 figures. Accepted for publication in MNRA
System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector
Reconstruction of the image in Positron Emission Tomographs (PET) requires
the knowledge of the system response kernel which describes the contribution of
each pixel (voxel) to each tube of response (TOR). This is especially important
in list-mode reconstruction systems, where an efficient analytical
approximation of such function is required. In this contribution, we present a
derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear
physics and innovative technologies, Cracow, 03-06 June 201
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