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تسجيل مستخدم جديدThe Broadband Spectrum of Galaxy Clusters
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We examine whether nonthermal protons energized during a cluster merger are simultaneously responsible for the Coma clusters diffuse radio flux (via secondary decay) and the departure of its intra-cluster medium (ICM) from a thermal profile via Coulomb collisions between the quasithermal electrons and the hadrons. Rather than approximating the influence of nonthermal proton/thermal electron collisions as extremely rare events which cause an injection of nonthermal, power-law electrons (the `knock-on approximation), we self-consistently solve (to our knowledge, for the first time) the covariant kinetic equations for the two populations. The electron population resulting from these collisions is out of equilibrium, yet not a power law, and importantly displays a higher bremsstrahlung radiative efficiency than a pure power law. Observations with GLAST will test this model directly.
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Recent radio VLBI observations of the ~parsec-scale nuclear region of the narrow line Seyfert 1 galaxy NGC 4051 hint toward the presence of outflowing plasma. From available literature we have collected high-quality, high-resolution broadband spectra
l energy distribution data of the nuclear region of NGC 4051 spanning from radio through X-rays, to test whether the broadband SED can be explained within the framework of a relativistically outflowing jet model. We show that once the contribution from the host galaxy is taken into account, the broadband emission from the active galactic nucleus of NGC 4051 can be well described by the jet model. Contributions from dust and ongoing star-formation in the nuclear region tend to dominate the IR emission even at the highest resolutions. In the framework of the jet model, the correlated high variability of the extreme ultraviolet and X-rays compared to other wavelengths suggests that the emission at these wavelengths is optically thin synchrotron originating in the particle acceleration site(s) in the jet very close (few $r_g=GM_{BH}/c^2$) to the central supermassive black hole of mass M_{BH}. Our conclusions support the hypothesis that narrow line Seyfert 1 galaxies (which NGC 4051 is a member of) harbor a jetted outflow with properties similar to what has already been seen in low-luminosity AGNs and stellar mass black holes in hard X-ray state.
We detect a weak unidentified emission line at E=(3.55-3.57)+/-0.03 keV in a stacked XMM spectrum of 73 galaxy clusters spanning a redshift range 0.01-0.35. MOS and PN observations independently show the presence of the line at consistent energies. W
hen the full sample is divided into three subsamples (Perseus, Centaurus+Ophiuchus+Coma, and all others), the line is significantly detected in all three independent MOS spectra and the PN all others spectrum. It is also detected in the Chandra spectra of Perseus with the flux consistent with XMM (though it is not seen in Virgo). However, it is very weak and located within 50-110eV of several known faint lines, and so is subject to significant modeling uncertainties. On the origin of this line, we argue that there should be no atomic transitions in thermal plasma at this energy. An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. Assuming that all dark matter is in sterile neutrinos with m_s=2E=7.1 keV, our detection in the full sample corresponds to a neutrino decay mixing angle sin^2(2theta)=7e-11, below the previous upper limits. However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model. This appears to be because of an anomalously bright line at E=3.62 keV in Perseus, possibly an Ar XVII dielectronic recombination line, although its flux would be 30 times the expected value and physically difficult to understand. In principle, such an anomaly might explain our line detection in other subsamples as well, though it would stretch the line energy uncertainties. Another alternative is the above anomaly in the Ar line combined with the nearby 3.51 keV K line also exceeding expectation by factor 10-20. Confirmation with Chandra and Suzaku, and eventually Astro-H, are required to determine the nature of this new line.(ABRIDGED)
Cosmological simulations are fundamental tools to study structure formation and the astrophysics of evolving structures, in particular clusters of galaxies. While hydrodynamical simulations cannot sample efficiently large volumes and explore differen
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The BL Lac object Mkn~421 was observed three times by the X-ray observatory BeppoSAX in consecutive days during 1997 April and May. The source was in a quiescent state, with an average 2-10 keV flux of 9.0 x 10^(-11) erg/cm/cm/s. Flux variation by a
factor of ~2 on timescales as short as a few 10 ks were more pronounced in the hard (i.e. above ~3 keV) than in the soft X-rays. The broadband (0.1-40 keV) spectrum is concave and can be most easily explained with a power-law model which steepens gradually with energy. In this framework, neither photoabsorption edges nor resonant absorption lines are required, strengthening the case against the ubiquity of such features in BL Lac objects, which had been previously suggested by Einstein observations. The broadband spectrum hardens with hard X-ray flux, mostly due to a flattening above ~4 keV. This suggests that the relativistic highest energy electron distribution properties drive the X-ray spectral dynamics: either a stratification of the distribution in the jet with energy or inhomogeneities in the electron injection mechanism could be consistent with the observed variability pattern.
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