Geschichtspolitik in Russland

Aktive Einmischung von Seiten des Staates in die Erinnerungspolitik und die professionelle Geschichtswissenschaft begann in Russland spätestens im Jahr 2006. Heute sind in Russland alle Elemente einer Geschichtspolitik vorhanden: erstens der Versuch, in den Schulen ein einziges Geschichtslehrbuch einzuführen, das vom politischen Zentrum aus redigiert wird; zweitens werden besondere politisch aktive Strukturen geschaffen, die die Organisation der Geschichtsforschung und die Kontrolle über Archive und Verlage vereinen; drittens gibt es den Versuch, die Interpretation von Geschichte gesetzlich zu regeln; viertens gibt es die für die Geschichtspolitik typischen Versuche, alle oben erwähnten Praktiken zu legitimieren und ideologisch abzusichern

Landing and catalytic characterization of individual nanoparticles on electrode surfaces

We demonstrate a novel and versatile pipet-based approach to study the landing of individual nanoparticles (NPs) on various electrode materials without any need for encapsulation or fabrication of complex substrate electrode structures, providing great flexibility with respect to electrode materials. Because of the small electrode area defined by the pipet dimensions, the background current is low, allowing for the detection of minute current signals with good time resolution. This approach was used to characterize the potential-dependent activity of Au NPs and to measure the catalytic activity of a single NP on a TEM grid, combining electrochemical and physical characterization at the single NP level for the first time. Such measurements open up the possibility of studying the relation between the size, structure and activity of catalyst particles unambiguously

On the Progenitor System of the Type Iax Supernova 2014dt in M61

We present pre-explosion and post-explosion Hubble Space Telescope images of the Type Iax supernova (SN Iax) 2014dt in M61. After astrometrically aligning these images, we do not detect any stellar sources at the position of the SN in the pre-explosion images to relatively deep limits (3 sigma limits of M_F438W > -5.0 mag and M_F814W > -5.9 mag). These limits are similar to the luminosity of SN 2012Z's progenitor system (M_F435W = -5.43 +/- 0.15 and M_F814W = -5.24 +/- 0.16 mag), the only probable detected progenitor system in pre-explosion images of a SN Iax, and indeed, of any white dwarf supernova. SN 2014dt is consistent with having a C/O white-dwarf primary/helium-star companion progenitor system, as was suggested for SN 2012Z, although perhaps with a slightly smaller or hotter donor. The data are also consistent with SN 2014dt having a low-mass red giant or main-sequence star companion. The data rule out main-sequence stars with M_init > 16 M_sun and most evolved stars with M_init > 8 M_sun as being the progenitor of SN 2014dt. Hot Wolf-Rayet stars are also allowed, but the lack of nearby bright sources makes this scenario unlikely. Because of its proximity (D = 12 Mpc), SN 2014dt is ideal for long-term monitoring, where images in ~2 years may detect the companion star or the luminous bound remnant of the progenitor white dwarf.Comment: 5 pages, 3 figures, submitted to ApJ

The Type II Superluminous SN 2008es at Late Times: Near-Infrared Excess and Circumstellar Interaction

SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN) showing no relatively narrow features in its early-time spectra, and therefore its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 days after explosion. Only broad H$\alpha$ emission is detected in a Gemini spectrum at 288 days. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, a NIR excess with blackbody temperature $\sim1500$ K and radius $\sim10^{16}$ cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with $\sim2$--3 $\textrm{M}_\odot$ of circumstellar material (CSM) and $\sim$10--20 $\textrm{M}_\odot$ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius $\sim 10^{15}$ cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount ($\lesssim 0.4$ $\textrm{M}_\odot$) of $^{56}$Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust

Deviations From Axisymmetry Revealed by Line Polarization in the Normal Type Ia SN 2004S

We present a single epoch of high signal-to-noise ratio spectropolarimetry of the Type Ia supernova (SN Ia) 2004S taken nine days after maximum light. The flux spectrum is normal, but with the additional presence of high-velocity (HV) line features in both Ca II and Fe II. The object shows continuum polarization at the 0.4% level in the red, a value which appears to be typical of SNe Ia. The continuum data are consistent with a ~10% global asphericity in an axisymmetric geometry. Unlike previous observations of other SNe Ia with HV features, the HV features in SN 2004S show no strong polarimetric signature, though this may be due to the timing of our observations. Instead, the object shows line polarization features (P < 0.5%) that are rotated with respect to the axis of symmetry of the continuum. The line features are visible in Si II, Fe II, and Ca II, and appear to be narrowly confined in velocity space just above the photosphere. These polarization features are a result of compositional inhomogeneities in the ejecta. They may represent newly synthesized elements whose clumpy spatial distribution within the ejecta is distinct from that of the globally aspherical ejecta as a whole.Comment: 25 pages, 6 figures, AJ, minor revisions to match accepted journal versio

Systematic Blueshift of Line Profiles in the Type IIn Supernova 2010jl: Evidence for Post-Shock Dust Formation?

