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The near infrared emission (NIR) of radio quiet active galactic nuclei is commonly attributed to dust, absorbing and re-emitting some of the nuclear UV radiation. The dust can survive only at distances larger than a few light months, and any rapid variation of the nuclear radiation, on timescales of a day or less, will be completely smeared out.
The TOCAMM (TOrino CAgliari Measuring Machine) project undertaken jointly between Torino and Cagliari Astronomical Observatories aimed to convert the old measuring machine ASCORECORD into an automatic and impersonal one. This program is intended to contribute to the link of the HIPPARCOS Catalogue to the ICRS through the determination of precise position of optical counterparts of 80 extragalactic radiosources taken from the IERS list and to investigate the astrometric accuracy of the Guide Star Catalog (version 1 and 2). The calibration test phase, carried out first at the Astronomical Observatory of Torino and after at Cagliari Observatory, where the machine has been now installed, indicate that the available positional accuracy is about 0.5 microns in both x and y coordinates.
For more than 20 years it has been known that extragalactic radio sources contain up to 1060–1062 ergs in the form of relativistic electrons and magnetic fields. One arrives at these figures if one assumes that the radio emission is due to the synchrotron process and the source contains an equal amount of energy in electrons and fields (Burbidge 1956). Any deviation from the postulated equipartition increases the energy required to account for the observed luminosities. Some authors believe that the real demands on the energy source may be still higher because of the probable presence of high energy protons. The ratio Ep/Ee is determined by the way in which particles gain and lose energy, and it is impossible to estimate it a priori. Observationally one has two conflicting lines of evidence: (a) in galactic cosmic rays one measures (Ep/Ee) ≃ 102; (b) in the Crab Nebula one infers (Ep/Ee) ≲ 1 (otherwise the dynamical pressure of the proton gas would cause a nebular expansion much faster than observed).
This paper is devoted to a discussion of the rapid variability observed in γ-ray blazars. We do this in the framework of a widely accepted scenario, according to which the blazar emission arises from a jet, i.e. a continuous flow of relativistic fluid, with perturbations occasionally superimposed. The jet is assumed to have a bulk Lorentz factor Γ ≫ 1, and length z and radius r such that r ã z/Γ.
The frequency-doubling efficiency and resultant
focal spot quality of a large aperture (140 × 89
mm) subpicosecond, chirped pulse amplified (CPA) 1054-nm
beam for laser–matter interaction studies has been
investigated using the Vulcan Nd:glass laser system (Danson
et al. 1998). The effect of B-integral on the
CPA beam quality was studied and is shown not to be the
dominant cause of the observed frequency-doubled beam break-up.
Conversion efficiency tests were carried out on small aperture
KDP (type 1) crystals at a range of incident intensities
up to 3 × 1011 W/cm2 giving
the optimum crystal thickness for pulses in the 0.3–3
ps region. A large-aperture frequency-doubled beam was
commissioned and delivered pulses of over 10 TW onto target
for an electron acceleration experiment.
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