Search Publications
Cosmic microwave background acoustic peak locations
Knox, L.; Narimani, A.; Pan, Z. +1 more
The Planck collaboration has measured the temperature and polarization of the cosmic microwave background well enough to determine the locations of eight peaks in the temperature (TT) power spectrum, five peaks in the polarization (EE) power spectrum and 12 extrema in the cross (TE) power spectrum. The relative locations of these extrema give a st…
The awakening of the γ-ray narrow-line Seyfert 1 galaxy PKS 1502+036
Pearson, T. J.; Giroletti, M.; Readhead, A. C. S. +7 more
After a long low-activity period, a γ-ray flare from the narrow-line Seyfert 1 PKS 1502+036 (z = 0.4089) was detected by the Large Area Telescope (LAT) on board Fermi in 2015. On 2015 December 20, the source reached a daily peak flux, in the 0.1-300 GeV band, of (93 ± 19) × 10-8 ph cm-2 s-1, attaining a flux of (23…
A comparative analysis of the observed white dwarf cooling sequence from globular clusters
Kepler, S. O.; Costa, J. E. S.; Montgomery, M. H. +8 more
We report our study of features at the observed red end of the white dwarf cooling sequences for three Galactic globular clusters: NGC 6397, 47 Tucanae and M 4. We use deep colour-magnitude diagrams constructed from archival Hubble Space Telescope (Advanced Camera for Surveys) to systematically investigate the blue turn at faint magnitudes and the…
KAT-7 observations of an unbiased sample of mass-selected galaxy clusters
Brunetti, G.; Venturi, T.; Dallacasa, D. +7 more
The presence of megaparsec-scale radio haloes in galaxy clusters has already been established by many observations over the last two decades. The emerging explanation for the formation of these giant sources of diffuse synchrotron radio emission is that they trace turbulent regions in the intracluster medium, where particles are trapped and accele…
Applications for edge detection techniques using Chandra and XMM-Newton data: galaxy clusters and beyond
Fabian, A. C.; Sanders, J. S.; Walker, S. A.
The unrivalled spatial resolution of the Chandra X-ray observatory has allowed many breakthroughs to be made in high-energy astrophysics. Here we explore applications of Gaussian gradient magnitude (GGM) filtering to X-ray data, which dramatically improves the clarity of surface brightness edges in X-ray observations, and maps gradients in X-ray s…
Ion chemistry in the coma of comet 67P near perihelion
Gunell, H.; Wurz, P.; Altwegg, K. +33 more
The coma and the comet-solar wind interaction of comet 67P/Churyumov-Gerasimenko changed dramatically from the initial Rosetta spacecraft encounter in 2014 August through perihelion in 2015 August. Just before equinox (at 1.6 au from the Sun), the solar wind signal disappeared and two regions of different cometary ion characteristics were observed…
A porosity gradient in 67P/C-G nucleus suggested from CONSERT and SESAME-PP results: an interpretation based on new laboratory permittivity measurements of porous icy analogues
Thomas, N.; Brouet, Y.; Pommerol, A. +12 more
The Rosetta spacecraft made a rendezvous with comet 67P/Churyumov-Gerasimenko (67P) in 2014 August, soon after the Philae module landed on the small lobe of the nucleus on 2014 November 12. The CONSERT instrument, onboard Rosetta and Philae, sounded the upper part of the interior of 67P with radiowaves at 90 MHz and determined an average of the re…
NLTE carbon abundance determination in selected A- and B-type stars and the interpretation of C I emission lines
Mashonkina, L. I.; Alexeeva, S. A.; Ryabchikova, T. A.
We constructed a comprehensive model atom for C I-C II using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for C I and C II in classical 1D models representing the atmospheres of A- and late B-type stars. Our NLTE calculations predict the emission that appears at effective tem…
A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar
Hallinan, G.; Laurent, P.; Moran, P. +4 more
We report on observations of the polarization of optical and γ-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope, Advanced Camera for Surveys and the International Gamma-Ray Astrophysics Laboratory satellite (INTEGRAL). These, when combined with other optical pola…
A low-luminosity soft state in the short-period black hole X-ray binary Swift J1753.5-0127
Altamirano, D.; Charles, P. A.; Gandhi, P. +6 more
We present results from the spectral fitting of the candidate black hole X-ray binary Swift J1753.5-0127 in an accretion state previously unseen in this source. We fit the 0.7-78 keV spectrum with a number of models, however the preferred model is one of a multitemperature disc with an inner disc temperature kTin = 0.252 ± 0.003 keV sca…