Comments: International Workshop on Wolf-Rayet Stars, Potsdam, Germany, 1 - 5 June 2015
Subjects:Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)
Eta Carinae is the nearest example of a supermassive, superluminous, unstable star. Mass loss from the system is critical in shaping its circumstellar medium and in determining its ultimate fate. Eta Car currently loses mass via a dense, slow stellar wind and possesses one of the largest mass loss rates known. It is prone to episodes of extreme mass ejection via eruptions from some as-yet unspecified cause; the best examples of this are the large-scale eruptions which occurred in 19th century. Eta Car is a colliding wind binary in which strong variations in X-ray emission and in other wavebands are driven by the violent collision of the wind of eta Car-A and the fast, less dense wind of an otherwise hidden companion star. X-ray variations are the simplest diagnostic we have to study the wind-wind collision and allow us to measure the state of the stellar mass loss from both stars. We present the X-ray lightcurve over the last 20 years from ROSAT observations and monitoring with the Rossi X-ray Timing Explorer and the X-ray Telescope on the Swift satellite. We compare and contrast the behavior of the X-ray emission from the system over that timespan, including surprising variations during the 2014 X-ray minimum.
The ESA's Planck satellite, dedicated to studying the early universe, was launched on May 2009 and has been surveying the microwave and submillimetre sky since August 2009. In March 2013, ESA and the Planck Collaboration publicly released the initial cosmology products based on the first 15.5 months of Planck operations, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper describes the mission and its performance, and gives an overview of the processing and analysis of the data, the characteristics of the data, the main scientific results, and the science data products and papers in the release. Scientific results include robust support for the standard, six parameter LCDM model of cosmology and improved measurements for the parameters that define this model, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for some of these parameters and others derived from them are significantly different from those previously determined. Several large scale anomalies in the CMB temperature distribution detected earlier by WMAP are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at 25 sigma. Planck finds no evidence for non-Gaussian statistics of the CMB anisotropies. There is some tension between Planck and WMAP results; this is evident in the power spectrum and results for some of the cosmology parameters. In general, Planck results agree well with results from the measurements of baryon acoustic oscillations. Because the analysis of Planck polarization data is not yet as mature as the analysis of temperature data, polarization results are not released. We do, however, illustrate the robust detection of the E-mode polarization signal around CMB hot- and cold-spots.
With the Planck data, we: (a) firmly establish a deviation from scale invariance for primordial matter perturbations, a key indicator of cosmic inflation; (b) detect with high significance lensing of the CMB by intervening matter, providing evidence for dark energy from the CMB alone; (c) find no evidence for significant deviations from Gaussianity in the statistics of CMB anisotropies; (d) find a low value of the Hubble constant, in tension with the value derived from the standard distance ladder; (e) find a deficit of power at low-`s with respect to our best-fit model; (f) confirm the anomalies at large angular scales first detected by WMAP; and (g) establish the number of neutrino species at three.
In the last 3000 yr, one significant and rapid
increase in the concentration of 14C in tree rings was observed; it corresponds
to a gamma-ray energy input of 7x10^24 erg at Earth within up to one year in AD
774/5 (Miyake et al. 2012). A normal supernova and a solar or stellar flare are
unlikely as cause (Miyake et al. 2012), so that the source remained unknown.
Here, we show that a short gamma-ray burst (GRB) in our Galaxy is consistent
with all observables: Such an event is sufficiently short and provides the
necessary energy in the relevant spectral range of $\gamma$-rays. Its spectral
hardness is consistent with the differential production rates of 14C and 10Be as
observed. The absence of reports about a historic sighting of a supernova in AD
774/5 or a present-day supernova remnant are also consistent with a short GRB.
We estimate the distance towards this short GRB to be ~ 1 to 4 kpc -
sufficiently far away, so that no extinction event on Earth was triggered. This
is the first evidence for a short GRB in our Galaxy.
The Sun’s
equator and the planets’ orbital planes are nearly aligned, which is
presumably a consequence of their formation from a single spinning
gaseous disk. For exoplanetary systems this well-aligned configuration
is not guaranteed: dynamical interactions may tilt planetary orbits, or
stars may be misaligned with the protoplanetary disk through chaotic
accretion1 , magnetic interactions2 or torques from neighbouring stars. Indeed, isolated ‘hot Jupiters’ are often misaligned and even orbiting retrograde3, 4. Here we report an analysis of transits of planets over starspots5, 6, 7 on the Sun-like star Kepler-30 (ref. 8),
and show that the orbits of its three planets are aligned with the
stellar equator. Furthermore, the orbits are aligned with one another to
within a few degrees. This configuration is similar to that of our
Solar System, and contrasts with the isolated hot Jupiters. The orderly
alignment seen in the Kepler-30 system suggests that high obliquities
are confined to systems that experienced disruptive dynamical
interactions. Should this be corroborated by observations of other
coplanar multi-planet systems, then star–disk misalignments would be
ruled out as the explanation for the high obliquities of hot Jupiters,
and dynamical interactions would be implicated as the origin of hot
Jupiters.
Palmer, D. M.;
Barthelmy, S.; Gehrels, N.; Kippen, R. M.; Cayton, T.; Kouveliotou, C.;
Eichler, D.; Wijers, R. A. M. J.; Woods, P. M.; Granot, J.; and 18 coauthors
A giant γ-ray flare from the magnetar SGR 1806 - 20
Kouveliotou, C.;
Fishman, G. J.; Meegan, C. A.; Paciesas, W. S.; van Paradijs, J.;
Norris, J. P.; Preece, R. D.; Briggs, M. S.; Horack, J. M.;
Pendleton, G. N.; Green, D. A.
The rarity of soft γ-ray repeaters deduced from reactivation of SGR1806 - 20
