Deg FWHM Research Articles

A Circularly Symmetric Antenna Design With High Polarization Purity and Low Spillover

We describe the development of two circularly symmetric antennas with high polarization purity and low spillover. Both were designed to be used in an all-sky polarization and intensity survey at 5 GHz (the C-Band All-Sky Survey, C-BASS). The survey requirements call for very low levels of cross-polar leakage and far-out sidelobes. Two different existing antennas, with 6.1-m and 7.6-m diameter primaries, were adapted by replacing the feed and secondary optics, resulting in identical beam performances of 0.73deg FWHM, cross-polarization better than -50 dB, and far-out sidelobes below -70 dB. The polarization purity was realized by using a symmetric low-loss dielectric foam support structure for the secondary mirror, avoiding the need for secondary support struts. Ground spill-over was largely reduced by using absorbing baffles around the primary and secondary mirrors, and by the use of a low-sidelobe profiled corrugated feedhorn. The 6.1-m antenna and receiver have been completed and test results show that the optics meet their design goals.

Constraints on the multi-TeV particle population in the Coma galaxy cluster with HESS observations

The H.E.S.S. (High Energy Stereoscopic System) telescopes observed Coma for ~8hr in a search for gamma-ray emission at energies >1TeV. The large 3.5deg FWHM field of view of H.E.S.S. is ideal for viewing a range of targets at various sizes including the Coma cluster core, the radio-relic (1253+275) and merger/infall (NGC 4839) regions to the southwest, and features greater than deg away. No evidence for point-like nor extended TeV gamma-ray emission was found and upper limits to the TeV flux F(E) for E>1, >5, and >10TeV were set for the Coma core and other regions. Converting these limits to an energy flux E^2F(E) the lowest or most constraining is the E>5TeV upper limit for the Coma core (0.2deg radius) at ~8Crab flux units or ~10^{-13}ph cm^{-2} s^{-1}. The upper limits for the Coma core were compared with a prediction for the gamma-ray emission from proton--proton interactions, the level of which ultimately scales with the mass of the Coma cluster. A direct constraint using our most stringent limit for E>5 TeV, on the total energy content in non-thermal protons with injection energy spectrum proportional to E^{-2.1} and spatial distribution following the thermal gas in the cluster, is found to be ~0.2 times the thermal energy, or ~10^{62}erg. The E>5 TeV gamma-ray threshold in this case corresponds to cosmic-ray proton energies >50TeV. Our upper limits rule out the most optimistic theoretical models for gamma ray emission from clusters and complement radio observations which constrain the cosmic ray content in clusters at significantly lower proton energies, subject to assumptions on the magnetic field strength.

Structure analysis of terbium aluminosilicate glass

Glasses rich in rare-earth ions have attracted a lot of interest due to their applications in optical isolators and optical amplifiers. Integrating optical isolators with various optoelectronic devices allows sources to be integrated with lower costs, easier alignment and longer lifetimes. Glasses rich in rare-earth ions have large Verdet constants, so large Faraday rotations. Among the rare-earth ions used in paramagnetic glasses, Tb3+ ions have largest Faraday rotation per ion and the glasses are transparent down to 1.6um. These glasses can also avoid the temperature incompatibility and lattice match problems which are encountered when magneto-optical garnets mare used for integration. The Tb3+doping is also widely used in optical amplifiers. In this paper we have explored the metastable phases present in the sputtered Tb-Al-Si-O system in order to fabricate paramagnetic films with the highest possible Faraday rotations, lowest optical losses and that are easily integrated with semiconductors. A broad peak was observed in the microdiffraction pattern around 2θ= 30deg. This peak corresponded with the close-packed Tb-O plane spacing (111 for FCC Tb4O7 or 002 for HCP Tb2O3), but it was an “amorphous” peak with a 5 deg FWHM. Amorphous films were obtained even when the Tb concentrations were very high. Since high concentrations of Tb are known to devitrify glasses, the discovery of a high-Tb concentrated glass is exciting.

Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured byMAP

We study the effects of diffuse Galactic, far-infrared extragalactic source, and radio point source emission on the cosmic microwave background (CMB) anisotropy data anticipated from the MAP experiment. We focus on the correlation function and genus statistics measured from mock MAP foreground-contaminated CMB anisotropy maps generated in a spatially-flat cosmological constant dominated cosmological model. Analyses of the simulated MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground effects on the correlation function are small compared with cosmic variance. However, the Galactic emission, even just from the region with |b| > 20 deg, significantly affects the topology of CMB anisotropy, causing a negative genus shift non-Gaussianity signal. Given the expected level of cosmic variance, this effect can be effectively reduced by subtracting existing Galactic foreground emission models from the observed data. IRAS and DIRBE far-infrared extragalactic sources have little effect on the CMB anisotropy. Radio point sources raise the amplitude of the correlation function considerably on scales below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit effectively eliminates this effect. Radio sources also result in a positive genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate radio point source data is essential for an unambiguous detection of CMB anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological origin can be detected from the foreground-subtracted CMB anisotropy map at the 2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04) or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3 (1.0) deg FWHM scale.

