keV Cm2 Research Articles

A Hydrodynamic Approach to Cosmology: Nonlinear Effects on Cosmic Backgrounds in the Cold Dark Matter Model

view Abstract Citations (42) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Hydrodynamic Approach to Cosmology: Nonlinear Effects on Cosmic Backgrounds in the Cold Dark Matter Model Scaramella, Roberto ; Cen, Renyue ; Ostriker, Jeremiah P. Abstract Using the CDM model as a testbed, we produce and analyze sky maps of fluctuations in the cosmic background radiation field due to Sunyaev-Zel'dovich effect, as well as those seen in X-ray background at 1 keV and at 2 keV. These effects are due to the shock heating of baryons in the nonlinear phases of cosmic collapses. Comparing observations with computations provides a powerful tool to constrain cosmological models. We use a highly developed Eulerian mesh code with 1283 cells and 2 × 106 particles. Most of our information comes from simulations with box size 64 h-1 Mpc, but other calculations were made with L = 16 h-1 and L = 4 h-1 Mpc. A standard CDM input spectrum was used with amplitude defined by the requirement (ΔM/M)rms = 1/1.5 on 8 h-1 Mpc scales (lower than the COBE normalization by a factor of 1.6±0.4), with H0 = 50 km s-1 Mpc-1 and Ωb = 0.05. For statistical validity a large number of independent simulations must be run. In all, over 60 simulations were run from z = 20 to z = 0. We produce maps of 50' x 50' with 1' effective resolution by randomly stacking along the past light cone for 0.02 ≤ z ≤ 10 appropriate combinations of computational boxes of different comoving lengths, which are picked from among different realizations of initial conditions. We also compute time evolution, present intensity pixel distributions, and the autocorrelation function of sky fluctuations as a function of angular scale. Our most reliable results are obtained after deletion of bright sources having 1 keV intensity greater than 0.1 keV cm-2 sr-1 s-1 keV-1. Then for the Sunyaev-Zel'dovich parameter γ the mean and dispersion are [barγ, σ(γ)] = (4, 3) × 10-7 with a lognormal distribution providing a good fit for values of y greater than average. The angular correlation function (less secure) is roughly exponential with scale length ∼2'.5. For the X-ray intensity fluctuations, in units of keV s-1 sr-1 cm-2 keV-1 we find barIX1, X2 = (0.02, 0.006) and σX1, X2 = (0.06, 0.03). The pixel distribution is roughly a power law in the intermediate range -f(Ix)dIX ∝ I-1.8X dIX. Also in these cases the angular autocorrelation function is roughly exponential with decay angles of θ0;X1,X2 found to be 1'.6 and 1'.3 but probably below our numerical resolution of 1'.0 in fact. If we scale our results to the COBE normalization, y values increase by approximately a factor of 9 and X-ray intensity by a factor of 8 to give a (δT/T)rms,SZ = 3.5 × 10-6 on the 1'.0 scale and I1keV = 0.2 keV cm-2 sr-1 s-1 keV-1 with both making nontrivial contributions to the observed background radiation fields. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173245 Bibcode: 1993ApJ...416..399S Keywords: COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: DARK MATTER; COSMOLOGY: DIFFUSE RADIATION; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; HYDRODYNAMICS; METHODS: NUMERICAL full text sources ADS |

ROSAT Deep Surveys

AbstractA series of 20 deep pointed observations with the ROSAT PSPC is discussed. 530 X-ray sources with 0.5-2 keV fluxes down to 3·10-15erg cm-2 s-1 have been discovered in 5.9 deg2. The N(>S) relation of the sources selected in the 0.5-2 keV band shows a density in excess of 200 deg-2 at the faintest fluxes and a flattening below 2·10-14erg cm-2 s-1. The average spectrum of those sources is a power law with energy index 1.2 ±0.1. The absorption column densities are consistent with the galactic HI columns. More than 50% of the 1-2 keV background has been resolved into discrete sources in the deepest field. The total background spectrum shows an emission line feature around 0.65 keV, most probably due to OVII-OVIII from a 2·106K plasma. Above ~ 1 keV the background is dominated by a power law spectrum with a normalization of 13.4 ± 0.2 keV cm-2 s-1 sr-1 keV-1 and a slope 1.2 ± 0.1, i.e. considerably steeper than the extrapolation from higher energies.

Enhanced X-ray emission above 50 keV in sco X-1

Balloon observations of the X-ray source Sco X-1 carried out in November 1978 have revealed a thermal spectrum withkT≅7 keV in the 20–60 keV energy band. In addition, there was evidence of a high energy component, possibly variable, above ∼50 keV. The spectral form of this component could not be determined but was hard with a 60 keV flux of ∼10−4 photons (keV cm2 s)−1.

Pulsed high-energy gamma rays from the Crab Nebula.

view Abstract Citations (41) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pulsed high-energy gamma rays from the Crab nebula. McBreen, B. ; Ball, S. E., Jr. ; Campbell, M. ; Greisen, K. ; Koch, D. Abstract The Cornell 100-inch gas-Cerenkov y-ray telescope has detected pulsed radiation at hundreds of MeV, up to more than 1 GeV, coincident in time with the optical pulses from NP 0532, and in direction within 1 of the Crab Nebula. Two spectral points lie on an extension of the pulsed X-ray spectrum: the expression 0.95E-'08 keV cm-2 1 keV-1 fits a synthesis of the data from 5 keV to 106 keV. The main pulse and the secondary pulse contain about equal numbers of events and show evidence of being narrower than at lower energies. There is weak evidence for further pulse structure in the interval between these two peaks, and also for an unmodulated y-ray component about equal to the time-averaged pulsed flux. The pulsar and nebular spectra appear to steepen somewhere between 1.5 and 150 GeV. No pulsed flux from NP 0525 was detectable in this flight. Subject headings: Crab Nebula - gamma rays - pulsars Publication: The Astrophysical Journal Pub Date: September 1973 DOI: 10.1086/152350 Bibcode: 1973ApJ...184..571M full text sources ADS | data products SIMBAD (2)