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The assassination of Mág Raghnaill and the taking of his ship in 1502
Get PDFThis article presents an edition and translation of a short memorandum found in RIA MS 23 N 29 (Cat. 467). The text records the assassination of Mág Raghnaill, chief of Muintear Eólais, by rival members of his family on Easter Sunday 1502, and describes the assassins’ journey from Lough Ree to Lough Key with the slain chief’s ship
A renormalisation group equation for transport co-efficients in (2+1)-dimensions derived from the AdS/CMT correspondence
Get PDFWithin the framework of the AdS/CMT correspondence asymptotically anti-de Sitter black holes in four space-time dimensions can be used to analyse transport properties in two space dimensions. A non-linear renormalisation group equation for the conductivity in two dimensions is derived in this model and, as an example of its application, both the Ohmic and Hall DC and AC conductivities are studied in the presence of a magnetic field, using a bulk dyonic solution of the Einstein-Maxwell equations in asymptotically AdS4 space-time. The Q-factor of the cyclotron resonance is shown to decrease as the temperature is increased and increase as the charge density is increased in a fixed magnetic field. Likewise the dissipative Ohmic conductivity at resonance increases as the temperature is decreased and as the charge density is increased. The analysis also involves a discussion of the piezoelectric effect in the context of the AdS/CMT framework
Review of C. Breatnach, M. Ní Úrdail and G. Ó Riain (eds), Lorg na Leabhar: a Festschrift for Pádraig A. Breatnach (Dublin, 2019)
Get PDFGround state wave functions for the quantum Hall effect on a sphere and the Atiyah–Singer index theorem
Get PDFThe quantum Hall effect is studied in a spherical geometry using the Dirac operator for non-interacting fermions in a background magnetic field, which is supplied by a Wu–Yang magnetic monopole at the center of the sphere. Wave functions are cross-section of a non-trivial U(1) bundle, the zero point energy then vanishes and no perturbations can lower the energy. The Atiyah–Singer index theorem constrains the degeneracy of the ground state. The fractional quantum Hall effect is also studied in the composite Fermion model. Vortices of the statistical gauge field are supplied by Dirac strings associated with the monopole field. A unique ground state is attained only if the vortices have an even number of flux units and act to counteract the background field, reducing the effective field seen by the composite fermions. There is a unique gapped ground state and, for large particle numbers, fractions are recovered
VARIUM. Cú Chulainn’s battle-scars: a new interpretation of a quatrain in Aided Guill meic Carbada 7 Aided Gairb Glinne Rige
Get PDFProbing the Magnetic Field in the GW170817 Outflow Using H.E.S.S. Observations
Get PDFThe detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short gamma-ray bursts and BNS mergers. It also confirmed the forging of heavy elements in the ejecta (a so-called kilonova) via the r-process nucleosynthesis. The appearance of nonthermal radio and X-ray emission, as well as the brightening, which lasted more than 100 days, were somewhat unexpected. Current theoretical models attempt to explain this temporal behavior as either originating from a relativistic off-axis jet or a kilonova-like outflow. In either scenario, there is some ambiguity regarding how much energy is transported in the nonthermal electrons versus the magnetic field of the emission region. Combining the Very Large Array (radio) and Chandra (X-ray) measurements with observations in the GeV-TeV domain can help break this ambiguity, almost independently of the assumed origin of the emission. Here we report for the first time on deep H.E.S.S. observations of GW170817/GRB 170817A between 124 and 272 days after the BNS merger with the full H.E.S.S. array of telescopes, as well as on an updated analysis of the prompt (<5 days) observations with the upgraded H.E.S.S. phase-I telescopes. We discuss implications of the H.E.S.S. measurement for the magnetic field in the context of different source scenarios
Resolving acceleration to very high energies along the jet of Centaurus A
Get PDFThe nearby radio galaxy Centaurus A belongs to a class of active galaxies that are luminous at radio wavelengths. Most show collimated relativistic outflows known as jets, which extend over hundreds of thousands of parsecs for the most powerful sources. Accretion of matter onto the central supermassive black hole is believed to fuel these jets and power their emission. Synchrotron radiation from relativistic electrons causes the radio emission, and it has been suggested that the X-ray emission from Centaurus A also originates in electron synchrotron processes. Another possible explanation is inverse Compton scattering with cosmic microwave background (CMB) soft photons. Synchrotron radiation needs ultrarelativistic electrons (about 50 teraelectronvolts) and, given their short cooling times, requires some continuous re-acceleration mechanism. Inverse Compton scattering, on the other hand, does not require very energetic electrons, but the jets must stay highly relativistic on large scales (exceeding 1 megaparsec). Some recent evidence disfavours inverse Compton-CMB models, although other work seems to be compatible with them. In principle, the detection of extended gamma-ray emission, which directly probes the presence of ultrarelativistic electrons, could distinguish between these options. At gigaelectronvolt energies there is also an unusual spectral hardening in Centaurus A that has not yet been explained. Here we report observations of Centaurus A at teraelectronvolt energies that resolve its large-scale jet. We interpret the data as evidence for the acceleration of ultrarelativistic electrons in the jet, and favour the synchrotron explanation for the X-rays. Given that this jet is not exceptional in terms of power, length or speed, it is possible that ultrarelativistic electrons are commonplace in the large-scale jets of radio-loud active galaxies
Ensemble forecasting of major solar flares: methods for combining models
Get PDFOne essential component of operational space weather forecasting is the prediction of solar flares. With a multitude of flare forecasting methods now available online it is still unclear which of these methods performs best, and none are substantially better than climatological forecasts. Space weather researchers are increasingly looking towards methods used by the terrestrial weather community to improve current forecasting techniques. Ensemble forecasting has been used in numerical weather prediction for many years as a way to combine different predictions in order to obtain a more accurate result. Here we construct ensemble forecasts for major solar flares by linearly combining the full-disk probabilistic forecasts from a group of operational forecasting methods (ASAP, ASSA, MAG4, MOSWOC, NOAA, and MCSTAT). Forecasts from each method are weighted by a factor that accounts for the method’s ability to predict previous events, and several performance metrics (both probabilistic and categorical) are considered. It is found that most ensembles achieve a better skill metric (between 5% and 15%) than any of the members alone. Moreover, over 90% of ensembles perform better (as measured by forecast attributes) than a simple equal-weights average. Finally, ensemble uncertainties are highly dependent on the internal metric being optimized and they are estimated to be less than 20% for probabilities greater than 0.2. This simple multi-model, linear ensemble technique can provide operational space weather centres with the basis for constructing a versatile ensemble forecasting system – an improved starting point to their forecasts that can be tailored to different end-user needs