XMM-Newton study of the ULIRG NGC 6240

A recently performed XMM-Newton observation of the ULIRG NGC 6240 clearly indicates the presence of an AGN contribution to its X-ray spectrum. In the 5.0 - 7.0 keV energy range there is a clear signature of the fluorescent Fe K lines at 6.4, 6.7 and 6.9 keV, respectively. The line strength of the 6.4 keV line cannot be produced by a thermal component. The 0.3 - 10.0 keV spectral energy distribution is characterized by the following components: (I) two hot thermal components (the starburst), (II) one direct component (heavily absorbed; AGN is hidden), (III) one reflection component (the AGN), (IV) three narrow Fe lines. The model parameters for the broad-band spectral energy distribution are consistent with the results of previously works.Comment: 2 pages incl. 2 figures, to appear in the proceedings of the "New Century of X-ray Astronomy" symposium held in Yokohama, Japan (March 6-8, 2001), eds. H. Kunieda and H. Inoue, ASP pres

Supernova Neutrino Spectra and Applications to Flavor Oscillations

We study the flavor-dependent neutrino spectra formation in the core of a supernova (SN) by means of Monte Carlo simulations. A high-statistics neutrino signal from a galactic SN may contain information that severely constrains the parameter space for neutrino oscillations. Therefore, reliable predictions for flavor-dependent fluxes and spectra are urgently needed. In all traditional hydrodynamic simulations the nu_mu,tau and nu_mu,tau-bar interactions commonly included are rather schematic. With our Monte Carlo simulations we find that the most relevant sources for nu_mu,tau and nu_mu,tau-bar are traditionally not included. In comparing our numerical results for all flavors we find the standard hierarchy of mean energies nu_e < nu_e-bar < nu_mu,tau, with, however, very similar values for nu_mu,tau and nu_e-bar. The luminosities of nu_mu,tau and nu_mu,tau-bar can differ by up to a factor of 2 from L_nue-bar and L_nue, the latter two are very similar. The Garching Group obtains similar results from their self-consistent simulation with the full set of interactions. These results are almost orthogonal to the previous standard picture of exactly equal luminosities of all flavors and differences in mean energies of up to a factor of 2. Existing concepts for identifying oscillation effects in a SN neutrino signal need to be revised. We present two methods for detecting the earth-matter effect that are rather independent of predictions from SN simulations.Comment: 138pp, Dissertation, Technische Universitaet Muenche

Identifying Earth matter effects on supernova neutrinos at a single detector

The neutrino oscillations in Earth matter introduce modulations in the supernova neutrino spectra. These modulations can be exploited to identify the presence of Earth effects on the spectra, which would enable us to put a limit on the value of the neutrino mixing angle $\theta_{13}$ and to identify whether the mass hierarchy is normal or inverted. We demonstrate how the Earth effects can be identified at a single detector without prior assumptions about the flavor-dependent source spectra, using the Fourier transform of the ``inverse-energy'' spectrum of the signal. We explore the factors affecting the efficiency of this method, and find that the energy resolution of the detector is the most crucial one. In particular, whereas water Cherenkov detectors may need a few ten thousand events to identify the Earth effects, a few thousand may be enough at scintillation detectors, which generically have a much better energy resolution. A successful identification of the Earth effects through this method can also provide $\Delta m^2_\odot$ to a good accuracy. The relative strength of the detected Earth effects as a function of time provides a test for supernova models.Comment: 18 pages, 10 figures, JCAP format. Final version to be published in JCAP. References and some minor clarifications added to the original versio

Ledoux-Convection in Protoneutron Stars --- a Clue to Supernova Nucleosynthesis?

Two-dimensional hydrodynamical simulations of the deleptonization of a newly formed neutron star were performed. Driven by negative lepton fraction and entropy gradients, convection starts near the neutrinosphere about 20-30 ms after core bounce, but moves deeper into the protoneutron star, and after about one second the whole protoneutron star is convective. The deleptonization of the star proceeds much faster than in the corresponding spherically symmetrical model because the lepton flux and the neutrino luminosities increase by up to a factor of two. The convection below the neutrinosphere raises the neutrinospheric temperatures and mean energies of the emitted neutrinos by 10-20%. This can have important implications for the supernova explosion mechanism and changes the detectable neutrino signal from the Kelvin-Helmholtz cooling of the protoneutron star. In particular, the enhanced electron neutrino flux relative to the electron antineutrino flux during the early post-bounce evolution might solve the overproduction problem of certain elements in the neutrino-heated ejecta in models of type-II supernova explosions.Comment: 17 pages, LaTeX, 8 postscript figures, uses epsf.sty. To appear in ApJ 473 (Letters), 1996 December 1

Supernova neutrinos: Flavor-dependent fluxes and spectra

Transporting nu_mu and nu_tau in a supernova (SN) core involves several processes that have been neglected in traditional simulations. Based on a Monte Carlo study we find that the flavor-dependent spectral differences are much smaller than is often stated in the literature. A full-scale SN simulation using a Boltzmann solver and including all relevant neutrino reactions confirms these results. The flavor-dependent flux differences are largest during the initial accretion phase.Comment: Proceedings NOON 03, Kanazawa, 10-14 Feb 200

XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the complex Fe K line emission

We report on an XMM-Newton observation of the ultraluminous infrared galaxy NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three collisionally ionized plasma components with temperatures of about 0.7, 1.4, and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a neutral Fe K_alpha and K_beta line. We detect a significant neutral column density gradient which is correlated with the temperature of the three plasma components. Combining the XMM-Newton spectral model with the high spatial resolution Chandra image we find that the temperatures and the column densities increase towards the center. With high significance, the Fe K line complex is resolved into three distinct narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due to reflection from optically thick material, the Fe XXV and Fe XXVI emission arises from the highest temperature ionized plasma component. We have compared the plasma parameters of the ultraluminous infrared galaxy NGC 6240 with those found in the local starburst galaxy NGC 253. We find a striking similarity in the plasma temperatures and column density gradients, suggesting a similar underlying physical process at work in both galaxies.Comment: 8 pages including 9 figures. Accepted for publication in A&

XMM-Newton discovery of a sharp spectral feature at ~7 keV in the Narrow-Line Seyfert 1 galaxy 1H 0707-495

We report the first detection of a sharp spectral feature in a Narrow-Line Seyfert 1 galaxy. Using XMM-Newton we have observed 1H0707-495 and find a drop in flux by a factor of more than 2 at a rest-frame energy of ~7 keV without any detectable narrow Fe K alpha line emission. The energy of this feature suggests a connection with the neutral iron K photoelectric edge, but the lack of any obvious absorption in the spectrum at lower energies makes the interpretation challenging. We explore two alternative explanations for this unusual spectral feature: (i) partial covering absorption by clouds of neutral material and (ii) ionised disc reflection with lines and edges from different ionisation stages of iron blurred together by relativistic effects. We note that both models require an iron overabundance to explain the depth of the feature. The X-ray light curve shows strong and rapid variability, changing by a factor of four during the observation. The source displays modest spectral variability which is uncorrelated with flux.Comment: 5 pages incl. 6 figures, accepted for publication in MNRA