119263159
Evaluating the Gamma-Ray Evidence for Self-Annihilating Dark Matter from the Virgo Cluster
Based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the b b-bar channel has been reported by Han et al. [1]. After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included.
53490118
Locating the γ-ray emission region of the flat spectrum radio quasar PKS 1510−089
I present a study of the high-energy γ-ray properties of the flat spectrum radio quasar, PKS 1510−089, based on 3.75 yr of observations with the Large Area Telescope detector on-board the Fermi γ-ray Space Telescope. Throughout the observing period, the 0.1 < Eγ < 300 GeV γ-ray flux was highly variable, undergoing several flaring events where the daily flux exceeded 10−5 photons cm−2 s−1 on three separate occasions. The increased photon statistics of these large flares allowed the observations to be re-analysed in 6 and 3 h intervals, revealing flux doubling time-scales as small as 1.3 ± 0.12 h during the flare rise time, and flux halving time-scales of 1.21 ± 0.15 h during the flare decay. These are the smallest variability time-scales measured to date at MeV–GeV energies for the flat spectrum quasar class of active galactic nuclei. 
 
The >10−5 photons cm−2 s−1 flare events were also studied in more detail in an attempt to uncover evidence for the location of PKS 1510−089's γ-ray emission region. In particular, two approaches were used: (i) searching for an energy dependence to the cooling time-scales, and (ii) searching for evidence of a spectral cut-off. The combined results of these two approaches, along with the confirmation of ≥20 GeV photon flux from PKS 1510−089, suggest the presence of multiple γ-ray emission regions being located in both the broad line region and molecular torus region of PKS 1510−089. 
 
An analysis of the highest photon events within the 3.75 yr data set finds PKS 1510−089 to be a source of ≥20 GeV γ-rays at the 13.5σ confidence level; a observational property which is difficult to explain in the traditional view that γ-ray emission from active galactic nuclei originates from the base of the relativistic jet. This gives further weight to the argument that there are multiple, simultaneously active γ-ray emission regions located along the relativistic jet of active galactic nuclei.
8789191
Study of the acoustic signature of UHE neutrino interactions in water and ice
The production of acoustic signals from the interactions of ultra-high energy (UHE) cosmic ray neutrinos in water and ice has been studied. A new computationally fast and efficient method of deriving the signal is presented. This method allows the implementation of up to date parameterisations of acoustic attenuation in seawater and ice that now includes the effects of complex attenuation, where appropriate. The methods presented here have been used to compute and study the properties of the acoustic signals which would be expected from such interactions. A matrix method of parameterising the signals, which includes the expected fluctuations, is also presented. These methods are used to generate the expected signals that would be detected in acoustic UHE neutrino telescopes.
55115943
On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright O stars in the sky as predicted from their spectral type with the absolute magnitude calculated from their apparent magnitude and the Hipparcos parallax. We find that many stars appear to be much fainter than expected, up to five magnitudes. We find no evidence for a correlation between magnitude differences and the stellar rotational velocity as suggested for OB stars by Lamers et al. (1997, AA Howarth & Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) and find that they are consistent with the Hipparcos measurements. Although O stars conform nicely to the simulation, we notice that some B stars in the sample of Lamers et al. have a magnitude difference larger than expected.
53618836
Design drivers for a wide-field multi-object spectrograph for the William Herschel Telescope
Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take advantage of a future prime-focus corrector and atmospheric-dispersion corrector (Agocs et al, this conf.) that will deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions (R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner technologies are considered. Several options for the spectrograph are discussed, building in part on published design studies for E-ELT spectrographs. Indeed, a WHT MOS will not only efficiently deliver data for exploitation of important imaging surveys planned for the coming decade, but will also serve as a test-bed to optimize the design of MOS instruments for the future E-ELT.
117895476
Stellar Imager (SI): developing and testing a predictive dynamo model for the Sun by imaging other stars
The Stellar Imager mission concept is a space-based UV/Optical interferometer designed to resolve surface magnetic activity and subsurface structure and flows of a population of Sun-like stars, in order to accelerate the development and validation of a predictive dynamo model for the Sun and enable accurate long-term forecasting of solar/stellar magnetic activity.
119640576
Thermal derivation of the Coleman-De Luccia tunneling prescription
We derive the rate for transitions between de Sitter vacua by treating the field theory on the static patch as a thermal system. This reproduces the Coleman-De Luccia formalism for calculating the rate, but leads to a modified interpretation of the bounce solution and a different prediction for the evolution of the system after tunneling. The bounce is seen to correspond to a sequence of configurations interpolating between initial and final configurations on either side of the tunneling barrier, all of which are restricted to the static patch. The final configuration, which gives the initial data on the static patch for evolution after tunneling, is obtained from one-half of a slice through the center of the bounce, while the other half gives the configuration before tunneling. The formalism makes no statement about the fields beyond the horizon. This approach resolves several puzzling aspects and interpretational issues concerning the Coleman-De Luccia and Hawking-Moss bounces. We work in the limit where the backreaction of matter on metric can be ignored, but argue that the qualitative aspects remain in the more general case. The extension to tunneling between anti-de Sitter vacua is discussed.
118567909
The quest for the Sun's siblings: an exploratory search in the Hipparcos Catalogue
We describe the results of a search for the remnants of the Sun’s birth cluster among stars in the Hipparcos Catalogue. This search is based on the predicted phase-space distribution of the Sun’s siblings from simple simulations of the orbits of the cluster stars in a smooth Galactic potential. For stars within 100 pc, the simulations show that it is interesting to examine those that have small space motions relative to the Sun. From amongst the candidate siblings thus selected, there are six stars with ages consistent with that of the Sun. Considering their radial velocities and abundances only one potential candidate, HIP 21158, remains, but essentially the result of the search is negative. This is consistent with predictions by Portegies Zwart on the number of siblings near the Sun. We discuss the steps that should be taken in anticipation of the data from the Gaia mission in order to conduct fruitful searches for the Sun’s siblings in the future.