1,149 research outputs found
The Atmospheric Monitoring Strategy for the Cherenkov Telescope Array
The Imaging Atmospheric Cherenkov Technique (IACT) is unusual in astronomy as
the atmosphere actually forms an intrinsic part of the detector system, with
telescopes indirectly detecting very high energy particles by the generation
and transport of Cherenkov photons deep within the atmosphere. This means that
accurate measurement, characterisation and monitoring of the atmosphere is at
the very heart of successfully operating an IACT system. The Cherenkov
Telescope Array (CTA) will be the next generation IACT observatory with an
ambitious aim to improve the sensitivity of an order of magnitude over current
facilities, along with corresponding improvements in angular and energy
resolution and extended energy coverage, through an array of Large (23m),
Medium (12m) and Small (4m) sized telescopes spread over an area of order
~km. Whole sky coverage will be achieved by operating at two sites: one in
the northern hemisphere and one in the southern hemisphere. This proceedings
will cover the characterisation of the candidate sites and the atmospheric
calibration strategy. CTA will utilise a suite of instrumentation and analysis
techniques for atmospheric modelling and monitoring regarding pointing
forecasts, intelligent pointing selection for the observatory operations and
for offline data correction.Comment: 6 pages. To appear in the proceedings of the Adapting to the
Atmosphere conference 201
BeppoSAX observation of the X-ray binary pulsar Vela X-1
We report on the spectral (pulse averaged) and timing analysis of the ~ 20
ksec observation of the X-ray binary pulsar Vela X-1 performed during the
BeppoSAX Science Verification Phase. The source was observed in two different
intensity states: the low state is probably due to an erratic intensity dip and
shows a decrease of a factor ~ 2 in intensity, and a factor 10 in Nh. We have
not been able to fit the 2-100 keV continuum spectrum with the standard (for an
X--ray pulsar) power law modified by a high energy cutoff because of the
flattening of the spectrum in ~ 10-30 keV. The timing analysis confirms
previous results: the pulse profile changes from a five-peak structure for
energies less than 15 keV, to a simpler two-peak shape at higher energies. The
Fourier analysis shows a very complex harmonic component: up to 23 harmonics
are clearly visible in the power spectrum, with a dominant first harmonic for
low energy data, and a second one as the more prominent for energies greater
than 15 keV. The aperiodic component in the Vela X-1 power spectrum presents a
knee at about 1 Hz. The pulse period, corrected for binary motion, is 283.206
+/- 0.001 sec.Comment: 5 pages, 4 PostScript figure, uses aipproc.sty, to appear in
Proceedings of Fourth Compton Symposiu
Cyclotron lines in X-ray pulsars as a probe of relativistic plasmas in superstrong magnetic fields
The systematic search for the presence of cyclotron lines in the spectra of
accreting X-ray pulsars is being carried on with the BeppoSAX satellite since
the beginning of the mission. These highly successful observations allowed the
detection of cyclotron lines in many of the accreting X-ray pulsars observed.
Some correlations between the different measured parameters were found. We
present these correlations and discuss them in the framework of the current
theoretical scenario for the X-ray emission from these sources.Comment: 5 pages, 2 figures, uses aipproc.sty, to appear in Proceeding of
Fifth Compton Symposiu
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