17355301
The Effect of Environment on the X-Ray Emission from Early-Type Galaxies
In order to further our understanding of the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 elliptical and S0 galaxies, observed with high and low angular resolution detectors on ROSAT. Our previous analysis of this sample suggested that the most X-ray-luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively and find a positive correlation between LX/LB and the local galaxy density. Since the local galaxy density is usually related to the density of hot intergalactic gas, we suggest that this correlation occurs because the X-ray luminosity is enhanced, either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing LX/LB. These effects lead to the large observed dispersion in LX at fixed LB. We discuss details of the data processing not previously presented, and examine the dependence of LX on the choice of outer source radius and background location. We also compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data. The ASCA and ROSAT temperatures are found to be similar, provided that the same metallicities and Galactic absorption columns are used.
118606402
Radial Photon Trajectories Near an Evaporating Black Hole
The radial motion of photons emitted near the horizon of a black hole that evaporates at a steady rate is examined. The space-time of the black hole is generated using non-orthogonal coordinates. It is shown that some photons that are initially drawn towards the singularity can escape falling into the horizon. The behaviors of various outgoing and ingoing photons are clearly demonstrated through the use of a Penrose diagram.
17737699
Construction of a Penrose diagram for an accreting black hole
A Penrose diagram is constructed for a spatially coherent black hole that accretes at stepwise steady rates as measured by a distant observer from an initial state described by a metric of Minkowski form. Coordinate lines are computationally derived, and radial lightlike trajectories verify the viability of the diagram. Coordinate dependences of significant features, such as the horizon and radial mass scale, are clearly demonstrated on the diagram. The onset of a singularity at the origin is shown to open a new region in space time that contains the interior of the black hole.
119084367
Emission mechanisms in X-ray-faint galaxies
Hot gas dominates the emission in X-ray-luminous early-type galaxies, but in relatively X-ray-faint systems, integrated X-ray emission from discrete stellar-like sources is thought to be considerable, although the amount of the contribution is controversial. To help resolve this issue, we examine the radial X-ray surface brightness distribution of 17 X-ray-faint galaxies observed with the ROSAT HRI and PSPC. We assume that the stellar contribution follows a de Vaucouleurs law while the hot gas component follows a King β model. For some galaxies, both models fit equally well, but for a number of systems, a dual component model yields the best fit, from which upper bounds are placed on the stellar contribution. Best-fit values for the stellar contribution are inconsistent with (lower than) that suggested by Fabbiano, Gioia, & Trinchieri and estimated from the bulge of M31 but are consistent with the Forman, Jones, & Tucker estimate of the stellar fraction in X-ray-faint elliptical and S0 galaxies. Our results indicate an upper limit to discrete sources of LX/LB = 1.6 × 1029 ergs s-1 L.
122407890
Inelastic scattering e 4 transition probabilities in the 0d, 1s shell
Theoretical E4 transition matrix elements calculated in the full d/sub 5/2/-s/sub 1/2/-d/sub 3/2/ shell-model space are presented for excitations of some ground states of stable nuclei for 18 < or = A < or = 38. These matrix elements have been used to calculate inelastic transition probabilities for electromagnetic and hadronic probes. Available data on the relative magnitudes and energy distributions of E4 excitation strengths are found to be well reproduced theoretically thereby. Based on several experimentally measured transition strengths, the empirical isoscalar E4 effective charge is found to be e/sub p/+e/sub n/2.0=(ts +- 0.2)e. This is similar in magnitude to the analogous isoscalar E2 effective charge, but is much larger than existing theoretical estimates.
45560684
Separation of isoscalar, isovector, orbital, and spin contributions in M1 transitions in mirror nuclei
Experimental data for $M1$ matrix elements in the $T=1/2$ mirror nuclei ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Si}$ are used to determine the isoscalar and isovector $M1$ components. The obtained isovector $M1$ matrix elements are compared to the Gamow-Teller matrix elements deduced from $\ensuremath{\beta}$ decay and the ${}^{27}\mathrm{Al}{(}^{3}\mathrm{He}{,t)}^{27}\mathrm{Si}$ charge exchange reaction to determine the contributions of the isovector spin and orbital components. The exchange current effects are taken into account. The results are compared with shell model calculations.