Discovery of a transient MeV range gamma-ray source

view Abstract Citations (14) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Transient MeV Range Gamma-Ray Source Briggs, M. S. ; Gruber, D. E. ; Matteson, J. L. ; Peterson, L. E. Abstract The University of California, San Diego (UCSD)/MIT hard X-ray and gamma-ray instrument on the HEAO 1 surveyed the region near the Galactic center 3 times during its lifetime in 1977-1979. During the 1977 September-October scan, a gamma-ray source was detected south of the Galactic center. The source was below the threshold sensitivity in the spring and fall of 1978. The source was detected with the medium energy phoswich scintillation counters which operated over the 80 keV-2 MeV range, had an area of 42 sq cm each, and a 17 deg FWHM aperture. The error box for the source is centered on l = 2.4 deg, b = -12.2 deg, with a 90% confidence error circle of approximately 3.5 deg radius. The flux in the 333-635 keV range was (1.89 +/- 0.29) x 10-5 photons/(sq cm s keV) and was constant within statistics during the 1 month period the source was in the field of view. The spectrum can be characterized as a Gaussian in the range 300 less than or = E less than or = 650 keV, with a FWHM of 249 +/- 51 keV centered on 461 +/- 22 keV. The flux of this broad Gaussian is (6.6 +/- 1.1) x 10-3 photons/(sq cm s). The source is tentatively identified with the 5.57 hr period low-mass X-ray-emitting binary system 1H 1822-371. Assuming this is correct, the ratio of gamma-ray to X-ray luminosity during the outburst was about 5; at a distance of 8 kpc, the gamma ray luminosity is 4 x 1037 ergs. The emission may be interpreted as a positron-pair plasma ejected from a compact object, possibly a black hole, and annihilating in a thick accretion disk surrounding the object. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175467 Bibcode: 1995ApJ...442..638B Keywords: Accretion Disks; Black Holes (Astronomy); Galactic Nuclei; Gamma Ray Astronomy; Gamma Ray Bursts; Gamma Ray Spectra; Milky Way Galaxy; X Ray Astronomy; X Ray Binaries; Astrometry; Astronomical Spectroscopy; Data Reduction; Flux Density; Heao 1; Spaceborne Astronomy; Stellar Luminosity; Astronomy; GALAXY: CENTER; GAMMA RAYS: BURSTS; STARS: BINARIES: CLOSE; X-RAYS: STARS full text sources ADS | data products SIMBAD (15)

Effects of long cosmic strings on the anisotropies of the cosmic background radiation

view Abstract Citations (14) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of Long Cosmic Strings on the Anisotropies of the Cosmic Background Radiation Hara, Tetsuya ; Mahonen, Petri ; Miyoshi, Shigeru Abstract We have examined the effects of infinitely long cosmic strings on the anisotropies of the 2.7 K cosmic microwave background (CMB) radiation using a simplified model. It is assumed that N long cosmic strings are moving fast in each horizon volume during the e-folding times of the expansion of the universe. From the simulated anisotropies of the CMB over the whole sky, we have calculated the rms sky variation with a 10 deg FWHM Gaussian smoothing, the quadrupole moment, and the chi-squared test for the correlation functions. The comparison of the simulation with the COBE DMR results constrains the parameters. The effective power spectrum index is n = 1.1 +/- 0.5. Since the COBE results are well reproduced by our simulation, there remains a possibility that the CMB anisotropies detected by COBE are mainly due to cosmic strings. The characteristic feature for the cosmic string model is the discontinuities in the amplitude of CMB anisotropy. We discuss this as well as the constraint from smaller angles. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/173088 Bibcode: 1993ApJ...414..421H Keywords: Cosmology; Radiation Distribution; Relic Radiation; String Theory; Anisotropy; Astronomical Models; Cosmic Background Explorer Satellite; Power Spectra; Space Radiation; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMIC STRINGS; COSMOLOGY: THEORY full text sources ADS |

A degree-scale measurement of anisotropy of the cosmic background radiation

We report on the preliminary result of a search for anisotropy in the cosmic background radiation (CBR) with a beam size of about 1.5 deg FWHM over a wavelength range of 8-12 mm. The system operated successfully for 500 hr at the South Pole during the 1990-1991 austral summer. The data from one region, representing 25 hr after editing, are presented here. A strong signal is present in the lower frequency channels with a spectrum unlike CBR fluctuations, and is probably due to foreground emission. The highest frequency channel has the smallest contribution from this signal and has been used to set a 95-percent confidence level upper limit of not greater than 1.4 x 10 exp -5 for fluctuations with a Gaussian autocorrelation function at a coherence angle of 1.2 deg. This is significantly more sensitive than previous experiments at this angle scale.