Type IIn SNe show spectral evidence for strong interaction between their blast wave and dense circumstellar material (CSM) around the progenitor star. SN2010jl was the brightest core-collapse SN in 2010, and it was a Type IIn explosion with strong CSM interaction. Andrews et al. recently reported evidence for an IR excess in SN2010jl, indicating either new dust formation or the heating of CSM dust in an IR echo. Here we report multi-epoch spectra of SN2010jl that reveal the tell-tale signature of new dust formation: emission-line profiles becoming systematically more blueshifted as the red side of the line is blocked by increasing extinction. The effect is seen clearly in the intermediate-width (400--4000 km/s) component of H$\alpha$ beginning roughly 30d after explosion. Moreover, we present near-IR spectra demonstrating that the asymmetry in the hydrogen-line profiles is wavelength dependent, appearing more pronounced at shorter wavelengths. This evidence suggests that new dust grains had formed quickly in the post-shock shell of SN 2010jl arising from CSM interaction. Since the observed dust temperature has been attributed to an IR echo and not to new dust, either (1) IR excess emission at $\lambda < 5 \mu$m is not a particularly sensitive tracer of new dust formation in SNe, or (2) some assumptions about expected dust temperatures might require further study. Lastly, we discuss one possible mechanism other than dust that might lead to increasingly blueshifted line profiles in SNeIIn, although the wavelength dependence of the asymmetry argues against this hypothesis in the case of SN2010jl.Comment: 6 pages, 4 figures, submitted to A

Spectral Evolution of the Extraordinary Type IIn Supernova 2006gy

We present a detailed analysis of the extremely luminous Type IIn supernova SN2006gy using spectra obtained between days 36 and 237 after explosion. We derive the temporal evolution of the effective temperature, radius, expansion speeds, and bolometric luminosity, as well as the progenitor wind density and total swept-up mass overtaken by the shock. SN2006gy can be interpreted in the context of shock interaction with a dense CSM, but with quite extreme values for the CSM mass of 20 Msun and an explosion kinetic energy of at least 5e51 erg. A key difference between SN2006gy and other SNeIIn is that, owing to its large CSM mass, the interaction region remained opaque much longer. At early times, H-alpha widths suggest that the photosphere is ahead of the shock, and photons diffuse out through the opaque CSM. The pivotal transition to optically thin emission begins around day 110, when we start to see a decrease in the blackbody radius and strengthening tracers of the post-shock shell. From the evolution of pre-shock velocities, we deduce that the CSM was ejected by the progenitor in a 1e49 erg precursor event 8yr before explosion. The large CSM mass rules out models involving stars with initial masses around 10Msun. With the full mass budget, even massive M_ZAMS=30-40 Msun progenitor stars are inadequate. At roughly solar metallicity, substantial mass loss probably occurred during the star's life, so SN 2006gy's progenitor is more consistent with LBV eruptions or pulsational pair-instability ejections in stars with initial masses above 100 Msun. This requires significant revision to current paradigms of massive-star evolution. (abridged)Comment: Really long. 30 pages, 26 figs, appendix. Submitted to ApJ - v2 corrected one referenc

Disappearance of the Progenitor of Supernova iPTF13bvn

Supernova (SN) iPTF13bvn in NGC 5806 was the first Type Ib SN to have been tentatively associated with a progenitor candidate in pre-explosion images. We performed deep ultraviolet (UV) and optical Hubble Space Telescope (HST) observations of the SN site 740 days after explosion. We detect an object in the optical bands that is fainter than the pre-explosion object. This dimming is likely not produced by dust absorption in the ejecta; thus, our finding confirms the connection of the progenitor candidate with the SN. The object in our data is likely dominated by the fading SN, which implies that the pre-SN flux is mostly due to the progenitor. We compare our revised pre-SN photometry with previously proposed progenitor models. Although binary progenitors are favored, models need to be refined. In particular, to comply with our deep UV detection limit, any companion star must be less luminous than a late-O star or substantially obscured by newly formed dust. A definitive progenitor characterization will require further observations to disentangle the contribution of a much fainter SN and its environment.Comment: 8 pages, 3 tables, 3 figures. Accepted for publication in ApJ