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The scientific performance evaluation of a photon countingimaging system is presented. The detector is constituted by an ICCD camera with RbTe photocathode(optimized for UV radiation), and dedicated electronics for the acquisition and analysis ofthe events. For each photon event on the CCD, a real-time centroid calculation is performed, inorder to reach spatial resolution down to 25 μm FWHM. The system has been tested usingthe 182 cm telescope of the Asiago Observatory.A standard stars field through U Johnson filter,and the Crab pulsar (PSR 0531+21) were observed. From the photometric data, relative magnitudes of the standard stars have been derived, showing a goodlinearity of the detector in the range of flux under consideration, as expected fromprevious laboratory measurements.The pulsar's data have been processed by FFT and epoch foldingtechniques to testthe detector's timing performances in the highest resolutionmode (4.512 ms).These observations show that a space resolved time analysis ofperiodic sources can be performed with 10-7 s accuracy.

Attempts carried out in the past to detect linear or circular polarization of the Cosmic Microwave Background (CMB) radiation have produced only upper limits to the degree of polarization. These limits are at least two orders of magnitude above the expected value of few times 10(-6) or less, as suggested by models combined with the measured values of the CMB anisotropy. Because detection of polarization of the Cosmic Microwave Background will improve our knowledge of the phenomena which accompanied the evolution of the Universe, we built a polarimeter whose sensitivity, 2.1/root t(s) mK, is sufficient to detect linear or circular polarization at level of few mu K. Details of the system are presented. A testing campaign carried out with a partial prototype of our polarimeter, in a noisy environment, gave an upper limit to the degree of linear polarization of the CMB on angular scales of 14 degrees of similar to 8 . 10(-5), comparable to the limits at similar angular scales so far published. (C) 1998 Elsevier Science B.V.

The absolute temperature of the sky around the south celestial pole has been measured at ν=0.82 GHz (λ=36.6 cm) and ν=2.5 GHz (λ=12 cm) during an observing campaign from the Amundsen Scott Base at the South Pole in 1989 December. The antennas had an angular resolution of 18°× 23°. The measured temperatures of the sky have been used to determine the temperature of the cosmic background radiation in a frequency region where large deviations from a pure Planckian spectrum are expected.

The absolute temperature of the sky at delta = 46.5 deg has been measured at 600 MHz (50 cm wavelength) using a differential radiometer and a cold calibrator at liquid helium temperature. To separate the cosmic background radiation (CBR) from the remaining components of the sky temperature, observations at other frequencies, now under way, are necessary. A preliminary estimate of the CBR temperature at 600 MHz made using data of T(sky) at 600 MHz and maps of the sky at 408 MHz already in the literature gives T(cbr) = (3.0 + or - 1.2) K, in good agreement with previous measurements at nearby frequencies. 45 refs.

MCG 8-11-11 was observed in the 0.5-8 keV band with the EXOSAT observatory at 9 epochs in 1983-1986. Quasi-simultaneous UV observations were obtained in all but one case. The X-ray spectra are well fitted by absorbed power laws. Small variations of the spectral shape are found with softening of the source at brighter states. No correlation between UV and X-ray fluxes is apparent, suggesting an independent origin of the UV, consistent with the absence of indication of a soft X-ray excess. 32 refs.

The absolute temperature T(sky) of the diffuse radiation from the sky at 12 cm wavelength has been measured at various positions along declination +38 deg. At alpha = 23 h 08 m and delta = +38 deg, T(sky) = 2.94 + or - 0.14 K, the Galactic temperature = 0.22 + or - 0.18 K, and the CMB temperature = 2.72 + or - 0.15 K. The equivalent thermodynamic temperature of the CMB is 2.79 + or - 0.15 K. The separation between the Galactic background and the CMB background is discussed. The absence of large distortions adds new questions concerning the transition from the uniform universe where the CMB originated and the present universe where large matter condensations are present. 21 references.

LBL-18602 Preprint Lawrence Berkeley Laboratory UNIVERSITY O F C A L I F O R N I A Physics Division ReeeIuro LAWRENCE BERKELEY LABmUiTORy O t V l ' 9 1984- Submitted t o The A s t r o p h y s i c a l L e t t e r s t o the E d i t o r Journal, LIBRARY AND DOCUMENTS SECTION LOW-FREQUENCY MEASUREMENTS OF THE COSMIC BACKGROUND RADIATION SPECTRUM G.F. Smoot, G. De Amici, S.D. Friedman, C . W i t e b s k y , G. S i r o n i , G. B o n e l l i , N. Mandolesi, S. C o r t i g l i o n i , G. M o r i g i , R.B. P a r t r i d g e , L. Danese, and G. De Z o t t i November 1984 TWO-WEEK LOAN COPY This is a Library Circulating which may be borrowed Copy for two weeks. Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098