2,556,082 research outputs found
Analysis of the thin layer of Galactic warm ionized gas in the range 20 < l < 30 deg, -1.5 < b < +1.5 deg
We present an analysis of the thin layer of Galactic warm ionized gas at an
angular resolution ~ 10'. This is carried out using radio continuum data at 1.4
GHz, 2.7 GHz and 5 GHz in the coordinate region 20 < l < 30 deg, -1.5 < b <
+1.5 deg. For this purpose, we evaluate the zero level of the 2.7 and 5 GHz
surveys using auxiliary data at 2.3 GHz and 408 MHz. The derived zero level
corrections are T_{zero}(2.7 GHz)=0.15 +/- 0.06 K and T_{zero}(5 GHz)=0.1 +/-
0.05 K. We separate the thermal (free-free) and non-thermal (synchrotron)
component by means of a spectral analysis performed adopting an antenna
temperature spectral index -2.1 for the free-free emission, a realistic spatial
distribution of indices for the synchrotron radiation and by fitting,
pixel-by-pixel, the Galactic spectral index. We find that at 5 GHz, for |b| = 0
deg, the fraction of thermal emission reaches a maximum value of 82%, while at
1.4 GHz, the corresponding value is 68%. In addition, for the thermal emission,
the analysis indicates a dominant contribution of the diffuse component
relative to the source component associated with discrete HII regions.Comment: 9 pages, 9 figures, accepted to MNRA
Spectral Analyses of the Nearest Persistent Ultraluminous X-Ray Source M33 X-8
We provide a detailed analysis of 12 XMM observations of the nearest
persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No
significant spectral evolution is detected between the observations, therefore
we combine the individual observations to increase the signal-to-noise ratio
for spectral fitting. The combined spectra are best fitted by the
self-consistent p-free disk plus power-law component model with p =
0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio
of the p-free disk component to the power-law component being 0.63:0.37 in the
0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of
\sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}),
and the phase of the accretion disk is close to a slim disk (p = 0.5). We
report, for the first time, that an extra power-law component is required in
addition to the p-free disk model for ULXs. In super-Eddington cases, the
power-law component may possibly result from the optically thin inner region f
the disk or a comptonized corona similar to that of a standard thin disk.Comment: 11 pages, 1 table, 2 figures, accepted by PAS
Spectrum of the Anomalous Microwave Emission in the North Celestial Pole with WMAP 7-Year data
We estimate the frequency spectrum of the diffuse anomalous microwave
emission (AME) on the North Celestial Pole (NCP) region of the sky with the
Correlated Component Analysis (CCA) component separation method applied to WMAP
7-yr data. The NCP is a suitable region for this analysis because the AME is
weakly contaminated by synchrotron and free-free emission. By modeling the AME
component as a peaked spectrum we estimate the peak frequency to be
\,GHz, in agreement with previous analyses which favored \,GHz. The ability of our method to correctly recover the position of the
peak is verified through simulations. We compare the estimated AME spectrum
with theoretical spinning dust models to constrain the hydrogen density . The best results are obtained with densities around 0.2--0.3\,cm,
typical of warm ionised medium (WIM) to warm neutral medium (WNM) conditions.
The degeneracy with the gas temperature prevents an accurate determination of
, especially for low hydrogen ionization fractions, where densities
of a few cm are also allowed.Comment: 13 pages, 6 figures, published in Advances in Astronom
Non-symmetric magnetohydrostatic equilibria:a multigrid approach
Aims. Linear magnetohydrostatic (MHS) models of solar magnetic fields balance plasma pressure gradients, gravity and Lorentz forces where the current density is composed of a linear force-free component and a cross-field component that depends on gravitational stratification. In this paper, we investigate an efficient numerical procedure for calculating such equilibria.Methods. The MHS equations are reduced to two scalar elliptic equations â one on the lower boundary and the other within the interior of the computational domain. The normal component of the magnetic field is prescribed on the lower boundary and a multigrid method is applied on both this boundary and within the domain to find the poloidal scalar potential. Once solved to a desired accuracy, the magnetic field, plasma pressure and density are found using a finite difference method.Results. We investigate the effects of the cross-field currents on the linear MHS equilibria. Force-free and non-force-free examples are given to demonstrate the numerical scheme and an analysis of speed-up due to parallelization on a graphics processing unit (GPU) is presented. It is shown that speed-ups of Ă30 are readily achievable
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