SAS 3 survey of the soft X-ray background

view Abstract Citations (122) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SAS 3 survey of the soft X-ray background. Marshall, F. J. ; Clark, G. W. Abstract The results of a survey of the soft X-ray sky in the C band (0.10-0.28keV) are reported. The observations were carried out using two independent flow proportional counters on board the SAS 3 X-ray satellite which had a total angular resolution of 2.9 deg FWHM, and a total exposure of 2.2 x 10 to the 4th per sq cm s sr. It is found that C band counting rates were generally inversely correlated with the column density of the neutral hydrogen on all angular scales down to the lowest angular resolution of the detectors. In the region 90-180 deg l and 0-10 deg b, the relation between C-band rates and the column densities of neutral hydrogen was fitted with a residual rms deviation of less than 13 percent by a two-component numerical model of the X-ray background. For the apparent attenuation column density a value of 2.7 x 10 to the 20th per sq cm was obtained. On the basis of a computer simulation of the SAS 3 data, it is shown that the observed clumping of interstellar matter was consistent with the magnitude of spatial fluctuations in the C-band map. When the background rates were subtracted from the survey map, the subsequent map showed foreground emission and absorption features with improved sensitivity and clarity. A series of computer-generated maps incorporating the SAS 3 data is given in an appendix. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162721 Bibcode: 1984ApJ...287..633M Keywords: Interstellar Gas; Milky Way Galaxy; Sas-3; X Ray Sources; Computerized Simulation; Data Processing; Hydrogen; Monte Carlo Method; Neutral Gases; Astrophysics full text sources ADS | data products SIMBAD (14) NED (2)

Observations of the giant radio lobes region of Centaurus A with SAS 3

Observations of the X-ray flux from the extended radio lobes of the galaxy Centaurus A obtained with the SAS 3 observatory are reported. The 15 x 15 deg region that includes the lobes was mapped by superposing data from raster scans with the horizontal tubular collimator detectors, which have a 1.7 deg FWHM circular field of view. Data obtained is consistent with the presence of superposed emission from the point sources NGC 5128 and MX 1312-42, a previously unreported source detected by the Einstein Observatory IPC. Fluxes of 4.63 + or - 0.14 x 10 to the -10th and 4.6 + or - 0.6 x 10 to the -11th ergs/sq cm per sec were measured for NGC 5128 and MX 1312-42, respectively, with best fit power law spectra of indices 0.83 + or - 0.04 and 0.62 + or - 0.10 and hydrogen column densities of 1.23 + or - 0.10 x 10 to the 23rd and 9.7 + or - 15.0 x 10 to the 21st atoms/sq cm. Results imply an upper limit of 2.9 x 10 to the 11th for the X-ray emission from the extended radio lobes of Cen A between 2 and 10 keV, which indicates a lower limit to the magnetic field in the lobes of 1.6 x 10 to the -6th gauss.

Spectra and angular distributions of atmospheric gamma rays from 0.3 to 10 MeV at λ = 40°

Measurements of the spectral and angular distributions of atmospheric gamma sq cm rays in the energy range 0.3-10 MeV over Palestine, Texas, at residual depths of 2.5 and 70 g/sq cm are reported. In confirmation of the general features of a model prediction, the measurements show at 2.5 g/sq cm upward moving fluxes greater than the downward moving fluxes, the effect increasing with energy, and approximate isotropy at 70 g/sq cm. Numerous characteristic gamma-ray lines were observed, most prominently at 0.511, 1.6, 2.3, 4.4, and 6.1 MeV. Their intensities were also compared with model predictions. Observations were made with an actively shielded scintillator counter with two detectors, one of aperture 50 deg FWHM and the other of 120 deg FWHM. Above 1 MeV, contributions to the counting rate from photons penetrating the shield annulus and from neutron interactions were large; they were studied by means of a Monte Carlo code and are extensively discussed.

Detection of a Gamma-Ray Spectral Line from the Galactic-Center Region

A ballon-borne experiment timed to observe a lunar occultation of the X- ray source GX 3+1 was conducted on 1971 November 20, from Parana, Argentina. Good data were obtained in the 30 keV-2.4 MeV energy band with two 24 deg FWHM instruments for over four hours, including the hour-long occulation. The observed spectra confirm our 1970 measurements of a spectral line superposed on a power-law continuum radiated from the galactic-center region. The combination of the 1970 and 1971 data places the line 5.3 standard deviations above the continuum. The line energy is 476 plus or minus 24 keV; its intensity is (1.8 plus or minus 0.5) x10 -3 photons cm -2 s-1. A result of the occultatio n observation is that, while it is ruled out as the origin of the bulk of the radiation from the galactic center region, a relatively faint, hard- exponential centinuum is radiated by GX 3+ 1, a result in agreement with an extrapolation of that measured at lower energies by the LRL group. The identification of the source of the 476-keV radiation is unclear, although there was a 2.3 standard deviation decrease in the spectral line during the occultation.