ALBERT

Beschreibung: The first two years of Cosmic Background Explorer (COBE) Differential Microwave Radiometers (DMR) observations of the cosmic microwave background (CMB) anisotropy are analyzed and compared with our previously published first year results. The results are consistent, but the addition of the second year of data increases the precision and accuracy detected CMB temperature fluctuations. The 2 yr 53 GHz data are characterized by rms temperature fluctuations of (delta-T)(sub rms) (7 deg) = 44 +/- 7 micro-K and (delta-T)(sub rms) (10 deg) = 30.5 +/- 2.7 micro-K at 7 deg and 10 deg angular resolution, respectively. The 53 x 90 GHz cross-correlation amplitude at zero lag is C(0)(sup 1/2) = 36 +/- 5 micro-K (68% CL) for the unsmoothed (7 deg resolution) DMR data. We perform a likelihood analysis of the cross-correlation function, with Monte Carlo simulations to infer biases of the method, for a power-law model of initial density fluctuations, P(k) proportional to R(exp n). The Monte Carlo simulations indicate that derived estimates of n are biased by +0.11 +/- 0.01, while the subset of simulations with a low quadrupole (as observed) indicate a bias of +0.31+/- 0.04. Derived values for 68% confidence intervals are given corrected (and not corrected) for our estimated biases. Including the quadrupole anisotropy, the most likely quadrupole-normalized amplitude is Q(sub rms-PS) = 14.3(sup + 5.2 sub -3.3) micro-K (12.8(sup + 5.2 sub -3.3) micro-K0 with a spectral index n = 1.42(sup + 0.49 sub -0.55)(n = 1.53(sup + 0.49 sub -0.55). With n fixed to 1.0 the most likely amplitude is 18.2 +/- 11.5 micro-K (17.4 +/- 1.5 micro-K). The marginal likelihood of n is 1.42 +/- 0.37 (1.53 +/- 0.37). Excluding the quadrupole anisotropy, the most likely quadrupole-normalized amplitude is Q(sub rms-PS) = 17.4(sup + 7.5 sub -5.2) micro-K (15.8(sup + 7.5 sub -5.2) micro-K) with a spectral index n = 1.11(sup + 0.60 sub -0.55) (n = 1.22(sup + 0.60 sub -0.55). With n fixed to 1.0 the most likely amplitude is 18.6 +/- 1.6 micro-K (18.2 +/- 1.6 micro-K). The marginal likelihood of n is 1.11 +/- 0.40 (1.22 +/- 0.40). Our best estimate of the dipole from the 2 yr DMR data is 3.363 +/- 0.024 mK toward Galactic coordinates (l, b) = (264.4 deg +/- 0.2 deg, 48.1 deg +/- 0.4 deg), and our best estimate of the rms quadrupole amplitude in our sky is 6 +/- 3 micro-K (68% CL).

Beschreibung: During the encounter of the International Cometary Explorer (ICE) with comet P/Giacobini-Zinner, the radio astronomy experiment observed occultation and propagation effects on several distant radio sources. The observations of the partial occultation of the galactic radio source between 360 and 1000 kHz show that the three-dimensional large scale structure of the coma is consistent with the structure determined from in-situ measurements made along the encounter trajectory. In addition, these observations remove a previously existing ambiguity in the position of the galactic source. Between 110 and 360 kHz the earth source is broadened by scattering by the comet random density inhomogeneities. The amount of broadening indicates that the electron density fluctuations measured in situ by ICE along its trajectory (100 pct fluctuations with a scale length of 1000-2000 km over a path length of 100,000 km) exist with the same properties in the perpendicular direction.

Beschreibung: Using the PSPC instrument on the ROSAT satellite, we have obtained deep exposures of the fields centered on the QSO's 1556+335, 1037-271, and 0854+191 in an effort to search for extended X-ray emission corresponding to complex QSO absorption-line systems (QALS's) that could be indicative of clusters of galaxies at high redshift. The QSO 1556+335 is known to have a pair of complicated C IV absorption systems at z equals 1.610 (Delta v = 988 km/s) and z equals 1.650 (Delta v = 1677 km/s) near the z equals 1.641 QSO redshift. It has been suggested that the absorption may be due to two rich clusters, one containing the QSO itself. The QSO 0854+191 (z(sub em) = 1.89) has 6 strong C IV absorption systems in 2 close groups at z equals 1.2954, 1.2973,1.3019 and z equals 1.3522, 1.3543, 1.3558. Assuming q(sub O) equals 0.5 and H(sub O) equals 50 km/s Mpc(exp -l), the redshift range of this absorption-line cluster corresponds to a radial distance of 44 Mpc. Interestingly, there is a nearby (approximately 30') QSO (0856+189) with a projected separation of 16 Mpc whose redshift (z = 1.29) is similar to that of the absorbing material toward 0854+191. In the case of 1037-271 (Z(sub em) = 2.18), common QALSs have been observed at z equals l.90, 1.96, 2.02, 2.08, and 2.14 (a radial range of 66 Mpc) in its spectrum and that of its neighbor Tol 1038-272 (Z(sub em) = 2.32) whose 18' separation corresponds to a linear distance of 9 Mpc at z approximately equals 2. The length scales implied by the absorbers toward 0854+191 and 1037-271 are interesting in that they suggest structures more akin to superclusters than clusters.

Beschreibung: The research under this grant resulted in the measurement of anisotropy of the Cosmic Microwave Background Radiation (CMBR) on angular scales from 90 degrees to 0.3 degrees. A bolometric radiometer was built with a sensitivity of better than 500 micro K divided by the square root of (Hz). The measurements complement the COBE anisotropy measurement in two ways. The large scale measurements were shown to cross-correlate with the COBE DMR anisotropy detection, confirming the results. The small scale measurements further the understanding of the structure in the CMBR on scales where we can begin to model the early stages in galaxy and galaxy cluster formation.

Beschreibung: The spectrum of the soft X-ray pulsar Geminga consists of two components, a softer one which can be interpreted as thermal-like radiation from the surface of the neutron star, and a harder one interpreted as radiation from a polar cap heated by relativistic particles. We have fitted the soft spectrum using a detailed magnetized hydrogen atmosphere model. The fitting parameters are the hydrogen column density, the effective temperature T(sub eff), the gravitational redshift z, and the distance to radius ratio, for different values of the magnetic field B. The best fits for this model are obtained when B less than or approximately 1 x 10(exp 12) G and z lies on the upper boundary of the explored range (z = 0.45). The values of T(sub eff) approximately = (2-3) x 10(exp 5) K are a factor of 2-3 times lower than the value of T(sub eff) obtained for blackbody fits with the same z. The lower T(sub eff) increases the compatibility with some proposed schemes for fast neutrino cooling of neutron stars (NSs) by the direct Urca process or by exotic matter, but conventional cooling cannot be excluded. The hydrogen atmosphere fits also imply a smaller distance to Geminga than that inferred from a blackbody fit. An accurate evaluation of the distance would require a better knowledge of the ROSAT Position Sensitive Proportional Counter (PSPC) response to the low-energy region of the incident spectrum. Our modeling of the soft component with a cooler magnetized atmosphere also implies that the hard-component fit requires a characteristic temperature which is higher (by a factor of approximately 2-3) and a surface area which is smaller (by a factor of 10(exp 3), compared to previous blackbody fits.